Improved mechanical properties of the cast Mg–2.5Gd–0.5Zr alloy via hot extrusion

Abstract

Microstructural evolution and mechanical properties of the Mg–2.5Gd–0.5Zr alloy in the as-cast and extruded conditions were studied. Their flow behavior was investigated at room and elevated temperatures of 100, 175 and 250 °C through the shear punch testing (SPT) method. The as-cast alloy exhibited a non-dendritic microstructure due to the presence of Zr, which provided nucleation sites during solidification. A recrystallized microstructure was developed in the extruded alloy, due to the counteraction of Zr against the retarding effect of Gd on DRX. The enhancement in the strength of the extruded alloy was mainly ascribed to grain boundary strengthening. The reduction of shear yield stress (SYS) and ultimate shear strength (USS) with increasing the testing temperature in both as-cast and extruded conditions was a direct result of dislocation annihilation and reduction in the CRSS of non-basal slip systems. Both conditions developed reasonable ductility that was slightly enhanced with increasing temperature. The as-cast alloy, however, showed higher ductility and a more ductile fracture behavior compared to the extruded one at each testing temperature, caused by the synergy of twinning and slip in this condition and the very fine-grained structure of the extruded condition.