Abstract
The influences of the quenching operation on the solidification structure and the solute distributions at the solid-liquid interface (the S-L int.) were investigated using unidirectionally solidified Al-4.5 wt%Cu alloys.
The substructures in front of the S-L int. obtained on quenching vary with the solidification conditions. In front of the planar interface, the micro cells periodically elongate to the solidification direction and then change to the micro dendritic substructure. In front of the simple cellular interface there appear the micro cells, but not so long as those in the case of planar interface, and the cellular substructure, which seems to be equiaxed, is observed. In the case of dendritic interface, the substructure directly changes to the micro-dendritic substructure.
Next, by EPMA analysis of the solute contents at the S-L int., it is observed that the solute contents in the solid at the interface increase with the solidification factor (Gm⁄RLn, where G is the temperature gradient in the liquid and RL is the solidification rate). The solute distribution coefficient at the tip of the S-L int. is constant (about 0.15) for various solidification factors, and the effective distribution coefficient increases with the solidification factor. From these results, it is concluded that the solute distribution coefficient at the tip of the S-L int. is constant for various interface morphologies, and the solute segregation parallel to the interface increases with the decrease of the solidification factor.
