Effects of Ce/La misch metal content on microstructure evolution and mechanical properties of Mg-Zn-Y alloy

Although reinforced by quasicrystal I-phase, Mg-Zn-Y castings with low contents of Zn and Y exhibits still inadequate strength at elevated temperature. In this study, different contents of low-cost misch metal (Mm, the mixture of Ce and La) were added to ZW61 (Mg-6Zn-1.4Y) alloy to develop a new series of Mg alloys simultaneously containing multiple rare earth elements. The effects of Mm content on the microstructure, mechanical properties and fracture mechanisms both at room and elevated temperatures were systematically investigated. The results showed that the addition of Mm contributed to the grain refinement and the formation of T-phase. Besides, the precipitation behaviors of I-phase and W-phase were also changed due to the variation of Mm content. The yield and tensile strengths at room temperature firstly increased with 1wt% Mm addition, but then deteriorated slightly when adding more Mm. In contrast, the strengths at 200°C kept a continually increasing trend and the yield strength and ultimate tensile strength of ZW61-3Mm alloy were respectively increased by 20.9% and 28.0% compared with the corresponding strengths of ZW61 alloy, which were mainly attributed to the reduction in grain size and the high volume fraction of thermally-stable T-phase and W-phase.