Evolution of Metallographic Parameters during Horizontal Unidirectional Solidification of Zn-Sn Alloys

Abstract

In the present research the horizontal directional solidification of Zn-Sn alloys (Zn-4wt.%Sn, Zn-6wt.%Sn, Zn-10wt.%Sn and Zn-30wt.%Sn) was carried out by extracting heat in two opposite directions. For this purpose, ceramic molds, a muffle, a horizontal furnace with two heat extraction systems at the ends, a measurement, acquisition and recording temperature system, eight K-type thermocouples and an electronic recorder were used. The main parameters involved in the columnar-to-equiaxed transition, CET, were: the moment of start and end of solidification at each position under consideration, cooling rates, the average temperature gradients and critical temperature gradients at the CET. Also, metallographic parameters evolution (secondary dendritic arm spacing) was analyzed in function of the position in the sample and correlated with thermal parameters. The values of the critical thermal gradients for each composition were 0.01 °C/cm (right side) and 0.23 °C/cm (left side) for Zn-4wt%Sn, 0.25 °C/cm (right side) and 0.41 °C/cm (left side) for Zn-6wt%Sn, 1.4 °C/cm (right side) and 1.7 °C/cm (left side) for Zn-10wt%Sn and -0.05 °C/cm (right side) and 0.15 °C/cm (left side) for Zn-30wt%Sn.