Effect of thermo-mechanical treatment on the microstructure and mechanical properties of a Mg-6Gd-2Nd-0.5Zr alloy

Thermo-mechanical treatments, through combined action of cold or hot work and heat treatment, were performed on a Mg-6Gd-2Nd-0.5Zr alloy to investigate their effect on the microstructure and mechanical properties of the alloy. Cold deformation of 5 or 10% between homogenization and aging produced high density of twins and dislocations in as-quenched alloys, and caused acceleration in age-hardening response at 200 °C. Cold-deformed and peak-aged alloys exhibited higher strength and lower elongation than those of peak-aged cast alloy. Alloys subjected to hot extrusion at 450 or 350 °C showed very fine grains, and meanwhile maintained a considerable supersaturation in matrix, leading to a significant age-hardening response at 200 °C. Hot extrusion and aging brought about an overall improvement in mechanical properties, and the best combination of strength and ductility was achieved for alloy after extrusion at 350 °C and aging at 200 °C for 24 h, namely ultimate tensile strength = 381 MPa, tensile yield strength = 273 MPa and elongation = 17.6%.