FERROUS ANDNON-FERROUS ALLOYS

INTRODUCTIONFerrous and non-ferrous alloys form the most important group among all engineering

materials in the world. These alloys have a very wide range of properties and are used inevery walk of our life. The study of ferrous and non-ferrous alloys, therefore, is very important.This chapter is wholly devoted to the study of these materials, their types, compositions,properties and applications.

FERROUS ALLOYSFerrous alloys can be broadly classified into two groups- Steels and Cast Irons.Steels are those alloys of iron and carbon which contain upto 2.1 % carbon by weight

whereas Cast Irons are those alloys which contain carbon between 2.1 % and 6.67%. Anotherdifference between them is that, steels always have carbon in the combined form i.e., combined.with iron to form phases like a -ferrite, austenite, cementite etc., whereas cast irons generallyhave carbon in the free form, i.e, as graphite. But there are a few exceptions in cast ironswhere carbon is also found in the combined form, as in the case of white cast iron. Ferrousalloys in practice are not made up of only iron and carbon but many alloying elements likesilicon, manganese, nickel, chromium and several others are added in order to enhance theirproperties.

STEELSSteels can be classified in several ways. Some of them are according to :

i) Carbon Content:1) Low-carbon, medium - carbon and high - carbon steels.2) Hypo-eutectoid steels «0.8 % C)

Hyper-eutectoid steels (>0.8 % C)

ii) Method of manufacture:1) Bessemer steel.2) Open - hearth steel.3) Electric furnace steel.

4) Crucible steel etc.,

Hi) Applications of steel:1) Machine steel2) Spring steel3) Boiler steel4) Structural steel5) Tool steel etc.,

iv) Chemical Composition:1) Plain carb~n steels and alloy steels

v) Standard Institutions:1) AISI - Americal Iron &.Steel Institute2) BIS - Bureau of Indian Standards.3) SAE - Society of Automotive Engineers.4) ASTM - American Society for Testing & Materials.

The above Institutions have classified steels also according to chemical composition.For convenience, we shall study the different types of steels classified according to

their chemical composition, i.e., Plain carbon steels and Alloy Steels. -

1) PLAIN CARBON STEELSP~ain carbon steels can be classified once again according to the percentage of carbon .. _

a) Low - carbon steel- up to 0.25% carbon.b) Medium - carbon steel - 0.25 % to 0.55 % carbon.c) High - carbon steel- above 0.55% carbon.

Although by definition, plain carbon steels contain only iron and carbon, they always comewith traces of sulphur and phosporous and also sometimes small quantities of Silicon & Manganese.

a) Low - Carbon Steels:Of all the different kinds of steels, those produced in the greatest quantities are low -

carbon steels. The charecteristics of low - carbon steels are :

CompositionMicrostructureProperties

- upto 0.25 % C- Predominantly cc-ferrite and small quantities of pearlite.- Relatively soft and weak but outstanding ductility and toughness.

They possess very good machinability and weldabilityEg. : Mild Steel.

- Least expensive to product.Advantages"

- Unresponsive to hardening heat treatment because mastensite isdifficult to form owing to very low carbon content. Strengtheningcan be accomplished only by cold work. Very low hardenability.

- Automobile body components, structural shapes (I - beams, Channeland angle irons), buildings, bridges and small cans.

b) Medium Carbon Steels:Composition - From 0.25% to 0.55% CMicrostructure - a - ferrite and pearliteProperties - Stronger than low - carbon steel but less toughner than it.Advantages - Best range for adding alloying elements.

Good mix of ductility & strength.- Railway wheels and tracks, gears, crant shafts and other machine

parts.

c) High - Carbon Steels:Composition - From 0.55% C upto 2.1 % CMicrostructure - Cementite (Fe

3C) and pearlite (when C > 0.8%), a - ferrite and

pearlite (when C < 0.8%)- Hardest, strongest and least ductile when compared with low and

medium carbon steels.- Best range to make tool steels.- Cannot be used for operations where ductlity & maIleaIiIity are

required.- Knives, razors, hack - saw blades, high strength wire etc.

