Morphological selection of Al-Zn alloy during directional solidification

The experiments on the cellular/dendritic selection of Al-0.53wt%Zn alloy at medium growth rate during unidirectional solidification were performed. The cellular/dendritic and dendritic/cellular transition of the Al-Zn alloy were observed. No dendrites appear within the whole growth rate range and full cellular growth is observed. The cellular/dendritic transition appears when the growth rate is in the range of 30-45 μm/s, which agrees with the predicted one by Trivedi model. The dendritic/cellular transition appears when the growth rate is in the range of 600-700 μ/s at temperature gradient of 145 K/min. If the freeze range of the alloy is sufficiently small and the temperature gradient is high enough during directional solidification, the dendritic/cellular transition velocity will be larger than cellular/dendritic one.