Developing superplasticity in a magnesium AZ31 alloy by ECAP

The processing of a magnesium AZ31 alloy by equal-channel angular pressing refines the grain size to *2.2 lm, but annealing for 30 min at 673 K coarsens the grains to *6.0 lm. Despite this microstructural instability, the alloy is superplastic when pulled in tension at temperatures in the range of 623–723 K with elongations up to [1000% at strain rates at and below 10-4 s-1. Experiments within the superplastic regime show the strain rate sensitivity is *0.5 and the activation energy is close to the value for grain boundary diffusion. It is demonstrated by calculation that the experimental results are in good agreement with a model for superplasticity based on grain boundary sliding.