Undercooling for nucleation and volume fraction of primary β-Sn phase in Sn-X alloys

Abstract

The undercooling for nucleation and volume fraction of primary (β-Sn)phase has been investigated in Sn-X hypoeutectic alloys where X were Pb, Ag, Al, Bi, Cu and Zn. The purities of raw materials were 4N and the solute content of the alloy was set for the volume fraction of primary phase to be from 0.3 to 0.45, according to the equilibrium phase diagram. Thermal history was measured during solidification of 5 g alloy sample at a cooling rate of 0.05 K/s, with fine K-type thermocouple. The volume fraction of primary (β-Sn)phase was measured on the longitudinal cross section of the sample. When the solute elements were Pb, Ag, Al, Bi and Cu, the undercooling was more than 5K and was large. Furthermore, the volume fraction of primary (β-Sn)was larger than the equilibrium value. On the other hand, when the solute element was Zn, the undercooling for the nucleation of primary (β-Sn) was 0.9 K and quite small. In addition to this, the volume fraction of primary phase agreed with the equilibrium value.