Influence of calcium on ignition-proof mechanism of AM50 magnesium alloy

In order to improve the ignition proof of AM50 magnesium alloy, 1wt% Ca was added to AM50 magnesium alloy to prepare investigated alloy. The ignition temperature, ignition-proof holding time at the predetermined temperature, microstructure of oxide film and thermodynamics of oxide film formation were studied. The results show that after adding 1wt% Ca, the ignition temperature of AM50-1wt%Ca alloy reaches 832 degrees C, which is 248 degrees C higher than 584 degrees C of AM50 magnesium alloy. The holding time of AM50 alloy varies with temperature. The higher the temperature, the shorter the holding time. AM50 magnesium alloy can remain for about 720 s at 525 degrees C without ignition, while it only remains for about 50 s at 550 degrees C. The oxide film of AM50 magnesium alloy is mainly loose and porous MgO. The oxide film of AM50-1wt.%Ca alloy is a bilayer oxide film of MgO and CaO and CaO is mainly distributed in the outer layer of the oxide film. When the temperature is lower than 949 degrees C, the oG of CaO formation is less than that of MgO formation during the oxidation process of AM50-1wt%Ca alloy, MgO formed in the early stage of oxidation can be reduced to [Mg] by [Ca] and the minimum [Ca] content required for the reaction is always less than 1wt%. The dense bilayer oxide film formed on the surface of AM50-1wt%Ca alloy can effectively protect alloy and its oxidation process conforms to the parabola variation law.