Microstructure and Superplastic Properties at Room Temperature in Zn-22Al Alloy after Equal-Channel-Angular Extrusion

Recently, it has been reported that high strain rate and/or low temperature superplasticity requires a very fine grain size, typically below 1 *mm. In order to obtain ultrafine-grained and suitably homogeneous microstructures, in the present work, Equal-channel-angular extrusion (ECAE) has been conducted on Zn-22Al alloy under three conditions. Route 1 is extrusion at room temperature during spinodal decomposition, Route 2 is extrusion at room temperature after spinodal decomposition and Route 3 is extrusion at 373K after spinodal decomposition. Microstructure observations showed that ECAE samples pressed under each condition had an equiaxed grain size about 0.35 *mm, 0.3 *mm, 0.6 *mm, respectively. As for the results of tensile testing at room temperature, the sample pressed at room temperature during spinodal decomposition exhibited the strain rate sensitivity exponent of 0.25#~0.3 and a high elongation over 200% below an initial strain rate of 10-2 s-1. Therefore, it is considered that deformation behavior like superplasticity may be attained. Conclusively, the deformation properties at room temperature in the present study were compared with the previous results.