Disadvantages.

Application

Applications

Properties

AdvantagesDisadvantages

Applications

2) ALLOY STEELSSteels which acquire some charecteristic properties due to the addition of alloying

elements, other than carbon, are known as alloy steels. Alloying elements are added to steelsfor many purposes.

Some of the reasons are to :i) increase hardenability

ii) improve strength at ordinary temperatures.iii) improve wear and corrosion resistances.iv) improve mechanical properties at either high or low temperature.v) improve toughness without greatly sacrificing strength.

vi) improve magnetic properties.vii) increase red hardness (elevated temperature hardness)

Effect of alloying elements on SteelAlloying elements that are added to steel may be classified according to the way they

affect the principal phases of steel i.e., a - ferrite, Iron carbide (Fe3C) and austenite.

i) Elements which tend.toform carbides: These elements combine with carbon to formcarbides just like iron forms Iron carbide (Fe3C). These carbides tremendously increasethe hardness and wear resistance of the steels but at the same time render them brittle.

Eg. : Chromium, tungsten, titanium, vanadium, molybdenum, manganese etc.

ii) Elements which tend to graphitize carbon : These elements when added to steelsoppose the formation of carbides where carbon is in the combined form but insteadstabilizes carbon to occur in its free form as graphite.

Eg : Silicon, cobalt, aluminium, nickel etc.. "

iii) Elements whech tend to stabilize austenite: These elements when added lowers theA3 temperatures and raises the peritectic point, thereby increasing the range in whichaustenite is stable.

Eg. : Manganese, nickel, cobalt, copper etc.

iv) Elements which tend to stabilize ferrite: These elements are more soluble in a-ironthan in y-iron. Hence they are ferrite stabilizers.

Eg. : Chromium, tungsten, molybdenum, silicon etc.

Some of the elements appear in more than one group and it means that they have morethan one effect.

Types of Alloy steelsAlloy steels may be dividedinto four classes:

i) Structural steelsii) Tool and die steels

iii) Magnetic alloysiv) Stainless and heat - resisting steels

i) Structural Steels:These are basically low - carbon steels with the carbon percentage between 0.15% to

0.30%. The principal alloying elements that are added are silicon, copper, chromium,phosphorous and manganese is that order. The combination of copper and phosphorus increasesthe resistance to atmospheric corrosion and the other elements improves its strength andother properties.

The following characteristics of structural steels are important:a) good yield strength.b) enough ductility to avoid brittle fracture.c) weldability.d) low cost.

As the name suggests, structural steels are used for ships, bridges and buildings.

ii) Tool and Die Steels:

These are basically high quality special steels used for cutting, forming and die-makingpurposes.

Different types of commonly employed tool steels are:a) Water hardening tool steels: They contain 0.7 to 1.3% carbon. They are used in

making drills, files, chisels, hammers and forging dies.b) Shock resistant tool steels: These are chromium-tungsten, silicon molybdenum or

silicon - manganese alloys. They are used in making tools, punches, chisels and dies onaccount of their outstanding toughness and ability to withstand repeated shocks.

c) Hot worked tool steels: In many applications the tool is subjected to excessive heat asin hot forging, extruding, die casting etc. Tool steels developed for these applicationsare known as hot-work tool steels and have good red hardness. The alloying elementsadded to improve red hardness are chromium, molybdenum and tungsten.

d) High - Speed steels: These steels are among the most highly al!oyed of the tool steelsand usually contain large amounts of tungsten or molybdenum along with chromium,vanadium and some times cobalt. The carbon content varies between 0.70 and 1.0%,although some types contain as much as 1.5%. High speed steels have excellent wearresistance, good red hardness and reasonably good shock resistance.The major application of high speed steels is for cutting tools, but they are also usedfor making extrusion dies, burnishing tools, blanking punches and dies.

