Aluminium Alloys Flashcards
What rank is Aluminium in the most abundant elements in the earths crust?
3rd
What are the three stages of aluminium production?
Bauxite - ore dug out of ground
Aluminium Oxide
Aluminium
What is the Bayer Process?
The refining of Bauxite in to Aluminium Oxide
What is the Hall-Heralt Process?
The refining of Aluminium Oxide into Aluminium
At each stage of aluminium production, roughly what percentage of mass is lost?
50%
Describe the Hall-Heralt Process
- Electrolysis of Alumina in cryolite
- Aluminium taped out of electrolysis tank in molten form
- Aluminium filtered, de-gassed, alloying elements added
- Aluminium is casted via DIRECT CHILL.
What is Direct Chill casting?
DC is a non equilibrum solidification sequence giving rise to a heterogenous material. (Micro segregated gamma phase and a by-product brittle eutectic phase)
Why does DC casted aluminium require homogenisation?
To remove the brittle eutectic phase.
What does microsegregated mean?
The same elements are present but different fractions have different concentrations of alloying elements.
What are the consequences of alloying aluminium?
- Worse corrosion resistance
- Worse deformability
- Worse surface finish
- Worse conductivity
- Worse density (in most cases)
Why do we alloy Aluminium?
For increased strength, UTS!!!!
What strengthening mechanisms can be used on Non Heat Treatable Alloys?
grain refinement
solid solution strengthening
cold working
What strengthening mechanisms can be used on Heat Treatable Alloys?
Homogenisation
Natural Ageing
Artificial Ageing
What are the three main classes of non heat treatable alloys?
1XXX - >99% Al
3XXX - 1% Mn
5XXX - up to 6% Mg
What are the three main classes of heat treatable alloys?
2XXX - Cu and sometimes Mg
6XXX - Mg and Si
7XXX - Zn and Mg
What do the last 2 digits in 1XXX alloys stand for?
the percentage of Al
What is Homogenisation?
Material to heated to single phase (just below the eutectic point) and held there (24 hrs) allowing eutectic phase to dissolve. Then rapidly quenched
What is Natural Ageing?
When a homogenised alloy is left to sit at room temperature. A natural precipicate forms by conventional homogenous nucleation.
What is Artificial Ageing?
When an homogenised alloy is heated to an aging temperature to form a controlled eutectic phase. Control is very important and over aging can result in reduced strength.
What are typical uses for 2XXX alloys?
Airframe and skin structure due to thermal stability and damage tolerance
What are typical uses for 6XXX alloys?
Mostly used in light aircraft for its weldability, machinability and corrosion resistance.
What are typical uses for 7XXX alloys?
Upper wing skin structure. Highest strength alloys on market with good weldability.
