Investigation Of Preparation And Properties Of Sn-Bi Eutectic Wire

Sn–58Bi alloy is an ideal material for low–temperature lead–free brazing with low melting point,good wettability and creep resistance.However,quantities of hard and brittle Bi phases cause the poor ductility of Sn–Bi alloys.Therefore,the preparation of Sn–Bi solder wires is still very difficult.The lack of thermal fatigue resistance also causes people to worry about the reliability of solder joints.Sn–(58–x)Bi–x Cu/P/Ni ternary alloys with diameter of 8mm were prepared by downward continuous casting.The results showed that the microstructure and mechanical properties of Sn–58Bi alloy can be effectively improved by micro–alloying.The melting range and wettability of the alloy were obtained,and the microstructure of the alloy was characterized using optical metallographic analysis(OM),scanning electron microscopy(SEM),X–ray diffractometry(XRD),etc.Microstructure and mechanical properties of Sn–58Bi eutectic alloy with Cu,P and Ni addition were systematically studied.In light of the above,the Sn–(58–x)Bi–x Cu/P/Ni solder wire with diameter of 0.8mm was successfully prepared by self–developed heating rolling device and drawing device.In addition,the effect of the growth of intermetallic compound(IMC)at the solder/Cu interface on the shear strength of the joint was also further studied.It was found that minor elements Cu,P and Ni additions can make Bi–rich phase,?–Sn phase and mesophase refined and evenly distributed.The better elongation at break of Sn–58Bi alloy attributed to the improvement of microstructure.The wettability of Sn–58Bi alloy increased on Cu substrate with the additions of Cu,P and Ni elements.The interfacial compound(IMC)layer was mainly composed of Cu and Sn elements.No Bi was found in the interfacial layer after soldering.During the process of isothermal aging,IMC layer thickened and Sn–rich and Bi–rich phases coarsened.At aging temperature of 80~oC,the addition of 0.5%Cu,0.01%P and 0.15%Ni can inhibit the growth of IMC layer to a certain extent.The inhibition of 0.5%Cu and 0.01%P was no longer obvious with the aging temperature increasing to 120~oC,while 0.15%Ni promoted the growth of IMC layer to a certain extent.The failure position of solder joint occurred in the matrix alloy structure before aging.In the process of aging,the fracture of solder joint shifted from alloy to IMC layer.The multi pass rolling of the alloy was carried out at the rolling speed of 300 mm/min by self–developed hot–rolling device,and it was found that the multi pass rolling of Sn–(58–x)Bi–x Cu/P/Ni alloy at the rolling temperature of 60~oC was stable.Compared with the as–cast alloy,the tensile strength of the alloy with diameter of 6mm and 3mm decreased,while the elongation increased greatly.Multi pass drawing of Sn–(58–x)Bi–x Cu/P/Ni alloy with diameter of 3mm–0.8mm can be realized stably at room temperature by using the self–developed drawing device.Compared with the as-cast alloy,the tensile strength of the alloys with diameter of 2mm and 0.8mm had no obvious difference,but the elongation of the alloy decreased gradually.