Following are the important classes of high speed steels:1) Class 18-4-1 steel

Composition .. 18% tungsten, 4% Chromium,

1% Vanadium, 0.7% Carbon

Cobalt, rest iron

2) CLass

CompositionHigh - Mo steel

8.5% Molybdenum, 4% Chromium,1.5% Tungsten, 1% Vanadium0.8% Carbon, rest iron

W-MoSteel3) CLass

Composition 6% Tungsten, 5% Molybdenum4% Chromium, 2% Vanadium0.8% Carbon, rest iron.

iii) Magnetic Alloys:Magnetic alloys are basically made of the three magnetic materials namely iron, nickel

and cobalt. Magnetic materials can be broadly classified into soft magnetic materials andhard magnetic materials .

. Soft magnetic materials are those whose hysteresis loop gives a small area under theB-H curve (flux density - magnetic field curve)

These materialsposses high permeability and are suitable for use in transformer cores.Eg. : Permalloy (45% Ni), Supermalloy (79% Ni, 5% Mo)Hard magnetic materials are those whose hysteris loop gives a large area under the

B-H curve. They make permanent magnetic materials and are used for making magneticpoles for alternators and motors.

Eg. : High carbon steel, Alnico (AI + Ni + Co + Fe), Cunife (Cu + Ni + Fe)

iv) Stainless steels or chromium steels:Excellent corrosion resistance, heat resistance and aesthetic properties have inade

stainless steel an outstanding material for both industrial and domestic purposes. Stainlesssteels owe their corrosion resistance largely to the presence of chromium in them. Corrosionresistance may also be enhanced by nickel and molybdenum additions.

Stainless steels are divided into three classes on the basis of the predominant phasepresent in their microstructure - martensitic, ferritic or austenitic stainless steels.

a) Ferritic stainless steels:Microstructure - Predominantly a. -ferriteComposition - 11.5% - 27% chromium

0.8 - 0.2 % carbon, 1% manganese, 1% nickel, rest iron.- Magnetic, heat and corrosion resistant, can be hardened and

strengthned only by strain hardening because they are not heat .treatable.

Properties

Applications - Valves (high temperatures), automotive exhaust components,combustion chambers etc.,

b) Austenitic stainless steel:Microstructure - predominantly austenitic (even at room temperature)

Composition - 16% - 26% Chromium,

6% - 22% Nickel

0.05% - 0.25% Carbon

2% - 4 % Molybdenum, rest iron.

Properties - Non - magnetic, heat and corrosion resistant, strengthened andhardened only by strain hardening because of low carbon.

Applications - Chemical and food processing equipment, cryogenic vessels,welding construction, kitchen utensils.

c) Martensitic stainless steel:M icrostructure

Composition

Properties

Applications

- Predominantly martensitic.

- 11.5% - 18% chromium1.25% - 2.25 % Nickel0.75% - 1% Molybdenum0.15% - 1.2% Carbon, rest iron.

- Magnetic, heat and corrosion resistant, heat - treatable, high strengthand hardness, wear resistant.

- Cutlery, rifle barrels, jet engine parts, bearings, surgical tools etc.,

AISI Designation SteelThe American Iron and Steel Institute has classified steels according to their composition

and has devised a numbering system to designate different steels.AISI designation steels normally have four or five digits. The first numeral always

represents the type to which the steel belongs. Thus 1 indicates a carbon steel, 2 indicates anickel steel, 3 a nickel - chromium steel etc. In other words, for plain carbon steels, the firstdigit is 1 whereas different alloy steels start with numbers other than 1. In the case of alloysteels, the second digit indicates the approximate parcentage of the predominant alloyingelement. The last two digits are common to all steels and usually indicate the mean carboncontent divided by 100. Thus the symbol 2520 indicates a nickel steel of approximately 5%Nickel and 0.2% carbon. The symbol 1060 would indicate a plain carbon steel with 0.6%carbon. The second digit of a plain carbon steel indicates usually the type of production ofsteel or the maximum residual percentages of sulphur, phosphorus or manganese.

The basic numbers for the four-digit series of a few grades of carbon and alloy steelswith approximate percentages of identifying elements are listed below. The last two digitshave been marked 'XX' indicating that carbon percentage in variable.

