Preparation of high-performance Mg-Gd-Y-Mn-Sc alloy by heat treatment and extrusion

A high-performance Mg-8Gd-4Y-0.5Mn-0.2Sc (wt%) alloy was fabricated by the combination of homogenization, hot extrusion and ageing. The microstructure evolution during the homogenization at 550 °C was investigated, and the optimum time of 18 h was obtained to minimize the volume fraction of second phase particles and to keep fine grain structure. The alloy was extruded after the optimized homogenization, and the mechanical properties were investigated with the detailed characterization of the strengthening mechanisms. A typical bimodal microstructure with coarse deformed un-DRXed grains and fine DRXed grains was fabricated. The as-extruded alloy contains amounts of fine precipitated particles as well as dense nano-scale γ’ precipitates. After peak-aged treatment, the alloy exhibited excellent age-hardenability and strength with a tensile yield stress of 441 MPa and an ultimate tensile strength of 506 MPa. The high yield strength was attributed to the co-existing of the bimodal microstructure, fine DRXed grains, dense dynamically precipitated particles, and nano-scale precipitated phases. The co-existing β’ precipitates and γ’ precipitates are the largest contributor to the strength of the peak-aged alloy, the dominant strengthening mechanism is revealed as precipitation strengthening.