Effects of Sn-Bi-Cu alloy melt structure change on solidification

In order to explore the correlation between alloy melt structure and solidification structure and to further improve the performance of Sn-Bi-Cu Pb-free solder alloys,the four-probe resistivity method is used to study the melt overheating behavior of Sn₇₀Bi₁₀Cu ternary alloy.The results show that during heating process,a sudden change of electric resistivity will happen in temperature range from 812 to 821℃ but won't during cooling process,which reveals the irreversible structure change in the melts.The results of microstructure observation and mechanical properties testing indicate that the structure change behavior has obvious effects on the solidified microstructure and mechanical properties.The ultimate compressive strength is improved about 8%,and the surface Vickers hardness is improved about 18%.