Microstructure evolution and mechanical properties of as-extruded Mg-Gd-Y-Zr alloy with Zn and Nd additions.

The microstructure evolution and mechanical properties of as-extruded Mg-11.5Gd-4.5Y-0.3Zr (wt%) alloy with Zn and Nd additions were investigated. The addition of Zn inhibits the dynamic recrystallization (DRX) due to the presence of the long-period stacking ordered (LPSO) phase. The addition of Nd promotes the precipitation of the Mg 5 RE (RE: rare earth) phase. The existence of the densely distributed Mg 5 RE phase before hot extrusion promotes the DRX in subsequent hot extrusion process and leads to grain refinement. The increase in the number of Mg 5 RE phase particles degrades the mechanical properties of the resultant alloy. After hot extrusion, the studied alloys exhibit a bimodal microstructure consisting of fine dynamic recrystallized (DRXed) grains of several microns and strongly textured course un-DRXed grains. The as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.3Zr alloy exhibits an excellent balance of strength and ductility (tensile yield strength of 371 ± 3.0 MPa and elongation of 7.2 ± 0.8%). The alloy strengthening is attributed to the bimodal microstructure, the Mg 5 RE and LPSO phases, and the basal texture. The tensile yield strength of the as-extruded Mg-11.5Gd-4.5Y-1.5Zn-0.3Zr alloy can be further increased to 425 ± 2.5 MPa by precipitation hardening with the T5 treatment. [ABSTRACT FROM AUTHOR]