Enhancement of superplasticity in a fine-grained Mg-3Gd-1Zn alloy processed by equal-channel angular pressing

Superplastic behavior of an Mg-3Gd-1Zn (GZ31) alloy, processed by extrusion at 653 K followed by equal-channel angular pressing (ECAP) at 553 K, was investigated by shear punch testing (SPT). A fine grained microstructure with a grain size of 1.7 μm and large fraction of high-angle grain boundaries was achieved after processing by ECAP. Shear punch tests were conducted at temperatures in the range of 573-773 K and shear strain rates in the range of 0.003-0.130 s−1. While the strain rate sensitivity (SRS) index of the as extruded condition was less than 0.22, a high SRS index of 0.51 at 673 K was achieved after ECAP. The SRS index of 0.51 and the activation energy of 73 kJ mol−1 imply that the responsible mechanism for superplasticity after ECAP is grain boundary sliding (GBS) accommodated by grain boundary diffusion.