Short CommunicationFormation of an incombustible oxide film on a molten Mg-Al-Ca alloy

•The nonflammable Mg85Al10Ca5 alloy exhibits a high ignition temperature of 1436 K.•The oxide film formed on the molten alloy was found to be a three-layered structure.•The outer layer of the three-layered structure consists of fine CaO grains.•The incombustibility may be due to the formation of the fine CaO outer layer.

A nonflammable Mg-10Al-5Ca (at.%) alloy that can be melted in air without a cover gas or flux is developed. The alloy immediately forms a protective oxide film consisting of three layers, a fine CaO outer layer, a fine MgO intermediate layer, and a coarse MgO innermost layer. The anionic volume ratio of the CaO/MgO interface is 1.48. This interface ratio is sufficiently large to suggest the generation of a strong compressive force in the CaO layer. The dense, uniform fine CaO layer may act as a protective layer preventing the diffusion of oxygen.

Graphical abstractDownload high-res image (334KB)Download full-size image