Aluminium Casting Alloys EnglishVersion

Aluminium Casting Alloys





Content

Introduction 5

Recycled aluminium 6

Technology and service

for our customers

• Quality Management 7

• Work safety and health 8

protection

• Environmental protection

Aluminium and aluminium 9

casting alloys

• Aluminium – Material properties

• Recycling of aluminium

• Shaping by casting 10

Product range and 11

form of delivery

• Technical consultancy 12

service

Selecting aluminium 13

casting alloys

• Criteria for the selection of 14

aluminium casting alloys

• Infl uence of the 18

most important alloying

elements on aluminium

casting alloys

Infl uencing the 19

microstructural formation of

aluminium castings

• Grain refi nement 20

• Modifi cation of AlSi eutectic 21

• Refi nement of 23

primary silicon

Melt quality and melt cleaning 24

• Avoiding impurities 25

• Melt testing and 28

inspection procedure

• Thermal analysis 30

Selecting the casting process 31

• Pressure die casting 32

process

• Gravity die casting process

• Sand casting process 34

Casting-compliant design 35

Solidifi cation simulation 37

and thermography

Avoiding casting defects 38

Heat treatment of 40

aluminium castings

• Metallurgy –

fundamental principles

• Solution annealing 41

• Quenching

• Ageing 42

Mechanical machining of 44

aluminium castings

Welding and joining 45

aluminium castings

• Suitability and behaviour

• Applications in the

aluminium sector

• Welding processes

• Weld preparation 47

• Weld fi ller materials

Surface treatment: corrosion 48

and corrosion protection

Information on physical data, 50

strength properties and

strength calculations

Notes on the casting 51

alloy tables

Overview: Aluminium casting 52

alloys by alloy group

Eutectic aluminium-silicon 59

casting alloys

Near-eutectic wheel 63

casting alloys

The 10 per cent aluminium- 66

silicon casting alloys

The 7 and 5 per cent 71

aluminium-silicon

casting alloys

Al SiCu casting alloys 76

AlMg casting alloys 81

Casting alloys for special 87

applications

4


In the second part, all technical aspects

which have to be taken into account in

the selection of an aluminium casting al-

loy are explained in detail. All details are

based on the DIN EN 1676: 2010 standard.

The third part begins with notes on the

physical data, tensile strength charac-

teristics and strength calculations of

aluminium casting alloys. Subsequently,

all standardised aluminium casting alloys

in accordance with DIN EN 1676 as well

as common, non-standardised casting

alloys are depicted in a summary table

together with their casting/technical and

other typical similarities in “alloy families”.

The aim of this new, revised and rede-

signed Aluminium Casting Alloys Cata-

logue is to give the user of aluminium

Many of you have most certainly worked

with the “old“ Aluminium Casting Alloys

Catalogue – over the years in thousands

of workplaces in the aluminium indus-

try, it has become a standard reference

book, a reliable source of advice about

all matters relating to the selection and

processing of aluminium casting alloys.

Even if you are holding this Aluminium

Casting Alloys Catalogue in your hands

for the fi rst time, you will quickly fi nd your

way around with the help of the following

notes and the catalogue‘s detailed index.

How is this Aluminium Casting Alloys

Catalogue structured? The catalogue

consists of three separate parts. In the

fi rst part, we provide details on our com-

pany – a proven supplier of aluminium

casting alloys.

Introduction

casting alloys a clear, well laid-out com-

panion for practical application. Should

you have any questions concerning the

selection and use of aluminium casting

alloys, please contact our foundry con-

sultants or our sales staff.

You can also refer to www.aleris.com.

We would be pleased to advise

you and wish you every success

in your dealings with aluminium

casting alloys!

5


Recycled aluminiumTechnology and service for our customers

Employing approx. 600 people, Aleris

Recycling produces high-quality cast-

ing and wrought alloys from recycled

aluminium. The company‘s headquar-

ters are represented by the “Erftwerk”

in Grevenbroich near Düsseldorf which

is also the largest production facility in

the group. Other production facilities

in Germany (Deizisau, Töging), Norway

(Eidsväg, Raudsand) and Great Britain

(Swansea) are managed from here. With

up to 550,000 mt, Aleris Recycling avails

of the largest production capacities in

Europe and is also one of the world‘s

leading suppliers of technology and

services relating to aluminium casting

alloys. Aleris Recycling also offers a wide

range of high-quality magnesium alloys.

Aluminium recycled from scrap and

dross has developed to become a

highly-complex technical market of the

future. This is attributable to the steady

increase in demand for raw materials,

the sustainability issue, increased envi-

ronmental awareness among producers

and consumers alike and, not least, the

necessity to keep production costs as

low as possible.

This is where aluminium offers some es-

sential advantages. Recycled aluminium

can be generated at only a fraction of the

energy costs (approx. 5%) compared to

primary aluminium manufactured from

bauxite with the result that it makes a

signifi cant contribution towards reduc-

ing CO2 emissions. This light-alloy metal

can be recycled any number of times

and good segregation even guarantees

no quality losses.

Its properties are not impaired when

used in products. The metallic value is

retained which represents a huge eco-

nomic incentive to collect, treat and melt

the metal in order to reuse it at the end

of its useful life.

For this reason, casting alloys from Aleris

Recycling can be used for manufacturing

new high-quality cast products such as

crankcases, cylinder heads or aluminium

wheels while wrought materials can be

used for manufacturing rolled and pressed

products, for example. Key industries

supplied include:

• Rolling mills and extrusion plants

• Automotive industry

• Transport sector

• Packaging industry

• Engineering

• Building and construction

• Electronics industry

• as well as other companies in the

Aleris Group.

State-of-the-art production facilities and

an extensive range of products made of

aluminium in the form of scrap, chips or

dross are collected and treated by Aleris

Recycling before melting in tilting rotary

furnaces with melting salt, for example,

whereby the salt prevents the aluminium

from oxidising while binding contami-

nants (salt slag). Modern processing and

melting plants at Aleris Recycling enable

effi cient yet environmentally-friendly re-

cycling of aluminium scrap and dross.

The technology used is largely based on

our own developments and – in terms of

yield and melt quality – works signifi cantly

more effi ciently than fi xed axis rotary

furnaces and hearth furnaces. The melt

gleaned from these furnaces has a very

low gas content thanks to the special gas

purging technique we use as well as

being homogeneous and largely free of

oxide inclusions and/or contaminants.

The resulting high quality of Aleris alloys

enables our customers to open up an in-

creasing number of possible applications.

All management processes and the en-

tire process chain from procurement

through production to sale are subject to

systematic Quality Management. Com-

bined with Quality Management certifi ed

to ISO/TS 16949 and DIN EN ISO 9001,

this guarantees that our clients‘ maximum

requirements and increasing demands

can be fulfi lled.

The product range offered by Aleris Re-

cycling comprises more than 250 differ-

ent casting and wrought alloys. They can

be supplied as ingots with unit weights

of approx. 6 kg (in stacks of up to 1,300

kg) as well as pigs of up to 1,400 kg or

as liquid metal. Based on our sophisti-

cated crucible technology and optimised

transport logistics, Aleris Recycling sup-

plies customers with liquid aluminium in

a just-in-time process and at the appro-

priate temperature.

6


Quality Management

We believe that our most important cor-

porate goal is to meet in full our custom-

ers‘ requirements and expectations in

terms of providing them with products

and services of consistent quality. In or-

der to meet this goal, our guidelines and

integrated management system specifi -

cations outline rules and regulations that

are binding for all staff.

As a manufacturer of aluminium casting

alloys, we are certifi ed according to ISO/

TS 16949. In addition, we operate ac-

cording to DIN EN ISO 9001 standards.

Due to its future-oriented corporate

structure, Aleris Recycling supplies the

market with an increasing number of

applications involving high-quality sec-

ondary aluminium. This service is not re-

stricted to the area of casting alloys but

also applies for 3000- and 5000-grade

wrought alloys, for example. Aleris Re-

cycling is also capable of offering some

6000-grade secondary aluminium alloys

largely required by the automotive sector.

For this so-called upgrade, Aleris applies

special production technologies when

it comes to manufacturing high-quality

alloys from scrap.

Recycled aluminium is increasingly be-

coming a complex range at the interface

between high-tech production, trade and

service. In addition, customers demand

intensive consulting as well as individual

service. Aleris Recycling enjoys an ex-

cellent position in this regard.

At its various locations, the company

units offer a high degree of recycling ex-

pertise, manufacturing competence and

delivery reliability for its customers. With

the result that Aleris Recycling guarantees

its customers a high level of effi ciency

and added value while supporting their

success on the market.

The principle of avoiding errors is para-

mount in all our individual procedures and

regulations. In other words, our priority

is to strive to achieve a zero-error target.

By effectively combating the sources of

errors, we create the right conditions for

reliability and high quality standards.

We have also established a comprehen-

sive process of continuous improvement

(PMO, Best Practice, Six Sigma etc.) in

our plants in response to the demands

being placed on our company by the

increasing trend towards business glo-

balisation. This creates the right cli-

mate for creative thinking and action.

All members of staff, within their own

area of responsibility, endeavour to en-

sure that operational procedures are

constantly improved, even if in small,

gradual stages, with a clear focus on

our customers‘ needs.

7


Work safety and health protection

Our staff are our most valuable asset. Work

safety and health protection, therefore,

have top priority for us, and also make

a valuable contribution to the success

of our company. Our “Work safety and

health protection” programme is geared

towards achieving a zero accident rate,

and towards avoiding occupational ill-

nesses. Depending on the respective

location, we are certifi ed to OHSAS

18001 or OHRIS.

All management members and staff are

obliged to comply with legal regulations

and company rules at all times, to pro-

tect their own health and the health of

other members of staff and, when en-

gaged in any company operations, to

do their utmost to ensure that accidents

and work-related illnesses are avoided,

as well as anything that might have a

negative impact on the general company

environment. Management provides the

appropriate level of resources required

to achieve these goals.

There are regular internal and external

training seminars on the topic of work

safety, and detailed programmes to im-

prove health protection. These help to

maintain our comparatively low accident

and illness rates.

Environmental protection

Following the validation of our environ-

mental management system in conformity

with EMAS II and certifi cation to DIN EN

ISO 14001, we have undertaken not only

to meet all the required environmental

standards, but also to work towards a

fundamental, systematic and continual

improvement in the level of environmental

protection within the company.

Our management system and environ-

mental policy are documented in the

company manual which describes all

the elements of the system in easily

understood terms, while serving as a

reference for all regulations concerning

the environment.

The environmental impacts of our com-

pany operations in terms of air purity,

protection of water bodies, noise and

waste are checked at regular intervals.

By modifying procedures, reusing mate-

rials and recycling residues, we optimise

the use of raw materials and energy in

order to conserve resources as effi ciently

as possible.

We pursue a policy of open information

and provide interested members of the

public with comprehensive details of

the company‘s activities in a particu-

lar location, and an explanation of the

environmental issues involved. For us,

open dialogue with the general pub-

lic, our suppliers, customers and other

contractual partners is as much a part

of routine operations as reliable co-op-

eration with the relevant authorities and

trade associations.

Likewise, ecological standards are in-

corporated in development and planning

processes for new products and produc-

tion processes, as are other standards

required by the market or society at large.

Our staff is fully conscious of all environ-

mental protection issues and is keen to

ensure that the environmental policy is

reliably implemented in day-to-day op-

erations within the company.

8


Aluminium and aluminium casting alloys

Recycling of aluminium

Long before the term “recycling” became

popular, recycling circuits already exist-

ed in the aluminium sector. Used parts

made from aluminium or aluminium alloys

as well as aluminium residue materials

arising from production and fabrication

are far too valuable to end up as land-

fi ll. One of the great advantages of this

metal, and an added plus for its use as a

construction material, is that aluminium

parts, no matter the type, are extremely

well suited to remelting.

• The energy savings made in

recycling aluminium are

considerable. Remelting requires

only about 5 % of the energy

initially required to produce

primary aluminium.

• As a rule, aluminium recycling

retains the value added to the

metal. Aluminium can be recycled

to the same quality level as the

original metal.

• Aluminium recycling safeguards

and supplements the supply of

raw materials while saving

resources, protecting the

environment and conserving

energy. Recycling is therefore also

a dictate of economic reason.

• Aluminium is light; its specifi c weight

is substantially lower than other

common metals and, at the same

time, it is so strong that it can with

stand high stress.

• Aluminium is very corrosion-

resistant and durable. A thin,

natural oxide layer protects

aluminium against decomposition

from oxygen, water or chemicals.

• Aluminium is an excellent

conductor of electricity,

heat and cold.

• Aluminium is non-toxic, hygienic

and physiologically harmless.

• Aluminium is non-magnetic.

• Aluminium is decorative and

displays high refl ectivity.

• Aluminium has outstanding

formability and can be

processed in a variety of ways.

• Aluminium alloys are easy to cast

as well as being suitable for all known

casting processes.

• Aluminium alloys are

distinguished by an excellent

degree of homogeneity.

• Aluminium and aluminium

alloys are easy to machine.

• Castings made from aluminium

alloys can be given an artifi cial,

wear-resistant oxide layer

using the ELOXAL process.

• Aluminium is an outstanding

recycling material.

Aluminium – Material properties

Aluminium has become the most widely

used non-ferrous metal. It is used in the

transport sector, construction, the pack-

aging industry, mechanical engineering,

electrical engineering and design. New

fi elds of application are constantly open-

ing up as the advantages of this material

speak for themselves:

9


Shaping by casting

Casting represents the shortest route

from raw materials to fi nished parts – a

fact which has been known for fi ve thou-

sand years. Through continuous further

development and, in part, by a selective

return to classic methods such as the

lost-form process, casting has remained

at the forefront of technical progress.

The most important advantage of the

casting process is that the possibilities

of shaping the part are practically limit-

less. Castings are, therefore, easier and

cheaper to produce than machined and/

or joined components. The general waiv-

ing of subsequent machining not only

results in a good density and path of

force lines but also in high form strength.

Furthermore, waste is also avoided. As a

rule, the casting surface displays a tight,

fi ne-grained structure and, consequently,

is also resistant to wear and corrosion.

The experience accumulated over ma-

ny decades, the use of state-of-the-art

technology in scrap preparation, remelt-

ing and exhaust gas cleaning as well

as our constant efforts to develop new,

environmentally-sound manufactur-

ing technology puts us in a position to

achieve the best possible and effi cient

recycling rates. At the same time, they

also help us to make the most effi cient

use of energy and auxiliary materials.

The variety of modern casting process-

es makes it possible to face up to the

economic realities, i.e. the optimisation

of investment expenditure and costs

in relation to the number of units. With

casting, the variable weighting of pro-

duction costs and quality requirements

are also possible.

When designing the shape of the cast-

ing, further possibilities arise from the

use of inserts and/or from joining the

part to other castings or workpieces.

In the last decade, aluminium has at-

tained a leading position among cast

metals because, in addition to its other

positive material properties, this light

metal offers the greatest possible variety

of casting and joining processes.

10


Product range and form of delivery

Our casting alloys are delivered in the

form of ingots with a unit weight of ap-

prox. 6 kg or as liquid metal.

We distinguish between ingots cast in

open moulds and horizontal continu-

ously cast ingots (so-called HGM). In-

gots are dispatched in bundles of up to

approx. 1,300 kg.

The delivery of liquid or molten metal is

useful and economic when large quanti-

ties of one homogeneous casting alloy are

required and the equipment for tapping

and holding the molten metal containers

is available. Supplying molten metal can

lead to a substantial reduction in costs

as a result of saving melting costs and

a reduction in melting losses. The sup-

ply of liquid metal also provides a viable

alternative in cases where new melting

capacities need to be built to comply

with emission standards or where space

is a problem.

As ecological and economic trends sen-

sibly move towards the development of

closed material circuits, the clear dividing

lines between the three classic quality

grades of aluminium casting alloys are

ever-decreasing. In future, people will

simply talk about “casting alloys”. In

practice, this is already the case. Metal

from used parts is converted back into

the same fi eld of application. The DIN

EN 1676 and 1706 standards with their

rather fl uid quality transitions take this

trend into account.

Aleris is one of only a few companies

to produce a wide range of aluminium

alloys; our product spectrum extends

from classic secondary alloys to high-

purity alloys for special applications.

Production is in full compliance with

the European DIN EN 1676 standard

or international standards and in many

cases, manufactured to specifi c cus-

tomer requirements. We have also been

offering several aluminium casting al-

loys as protected brand-name alloys

for many years, e.g. Silumin®®, Pantal®®

and Autodur®.

11


Technical consultancy service

The technical consultancy service is

the address for questions relating to

foundry technology. We provide assis-

tance in clarifying aluminium casting alloy

designations as stated in German and

international standards or the temper

conditions for castings. We also offer

advice on the selection of alloys and can

provide aluminium foundries or users of

castings with information on:

• Aluminium casting alloys

• Chemical and physical properties

• Casting and solidifi cation

behaviour

• Casting processes and details

regarding foundry technology

• Melt treatment possibilities, such as

cleaning, degassing, modifi cation

or grain refi nement

• Possibilities of infl uencing the

strength of castings by means

of alloying elements or heat

treatment

• Questions relating to surface

fi nish and surface protection.

Technical consultants also provide as-

sistance in evaluating casting defects or

surface fl aws and offer suggestions with

regard to eliminating defects. They sup-

ply advice on the design of castings, the

construction of dies, the casting system

and the confi guration of feeders.

Technical consultants also provide tech-

nical support to aluminium foundries in

the preparation of chemical analyses,

microsections and structural analyses.

Customer feedback coupled with exten-

sive experience in the foundry sector fa-

cilitates the continuous optimisation and

quality improvement of our aluminium

casting alloys.

In co-operation with our customers, we

are working on gaining wider acceptance

of our aluminium casting alloys in new

fi elds of application.

Where required and especially where

fundamental problems arise, we arrange

contracts with leading research institutes

in Europe and North America.

12


As far as possible, the use of common

aluminium casting alloys is recommended.

These involve well-known and proven

casting alloys and we stand fully behind

the quality properties of these casting

alloys which are often manufactured in

large quantities, are more cost-effective

than special alloys and, in most cases,

can be delivered at short notice.

In the European DIN EN 1676 and DIN

EN 1706 standards, the most important

aluminium casting alloys have been col-

lated in a version which is valid Europe-

wide. Consequently, there are already

more than 41 standard aluminium casting

alloys available.

Aluminium foundries should – according

to their respective structure – limit them-

selves to as small a number of casting

alloys as possible in order to use their

melting equipment economically, to keep

inventories as low as possible and to re-

duce the risk of mixing alloys.

With regard to the quality of a casting,

it is more sensible to process a casting

alloy which is operational in use than one

which displays slightly better properties

on paper but is actually more diffi cult to

process. The quality potential of a cast-

ing alloy is only exploited in a casting if

the cast piece is as free as possible of

casting defects and is suitable for subse-

quent process steps (e.g. heat treatment).

Our sales team and technicians are on

hand to provide foundries and users

of castings with assistance in select-

ing the correct aluminium casting alloy.

To supplement and provide greater depth

to our technical explanations, we refer

you to standard works on aluminium

and aluminium casting alloys. Further

details on other specialist literature are

available and can be requested at any

time. We would be delighted to advise

you in such matters.

Should you have any queries or com-

ments, which are always welcome,

please contact our technical service.

Standard works on aluminium and alu-

minium casting alloys:

• “Aluminium-Taschenbuch”, Verlag

Beuth, Düsseldorf

• “Aluminium viewed from within -

Profi le of a modern metal”, Prof.

Dr. D. G. Altenpohl, Verlag Beuth,

Düsseldorf.

Once the requirements of a casting

have been determined, the selection of

the correct casting alloy from the mul-

titude of possibilities often represents

a problem for the designer and also for

the foundryman. In this case, the “Alu-

minium-Taschenbuch” can be of great

assistance.

Selecting aluminium casting alloys

13


different casting alloys are compared.

These casting alloys are used for high-

grade construction components, espe-

cially for critical parts.

“hard”

The casting alloys of this group must

display a certain tensile strength and

hardness without particular requirements

being placed on the metal‘s elongation.

First of all, Al SiCu alloys belong to this

group. Due to their Cu, Mg and Zn con-

tent, these casting alloys experience a

certain amount of self-hardening after

casting (approx. 1 week). These alloys

are particularly important for pressure

die casting since it is in pressure die

casting – except for special processes

such as vacuum die casting – that pro-

cess-induced structural defects occur,

preventing high elongation values. Due

to its particularly strong self-hardening

characteristics, the Autodur casting al-

Criteria for the selection of

aluminium casting alloys

In the following section, we provide an

insight into the chemical and physical

potentials of aluminium casting alloys by

describing their various properties. The

standardisation provided here helps to

establish whether a casting alloy is suit-

able for the specifi c demands placed

on a casting.

Degree of purity

One important selection criteria is the de-

gree of purity of a casting alloy. With the

increasing purity of a casting alloy family,

the corrosion resistance and ductility of

the as-cast structure also increase; the

selection of pure feedstock for making

casting alloys, however, will necessarily

cause costs to rise.

The increasing importance of the closed-

circuit economy means that, for the pro-

ducer of aluminium casting alloys, the

transition between the previous quality

grades for aluminium casting alloys is

becoming ever more fl uid.

Due to their high purity, casting alloys

made from primary aluminium display the

best corrosion resistance as well as high

ductility. By way of example, Silumin-Beta

with max. 0.15 % Fe, max. 0.03 % Cu

and max. 0.07 % Zn can be mentioned.

In many countries, the Silumin trademark

has already become a synonym for alu-

minium-silicon casting alloys.

Casting alloys made from scrap are,

with regard to ductility and corrosion

resistance, inferior to other casting alloy

groups due to their lower purity. They are,

however, widely applicable and meet the

set performance requirements.

Strength properties

Strength properties should be discussed

as a further selection criterion (Table 1).

