Comparative study of the effects of CaO and Ce-La misch metal on the microstructure and properties of AZ91 alloy

As the lightest structural metal material, magnesium alloy has the potential to replace aluminum alloy and steel parts, but its development is limited by problems such as poor plasticity, processing difficulties, and casting defects. In this paper, CaO and Ce-La misch metal(RE) were used as grain refiners in AZ91 and their effects on alloy microstructure and properties were investigated. In comparison with AZ91 alloy, the grain size decreased from 237.290 ?m to 31.390 mu m and 27.49 mu m with the addition of CaO and RE, respectively and the proportion of the second phase decreased from 19.029% to 11.414% and 8.644%, respectively; the effect of CaO on grain size and second phase was only 0.6% and 2.77% lower than that of the RE, respectively. The refined grain made the maximum compressive strength and com- pressive yield strength of AZ91-CaO alloy and AZ91-RE alloy 82% and 67% (Ca-O) 97% and 112% (RE) higher than that of AZ91 alloy and the compression ratio of the mixed alloys were similar. Electrochemical experiments and salt spray corrosion experiments confirmed the two mixed alloys had similar properties. Although the mechanical strength properties of the AZ91-CaO alloy were slightly lower than AZ91-RE alloy, the 100x cost-saving and energy- saving of high-energy consumption vehicles support the use of CaO as a more suitable grain refiner material than RE elements for large-scale industrial production.