Uses of aluminium
2 marks · NormalState why pure aluminium is rarely used for making structures. Briefly explain how adding other elements strengthens aluminium alloys.
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Pure aluminium is rarely used because it is not very strong. Adding other elements of different atom sizes disrupts the regular lattice and makes it harder for the layers to slide past each other, thus strengthening the alloy.
Also accept: Pure aluminium is soft/not strong; alloys are stronger because the different sized atoms in the alloy stop layers sliding easily
Common mistakes: Saying pure aluminium is too expensive; Alloying always makes metals weaker
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Marking points
B1 · 1 mark · States that pure aluminium is not strong/rarely used for structures because it is weak.
B2 · 1 mark · Explains that alloying adds different sized atoms that break up the lattice, making it harder for layers to slide.
Worked solution
Pure aluminium is rarely used because it is not strong enough for most structural purposes.
When other elements are added to make an alloy, the different sized atoms disrupt the regular lattice structure. This makes it harder for the layers to slide over each other, so the alloy is stronger.