純AlおよびAl-0.2%Cu合金鋳塊における等軸晶の生成について

Abstract

The origin of the equiaxed zone has been investigated in 99.99% purity Al and Al-0.2%Cu alloy ingots in which columnar grains grow in a cellular or cellular dendritic manner. Experiments on the conventional ingots and bottom chilled, unidirectionally solidified ingots show that there is a critical pouring temperature for the formation of equiaxed zone, above which no equiaxed zone forms. In the absence of pouring turbulence, however, no equiaxed zone forms even though the ingot is quenched from the temperature below the critical one. These results indicate that the pouring turbulence is an essential element in the formation of the equiaxed zone. It is also found that the chill grains in the very surface layer of the ingots have dendritic morphology.So it is concluded that the equiaxed zone in pure Al and Al-0.2%Cu alloy ingots is caused by the multiplication of dendritic chill crystals induced by pouring turbulence.