Simplified three-dimensional macro segregation simulation model and its application to directional solidification of Sn-Bi alloys

A simplified macro segregation simulation model that can be applied to three-dimensional channel type macro segregation prediction is proposed. The model consists of thermosolutal convection analysis, heat transfer analysis and solidification analysis with utilizing "jump condition" for taking remelting phenomena into calculation. Lateral directional solidification experiments of Sn-Bi alloys with permanent mold were carried out to examine the effectiveness of the proposed simulation model. Two- and three-dimensional calculations by the proposed model were performed to simulate the channel segregation observed in the experiments. Also, three-dimensional observations by X-ray CT were performed to examine the stereoscopic structure of the channel segregations. Many channel segregations were observed in the experiments and similar channel segregations were simulated in the calculations. Observed number of channel segregation were decreased when the mold coolant temperature were decreased. According to the simulated results, evaluation by total variant of solute concentration distribution was effective to predict the number of channel segregation. Moreover, pour out technique was used to observe overhang solidification front shape caused by Bi concentration in bottom. Similar solidification front shape was successfully simulated by the model.