A rough subdivision into four groups is

practical:

“strong and ductile”

The most important age-hardenable

casting alloys belong to this group. By

means of different kinds of heat treat-

ment, their properties can be adjusted

either in favour of high tensile strength

or high elongation. In Table 1, the typi-

cal combinations of Rm and A values for

Classifi cation of casting alloys acc. to strength properties 1)

Casting alloy Temper Tensile Elongation Brinell strength hardness Rm A5

[MPa] [%] HB

Strong Al Cu4Ti T6 330 7 95and ductile Silumin-Beta T6 290 4 90 Al Si10Mg(a) T6 260 1 90

Hard Al Si8Cu3 F 170 1 75 Al Si18CuNiMg F 180 1 90

Ductile Silumin F 170 7 45

Other Al Mg3 F 150 5 50

1) Typical values for permanent mould casting, established on separately-cast test bars.

Table 1

14


Casting properties

Further selection criteria comprise cast-

ing properties such as the fl uidity or

solidifi cation behaviour which sets the

foundryman certain limits. Not every

ideally-shaped casting can be cast in

every casting alloy.

A simplifi ed summary of the casting prop-

erties associated with the most impor-

tant casting alloys is shown in Table 2.

Co-operation between the technical de-

signer and an experienced foundryman

works to great advantage when looking

for the optimum casting alloy for a par-

ticular application.

Given constant conditions, the fl uidity

of a metallic melt is established by de-

termining the fl ow length of a test piece.

Theoretically, low fl uidity can be offset

by a higher casting temperature; this is,

however, linked with disadvantages such

as oxidation and hydrogen absorption as

well as increased mould wear. Eutectic

AlSi casting alloys such as Silumin or

Al Si12 display high fl uidity. Hypoeutectic

AlSi casting alloys such as Pantal 7 have

medium values. AlCu and AlMg casting

alloys display low fl uidity.

Hypereutectic AlSi casting alloys such

as Al Si17Cu4Mg occupy a special posi-

tion. In their case, very long fl ow paths

are observed. This does not however

necessarily lead to a drop in the melt

temperature since primary silicon crys-

tals already form in the melt. The melt

still fl ows well because the latent heat

of solidifi cation of the primary silicon

“ductile”

Casting alloys which display particu-

larly high ductility, e.g. Silumin-Kappa

(Al Si11Mg), come under this general

heading. This casting alloy is frequently

used for the manufacture of automobile

wheels.

In this particular application, a high elon-

gation value is required for safety reasons.

“other”

Casting alloys for more decorative pur-

poses with lower strength properties, e.g.

Al Mg3, belong to this category.

loy represents a special case allowing

hardness values of approx. 100 HB and

a corresponding strength – albeit at very

low ductility – in all casting processes.

Hypereutectic AlSi casting alloys such

as Al Si18CuNiMg and Al Si17Cu4Mg,

for example, which display particularly

high wear resistance due to their high

silicon content, can also be classifi ed

in this group.

Classifi cation of casting alloys acc. to casting properties

Fluidity Thermal Casting alloy Type of solidifi cation crack susceptibility

High Low Silumin Exogenous-shell forming

Al Si12

Al S12(Cu) Exogenous-rough wall

Al Si10Mg Endogenous-dendritic

Silumin-Beta

Al Si8Cu3

Pantal 7

Al Si5Mg

Al Cu4Ti

Al Mg3 Endogenous-globular

Low High Al Mg5 Mushy

Table 2

15


heats up the remainder of the melt. The

already solidifi ed silicon, however, causes

increased mould wear and very uneven

distribution in the castings. In these

casting alloys, high melting and holding

temperatures are necessary so that a

casting temperature of at least 720 °C

for pressure die casting and 740 °C

for sand and gravity die casting has to

be attained.

The susceptibility to hot tearing is almost

the opposite of fl uidity (Tables 2 and 3).

By hot tearing, we mean a separation of

the already crystallised phases during

solidifi cation, e.g. under the infl uence of

shrinkage or other tensions which can

be transmitted via the casting moulds.

The cracks or tears arising can be healed

by, among other things, the feeding of

residual melt. Eutectic and near-eutectic

AlSi casting alloys also behave particularly

well in this case, while AlCu and AlMg

casting alloys behave particularly badly.

In practice, there are mixed forms and

transitional forms of these solidifi cation

modes. The solidifi cation behaviour is

responsible for the formation of shrink-

age cavities and porosity, for example,

or other defects in the cast structure

as it determines the distribution of the

volume defi cit in the casting. To curb

the aforementioned casting defects,

casting/technical measures need to be

taken: e.g. by making adjustments to

the sprue system, the thermal balance

of the mould or by controlling the gas

content of the melt. A volume defi cit

occurs during transition from liquid to

solid state. This is quite small in high

silicon casting alloys since the silicon

increases in volume during solidifi cation.

In any case, the volume defi cit incurred

Selection criteria for aluminium casting alloys

Casting properties Strength characteristics Corrosion resistance*Shrinkage Fluidity Thermal crack High strength Strong Ductile Hard formation susceptibility and ductile (T6) and ductile

Coarse High Low Silumin

Silumin-Kappa

Silumin-Delta

Al Si12

Al Si12(Cu) Al Si12CuNiMg

Al Si17Cu4Mg

Al Si18CuNiMg

Autodur

Silumin-Beta

Al Si10Mg

Al Si10Mg(Cu)

Al Si8Cu3

Pantal 7

Al Cu4Ti

Al Mg3Si

Al Mg3

Al Mg5

Fine Low High Al Mg9

* Analogue to DIN EN 1706

Table 3

16


needs to be offset as far as possible by

casting/technical means (see also the

section on “Avoiding casting defects”).

Figure 1 indicates the main types of so-

lidifi cation; each type is shown at two

successive points in time. With regard

to aluminium, only high-purity aluminium

belongs to Solidifi cation Type A (“exog-

enous-shell forming”). The only casting

alloy which corresponds to this type is

the eutectic silicon alloy or Al Si12 with

approx. 13 % silicon.

The hypoeutectic AlSi casting alloys

solidify according to Type C (“spongy”),

AlMg casting alloys according to a mix-

ture of Types D and E (“mushy” or “shell-

forming”). The remaining casting alloys

also represent intermediate types. At high

solidifi cation speeds, the solidifi cation

types move upwards, i.e. in the direction

of “exogenous-rough wall”.

Shell-forming casting alloys with “smooth-

wall” or “rough-wall” solidifi cation are sus-

ceptible to the formation of macroshrink-

age which can only be prevented to a

limited extent by feeding. Casting alloys

of a spongy-mushy type are susceptible

to shrinkage porosity which can only be

avoided to a limited extent by feeding.

In castings which demand feeding by

material accumulation in particular and

which should be extensively pore-free –

as well as pressure-tight – the preferred

casting alloys are to be found at the top

of Table 3.

For complex castings whose geometry

does not allow each material accumu-

lation to be achieved with a feeder, the

casting alloys listed in Table 3 offer ad-

vantages provided that a certain amount

of microporosity is taken into account.

Picture 1

A Smooth wall B Rough wall C Spongy

Exogenous solidifi cation types

D Mushy E Shell forming

Endogenous solidifi cation types

Mould

Fluid

Strong

17

SiSiFe


Copper

• increases the strength, also at

high temperatures (high-

temperature strength)

• produces age-hardenability

• impairs corrosion resistance

• in binary AlCu casting alloys, the

large solidifi cation range needs to

be taken into account from a

casting/technical point of view.

Manganese

• partially offsets iron‘s negative

effect on ductility when iron

content is > 0.15 %

• segregates in combination with

iron and chromium

• reduces the tendency to stickiness

in pressure die casting.

Magnesium

• produces age-hardenability in

combination with silicon,

copper or zinc; with zinc also

self-hardening

• improves corrosion resistance

• increases the tendency towards

oxidation and hydrogen

absorption

• binary AlMg casting alloys are

diffi cult to cast owing to their large

solidifi cation range.

Zinc

• increases strength

• produces (self) age-hardenability

in conjunction with magnesium.

Infl uence of the most important

alloying elements on aluminium

casting alloys

Silicon

• improves the casting properties

• produces age-hardenability in

combination with magnesium but

causes a grey colour during anodi-

sation

• in pure AlCu casting alloys (e.g.

Al Cu4Ti), silicon is a harmful im-

purity and leads to hot tearing

susceptibility.

Iron

• at a content of approx. 0.2 % and

above, has a decidedly negative

infl uence on the ductility (elonga-

tion at fracture); this results in a

very brittle AlFe(Si) compound in

the form of plates which appear in

micrographs as “needles”; these

plates act like large-scale micro-

structural separations and lead to

fracture when the slightest strain

is applied

• at a content of approx. 0.4 % and

above, reduces the tendency to

stickiness in pressure die casting.

Nickel

• increases high-temperature

strength.

Titanium

• increases strength (solid-solution

hardening)

• produces grain refi nement on its

own and together with boron.

18


Infl uencing the microstructural formation of aluminium castings

The marked areas in Figure 1 denote

where it makes sense to carry out the

respective types of treatment on AlSi

casting alloys.

Some of these measures are explained

in more detail in the following section.

Common treatment measures include:

• grain refi nement of the solid

solution with Ti and/or B

• transformation of the eutectic Si

from lamellar into granular form

• modifi cation of the eutectic Si

with Na or Sr

• refi nement of the eutectic

Si with Sb

• refi nement of the Si primary

phase with P or Sb.

Measures infl uencing microstructural

formation are aimed at improving the

mechanical and casting properties. In

practice, apart from varying the cool-

ing speed by means of different mould

materials, additions to the melt are usu-

ally used.

Types of treatment to infl uence grain structure Figure 1

Temperature [°C]

700

600

500

400

Primary Si refi nement

Grain refi nement

0 2 4 6 8 10 12 14 16 18 20 22 24

Modifi cation

Eutectic temperature 577 C°

Melt + Si

Melt

Melt + Al 660 °C

Al Al + Si

Al Si5 Al Si7 Al Si9 Al Si12 Al Si18

Silicon [wt. – %]

19


Grain refi nement

The solidifi cation of many aluminium

casting alloys begins with the formation

of aluminium-rich dendritic or equiaxed

crystals. In the beginning, these solidifi ed

crystallites are surrounded by the remain-

ing melt and, starting from nucleation

sites, grow on all sides until they touch

the neighbouring grain or the mould wall.

The characterisation of a grain is the

equiaxed spatial arrangement on the

lattice level. For casting/technical or

optical/decorative reasons as well as

for reasons of chemical resistance, it is

often desirable to set the size of these

grains as uniformly as possible or as fi nely

as technically possible. To achieve this,

so-called grain refi nement is frequently

carried out. The idea is to offer the so-

lidifying aluminium as many nucleating

agents as possible.

Since grain refi nement only affects the

α-solid solution, it is more effective when

the casting alloy contains little silicon,

i.e. a lower fraction of eutectic (Figure 2).

Grain refi nement is particularly important

in AlMg and AlCu casting alloys in order

to reduce their tendency to hot tearing.

From a technical and smelting perspec-

tive, grain refi nement mostly takes place

by adding special Al TiB master alloys.

We pre-treat the appropriate casting al-

loys when producing the alloys so that

grain refi nement in the foundry is either

unnecessary or only needs a freshen-

up. The latter can be done in the form of

salts, pellets or preferably with titanium

master alloy wire, following the manu-

facturer’s instructions.

Since every alloying operation means

more contaminants in the melt, grain

refi nement should only be carried out

for the reasons referred to above.

To make a qualitative assessment of a

particular grain refi nement treatment,

thermal analysis can be carried out (see

section on “Melt testing and inspection

procedure”).

Effect of silicon content on grain refi nement with Al Ti5B1 master alloy

Mean grain diameter Casting temperature 720 °C[µm] holding time 5 min

1400

1200

1000

800

600

400

200

0

Silicon [%]

Columnar and equiaxed crystals

Without grain refi nement

With grain refi nementAl Ti5B1: 2,0 kg/mt

0 2 4 6 8 10 12

Figure 2

20


Figures 3 and 4 depict the formation of

microstructural conditions or the degree

of modifi cation as a result of interaction

between sodium and strontium and the

phosphorous element. It can be ascer-

tained that the disruption of modifi cation

due to small amounts of phosphorous

is relatively slight. In Sr modifi cation, a

high phosphorous content can be offset

by an increased amount of modifying

agent. In aluminium casting alloys with a

silicon content exceeding 7 %, eutectic,

silicon takes up a larger part of the area

of a metallographic specimen. From a

silicon content of approx. 7 to 13 %,

the type of eutectic formation, e.g.

grained or modifi ed, thus plays a key

role in determining the performance

characteristics, especially the ductility

or elongation. When higher elongation is

required in a workpiece, aluminium cast-

ing alloys containing approx. 7 to 13 %

silicon will thus be modifi ed by adding

approx. 0.0040 to 0.0100 % sodium (40

to 100 ppm).

In casting alloys with approx. 11 % silicon,

particularly for use in low-pressure die

casting, strontium can also be used as a

long-term modifi er since the melting loss

behaviour of this element is substantially

better than that of sodium. In this case,

the recommended addition is approx.

0.014 to 0.04 % Sr (140 to 400 ppm).

With suitable casting alloys, the required

amount of strontium can be added

during alloy manufacture so that, as

a rule, the modifi cation process step

Modifi cation of AlSi eutectic

(refi nement)

By “modifi cation”, we mean the use

of a specifi c melt treatment to set a

fi ne-grained eutectic silicon in the cast

structure which improves the mechanical

properties (and elongation in particular)

as well as the casting properties in many

cases. As a general rule, modifi cation

is carried out by adding small amounts

of sodium or strontium. To facilitate an

understanding of the possible forms of

eutectic silicon, these are depicted in

Figure 2 (a-e) for Al Si11 with a varying

Na content:

a) The lamellar condition only

appears in casting alloys which

are virtually free of phosphorous

or modifi cation agents, e.g.

Na or Sr.

b) In granular condition which

appears in the presence of

phosphorous without Na or Sr, the

silicon crystals exist in the form of

coarse grains or plates.

c) In undermodifi ed and

d) to a great extent in fully-modifi ed

microstructural condition, e.g.

by adding Na or Sr, they are

signifi cantly reduced in size,

rounded and evenly distributed

which has a particularly positive

effect on elongation.

e) In the case of overmodifi cation

with sodium, vein-like bands with

coarse Si crystals appear.

Overmodifi cation can therefore

mean deterioration as regards

mechanical properties.

a) Lamellar b) Granular

e) Overmodifi ed

c) Undermodifi ed

d) Modifi ed

Picture 2Types of grain structure

21


can be omitted in the foundry. At low

cooling rates, strontium modifi cation is

less effective so that it is not advisable

to use this in sand casting processes.

To avoid the burn-off of strontium, any

cleaning and degassing of Sr-modifi ed

melts should be carried out with chlorine-

free preparations only, preferably using

argon or nitrogen. Strontium modifi ca-

tion is not greatly impaired even when

remelting revert material. Larger losses

can be offset by adding Sr master alloy

wire in accordance with the respective

manufacturer‘s instructions. At the right

temperature, the addition of sodium to

the melt is best done by charging stand-

ard portions. For easy handling, storage

and proportioning, the manufacturer‘s

recommendations and safety instruc-

tions should be followed.

Since sodium burns off from the melt

relatively quickly, subsequent modifi -

cation must take place in the foundry

at regular intervals. In melts modifi ed

with sodium, any requested cleaning

and degassing should be carried out

with chlorine-free compounds only

(argon or nitrogen). A certain amount

of sodium burn-off is to be reckoned

with, however, and needs to be taken

into account in the subsequent addition

of sodium. When absolutely necessary,

the melt can be treated with chlorine-

releasing compounds long before the

Phosphorous [ppm]

Overmodifi ed

Granular

Modifi ed

Lamellar

Undermodifi ed

Microstructural formation in relation to the content of phosphorous and sodium Al Si7Mg

Sodium Sand casting[ppm] cooling rate 0.1 K/s

140

120

100

80

60

40

20

0

0 5 10 15 20 25 30 35 40 45 50 55 60

Figure 3

Phosphorous [ppm]

Modifi ed Undermodifi ed Granular Lamellar

Microstructural formation in relation to the content of phosphorous and strontium Al Si7Mg

Strontium Gravity die casting[ppm] gravity die cast test bar cooling rate 2.5 K/s

450

400

350

300

250

200

150

100

50

0

0 10 20 30 40 50 60 70 80 90 100

Figure 4

22


fi rst addition of sodium. If such treat-

ment is carried out after adding sodium

or strontium, chlorine may react with

these elements and remove them from

the melt, thereby preventing any further

modifi cation.

Modifi cation with sodium or strontium

increases the tendency to gas absorp-

tion in the melt. As a result of the reac-

tion of the precipitating hydrogen with

the rapidly-forming oxides, defects can

occur in the casting, especially cumulant

microporosity. In many practical cases,

this potential for micropore formation

is even desirable. Then, the purpose

of modification is also to offset the

expected macroshrinkage by forming

many micropores.

An accurate assessment of the effects

of modifi cation can only be made by

means of metallographic examination.

As a quick test, thermal analysis can be

carried out if it is possible to establish by

means of a preliminary metallographic

examination which depression value is

necessary to attain a suffi ciently-modi-

fi ed grain structure (for more information

on thermal analysis, please refer to the

section on “Methods for monitoring the

melt”). Under the same conditions, rapid

determination of the modifi ed condition

is also possible by measuring the elec-

trical conductance of a sample.

In aluminium casting alloys of the type

Al Si7Mg, a refi nement of the eutectic

silicon with antimony (Sb) is possible.

A Sb content of at least 0.1 % is required.

This treatment, however, only produces

a fi ner formation of the lamellar eutec-

tic silicon and is not really modifi cation

in the traditional sense. The danger of

contamination of other melts by closed-

circuit material containing Sb exists as

even a Sb content of approx. 100 ppm

can disturb normal sodium or strontium

modifi cation. What‘s more, refi nement

with antimony can be easily disturbed

by only a low level of phosphorous (a

few ppm) (Figure 5). In contrast to modi-

fi cation, refi nement with antimony can

not be checked by means of thermal

analysis of a melt sample.

Refi nement of primary silicon

In hypereutectic AlSi casting alloys

(e.g. Al Si18CuNiMg), the silicon-rich,

polygonal primary crystals solidify fi rst.

To produce as many fi ne crystals as pos-

sible in the as-cast structure, nucleating

agents need to be provided.

This is done with the aid of prepara-

tions or master alloys which contain

phosphorous-aluminium compounds.

This treatment can also be carried out

when the alloy is being manufactured

and, in most cases, the foundryman

does not need to repeat the process.

If required, the quality of such primary

refi nement can be checked by means

of thermal analysis.

Phosphorous [ppm]

Infl uence of antimony and phosphorous content on the form of the eutectic silicon of Al Si7Mg

Antimony[%]

0.30

0.20

0.10

0.00

0 2 4 6 8 10

Coarse-lamellar

Acceptable Coarse-lamellarto granular

High-purity base

Figure 5

23


Melt quality and melt cleaning

To achieve good melt quality, the for-

mation of oxides and the absorption

of hydrogen have to be suppressed as

much as possible on the one hand, while

other hydrogen and oxides have to be

removed from the melt as far as pos-

sible on the other, although this is only

possible to a certain extent.

All factors which come under the gen-

eral term of “melt quality” have a direct

effect on the quality of the casting to be

produced. Inversely, according to DIN EN

1706, the cast samples play a valuable

role in checking the quality of the melt.

Most problems in casting are caused by

two natural properties of liquid melts, i.e.

their marked tendency to form oxides

and their tendency towards hydrogen

absorption. Furthermore, other insolu-

ble impurities, such as Al-carbides or

refractory particles as well as impurities

with iron, play an important role.

As mentioned in other sections, the

larger oxide fi lm can lead to a material

separation in the microstructure and,

consequently, to a reduction in the load-

bearing cross-section of the casting.

The solubility of hydrogen in aluminium

decreases discontinuously during the

transition from liquid to solid so that as

solidifi cation takes place, precipitating

gaseous hydrogen reacting with exist-

ing oxides can cause voids which can

in turn take various forms ranging from

large pipe-like blisters to fi nely-distrib-

uted micro-porosity.

Segregation factor [(Fe)+2(Mn)+3(Cr)]

Al Si8Cu3 Al Si6Cu4 Al Si12(Cu)

Critical melting temperatures in relation to the segregation factor

Temperature[°C]

650

640

630

620

610

600

590

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Figure 6

24


Avoiding impurities

Ingot quality

An essential prerequisite for a good

casting is good ingot quality. The metal

should be cleaned effectively and the in-

gots should display neither metallic nor

non-metallic inclusions. The ingots must

be dry (there is a risk of explosion when

damp) and no oil or paint residue should

be present on their surface. When using

revert material, this should be in lumps,

if possible, and well cleaned.

Melting

When melting ingots or revert material,

it must be ensured that the metal is not

exposed unnecessarily to the fl ame or

furnace atmosphere. The pieces of metal

should be melted down swiftly, i.e. follow-

ing short preheating, immersed directly

in the liquid melt.

Large-volume hearth or crucible furnaces

are best suited to melting. Furnaces with

melting bridges are oxide producers and

they lead to expensive, unnecessary and

irretrievable metal losses.

The type and state of the melt in contact

with refractory materials are of particular

importance in the melting and holding

of aluminium.

Aluminium and aluminium casting alloys

in a molten state are very aggressive, es-

pecially when AlSi melts contain sodium

or strontium as modifying agents. With

an eye to quality, reactions, adherences,

infi ltrations, abrasive wear and decompo-

sition have to be kept within limits when

using melting crucibles and refractory

materials as well as during subsequent

processing. The care and maintenance

as well as cleanliness of equipment are

equally important. Adhering materials

can very easily lead to the undesired

redissolving of oxides in the melt and

cause casting defects.

Melting temperature

The temperature of the melt must be set

individually for each alloy.

Too low melting temperatures lead to

longer residence times and, as a result,

to greater oxidation of the pieces jut-

ting out of the melt. The melt becomes

homogeneous too slowly, i.e. local un-

dercooling allows segregation to take

place, even as far as tenacious gravity

segregation of the FeMnCrSi type phases.

The mathematical interrelationship for

the segregation of heavy intermetallic

phases is depicted in Figure 6.

Furthermore, at too low temperatures,

autopurifi cation of the melt (oxides ris-

ing) can not take place.

