Non-Ferrous Metalsand Their alloys

Aluminium and its alloys

Aluminium

• Large growth in use since 1950 (6 times)• Abundant metal - 8% of earth’s crust• Light weight SG = 2.7 • Moderate to high strength (depending on alloy)• Conductivity high (pure metal & low alloys)

• Corrosion resistant (Al2O3 coating)

• Reflectivity high• Non-magnetic

Extraction• Al2O3 obtained from bauxite by the Bayer process

• Al2O3 reduced electrolytically by the Hall-Heroult process to make aluminium– The large energy requirement for this process is the

major proportion of the cost of aluminium, even with cheap energy sources.

Work Hardening of Aluminium

Fabrication

• Ductile metal easily fabricated by rolling and extrusion– Commercially pure metal can undertake a cold reduction

of 80 - 90% without annealing– Anneal at 350˚C

• Machineability is good, but limited by the tendency to gall

Aluminium alloysDeformable and heat treatable1) Al-Cu-Mg-alloys (duraluminium) 2) Al-Cu-Mg-Si-alloys (forgable) 3) Al-Mg-Si-alloys (corrosion resistance)4) Al-Zn-Mg-Cu-alloys (high strength)5) Al-Cu-Mg-Ni-Fe-alloys (heat resistance)

Rm → 500 N/mm2; Rp0,2 → 390 N/mm2; A → 25%

Deformable and non heat treatable1) Al-Mn-alloys 2) Al-Mg-alloys (magnalium)

Rm → 300 N/mm2; Rp0,2 → 150 N/mm2; A → 25%

Plane bearing alloys (for mono- and bimetallic bearing shells)Al-Sn; Al-Ni; Al-Cu-Sb Typical structure of bearing material

Aluminium alloysCast alloys

1) Al-Si-alloys ↓ Rm (250), A = 1,7 % Pumps and engine bodies, cylinder heads

2) Al-Cu-alloys Rm ↑ than I group

↓ high temp. strength

Cylinder heads, apparatures bodies

3) Al-Si-Cu-alloys Rm ↑ than I group

↓ high temp. strength

→ 350 °C

4) Al-Mg-alloys (magnalium)

Rm, A; good corr. resist.; ↓ castability

→ 100 °C

5) Al- other inclusions high temperature strength

→ 350 °Cparts of aircraft engines

Rm → 340 N/mm2; A → 8% (depending on casting mode)

Aluminium Lithium• 1 to 4% Lithium raises strength, raises elastic modulus by up to

6%, lowers density by up to 4%

• Strengthened by Al3Li, Al2CuMg, AL2CuLi precipitates on aging (depending on composition)– Up to 585 MPa yield typical

• Good weldability as well as high strength• Inferior toughness, ductility & stress corrosion performance• Aerospace applications

Fabrication• Machineability better than steel• Cold and hot workability excellent• Complex extrusion forms common• Joined by fusion and non-fusion welding, brazing, soldering,

adhesive bonding and mechanical methods

Aluminium alloy designations

Deformable alloysSeries 1000 – pure Al

2000 – Al-Cu-alloys (for ex EN-AW-2014)3000 – Al-Mn-alloys4000 – Al-Si-alloys5000 – Al-Mg-alloys6000 – Al-Mg-Si-alloys7000 – Al-Zn-alloys8000 – Al-Fe-alloys

Cast alloysSeries 10000 – pure Al

20000 – Al-Cu-alloys 40000-48000 – Al-Si-alloys (for ex EN-AC-

44000)50000 – Al-Mg-alloys70000 – Al-Zn-alloys

Designation (chemical composition based)• deformable alloys – EN-AW...(EN-AW-AlCu4Mg1)• cast alloys – EN-AC...(EN-AC-AlSi11)

Designation of heat treatment (EN515)• O – annealed (for ex. 01, 02, 03)• H – work hardened (for ex. H1, H2...H9)• W – quenched• T – heat treated (for ex. T1, T2...T10, T31, T3510)

Mainly used: T4 – quenching + natural ageing T6 – quenching + artificial ageing

5000 series alloy applications

• Very popular alloys• Marine, auto and aircraft applications• Pressure vessels, cryogenics• Communication towers• Armour plate

• Some alloys prone to exfoliation or stress corrosion if Al8Mg5 forms in grain boundaries – Avoid high Mg over 65˚C

