Effect of trace Y/Sm addition on high temperature oxidation behavior and oxide film structure evolution of Mg-Al-Ca alloy

In order to clarify the influence mechanism of trace rare earth (RE) Y/Sm composite addition on the high temperature oxidation behavior of Mg-Al-Ca alloys, AX series alloys with different Y/Sm ratios were prepared in this study. The results show that Y/Sm microalloying can refine grains and form thermally stable Al 2 (Y, Sm) phase. Confocal Laser Scanning Microscopy (CLSM) showed that Mg-5.5Al-1.5Ca-0.4Y-0.6Sm (AX5146) had the highest initial oxidation temperature (500 °C) and the best oxidation resistance. The oxidation film thickening rate of AX5146 is the lowest (about 10%) when oxidized at 500 °C. At 560 °C, Ca element is preferentially enriched on the surface, and CaO is the main oxide. The RE in the long-term oxidation at 620 °C can thin the oxide film and reduce the internal stress. X-ray Photoelectron Spectroscopy (XPS) confirmed the existence of Y 2 O 3 /Sm 2 O 3 in the oxide film. Due to the loose and porous primary MgO, AX52 continued to undergo internal oxidation and formed oxidation blisters/nodules. AX5146 forms a composite layered oxide film of outer MgO-CaO, middle RE oxide sublayer and inner MgO through the mechanism of Y/Sm element being “second phase release” and blocking the oxidation pathway, which promotes the transformation of oxidation from internal oxidation to external oxidation, and significantly improves the high temperature oxidation resistance of the alloy.