When the temperature of the melt is too

high, increased oxide formation and

gassing can occur. Lighter alloying ele-

ments, e.g. magnesium, are subject to

burn-off in any case; this must be off-

set by appropriate additions. Too high

melting temperatures aggravate this loss

by burning.

25


Conducting the melting operation

As long as the melt is in a liquid condi-

tion, it has a tendency to oxidise and

absorb hydrogen. Critical points during

subsequent processing include decanta-

tion, the condition or maintenance of the

transfer vessel, possible reactions with

refractory materials as well as transport

or metal tapping. The addition of grain

refi ners and modifying agents above the

required amount can lead to an increase

in non-metallic impurities and greater

hydrogen absorption.

To minimise an enrichment of iron in the

melt, direct contact between ferrous

materials and the melt is to be avoided.

For this reason, steel tools and contain-

ers (casting ladles) must be carefully

dressed. Similarly, but also on economic

grounds, the feed tubes for low-pressure

die casting – made from cast iron up to

now – should be replaced by ceramic

feed tubes.

Even during the casting process itself

and especially due to turbulence in the

fl ow channel, oxide skins can once again

form which in turn can lead to casting

defects. Casting technology is thus re-

quired to fi nd ways of preventing the

excessive oxidation of the melt, e.g. by

means of intelligent runners and gating

systems (please refer to the section on

“Selecting the casting process”).

Type of melt treatment

Al Si8Cu3 Pantal 7 Al Mg5

Hydrogen content of various casting alloy melts after different types of treatment

Hydrogen[ml/100g]

0.50

0.40

0.30

0.20

0.10

0.00

10 20 30 0.5 2 4 24 10 20

Aft

er m

eltin

g

Rot

ary

deg

assi

ng

[min

]

Rot

ary

deg

assi

ng

[min

]

Gas

sing 24

h

Hol

din

g in

[h]

Figure 7

26


Cleaning and degassing the melt

Our casting alloys consist of effectively

cleaned metal. Since reoxidation always

takes place during smelting, and in

practice revert material is always used,

a thorough cleaning of the melt is nec-

essary prior to casting.

Holding the aluminium melt at the cor-

rect temperature for a long time is an ef-

fective cleaning method. It is, however,

very time-intensive and not carried out

that often as a result. Foundrymen are

thus left with only intensive methods, i.e.

using technical equipment or the usual

commercially available mixture of salts.

In principle, melt cleaning is a physical

process: the gas bubbles rising through

the liquid metal attach oxide fi lms to their

outer surfaces and allow hydrogen to dif-

fuse into the bubbles from the melt. Both

are transported to the bath surface by the

bubbles. It is therefore clear that in order

for cleaning of the melt to be effective, it

is desirable to have as many small gas

bubbles as possible distributed across

the entire cross-section of the bath.

Dross can be removed from the surface

of the bath, possibly with the aid of ox-

ide-binding salts.

Inert-gas fl ushing by means of an im-

peller is a widely-used, economical and

environmentally-sound cleaning process.

The gas stream is dispersed in the form

of very small bubbles by the rapid turn-

ing of a rotor and, in conjunction with the

good intermixing of the melt, this leads

to very effi cient degassing. To achieve

an optimum degassing effect, the vari-

ous parameters such as rotor diameter

and revolutions per minute, gas fl ow

rate, treatment time, geometry and size

of the crucible used as well as the alloy,

have to be co-ordinated. The course of

degassing and reabsorption of hydrogen

is depicted for various casting alloys

in Figure 7.

When using commercially available salt

preparations, the manufacturer‘s instruc-

tions concerning use, proportioning,

storage and safety should be followed.

Apart from this, attention should also be

paid to the quality and care of tools and

auxiliary materials used for cleaning so

that the cleaning effect is not impaired.

If practically feasible, it is also possible

to fi lter the melt using a ceramic foam

fi lter. In the precision casting of high-

grade castings, especially in the sand

casting process, the use of ceramic

fi lters in the runner to the sand mould

has proved to be a success. Above all,

such a fi lter leads to an even fl ow and

can retain coarse impurities and oxides.

In the gravity die casting of sensitive

hydraulic parts, or when casting sub-

sequently anodised decorative fi ttings

in Al Mg3, ladling out of a device which

is fi tted with in-line fi lter elements and

separated from the remaining melt bath

is very common.

27


Melt testing and inspection procedure

To assess the effectiveness of the clean-

ing process or the quality of the melt, the

following test and inspection methods

can be used to monitor the melt:

Reduced pressure test

This method serves to determine the

tendency to pore formation in the melt

during solidifi cation. A sample, which

can contain a varying number of gas

bubbles depending on the gas content,

is allowed to solidify at an underpressure

of 80 mbar. The apparent density is then

compared with that of a sample which

is solidifi ed at atmospheric pressure.

The so-called “Density Index” is then

calculated using the following equation:

DI = (dA - d80)/dA x 100 %

DI = Density Index

dA = density of the sample solidifi ed

at atmospheric pressure

d80 = density of the sample solidifi ed

at under 80 mbar

The Density Index allows a certain infer-

ence to be drawn about the hydrogen

content of the melt. It is, however, strongly

infl uenced by the alloying elements and,

above all, by varying content of impurities

so that the hydrogen content must not

on any account be stated as a Density

Index value (Figure 8).

The assessment of melt quality by means

of an underpressure density sample there-

fore demands the specifi c determination

of a critical Density Index value for each

casting alloy and for each application.

The underpressure density method is,

however, a swift and inexpensive meth-

od with the result that it is already used

in many foundries for quality control.

To keep results comparable, sampling

should always be carried out according

to set parameters.

Determination of the hydrogen

content in the melt

Reliable instruments have been in opera-

tion for years for measuring the hydrogen

content in aluminium melts. They work

according to the principle of establish-

ing equilibration between the melt and a

measuring probe so that the actual gas

content in the melt is determined and not

in the solid sample. In this way, the effec-

tiveness of the degassing treatment can

be assessed quickly. The procurement of

such an instrument for continuous quality

monitoring is only worthwhile when it is

used frequently; in small foundries, the

hiring of an instrument to solve problems

is suffi cient.

28


Determination of insoluble

non-metallic impurities

For determining the number and type

of insoluble non-metallic impurities in

aluminium melts, the Porous Disc Filtra-

tion Apparatus (PoDFA) method, among

others, can be used. In this particular

method, a precise amount of the melt

is squeezed through a fi ne fi lter and

the trapped impurities are investigated

metallographically with respect to their

type and number. The PoDFA method

is one of the determination procedures

which facilitates the acquisition, both

qualitatively and quantitatively, of the

impurity content. It is used primarily for

evaluating the fi ltration and other clean-

ing treatments employed and, in casting

alloys production, is utilised at regular

intervals for the purpose of quality control.

This method is not suitable for making

constant routine checks since it is very

time-consuming and entails high costs.

Hydrogen content [ml/100g]

Correlation between the hydrogen content and density index in unmodifi ed Al Si9Mg alloy

Density index Measurement acc. to Chapel [%] at vacum 30 mbar

35

30

25

20

15

10

5

0

0 0.1 0.2 0.3 0.4 0.5 0.6

Figure 8

29


Thermal analysis

To evaluate the effectiveness of melt

treatment measures, e.g. modifi cation,

grain refi nement and primary silicon re-

fi ning, thermal analysis has proved itself

to be a fast and relatively inexpensive

method in many foundries. The test

method is based on the comparison of

two cooling curves of the investigated

melts (Figures 9 and 10).

The undercooling effect (recalescence)

occurring during primary solidifi cation

allows conclusions to be made about

the effectiveness of a grain refi nement

treatment, whereby the recalescence

values do not however allow conclusions

to be drawn as regards the later grain

size in the microstructure. Modifi cation is

shown in thermal analysis by a decrease

in the eutectic temperature (depression)

in comparison to the unmodifi ed state.

Here too, the level of the depression

values depend strongly on the content

of accompanying and alloying elements

(e.g. Mg) and, consequently, the de-

pression values required for suffi cient

modifi cation must be established case

by case, by means of parallel microstruc-

tural investigations.

Time [t]

Thermal analysis for monitoring the grain refi nement of Al casting alloys

Temperature [T]

With grain refi nement Without grain refi nement

Liquidus temperature [TL]

TL

TL

Figure 9

Time [sec]

Thermal analysis for monitoring the modifi cation of Al casting alloys

Temperature [°C]

585

580

577575

570

565

560

0 10 20 30 40 50

Modifi ed Undermodifi ed Eutectic temperature

Figure 10

30


Selecting the casting process

Squeeze-casting is another casting pro-

cess to be mentioned; here, solidifi cation

takes place at high pressure. In this way,

an almost defect-free microstructure

can be produced even where there are

large transitions in the cross-section

and insuffi cient feeding.

Other special casting processes include:

• Precision casting

• Evaporative pattern casting

• Plaster mould casting

• Vacuum sand casting

• Centrifugal casting.

The considerations above concern cast-

ing as an overall process.

In the following notes on casting prac-

tice, the actual pouring of the molten

metal into prepared moulds and the

subsequent solidifi cation control are

looked at in more detail.

From the numerous casting processes,

which differ from one another in the type

of mould material (sand casting, per-

manent dies etc.) or by pressurisation

(pressure die casting, low-pressure die

casting etc.), a few notes are provided

here on the most important processes.

nesses can be favourably infl uenced

with the help of risers. Cylinder heads

for water-cooled engines represent a

typical application.

In the low-pressure gravity die process

with its upward and controllable cavity

fi lling, the formation of air pockets is re-

duced to a minimum and, consequently,

high casting quality can be achieved. In

addition to uphill fi lling, the overpressure

of approx. 0.5 bar has a positive effect

on balancing out defects caused by

shrinkage. The low-pressure die casting

process is particularly advantageous in

the casting of rotationally symmetrical

parts, e.g. in the manufacture of pas-

senger vehicle wheels.

Pressure die casting is the most widely

used casting process for aluminium

casting alloys. Pressure die casting is

of particular advantage in the volume

production of parts where the require-

ment is on high surface quality and the

least possible machining. Special ap-

plications (e.g. vacuum) during casting

enable castings to be welded followed

by heat treatment which fully exploits

the property potential displayed by the

casting alloy.

In addition to conventional pressure die

casting, thixocasting is worthy of men-

tion since heat-treatable parts can also

be manufactured using this process.

The special properties are achieved

by shaping the metal during the solid-

liquid phase.

As mentioned in the introduction, the

entire “casting” process is the shortest

route from molten metal to a part which

is almost ready for use. All sections of

this catalogue contain advice on how the

entire experience should be carried out.

The casting process is selected ac-

cording to various criteria such as batch

size, degree of complexity or requisite

mechanical properties of the casting.

Some examples:

The sand casting process is used

predominantly in two fi elds of appli-

cation: for prototypes and small-scale

production on the one hand and for the

volume production of castings with a

very complex geometry on the other.

For the casting of prototypes, the main

arguments in favour of the sand casting

process are its high degree of fl exibility

in the case of design changes and the

comparably low cost of the model. In vol-

ume production, the level of complexity

and precision achieved in the castings

are its main advantages.

When higher mechanical properties are

required in the cast piece, such as higher

elongation or strength, gravity die cast-

ing, and to a limited extent pressure die

casting, are used. In gravity die casting,

there is the possibility of using sand

cores. Large differences in wall thick-

31


Gravity die casting process

The gravity die casting which includes

the well-known low-pressure die casting

process is applied. The main fi elds of

application are medium- or high-volume

production using high-grade alloys, and

also low to medium component weight

using heat-treatable alloys. Compared

with sand casting, the aluminium cast-

ings display very good microstructural

properties as well as good to very good

mechanical properties which result from

the rapid cooling times and the other

easily-controlled operating parameters.

The castings have high dimensional ac-

curacy and stability as well as a good

surface fi nish, are heat-treatable and

can also be anodised.

The basis for good quality castings is,

not least, the right melt treatment and

the appropriate casting temperature (see

section on “Melt quality and melt clean-

ing”). For castings with high surface or

microstructural quality requirements,

such as in decorative or subsequently

anodised components or in pressure-

tight hydraulic parts, it is useful to fi lter

the melt before casting.

Parts generated using the horizontal

pressure die casting process are light-

weight as low wall thicknesses can be

achieved. They have a good surface

fi nish, high dimensional accuracy and

only require a low machining allowance

in their design. Many bore holes can be

pre-cast.

The melting and casting temperatures

should not be too low and should be

checked constantly. Pre-melting alu-

minium casting alloys is useful. The melt

can thus be given a good clean in order

to keep the melt homogeneous and to

avoid undesirable gravity segregation

(see Figure 6). From a statistical point

of view, more casting defects arise from

cold metal than from hot. It is particu-

larly important to keep a suffi ciently high

melting temperature, even with hypere-

utectic alloys. These comments are also

valid for other casting processes.

Pressure die casting process

This process takes up the largest share.

The hydraulically-controlled pressure

die casting machine and the in-built

die make up the central element of the

process. The performance, the precise

control of the hydraulic machine, the

quality of the relatively expensive tools

made from hot work steel are the deci-

sive factors in this process. In contrast,

the fl ow properties and solidifi cation

of the aluminium casting alloys play a

rather subordinate role in this “forced”

casting process.

The pouring operation in horizontal pres-

sure die casting begins with the casting

chamber being fi lled with metal. The

fi rst movement, i.e. the slow advance of

the plunger and the consequent pile-up

of metal until the sleeve is completely

fi lled, is the most important operation.

In doing this, no fl ashover of the metal

or other turbulence may occur until all of

the air in the sleeve has been squeezed

out. Immediately afterwards, the actual

casting operation begins with the rapid

casting phase. High injection pressure is

essential to achieve high fl ow velocities

in the metal. In this way, the die can be

fi lled in a few hundredths of a second.

Throughout the casting operation, the

liquid metal streams are subject to the

laws of hydrodynamics. Sharp turns

and collisions with the die walls lead

to a clear division of the metal stream.

32


Demands on the casting system

To keep disadvantages and defects –

which constantly arise from an oxide

skin forming on the melt – within limits,

the gating system must guarantee low

turbulence in the metal stream and also

a smooth, controlled fi lling of the die

cavity. With the transition from a liquid

to a solid condition, volume contraction

occurs; this can amount to up to 7 %

of the volume. This shrinkage is con-

trollable when the solid-liquid interface

runs – controlled or directed – through

the casting, mostly from the bottom to

the top. This task, namely to effect a

directed solidifi cation, can be achieved

with a good pouring system.

The castings are usually arranged “up-

right” in the die. The greatest mass can

thus be placed in the bottom of the die.

Quality requirements can be, for example,

high strength, high-pressure tightness or

decorative anodising quality.

One example of an “ideal” gating system

which meets the highest casting require-

ments is the so-called “slit gate system”.

Here, the metal is conducted upwards

continuously or discontinuously to the

casting via a main runner. During mould

fi lling, the melt is thus superimposed layer

upon layer with the hotter metal always

fl owing over the already solidifying metal.

The standpipe ends in the top riser and

supplies it with hot metal. This way, the

solidifi cation can be directed from below,

possibly supported by cooling, towards

the top running through the casting and

safeguarding the continuous supply of

hot metal. When there is a wide fl are in

the casting, the gating system has to be

laid out on both sides. This symmetry en-

sures a division of the metal and also an

even distribution of the heat in the die.

In low-pressure die casting, directing

the solidifi cation by means of the gat-

ing system is not possible. Nor is there

any great possibility of classic feeding.

Directional solidifi cation is only possible

by controlling the thermal balance of the

die during casting. This mostly requires

the installation of an expensive cooling-

heating system.

Simulation calculations for die fi lling and

solidifi cation can be useful when laying

out and designing the die and possibly

the cooling. In actual production, the

cooling and cycle time can be optimised

by means of thermography (see section

on “Solidifi cation simulation and ther-

mography”).

33


Sand casting process

This process is used especially for in-

dividual castings, prototypes and small

batch production. It is, however, also

used for the volume production of cast-

ings with a very complex geometry (e.g.

inlet manifolds, cylinder heads or crank-

cases for passenger vehicle engines).

During shaping and casting, most large

sand castings display in-plane expan-

sion. With this fl at casting method, gating

systems like those which are normal in

gravity die casting for directing solidifi ca-

tion are often not applicable. If possible,

a superimposed fi lling of the die cavity

should be attempted here.

Another generally valid casting rule for

correct solidifi cation is to arrange risers

above the thick-walled parts, cooling (e.g.

by means of chills) at opposite ends. This

way, the risers can perform their main

task longer, namely to conduct the sup-

ply of molten metal into the contracted

end. Insulated dies are often helpful.

The cross-section ratio in the sprue system

should be something like the following:

Sprue :

Sum of the runner cross-section :

Sum of the gates:

like 1 : 4 : 4.

This facilitates keeping the run-in laun-

der full and leads to a smoother fl ow

of the metal. This way, the formation of

oxides due to turbulence can be kept

within limits. The main runner must lie

in the drag, the gates in the cope. In the

production of high-grade castings, it is

normal to install ceramic fi lters or sieves

made from glass fi bre. The selection of

the casting process and the layout of

the casting system should be carried

out in close co-operation between the

customer, designer and foundryman (see

section on “Casting-compliant design”).

34


Casting-compliant design

Only through good cast quality can the

technical requirements be met and the

full potential of the casting alloy be ex-

ploited. Every effort and consideration

must be made therefore to design a light,

functionally effi cient part whose manu-

facture and machining can be carried out

as effi ciently as possible. For this and

subsequent considerations, the use of

solidifi cation simulation is available (see

section on “Solidifi cation simulation and

thermography”).

Casting alloys shrink during solidifi ca-

tion, i.e. their volume is reduced. This

increases the risk of defects in the cast

structure, such as cavities, pores or

shrinkage holes, tears or similar. The

most important requirement is thus to

avoid material accumulations by hav-

ing as even a wall thickness as possible.

In specialist literature, the following lower

limits for wall thickness are given:

• Sand castings: 3-4 mm

• Gravity die castings: 2-3 mm

• Pressure die castings: 1-1.5 mm.

In the valid European standard, DIN EN

1706 for aluminium castings, there are

strength values only for separately-cast

bars using sand and gravity die casting.

For samples cut from the cast piece,

a reduction in the 0.2 % proof stress

and ultimate tensile strength values of

up to 70 % and a decrease in elonga-

tion of up to 50 % from the test bar can

be anticipated. When the alloy and the

casting process are specifi ed, so too is

the next point within the framework of

the design, i.e. determination of the die

parting line. Die parting on one level is

not only the cheapest for patterns and

dies but also for subsequent working and

machining. Likewise, every effort should

be made to produce a casting without

undercuts. This is followed by designing

and determining the actual dimensions

of the part. The constant guideline must

be to achieve a defect-free cast structure

wherever possible.

The following notes on the design of

aluminium castings are provided to help

exploit in full the advantages and design

possibilities of near net shape casting.

They also align practical requirements

with material suitability.

Aluminium casting alloys can be pro-

cessed in practically all conventional

casting processes, whereby pressure die

casting accounts for the largest volume,

followed by gravity die casting and sand

casting. The most useful casting process

is not only dependent on the number and

weight of pieces but also on other tech-

nical and economic conditions (see sec-

tion on “Selecting the casting process”).

To fi nd the optimum solution and produce

a light part as cheaply and rationally as

possible, co-operation between the de-

signer, caster and materials engineer is

always necessary. Knowledge concern-

ing the loads applied, the distribution of

stress, the range of chemical loading and

operation temperatures is important.

35


The minimum values are also dependent

on the casting alloy and the elongation of

the casting. In pressure die casting, the

minimum wall thickness also depends

on the position of and distance to the

gate system.

Generally speaking, the wall thickness

should be as thin as possible and only

as thick as necessary. With increasing

wall thickness, the specifi c strength of

the cast structure deteriorates.

Determining casting-compliant wall

thicknesses also means, especially with

sand and gravity die casting, that the die

must fi rst of all be fi lled perfectly. During

subsequent solidifi cation, a dense cast

structure can only occur if the shrinkage

is offset by feeding from liquid melt. Here,

a wall thickness extending upwards as a

connection to the riser may be necessary.

Another possible way of avoiding material

accumulations is to loosen the nodes.

At points where fi ns cross, a mass ac-

cumulation can be prevented by stag-

gering the wall layout.

The corners where walls or fi ns meet

should be provided with as large transi-

tions as possible. Where walls of different

thickness meet, the transitions should

be casting-compliant.

Where the casting size and process

permit, bores should be pre-cast. This

improves the cross-section ratio and

structural quality.

Apart from the points referred to above,

a good design also takes account of

practical points and decorative appear-

ance as well as the work procedures

and machining which follow the actual

casting operation.

Fettling the casting, i.e. removing the

riser and feeders, must be carried out as

effi ciently as possible. Grinding should

be avoided where possible. Reworking

and machining should also be easy to

carry out. Machining allowances are to

be kept as small as possible.

Essential inspections or quality tests

should be facilitated by constructive

measures.

36


Solidifi cation simulation and thermography

Thermography

Even after a casting goes into volume

production, it is often desirable and nec-

essary to optimise the casting process

and increase process stability. Besides

the aforementioned solidifi cation simula-

tion, periodic thermal monitoring of the

dies by means of thermography is used

in particular.

In this process, a thermogramme of the

die or casting to be investigated is made

with the aid of an infrared camera. This

way, the effectiveness of cooling, e.g. in

pressure or gravity die casting, can be

checked or optimised and the optimum

time for lifting determined.

Possible positive effects of simulation

calculations include:

• Optimisation of the casting before

casting actually takes place

• Avoiding casting defects

• Optimisation of the feeding system

(reducing material in the recycling

circuit)

• Optimisation of the casting

process (reducing cycle times)

• Increasing process stability

• Visualisation of the die-fi lling and

solidifi cation process.

A simulation programme does not opti-

mise on its own and can not, and should

not, replace the experienced foundry-

man. To exploit the potential of die-fi lling

and solidifi cation simulation to the full,

it should be applied as early as possi-

ble, i.e. already at the design stage of

the casting.

Solidifi cation simulation

A basic aim in the manufacture of cast-

ings is to avoid casting defects while

minimising the amount of material in the

recycling circuit.

