Aluminium and its alloys Flashcards
aluminium is extracted from
bauxite ore
method of decomposing aluminium oxide
electrolysis
Properties of aluminium
excellent resistance to corrosion high thermal & electrical conductivity high malleability (compressible) non-magnetic soft and ductile
methods to improve aluminium low strength
cold working
alloying
alloying followed by heat treatment
Uses of aluminium
frying pans, kettles
drink cans, food packaging foils
telescopes
how can wrought materials be shaped
forging
rolling
properties of wrought materials
ductile and malleable
how can cast materials be shaped
sand casting
pressure die-casting
properties of cast materials
good fluidity
low shrinkage
short freezing range
aluminium alloy number system and meaning of each digit
first digit: major alloying element
last 2 digits: identify the aluminium alloy or aluminium purity
effects of cold working on wrought alloys (not heat treatable)
the higher the cold working %, the higher the strength, but lower ductility
Elements added to aluminium alloys
copper, magnesium, silicon
Duralumin applications
aircraft bodywork
How does copper affect aluminium alloy properties and how to prevent it
copper reduces corrosion resistance
improve corrosion resistance by cladding a thin layer of high purity Al (Alclad)
Solution treatment temperature for aluminium alloys to reach pure alpha-Al
550 degree C
Steps for heat treating of aluminium alloys for 4% copper
1) Coarse precipitates in alpha-Al heated slowly to 550 degree C
2) Quenched in water or oil to form supersaturated solid solution that is ductile
3) Precipitation hardening at 165 degree C for 10 hours (artificial ageing) to obtain extremely fine precipitates in alpha-Al
best time to work on aluminium alloys
after solution treatment but before precipitation hardening
