Effect of Ca on Oxidation Resistance of Magnesium Alloys (AZ91)

Since magnesium has very low density, it is always attractive in aerospace and transportation industries. However, due to high reactivity with environment, melting, alloying and casting of magnesium is always faced with problems about melt quality. So these alloys have low resistance to oxidation and combustion. Recent studies show that addition of alkali earth metals reduces the oxidation tendency of molten magnesium alloys. This study aimed to investigate the effect of calcium on oxidation resistance of magnesium alloys melt through microstructural studies, XRD and melt oxidation test. Results show that addition of calcium forms intermetallic compounds such as AL(2)Ca. Formation of these type of compounds in grain boundaries with surface oxide film of CaO, prevents the melt oxidation and minimizes the oxidation during atmosphere exposure. The most important advantage of these alloys is minimizing the use of shielding gases like SF6 which is considered a greenhouse gas that causes many environmental problems.