Cavity growth rate in superplastic 5083 Al and AZ31 Mg alloys

The plasticity-controlled growth rate of cavities during superplastic deformation was statistically investigated for 5083 Al alloy and AZ31 Mg alloy. When the cavity growth rate was evaluated on the basis of macroscopic strain calculated using the displacement of the specimen, the growth rate for the Al alloy was larger than that for the Mg alloy. However, the growth rate of the Al alloy was in agreement with that of the Mg alloy when the cavity growth rate was evaluated on the basis of the microscopic strain due to grain boundary sliding. The results obtained lead to two conclusions: (i) them rate of cavity growth is not affected by the kind of materials, that is, the nature of the grain boundary, and (ii) the microscopic strain due to grain boundary sliding should be used to evaluate exactly the rate of cavity growth for superplastic deformation.