Unidirectional Solidified Zn-Al-Si-Cu Alloys: Columnar-to-Equiaxed Transition (CET)

Abstract

The present investigation was undertaken to investigate the directional solidification of Zinc-Aluminum alloys with addition of Silicon and Copper, specifically Zn-20%Al-10%Si-3%Cu alloys (weight percent) under different conditions of heat transfer at the metal/mould interface. The columnar-to-equiaxed transition, CET, was observed and related to the solidification thermal parameters such as cooling rates, interphase velocities, thermal gradients and recalescence values which were determined from the temperature versus time curves. The results indicate that there is an increase in the velocity of the liquidus front faster than the solidus front, which increases the size of the mushy zone. The observations indicate that the transition is the result of a competition between columnar grains and finer equiaxed grains.