Optimisation of the manufacture of cast-

ings with regard to casting geometry,

gating and feeding system and cast-

ing parameters can be achieved via

numerical simulation of die fi lling and

the mechanisms of solidifi cation on the

computer. Casting defects can thus be

detected in good time and the casting

design and casting system optimised

before the fi rst casting operation takes

place. In principle, fl ow and thermal con-

duction phenomena which occur during

casting can be calculated numerically

using simulation programmes.

In calculation models, the casting and

die geometry – which fi rst of all must be

available in a CAD volume model – is thus

divided into small volume elements (Finite

Difference Method). The fl ow velocities

and temperatures in the individual vol-

ume elements are then calculated using

a numerical method.

37


Avoiding casting defects

The type of solidifi cation is also impor-

tant when considering suitable casting/

technical measures. In AlSi casting al-

loys with approx. 13 % Si, a frozen shell

forms during solidifi cation while, in hy-

poeutectic AlSi casting alloys as well

as in AlMg and AlCu casting alloys, a

predominantly dendritic or globular so-

lidifi cation occurs.

In gravity die casting processes, the

feeders are laid out in particularly critical

or thick areas of the casting. The feed-

ers require hot metal in appropriately

large volumes to execute their task. The

combination of feeding and cooling is

useful. Heat removal to accelerate and

control solidifi cation at the lower end

of the casting or in solid areas can be

effected by means of metal plates or

surface chills (cooling elements).

quality and melt cleaning” as well as

“Methods for melt monitoring” and “Se-

lecting the casting process”. Here are a

few key points:

• Use good quality ingots

• Quality-oriented melting technology

and equipment

• Correct charging of the ingots

(dry, rapid melting)

• Temperature control during

melting and casting

• Melt cleaning and melt control

• Safety measures during treatment,

transport and casting

Volume contraction during the transition

from liquid to solid state can - depend-

ing on the casting alloy - be up to 7 %

volume. Under unfavourable conditions,

part of this volume difference can be the

cause of defects in castings, e.g. shrink

marks, shrink holes, pores or tears. To

produce a good casting, the possibility

of feeding additional molten metal into

the contracting microstructure during

solidifi cation must exist. In pressure

casting processes, this occurs by means

of pressurisation; in gravity die casting,

this is done primarily by feeding.

As shown in Table 4, there are two

phenomena which – individually or in

combination – can lead to defects in

emergent castings:

1. The continuous (new) formation of

oxides in the liquid state and

2. volume contraction during the trans-

ition from liquid to solid state.

During transition from liquid to solid

state, the dissolved hydrogen in the melt

precipitates and, on interacting with ox-

ides, causes the well-known problem of

microporosity or gas porosity.

The task of melt management and

treatment is to keep oxide formation

and, consequently, the dangers to cast

quality within limits. Information about

this is provided in the sections on “Melt

38


As already shown in the section on cast-

ing processes, an uncontrolled or tur-

bulent fi lling of the die cavity can have a

negative infl uence on the quality of the

casting. A gating system which allows

the solidifi cation front to be controlled

upwards through the casting from the

bottom up to the feeder is helpful. A

good casting system, e.g. side stand

pipe-slit gate, begins the fi lling in the

lower part of the die and always layers

the new hot metal on the lower, already

solidifi ed part and also supplies the

feeder with hot metal.

A casting system of this type can par-

tially cushion the negative effect caused

by volume contraction while conducting

the molten metal in such a way that fresh

oxidation of the melt due to turbulence

is avoided.

Two methods can be used to reduce

the number of defective parts due to

porosity: In hot isostatic pressing (HIP),

porous castings are subjected to high

pressure at elevated temperatures so

that shrinkage and pores inside the cast-

ings are reduced; they do not, however,

completely disappear. A second and

less costly possibility is the sealing of

castings by immersing them in plastic

solutions. The shrinkage and pores,

which extend to the surface, are fi lled

with plastic and therefore sealed.

Classifi cation of casting defects

Source of defect Consequences Optimisation for the casting possibilities

• Oxidation and • Pores • Melt treatment hydrogen- • Aeration and degassing absoption • Inclusions • Melting and • Leakiness casting temperature • Surface defects • Filter • Machining • Loss of strength and elongation

• Volume contraction • Cavity • Gating system • Shrinkage • Solidifi cation control • Aeration • Feeding • Leakiness • Grain refi nement • Loss of strength • Modifi cation and elongation

Table 4

39


Heat treatment of aluminium castings

In ageing, mostly artifi cial ageing, pre-

cipitation of the forcibly dissolved com-

ponents takes place in the form of small

sub-microscopically phases which cause

an increase in hardness and strength.

These tiny phases, which are techni-

cally referred to as “coherent or semi-

coherent phases”, represent obstacles

to the movement of dislocations in the

metal, thereby strengthening the previ-

ously easily-formable metal.

The following casting alloy types are

age-hardenable:

• Al Cu

• Al CuMg

• Al SiMg

• Al MgSi

• Al ZnMg.

Metallurgy – fundamental principles

For age-hardening to take place, there

must be a decreasing solubility of a par-

ticular alloy constituent in the α-solid so-

lution with falling temperature. As a rule,

age-hardening comprises three steps:

In solution annealing, suffi cient amounts

of the important constituents for age-

hardening are dissolved in the α-solid

solution.

With rapid quenching, these constituents

remain in solution. Afterwards, the parts

are relatively soft.

Heat treatment gives users of castings

the possibility of specifi cally improv-

ing the mechanical properties or even

chemical resistance. Depending on the

casting type, the following common and

applied methods for aluminium castings

can be used:

• Stress relieving

• Stabilising

• Homogenising

• Soft annealing

• Age-hardening.

The most important form of heat treat-

ment for aluminium castings is artifi cial

ageing. Further information is provided

below.

Ageing time [h]

Yield strength of gravity die cast test bars (Diez die) in Al Si10Mg alloy

Yield strength Rp0,2

[MPa]

280

240

200

160

120

0

0 2 4 6 8 10 12 14 16

As-cast state160 °C 180 °C 200 °C

Figure 11.1

Ageing time [h]

Elongation of gravity die cast test bars (Diez die) in Al Si10Mg alloy

Elongation A5

[%]

5

4

3

2

1

0

0 2 4 6 8 10 12 14 16


Figure 11.2

40


Ageing time [h]

Tensile strength of gravity die cast test bars (Diez die) in Al Si10Mg alloy

Tensile strength Rm [MPa]

360

320

280

240

200

160

0 2 4 6 8 10 12 14 16


Figure 11.3

Solution annealing

To bring the hardened constituents into

solution as quickly as possible and in a

suffi cient amount, the solution anneal-

ing temperature should be as high as

possible with, however, a safety margin

of approx. 15 K to the softening point

of the casting alloy in order to avoid in-

cipient fusion. For this reason, it is often

suggested that casting alloys containing

Cu should undergo step-by-step solution

annealing (at fi rst 480 °C, then 520 °C).

The annealing time depends on the wall

thickness and the casting process. Com-

pared with sand castings, gravity die cast-

ings require a shorter annealing time to

dissolve the constituents suffi ciently due

to their fi ner microstructure. In principle,

an annealing time of around one hour

suffi ces. The normally longer solution

annealing times of up to 12 hours, as

for example in Al SiMg alloys, produce

a good spheroidising or rounding of the

eutectic silicon and, therefore, a marked

improvement in elongation.

The respective values for age-hardening

temperatures and times for the individual

casting alloys can be indicated on the

respective data sheets.

During the annealing phase, the strength

of the castings is still very low. They must

also be protected against bending and

distortion. With large and sensitive cast-

ings, it may be necessary to place them

in special jigs.

Quenching

Hot castings must be cooled in water as

rapidly as possible (5-20 seconds de-

pending on wall thickness) to suppress

any unwanted, premature precipitation of

the dissolved constituents. After quench-

ing, the castings display high ductility.

This abrupt quenching and the ensuing

increase in internal stresses can lead

to distortion of the casting. Parts are

often distorted by vapour bubble pres-

sure shocks incurred during the rapid

immersion of hollow castings. If this is

a problem, techniques such as spraying

under a water shower or quenching in

hot water or oil have proved their value

as a fi rst cooling phase.

Nevertheless, any straightening work

necessary at this stage should be carried

out after quenching and before ageing.

41


Ageing

The procedure of ageing brings about

the decisive increase in hardness and

strength of the cast structure through

the precipitation of the very small hard-

ening phases. Only after this does the

part have its defi nitive service properties

and its external shape and dimensions.

Common alloys mostly undergo artifi cial

ageing. The ageing temperatures and

times can be varied as required. In this

way, for example, the mechanical prop-

erties can be adjusted specifi cally to at-

tain high hardness or strength although,

in doing this, relatively lower elongation

must be reckoned with. Conversely, high

elongation can be also achieved while

lower strength and hardness values will

be the result. When selecting the age-

ing temperatures and times, it is best to

refer to the ageing curves which have

been worked out for many casting al-

loys (Figures 11.1-11.4).

In Al SiMg casting alloys, a further pos-

sibility of specifi cally adjusting strength

and elongation arises from varying the

Mg content in combination with different

heat treatment parameters (Figure 12).

Ageing time [h]

Brinell hardness of gravity die cast test bars (Diez die) in Al Si10Mg alloy

Brinell hardness [HB]

160

140

120

100

80

60

0 2 4 6 8 10 12 14 16


Figure 11.4

Magnesium [%]

Infl uence of Magnesium on the tensile strength (Diez bars)

Tensile strength Rm Alloy Al Si7 auf 99.9 base[MPa] + 200 ppm Sr + 1 kg/mt Al Ti3B1 n=5

300

250

200

150

100

50

0

0 0.1 0.2 0.3 0.4 0.5 0.6

8 h to 525 °C, H2O As-cast state

8 h to 525 °C, H2O +6 h to 160 °C

Figure 12

42


If the heat treatment does not work fi rst

time, it can be repeated beginning with

solution annealing. By doubling the so-

lution time, a coarsening of the eutectic

silicon can arise in the grain structure.

Since the solution treatment is performed

close to the alloy‘s melting temperature

and the precipitation rate is highly sen-

sitive to variations in ageing tempera-

ture, it is essential that a high degree

of consistency and control is assured.

Regular maintenance, especially of the

measuring and control equipment, is

therefore absolutely essential.

For slightly higher hardness or strength

requirements, there is the non-standard

possibility of “simplifi ed age-hardening”.

This can be used in gravity die casting

and pressure die casting when age-

hardenable alloys are being poured.

Decisive here is a further rapid cooling

after ejection from the die, e.g. by im-

mediately immersing the part in a bath

of water. Artifi cial ageing in a furnace at

approx. 170 °C brings about the desired

increase in hardness and strength.

The procedure used in artifi cial ageing as

well as typical temperatures and times

are shown in Table 5.

Procedures used in artifi cial ageing 1)

Casting type Example Solution heat treatment Age-hardening Temperature Time Temperature Time [°C] [h] [°C] [h]

Al SiMg Al Si10Mg 530 4 - 10 160 - 170 6 - 8

Al SiCu Al Si9Cu3 480 6 - 10 155 - 165 6 - 2

Al MgSi Al Mg3Si 550 4 - 10 155 - 175 8 - 0

Al CuMg 530* 8 - 18 140 - 170 6 - 8

1) Typical temperature and time values* Poss. gradual annealing at approx. 480 °C / approx. 6 h

Table 5

43


Mechanical machining of aluminium castings

High-speed steel and hard metal or

ceramic plates are used as cutting tool

materials; for microfi nishing, diamonds

are often utilised.

The following machining allowances are

given for the main casting processes:

• sand castings: 1.5-3 mm

• gravity die castings: 0.7-1.5 mm

• pressure die castings: 0.3-0.5 mm.

In order to minimise value losses, turnings

and chips should be sorted out according

to casting alloy type and stored possi-

bly in briquettes. In addition, dampness,

grease and free iron reduce the value of

chips and turnings. Aluminium chips and

turnings are not hazardous materials and

there is no risk of fi re during storage.

When grinding aluminium parts, explosion-

proof separation of the dust is stipulated.

With softer materials and also with most

hypoeutectic AlSi casting alloys, narrow

tools, i.e. with a large rake angle, cause

the least possible surface roughness.

These casting alloys produce narrow-

spiral or short-breaking turnings. When

machining aluminium, suitable emul-

sions with water are used as cooling

agents and lubricants. Friable and chips

and fi ne to powdery Si dust arise when

machining hypereutectic casting alloys.

In combination with the lubricant, this

powder produces an abradant which is

often processed when dry. In some re-

spects, the machining of these casting

alloy types is similar to grey cast iron.

With workpieces made from Al Si12

casting alloys with their very soft matrix,

a large volume of long curly spirals are

produced. In addition, the plastic mate-

rial tends to build up edges on the tool.

This leads to lubrication and, as a result,

a poor surface appearance. When this

occurs, it often gives the machinist the

subjective impression of bad machina-

bility although tool wear is not the cause

in this case.

In general, parts made from aluminium

casting alloys are easy-machinable.

This also applies for all metal-cutting

processes. Low cutting force allows a

high volume of metal to be removed. The

surface fi nish of the cast piece depends

on the machining conditions, such as

cutting speed, cutting geometry, lubri-

cation and cooling.

The high cutting speeds required in alu-

minium to achieve minimum roughness

necessitate, with regard to processing

machines and tools, stable, vibration-

free construction and good cutting tools.

Besides the microstructure – including

defects, pores or inclusions – the silicon

content of the casting has a strong ef-

fect on tool wear. Modifi ed, hypoeutectic

AlSi casting alloys have, e.g. the highest

tool time, while hypereutectic aluminium-

silicon piston casting alloys can cause

very considerable tool wear.

44


Welding and joining aluminium castings

using argon. The process is suitable

for both manual welding and for fully-

mechanised and automatic welding. In

fully-mechanised and automatic welding,

both the power source and burner are

water-cooled. With the wire electrode

acting as the positive pole, the energy

density is so high that it is able to break

open the tenacious and high-melting

oxide layer by means of local, explosive

metal vaporisation underneath the ox-

ide. With appropriate heat conduction,

it is possible to achieve a relatively nar-

row heat-affected zone with satisfactory

strength and elongation values.

A further development of MIG welding is

represented by MIG pulse welding. Here,

the welding current alternates between a

so-called pulsed current and background

current. Using this process, it is possible

to carry out diffi cult tasks, i.e. thin wall

thicknesses (1 mm) and out-of-position

work (overhead).

Today, MIG welding is the most frequently

used aluminium welding process be-

cause, in addition to its easy manipula-

tion, the investment and running costs

are favourable.

The production welding sector should

not be underestimated, e.g. for repair-

ing defects in castings. Besides casting

defects, there is also the possibility of

correcting dimensional discrepancies,

removing wear by build-up welding and

repairing broken components.

Welding processes

The most frequently used fusion weld-

ing processes for joining castings are

metallic-insert-gas welding (MIG weld-

ing) and Tungsten-inert-gas welding

(TIG welding).

Metal inert-gas welding (MIG welding)

In MIG welding, an inert-gas arc weld-

ing process, a continuous arc burns

between a melting wire electrode and

the workpiece. The process works with

direct current, the wire electrode acting

as the positive pole. The process is car-

ried out under an inert gas in order to

protect the melt area from the hazard-

ous infl uences of the oxygen contained

in air and moisture. Argon and/or helium,

both inert gases, are used as shielding

gases. Normally, it is cheaper to weld

Suitability and behaviour

Similar to most wrought aluminium alloys,

castings made from aluminium casting

alloys can, in principle, also be joined by

means of fusion welding. Near-eutectic

and hypoeutectic aluminium-silicon cast-

ing alloys are the best to weld. Poor to

unweldable are parts made from Al Cu4Ti

alloys types since the Cu-content can

cause the casting alloy to crack during

welding. In AlMg casting alloys, the ten-

dency to tearing must be counteracted

by selecting a suitable weld fi ller.

Applications in the aluminium sector

Although near net shape casting gives

the designer the greatest possible free-

dom in the design of castings, welding is

becoming increasingly important for the

joining of aluminium cast components,

either for welding two or more easy-to-

cast parts (e.g. half shells) – whereas

they would be diffi cult to cast as one –

to form hollow bodies on the one hand

or for joining extruded sections or sheet

to castings to give a subassembly on

the other, such as the case in vehicle

construction, lamp posts, lamp fi ttings

and heat exchangers.

45


Tungsten-insert-gas welding

(TIG welding)

In TIG welding, an inert-gas shielded

arc welding process, an arc burns con-

tinuously between a non-consumable

electrode made of a tungsten alloy and

the casting. Alternating current is nor-

mally used when welding aluminium. The

welding fi ller is fed in separately from

outside either by hand or mechanically.

The process is carried out under an in-

ert gas in order to protect the melt area

from the hazardous infl uences of the

oxygen contained in air and moisture.

Argon and/or helium, both inert gases,

are used as shielding gases. Welding is

usually carried out with alternating cur-

rent and argon which is cheaper. This is

primarily a manual welding process but

there is a possibility to work with a full

degree of mechanisation. In TIG weld-

ing, the power source and the burner are

both water-cooled. By using alternating

current, the tenacious and high-melting

oxide layer is broken open during weld-

ing, similar to the MIG process. Weld-

ing normal diameter material with direct

current and a reverse-polarity tungsten

electrode would lead to destruction due

to electric overload. The electrode diam-

eter, however, can not be increased since

the current density required for welding

is no longer suffi cient.

In one process variant, which has an

electrode with negative polarity as in the

welding of steel, welding is carried out

using direct current under a helium shield.

Compared with argon, helium displays

better thermal conductivity so that less

current is required to break open the ox-

ide layer. Consequently, the electrode is

not overloaded. In TIG welding, there are

also process variants which work with

the pulsed-current technique.

With regard to freedom from porosity,

the cleanest seams can be achieved

using TIG welding. One disadvantage

of the TIG welding process, however, is

the high local energy input. This leads

to considerable softening of the zone

adjacent to the weld which is also the

case with MIG welding. TIG welding, for

example, is an excellent process for the

repair of small casting defects. Com-

pared with the MIG process, however,

TIG welding operates at lower speeds.

Other thermal joining processes

The group of so-called “pressure welding

processes” also includes friction stear

welding (FSW) which is frequently used

for welding aluminium castings. Since this

welding process works without any fi ller

material, it is possible to join materials

together which are not fusion-weldable

since they would form brittle inter-metallic

phases. By means of friction welding,

aluminium and steel, for example, can

be joined together.

The principle behind the process is to heat

the workpieces up to a pasty condition

followed by subjecting them to strong

compression. A weld upset is thus de-

veloped and, if necessary, subsequently

machined. The heating is done by rotat-

ing one or both parts and fi nally press-

ing them against each other until they

stop moving. It even allows workpieces

of circular and square cross-sections to

be joined together.

As a result of the rotary movement and

in order to keep the compression load

from increasing too much, a certain cross-

sectional area may not be exceeded.

Another welding process is represented

by electron beam welding. Particular in-

terest is being shown in this process at

the moment for the welding of aluminium

pressure die castings.

46


The process operates mostly under high

vacuum. There are also process variants

which work under partial vacuum and

atmosphere although in these the advan-

tages of this welding process, namely the

production of narrower seams even with

thick workpieces, are extensively lost.

The welding of workpieces takes place

without fi ller material. The welding en-

ergy is imparted by means of a bundled

electron beam which is directed at the

welding point. The electron beams are

generated like those of a cathode ray

tube (television) in a high vacuum. Using

electron-optical focussing, different dis-

tances to the workpiece can be had with

this equipment, even when the workpiece

has undulating contours. Welding inside

closed containers is possible.

In addition to diffi cult-to-weld pressure

die castings, e.g. inlet manifolds, this

process has been successfully used with

cast semi-fi nished products in heat ex-

changers and in the welding of pistons

for internal combustion engines.

Weld preparation

To produce a sound weld, it is necessary

to observe certain “rules”. Weld prepa-

ration must match the welding process

being used and the wall thicknesses to

be joined. Excessive oxide formation is

worked off by metal-cutting. When grind-

ing, resin-bonded grinding discs may

not be used (danger of pore formation).

Another possible way of removing ox-

ides is to etch the component. Grease

and dirt in the welding area have to be

removed using suitable means (danger

of pore formation). Components with

greater wall thicknesses to be joined

should be pre-heated before welding.

Weld fi ller materials

Weld fi ller materials are standardised.

The selection of weld fi ller materials is

guided by the materials of the parts to

be joined. For the most commonly used

aluminium materials, such as near- and

hypoeutectic AlSi casting alloys as

well as age-hardenable Al Si10Mg and

Al Si5Mg variants, S-Al Si12 and S-Al Si5

weld fi ller materials are recommended.

A great danger in welding is the tendency

of many materials to form cracks during

the transition from liquid to solid state.

The cause of these cracks is weld shrink-

age stresses which occur during cooling.

Often the low melting point phases of

the weld fi ller materials are insuffi cient

to “heal” the cracks arising. Through the

selection of a softer weld fi ller material

with a larger share of low melting point

phases, this danger is reduced. In do-

ing this, however, the optimum strength

properties in the weld seam must be

frequently foregone.

The decorative anodisation of a welded

joint with the aforementioned fi ller ma-

terials is not possible because the weld

seam would appear dark. Technical an-

odic oxidation for protective and adhesive

purposes is, however, always possible.

47


Surface treatment: corrosion and corrosion protection

remove the oxide fi lm completely and,

as a rule, act as a preparation to further

surface treatment. Possible sources of

defects leading to subsequent faults

comprise the use of brushes made of

brass or non-stainless steel as well as

sand or steel shot.

When grinding, the use of ceramic

grinding elements without further pre-

treatment frequently leads to good paint

adhesion. One precondition is that no

fi nes from the grinding elements are

pressed into the surface of the cast-

ing. Chemical degreasing agents with

a pickling or etching effect remove the

oxide layer and, as a consequence, all

impurities. It is also worth mentioning

that there is also matt or bright pickling

before anodic oxidation to produce a

special surface fi nish.

Following the alkaline pickling of AlMg

or AlSi casting alloys, the pickling fi lm

must be removed by means of an acid

after-treatment with nitric acid, nitric/

hydrofl uoric acid or sulphuric/hydro-

fl uoric acid. Instead of alkaline pickling

with fi nal dipping, it is more benefi cial

to use an acidic fl uoride-containing

pickling solution immediately.

slightly alkaline media (e.g. ammonia

solutions) since magnesium oxide in

contrast to aluminium oxide is insoluble

in alkaline solutions.

