Effect of Ca and Y microalloying on oxidation behavior of AZ31 at high temperature

The microstructure, oxidation behaviour and oxide film morphology of AZ31, AZ31-0.5Ca, AZ31-0.5Y and AZ31-0.5Ca-0.5Y alloys were investigated. The results demonstrate that the oxidation behaviour of all the experimental alloys can be divided into two distinct parts: the incubation zone, which follows a parabolic law, and the non-protective oxidation zone. The resistance to high-temperature oxidation of AZ31 was enhanced by the incorporation of Ca or Y. The outcomes demonstrated that the oxidation behaviour of AZ31 was highly commendable. The observation of the micro-morphology by scanning electron microscopy (SEM) revealed that the presence of calcium (Ca) and yttrium (Y) can reduce the amount and change the shape of the low-meltingpoint phase of magnesium (Mg) and aluminium (Al) (Mg17Al12). The morphology and composition of the oxide films were analysed, and it was found that the AZ31-0.5Ca and AZ31-0.5Ca-0.5Y oxides are thinner and more dense, and that the failure is in the form of peeling and detachment. Furthermore, it was observed that the oxides of AZ31 and AZ31-0.5Y become loose and porous at high temperatures. The antioxidant capacity of calcium is enhanced by increasing the film density, while yttrium enhances the resistance to high-temperature oxidation by depleting the low-melting phase and changing the nature of alpha-Mg. The simultaneous addition of Ca and Y results in cracking and peeling of the film layer.