Study of directional solidification of Zn-Al alloys

Abstract

Directional growth of Zn-Al alloys of different concentration was carried out by using a Bridgmann like apparatus. The

compositions of studied systems were a) dilute Zn-0,5 wt.%Al, below the maximum solubility limit, b) hypo-eutectic Zn-
2 and 4 %wt. Al, and c) hyper-eutectic Zn-8wt.% Al. Proper metallographic analysis of the segregation patterns behind
the solid-liquid (S-L) interface gives information about the effect of the local solidification conditions to obtain different
microstructures. It was found that the dilute alloy grows in a similar fashion than other alloys with atomistically rough
interfaces. For alloys with composition above the maximum solubility limit, it was found that a single primary phase
grows surrounded by liquid eutectic. In the case of hypo-eutectic alloys, a dendritic hcp primary phase is formed, whilst
for hyper-eutectic alloys, the primary phase is an fcc Al-rich dendrite. In both cases, a secondary interface for eutectic
solid-liquid is formed below the dendrite tips, in such a way the eutectic seems to growth independently of the primary
phase.