Ultrafine-grained Mg–9Li–1Zn alloy sheets exhibiting low temperature superplasticity

The microstructure and mechanical properties of the ultrafine grained Mg–9Li–1Zn (LZ91) alloy sheets prepared through HRDSR (high-speed-ratio differential speed rolling) process were examined. During HRDSR for a thickness reduction of 65% by a single pass at 398 K, the microstructure was significantly refined to grains with submicron size and the refined microstructure was homogeneous along thickness direction of a sheet. The HRDSRed alloy exhibited enhanced strength and ductility at room temperature, and excellent low temperature superplasticity in the temperature range 423–523 K (0.49–0.6 Tm). The superplastic elongations were comparable with those obtained by other severe-plastic-deformation techniques or even better. The superplastic deformation mechanism of the ultrafine grained LZ91 alloy in the temperature range between 423 and 523 K was found to be grain-boundary-diffusion controlled grain boundary sliding.