Properties of a ZK60 magnesium alloy processed by high-pressure torsion

An extruded ZK60 magnesium alloy with an initial grain size of ∼9.4 μm was processed by high pressure torsion (HPT) for up to 5 revolutions and microstructural observations were carried out using optical and scanning electron microscopy. Measurements of the Vickers microhardness over the disk surfaces revealed lower values in the central areas of the disks after low numbers of HPT turns but with a reasonable level of homogeneity across the disks after processing by HPT through 5 turns at 2.0 GPa. The average grain size after 5 revolutions was ∼1.0 μm. Samples were processed by HPT through 5 turns and then tested in tension at a temperature of 473 K. The results show the occurrence of superplastic behavior with a maximum elongation to failure of about 535% when testing with an initial strain rate of 1.0 × 10−4 s−1. These results are consistent with earlier data obtained on the ZK60 alloy after processing by equal-channel angular pressing (ECAP) but the elongations to failure are lower because of using miniature tensile specimens cut from the HPT disks.