High Temperature Creep and Superplasticity in a Mg–Zn–Zr Alloy

Creep and superplasticity were investigated by testing a fine-grained extruded Mg–Zn–Zr magnesium alloy under a wide range of applied stress in the temperature range between 100 and 300 ◦C. Grain boundary sliding became the dominating mechanism at 200 ◦C, leading to a true superplastic behaviour at 300 ◦C, where superplasticity was attained even under relatively high strain rates (5×10−3 s−1). By contrast, for lower temperatures, the straining process was controlled by dislocation climb. A comprehensive model, taking into account the simultaneous operation of the different mechanisms, was developed to describe the strain rate dependence on applied stress.