Microstructure and mechanical properties of a die-cast Mg-9Al alloy containing oxygen atoms

•The Mg-9Al alloy containing oxygen atoms is produced by the high-pressure die-casting method.•The microstructure features and mechanical properties are characterized.•Oxygen atoms act as the nucleation site of α-Mg. In this study, the microstructural features and mechanical properties of a high-pressure die-cast (DC) Mg-9Al alloy containing oxygen atoms (Mg-O-9Al alloy) were characterized. The oxygen atoms promoted the formation of nucleation sites of α-Mg under high pressure, including fine cells (12–13 μm), and reduced the number of defect bands compared to the DC Mg-9Al alloy (14–15 μm). The relation between hardness and phase spacing indicated that the dispersion strengthening of the β-phase was dominant. The DC Mg-O-9Al alloy exhibited enhanced tensile properties as compared to the DC Mg-9Al alloy.