Copper as an alloying element causes

a deterioration in corrosion properties.

This increases slightly with a rising Cu-

content in the range below 0.2 % cop-

per, above 0.2 to 0.4 % more strongly.

Already with a Cu-content of 0.2 %,

permanent action from aqueous solu-

tions containing chlorine can have a very

negative effect on corrosion behaviour.

The negative infl uence of iron on cor-

rosion behaviour is not as distinctive

as that of copper. With an Fe-content

of up to 0.6 %, there is no signifi cant

deterioration in the corrosion behaviour

of casting alloys.

The surface treatment of aluminium cast

products is carried out to improve their

corrosion resistance, for decorative

purposes or to increase the strength

of the components.

A homogeneous, non-porous cast struc-

ture free from shrink holes and cracks

makes coating easier. The quality of the

coating is infl uenced decisively by the

pre-treatment.

Wiping, immersion and steam degreas-

ing (in that order) produce increasingly

grease-free surfaces without removing

the surface oxide fi lm. Grinding, brush-

ing, abrasive blasting or polishing do not

Aluminium casting alloys – like wrought

aluminium alloys – owe their corrosion

resistance to a thin, tenacious coating

layer of oxides and hydroxides. In the pH

range from 4.5 to 8.5, this oxide layer is

practically insoluble in aqueous media

and aluminium casting materials suffer

only negligible mass disappearance.

This passivity can, however, be annulled

locally at weak points in the oxide layer

due to the action of water containing

chloride. Since the aqueous medium,

e.g. weather, only acts periodically, a

protective oxide layer forms again at

small, local corrosion sites, e.g. repas-

sivation occurs. Deep pitting corrosion

can only arise when there is a long-term

effect from aggressive water contain-

ing chloride (e.g. sea water). Beside the

chloride content, the amount of oxygen

in the water also plays a role; corrosion

reaction can only occur in neutral me-

dia (pH = 4.5-8.5) in the presence of

oxygen. The remedy for this can come

in the form of passive protection by

coating or by means of active cathodic

corrosion protection using a sacrifi cial

anode, for example.

Magnesium as an alloying element

causes the formation of a thicker oxide

layer containing MgO and, consequently,

provides greater corrosion protection

against water containing chlorides and

48


Of the unlimited number of application

techniques used for volume lacquering,

electrostatic powder coating, whirl sin-

tering and electrophoretic dip coating

are to be stressed in particular because

of their environmental soundness, in

addition to the dip coating and spray-

ing (air, airless and electrostatic) of wet

paint containing solvents.

With the aid of anodic oxidation, the

fi nish achieved using mechanical or

chemical surface treatment can be con-

served permanently. These anodically

produced oxide layers are connected

solidly to the aluminium and, in contrast

to lacquering, the surface structure of

the original metal is unchanged. This

can prove disadvantageous, especial-

ly in pressure die casting. In today‘s

widely-used sulphuric acid anodising

process, the anodically-formed oxide

layers become resistant to touch (e.g.

fi nger marking) and abrasion resistant

after sealing in hot water and possess

good electric strength. The appearance

of anodically-oxidised aluminium cast-

ings is considerably infl uenced by the

alloy composition and the microstruc-

tural condition. For decorative purposes,

Al Mg3H, Al Mg3, Al Mg3Si, Al Mg5,

Al Mg5Si and Al 99.5 and/or Al 99.7

casting alloys have proved their worth.

A decorative anodic oxidation of alloys

with an Si-content > 1 % is not possi-

ble (with the exception of Al Si2MgTi).

Despite careful acid cleaning, a lac-

quered aluminium surface can still dis-

play adhesive failure after a certain time

due to environmental effects. Firstly,

a conversion layer, which forms as a

result of the reaction between chemi-

cals containing chrome and the metal,

passivates the aluminium surface and

protects it from the water diffused by

each layer of lacquer. With respect to

the promotion of adhesion and corro-

sion inhibition, the almost equivalent

green and yellow chromate coatings

have proved their worth over many

years. A clear chromate coating, pref-

erably used under clear lacquer, offers

slightly less corrosion protection due

to the layer being thinner. Cr-VI-free

chromate-phosphate coatings meet the

requirements of food processing and

distribution laws and are permitted for

the pre-treatment of aluminium which

is used in food production, processing

and packaging.

A chrome-free epoxy primer should

be mentioned as a possible but also

qualitatively less favourable alternative.

A precondition for the effectiveness of

this alternate process, however, is also

the removal of the aluminium oxide layer

by chemical or mechanical means.

The possibility of producing coloured

oxide layers also exists by means of dip

painting, electrolytic colouring and in-

tegral colouring in special electrolytes

(integral process).

For surfaces which have to meet particular

requirements with regard to hardness,

resistance to abrasion and wear, slid-

ing capacity and electric strength, the

special possibility of using hard anodis-

ing should be taken into consideration.

49


Information on physical data, strength properties and strength calculations

Strength at varying temperatures

At low temperatures, the strength and

elongation values of aluminium parts

scarcely change. Due to the crystal

structure of aluminium alloys, no sharp

decrease in impact ductility can occur

at low temperatures – as can happen

with some ferrous metals.

At higher temperatures, the strength and

hardness values decrease while elonga-

tion increases. Up to approx. +150 °C,

these changes are relatively small. With

further increases in temperature, strength

and hardness decrease even more and

elongation rises. Table 6 depicts the 0.2

proof stress values for gravity die cast

samples at various test temperatures.

The actual values reached in the casting

depend on the casting/technical meas-

ures taken, the solidifi cation speed and

also, where applicable, the heat treat-

ment. When the end product has to meet

special requirements, an appropriate

casting alloy is required which, corre-

spondingly, also incurs higher casting/

technical expenses. A few details for

calculating the strength of constructions

which are subjected to static stress are

given below. With dynamic stress, lower

values are estimated.

• Surface pressure:

p = approx. 0.8 Rp0,2 [MPa]

• Shear strength:

B = approx. 0.5 Rp0,2 [MPa]

• Modulus of elasticity in shear:

G = approx. 0.4 modulus of

elasticity [GPa]

• Modulus of elasticity:

E = approx. 70 GPa

The SI unit for force is the Newton (N).

Strength, or proof stress, is expressed in

“MPa” (Mega Pascal). The Brinell hard-

ness of aluminium parts is excluded from

this regulation.

For the tensile strength, 0.2 proof stress,

elongation and Brinell hardness of cast-

ings, DIN EN 1706 contains only binding

minimum values at room temperature

for separately-cast test bars using sand

casting, gravity die casting and invest-

ment casting. The mechanical values

for pressure die cast samples are not

binding and are included only for infor-

mation. The values for fatigue strength

or endurance are valid for the best avail-

able casting process and again are only

for information. For samples taken from

the casting, DIN EN 1706 sets out the

following: with respect to the 0.2 proof

stress and tensile strength, the values

reached in castings can be above the

set values in the tables (for separately-

cast test pieces) but not below 70 % of

these set values. With regard to elon-

gation, the values determined for the

castings can be above the set values

in the tables (for separately-cast test

pieces) or at certain critical points up

to 50 % below these values. Individual

details about the mechanical, physical

and other properties as well as the ap-

proximate working fi gures can be taken

from the casting alloy sheets.

Yield strength of gravity die cast samples

Alloy / Temper Yield strength Rp0,2 [MPa]

-100 °C +20 °C +100 °C +200 °C +250 °C

Al Mg3Si T6 160 150 140 60 30

Silumin F 120 80 60 40 30

Al Si12Cu F 110 90 80 35 30

Al Si8Cu3 F 120 100 90 50 25

Silumin-Kappa F 90 80 70 50 30

Al Mg5Si T6 130 120 110 100 70

Al Si18CuNiMg F 180 170 150 100 80

Al Si12CuNiMg F 200 190 170 100 70

Al Si10MgCu T6 220 200 170 80 35

Pantal 7 T6 215 210 180 80 30

Silumin-Beta T6 220 210 200 80 30

Pantal 5 T6 220 210 200 80 30

Table 6

50


Notes on the casting alloy tables

The following tables contain all standard-

ised casting alloys in accordance with

DIN EN 1676 as well as other common

non-standardised alloys with details of

their chemical composition. Provided that

deviations are envisaged for castings,

the corresponding details (in conformity

with DIN EN 1706) are shown in brackets.

Where available, the well-known and very

commonly used VDS numbers (e.g. 231,

226 etc.) are given in these lists.

The aluminium casting alloys are arranged

into seven families according to their typi-

cal casting and alloying similarities. The

data, properties, rankings and standard

values of the casting alloys, or the castings

subsequently made from them, have been

taken from DIN EN 1676 and 1706 or are

based on these standards in the case of

non-standardised alloys. The details are

included for information only and do not

represent any guarantees.

Thermal and electrical conductivity are

dependent on the chemical composition

within the given specifi cation, solidifi ca-

tion conditions and temper. In order to

produce a casting with high conductivity,

it is necessary to keep the content of al-

loying and accompanying elements low

within the specifi cation.

The following designation

abbreviations are used in DIN EN 1676:

A Aluminium

B Ingots (solid or liquid metal)

In DIN EN 1706, the following

abbreviations refer to product

designations:

A Aluminium casting alloy

C Casting

The following abbreviations are used

for the various casting processes:

S Sand casting

K Gravity die casting

D Pressure die casting

L Precision casting

In DIN EN 1706, the following symbols

apply for material conditions:

F as cast

O annealed

T1 controlled cooling from casting

and naturally aged

T4 solution heat-treated and natu-

rally aged where applicable

T5 controlled cooling from casting

and artifi cially aged or over-aged

T6 solution heat-treated and fully

artifi cially aged

T64 solution heat-treated and artifi cially

under-aged

T7 solution heat-treated and artifi cially

over-aged (stabilised)

Chemical composition

(all data in wt.-%)

Casting characteristics and

other properties

Physical properties

Mechanical properties at room

temperature +20 °C

Heat treatment of aluminium

castings

Mechanical properties of gravity

die cast samples

Processing guidelines

51


Overview: Aluminium casting alloys by alloy group

Chemical composition (all data in wt.-%)

Alloy Numerical Other denomination 1) / Si Fe Cu Mn Mg Cr Ni Zn Pb Sn Ti VDS-No.

Silumin min 12.5 max 13.5 0.15 0.02 0.05 0.05 0.07 0.15 0.03 0.10 Na

Al Si12(a) min 10.5 max 13.5 0.40 0.03 0.35 0.10 0.15 0.05 0.15 Na (0.55) (0.05) 44200 / 230

Al Si12(b) min 10.5 max 13.5 0.55 0.10 0.55 0.10 0.10 0.15 0.10 0.15 0.05 0.15 (0.65) (0.15) (0.20) 44100

Al Si12(Fe)(a) min 10.5 0.45 max 13.5 0.9 0.08 0.55 0.15 0.15 0.05 0.25 (1.0) (0.10) 44300 / 230D

Al Si12(Fe)(b) min 10.0 0.45 max 13.5 0.9 0.18 0.55 0.40 0.30 0.15 0.05 0.25 (1.0) (0.20) 44500

Al Si12(Cu) min 10.5 0.05 max 13.5 0.7 0.9 0.55 0.35 0.10 0.30 0.55 0.20 0.10 0.15 0.05 0.25 (0.8) (1.0) (0.20) 47000 / 231

Al Si12Cu1(Fe) min 10.5 0.6 0.7 max 13.5 1.1 1.2 0.55 0.35 0.10 0.30 0.55 0.20 0.10 0.15 0.05 0.25 (1.3) (0.20) 47100 / 231D

Values in brackets are valid for castings according to DIN EN 1706: 20101) According to DIN EN 1676: 2010

Otherstotalindiv.

Eutectic aluminium-silicon casting alloys

Near-eutectic wheel casting alloys


Alloy Numerical Other denomination 1) Si Fe Cu Mn Mg Cr Ni Zn Pb Sn Ti Silumin-Kappa Sr min 10.5 0.05 max 11.0 0.15 0.02 0.10 0.25 0.07 0.15 0.03 0.10 Sr

Silumin-Beta Sr min 9.0 0.20 max 10.5 0.15 0.02 0.10 0.45 0.07 0.15 0.03 0.10 Sr

Al Si11 min 10.0 max 11.8 0.15 0.03 0.10 0.45 0.07 0.15 0.03 0.10 Sr (0.19) (0.05) 44000


Otherstotalindiv.

52




Silumin-Beta / Al Si9Mg min 9.0 0.30 (0.25) max 10.0 0.15 0.03 0.10 0.45 (0.19) (0.05) (0.45) 0.07 0.15 0.03 0.10 Na 43300

Al Si10Mg(a) min 9.0 0.25 (0.20) max 11.0 0.40 0.03 0.45 0.45 0.05 0.10 0.05 0.05 0.15 0.05 0.15 Na (0.55) (0.05) (0.45) 43000 / 239

Al Si10Mg(b) min 9.0 0.25 (0.20) max 11.0 0.45 0.08 0.45 0.45 0.05 0.10 0.05 0.05 0.15 0.05 0.15 (0.55) (0.10) (0.45) 43100

Al Si10Mg(Fe) min 9.0 0.45 0.25 (0.20) max 11.0 0.9 0.08 0.55 0.50 0.15 0.15 0.15 0.05 0.15 0.05 0.15 (1.0) (0.10) (0.50) (0.20) 43400 / 239D

Al Si10Mg(Cu) min 9.0 0.25 (0.20) max 11.0 0.55 0.30 0.55 0.45 0.15 0.35 0.10 0.15 0.05 0.15 (0.65) (0.35) (0.45) (0.20) 43200 / 233

Al Si9 min 8.0 max 11.0 0.55 0.08 0.50 0.10 0.05 0.15 0.05 0.05 0.15 0.05 0.15 (0.65) (0.10) 44400

Silumin-Delta min 9.0 0.3 0.3 max 10.5 0.4 0.02 0.4 0.03 0.07 0.15 0.03 0.10

Silumin-Gamma min 9.0 0.4 0.15 max 11.3 0.15 0.02 0.9 0.6 0.10 0.15 0.03 0.10 Sr

Al Si10MnMg min 9.0 0.40 0.15 (0.10) max 11.5 0.20 0.03 0.80 0.60 0.07 0.15 0.05 0.15 Sr (0.25) (0.05) (0.60) (0.20) 43500


Otherstotalindiv.

The 10 per cent aluminium-silicon casting alloys

53



The 7 und 5 per cent aluminium-silicon casting alloys



Pantal 7 / Al Si7Mg0.3 min 6.5 0.30 (0.25) max 7.5 0.15 0.03 0.10 0.45 0.07 0.18 0.03 0.10 Na / Sr (0.19) (0.05) (0.45) (0.25) 42100

Al Si7Mg0.6 min 6.5 0.50 (0.45) max 7.5 0.15 0.03 0.10 0.70 0.07 0.18 0.03 0.10 (0.19) (0.05) (0.70) (0.25) 42200

Al Si7Mg min 6.5 0.25 (0.20) max 7.5 0.45 0.15 0.35 0.65 0.15 0.15 0.15 0.05 0.20 0.05 0.15 (0.55) (0.20) (0.65) (0.25) 42000

Pantal 5 min 5.0 0.40 0.05 max 6.0 0.15 0.02 0.10 0.80 0.07 0.20 0.03 0.10

Al Si5Mg min 5.0 0.40 0.05 max 6.0 0.3 0.03 0.4 0.80 0.10 0.20 0.05 0.15 - / 235

Al Si5Cu1Mg min 4.5 1.0 0.40 (0.35) max 5.5 0.55 1.5 0.55 0.65 0.25 0.15 0.15 0.05 0.20 0.05 0.15 (0.65) (0.65) (0.25) 45300

Al Si7Cu0.5Mg min 6.5 0.2 0.25 (0.20) max 7.5 0.25 0.7 0.15 0.45 0.07 0.20 0.03 0.10 (0.45) 45500


Otherstotalindiv.

54




Al Si8Cu3 min 7.5 2.0 0.15 0.15 (0.05) max 9.5 0.7 3.5 0.65 0.55 0.35 1.2 0.25 0.15 0.20 0.05 0.25 (0.8) (0.55) (0.25) 46200 / 226

Al Si9Cu3(Fe) min 8.0 0.6 2.0 0.15 (0.05) max 11.0 1.1 4.0 0.55 0.55 0.15 0.55 1.2 0.35 0.15 0.20 0.05 0.25 (1.3) (0.55) (0.25) 46000 / 226D

Al Si11Cu2(Fe) min 10.0 0.45 1.5 max 12.0 1.0 2.5 0.55 0.30 0.15 0.45 1.7 0.25 0.15 0.20 0.05 0.25 (1.1) (0.25) 46100

Al Si7Cu3Mg min 6.5 3.0 0.20 0.35 (0.30) max 8.0 0.7 4.0 0.65 0.60 0.30 0.65 0.15 0.10 0.20 0.05 0.25 (0.8) (0.60) (0.25) 46300

Al Si9Cu1Mg min 8.3 0.8 0.15 0.30 (0.25) max 9.7 0.7 1.3 0.55 0.65 0.20 0.8 0.10 0.10 0.18 0.05 0.25 (0.8) (0.65) (0.20) 46400

Al Si9Cu3(Fe)(Zn) min 8.0 0.6 2.0 0.15 (0.05) max 11.0 1.2 4.0 0.55 0.55 0.15 0.55 3.0 0.35 0.15 0.20 0.05 0.25 (1.3) (0.55) (0.25) 46500 / 226/3

Al Si7Cu2 min 6.0 1.5 0.15 max 8.0 0.7 2.5 0.65 0.35 0.35 1.0 0.25 0.15 0.20 0.05 0.15 (0.8) (0.25) 46600

Al Si6Cu4 min 5.0 3.0 0.20 max 7.0 0.9 5.0 0.65 0.55 0.15 0.45 2.0 0.30 0.15 0.20 0.05 0.35 (1.0) (0.25) 45000 / 225

Al Si5Cu3Mg min 4.5 2.6 0.20 (0.15) max 6.0 0.50 3.6 0.55 0.45 0.10 0.20 0.10 0.05 0.20 0.05 0.15 (0.60) (0.45) (0.25) 45100

Al Si5Cu3 min 4.5 2.6 max 6.0 0.50 3.6 0.55 0.05 0.10 0.20 0.10 0.05 0.20 0.05 0.15 (0.60) (0.25) 45400


Otherstotalindiv.

Al SiCu casting alloys

55



AlMg casting alloys



Al Mg3(H) min 2.7 max 0.45 0.15 0.02 0.40 3.2 0.07 0.02 0.03 0.10 B/Be

Al Mg3 min 2.7 (2.5) max 0.45 0.40 0.03 0.45 3.5 0.10 0.15 0.05 0.15 B/Be (0.55) (0.55) (0.05) (3.5) (0.20) 51100 / 242

Al Mg3(Cu) min 2.5 max 0.60 0.55 0.15 0.45 3.2 0.30 0.20 0.05 0.15 B/Be - / 241

Al Mg3Si(H) min 0.9 2.7 max 1.3 0.15 0.02 0.40 3.2 0.07 0.15 0.03 0.10 B/Be

Al Mg5 min 4.8 (4.5) max 0.35 0.45 0.05 0.45 6.5 0.10 0.15 0.05 0.15 B/Be (0.55) (0.55) (0.10) (6.5) (0.20) 51300 / 244

Al Mg5(Si) min 4.8 (4.5) max 1.3 0.45 0.03 0.45 6.5 0.10 0.15 0.05 0.15 B/Be (1.5) (0.55) (0.05) (6.5) (0.20) 51400 / 245

Al Mg9(H) min 1.7 0.2 8.5 max 2.5 0.50 0.02 0.5 10.5 0.07 0.15 0.03 0.10 B/Be

Al Mg9 min 0.45 8.5 (8.0) max 2.5 0.9 0.08 0.55 10.5 0.10 0.25 0.10 0.10 0.15 0.05 0.15 B/Be (1.0) (0.10) (10.5) (0.20) 51200 / 349

Al Mg5Si2Mn min 1.8 0.4 5.0 (4.7) max 2.6 0.20 0.03 0.8 6.0 0.07 0.20 0.05 0.15 (0.25) (0.05) (6.0) (0.25) 51500

Al Si2MgTi min 1.6 0.30 0.50 0.07 (0.45) (0.05) max 2.4 0.50 0.08 0.50 0.65 0.05 0.10 0.05 0.05 0.15 0.05 0.15 (0.60) (0.10) (0.65) (0.20) 41000


Otherstotalindiv.

56


Continuation of the table on the next page.

Casting alloys for special applications



Otherstotalindiv.

