Abstract:The superplasticity of coarsed grain AZ31 magnesium alloy was investigated in the temperature range of 623−723 K at strain rates from 10⁻³ to 10⁻¹ s⁻¹. It is found that with increasing strain rates, the elongation increases firstly, and then reaches the maximum value of 278% nearly at the strain rate of 5×10⁻² s⁻¹. The best superplastic conditions are at 723 K and at the strain rate of 5×10⁻² s⁻¹. During superplastic deformation, it is found that the mean grain size decreases from original 30 μm to 18 μm, indicating grain refinement is the dominant process at the initial stage of the superplastic deformation, meanwhile the grains become more homogenous and most of the grains are still equiaxed. However, the size and distribution of deformation cavity vary with deformation conditions at the last stage of deformation. At best superplastic condition, the cavity exhibits homogenous and ball-like. It is indicated that the dominant superplastic deformation mechanism at high strain rate is both grain refinement and grain boundary sliding.

Key words: AZ31 magnesium alloy; high strain rate superplasticity; cavity