Process And Performance Of Cu/Al Thin Tubes By High Frequency Induction Soldering

In the refrigeration industry, the aluminum has more advantages in pricethan copper and also has good conductivity and thermal conductivity,a lot ofenterprises have been adopt with aluminum instead of copper.Referred to as“aluminum Instead of copper”.The current approaches is copper/aluminumcombination way: the middle is aluminum tube,the structure of copper at bothends, this structure can reduce the cost and guaranteed performance at the sametime.Relative to other methods welding is the best way,but the study of variouswelding effect are flawed,the problems are the generation of α-Al and CuAlbrittle eutectic structure in the brazing,poor mechanics performance, poorcorrosion resistance,low production efficiency and the residual of The soft solderwill Produce chemical reaction with refrigerant that will jam the tube.The method of high frequency induction brazing has a lot of advantagessuch as Simple process、high efficiency、low cost、simple operation. In Thistest we used the new brazing structure and avoid the eutectic structure generationeffectively.At present the mainstream copper/aluminum solderis Sn-Zn,Sn-Pb,Cd-Zn, Al-Si,but there were some serious defects.According to the differentcontent of Al we can control the fusion temperature of Zn-Al in382-500℃,Zn、Al numerical of melting point and Electrodepotential is very closed,and the priceis low, with CsF-AlF3soft the Zn-Al is the best brazing solder in brazingCu/Al.The study mainly use three kinds of Zn-Al cored wire and SAC0705-Bi-Ni low silver lead-free solder by our self-designed,and through the highfrequency induction welding method to make some studies in Cu/Al brazing joint.The results of the study show that:Through the reasonable design of brazingstructure we can create excellent with Less defects joint.From the observation tothe microstructure of the joint we found that in Cu/Al solder joints thecompositions of the interfacial microstructures were Zn(Al) solid solution,Zn-Cu intermetallic compound, and Cu-Zn-Al intermetallic compound when the solderwire used was E02NC.In the interface there are so many kinds of differentorganizations, the performance is difficult to coordinate and there were air holesand a lot of intermetallic compounds at the interface in this kind of brazingjoint.Joint shear strength is32.5MPa, but the performance of corrosion resistantis poor.Meanwhile the compositions of the interfacial microstructures were Zn(Al)solid solution and Cu-Al intermetallic compound using SUPER5A solder wire. Inthis kind of brazing joint, less intermetallic compounds and soldering defectswere observed at the soldering interface than the solder joints using E02NCsolder wire.Corrosion resistant properties and joint shear strength to achievemaximum43.4MPa.The wettability of E22NC solder wire was poor on Al andwas not suggested in the high frequency induction soldering between Cu/Al thintubes.Finally low-Ag lead-free of SAC0705-Bi-Ni is very good in wettability ofCu/Al and Corrosion resistance,but its Shear strength is low.