High-strength casting alloys

Al Cu4Ti min 4.2 0.15 (0.15) max 0.15 0.15 5.2 0.55 0.07 0.25 0.03 0.10 (0.18) (0.19) (0.30) 21100

Al Cu4MgTI min 4.2 0.20 0.15 (0.15) (0.15) max 0.15 0.30 5.0 0.10 0.35 0.05 0.10 0.05 0.05 0.25 0.03 0.10 (0.20) (0.35) (0.35) (0.30) 21000

Al Cu4MnMg min 4.0 0.20 0.20 (0.15) max 0.10 0.15 5.0 0.50 0.50 0.03 0.05 0.03 0.03 0.05 0.03 0.10 (0.20) (0.50) (0.05) (0.10) (0.10) 21200

Al Cu4MgTiAg min 4.0 0.01 0.15 0.5 Ag 0.4 max 0.05 0.10 5.2 0.50 0.35 0.05 0.35 0.03 0.10 1.0

Al Cu5NiCoSbZr min 4.5 0.1 1.3 0.15 **** max 0.20 0.30 5.2 0.3 0.10 1.7 0.10 0.30 0.05 0.15

Piston casting alloys

Al Si12CuNiMg min 10.5 0.8 0.9 0.7 (0.8) max 13.5 0.6 1.5 0.35 1.5 1.3 0.35 0.20 0.05 0.15 P (0.7) (1.5) (0.25) 48000 / 260

Al Si18CuNiMg min 17.0 0.8 0.8 0.8 max 19.0 0.3 1.3 0.10 1.3 1.3 0.10 0.15 0.05 0.15 P

****) Co 0.10-0.40 Sb 0.10-0.30 Zr 0.10-0.30


57





Alloy Numerical Other denomination 1) Si Fe Cu Mn Mg Cr Ni Zn Pb Sn Ti

Hyper eutectic casting alloys

Al Si17Cu4Mg* min 16.0 4.0 0.5 max 18.0 0.3 5.0 0.15 0.65 0.10 0.10 0.20 0.05 0.15 P

Al Si17Cu4Mg** min 16.0 4.0 0.45 (0.25) max 18.0 1.0 5.0 0.50 0.65 0.3 1.5 0.15 0.20 0.05 0.25 (1.3) (0.65) (0.25) 48100

Self-hardening casting alloys

Autodur min 8.5 0.3 9.5 max 9.5 0.15 0.02 0.05 0.5 10.5 0.15 0.03 0.10

Autodur (Fe)* min 8.5 0.3 9.5 max 9.5 0.40 0.02 0.30 0.5 10.5 0.15 0.03 0.10

Autodur (Fe)** min 7.5 0.25 9.0 (0.20) max 9.5 0.27 0.08 0.15 0.5 10.5 0.15 0.05 0.15 (0.30) (0.10) (0.5) 71100

Rotor-Aluminium

Al 99.7E*** min max 0.07 0.20 0.01 0.005 0.02 0.004 0.04 Mn+Cr+ 0.03 B 0.04 V+ Ti= 0.02

Al 99.6E*** min max 0.10 0.30 0.01 0.007 0.02 0.005 0.04 Mn+Cr+ 0.03 B 0.04 V+Ti= 0.030

*) Non-standardised version**) According to DIN EN 1706: 2010 ***) According to DIN EN 576


Otherstotalindiv.

58





Silumin min 12.5 max 13.5 0.15 0.02 0.05 0.05 0.07 0.15 0.03 0.10 Na

Al Si12(a) min 10.5 max 13.5 0.40 0.03 0.35 0.10 0.15 0.05 0.15 Na (0.55) (0.05) 44200 / 230

Al Si12(b) min 10.5 max 13.5 0.55 0.10 0.55 0.10 0.10 0.15 0.10 0.15 0.05 0.15 (0.65) (0.15) (0.20) 44100

Al Si12(Fe)(a) min 10.5 0.45 max 13.5 0.9 0.08 0.55 0.15 0.15 0.05 0.25 (1.0) (0.10) 44300 / 230D

Al Si12(Fe)(b) min 10.0 0.45 max 13.5 0.9 0.18 0.55 0.40 0.30 0.15 0.05 0.25 (1.0) (0.20) 44500

Al Si12(Cu) min 10.5 0.05 max 13.5 0.7 0.9 0.55 0.35 0.10 0.30 0.55 0.20 0.10 0.15 0.05 0.25 (0.8) (1.0) (0.20) 47000 / 231

Al Si12Cu1(Fe) min 10.5 0.6 0.7 max 13.5 1.1 1.2 0.55 0.35 0.10 0.30 0.55 0.20 0.10 0.15 0.05 0.25 (1.3) (0.20) 47100 / 231D


Otherstotalindiv.

59



Casting characteristics and other properties of castings

Alloy Fluidity Thermal Pressure As-cast Ageability Corrosion Decorative Weldability Polishability crack tightness state resistance anodisation stability

Silumin

Al Si12(a)

Al Si12(b)

Al Si12(Fe)(a)

Al Si12(Fe)(b)

Al Si12(Cu)

Al Si12Cu1(Fe)

Physical properties

Alloy Density E-Modulus Thermal Solidifi cation Coeffi cient Electrical Thermal capacity temperature of thermal conductivity conductivity at 100 °C expansion

g/cm3 MPa J/gK °C 10-6/K MS/m W/(m . k) 293 K - 373 K

Silumin 2.68 75,000 0.91 ~ 577 21 18 - 24 140 - 170

Al Si12(a) 2.68 75,000 0.90 ~ 577 20 17 - 24 140 - 170

Al Si12(b) 20 16 - 23 130 - 160

Al Si12(Fe)(a) 2.68 75,000 0.90 ~ 577 20 16 - 22 130 - 160

Al Si12(Fe)(b) 20 16 - 22 130 - 160

Al Si12(Cu) 2.70 75,000 0.89 ~ 577 20 16 - 22 130 - 150

Al Si12Cu1(Fe) 2.70 75,000 0.89 ~ 577 20 15 - 20 120 - 150

60


Mechanical properties at room temperature +20 °C

Alloy / Temper Casting method Tensile strength Rm Yield strength Rp0,2 Elongation A Brinell Fatigue hardness HB resistance MPa MPa % MPa

min min min min

Silumin F Sand casting 150 70 6 45 60 - 90

Al Si12(a) F Sand casting 150 70 5 50 60 - 90

Al S12(b) F Sand casting 150 70 4 50

Al Si12(Cu) F Sand casting 150 80 1 50 60 - 90

Silium F Gravity die casting 170 80 7 45 60 - 90

Al Si12(a) F Gravity die casting 170 80 6 55 60 - 90

Al Si12(Cu) F Gravity die casting 170 90 2 55 60 - 90

Al Si12(Fe)(a) F Pressure die casting 240 130 1 60 60 - 90

Al Si 12(Fe)(b) F Pressure die casting 240 140 1 60

Al Si12Cu1(Fe) F Pressure die casting 240 140 1 70 60 - 90

The values apply for separately-cast sample bars in sand and gravity die casting. Mechanical properties of pressure die casting samples are not binding and merely serve as information. The values representing vibration testing and/or fatigue strength apply for the best available casting process and merely serve as information.

Mechanical properties of gravity die casting samples 1)

Alloy / Temper Tensile strength Rm Yield strength Rp0,2 Elongation A Brinell hardness HB MPa MPa %

-100°C +20°C +100°C +200°C -100°C +20°C +100°C +200°C -100°C +20°C +100°C +200°C -100°C +20°C +100°C +200°C

Silumin 220 180 150 110 120 80 60 40 6 8 10 12 50 50 45 35

Al Si12(a) 220 180 150 110 120 80 60 40 2,5 3 4 10 50 50 45 35

Al Si12(b) 220 180 150 110 120 80 60 40 2.5 3.4 10 10 50 50 45 35

Al Si12(Cu) 190 170 110 100 80 35 1 3 8 55 45 25

1) Mechanical properties in minimum values / values after long-term maintenance of the respective temperature.

Typical process parameters

Alloy Casting temperature Contraction allowance Sand Gravity Pressure Sand Gravity Pressure casting die casting die casting casting die casting die casting

°C °C °C % % %

Silumin 670 - 740 670 - 740 620 - 660 1.0 - 1.2 0.5 - 0.8

Al Si12(a) 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si12(Fe)(a) 620 - 660 0.4 - 0.6

Al Si12(Cu) 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si12Cu1(Fe) 620 - 660 0.4 - 0.6

61


Application notes

Universal aluminium casting alloy with

medium strength; in part, very good elon-

gation and very good fl ow properties.

Suitable for thin-walled, complicated,

pressure-tight, vibration- and impact-

resistant constructions.

Properties and processing

From the range of AlSi casting alloys,

this type of alloy containing 13 % silicon

has the best fl uidity. In some respects,

the behaviour of the casting alloys in this

range represents a special case. Some

advice is provided below.

In the case of free solidifi cation, e.g. a

dense, bevel-shaped surface, the so-

called “hammer blow”, forms on the top

of the ingot. This type of solidifi cation is

“shell-forming”, i.e. the crystallisation of

the subsequent casting begins with the

formation of a solid shell which then grows

towards the middle of the cast wall. In

this type of casting alloy, there are only

two states, i.e. “solid” and “liquid”. Full

solidifi cation of a casting takes place

at the eutectic temperature of approx.

577 °C). During the solidifi cation process,

the volume can contract by up to 7 %.

The shell thickness does not decrease.

If the fl ow of liquid metal is interrupted

in the middle wall region during feeding,

a coarse cavity can evolve. (Additional

notes also provided in the sections en-

titled “Infl uencing the microstructural

formation of aluminium castings” and

“Avoiding casting defects”.)

This type of aluminium casting alloy can

only be modifi ed with sodium. Sodium

modifi cation is indicated for sand cast-

ings and gravity die castings if particular

requirements are placed on elongation

of the microstructure (see Figure 2). As

a general rule, casting alloys for use in

sand and gravity die casting are offered

in a slightly modifi ed version. Chemical

resistance as well as resistance to weath-

ering and a marine climate increase with

the purity of the casting alloy used. A pri-

mary silicon casting alloy thus meets the

highest requirements in a variety of fi elds

of application, e.g. in the food industry

or in shipbuilding. The elongation of the

cast structure is signifi cantly determined

by the iron content and other impurities.

The demand for high proof stress values

in the casting often requires the use of

primary casting alloys with the lowest

possible content of iron and impurities.

Heat treatment

In the case of sand and gravity die cast-

ings made from casting alloys low in

Cu and Mg, a selective improvement

in ductility can be achieved. This is ef-

fected by means of solution annealing at

520-530 °C with subsequent quenching

in cold water.

Comments

The DIN EN 1676 and DIN EN 1706

standards allow a very wide range of

major alloying elements – silicon from

10.5 to 13.5 %. The practical range for

the silicon content is from 12.5 to 13.5

and, in a slightly hypoeutectic range of

10.5 to 11.2 %. However, these two al-

loys display entirely different solidifi cation

behaviour. The intermediate range, with

approx. 11.5 to 12.5 % silicon, runs the

risk of shrinkage cavities. Casting alloys

in this critical range are not offered. Even

a blend of these different yet similar-

sounding alloys is not recommended.


62





Silumin-Kappa Sr

Silumin-Beta Sr

Al Si11

Physical properties



Silumin-Kappa Sr 2.68 74,000 0.91 600 - 555 21 20 - 26 150 - 180

Silumin-Beta Sr 2.68 74,000 0.91 600 - 550 21 20 - 26 150 - 180

Al Si11 2.68 74,000 0.91 600 - 550 21 18 - 24 140 - 170


Alloy Numerical Other denomination 1) Si Fe Cu Mn Mg Cr Ni Zn Pb Sn Ti Silumin-Kappa Sr min 10.5 0.05 max 11.0 0.15 0.02 0.10 0.25 0.07 0.15 0.03 0.10 Sr

Silumin-Beta Sr min 9.0 0.20 max 10.5 0.15 0.02 0.10 0.45 0.07 0.15 0.03 0.10 Sr

Al Si11 min 10.0 max 11.8 0.15 0.03 0.10 0.45 0.07 0.15 0.03 0.10 Sr (0.19) (0.05) 44000


Otherstotalindiv.

63





min min min min

Silumin-Kappa Sr F Gravity die casting 170 80 6 45 60 - 90

Silumin-Beta Sr F Gravity die casting 170 90 5 50 60 - 90

T6 Gravity die casting 290 210 4 90 60 - 90


Al Si11 F Gravity die casting 170 80 7 45 60 - 90





Silumin-Kappa Sr F 180 170 160 120 90 80 70 50 5 6 6 10 65 45 45 40

Silumin-Beta Sr T64 260 250 210 120 200 180 170 80 4,5 6 7 10 85 80 75 60

Al Si11 F 230 170 160 130 130 80 70 50 3 7 7 10 65 45 40 35




°C °C °C % % %

Silumin-Kappa Sr 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Silumin-Beta Sr 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si11 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8


Alloy / Temper Solution heat Annealing time Water Ageing Ageing time treatment temperature tempetarure temperature for quenching

°C h °C °C h

Silumin-Kappa Sr T4 520 - 535 4 - 10 20 160 - 170 6 - 8

Silumin-Beta Sr T4 520 - 535 4 - 10 20 150 - 160 2 - 3

64


Application notes

These casting alloy types have been

developed primarily for the casting of

car wheels by means of low-pressure

die casting processes.


These casting alloys have good fl uidity;

the grain structure displays very high

ductility and good corrosion resistance.

The casting alloy Silumin-Kappa has an

optimum silicon content of 10.5 to 11.0 %.

In Silumin-Beta, the silicon content ranges

from 9.0 and 10.5 % silicon. As a rule,

these casting alloys already undergo a

long-lasting strontium modifi cation (HV)

during production of the ingots. The

strontium addition is approx. 0.020 to

0.030 %. Normally, this smelter modifi -

cation does not need to be repeated at

the foundry. The modifi cation of eutectic

silicon, i.e. the formation of a modifi ed

microstructure, is a necessity since the

ductility of the cast structure of the wheels

produced from these casting alloys meas-

ured by means of the elongation value,

for example, plays a vital role. The level

of the iron content and the level of the

other additions are particularly important

quantities for the ductility or elongation

of the cast structure. On request, these

casting alloys can have a magnesium

content of between 0.05 and 0.45 %.

With an increasing Mg content, the al-

loys‘ strength can be improved slightly,

their elongation decreases a little with the

level of the Mg content, their machinabil-

ity – with respect to chip formation, chip

removal and surface appearance – is

improved, the resistance of the casting

to chemical attack increases, lacquer

adherence, however, can be impaired

by the magnesium content. Only some

of the Silumin-Beta casting alloys are

age-hardenable. The age hardening of

wheels made from alloys of the Silumin-

Kappa type is not recommended. It could

cause partial embrittlement which would

reduce the fatigue strength of the material.

For wheels which have to be heat-treated,

casting alloys of the Al Si7Mg (Pantal 7)

type are recommended. The solidifi cation

characteristics of these casting alloys

are hypoeutectic. During solidifi cation,

the transition is from pasty to mushy.

In the course of subsequent solidifi ca-

tion, aluminium dendrites grow into the

liquid melt. They form an interconnect-

ing network whose intervening spaces

are then fi lled with the highly-fl uid AlSi

eutectic which then solidifi es. If feeding

is incomplete or the highly-fl uid eutectic

is drawn to another place, defects such

as sinks or microporosity occur. The so-

lidifi cation range is approx. 30 to 45 K.

With this type of casting alloy, cleaning

the melt can only be effected by means

of inert gas or using a vacuum. Cleaning

agents containing chlorine would remove

strontium from the melt. In practice, the

use of purging lances or impeller equip-

ment have proven their worth.

65





Silumin-Beta / Al Si9Mg min 9.0 0.30 (0.25) max 10.0 0.15 0.03 0.10 0.45 (0.19) (0.05) (0.45) 0.07 0.15 0.03 0.10 Na 43300

Al Si10Mg(a) min 9.0 0.25 (0.20) max 11.0 0.40 0.03 0.45 0.45 0.05 0.10 0.05 0.05 0.15 0.05 0.15 Na (0.55) (0.05) (0.45) 43000 / 239

Al Si10Mg(b) min 9.0 0.25 (0.20) max 11.0 0.45 0.08 0.45 0.45 0.05 0.10 0.05 0.05 0.15 0.05 0.15 (0.55) (0.10) (0.45) 43100

Al Si10Mg(Fe) min 9.0 0.45 0.25 (0.20) max 11.0 0.9 0.08 0.55 0.50 0.15 0.15 0.15 0.05 0.15 0.05 0.15 (1.0) (0.10) (0.50) (0.20) 43400 / 239D

Al Si10Mg(Cu) min 9.0 0.25 (0.20) max 11.0 0.55 0.30 0.55 0.45 0.15 0.35 0.10 0.15 0.05 0.15 (0.65) (0.35) (0.45) (0.20) 43200 / 233

Al Si9 min 8.0 max 11.0 0.55 0.08 0.50 0.10 0.05 0.15 0.05 0.05 0.15 0.05 0.15 (0.65) (0.10) 44400

Silumin-Delta min 9.0 0.3 0.3 max 10.5 0.4 0.02 0.4 0.03 0.07 0.15 0.03 0.10

Silumin-Gamma min 9.0 0.4 0.15 max 11.3 0.15 0.02 0.9 0.6 0.10 0.15 0.03 0.10 Sr

Al Si10MnMg min 9.0 0.40 0.15 (0.10) max 11.5 0.20 0.03 0.80 0.60 0.07 0.15 0.05 0.15 Sr (0.25) (0.05) (0.60) (0.20) 43500


Otherstotalindiv.

66




Silumin-Beta / Al Si9Mg

Al Si10Mg(a)

Al Si10Mg(b)

Al Si10Mg(Fe)

Al Si10Mg(Cu)

Al Si9

Silumin-Delta

Silumin-Gamma

Al Si10MnMg

Physical properties



Silumin-Beta / Al Si9Mg 2.68 74,000 0.91 600 - 555 21 20 - 26 150 - 180

Al Si10Mg(a) 2.68 74,000 0.91 600 - 550 21 19 - 25 150 - 170

Al Si10Mg(b) 2.68 74,000 0.91 600 - 550 21 18 - 25 140 - 170

Al Si10Mg(Fe) 2.68 74,000 0.91 600 - 550 21 16 - 21 130 - 150

Al Si10Mg(Cu) 2.68 74,000 0.91 600 - 550 21 16 - 24 130 - 170

Al Si9 2.69 74,000 0.91 605 - 570 21 16 - 22 130 - 150

Silumin-Delta 2.69 74,000 0.91 605 - 570 21 18 - 26 130 - 170

Silumin-Gamma 2.68 74,000 0.91 610 - 560 21 20 - 26 140 - 180

Al Si10MnMg 21 19 - 25 140 - 170

67





min min min min

Silumin-Beta / Al Si9Mg F Sand casting 150 80 2 50

T6 Sand casting 230 190 2 75

Al Si10Mg(a) F Sand casting 150 80 2 50


Al Si10Mg(b) F Sand casting 150 80 2 50


Al Si10Mg(Cu) F Sand casting 160 80 1 50


Silumin-Beta / Al Si9Mg T6 Gravity die casting 290 210 4 90 80 - 110


Al Si10Mg(a) F Gravity die casting 180 90 2.5 55 80 - 110


T64 Gravity die casting 240 200 2 80

Al Si10Mg(b) F Gravity die casting 180 90 2.5 55 80 - 110



Al Si10Mg(Cu) F Gravity die casting 180 90 1 55 80 - 110


Al Si10Mg(Fe) F Pressure die casting 240 140 1 70 60 - 90

Al Si9 F Pressure die casting 220 120 2 55 60 - 90

Silumin-Delta F Pressure die casting 220 120 4 55 60 - 90

Silumin-Gamma F Pressure die casting 240 120 5 70 80 - 90

T6 Pressure die casting 290 210 7 100


68




°C °C °C % % %

Silumin-Beta / Al Si9Mg 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si10Mg(a) 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si10Mg(b) 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si10Mg(Fe) 620 - 660 0.4 - 0.6

Al Si10Mg(Cu) 670 - 740 670 - 740 1.0 - 1.2 0.5 - 0.8

Al Si9 660 - 740 660 - 740 620 - 700 0.5 - 0.8 0.4 - 0.6

Silumin-Delta 620 - 700 0.4 - 0.6

Silumin-Gamma 620 - 730 0.4 - 0.6




Silumin-Beta / Al Si9Mg T6 290 290 260 120 220 210 200 80 3.5 4 4 10 90 90 80 60

Al Si10Mg(a) T6 280 260 230 120 220 220 170 80 1 1 2 8 85 90 80 60

Al Si10Mg(Cu) T6 280 240 210 120 220 200 180 90 1 1 2 7 85 80 75 45




°C h °C °C h

Silumin-Beta / Al Si9Mg T6 520 - 535 4 - 10 20 160 - 170 6 - 8

T64 520 - 535 4 - 10 20 150 - 160 2 - 3

Al Si10Mg(a) T6 520 - 535 4 - 10 20 160 - 170 6 - 8

T64 520 - 535 4 - 10 20 150 - 160 2 - 3

Al Si10Mg(b) T6 520 - 535 4 - 10 20 160 - 170 6 - 8

T64 520 - 535 4 - 10 20 150 - 160 2 - 3

Al Si10Mg(Cu) T6 520 - 535 4 - 10 20 160 - 170 6 - 8

Silumin-Gamma T6 500 - 530 4 - 8 20 150 - 170 2 - 6

T64 500 - 530 4 - 8 20 180 - 340 2 - 6

69


Application notes

This important group of casting alloys

is used for castings with medium wall

thicknesses which require higher, to the

highest strength properties. The fi elds of

application comprise mechanical and

electrical engineering, the food industry

as well as in engine and motor vehicle

construction. Silumin-Beta casting alloys

are also used for car wheels. Silumin-

Gamma is a heat-treatable high-pressure

die casting alloy. However, successful

treatment requires the use of an adequate

casting process (e.g. vacuum-assisted

high-pressure die casting).


The fl uidities of these casting alloys are

still good. Heat-treatable castings made

from alloys containing magnesium dis-

play particularly good machinability. With

increasing purity, the ductility of the cast

structure also increases. Where the re-

quirements on corrosion resistance are

high, high-purity grades are selected.

Sand and gravity die castings can be

artifi cially aged. In doing so, however,

ductility decreases. The solidifi cation

characteristics of this group of casting

alloys are hypoeutectic. During the so-

lidifi cation process, aluminium dendrites

grow into the melt fi rst. The highly-fl uid

AlSi eutectic then penetrates the inter-

vening spaces of the network and clamps

the microstructural framework together.

If the feeding of the remaining eutectic

melt is hindered in any way, defects such

as sinks or micro/macrocavities occur.

This causes porous areas and also leads

to a weakening of the structural cross-

section. During casting, therefore, atten-

tion must be paid to ensure good feed-

ing and, as far as possible, controlled

solidifi cation. The solidifi cation range

amounts to approx. 45 K.

Where requirements on elongation or

ductility are higher, modifi cation of the

melt is recommended. The casting alloys

for use in gravity die casting are modi-

fi ed with sodium or strontium. For sand

casting, modifi cation with sodium only

is recommended. As a general rule, the

casting alloys for sand and gravity die

casting are offered in versions which can

be easily modifi ed.


