Effect of Ag on High-Temperature Oxidation Behavior of Mg–6.5Gd–5.6Y–0.1Nd–0.01Ce–0.4Zr Alloy

Abstract

In this paper, the isothermal oxidation experiments were used to study the effect of Ag on the high-temperature oxidation behavior of Mg–6.5Gd–5.6Y–0.1Nd–0.01Ce–0.4Zr (wt%) alloy oxidized at 350 °C, 400 °C and 450 °C for 120 h. The results show that the oxidation weight gain of the alloy mainly occurs in the early oxidation stage (0–20 h). This reason attributes to the lack of protective oxide film and the rapid inward diffusion of oxygen through the macroscopic defects of the incomplete oxide film. When dense oxide films such as Y₂O₃, Gd₂O₃, and ZrO₂ form, they hinder the inward transport of oxygen ions and improve the high-temperature oxidation resistance of the alloy. In addition, the role of the Ag element at three temperatures is different. The addition of Ag mainly promotes the formation of eutectic phases such as Mg₃Gd, Mg₂₄Y₅, and Ag₂Gd, which reduces the content of Gd and Y elements in the alloy matrix, resulting in a decrease in the diffusion rate of Gd and Y elements during the oxidation process at 350 °C and 400 °C, and weakens the oxidation resistance of Ag-containing alloys. However, in the oxidation experiment at 450 °C, a large amount of eutectic phase is solid dissolved into the matrix, reducing the difference in element content. At this time, it is detected that the Ag element promoted the outward diffusion of Gd and Y elements, accelerating the formation of the oxide film. The oxidation resistance of Ag-containing alloys is improved.