Thermomechanical processing and superplasticity of AZ91 magnesium alloy

The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain size smaller than 10 mum can be obtained by the extrusion processing. Vickers hardness measurements were also carried out to evaluate the effect of these processes on the room temperature mechanical properties. The experimental results of high temperature tensile tests revealed that the stress was inversely proportional to the square of the grain size and that the activation energy for superplastic flow was higher than that for grain boundary diffusion.