Microstructure and superplasticity of AZ31 sheet fabricated by differential speed rolling

Abstract

Microstructure evolution and superplasticity in AZ31 alloy by differential speed rolling (DSR) with a highspeed ratio (=3) between the upper and lower rolls was examined. With increase in thickness reduction by DSR at 473 K, degree of grain refinement and microstructure homogeneity increased. The microstructure obtained by a single rolling pass for a 70% reduction in thickness consisted of recrystallized grains with a mean size of similar to 2 mu m, and fraction of HAGBs and average misorientation angle determined by the EBSD analysis were 0.47 and 23.21 degrees, respectively. The DSR AZ31 alloy exhibited enhanced superplasticity as compared with the conventionally processed AZ31. A maximum elongation of 830% was obtained at 2 x 10(-4) s(-1) and 673 K. The strain hardening exponent measured at 2 x 10(-4) s(-1) and 673 K was as high as 0.71, which could be related to accelerated grain growth in the highly refined microstructure during superplastic flow. (C) 2008 Elsevier B.V. All rights reserved.