Lightweight magnesium alloy has recently attracted a considerable interest in the automotive and aerospace industries to improve fuel efficiency and reduce CO2 emissions via the weight reduction of vehicles.Rare-earth（RE） element addition can remarkably improve the mechanical properties of magnesium alloys through weakening crystallographic textures associated with the strong mechanical anisotropy and tension-compression yield asymmetry.While the addition of RE elements sheds some light on the alteration in the mechanical anisotropy,available information on the constitutive relationships used to describe the flow behavior of RE-containing magnesium alloys is limited.To establish such a constitutive relationship,uniaxial compressive deformation tests were first conducted on an extruded Mg-10Gd-3Y-0.5Zr（GW103K） magnesium alloy at the strain rates ranging from 1×10–1 to 1×10–4s–1 at room temperature.A modified Johnson-Cook constitutive equation based on a recent strain hardening equation was proposed to predict the flow stresses of GW103K alloy.Comparisons between the predicted and experimental results showed that the modified Johnson-Cook constitutive equation was able to predict the flow stresses of the RE-containing magnesium alloy fairly accurately with a standard deviation of about 1.8%.
The microstructure, the content of compounds, mechanical properties and fracture behavior of high vacuum die casting Mg-8Gd-3Y-0.4Zr alloy （mass fraction, %） under T4 condition and T6 condition were investigated. The microstructure for the as-cast Mg-8Gd-3Y-0.4Zr alloy mainly consists ofα-Mg and eutectic Mg24（Gd,Y）5 compound. After solution treatment, the eutectic compounds dissolve massively into the Mg matrix. The main composition of solution-treated alloys is supersaturated α-Mg and cuboid-shaped phase. The T4 heat treated samples have increasing cuboidal particles with the increase of heat treatment temperature, which turn out good mechanical properties. The optimum T4 heat treatment for high vacuum die cast Mg-8Gd-3Y-0.4Zr alloy is 475 ℃, 2 h according to microstructure results. The optimum ultimate strength and elongation of solution-treated Mg-8Gd-3Y-0.4Zr alloy are 222.1 MPa and 15.4%, respectively. The tensile fracture mode of the as-cast, and T6 heat treated alloys is transgranular quasi-cleavage fracture.