AISI No. Type, Composition

10XX

llXX

12XX

13XX

23XX

25XX

31XX

33XX

40XX

43XX

50XX

61XX

86XX

92XX

94BXX

Plain carbon steels made from basic open - hearth and Bessemerprocess.

Basic open-hearth and Bessemer carbon steels, high sulphur, lowphosphorus.

Basic open - hearth carbon steels, high sulphur and high phosphorus.

Manganese - 1.75%

Nickel - 3.5

Nickel- 5.0

Nickel - 1.25, Chromium - 0.60

Nickel- 3.5, Chromium - 1.5

Molybdenum - 0.20 or 0.25

Nickel - 1.05, Chromium - 0045, Molybdenum - 0.2

Chromium 0040

Chromium, Vanadium steels

Nickel, Chromium molybdenum

Silicon - 2.00

Nickel, Chromium, Molybdenum, 'Boron'

The above classification is for only carbon and alloy steels. As far as tool steels areconcerned. they have been grouped into seven major headings, and each group or subgrouphas been assigned analphabeticalletter as follows:

GROUP Symbol and Type

Water hardening W

Shock - resisting S

Cold - work a - Oil hardeningA - Medium alloy air hardeningD - High - carbon, high - chromium

Hot work H - HI to Hl9 - Chromium basedH20 to H39 - Tungsten basedH40 to H59 - Molybdenum based

High Speed T - Tungsten baseM- Molybdenum base

Mould Steels P - PI to PI9 - low carbonP20 to P39 - other types .

Special purpose L - Low - alloyF - Carbon - tungsten

BIS Designation Steels and Cast IronsThe Bureau of Indian Standards was set up in 1956 to establish standards for aI

engineering materials, products and different processes in India. As far as steels and castirons are concerned, each and every ferrous alloy or group of ferrous alloys are desigriatedparticular numbers. Under each Indian Standard Number, the composition, properties,production, testing and applications of the particular alloy are explained. The Indian Standardnumbers of some importnat steels and cast irons are listed below.

BIS CODE Alloy or Alloy group

IS 7887 : 1992 Mild steel (low carbon steel)

IS 3748 : 1990 Tool & die steels

IS 6528 : 1995 }IS 6527 : 1995

Stainless steelsChrome steel

IS 963 : 19581

IS 4522 : 1986 Heat resistant alloy steelsIS 7806 : 1975 Martensitic & Austenitic (high alloy) stainless steels.

IS 210 : 1993 } Grey cast ironIS 7754 : 1975

IS 9630 : 1980 Spheroidal graphite iron

IS 14329: 1995 Malh~able iron

IS 1570 Part I - 1978While the above list gives the IS codes for various grades of steels, IS 1570 Part I -

1978 lays dows exclusively the various basis for classifying steels. One such classification isA-I which designate steels on the basis of their mechanical properties. Under this A-I.lgives the designation forplain carbon & low alloy steels.

A few grades of steels according to this classification is :Fe410CuK, FeE300P35, Fe41OQl, Fe520L

Fe 600 T4' Fe E 555 F" Fe 400 R, Fe E 500 S5

· Explanation of the grades1) Symbol 'Fe' or 'FeE' are specified depending on whether the steel has been specified

on the basis of tensile strength or yield strength respectively.2) The digits following this symbol give the tensile strength or yield strength as the case

may be in Nzrnrrf

For example in Fe E300 P35, the yield strength of the steel is 300 Nzmm'.

3) The value of strength is followed by the major alloying element present in the steel. Forego Copper as in Fe 410. Cu K: ..

4) The alphabet or the alphabet - numeral combination that follows alloying element givesthe various charecteristics of steel which is explained as follows:

a) Method of oxidation:R (Rimming steel)K (Killed steel)

b) Steel Quality - Q, to Q5

(depending on grain structures)

c) Resistance to brittle fractureB, BO, B2 or B4 (Extent of resistance)

d) Surface conditions - SI to S7(Peeled, rolled, scaled etc.,)

e) Formability - DI to D3 (drawing quality)

fJ Surface finish - F 1 to F14g) Heat treatment - TI to T14h) Cryogenic quality - L

CAST IRONSCast irons are those alloys of iron and carbon where the carbon content varies between

2.1 % and 6.67%. However, since high carbon content tends to make the cast iron very brittle,most commercially available types of cast irons are in the range of 2.5% to 4% carbon.

