Effects of Al and Y additions on the oxidation behavior of Mg-Ca base molten alloys

The effects of Aluminum and Yttrium additions on the high temperature oxidation behavior were investigated in the Mg-Ca base molten alloys. In comparison with the Mg-Ca binary alloy, the spontaneous ignition temperatures of the ternary alloy chips containing Al and Y respectively were dramatically increased. In 700DGC oxidation of the molten alloy in the air, Mg-Ca binary alloy was easily ignited and burnt, whereas the Mg-Ca alloys containing either Al or Y showed the improved oxidation resistance because of the dense/compact and protective oxide layers formed on the surface. The surface analyses indicated that the oxide layer of Mg-Ca-Al alloy consisted of a single-layered oxide with the mixed structure of MgO, CaO and Al2O3, becoming thinner by Al addition. On the other hand, the oxide layer of the Mg-Ca-Y alloy had a double-layered structure of MgO/CaO and Y2O3, playing a role of very effective barriers to improve the high temperature oxidation resistance.