Pilling-Bedworth Ratio Approach to Surface Oxidation of Al–Mg Alloys Containing Al2Ca and Its Experimental Verification

Pilling-Bedworth ratio (PBR) of metal/dissimilar metal oxide and metal/mixed metal oxide for Al-Mg alloys containing Al2Ca was experimentally examined. The Al-7.5mass%Mg alloy exhibits a thick oxide layer due to the formation of MgO, primarily during the initial stage of oxidation at 788 K. As oxidation continues, the oxide layer of Al-7.5mass%Mg alloy develops an MgAl2O4-spineI. With the addition of 0.3mass%Al2Ca, the surface of the alloy exhibits a passivation effect. The alloy containing Al2Ca additive displays a combination of CaO, MgO and Al2O3 on its surface, and results in a PBR of similar to 1.