70


The 7 and 5 per cent aluminium-silicon casting alloys



Pantal 7 / Al Si7Mg0.3 min 6.5 0.30 (0.25) max 7.5 0.15 0.03 0.10 0.45 0.07 0.18 0.03 0.10 Na / Sr (0.19) (0.05) (0.45) (0.25) 42100

Al Si7Mg0.6 min 6.5 0.50 (0.45) max 7.5 0.15 0.03 0.10 0.70 0.07 0.18 0.03 0.10 (0.19) (0.05) (0.70) (0.25) 42200

Al Si7Mg min 6.5 0.25 (0.20) max 7.5 0.45 0.15 0.35 0.65 0.15 0.15 0.15 0.05 0.20 0.05 0.15 (0.55) (0.20) (0.65) (0.25) 42000

Pantal 5 min 5.0 0.40 0.05 max 6.0 0.15 0.02 0.10 0.80 0.07 0.20 0.03 0.10

Al Si5Mg min 5.0 0.40 0.05 max 6.0 0.3 0.03 0.4 0.80 0.10 0.20 0.05 0.15 - / 235

Al Si5Cu1Mg min 4.5 1.0 0.40 (0.35) max 5.5 0.55 1.5 0.55 0.65 0.25 0.15 0.15 0.05 0.20 0.05 0.15 (0.65) (0.65) (0.25) 45300

Al Si7Cu0.5Mg min 6.5 0.2 0.25 (0.20) max 7.5 0.25 0.7 0.15 0.45 0.07 0.20 0.03 0.10 (0.45) 45500


Otherstotalindiv.

71





Pantal 7 / Al Si7Mg0.3

Al Si7Mg0.6

Al Si7Mg

Pantal 5

Al Si5Mg

Al Si5Cu1Mg

Al Si7Cu0.5Mg

Physical properties



Pantal 7 / Al Si7Mg0.3 2.66 73,000 0.92 625 - 550 22 21 - 27 160 - 180

Al Si7Mg0.6 2.66 73,000 0.92 625 - 550 22 20 - 26 150 - 180

Al Si7Mg 2.66 73,000 0.92 625 - 550 22 19 - 25 150 - 170

Pantal 5 2.67 72,000 0.92 625 - 550 23 21 - 29 150 - 180

Al Si5Mg 2.67 72,000 0.92 625 - 550 23 21 - 26 150 - 180

Al Si5Cu1Mg 2.67 72,000 0.92 625 - 550 22 19 - 23 140 - 150

Al Si7Cu0.5Mg 22 16 - 22 150 - 165

72




min min min min

Pantal 7 / Al Si7Mg0.3 T6 Sand casting 230 190 2 75

Al Si7Mg0.6 T6 Sand casting 250 210 1 85

Al Si7Mg F Sand casting 140 80 2 50


Pantal 5 T6 Sand casting 240 220 2 80


Al Si5Mg T6 Sand casting 240 220 1 80


Al Si5Cu1Mg T6 Sand casting 230 200 <1 100


Pantal 7 / Al Si7Mg0.3 T6 Gravity die casting 290 210 4 90 80 - 110


Al Si7Mg0.6 T6 Gravity die casting 320 240 3 100


Al Si7Mg F Gravity die casting 170 90 2.5 55 80 - 110


Al Si7Mg T64 Gravity die casting 240 200 2 80

Pantal 5 F Gravity die casting 160 120 2 60 70 - 90



Al Si5Mg F Gravity die casting 160 120 2 60 70 - 90



Al Si5Cu1Mg T6 Gravity die casting 280 210 <1 110 70 - 100


Al Si7Cu0.5Mg T6 Gravity die casting 320 240 4 100


73






Pantal 7 / Al Si7Mg0.3 T6 290 290 240 120 210 210 180 80 3 4 6 10 90 90 75 45

Pantal 5 T6 280 260 200 120 250 240 170 80 1 2 3 7 90 90 80 45

Al Si5Mg T6 280 260 200 120 250 240 170 80 0.5 1 2 7 90 90 80 45




°C °C °C % % %

Pantal 7 / Al Si7Mg0.3 680 - 750 680 - 750 1.0 - 1.2 0.7 - 1.1

Al Si7Mg0.6 680 - 750 680 - 750 1.0 - 1.2 0.7 - 1.1

Al Si7Mg 680 - 750 680 - 750 1.0 - 1.2 0.7 - 1.1

Pantal 5 690 - 760 690 - 760 1.1 - 1.2 0.8 - 1.1

Al Si5Mg 690 - 760 690 - 760 1.1 - 1.2 0.8 - 1.1

Al Si5Cu1Mg 690 - 760 690 - 760 1.0 - 1.2 0.8 - 1.1



°C h °C °C h

Pantal 5 T4 520 - 535 4 - 10 20 20 - 30 120

T6 520 - 535 4 - 10 155 - 165 6 - 10

Al Si5Mg T4 520 - 535 4 - 10 20 20 - 30 120

T6 520 - 535 4 - 10 155 - 165 6 - 10

Al Si5Cu1Mg T4 520 - 535 4 - 10 20 20 - 30 120

T6 520 - 535 4 - 10 155 - 165 6 - 10

Pantal 7 / Al Si7Mg0.3 T6 520 - 545 4 - 10 155 - 165 6 - 10

T64 520 - 545 4 - 10 20 150 - 160 2 - 5

Al Si7Mg0,6 T6 520 - 545 4 - 10 155 - 165 6 - 10

T64 520 - 545 4 - 10 20 150 - 160 2 - 5

Al Si7Mg T6 520 - 545 4 - 10 155 - 165 6 - 10

T64 520 - 545 4 - 10 20 150 - 160 2 - 5

74


Application notes

These casting alloys are used in the

motor vehicle industry (chassis compo-

nents, motor car and lorry wheels), for

components in the aerospace industry,

for parts in mechanical engineering, for

hydraulic elements, in the food industry,

in shipbuilding, for fi ttings and apparatus

as well as for fi re extinguisher compo-

nents. Their use makes particular sense

when the castings undergo age harden-

ing. As a result of age hardening, these

casting alloys are used in structures

requiring high strength. In addition, the

cast structure – particularly of primary

casting alloys – still displays remarkable

toughness and ductility. Resistance to

chemical attack increases with purity

and is very good in the case of primary

casting alloys.


Owing to the low silicon content, fl uid-

ity is only moderate. Castings with very

thin walls can not, therefore, be cast in

these alloys. This group of casting al-

loys containing around 7 % silicon is in

some respects an exception. Looking

at a micrograph, it can be seen that the

proportion by area of light matrix (i.e.

the aluminium-rich solid solution) and

the proportion by area or eutectic silicon

(i.e. the dotted grey areas) each amount

to approx. 50 %. Like in all hypoeutectic

AlSi casting alloys, solidifi cation takes

place in phases. First of all, the dendritic

network made up of aluminium-rich solid

solution grows into the still liquid melt.

The remaining highly-fl uid eutectic melt

infi ltrates this sponge and locks the struc-

ture together like in a two-component

composite. By means of age-harden-

ing, the aluminium-rich solid solution

in particular is strengthened while the

connecting eutectic remains ductile. In

this way, the ideal microstructure occurs,

giving the highest possible strength with

still acceptable elongation. The variable

magnesium content which ranges from

0.20 to 0.70 % gives the user the pos-

sibility of adjusting the elongation of the

castings to the particular requirements.

With a low magnesium content of around

0.25 %, relatively high elongation values

can be achieved. Where greater hardness

is required, casting alloys with a mag-

nesium content of 0.70 % can be used.

The group of casting alloys with approx.

5 % silicon displays many sequences

and properties which are similar to the

7 per cent group. The solidifi cation range

is slightly greater, fl uidity is slightly less.

Due to the lower silicon content, the ef-

fect of the aluminium-rich solid solution

dominates. The casting alloy variants

with low copper content display the best

possible corrosion-resistance behaviour

of all aluminium-silicon casting alloys.

Castings made from these alloys fi nd

application in such areas as the food

industry, in domestic appliances or in

parts for the food processing industry.

75





Al Si8Cu3 min 7.5 2.0 0.15 0.15 (0.05) max 9.5 0.7 3.5 0.65 0.55 0.35 1.2 0.25 0.15 0.20 0.05 0.25 (0.8) (0.55) (0.25) 46200 / 226

Al Si9Cu3(Fe) min 8.0 0.6 2.0 0.15 (0.05) max 11.0 1.1 4.0 0.55 0.55 0.15 0.55 1.2 0.35 0.15 0.20 0.05 0.25 (1.3) (0.55) (0.25) 46000 / 226D

Al Si11Cu2(Fe) min 10.0 0.45 1.5 max 12.0 1.0 2.5 0.55 0.30 0.15 0.45 1.7 0.25 0.15 0.20 0.05 0.25 (1.1) (0.25) 46100

Al Si7Cu3Mg min 6.5 3.0 0.20 0.35 (0.30) max 8.0 0.7 4.0 0.65 0.60 0.30 0.65 0.15 0.10 0.20 0.05 0.25 (0.8) (0.60) (0.25) 46300

Al Si9Cu1Mg min 8.3 0.8 0.15 0.30 (0.25) max 9.7 0.7 1.3 0.55 0.65 0.20 0.8 0.10 0.10 0.18 0.05 0.25 (0.8) (0.65) (0.20) 46400

Al Si9Cu3(Fe)(Zn) min 8.0 0.6 2.0 0.15 (0.05) max 11.0 1.2 4.0 0.55 0.55 0.15 0.55 3.0 0.35 0.15 0.20 0.05 0.25 (1.3) (0.55) (0.25) 46500 / 226/3

Al Si7Cu2 min 6.0 1.5 0.15 max 8.0 0.7 2.5 0.65 0.35 0.35 1.0 0.25 0.15 0.20 0.05 0.15 (0.8) (0.25) 46600

Al Si6Cu4 min 5.0 3.0 0.20 max 7.0 0.9 5.0 0.65 0.55 0.15 0.45 2.0 0.30 0.15 0.20 0.05 0.35 (1.0) (0.25) 45000 / 225

Al Si5Cu3Mg min 4.5 2.6 0.20 (0.15) max 6.0 0.50 3.6 0.55 0.45 0.10 0.20 0.10 0.05 0.20 0.05 0.15 (0.60) (0.45) (0.25) 45100

Al Si5Cu3 min 4.5 2.6 max 6.0 0.50 3.6 0.55 0.05 0.10 0.20 0.10 0.05 0.20 0.05 0.15 (0.60) (0.25) 45400


Otherstotalindiv.

76




Al Si8Cu3

Al Si9Cu3(Fe)

Al Si11Cu2(Fe)

Al Si7Cu3Mg

Al Si9Cu1Mg

Al Si9Cu3(Fe)(Zn)

Al Si7Cu2

Al Si6Cu4

Al Si5Cu3Mg

Al Si5Cu3

Physical properties



Al Si8Cu3 2.77 75,000 0.88 600 - 500 21 14 - 18 110 - 130

Al Si9Cu3(Fe) 2.76 75,000 0.88 600 - 500 21 13 - 17 110 - 120

Al Si11Cu2(Fe) 2.75 75,000 0.88 600 - 500 20 14 - 18 120 - 130

Al Si7Cu3Mg 2.77 75,000 0.88 600 - 500 21 14 - 17 110 - 120

Al Si9Cu1Mg 2.76 75,000 0.88 600 - 500 21 16 - 22 130 - 150

Al Si9Cu3(Fe)(Zn) 2.76 75,000 0.88 600 - 500 21 13 - 17 110 - 120

Al Si7Cu2 2.77 75,000 0.88 600 - 500 21 15 - 19 120 - 130

Al Si6Cu4 2.80 74,000 0.88 630 - 500 22 14 - 17 110 - 120

Al Si5Cu3Mg 2.79 74,000 0.88 630 - 500 22 16 - 19 130

Al Si5Cu3 2.79 74,000 0.88 630 - 500 22 16 - 19 120 - 130

77





min min min min

Al Si8Cu3 F Sand casting 150 90 1 60

Al Si7Cu3Mg F Sand casting 180 100 1 80

Al Si9Cu1Mg F Sand casting 135 90 1 60



Al Si5Cu3Mg T4 Sand casting 140 70 1 60

T6 Sand casting 230 200 <1 90

Al Si5Cu3 F Gravity die casting 170 100 1 75 60 - 90

Al Si7Cu3Mg F Gravity die casting 180 100 1 80 60 - 90


Al Si9Cu1Mg F Gravity die casting 170 100 1 75 60 - 90

T6 Gravity die casting 275 235 1.5 105

Al Si5Cu3Mg F Gravity die casting 270 180 2.5 85 80 - 110

T6 Gravity die casting 320 280 <1 110



Al Si8Cu3 F Pressure die casting 240 140 1 80 60 - 90

Al Si11Cu2(Fe) F Pressure die casting 240 140 <1 80 60 - 90


78





Al Si8Cu3 F 170 160 120 80 100 90 50 25 1 1 2 5 75 65 45 35

Al Si6Cu4 F 170 160 130 100 100 90 60 30 1 1 1.5 4 75 65 50 40




°C °C °C % % %

Al Si8Cu3 680 - 750 680 - 750 630 - 680 1.0 - 1.2 0.6 - 1.0 0.4 - 0.6

Al Si9Cu3(Fe) 630 - 680 0.4 - 0.7

Al Si11Cu2(Fe) 630 - 680 0.4 - 0.8

Al Si7Cu3Mg 680 - 750 680 - 750 1.0 - 1.2 0.6 - 1.0

Al Si9Cu1Mg 680 - 750 680 - 750 1.0 - 1.2 0.6 - 1.0

Al Si9Cu3(Fe)(Zn) 630 - 680 0.4 - 0.7

Al Si7Cu2 680 - 750 680 - 750 1.0 - 1.2 0.6 - 1.0

Al Si6Cu4 690 - 750 690 - 750 640 - 690 1.0 - 1.2 0.6 - 1.0 0.4 - 0.6

Al Si5Cu3Mg 690 - 750 690 - 750 1.0 - 1.2 0.6 - 1.0

Al Si5Cu3 690 - 750 690 - 750 1.0 - 1.2 0.6 - 1.0



°C h °C °C h

Al Si5Cu3Mg T4 480 6 - 10 20 - 60 20 - 30 120

T6 480 6 - 10 20 160 6 - 12

Al Si5Cu3 T4 480 6 - 10 20 - 60 20 - 30 120

Al Si9Cu1Mg T6 480 6 - 10 20 160 6 - 12

79


Application notes

The alloys in this group are among the

most commonly used aluminium cast-

ing alloys around. They are regarded

as universal casting alloys for the most

important casting processes and are

widely used in pressure die casting in

particular. They are easily cast and are

suitable for parts which are subjected

to relatively high loads. They are heat

resistant and, as such, are used for en-

gine components and cylinder heads.


Aluminium casting alloys with approx. 6

to 8 % silicon, 3 to 4 % copper as well

as 0.3 to 0.5 % magnesium have the

optimum high-temperature strength.

The cast structure hardens on its own

within a week of casting. Afterwards, the

mechanical machinability of the casting

is very good. Age hardening is some-

times possible. Treatment of the melt:

In sand castings or thick-walled grav-

ity die castings, sodium modifi cation is

possible. Often, grain refi nement is also

carried out. The casting and solidifi ca-

tion behaviour usually poses no problem.

The type of solidifi cation is hypoeutec-

tic. During the transition from liquid to

solid state, there is a wide solidifi cation

range of a pasty-mushy character. At-

tention must be paid to controlling the

solidifi cation and feeding of the metal.

There is no distinctive tendency to hot

cracking or draws.

Heat treatment

With castings made from these casting

alloys, age hardening is possible when

the Cu and Mg content is appropriate. It

is, however, seldom carried out. In these

castings, due to the Cu content in con-

nection with the Mg and Zn content, an

independent structural hardening occurs.

This process is complete within about a

week. Only then should the castings be

fi nished followed by checking the me-

chanical properties. To achieve thermal

and dimensional stability in parts suit-

able for high-pressure applications, e.g.

crankcases, cylinder heads or pistons,

solution annealing with artifi cial ageing

beyond the peak aged condition is sug-

gested (T7). This process is also known

as “stabilising” or “overageing”.


80


AlMg casting alloys



Al Mg3(H) min 2.7 max 0.45 0.15 0.02 0.40 3.2 0.07 0.02 0.03 0.10 B/Be

Al Mg3 min 2.7 (2.5) max 0.45 0.40 0.03 0.45 3.5 0.10 0.15 0.05 0.15 B/Be (0.55) (0.55) (0.05) (3.5) (0.20) 51100 / 242

Al Mg3(Cu) min 2.5 max 0.60 0.55 0.15 0.45 3.2 0.30 0.20 0.05 0.15 B/Be - / 241

Al Mg3Si(H) min 0.9 2.7 max 1.3 0.15 0.02 0.40 3.2 0.07 0.15 0.03 0.10 B/Be

Al Mg5 min 4.8 (4.5) max 0.35 0.45 0.05 0.45 6.5 0.10 0.15 0.05 0.15 B/Be (0.55) (0.55) (0.10) (6.5) (0.20) 51300 / 244

Al Mg5(Si) min 4.8 (4.5) max 1.3 0.45 0.03 0.45 6.5 0.10 0.15 0.05 0.15 B/Be (1.5) (0.55) (0.05) (6.5) (0.20) 51400 / 245

Al Mg9(H) min 1.7 0.2 8.5 max 2.5 0.50 0.02 0.5 10.5 0.07 0.15 0.03 0.10 B/Be

Al Mg9 min 0.45 8.5 (8.0) max 2.5 0.9 0.08 0.55 10.5 0.10 0.25 0.10 0.10 0.15 0.05 0.15 B/Be (1.0) (0.10) (10.5) (0.20) 51200 / 349

Al Mg5Si2Mn min 1.8 0.4 5.0 (4.7) max 2.6 0.20 0.03 0.8 6.0 0.07 0.20 0.05 0.15 (0.25) (0.05) (6.0) (0.25) 51500

Al Si2MgTi min 1.6 0.30 0.50 0.07 (0.45) (0.05) max 2.4 0.50 0.08 0.50 0.65 0.05 0.10 0.05 0.05 0.15 0.05 0.15 (0.60) (0.10) (0.65) (0.20) 41000


Otherstotalindiv.

81


AlMg casting alloys

Physical properties



Al Mg3(H) 2.68 70,000 0.93 650 - 600 24 17 - 22 130 - 140

Al Mg3 2.68 70,000 0.93 650 - 600 24 17 - 22 130 - 140

Al Mg3(Cu) 2.68 70,000 0.93 650 - 600 24 17 - 22 130 - 140

Al Mg3Si(H) 2.68 70,000 0.93 650 - 600 24 17 - 22 130 - 140

Al Mg5 2.66 69,000 0.94 630 - 550 24 15 - 21 110 - 130

Al Mg5(Si) 2.66 69,000 0.94 630 - 550 24 15 - 21 110 - 140

Al Mg9(H)/Fe 2.63 68,000 0.94 620 - 520 24 11 - 14 60 - 90

Al Mg9 2.63 68,000 0.94 620 - 520 24 11 - 14 60 - 90

Al Mg5Si2Mn 24 14 - 16 110 - 130

Al Si2MgTi 23 19 - 25 140 - 160



Al Mg3(H)

Al Mg3

Al Mg3(Cu)

Al Mg3Si(H)

Al Mg5

Al Mg5(Si)

Al Mg9(H)/Fe

Al Mg9

Al Mg3(Zr)

Al Mg5Si2Mn

Al Si2MgTi

82




min min min min

Al Mg3(H) F Sand casting 140 70 5 50

Al Mg3 F Sand casting 140 70 3 50

Al Mg3(Cu) F Sand casting 140 70 2 50

Al Mg3Si(H) F Sand casting 140 70 3 50

Al Mg5 F Sand casting 16 90 3 55

Al Si2MgTi F Sand casting 140 70 3 50


Al Mg5(Si) F Sand casting 160 100 3 60

Al Mg3(H) F Gravity die casting 150 70 5 50 60 - 90

Al Mg3 F Gravity die casting 150 70 5 50 60 - 90

Al Mg3(Cu) F Gravity die casting 150 70 3 50 60 - 90

Al Mg3Si(H) F Gravity die casting 150 70 3 50 70 - 80


Al Mg5 F Gravity die casting 180 100 4 60 60 - 90

Al Si2MgTi F Gravity die casting 140 70 3 50


Al Mg5(Si) F Gravity die casting 180 110 3 65 60 - 90


Al Mg3 F 140 70 3 50

Al Mg5 F 160 90 3 55

Al Mg5(Si) F 180 110 3 65

Al Mg9(H)/Fe F Pressure die casting 200 140 1 70 60 - 90

Al Mg9 F Pressure die casting 200 130 1 70 60 - 90

Al Si2MgTi F Gravity die casting 170 70 5 50

Al Si2MgTi T6 Gravity die casting 260 180 5 85




°C h °C °C h

Al Mg3Si(H) T6 545 - 555 4 - 10 20 160 - 170 8 - 10

Al Mg5(Si) T6 540 - 550 4 - 10 20 160 - 170 8 - 10

Al Si2MgTi T6 520 - 535 4 - 10 20 155 - 165 7 - 10

83


AlMg casting alloys




Al Mg3Si(H) T6 220 210 120 80 150 140 60 30 4 4 5 14 75 45 40 20

Al Mg5(Si) T6 210 200 170 140 120 110 100 70 4 4 5 8 70 70 60 30




°C °C °C % % %

Al Mg3(H) 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg3 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg3(Cu) 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg3Si(H) 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg5 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg5(Si) 700 - 750 700 - 750 1.0 - 1.5 0.7 - 1.2

Al Mg9(H)/Fe 680 - 640 0.5 - 0.7

Al Mg9 680 - 640 0.5 - 0.7

84


Application notes

We produce Al Mg3-type casting alloys

for handles, window handles or security

covers in decorative anodised quality.

For structures in the chemical industry, in

shipbuilding or the food industry, which

demand the highest possible resistance

to chemical attack and the infl uences of

maritime climates, Al Mg5-type cast-

ing alloys are suitable. Heat-resistant

Al Mg5Si-type casting alloys are suit-

able for high-temperature applications

such as engine construction. In France,

the Al Si2MgTi alloy is used for handles.

For pressure die castings with good cor-

rosion resistance, Al Mg9-type casting

alloys are used.