Cast irons are low in ductility and therefore cannot be rolled, drawn or worked easilyat room temperature. Most of the cast irons are not malleable at any temperature. But theirmelting temperature are considerably lower than those of steels and therefore can be meltreadily. Fluidity of molten cast iron is very good and therefore can be cast into complicatedshapes which can be later machined to final dimensions. Since casting is the only suitableprocess applied to these alloys, they are known as cast irons.

Cast irons are brittle and have lower strength properties than most steels but are muchcheaper than them. In addition, a wide range of properties can be given to cast irons byproper alloying. good foundry control and appropriate heat treatment. All these advantageshave combined to make cast iron the most popular material for casting and has led to the.production of large tonnages of cast iron in the industry.

According to the Iron carbon equilibrium diagram (fig 4.1), the phases that are observedin the microstructure of cast iron at room temperature are a-ferrite and cementite (Fe3C),.which occur at equilibrium conditions. But cementite being a meta stable compound, undercertain circumstances, decomposes to form a - ferrite and graphite, according to the reaction,

Fe3C • 3Fe(a) + C (graphite)

Thus the actual microstructure of cast irons would contain the phases a - ferrite andfree carbon in the form of graphite rather than a - ferrite and cementite. '

Therefore, cast irons can be generally distinguished by the presence of free carbon intheir microstructure. But there are a few exceptions like white cast iron which contain carbonin the combined form of cementite and pearlite.

Types of Cast Irons :Cast irons are classified according to their microstructure. In other words cast irons

are classified accordi ng to the shape of the free carbon (graphite) present in their microstructureor the absence of.carbon itself.

1) Gray cast irons2) White cast irons3) Mat'leable cast irons

4) Nodular or S.G. Iron or Ductile iron.Cast irons are also classified according to carbon content - hypo-entectic cast irons

(between 2.1 & 4.3 %C) and hyper-eutectic cast irons (between 4.3 and 6.67%C). Whatever be the classification, in all types of cast irons, apart from carbon, silicon isalso a principalalloying element. Fig 6.1 shows the approximate carbon content and silicon content of differenttypes of cast irons and also that of steel. Please note.the overlapping compositions of thevarious grades.

5.0.------------------------------------,

4.0

r 3.0

Carbon % 2.0

1.0 STEELS

1.0o 2.0 3.0 4.0Silicon % ~

Fig. 6.1 : Carbon and Silicon percentages in various-Cast irons

1) Gray Cast Irons:Gray cast irons are the most widely used type of cast irons. They are distinguished by

the presence of graphite in the form of flakes (like fibres). Gray cast irons can be divided intodifferent types based on the average length of the flakes in them. The general charecteristicsof gray irons are:Composition - 2.5% - 4% carbon

1% - 3% silicon, rest iron- a-ferrite and flake graphites (fig 6.2 and fig 4.13)- High fluidity, very high compressive strength, very effective in

damping vibrations, low cost.- Greyish, blackish surface when fractured (because of graphite

flakes). Hence the name grey iron too.- Pressure vessels, cylinder heads, pistons, clutch plates, base

structure for machines and heavy equipment that are exposed tovibrations, valves, fittings, levers etc.

MicrostructureProperties

Fracture surface

Applications

Fracture surface

2) White Cast Iron:White cast irons are those alloys which are hypo - eutectic in composition and an

exception among cast irons. This is because all the carbon present in them are in the combinedform as cementite (Fe3C) & pearlite as against the free carbon (graphite) form present inother cast irons. White cast iron is also an intermediate stage for producing malleable iron.Composition - 1.8% - 3.2% Carbon

0.3% - 1.8% Silicon, rest iron- Iron carbide (lightphase), pearlite (dark phase)

No graphite (fig. 6.3 and fig 4.15)Very hard and brittle, highly wear resitant, no ductility and

malleability, not machinable- Whitish surface (hence the name too)- Liners for cement mixers, ball mill, certain types of drawing dies,

extrusion nozzles etc.,

Microstructure

Properties

Applications

Fig. 6.2 : Grey Cast iron(ferrite + flake graphite)

Fig. 6.3 : White casf iron(cementite + pearlite)

• 0' •" .••••t ••.•• •~< •• , ..

