Discussion
In age-hardening of an aluminium alloy, the purpose of solution treatment followed by quenching is to
Answer: C
The purpose is to form supersaturated solid solution.
Age hardening (precipitation hardening) has three stages. Solution treatment heats the alloy into the single-phase region so that the alloying element, such as copper in Al-Cu, dissolves completely. Quenching then cools it too fast for the solute to come out, trapping it in a supersaturated solid solution. Ageing, at room or a moderate temperature, finally lets fine coherent precipitates form throughout the grains, and these block dislocations.
Martensite forms in quenched steels, not in aluminium alloys. Growing precipitates is what over-ageing does, and it softens the alloy. Precipitates at grain boundaries are undesirable and are what the quench is meant to prevent.
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