過熱処理したMg-Al合金の鋳造組織と結晶粒微細化

抄録

In order to understand the mechanisms of grain refinement of a superheat-treated magnesium alloy, pure magnesium samples containing 0 to 10at%Al were heated at 900°C and held for 1800s. The samples were then cooled at a constant rate and cast into a metallic mold at 660 or 680°C. Samples were melted ln the graphite, cast iron, and magnesla crucibles to clarify the influences of impurity elements in the crucible on the grain size. Metallographic examinations were performed to measure the grain size of solidified structures. An electron probe micro analyzer was used to find the foreign particles for heterogeneous nucleation in the fine grains. The grain refinement of superheat-treated Mg-Al alloys depends on aluminum content. The finest grain size was obtained in the Mg-6at%Al alloy. The grain size became coarser as the aluminum content increased or decreased from 6%. The molten magnesium alloy attacked the iron and magnesia crucibles, so Fe and Si contents of samples increased. However, no foreign particles such as metallic compounds which occur in heterogeneous nucleation were observed in any grain.