Rapid directional solidification in Sn-Cu lead-free solder

An experimental study on the microstructures of a rapid directionally solidified metallo-eutectic Sn-Cu alloy was carried out. This material is an important alloy that is used as a lead-free solder. The results showed that the kinetic undercooling due to the rapid solidification process led to the formation of a pseudoeutectic zone, whereas the hypereutectic reaction produced the regular lamellar structure in the hypereutectic Sn-1.0Cu alloy. The corresponding arm spacing in the obtained lamellar phases decreased gradually with the increase of the applied cooling rate, which corresponded well with the prediction of a rapid directional solidification model.