Thermal compression, processing maps and microstructural evolution of as-cast Mg-Gd-Y-Zn-Zr alloy with long period stacking ordered phase

Abstract

Thermal deformation of Mg-7.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) as-cast alloy containing LPSO phase was been studied in a temperature range from 623 K to 723 K and a strain rate range from 0.001 to 1 s−1. The microstructural evolution at the various strain rates was also analyzed. The results show that the flow stress decreases significantly with the increase of the deformation temperature. But the peak flow stresses of the alloy increase significantly at high deformation temperature, due to existing both the plentiful lamellar LPSO phase and the fine dynamic DRXed grains. Under the high strain rate conditions, the LPSO phase distorted and formed kink bands. The deformational activation energy (Q) of the alloy is about 234.6 kJ·mol−1. This high Q value mainly owe to profuse lamellar LPSO phase hindering the movement of atoms. With the observation of established processing map of the alloy, some good thermal workabilities are observed in following zones: 723 K, 0.001 < ε < 1 s−1; and the zone with middle temperature and moderate strain rate condition, 673 K, 0.01 < ε < 0.1 s−1. The thermal deformation instability zones are mainly located in the region with high strain rate and lower temperature.