The evolution of homogeneity in an aluminum alloy processed using high-pressure torsion

Disks of a commercial Al-6061 alloy were processed by high-pressure torsion (HPT) through one and five turns at room temperature using two different applied pressures. The values of the Vickers microhardness were recorded along diameters in each disk and following a regular rectilinear grid pattern. The results show the hardness increases in the first turn of HPT but the microhardness distribution is then inhomogeneous with lower hardness values recorded in the central regions of the disks. The size of this inhomogeneous central region decreases with increasing numbers of turns and/or increasing pressure. The results contrast with earlier data for high-purity Al where higher hardness values were recorded in the central regions. The results are interpreted in terms of the high stacking fault energy in pure Al and the consequent rapid rate of dynamic recovery.