The effects of Ni on the properties of the Sn-2.5Ag-0.7Cu-0.1Re solder alloy and its creep properties of solder joints are researched. The results show that with adding 0.05wt% Ni in the Sn-2.5Ag-0.7Cu-0.1Re solder alloy, the elongation can be sharply improved without decreasing its tensile strength and it is 1.4 times higher than that of the commercial Sn-3.8Ag-0.7Cu solder alloy. Accordingly the creep rupture life of Sn-2.5Ag-0.7Cu-0.1Re-0.05Ni solder joints is the longest, which is 13.3 times longer than that of Sn-2.5Ag-0.7Cu-0.1Re and is also longer than that of the commercial Sn-3.8Ag-0.7Cu solder alloy. In the same environmental conditions, the creep rupture life of Sn-2.5Ag-0.7Cu-0.1Re-0.05Ni solder joints can sharply decrease with increasing the temperature and stress.

Creep property of solder alloys is one of the important factors to effect the reliability of surface mount technology (SMT) soldered joints. The creep behavior and its rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints were separately investigated and predicted under constant temperature by a single shear lap creep specimen with a 1mm2 cross sectional area and finite element method (FEM) in this paper. Results show that the creep property of Sn2.5Ag0.7Cu0.1RE is superior to that of the commercial employed lead-free solder Sn3.8Ag0.7Cu and the creep rupture life of its soldered joints is 8.4 times more than that of Sn2.5Ag0.7Cu solder. The creep rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints indirectly predicted by FEM is better in accord with that of actual testing results, which are important to design the reliability of lead-free soldered joints for SMT.

Effect of rare earth content on microstructure and interfacial reactions of low Ag content SnAgCu solder is researched by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope, energy spectrum analysis and JEM2100 ultrahigh resolution electron microscopy. The results show that proper quantities of rare earth (0.1%) can refine the eutectic microstructure of the solder alloy; and petal-like rare earth compound can be found in the solder alloy while the rare earth addition is 0.5%. The growing rate of the interfacial intermetallic compound can be reduced during the soldering with adding 0.1% rare earth in the Sn2.5Ag0.7Cu solder alloy.

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Strengthened coating on the surface of 35CrMo steel alloy was deposited by electrospark process using NiCr electrode. The bond strength and microhardness of the coating was checked and the microstructure of the strengthened coating was analyzed using the optical micro-scope, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectrum (EDS). The results show that the bond strength between the coating and the base metal is 495.1MPa, and the hardness of the coating surface is about 2 times than that of the base metal, and the property of the workpieces surface has become better. The coating is a metallurgical reacting bonding layer between the base metal and the NiCr electrode, and its main ingredients are FeNi and NiCrFe.