Microstructures and microhardness of an aluminum alloy and pure copper after processing by high-pressure torsion

Experiments were conducted on an Al-3 wt.% Mg-0.2 wt.% Sc alloy and pure Cu to evaluate the effect of high-pressure torsion (HPT). The results show that very substantial grain refinement is achieved in both materials with as-strained grain sizes of ∼150 and ∼140 nm, respectively. Microhardness measurements demonstrate increases in the hardness near the edges of the disks by factors of approximately three and two over the solution-treated conditions for these two materials, respectively. It is shown in experiments on the Al-Mg-Sc alloy that no additional hardening is achieved by reversing the direction of the torsional straining during the HPT processing. In addition, experiments on pure Cu confirm that the high values of hardness are not retained when samples are subjected to short-term anneals for 15 s or 3 min at a temperature of 473 K.