LXXXIII. Quench hardening in aluminium single crystals

Summary A large increase in the critical shear stress of high-purity aluminium single crystals can be achieved by water quenching, instead of furnace cooling, after annealing at a high temperature. This quench-hardening effect is insensitive to purity and is present in crystals of zone-refined aluminium. It increases rapidly with increase in the quenching temperature. The fully hardened state is reached, not instantly upon quenching, but only after ageing at room temperature. Various observations suggest that while quenching strains may be partly responsible for the hardening they cannot account for the whole effect, and that quenched-in vacancies also make an important contribution.