過共晶Al-Si合金の複合鋳込み鋳塊の初晶微細化に及ぼす鋳造条件の影響

抄録

The primary silicon crystals of hypereutectic Al-Si alloy are refined by the Duplex Casting process. In this process, two kinds of alloy melts, i.e. “the first alloy” with a relatively low liquidus temperature and “the second alloy” with a relatively high liquidus temperature, are cast in a mold in sequence at a given time interval. Concerning the refining mechanism, the authors have explained that the second alloy melt is rapidly cooled during mixing with the first alloy which acts as a coolant.
In this study, the influences of alloy composition and mold properties on the refinement of the primary silicon crystals in the Duplex Casting process were examined. As a result, it was shown that the grain size of primary silicon varied intricately depending on these conditions. The decantation technique showed that a considerable amount of solidified shell had formed in the first alloy before the pouring of the second alloy melt. Several comparative experiments were carried out in order to examine the effect of heat extraction by the solidified shell, which is to be remelted during the mixing with the second alloy melt, on the refinement of primary silicon crystals. In those experiments, the second alloy melt was mixed with the first alloy which was in the liquid or solid state. As a result, it was proved that the solidified shell contributes greatly to the refinement of the primary silicon crystals through the remarkable enhancement of the cooling capacity of the first alloy. Considering this effect, the influences of alloy composition and mold properties on the primary silicon size can be explained.