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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.

To realize high-strength and high-ductility aluminum alloys, an Al-Zn-Mg-Cu-based alloy was produced by high-pressure torsion (HPT) processing. The chromium in the alloy was replaced with zirconium, and the iron content of the alloy was decreased to avoid ductility loss due to iron-containing intermetallic compounds formed during crystallization. The microstructures and mechanical properties of the processed alloy were investigated. The grains were elongated perpendicular to the rotation axis. The elongation of the alloy containing chromium decreased with increasing number of turns. In the case of the alloy in which chromium was replaced with zirconium, the strength increased with increasing number of turns, without reducing the elongation. The alloy exhibited an ultimate tensile strength of 929 MPa and an elongation of 6.4%.

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.

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