The effect of melt overheating on the melt structure transition and solidified structures of Sn-Bi40 alloy

Evolution of the electrical resistivity of Sn-40wt%Bi melt with time under different overheating temperatures during isothermal experiments has been studied, and the relationship between different melt state, solidification behavior and solidified structure has also been investigated. The results show that the melt structure transition revealed by the abnormal change of resistivity would take place within a certain holding time just when the holding temperature is above a certain critical, and that the higher the temperature above the critical, the shorter the “incubation period” of the melt structure transition, and the faster the transition speed. The results of solidification experiments suggest that the melt structure transition caused by different holding time at the same temperature can lead to a higher solidification undercooling degree, finer grain size and change of microscopic pattern. Further exploration indicates that the solidification undercooling degree can come to a head when the melt is held at the specific temperature for a given time. The functionary mechanism of the phenomena above is also discussed briefly. Supported by the National Natural Science Foundation of China (Grant Nos. 50571033, 50371024) and the Natural Science Foundation of Anhui Province(Grant No.070414178)