Hot deformation behavior, processing map, microstructure evolution and dynamic recrystallization mechanism of Mg-5Al-0.6Sc alloy

Abstract

In this study, the hot compression test of as-cast Mg-5Al-0.6Sc alloy was performed on Gleeble-3500 simulator, and the effect of deformation temperature (T: 250–400 °C) and strain rate (ε̇: 0.001 –1 s−1) on hot deformation mechanism of the alloy were systematically investigated. The thermal deformation behavior, microstructure evolution, texture and dynamic recrystallization (DRX) mechanism of the alloy were analyzed in detail by combining the constitutive equation, processing map and electron backscatter diffraction (EBSD) technology. The results demonstrated that the flow stress decreased with the increase of T and decrease of ε̇. The established constitutive equation could accurately predict the hot deformation behavior of the alloy, and the calculated average activation energy (Q) is 144.58 kJ/mol. Based on processing map, the optimal processing area is within 300–350 °C, 0.001 s − 1 and 350–400 °C, 0.001 s−1 - 0.01 s−1. The microstructure at 350 °C and 0.001 s−1 is more uniform and exhibits low residual stress level. The increase of T and decrease of ε̇ are both conducive to the occurrence of DRX. DRX mechanism includes discontinuous DRX (DDRX), continuous DRX (CDRX), deformation twin induced DDRX and CDRX. In addition, both DRXed grains and unDRXed grains showed typical<0001>// CD texture. Combined with the in-grain misorientation axis (IGMA) analysis, when T is 250 °C and 300 °C, the deformation is dominated by basal<a>dislocations and prismatic<a>dislocations, and the proportion of twinning and DRX is extremely low. When T is 350 °C and 400 °C, the pyramidal Ⅱ<c+a>dislocations is activated greatly, and the DRX fraction increases significantly, which become the predominant deformation mechanism.