Study on Zn-Based Solder for Cu/Al Joint with High Strength and Coating on Cu Surface
Cu/Al joints are widely applied in power electronic industry.However,brittle fracture occurs in the Cu/Al joints during long-term service,which seriously deteriorates the service safety.Zn-based solders were designed,and the properties were analyzed and optimal solder composition was obtained.The copper plate surface was modified by electroless Ni-P plating,and the Cu/Al lap brazing tests were carried out by using induction brazing and the optimal solder.The results show that increasing the Al content in the Zn-based brazing material and adding a certain amount of Cu,Ag and rare earth elements can enhance the wettability,strength and corrosion resistance of the brazing material.The nickel-phosphorus coating significantly improves the wetting performance of the Zn-based brazing material on the copper plate,changes the interface reaction of the copper-aluminum joints,and significantly refines the weld grain.The mechanical properties of the Cu/Al joint obtained using the optimized Zn-based brazing material and the electroless Ni-P plating process are significantly improved,the shear strength reaches 37 MPa and the fatigue life reaches 85000 times.
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