Selective Oxidation and the Third-Element Effect on the Oxidation of Mg-Y Alloys at High Temperatures

Excellent ignition-proof performance is realized in the system of Mg-Y-Ca, which can be melted at 1173 K directly in air without any protections. When the concentration of Y is greater than 10 wt pct, a dense and compact oxide film is obtained on the surface of molten Mg-Y alloy. With the addition of Ca, the critical concentration of Y in Mg-Y alloys for forming the protective film is decreased significantly from 10 to 3.5 wt pct. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Auger electron spectroscopy (AES) analyses indicate that the protective film formed on the surface of Mg-Y-Ca alloy melt is mainly composed of Y2O3. Based on the theoretic analysis and experimental results, a selective oxidation model of Mg-Y alloys at high temperatures is developed, and the third-element effects of Ca are discussed in detail.