Grain refinement and superplastic flow in an aluminum alloy processed by high-pressure torsion

An aluminium-2024 alloy was prepared in the annealed and the solution treated conditions. Specimens in both conditions were processed by high-pressure torsion (HPT) at temperatures of either 293 or 673 K giving grain sizes for both conditions of ∼0.15 and ∼0.30 μm for these two processing temperatures, respectively. Tensile testing was conducted at 673 K and superplastic elongations were achieved in both the annealed and the solution treated samples, with a maximum elongation of 570% for an annealed specimen processed by HPT at 293 K. To check on the significance of microstructural inhomogeneities across the HPT disks, samples were machined either from the center of the disks or from an off-center position. The experimental results show that higher elongations are achieved at the off-center position. The similarity between the annealed and the solution treated conditions after HPT is attributed to a dissolution of precipitates during HPT processing.