Effects of Ga Content on Dynamic Recrystallization and Mechanical Properties of High Strain Rate Rolled Mg–Ga Alloys

Abstract

The Mg–xGa (x = 1, 2, 3 and 5 in mass%) alloys are subjected to high strain rate rolling (HSRR) at 275 °C with the rolling strain rate of 9.1 s−1 to develop high performance Mg alloy sheets with high plasticity. Effects of Ga content on microstructure and mechanical properties of the Mg–Ga alloys are investigated by SEM, XRD, tensile testing and etc. The Ga addition can reduce the critical strain of DRX in Mg alloys, which is associated with the reduced stacking fault energy, the increased twinning density during deformation and the more DRX nucleation sites during HSRR. With the Ga content increasing from 2 to 3%, the reduced DRX degree is attributable to the hindrance of dynamic precipitates. With the Ga content increasing from 3 to 5%, the slightly increased DRX degree can be ascribed to the relatively coarse precipitates. The Mg–2 Ga alloy sheet, featured with complete DRX, exhibits an ultra-high plasticity (with the elongation to rupture of 36.6%) and a relatively low anisotropy of yield strength and plasticity. The Mg–5 Ga alloy sheet has the best comprehensive mechanical properties, with the ultimate tensile strength of 292 MPa, yield strength of 230 MPa and elongation to rupture of 30.3%, which can be ascribed to the combination of grain refinement strengthening and precipitation strengthening. Effects of Ga content on microstructure, dynamic recrystallization (DRX) and mechanical properties of the Mg-Ga alloys prepared by high strain rate rolling (HSRR) are systematically studied. Among all the alloys, the HSRRed Mg-2Ga alloy exhibits the smallest DRX critical strain, an ultrahigh plasticity (δ up to 36.6%) and a low anisotropy of yield strength and plasticity, due to the complete DRX. The HSRRed Mg-5Ga alloy shows the optimal mechanical properties, with σb of 292 MPa, σ0.2 of 230 MPa and δ of 30.3%. The high strength is mainly attributed to precipitation strengthening and grain refinement strengthening.