Fig. 6.4 : Malleable iron(ferrite + temper carbon)

Fig. 6.5 : SG Iron(ferrite + nodular carbon)

3) Malleable Cast Iron:Malleable cast irons are those alloys where almost all the carbon is in the free form in

the shape of irregular particles known as temper carbon. As the name suggests, they areextremly malleable, and are obtained by heat treatment of white cast iron.

This heat treatment process is known as malleablization and is carried out toconvertall the combined carbon in white iron to temper carbon and a. - ferrite. Fig 6.6 shows thecycle of temperature and time for malleablizing white iron, which is self -explanatory.

1000

900

9500C/ \

/ \1/ 1\ --:: -- 1---

/ --1\-/ \

6800CU 700o8-d)

r< 600

500o 10 20 30 40 50 60 70 80 90 100

HoursFig.,6.6: Malleablization of White Iron

The Charecteristics of malleable iron areComposition - 1.8% - 3.2% carbon,

0.3% - 1.8% siliconrest iron

Microstructure - dark graphite rosettes (temper carbon) in an a. - ferrite matrix(fig 6.4 and fig 4.16)

- Highly malleable, very good machinability, good magneticproperties, wear resistance

- Connecting rods, transmission gears, flanges, pipe fittings,differential cases for automative industry, valves, parts for rail roadsand marine works.

Properties

Applications

4) Spheroidal Graphite (SG)Iron:S.G. Iron is characterised by the presence' of free carbon in the shape of compact

spheroids or nodules. S.G. Iron is also very well known for its ductility. Hence the othernames of SG iron are Nodular Iron or Ductile Iron. Spheriodal shaped graphite is obtainedby adding a small percentage of magnesium or Cerium to the alloy in the molten state.Composition - 3% - 4% Carbon,,

1.6% - 2.8% Silicon, rest ironMicrostructure - Dark graphite nodules surrounded by a -ferrite matrix

(fig 6.5 and fig 4.14) .Properties - Highly ductile, very good machinablility, high corrosion resistance

and good creep properties at elevated temperatures.Applications - Flywheels, furnace doors, wrenches, lathe chucks, motor frames,

pump bodies etc.,

NON - FERROUS ALLOYSWe know that steels and other ferrous alloys are consumed in exceedingly large quantities

because they have such a wide range of mechanical properties, may be fabricated with relati veease, and are economical to produce. However, they have some distinct limitations like:

i) a relatively high densityii) a comparatively low electrical conductivity

iii) susceptibility to corrosion in some common environments.Therefore, for many applications it is advantageous or even necessary to use non-

ferrous alloys rather than ferrous alloys in order to have more suitable property combinationsand overcome the limitations. Among non-ferrous materials, the bulk of them are made up ofthe alloys of copper, aluminium, magnesium, nickel, tin, lead and zinc. Other non-ferrousmetals and alloys that are used to a lesser extent inlude cadmium, molybdenum, cobalt,zirconium, beryllium, titanium, tantalum and theprecious metals gold, silver and the platinumgroup.

Among the wide variety of non-ferrous alloys, the following alloy groups are discussedin detail :

I) Copper and its alloys.2) Aluminium and its alloys.

COPPER AND ITS ALLOYSCopper and copper based alloys which posses a desirable combination of several

properties have been utilized in a variety of applications since antiquity. The properties ofcopper that are most important are high electrical and thermal conductivity, good corrosionresistance, machinability, strength and ease offabrication. In addition, copper is non-magnetic,has a pleasing colour, can be welded, brazed and soldered and is easily finished by electroplating. And all these properties can be further improved by adding alloying elements!. Allthese have made copper and its alloys very popular and widely used range of materials.

