COLUMNAR-TO-EQUIAXED TRANSITION IN Zn-27wt.Al ALLOYS: A COMPARATION BETWEEN VERTICAL AND HORIZONTAL DIRECTIONAL SOLIDIFICATIONS

摘要

The columnar to equiaxed transition (CET) was studied in Zn-27wt.%Al alloys, which were directionally solidified from a chill face in both vertical and horizontal arrangement of experimental device. The main parameters analyzed include cooling rate of the melt, position of the solidification fronts for solidus and liquidus temperatures, velocity of solidification fronts and temperature gradients. In both type of solidifications the CET does not occur in abrupt form in the samples and the phenomenon is present when the gradient in the liquid ahead of the columnar dendrites reaches critical and minimum values, being negative in most of the cases. In addition, there is an increase in the velocity of the liquidus front faster than the solidus front, which increases the size of the mushy zone.