Light Metals, Non Ferrous alloys (Aluminium)

Advantages of Al for plastic deformation and forming

FCC crystal structure

Good formability

Low hot-strength

Mill products

1. Flat rolled products

2. Rod bar wires

3. Tubular products

4. Extruded shapes

Two classes of Al wrought products

1. Mill products

2. Forging

Flat rolled products divisions

Foil

Sheet

Plate

Foil thickness

Less than 0.2mm

Sheet thickness

0.2-6mm

Plate thickness

Over 6mm

Flat product production

Ingot casting and Hot and Cold rolling

Strip casting and finish rolling

Ingot casting and hot and cold rolling

1. ingot casting and homogenization

2. hot rolling

3. cold rolling

Strip casting and finish rolling

Dont solidify metal completely

Solidifies when it is plastically deforming at the same time

Only for certain Al alloys

International Allot Designation System (IADS)

PUT IN TABLE

Designation system for aluminum alloys

Can you age harden pure Al?

No → no secondary phases

Only certain Al alloys are age hardenable

Non heat treatable Al alloys (Strain hardened)

• Al

• Al-Mn

• AL-Mg-Mn

Al-Mg (5000 series)

• Work hardening

• High corrosion resistance

• Reduces ductility

• Weldable

• Work hardened Al-Mg have 4 times higher yield strength than pure Al

• Work hardening rate is not the same for every alloy.

Heat treatable Al alloys

• AL-Mg-Si (6xxx)

• Al-Cu-Mg (2xxx)

• Al-Zn-Cu (7xxx)

Al-Cu-Mg (2000 series)

• If cold worked some of the 2000 series alloys respond better to ageing.

• High strength good ductility.

• Often stored in a fridge to slow down age hardening to keep the metal in a workable condition.

Aluminium wrought alloys

Aluminum casting alloys are specific types of aluminum alloys that are designed to be used in the casting process.

Molten aluminum is poured into a mold to form a desired shape.

Ability to be melted and cast into complex geometries while maintaining desirable mechanical and physical properties.

Maintains strength, ductility, corrosion resistance, and heat tolerance.

Can aluminium alloys be cast by any of the casting processes?

Yes

Casting affects properties mainly porosity through solidification rate → which determines grain size. (dendrite arm spacing.

Most important casting processes for Al

Sand

Permanent mold

Die casting

Sand casting

Disposable sand mold, slow cooling rate

Permanent mold

Metallic permanent mold, gravity cast or low pressure assisted, medium cooling rate

Die casting

Metallic permanent mold, high pressure injection, very high cooling rate.

Aluminium

• FCC crystal structure

• MP → 600 degrees celcius

• Maleable → 12 slip systems

• Low yield strength → 7-17MPa

• Strain hardenable

• G → 70Gpa

• Excellent corrosion resistance

• high electrical and thermal conductivity

Most effective strengthening mechanism for Al?

Age hardening

Two types of Aluminium alloys

Wrought alloys

Casting alloys

Advantages of Al for casting

• Low melting temps

• Relatively goof fluidity

• Excellent melt-oxidation resistance

• Negligible solubility for all gases bar hydrogen

• Relatively good surface finish

Disadvantages of Al for casting

• Shrinkage

• Hydrogen porosity

• Hot-tearing / hot-cracking

• Reactivity with steel tools

Shrinkage in Al

1. Volumetric shrinkage: (3.5-8%) occurs during solidification due to density difference between liquid Al and solid Al

2. Linear shrinkage: (~1.3%) occurs during cooling from solidus to RT

Hydrogen porosity in Al

• Effects impact and ductility

• Due to the difference in liquid and solid solubility of H in Al.

• H2 precipitates out and produces rounded gas holes with smooth internal surfaces.

• can be reduced by argon degassing

Hot-tearing or hot-casting (Disadvantage of Al for casting)

Macroscopic tears or cracks in the casting

• Occur due to thermal and mech stresses during solidification

• Die design and hot-strength of the alloy are important

What elements may casting alloys contain?

Si, Mg, Cu, Zn, Fe, Li, Mn, Ni, Sn, Ti

Why is Silicon important for casting alloy systems?

• Increases fluidity

• Reduces Coefficient of thermal expansion.

• Good weldability

• Good corrosion resistance

Aluminium 3xx series

Aluminium-Silicon with magnesium and/or copper (Most important alloys)

Most important alloy system

Al-Si

Al-Si hypoeutectic

A356

• Main alloy used in automotive applications.

• Contains some Mg

• Si particles (phase) are pointed and coarse.

• Adding sodium or strontium can can modify Si shape from coarse to fine → Increasing strength and ductility.

Al-Si Hypereutectic alloys

• Excellent wear resistance

• Contains some Cu

• Phosphorus modifies silicon shape to spherical precipitates → inscreasing ductility.

F (Temper designation for aluminium casting alloys)

As-cast condition.

T1 (Temper designation for aluminium casting alloys)

Quenched from casting temperature and naturally aged at room temperature.

T4 (Temper designation for aluminium casting alloys)

Solution heat treated

Quenched

And naturally aged at room temperature.

T5 (Temper designation for aluminium casting alloys)

Quenched from casting temperature

Artificially aged.

T6 (Temper designation for aluminium casting alloys)

Solution heat treated

Quenched

Artificially aged

T7 (Temper designation for aluminium casting alloys)

Solution heat treated

Quenched

Artificially overaged (stabilized)

Aluminium 8xxx series

Aluminium-Lithium Alloys

Properties of lithium in al alloys

• Light

• Reactive with moisture

Problems with Al-Li

• Low thermal stability

• High anisotropy (directionally dependant ) of properties.

• Susceptible to local deformation

• Scattered values of fracture toughness

With increasing lithium → Density decreases and youngs modulus increases