The most important commercial copper alloys may be classified as follows:i) Brasses (alloys' of copper and zinc)

J) Alpha brassesa) Yellow alpha brassesb) Red brasses

2) Alpha plus beta brassesii) Bronzes (alloys of copper and elements other than zinc)

1) Tin bronzes2) Silicon bronzes3) Aluminium bronzes4) Beryllium bronzes

iii) Cupronickels - alloys of copper and nickeliv) Nickel silver - alloys of copper, nickel and zinc.

(i) BRASSES:Brasses are essentially alloys of copper and zinc. But they may have small amounts of

other elements such as lead, tit).or aluminium added to improve their properties.Fig 6.7 shows a portion of the copper - zinc phase diagram which is applicable to

commercial alloys. The two important types of commercially used brasses are shown in thephase diagram - a - Brasses and (a+ P) Brasses.

1) Alpha Brasses:Composition - Copper + upto 36% zincMicrostructure Only solid solution a -brass (FCC structure) (fig 4.17)Properties - High corrosion properties, suitable for cold working.Types of a -brasses - a) Yellow a -brasses

b) Red brasses

110010831000

900

800

700r-c

600

500

4000

Cu 100%

Liquid iI-----+--~~~,___-__+---.- +-----1

10 20 30 50%Zinc % )

Fig. 6.7 : Portion of Cu - Zn phase diagram

a) Yeilow a -brasses:Composition - Copper + 20 to 36% zincProperties - High ductility, good strength, yellow in colour, susceptile to season

cracking (weakening due to inter-granular corrosion)Common Type i) Cartridge brass

ii) Leaded yellow brassiii) Admiralty brass

i) Cartridge Brass:Composition 70% Cu + 30% ZnApplications - Bullet shots, military ammunition, automotive radiator core, storage

batteries etc.,ii) Leaded Yellow Brass:

Composition - Cu + 29% Zn + 3% Pb + 1% SnApplications - Furniture hardware, radiator fittings, light fixtures etc.,

I

iii) Admiralty Brass:Composition - 70% Cu + 29% Zn + 1% SnApplications - Ship parts, general marine use, pump parts,

b) Red Brasses:- Copper + 5 - 20% Zinc.- Better Corrosion resistance than yellow a brasses, not susceptible

to season cracking, red in colour.- (i) Gilding metal (95% Cu + 5% Zn)

(ii) Low Brass (80 Cu + 20% Zn)- Coins, medals, tokens, name plates, musical instruments, rivets,

screws, costume jewellery etc.,

2) Alpha Plus Beta Brasses:Composition - Copper + 38 ~46% zincMicrostructure - Solid solution a -brass (FCC)

Electron compound P - brass (BCC) (fig 4.18)- Suitable for hot working, harder and more brittle at room temperature

than a -brass and therefore difficult to cold - work.- a) Muntz metal

b) Naval Brass

CompositionProperties

Common Types

Applications

Properties

Types

a) Muntz Metal:CompositionApplications

b) Naval Brass:CompositionApplications

- 60% Cu + 40% Zn- architectural work, condenser tubes, brazing rods etc.,

- 69% Cu + 39.25% Zn + 0.75 % Sn- Marine hardware, propeller shafts, condenser plates etc.,

II) BRONZESBronzes are those copper alloys which contain upto approximately 12% of the principal

alloying element, with the exception of copper - zinc alloys. Bronzes are generally higherclass alloys than brasses. Commercial bronzes are primary alloys of copper and tin, aluminium,silicon and beryllium. In addition they may also contain phosphorus, lead, zinc or nickel.Based on the alloying addition bronzes are classified as tin bronzes, silicon bronzes, aluminiumbronzes and beryllium bronzes.

