Ａｌ‐ＳｉおよびＡｌ‐Ｇｅ合金の凝固現象の直接観察

Abstract

In order to understand the solidification mechanism of Al-Si and Al-Ge alloys, in-situ observation of the solidication phenomena on the molten surface has been carried out during unidirectional solidification. In hypoeutectic alloy containing 8 to 10mass% Si or 46 to 51mass% Ge, eutectic solidification starts at the cooling end and then unidirectionally proceeds independently of the primary crystal of α aluminum dendrites which exists in the eutectic melt. In eutectic compositions containing 11.7mass% Si or 53mass% Ge, only unidirectional solidification of eutectic occurs. In this case, eutectic Si or Ge crystals are always observed to precede at the competitive growth with eutectic aluminum. These phenomena show that the silicon and germanium are the leading phases of the eutectic in these alloys. In hypereutectic composition containing 14 to 18mass% Si or 55 to 60mass% Ge, eutectic solidification starts on primary crystals of angular silicon or germanium and then spreads radially in the melt. These results are consistant with those previously obtained on Al-Cu, Al-Ni, Zn-Al and Sn-Zn eutectic alloys.