Microstructural evolution of friction stir processed cast Mg-5.9 mass%Y-2.6 mass%Zn alloy in high temperature deformation

Abstract

Cast Mg-Y2-Zn1 alloy was friction stir (FS) processed to obtain fine grain structure. Then the elevated temperature tensile tests were carried out to investigate the deformation behavior of the FS processed alloy. The starting structure for FS processing was coarse dendritic microstructure (secondary dendrite arm spacing ca. 75 μm) with a plate-like second phase, which developed from inter-dendritic eutectic pockets after homogenization heat treatment. The α-Mg matrix and second phases were broken mechanically and distributed homogeneously by FS processing. The refined grain size at the fully stirred zone had the average size of ca. 2.0 μm. Different deformation behavior occurred as a result of varying microstructural evolution according to temperatures (623 K and 723 K). © 2007 The Japan Institute of Metals.