The development of hardness homogeneity in pure aluminum and aluminum alloy disks processed by high-pressure torsion

Processing by high-pressure torsion was conducted on four different materials: high-purity (99.99%) aluminum, commercial purity (99.5%) aluminum, an Al-1% Mg solid solution alloy and a commercial aluminum Al-6061 alloy. Disks of each material were processed through 1/4, 1 and 5 turns and detailed microhardness measurements were recorded to permit the construction of color-coded hardness maps and three-dimensional representations of the hardness distributions. There are significant differences between these four materials. Whereas the hardness is initially high in the centers of the HPT disks of high-purity aluminum, the hardness is initially low in the centers of the disks for the other three materials. The hardness achieves saturation values after 5 turns in high-purity Al and the commercial purity Al but more torsional strain is required to achieve homogeneity in the other two alloys. There is evidence that it is difficult to achieve a well-defined saturation hardness in the Al-6061 alloy.