Cellular/dendritic transition during unsteady-state unidirectional solidification of Sn–Pb alloys

Structural parameters such as grain size, dendritic and cellular spacings, segregated products, porosity and other phases are strongly influenced by the thermal behavior of the metal/mold system during solidification, imposing a close correlation between this and the resulting microstructure. Numerous unidirectional solidification studies have been carried out with the objective of characterizing cellular and dendritic spacings and most of the published work has involved solidification in steady-state heat flow conditions. The objective of this article is to determine the thermal solidification parameters affecting the cellular/dendritic transition as well as to compare theoretical models that predict cellular and primary dendritic spacings with experimental results for unsteady-state solidification. Experiments were carried out in a water cooled unidirectional solidification apparatus and dilute alloys of the Sn–Pb system have been used (Sn 1.5 wt.% Pb, Sn 2.5 wt.% Pb and Sn 5 wt.% Pb).