1) Tin Bronzes (Phosphor bronzes) :Composition - Copper + 1 - 11% Tin + 0.01 - 0.5% PMicrostructure - a -phase and dark 0 - phase (fig 4.19)Properties - High strength, toughness. low co-efficient of friction, free from

season cracking, high corrosion resistance.Types of tin bronzes - a) Admiralty gun metal

b) Bell metala) Admiralty Gun Metal:

Composition - Cu - 88%, Tin 10%, Zn 2%Applications - Bearings, steam pipe fittings

b) Bell Metal:- Cu - 70%, Tin 30%- Casting of bells, canons. (Eg. Malik-e-rnaidan - a 55 ton canon in

Bijapur, North Karnataka)

2) Silicon Bronzes:Composition - Copper + upto 5% siliconMicrostructure - Single a -phase

Properties - Very strong, mechanical properties comparable to those of mildsteel, high corrosion resistance.

Applications - tanks, pressure ressels, marine construction. hydraulic pressure lines.

3) Aluminium Bronzes:Composition - Copper + 4 - 11% aluminiumMicrostructure - Two phases primary a - phase, Eutectoid (a+ Y2) (fig 4.20)Properties - Suitable for cold working, good strength combined with corrosion

resistance to atmosphere, and water attack.- Corrosion resistant vessels, nuts and bolts, blades, bearings,

bushings etc.,

4) Beryllium Bronzes:Composition Copper + 1.5 - 2% Be + 0.2% CoMicrostructure - dark y - phase at the grain boundaries of a -phase (fig 4.21)Properties - Excellent formability, good fatigue and creep resistance when

hardened, high electrical conductvity.- Diaphragms, surgical instruments, bolts, firing pins etc.

CompositionApplications

Applications

Applications

ALUMINIUM AND ITS ALLOYSAluminium and its alloys are charecterized by a relatively low density (2.7 g/cm' as

compared to 7.9 g/cm' for steels), high electrical and thermal conductivities, and a resistanceto corrosion in some common environments, including the ambient atmosphere. Aluminiumand most of its alloys are highly ductile and malleable as observed by the thin foil sheetsmade out of them and being used to cover and roll other materials. Aluminium is non-toxic,non-magnetic and non-sparking. Other important characteristics of aluminium are that it ismachinable, it ca~ be cast by any known method, rolled to any desired thickness and so on.

Aluminium alloys are generally classified according to the principal alloying elementsthat are added to them.

1) Aluminium Copper Alloys:AI - Cu alloys generally contain from 2.5 to 5% copper. These alloys may also contain

small amounts of silicon. iron, magnesium, manganese, chromium and zinc. The most wellknown aluminium copper alloy is the Duralium which contains 4% copper.Name of the alloy - DuraliumComposition - AI + 4% CuMicrostructure - Solid solution a -phase, Intermediate phase - Cu Al2 (fig 6.8)Properties - One of the best non-ferrous alloys for age - hardening, high strength,

corrosion resistant etc.,Applications - rivets in air craft construction, electrical cables, automobile

components etc.,

2) Aluminium - Silicon alloys:The aluminium - silicon series of alloys is most widely used for the production of all

types of castings due to excellent fluidity and casting characteristics of the molten metal.This alloy system forms an eutectic at 11.7% silicon at 577°C (fig 6.9). One of the

most used commercial alloys, LM6, is of approximately eutectic composition.Compostion - upto 12.5% siliconMicrostructure - Solid solution ex - phase + Eutectic (a + B)Properties - Good forgeability, low co-efficient ofthermal expansion, excellent

castability and resistance to corrosion.Applications - Intricate castings, food - handling equipment. marine fittings.

700

600~1.65%

500

400

300

200oAl 100%

Liquid

2 10 16%4 6 8

Silicon, %

12 14

Fig. 6.9 : Portion of At - Si phase diagram

3) Aluminium - Magnesium alloys:Composition - upto 5% magnesiumProperties - good weldability, good corrosion resistance, moderate strength, poor

casting properties.- architectural extrusions, tubings for automotive gas and oil lines,

fittings for chemical and sewage use, aircraft brake shoes etc.,

4) Aluminium - Lithium alloys:Composition - upto 2.5% Lithium, 1% MgProperties - Very low densities (2.5 to 2.6 g / em') excellent fatigue strength,

low - temperature toughness, high specific modulus (elastic modulusI specific gravity), very expensive.air craft and aerospace industries

Applications

Applications

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