1. Noteworthy advantages of using aluminum alloys
Light weight
Good machinability
Good formability
High electrical / thermal conductivity
High corrosion resistance

2. Important alloying elements in aluminum alloy systems
•Copper (2xxx)
Manganese (3xxx)
Silicon (4xxx)
Magnesium (5xxx)
Zinc (7xxx)
• Cr, Ti and Zr are used in some alloys for grain refinement

3. Wrought alluminum alloys
There exists an internationally
agreed classification system for wrought alloys.
Classification for wrought aluminium alloys.
8XXX Miscellaneous alloys, e.g. aluminium-lithium alloys
7XXX Al - Zn - Mg alloys
6XXX Al - Mg - Si alloys
5XXX Al - Mg alloys
4XXX Al - Si alloys
3XXX Al - Mn alloys
2XXX Al - Cu alloys
1XXX Al of 99% minimum purity
Each alloy is described by a four digit number

4. Designations of wrought aluminum alloys
Non-heat-treatable alloys
1xxx series (super purity & commercial purity aluminum)
3xxx series (Al-Mn & Al-Mn-Mg alloys)
5xxx series (Al-Mg alloys)
8xxx series (Miscellaneous alloys)
Heat-treatable alloys
2xxx series (Al-Cu & Al-Cu-Mg alloys)
6xxx series (Al-Mg-Si alloys)
7xxx series (Al-Zn-Mg and Al-Zn-Mg-Cu alloys)
Designation of each alloy includes a further
letter and number indicating the temper, or condition of the alloy.

5. Denoting the thermal/mechanical treatment of wrought alloys
O: annealed
H: work hardened
H12: quarter hard; H14: half hard: H18: full hard
T1: naturally aged after hot working
T4: solution treated, quenched and naturally aged
T6: solution treated, quenched and artificially aged
T8: same as T6, except cold worked before aging

9. Principle of age-hardening
Age hardening requires a decrease in solid solubility of the alloying elements with decreasing temperature.

10. The Al-Zn phase diagram shows the rapid decrease of the solubility of zinc in aluminum with decreasing temperature.

11. 5.65 wt% solubility of Cu in Al at 548C
The solubility drops down to 0.02 wt% at room temperature
Precipitation hardening is thus possible.
Al-Cu phase diagram (Al-rich side)

12. Heat treatment usually involves the three following stages:
1. Solution treatment at a relatively high temperature to dissolve the alloying elements.
2. Rapid cooling or quenching usually to room temperature to obtain supersaturated solid solution (SSSS) of these elements in aluminum.
3. Controlled decomposition of the SSSS to form a finely dispersed precipitates, normally accompanied with ageing at appropriate temperature(s).

13. Heat treatment for precipitation hardening
• Solution heat treatment: at T0, all the solute atoms A are dissolved to form a single-phase (α) solution.
• Rapid cooling across the solvus line to exceed the solubility limit. This leads to a metastable supersaturated solid solution at T1. Equilibrium structure is α+β, but
limited diffusion does not allow β to form.
• Precipitation heat treatment: the supersaturated solution is heated to T2 where diffusion is appreciable – finely dispersed particles rich in element B start forming : aging.

14. Precipitation hardening in Al-Cu System

15. Heat treatment for precipitation hardening
Discs of Cu atoms 1 or 2
monolayers thick

20. Surface treatments
Many coatings are commercially used – organic coatings, chemical conversion coatings and platings
Most important are anodizing and hard coating – coating is aluminum oxide, electrochemically induced. The coating provides a good corrosion barrier and wear resistance.s

21. Corrosion
Aluminum is susceptible to pitting and accelerated corrosion seawater and halide environments. These environments should be avoided.
Pure aluminum has better corrosion resistance than any of the aluminum alloys. This is because alloy micro-constituents impair the protective oxide film.
To improve the corrosion resistance, Al-Cu and Al-Zn-Mg alloys are sandwiched between two pure aluminum sheets and rolled to produce the composite Alclad.

22. Designations of cast aluminum alloys
Alloy designation
Major alloying elements
1xx.x
99.5 min. aluminum
2xx.x
Copper
3xx.x
Silicon + copper or magnesium
4xx.x
Silicon
5xx.x
Magnesium
6xx.x
Unused series
7xx.x
Zinc
8xx.x
Tin
9xx.x
Other element
Last digit after decimal point indicates the product form (0: casting, 1: ingot)

23. Casting techniques The most common aluminium casting techniques are;
1) Sand casting
2) Die casting - gravity casting
- high pressure die casting
- low pressure die casting
- vacuum die casting
- squeeze casting
Selection of casting process depends upon alloy composition which is related to controlled characteristics such as solidification range,fluidity, susceptibility to hot-cracking.
Castability 3xx.x > 4xx.x > 5xx.x > 2xx.x > 7xx.x
Si,Cu,Mg Si Mg Cu Zn

24. Modification of microstructure
Apart from fast cooling to refine the microstructure, modification can be carried out by adding certain alkali fluorides to the melt prior to pouring.
Additions of Sr or Na change eutectic microstructure from needle-like or lamellar
to fibrous.
A concentration of 0.02% Sr is enough to cause 100% modification to fibrous structure.

25. Eutectic silicon crystals with acicular morphology in an unmodified sample of alloy A365. Etchant: Keller's reagent
Eutectic silicon crystals with fibrous morphology in a modified sample of alloy A365. Etchant:Keller's reagent

26. Why add modifiers Controlling silicon morphology
Improving mechanical properties
Improving machinability
Reducing hot tearing
Reducing heat treatment times
Controlling porosity distribution
Improving die filling
Suppressing primary silicon formation
Reducing die sticking

27. Cast aluminium alloys are widely used
for transport applications, e.g., Cast engine block