Effect of Ca addition on microstructure and elevated temperature properties of as-extruded magnesium alloys

Three kinds of magnesium alloys AZ113, X7 and X20 were prepared by the method of smelting and extruding. The microstructure of three magnesium alloys was observed by both optical microscope (OM) and scanning electron microscope (SEM). The phase composition and elements distribution were confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical states of elements and determined the composition of oxidation film on the surface. The elevated temperature tensile strength was carried out at the temperature of 250 °C. The results showed β-Mg17Al12 phase in magnesium alloys was refined by the addition of Ca, but the phase composition did not change. The tensile strength of magnesium alloys was enhanced obviously at elevated temperature, which was attributed to solid solution of Ca in the β-Mg17Al12 phase that led the thermally stable of β-Mg17Al12 phase to be improved. The antioxidant properties of X7 and X20 alloys at elevated temperature were improved by the addition of Ca, which led the complex oxidation film CaO·MgO to be formed on the surface of alloys.