一方向凝固したAl-CuAl<SUB>2</SUB>共晶の組織

Abstract

The authors have studied the microstructure of the Al-CuAl2 eutectic frozen unidirectionally under a steady or non-steady state, in order to determine factors governing the microstructure of lamellar eutectic. The degeneration of the lamellae in the slowly frozen eutectic is facilitated as the orientation of the lamellae boundary of the Al phase deviates from the equilibrium orientation (111)Al. Since in the case of steady state freezing of the eutectic alloy the colony structure is easily formed by vertical freezing than by horizontal freezing, the latter must cause a severer mixing of melt during freezing as compared with the former. This may have an effect on the formation of wider interlamellar spacing in the horizontally frozen eutectic than the vertically frozen eutectic, particularly, when frozen at low freezing rate. In the case of the horizontal freezing, the interlamellar spacing is inversely proportional to the square root of freezing rate. The interlamellar spacing of the eutectic frozen at a high freezing rate under the non-steady state is fairly larger than would be expected from the extrapolation of data for the eutectic frozen at a lower freezing rate under the steady state. The colony size has a linear relationship against the reciplocal of the square root of freezing rate, or against the reciplocal of the product of freezing rate and temperature gradient. The eutectic CuAl2 phase in the hyper-eutectic alloy can partially grow from the primary CuAl2 phase, while the eutectic Al phase in the hypo-eutectic alloy cannot grow from the primary Al phase.