Achieving excellent oxidation resistance in a Mg alloy by grain boundary adhesion and in-situ phase transformation

The oxidation resistance of Mg-Zn-Zr (ZK60) alloys with the addition of minor rare-earth element (RE) oxides (CeO2, La2O3) was investigated in 420ºC in air and pure O2 environments. It was revealed that the oxidation behavior of ZK60, ZK60-La2O3 and ZK60-CeO2 is different. In comparison to typical intergranular oxidation in ZK60 alloy, owing to diverse phase transformations between La and Mg, the La-Mg phase is continuously distributed in the grain boundaries, and furthermore, a dense and protective layer consisting La-Mg intermetallic phase is coated on the surface, which can effectively inhibit the oxidation of the Mg substrate, exhibiting excellent oxidation resistance. However, the presence of discontinuously distributed Ce-rich phases at the grain boundaries and the chain reaction during high-temperature exposure are the reasons for the deterioration of the oxidation resistance in ZK60-CeO2. It is anticipated that our findings will inspire the development of next-generation low-cost and excellent high-temperature performance Mg alloys.