Aging behavior and mechanical properties of Mg–Gd–Ho alloys

The Mg–8Gd–0.6Zr–xHo (x = 1, 3 and 5, mass%) alloys were prepared by casting technology, and structures, aging strengthening mechanism and mechanical properties of the alloys were investigated. The age behaviors and the mechanical properties are improved by adding Ho addition. The structures of the alloys are characterized by the present of rosette-shaped equiaxed grains. The peak hardness value of the Mg–8Gd–0.6Zr–3Ho alloy is 100 Hv, which is about 30% higher than that of Mg–8Gd–0.6Zr alloy. The Mg–8Gd–0.6Zr–3Ho alloy exhibits maximum ultimate tensile strength and yield strength at peak aged hardness, and the values are 279 MPa and 175 MPa, at room temperature, 191 MPa and 131 MPa at 250 °C, respectively. This increased peak hardness and improved mechanical properties are mainly ascribed to the formation of a fine β′-Mg15RE3 (Gd/Ho) metastable precipitate.