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Abstract
Constant strain rate tensile tests have been conductedfor fine grained Mg-Al-Zn (AZ91) and Mg-Zn-Zr (ZK60 and ZK61) alloys processed by powder metallurgy (PM) and ingot metallurgy (IM) routes. The experimental results revealed that the strain rate was inversely proportional to the cube of the grain size and that the activation energy for superplastic flow was higher than that for grain boundary diffusion. The PM Mg alloys showed superplastic behaviour at higher strain rates than the IM Mg alloys. This is because of smaller grain sizes of the PM Mg alloys. The origin of the high strain rate superplasticity for the PM Mg alloys is unlikely to be associated with the presence of a liquid phase.