Why is aluminum alloy quenching performed immediately after removal from the heat-treating oven?

• A. To reduce grain size
• B. To prevent intergranular corrosion
• C. To increase ductility
• D. To improve surface finish.

Answer: (B)

Immediately quenching after the heat-treating step is about stopping diffusion and preventing precipitation from forming as the alloy cools. In many aluminum heat-treatable alloys, slower cooling allows precipitates to develop, and those precipitates can form along grain boundaries, creating pathways for intergranular corrosion. By rapidly cooling, you lock the alloy into a supersaturated solid solution and largely suppress grain-boundary precipitation, which reduces the risk of intergranular corrosion later in service. The other effects—grain size changes, surface finish, or merely increasing ductility—aren’t the primary reasons for the quench in this context.