Alclad

• Many multiphase alloys have inferior corrosion resistance• These alloys are available as Alclad sheet or plate• This material has a thin layer of pure aluminium roll bonded

to one or both surfaces to provide corrosion resistance• Fabrication must be undertaken so as to maintain the

integrity of this coating

Alloy types and properties

• Strain hardened alloys (plus solid solution hardening)• Precipitation (age) hardened alloys• Dispersion strengthened alloys• Yield strength from 28 MPa for 1050-O to 455 MPa for 2024-

T815• Strength increases at low temperature• No ductile-brittle transition

Precipitation (age) hardening

• Solution treatment - α+β alloy is heated into a temperature range to dissolve all B. Quenching retains B in solution (supersaturated)– Soft & ductile condition

• Aging - holding solution treated alloy at a temperature at which fine precipitates of β are formed– Strengthened condition

T (deg C)

Percentage BPure A

Liquid

L +

Composition effects

• Alloys with low levels of B will only display a weak age hardening effect

• Alloys with a high level of b, which cannot be dissolved on solution treatment only display a weak hardening effect

• Alloys with with intermediate levels of B have the highest strengthening effect

• These alloys only display a narrow temperature range for the single phase phase field

• These alloys also have a wide solidification range, are likely to crack during welding, and therefore have low weldability and castability

Heat treatment of Al-alloys

Quenching → water → α-structure Rm, Rp0,2 ↓; A, Z ↑Ageing: Naturally aged (20 °C) → structure + Guinier`-Preston zones

artificially aged Rm, Rp0,2↑, A, Z ↓

low (100...150 °C) high (200...250 °C) (Rp0,2/Rm = 0,6...0,7) (Rp0,2/Rm=0,90...95)

Result – precipitation hardening

Casting processes

• Die casting• Permanent mould casting• Sand mould casting• Plaster casting• Investment casting

– Lost wax• Centrifugal• Continuous casting

Cutting and machining• Plasma cutting - edges require further dressing• Shearing• Sawing

– Extra clearance for chip release• Planing and milling

– Power plane or rotary tungsten burrs• Filing and scraping

Joining• GTAW and GMAW are the most common processes• OFW and MMAW require powerful fluxes• Resistance and pressure processes can be used for many

alloys• Brazing and soldering some application• Adhesives and mechanical fastening widely applicable

• Depends on welding process and alloy composition• Varies from readily weldable to not recommended

• Tenacious oxide film• Prone to contamination

by O2, N2, H2

• High conductivity, low melting temperature

• Slags are tenacious, corrosive

• Welds tend to under match strength

• Solidification cracking, particularly of many heat treatable alloys

Weldability

Fusion WeldingSolid Phase Welding• Cold welding - 75% thickness

reduction at lap joint• Ultrasonic welding - 1.5mm lap

joints• Explosion welding - cladding and

lap joints• Friction welding - Low weldability

alloys and dissimilar combinations,

• Friction-stir welding

Brazing

• Restricted range of alloys– 1000, 3000, 5000 with <2% Mg, 6000

• Al-Si filler materials• Torch, dip, furnace or vacuum processes• Clean parts by etching• Fluxes are fluoride and chloride salts

– Residues MUST be removed• Temperature control is critical

Mechanical properties

• Depend on– Casting process– Composition

• Alloy modification with sodium finer grain– Heat treatment

• Up 435 MPa Yield strength possible• Ductility up to 20%, but mostly <5%

Aluminium Products

• Cast alloys• Wrought products

– Sheet, plate, foil– Rod, bar, wire, tube– Standard and special extruded shapes– Forgings, impacts (combined extrusion and forging)

• Powder metallurgy (dispersion strengthened) products

Structural applications

• Static building structures (AS1664 series)• Scaffolding and ladders• Transportation

– Aerospace, road (trucks, buses, trailers), railway• Machinery and industrial equipment

– Non-sparking tools, roofs to tanks, chemical process vessels, jigs, patterns, instruments

• Consumer durables– Structure of appliances: refrigerators, furniture, cooking

utensils

Thermal and Electrical• Electrical

– Pure Al has 200% of the conductivity of copper weight for weight

– Conductors, heat sinks, capacitors, wave guides, antennas

• Reflectors– Mirrors, search lights, loft insulation

Miscellaneous applications• Packaging

– Drink cans, foil, hermetically sealed packs• Powders and pastes

– Reflective paint, printing inks, pyrotechnics, thermit welding

Limitations

• Temperature range of -240˚C to +200˚C for normal alloys• Up to 350˚C for special alloys• Up to 480˚C for short periods for dispersion strengthened

alloys• Low modulus of elasticity, requires stiffening• Inferior wear, creep, & fatigue properties to steel