By means of electric conductivity meter, Brinell hardness tester and optical microscope, effects of addition of RE and Al to Sn-9Zn lead-free solder on its conductivity, hardness, wetting property and the microstructure were analyzed through orthogonal experiment. Meanwhile, comparative tests with traditional Sn-Pb solder were studied. The results show that Sn-9Zn solder has better electrical property and mechanical property, but wetting property is worse, compared with traditional Sn-Pb solder. Trace RE and Al elements can significantly improve the spreading ratio and refine microstructure of Sn-9Zn solder, while conductivity and hardness still can be maintained on the original level. The comprehensive properties of solder was optimized by adding w(RE) 0.05% and w(Al) 0.10%; the spreading ratio increases by 13.4% compared to Sn-9Zn and reaches 61.98%, with hardness 20.90 HB and conductivity 8.15×106 S/m.

The microstructure and shear property of Sn-9Zn/Cu brazed joint under 150 ℃ thermal exposure conditions were investigated by means of scanning electron microscope and universal material machine.The results show that interface layer(IMC) of Sn-9Zn/Cu is leveling serrate consisting of Cu-Zn compounds.After long-time aging treatment,the growth of compounds made IMC layer thicker and coarser meanwhile the formation of Cu-Sn compounds could be found in interface layer.Accordingly,the shear strength of the joints decreased significantly,and decreased to 40.65% of its original value till 1 000 h.And the brittle fracture features of brazed joint shear fracture surface were increased during the aging treatment.

In this paper,the effect of Cu and Ce on physics and chemistry properties of Sn-Zn solder alloys was studied by means of optical microscopy(OM),differential thermal analysis(DTA)and thermo-gravimetric analysis(TGA)with adding Cu and Ce into Sn-Zn system solders alloys.The results show that,the melting temperature of alloys can be improved when adding Cu and Ce,that's because the melting temperature of Cu and Ce are higher than melting temperature of Sn-Zn system solder alloys,then the pasty range of alloy are longer and melting temperature are enhanced.When adding content of Cu is 4% and content of rare earth Ce is 0.05%,contact angle of alloy is 49°,which is the most small.From the chemistry property of alloy seeing,when the content of Cu added into solder alloys is 2%,there is a phenomenon that alloy oxidation is overweight at the beginning and weightless subsequently with adding the content of rare earth Ce;when the content of Cu added into solder alloys is 4%,alloy oxidation are agravic all the way with adding the content of rare earth Ce.In a word,the optimum alloy component is Sn-8Zn-2Cu-0.05Ce from comprehensive properties.

Effects on mechanical properties and practicality of Sn-Ag-Cu lead-free solder alloys were investigated by adding a suitable amount of Ce. The microstructure, morphology and compositions of alloys were analyzed by optical microscope, SEM and EDX. The results show that adding a suitable amount of Ce into Sn-Ag-Cu solders would make the structure of alloy fined, and the distribution of alloy structure become more homogeneous. Moreover, addition of Ce can distinctly improve ductility, the elongation ratio enhanced 6.1% after adding rare earch Ce, then making mechanical properties promoted greatly. The combination between solder alloys and substrate is tighter and the facieses are smoother by adding appropriate Ce, leading to practical properties advanced.