Investigation on the microstructure, texture and mechanical properties of Mg-Gd-Y(-Zn)-Zr alloys under indirect extrusion

Abstract

This work mainly studies the microstructure, texture and mechanical properties of Mg-8.5Gd-2.5Y-0.3Zr (wt%) (0Zn) and Mg-8.5Gd-2.5Y-0.5Zn-0.3Zr (wt%) (0.5Zn) alloys under indirect extrusion at different temperatures. Dynamic recrystallization in the two alloys occurs via discontinuous dynamic recrystallization (DDRX) as well as continuous dynamic recrystallization (CDRX) mechanisms under extrusion at both 450 °C and 500 °C. Dynamic precipitation of β-Mg5RE phases takes place along with the DRX process in both alloys when extruded at 450 °C, while it is absent at 500 °C. The addition of 0.5 wt% Zn promotes the dynamic precipitation, leading to a well distribution of β phases in all the DRXed regions of 0.5Zn alloy, compared to a local distribution only in partial DRXed regions of 0Zn alloy. The well distributed β phases and the existence of γ’ phase caused by adding trace Zn result in finer DRXed grains and lower recrystallization fraction in the 0.5Zn alloy than that in the 0Zn alloy. The as-extruded 0Zn and 0.5Zn alloys exhibit quite weak texture in the DRXed regions. In particular, a prismatic texture component with basal plane perpendicular to the extrusion direction is formed, which is slightly strengthened by the addition of Zn and the promotion of extrusion temperature. The experimental results suggest the formation of this texture is primarily correlated with the growth advantage of relevant grains. The addition of trace Zn can obviously enhance the strength and stimulate the occurrence of yield point under tension, which is weakened with increasing the extrusion temperature. The present results demonstrate the important role of Zn addition and extrusion temperature on the microstructure, texture and mechanical properties of Mg-Gd-Y alloys.