Cellular growth of Zn-rich Zn-Ag alloys processed by rapid solidification

Rapid solidification experiments were carried out on single-phase Zn-rich Zn-Ag alloys processed by laser remelting and melt-spinning techniques. For comparison, Bridgman solidification was performed as well. Three solidification morphologies were mainly identified with increasing growth velocity from 0.02 to 300 mm/s: regular cells or dendrites of η, plate-like cells of η, and plane front of η. Plate-like and regular cells were found to be velocity-dependent and occurred in high-velocity and low-velocity domains, respectively. The development of solidification interface morphologies in the present Zn-Ag alloys was proposed accordingly over a wide range of growth velocities from the limit of constitutional supercooling to the limit of absolute stability. Four microstructure transitions were identified: low-velocity plane front of η→low -velocity plate-like cells of η→regular cells or dendrites of η→high-velocity plate-like cells of η→high-velocity plane front of η. It implies that a plate-like cell would be the favorable morphology at growth conditions approaching a stable planar solid/liquid interface in comparison with the regular one.