Microstructure and mechanical performance of Mg-Gd-Y-Nd-Zr alloys prepared via pre-annealing, hot extrusion and ageing

Abstract

Mg-xGd-3Y-yNd-0.5Zr alloys (x = 6, 8, 10; y = 0.5, 1 wt%) were prepared by hot extrusion, pre-annealing and ageing treatments. After hot extrusion, the alloys exhibit a bimodal structure consisting of coarse deformed grains with strong basal texture and fine recrystallized grains with weak < 0001 > texture. The increases of Gd and Nd contents in the alloys effectively refine the grains, weaken the texture, promote the precipitation of fine Mg5RE (RE: rare earth) particles and enhance the age-hardening response. The pre-annealing treatments generate a large number of plate-like Mg5RE particles in grain interiors and the bulk Mg5RE particles at the grain boundaries. These Mg5RE particles crack into small fragments during hot extrusion, and hence promote the dynamic recrystallization and further refine the recrystallized grains by pinning the grain boundaries. The ductility and strength of the alloy are simultaneously improved due to the pre-annealing treatment prior to the hot extrusion. In the studied alloys, the peak-aged Mg-10Gd-3Y-0.5Nd-0.5Zr alloy exhibits the best mechanical performance with tensile yield strength of 415 MPa and elongation to failure of 4.6 %. The alloy strengthening is mainly attributed to the bimodal structure, Mg5RE phase at grain boundaries and β′ phase in the grain interiors.