Influence of Zn Addition on the Solid/Liquid Interfacial Energy in Sn-Ag Alloy

In order to assess the effect of Zn addition in Sn-2Ag alloy on the undercooling of the primary (beta-Sn) phase, tip radii of the columnar dendrites of primary (beta-Sn) have been systematically investigated. Sn-2Ag-x Zn alloys were prepared for the experiments, where x= 0, 0.05 and 0.6 mass%. These alloys were unidirectionally solidified at growth velocities of 4, 10, 20, 30 and 40 mu m/s. The tip radii of columnar dendrites of primary (beta-Sn) on the longitudinal cross section of quenched samples were characterized. It was found that the tip radius decreased with increasing growth velocity and with increasing amounts of Zn. The effect of Zn addition on the solid/liquid interfacial energy was analyzed by assuming that the addition of Zn to Sn-2Ag alloy will not change the physical parameters such as the diffusion coefficient of the solute, solidification temperature range, and entropy of fusion. The addition of small amounts of Zn may considerably decrease the solid/liquid interfacial energy of primary (beta-Sn). This may possibly decrease the undercooling for nucleation of the primary (beta-Sn) phase in Sn-2Ag-x Zn alloy.