The highest requirements are placed on

the quality of these casting alloys – par-

ticularly for decorative parts which are

anodised. The manufacture of these cast-

ing alloys represents a special challenge

for smelters requiring much experience,

the best raw materials and quality-ori-

ented work.

Notes about surface treatment

As a pre-treatment, the surfaces of cast-

ings made from Al Mg3, for example, are

mechanically machined as well as often

being chemically polished. In the anodis-

ing process (electrolytically-oxidised alu-

minium), a protective oxide layer, which

grows inwards and is essentially more

impervious, thicker, more wear resistant

and more homogeneous than a natural

oxide skin, is produced on the surface

of a casting. On pure aluminium and on

aluminium alloys which are low in pre-

cipitates, these layers are transparent.

All defects such as precipitated inter-

metallic phases, inclusions, heteroge-

neities, oxide fi lms, wrinkles and other

casting defects lead to disturbances in

the growth of the layer formation and,

consequently, impairment of the deco-

rative appearance.

As the electro-chemically formed oxide

layer is also the possible carrier of dis-

colouring substances, defects near the

surface can lead to the parts having a

blemished, non-decorative appearance.

Hollow spaces such as wrinkles or pores

which have been cut can be taken up

by the aqueous solutions or electrolyte

during treatment. Even later, due to a

secondary reaction, the remainder of this

medium can lead to local decomposi-

tion of the anodised or colour coating.

85


AlMg casting alloys

The following alloying constituents can

have an infl uence on the quality and ap-

pearance of anodised layers:

Silicon

With Si concentrations higher than

0.6 %, the precipitated silicon or Mg2Si

impairs transparency. The anodised layer

loses its brilliance.

Iron, chromium and manganese

The sum total of these elements can

have a yellowing effect on the anodised

layer. Limiting concentrations can not

be established. Their infl uence depends

on the phase composition and chemi-

cal back-dissolution during anodising.

Copper

It has no negative infl uence when found

in normal concentrations. In the case of

higher additions, the layer becomes softer

and the composition rougher.

Zinc

This element has no infl uence on the

anodising process or pigmentation.

Titanium

Concentrations of Ti above 0.02 % have

a negative effect on the electrolytic col-

ouration of aluminium castings.

Notes on casting techniques

To avoid the tendency to hot tearing

during casting and particularly for deco-

rative reasons, the cast structure must

be fi ne-grained. This fi ne-grained struc-

ture can already be achieved during the

production of the ingots by means of

intensive grain refi nement. As a general

rule, this grain refi nement does not have

to be repeated during pouring. Should

grain refi nement decrease as a result

of prolonged holding, we recommend

that it be freshened up using TiB grain

refi ning wire. Melt cleaning or keeping

the melt clean is important in order to

produce a cast piece of good quality.

We recommend that only those refi n-

ing fl uxes which are specifi cally suited

to AlMg casting alloys be used.

Bale-out vessels with ceramic fi lter ele-

ments have also proven their worth. Dur-

ing casting, only the fi ltrate is baled out;

the ladle remainder and subsequently

charged metal enter into the outside

areas of the melting or holding crucible.

The casting operation requires particular

care in order to produce a sound cast-

ing despite the constant risk of forming

oxides and shrinkage. In doing this, the

confi guration of the dies and the cast-

ing system play an important role. The

type of solidifi cation is globular-mushy.

A good feeding system is an essen-

tial prerequisite for producing a dense

structure.

86






Otherstotalindiv.


Al Cu4Ti min 4.2 0.15 (0.15) max 0.15 0.15 5.2 0.55 0.07 0.25 0.03 0.10 (0.18) (0.19) (0.30) 21100

Al Cu4MgTI min 4.2 0.20 0.15 (0.15) (0.15) max 0.15 0.30 5.0 0.10 0.35 0.05 0.10 0.05 0.05 0.25 0.03 0.10 (0.20) (0.35) (0.35) (0.30) 21000

Al Cu4MnMg min 4.0 0.20 0.20 (0.15) max 0.10 0.15 5.0 0.50 0.50 0.03 0.05 0.03 0.03 0.05 0.03 0.10 (0.20) (0.50) (0.05) (0.10) (0.10) 21200

Al Cu4MgTiAg min 4.0 0.01 0.15 0.5 Ag 0.4 max 0.05 0.10 5.2 0.50 0.35 0.05 0.35 0.03 0.10 1.0

Al Cu5NiCoSbZr min 4.5 0.1 1.3 0.15 **** max 0.20 0.30 5.2 0.3 0.10 1.7 0.10 0.30 0.05 0.15


AlSi12CuNiMg min 10.5 0.8 0.9 0.7 (0.8) max 13.5 0.6 1.5 0.35 1.5 1.3 0.35 0.20 0.05 0.15 P (0.7) (1.5) (0.25) 48000 / 260

Al Si18CuNiMg min 17.0 0.8 0.8 0.8 max 19.0 0.3 1.3 0.10 1.3 1.3 0.10 0.15 0.05 0.15 P

****) Co 0.10-0.40 Sb 0.10-0.30 Zr 0.10-0.30


87




Alloy Numerical Other denomination 1) Si Fe Cu Mn Mg Cr Ni Zn Pb Sn Ti Hyper eutectic casting alloys

Al Si17Cu4Mg* min 16.0 4.0 0.5 max 18.0 0.3 5.0 0.15 0.65 0.10 0.10 0.20 0.05 0.15 P

Al Si17Cu4Mg** min 16.0 4.0 0.45 (0.25) max 18.0 1.0 5.0 0.50 0.65 0.3 1.5 0.15 0.20 0.05 0.25 (1.3) (0.65) (0.25) 48100


Autodur min 8.5 0.3 9.5 max 9.5 0.15 0.02 0.05 0.5 10.5 0.15 0.03 0.10

Autodur (Fe)* min 8.5 0.3 9.5 max 9.5 0.40 0.02 0.30 0.5 10.5 0.15 0.03 0.10

Autodur (Fe)** min 7.5 0.25 9.0 (0.20) max 9.5 0.27 0.08 0.15 0.5 10.5 0.15 0.05 0.15 (0.30) (0.10) (0.5) 71100

Rotor-Aluminium

Al 99.7E*** min max 0.07 0.20 0.01 0.005 0.02 0.004 0.04 Mn+Cr+ 0.03 B 0.04 V+ Ti= 0.02

Al 99.6E*** min max 0.10 0.30 0.01 0.007 0.02 0.005 0.04 Mn+Cr+ 0.03 B 0.04 V+Ti= 0.030

*) Non-standardised version**) According to DIN EN 1706: 2010 ***) According to DIN EN 576


Otherstotalindiv.

88





Al Cu4Ti

Al Cu4TiMgTi

Al Cu4TiMgAg

Al Cu5NiCoSbZr


Al Si12CuNiMg

Al Si18CuNiMg


Al Si17Cu4Mg 1)

Al Si17Cu4Mg 2)


Autodur

Autodur(Fe)

Al Zn10Si8Mg 1)

Rotor-Aluminium

Al 99.7E

Al 99.6E

1) Non-standardised version2) According to DIN EN 1706: 2010

89



Physical properties




Al Cu4Ti 2.79 72,000 0.91 640 - 550 23 16 - 23 120 - 150

Al Cu4MgTi 2.79 72,000 0.91 640 - 550 23 16 - 23 120 - 150

Al Cu4TiMgAg 2.79 72,000 0.91 640 - 550 23 16 - 23 120 - 150

Al Cu5NiCoSbZr 2.84 76,000 0.91 650 - 550 23 18 - 24 120 - 155


Al Si12CuNiMg 2.68 77,000 0.90 600 - 540 20 15 - 23 130 - 160

Al Si18CuNiMg 2.68 81,000 0.90 680 - 520 19 14 - 18 115 - 140


Al Si17Cu4Mg 1) 2.73 81,000 0.89 650 - 510 19 14 - 18 115 - 130

Al Si17Cu4Mg 2) 18 14 - 17 120 - 130


Autodur 2.85 75,000 0.86 640 - 550 21 15 - 20 115 - 150

Autodur(Fe) 2.85 75,000 0.86 640 - 550 21 15 - 20 115 - 150

Al Zn10Si8Mg 2) 21 17 - 20 120 - 130

Rotor-Aluminium

Al 99.7E 2.70 70,000 0.94 660 24 34 - 36 180 - 210

Al 99.6E 2.70 70,000 0.94 660 24 32 - 34 180 - 210

1) Non-standardised version2) According to DIN EN 1706: 2010

90



Al Cu4Ti T6 Sand casting 300 200 3 95


Al Cu4TiMg T4 Sand casting 300 200 5 90

Al Cu4TiMgAg T6 Sand casting 460 - 510 410 - 450 7 130 - 150

T64 Sand casting 370 - 430 200 - 270 14 - 18 105 - 120

Al Cu5NiCoSbZr T7 Sand casting 180 - 220 145 - 165 1 - 1.5 85 - 95 90 - 100

T5 Sand casting 180 - 220 160 - 180 1 - 1.5 80 - 90 90 - 100

Al Cu4Ti(H) T6 Gravity die casting 330 220 7 95 80 - 110


Al Cu4MgTi T4 Gravity die casting 320 200 8 95 80 - 110

Al Cu4TiMgAg T6 Gravity die casting 460 - 510 410 - 460 8 130 - 150 100 - 110


Al Si12CuNiMg F Sand casting 140 130 ≤1 80

T6 Sand casting 220 190 ≤1 90



Al Si17Cu4Mg F Sand casting 140 130 ≤1 80



Al Si18CuNiMg F Sand casting 140 130 ≤1 85



Al Si12CuNiMg F Gravity die casting 200 190 ≤1 90 80 - 110

T6 Gravity die casting 280 240 ≤1 100


Al Si17Cu4Mg F Gravity die casting 180 170 ≤1 100 80 - 110



Al Si18CuNiMg F Gravity die casting 180 170 ≤1 90 80 - 110






min min min min

91





min min min min Piston casting alloys

Al Si12CuNiMg F Pressure die casting 240 140 ≤1 90

T5 Pressure die casting 240 140 ≤1 90

Al Si17Cu4Mg 1) F Pressure die casting 220 200 ≤1 100

T5 Pressure die casting 230 210 ≤1 100

Al Si18CuNiMg F Pressure die casting 210 180 ≤1 100


Autodur T1 Sand casting 210 190 ≤1 90

Al Zn10Si8Mg T1 Sand casting 210 190 1 90

Autodur T1 Gravity die casting 260 210 ≤1 100 80 - 100

Autodur(Fe) T1 Pressure die casting 290 230 ≤1 100

Rotor-Aluminium

Al 99.7E F Gravity die casting 60 20 30 14

Al 99.6E F Gravity die casting 60 20 30 14

Al 99.7E F Pressure die casting 80 20 10 15

Al 99.6E F Pressure die casting 80 20 10 15

1) Non-standardised versionThe values apply for separately-cast sample bars in sand and gravity die casting. Mechanical properties of pressure die casting samples are not binding and merely serve as information. The values representing vibration testing and/or fatigue strength apply for the best available casting process and merely serve as information.

92




°C h °C °C h


Al Cu4TiMg T4 520 - 530 8 - 16 20 - 80 15 - 30 > 120

Al Cu5NiCoSbZr T5 Air 345 - 355 8 - 10

T7 535 - 545 10 - 15 20 - 80 210 - 220 12 - 16

Al Cu4Ti T6 515 - 535 8 - 18 20 - 80 170 - 180 6 - 8

Al Cu4TiMgAg T6 525 - 535 8 - 18 20 - 80 170 - 180 6 - 7

Al Cu4Ti(H) T64 515 - 535 8 - 18 20 - 80 135 - 145 6 - 8


Al Si12CuNiMg T5 Air quenching None 210 - 230 10 - 14

T6 520 - 530 5 - 10 20 - 80 165 - 185 5 - 10

Al Si18CuNiMg T5 Air quenching None 225 - 235 7 - 12

T6 495 - 505 7 - 10 20 - 80 165 - 185 7 - 10

T7 495 - 505 7 - 10 20 - 80 225 - 235 7 - 10


Al Si17Cu4Mg 1) T5 Air quenching None 225 - 235 7 - 12

T6 495 - 505 7 - 10 20 - 80 165 - 185 7 - 10

T7 495 - 505 7 - 10 20 - 80 225 - 235 7 - 10

1) Non-standardised version





Al Si12CuNiMg F 200 200 160 100 190 170 100 70 ≤ 1 1.5 2.5 3 90 85 60 35

Al Si18CuNiMg F 180 180 160 120 170 150 100 80 ≤ 1 1 2 3 90 90 70 50


Al Si17Cu4Mg 2) F 180 180 160 120 170 150 100 80 ≤ 1 1 2 3 100 90 70 50

1) Mechanical properties in minimum values / values after long-term maintenance of the respective temperature. 2) Non-standardised version

93





°C °C °C % % %


Al Cu4Ti 690 - 750 690 - 750 1.1 - 1.5 0.8 - 1.2

Al Cu4MgTi 690 - 750 690 - 750 1.1 - 1.5 0.8 - 1.2

Al Cu4TiMgAg 690 - 750 690 - 750 1.1 - 1.5 0.8 - 1.2

Al Cu5NiCoSbZr 690 - 750 690 - 750 1.1 - 1.5


Al Si12CuNiMg 670 - 740 670 - 740 620 - 660 1.0 - 1.2 0.5 - 1.0 0.4 - 0.6

Al Si18CuNiMg 730 - 760 730 - 760 730 - 760 0.6 - 1.0 0.4 - 0.8 0.3 - 0.6


Al Si17Cu4Mg 1) 720 - 760 720 - 760 720 - 760 0.6 - 1.0 0.4 - 0.8 0.3 - 0.6


Autodur 740 - 690 740 - 690 1.0 - 1.2 0.8 - 1.0

Autodur(Fe) 700 - 650 0.5 - 0.8

Rotor-Aluminium

Al 99.7E 700 - 730 700 - 730 690 - 730 1.5 - 1.9 1.2 - 1.6 1.0 - 1.4

Al 99.6E 700 - 730 700 - 730 690 - 730 1.5 - 1.9 1.2 - 1.6 1.0 - 1.4

1) Non-standardised version

94


High-strength casting alloy

Application notes

These casting alloys are used for parts

which – compared to all other aluminium

casting alloys – require maximum strength.

Where their reduced corrosion resistance

represents no obstacles, these casting

alloys can be used to manufacture high-

strength components, for example, for

the defence industry, aerospace, auto-

motive, rail vehicles, mechanical engi-

neering and the textile industry.


The use of these relatively demanding

casting alloys only makes sense if the

component undergoes heat treatment.

Only then, can the potential of these

casting alloys be fully utilised. Following

heat treatment, the castings still have ex-

cellent elongation as well as displaying

the highest possible strength and hard-

ness. This combination of high strength

and good elongation values gives these

casting alloys the highest possible Qual-

ity Index “Q”.

By means of special heat treatment,

hardness and elongation values can be

adjusted within determined limits. There

are other variants of these aluminium

casting alloys, e.g. with nickel and cobalt

being added to optimise their strength.

Furthermore, there are also casting al-

loy types which contain silver so as to

meet the maximum strength require-

ments. The corrosion resistance of cast

pieces is reduced, however, due to the

high copper content.

The casting technique for these alloys is

demanding. Most defects in the castings

stem from “contamination” with silicon.

The silicon content should be kept as

low as possible and always lower than

the iron content. An excess of silicon

produces a low melting phase and in-

creases the susceptibility to hot tearing

during solidifi cation. Even slight impedi-

ments to solidifi cation shrinkage can

lead to structural separation. The most

important requirement in the foundry is

therefore cleanliness to prevent the take-

up of silicon. Here are some recommen-

dations: The melting crucible must not

contain any remainder of silicon alloys.

It also makes good sense to melt several

batches of an alloy which is low in sili-

con in a new crucible to free the crucible

material of silicon. There are users who,

for this reason, use melting crucibles

made of graphite or cast iron for these

casting alloys. Return material should

also be checked very strictly and stored

separately; residual sand and other return

material must be painstakingly removed

from all sprues. From practical experi-

ence, some users recommend having a

separate foundry department for these

casting alloys. Melt cleaning and degas-

sing can be carried out without any trou-

ble using normal means. Melt treatment

is restricted to grain refi nement which,

among other things, slightly counteracts

the susceptibility to hot cracking. Inten-

sive grain refi nement is already performed

by us so it does not usually need to be

repeated in the foundry. The fl uidity of

these casting alloys is comparable with

other hypoeutectic AlSi casting alloys.

The solidifi cation characteristics are best

described as being globular-mushy. At

approx. 90 K, the solidifi cation range is

relatively high. Using a good fi lling system

in conjunction with steered or controlled

solidifi cation and suitable feeding, opti-

mum structural qualities can be achieved

with the sand and gravity die casting

processes. Thanks to their good struc-

tural quality and optimum heat treatment,

these high-strength casting alloys are

suitable for the manufacture of castings

whose unmatched mechanical proper-

ties comply with maximum demands.

95


Heat treatment

The heat treatment of castings is another

important step in the production of quality

cast parts. Exact temperature regulation

of the annealing furnace, good tempera-

ture distribution by means of circulating

air and the correct positioning of the

casting in the baskets, holders or racks

are essential prerequisites for success.

In solution annealing, the temperature

increase should be moderate in order

to allow enough time for temperature

equalisation to take place in the castings

and to avoid incipient fusion. The relief

of casting strain, the removal of micro-

structural inhomogeneity and the diffu-

sion of hardening constituents require

longer periods of time. In these casting

alloys, especially in thick-walled, slow-

solidifying castings, stepped annealing

is recommended. First of all, the cast

pieces undergo preliminary annealing

at 480 to 490 °C for between 4 and 8

hours; they are then given a solution heat

treatment at approx. 515 to 535 °C for a

further 6 to 10 hours. To avoid distortion,

quenching of the casting after anneal-

ing can be effected by means of a water

shower followed by immersion in warm

water at temperatures of up to 80 °C.

Fully-annealed Al Cu4TiMg castings have

a susceptibility to stress corrosion. This

condition is therefore not standardised

for this casting alloy. Such parts are only

used in naturally-aged condition (T4).

High-strength casting alloy

96


Piston alloys

Application notes

These casting alloys are used for cast-

ings with wear-resistant surfaces and for

structures which have to possess good

strength properties at high temperatures.

The main applications comprise: pistons

for combustion engines, crankcases

without additional cylinder liners, pump

casings, valve casings, valve slides, gear

elements etc.


The wear resistance of these casting al-

loys is due to many hard, rectangular or

polygonal primary silicon crystals which

are embedded in the ductile base mate-

rial and jut out of the surface of the track

with an edge (while the neighbouring

troughs act as reservoirs for lubricant).

In addition, alloying elements such as

Cu, Mg or Ni give these casting alloys

remarkable high-temperature strength.

In order to produce as many small and

evenly-distributed silicon crystals as

possible in the cast structure, phospho-

rous is added. This treatment is already

carried out during production of the in-

gots in our secondary smelters and, as

a rule, does not need to be repeated by

the foundry. The fl uidity of these types

of casting alloy is very good. In spite of

this, silicon crystals forming in the melt

at too low casting temperatures are to

be avoided because of their abrasive ef-

fect. Additional information is provided

in the section on “Selecting aluminium

casting alloys”.

97


Self-hardening aluminium-silicon-zinc casting alloys

Application notes

These casting alloys are used in the

manufacture of models, foamed shapes,

wearing parts or the bases of electric

irons, for example. The use of these

casting alloys is not recommended for

machine parts which are subject to al-

ternating or impact stress, are obliged

to absorb bending and shearing stress

or requiring a specifi c ductility.


The fl uidity of Autodur in particular is very

good. Solidifi cation behaviour is similar

to that of other casting alloys containing

approx. 9 % silicon. Alloys of this type

are self-hardening, i.e. after casting, the

castings are stored at room tempera-

ture and within approx. 10 days reach

their service properties. This hardening

takes place as a result of precipitation

of the complex Al ZnMg. The advantage

of these casting alloys lies exclusively

in their saving of heat treatment costs.

There are, however, disadvantages in

using these casting alloys. The following

information should serve as a warning:

Under unfavourable conditions whilst

molten, the zinc content is reduced due

to its high vapour pressure. The resis-

tance of Autodur to corrosion is sharply

reduced as a result of its high zinc con-

tent of around 10 %.

In cases where the exposure to corrosion

is great or where parts made from Auto-

dur are assembled with other castings or

parts made from other aluminium alloys,

or indeed fi tted to steel parts, there is a

strong tendency to contact corrosion.

Compared with all other aluminium cast-

ing alloys, castings made from these al-

loys display the lowest high-temperature

strength. (Precipitation treatment carried

out at room temperature to increase hard-

ness has no clearly defi nable effect.) Ex-

perience shows that castings, even after

many years, can fracture spontaneously

under the slightest impact or shock load.

Over time, the microstructure appears to

be embrittled.

98


Rotor aluminium

Application notes

This pure aluminium is mostly used in

pressure die casting and goes into the

manufacture of rotors (short-circuit ar-

matures) and stators for the electric mo-

tor sector. It can also be cast into other

construction elements which require

high electrical and thermal conductivity.


There is a particular hurdle in the near

net shape casting of pure aluminium,

i.e. sensitivity to hot tearing. The most

important prerequisite for keeping this

problem within limits is to maintain the

correct ratio between iron and silicon. The

silicon content must be as low as possible

and the iron content must always be at

least double the silicon content. Molten

pure aluminium readily absorbs silicon

from any standing material it comes into

contact with. This can easily lead to an

“imbalanced ratio”. Cleanliness is there-

fore important during processing and it

is also essential to check tools and the

melting crucible. In extreme emergen-

cies when silicon enrichment occurs, it

helps to increase the iron content within

the permitted tolerance range.

99



If you require any additional data or

support at short notice, please refer

to our contact details on the back

of this brochure or simply visit us

online at www.aleris.com.

We have taken the relevant special-

ist literature into consideration while

drawing up this Aluminium Casting

Alloy Catalogue. Please do not hesi-

tate to contact us if you require more

detailed literary explanations.

www.aleris.comwww.aleris.com

Aleris

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Aleris Recycling

(German Works) GmbH

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Aluminium Casting Alloys EnglishVersion