Chapter Two

Aluminum Extrusion Alloys

• Recyclable and Nontoxic• Lightweight• Strong• High Strength to Weight Ratio• Resilient• Corrosion-Resistant• Thermally Conductive• Reflective• Electrically Conductive• Nonmagnetic Noncombustible and Non-sparking• Cryogenically Strong

• Attractive• Wide Range of Finishes• Virtually Seamless• Complex Integral Shapes• Fastening and Assembly• Joinable• Fabrication• Tolerancing• Cost-Effective• Short Lead Times

Aluminum’s Material Advantages:

Aluminum Extrusion’s Process Advantages:

Advantages of Aluminum Extrusions

Temperature Classification of Extruded Metals

Aluminum Alloys

• Heat treatable and non heat treatable– 2xxx, 6xxx, 7xxx (HT)– 1xxx, 3xxx, 5xxx (NHT)

• Mechanical performance – Product properties (Strength, ductility)– Workability (during forming)

• Corrosion characteristics - composition• Processing aspects• Cost • Applications

6xxx Alloys Profiles

Aluminum Alloys

Designation Principal Alloying Element Typical Alloy Characteristics1xxx Minimum 99% aluminum High corrosion resistance

Excellent finishabilityEasily joined by all methodsLow strengthPoor machinabilityExcellent workabilityHigh electrical and thermalconductivity

2xxx Copper High strengthRelatively low corrosion resistanceExcellent machinabilityHeat treatable

3xxx Manganese Low to medium strengthGood corrosion resistancePoor machinabilityGood workability

4xxx Silicon Not available as extruded products5xxx Magnesium Low to moderate strength

Excellent marine corrosionresistanceVery good weldablity

6xxx Magnesium & Silicon Most popular extrusion alloy classGood extrudabiltyGood strengthGood corrosion resistanceGood machinabilityGood weldabilityGood formabilityHeath treatable

7xxx Zinc Ver high strengthGood machinabilityHeat treatable

8xxx Other ----------------------

Common Tempers

• O Fully annealed• H112 Strain-hardened; used for non-heat-treatable

alloys• T1 Cooled from elevated temperature and

naturally aged • T4 Solution heat-treated and naturally aged• T5 Cooled from elevated temperature and

artificially aged• T6 Solution heat-treated and artificially aged

Aluminum Extrusion Process

• Billet casting • Homogenization• Extrusion process• Cooling/quenching• Straightening

– ~1/2 % (plastic “permanent”deformation)– 1- 3% (“elimination” of residual stresses)

• Precipitation treatment (age hardening)• Finishing operations:

– Machining, Anodizing, Painting, Joining

Temperatures

Aluminum Extrusion Parameters

Press Force 10-100 MN …….tonContainer Diameter 100 - 650 mm ……inchesFlow Stress 300-1500 N/mm2 ……ksiBillet Length 300-1500 mm ……inchesBillet Temp. 450-550 oC ……FExit Speed- High Extrudability 25-100 m/min …….ft./min- Low Extrudability 0.5-10 m/min …….ft./minExtrusion Ratio, R 20:1 to 100:1

Chemical Composition vs. Performance – T6 Conditions

Phase Diagram

Al -Mg2Si

Extrusion Sequence

Press Quenching

Physical Simulation of Extrusion of 6xxx AA

OBJECTIVES• To predict the physical response of an

aluminum alloy to specific processing conditions (temperature, strain, strain rate).

• Thermal cycle simulation– homogenization through ageing

• Compression testing– deformation modeling

Extrusion Thermal Cycle

O. Reiso, Dr. Tech. Thesis, Trondheim, Norway, 1992.

ProcedureThermal Simulation

Extrusion (Exit Temperature)

Preheat

High

Low

Low High

Low Preheat Low Extrusion

Low Preheat High Extrusion

High Preheat High Extrusion

High Preheat Low Extrusion

(Gas or Induction)

Gleeble Setup

Jaws

Sample

Quench Spray Head

Homogenized Microstructure

6063 AA

SEM Image AlFeSi

Low Preheat (7900F) - Low Extrusion (9250F)

6063 AA

Keller’s etch

60 m

Mg2Si

AlFeSi

High Preheat (8600F) -High Extrusion (10400F)

6063 AA

Keller’s etch

26 m

AlFeSi

Low Preheat (7900F) - Low Extrusion (9250F) + T6 aged

6063 AA

SEM Image Mg2Si

3 m

High Preheat (8600F) - High Extrusion (10400F) + T6 age

6063 AA

Keller’s etch

26 m

1xxx Series (NHT)

• Super purity (SP) aluminum (99.99%)• Commercial purity (CP) aluminum (99%)• Low mechanical properties

– Annealed SP - YS: 7-11 MPa• Decorative finish (architecture)• Chemical process equipment• Electrical conductors

3xxx Series (NHT)

• Al-Mn– Mn up to 1.25% (solubility @ 1.82%)– To avoid formation of Al6Mn - low ductility

• Al-Mn-Mg (3105; Al-0.55Mn-0.5Mg)• Combination of properties

– Moderate strength– High ductility– Very good corrosion resistance

5xxx Series (NHT)

• Al-Mg alloys• Medium strength alloys • Good corrosion resistance • Excellent resistance to marine environment• Good extrudability• UTS from 125 MPa (5005; Al-0.8Mg) to

310 MPa for 5456 in annealed conditions

2xxx Series (Al-Cu) (HT)

• High mechanical properties– Enhanced age hardening by strain hardening– T8 temper can be up to 35% stronger than T6

• Good welding performance • Complex physical metallurgy

2xxx Series (Al-Cu-Mg) (HT)

• Duraluminum discovered in Berlin in 1906 by Alfred Wilm (Al-3.5Cu-0.5-0.5Mg-0.5Mg)

• Used for Zeppelin airships• Alloy 2017 is a modified version of

duraluminum• Lower fracture toughness than 7xxx alloys

7xxx Series (HT) (Al-Zn-Mg-Cu)

• The strongest alloys in the Al family• Cu added to improve resistance to stress

corrosion cracking• Significantly lower extrudability• Aerospace application

8xxx Series

• Other alloys• 8001 (Al-1.1Ni-0.6Fe) with excellent

corrosion resistance• 8011 (Al-0.75Fe-0.7Si) bottle caps because

of very good ductility• Amorphous aluminum alloys belong to this

group as well

Homogenization

• Uniform chemistry (no chemical segregation)

• Uniform microstructure– dendrites– grain size– alloying elements

• Elimination of casting defects

• Form at the interdendritic regions upon casting• Almost a continuous network

-Al9Fe2Si2

AlFeSi Intermetallics

• Form from pre-existing - during homogenization• “necklace structure”

-Al8Fe2Si

25 um

6063 Homogenization

• Examine 3D AlFeSi particle morphology as function of heat treatment time– Size, Shape, Interconnectivity

Unhomog.

-AlFeSiHomog.

-AlFeSi

Morphological Evolution

Case Study - Homogenization

•2D and 3D Microstructure Characterization Tools–Light Optical Microscopy (2D)–Scanning Electron Microscopy (2D)

•EBSD (2D) and FIB (3D)–Transmission Electron Microscopy

FIB Milling

2D and 3D Projections

3 D Morphology

•Import each 2D section into Matlab•Input distance between each “slice”•Plot using MathCad