No abstract

In this study, to obtain guidelines for inhibiting the combustion of the molten metal in magnesium alloys, AZ91D magnesium alloy and AZ91 magnesium alloy with added calcium were exposed to the atmosphere, and the surfaces of the alloys were observed. In the case of AZ91D magnesium alloy, aggregated products were observed on the surface of the molten alloy. In the case of AZ91 alloy with added calcium, aggregated products were not observed. A CaO layer was formed on the outermost surface of the molten alloy, and a MgO layer was formed below the CaO layer. With increasing exposure time, the thicknesses of these layers remained almost constant. It was considered that the CaO layer, in which aluminum did not appear, inhibited combustion by limiting the ow of magnesium vapor from the molten alloy to the atmosphere and the oxidation of magnesium over a long time.

In this study, to obtain guidelines for inhibiting the combustion of the molten metal in magnesium alloys, AZ91D magnesium alloy and AZ91 magnesium alloy with added calcium were exposed to the atmosphere, and the surfaces of the alloys were observed. In the case of AZ91D magnesium alloy, aggregated products were observed on the surface of the molten alloy. In the case of AZ91 alloy with added calcium, aggregated products were not observed. A CaO layer was formed on the outermost surface of the molten alloy, and a MgO layer was formed below the CaO layer. With increasing exposure time, the thicknesses of these layers remained almost constant. It was considered that the CaO layer, in which aluminum did not appear, inhibited combustion by limiting the ow of magnesium vapor from the molten alloy to the atmosphere and the oxidation of magnesium over a long time.

In a previous study, we reported that adding tin to Mg-Al-Ca alloys inhibits cast cracking while maintaining excellent heat resistance. In this study, to clarify the mechanism resulting in the improved castability, Mg-Al-Ca alloys with different compositions were cast by high-pressure die casting into an I-shaped die with strain gauge instrumentation. The solidi cation shrinkage and thermal contraction of the alloys during the solidi cation and cooling process were investigated. The addition of tin decreased the solidi cation shrinkage of the alloys, and the tensile stress in the alloys was relaxed. On the basis of these results, the addition of tin is considered to improve the castability.