Evaluating the flow properties of a magnesium ZK60 alloy processed by high-pressure torsion: A comparison of two different miniature testing techniques

A ZK60 magnesium alloy was processed through 5 turns of high-pressure torsion (HPT) at room temperature under an applied pressure of 2.0 GPa to produce a reasonably homogeneous ultrafine microstructure with a grain size of ~ 700 nm. The potential superplastic behavior of this alloy was investigated by measuring the strain rate sensitivity using two different procedures of miniature tensile testing and miniature shear punch testing (SPT). The tensile experiments were conducted at initial strain rates of 3.0 × 10−5 to 1.0 × 10−1 s−1 and the SPT was performed at shear strain rates from 3.3 × 10−3 to 3.3 × 10−1 s−1 at temperatures of 473 and 523 K. It is shown that the strain rate sensitivity index, m, has a maximum value of ~ 0.5 at intermediate strain rates in both tensile testing and SPT and there was a maximum elongation to failure of 940% in the tensile testing. The results demonstrate that tensile testing and SPT are both effective procedures in indicating the potential for achieving superplasticity.