Clarification of Strain-Rate-Dependent High Temperature Deformation Mechanism in Superplastic Zn-22Al Alloy Foams

Closed-cell Zn-22Al superplastic alloy foams were manufactured through the melt foaming process. The Zn-22Al foams were produced with varying porosity of 51-82%. The cell wall consisted of fine equiaxial crystal grains after solution treatment. The compressive properties of the Zn-22Al foams were investigated at 523 and 298 K. The Zn-22Al foams have strain rate sensitivity exponent of 0.55 in Region II. This is because of the superplastic deformation induced by the fine microstructure of the cell wall. High temperature deformation mechanism can be explained using the new parameter of local strain rate. We developed new constitutive equation of metal foam including relative density, local strain rate and strain rate sensitivity exponent.