Internal and external shrinkages in unidirectionally solidified Al4.5wt.%Cu alloy

Abstract

Abstract Solidification shrinkage and macrosegregation were investigated in Al4.5wt%Cu alloy ingots solidified unidirectionally upwards from the bottom. Large external shrinkage was generated, while the amount of internal shrinkage (porosity) was small. The amount of external shrinkage increased with increasing distance from the bottom and with decreasing temperature gradient in the ingots. Inverse segregation, which usually occurs in unidirectionally solidified ingots, was not severe in the present work. This was because when the top of the ingot reached a pasty state, the capillary pressure acting on the liquid made it impossible for the interdendritic liquid to flow downwards to compensate for the solidification shrinkage, and the major part of the solidification shrinkage was compensated for by the formation of external shrinkage. The amount of solidification shrinkage and the degree of macrosegregation in the ingots were computer simulated and compared with the experimental results.