Ultrasonic Liquid Phrase Diffusion Soldering And Microstructural Properties Near The Interface Of Cu/Al Dissimilar Materials

Cu/Al dissimilar joints by soldering have been used widely in modern industry. The aluminum can be used as conductor of electricity instead of copper to save resources, which it also can optimize structural properties to achieve best performance. The ultrasonic liquid phrase diffusion soldering technology is to utilize ultrasonic vibration to conduct the liquid phrase diffusion soldering for Cu/Al dissimilar joints. This method is a new technology combining with ultrasonic soldering and diffusion soldering, especially uses in the complex joint and ultra-narrow interval joint. Therefore, this technology will have a good prospect of application and extension.In the article, the Cu/Al soldering joints were obtained by ultrasonic liquid phase diffusion soldering technology, as Sn-9Zn eutectic alloy. The soldering temperature of aluminium wire pretreatment was studied by utilizing high and low temperature impact test and salt fog test. The soldering temperature, ultrasonic power density and soldering time were also examined by means of orthogonal experiment to obtain optimized parameters. The optimum soldering temperature of aluminium wire pretreatment is 380℃. The soldering temperature of Cu/Al soldering joints is 330℃, the ultrasonic power density is 0.30W/mm2 and the soldering time is 4s.The microstructure characteristics, phase constitution, fracture, element distribution and mechanical properties of soldering joints and interfacial zone were studied by means of optical microscope, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and micro-hardness tester. Moreover, the forming mechanism of Cu/Al soldering joints, elements diffusion mechanism and the effect of ultrasonic on soldered joint forming process were also analyzed and discussed. The test results indicated that the soldering seam is composed of the grayβ-Sn phrases and the needle-shaped rich-Zn phrases. It was found that lots of needle-shaped rich-Zn phrase grew from Al side interface and Cu side interface to soldering seam, and the whiskers on Cu side were fistly observed in this study. Furthermore, the inter-diffusion in the interfacial zone of Cu/Al joints was produced. Small amount of intermetallic compounds were formed in the soldering seam of Cu side near the interface, and in this region the micro-hardness is higher than that around the interface. The fracture analysis indicated that all the fractured areas of Cu/Al joints occurred near the Cu side interface, which shows a typical ductile fracture characteristic to improve creep crack resistant ofjoints.During the soldering, the cavitation and acoustic streaming of ultrasonic can not only improve the solder wetting and the interfacial atomic diffusion, but also clear the surfacial oxidation films and impurities to achieve good soldered joint. Moreover, the solder during the soldering crystallized firstly from the interface of Cu and Al side, and the diffusion velocity of Al elements is faster than Cu elements. The analysis indicated that the diffusion distance of Al elements is also longer than Cu elements in this region.