Surface oxidation of molten AZ31, AM60B and AJ62 magnesium alloys in air. (October 2014) - Balart, M. J.
Abstract The surface of stagnant Mg–Al based alloy melts has been exposed to air: AZ31 alloy, at 640°C for 10 min and at 650°C for 10 s; AM60B alloy at 650°C for 10 s and AJ62 alloy at 690°C for 10 s. After oxidising, the samples were sand quenched. The macroscopic morphology of the surfaces exhibited regions of non-nodular growth (in a layer manner) and regions of nodular growth. The microscopic morphology of the surfaces and the nature of the surface reaction products have been analysed using field emission gun (FEG)–SEM and X-ray diffraction (XRD) techniques, respectively. FEG–SEM results revealed that all these morphologies, namely, sponge-like, nodular and layer, were porous and, therefore, were non-protective with respect to evaporation and oxidation of Mg, Zn and Sr. XRD results indicated that in all these regions, MgO was the main oxidation product along with traces of AlN. Additionally, traces of ZnO were found in the non-nodular and nodular regions of AZ31 alloy containing 1·16 wt-%Zn for both oxidation conditions and, in the nodular region of AM60B alloy containing 0·05 wt-%Zn, relative to a more vigorous reaction condition. This trace ZnO content reflected the Zn levels of the three magnesium alloys investigated and the oxidation conditions. Traces of SrO were found in the nodular region of AJ62 alloy containing 2·5 wt-%Sr, relative to a more vigorous reaction condition.