Effect of Ca addition on selective oxidation of Al₃Mg₂ phase in Al-5 mass% Mg alloy

This study examined the effect of Ca addition on the selective oxidation of the Al₃Mg₂ phase in an Al-5 mass%Mg alloy during oxidation at 400 °C and 500 °C for 72 h. Ca addition led to the formation of the Al₄Ca and Laves_C36 phases besides the primary Al solid solution and Al₃Mg₂. After the oxidation test, there was no significant oxidation in both the Ca-free and Ca-added alloy samples and no visible change in the surfaces between them at 400 °C, which is lower than the melting temperature of Al₃Mg₂ (451 °C). At 500 °C, the surface of the Ca-free alloy showed the formation of oxide blisters, which was not observed in the Ca-added alloy. The presence of an Al₄Ca phase at the grain boundaries led to the formation of multi-element oxides containing Al, Mg, and Ca, which can contribute to the formation of a compact oxide layer.