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

Abstract

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-melting-point 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 α-Mg. The simultaneous addition of Ca and Y results in cracking and peeling of the film layer.