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

Abstract

The oxidation resistance of Mg–Zn–Zr (ZK60) alloys with the addition of minor rare-earth element (RE) oxides (CeO2, La2O3) was investigated in 420 °C 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.

Keywords

• Mg alloy
• Oxidation resistance
• Rare-earth element oxide
• Intergranular oxidation
• Phase transformation