Effect of Solidification Rate and Temperature Gradient on the Changes of Mushy Zone Length in Pb-36mass%Sn Binary Alloys during Upward Directional Solidification.

Upward directional solidification experiments have been carried out on Pb-36mass%Sn binary alloys with varying the solidification rate and temperature gradient. Results show that due to solute convection, the length of the mushy zone was not constant even when the dendritic growth at a constant temperature gradient was maintained during upward directional solidification. The length of the mushy zone decreased with increasing fraction solidified if solute convection occured. At a constant solidification rate, the greater the temperature gradient is, the greater the change of length of mushy zone is. At a constant temperature gradient, the smaller the solidification rate is, the greater the change in length of the mushy zone is. Effect of solute convection on the length of the mushy zone during upward directional solidification is responsible for the composition change of Sn at ahead of the mushy zone. If the composition at ahead of the mushy zone changes greatly as increasing the fraction solidified, the change of length of the mushy zone is greater.