| The connection between aluminum and copper is the key technology in promoting the process of aluminum instead of copper in refrigeration industry, while soldering is a reliable way to solve the problem of joining aluminum and copper. For the deficiencies of the existing solders used in aluminum-copper soldering, the lead-free solder composition based on Sn-Zn system is designed optimally in order to obtain good performance of aluminum-copper connections. In this paper, the author mainly discussed melting properties, wetting properties, corrosion resistance properties and mechanical properties of Sn-Zn-Ni and Sn-Zn-Bi-Al(Ni) solder alloy, which were designed by "cluster+glue atoms". The effect of solder composition on solder microstructure and the effect of solder microstructure on wetting properties and corrosion resistance properties as well as the effect of interfacial reactions of solder joints on mechanical properties of joints were analyzed.The main conclusions were as follows:1. The study on Sn-Zn-Ni alloy solder performance shown that the addition of Ni could improve the corrosion resistance of Sn-Zn solder; In the Al/Sn-Zn-Ni/Cu joints, Al/Sn-Zn-Ni interface was mainly combined by Al-Zn-Sn solid solution, while Sn-Zn-Ni/Cu interface were connected by different Cu-Zn intermetallic compounds according to different solder composition:in the interface of A-1solder/Cu, there was only one layer of Cu5Zn8intermetal compound; However, in the interface of A-2solder/Cu, there were two layers of Cu5Zn8and Al4.2Cu3.2Zn0.7intermetal compounds; While in the interfaces of A-3solder/Cu and A-4solder/Cu, there formed two layers of Cu5Zn8and CuZns intermetal compounds.2. Three peaks were found in the DSC heating curve of Sn-Zn-Bi-Al(Ni) solder. The three peaks correspond to the melting of Sn-Zn-Bi ternary eutectic, Sn-Zn eutectic and remaining Zn respectively; In Sn-Zn based solder, the addition of Bi could reduce the surface tension of the liquid solder and improve the wetting properties of the solder, so the wettability of Sn-Zn-Bi-Al (Ni) solder was better than the Sn-9Zn solder.3. According to the solder joints of the Al/Sn-Zn-Bi-Al(Ni)/Cu, a granular Al4.2Cu3.2Zn0.7layer formed at Cu interface and a Al-Zn solid solution region formed at the Al interface. During the aging process of Al/Sn-Zn-Bi-Al/Cu solder joints, no significant transformation in the microstructure at the Al interface of the solder joints was observed. The layer of intermetallic compounds at Cu interface increased with the increase of the aging time, while the joint shear strength decreased gradually. And the fracture location of joint turned from Al/solder interface to Cu/solder interface, which was caused by the increasing thickness of the IMCs at the Cu interface. The decrease rate of the shear strength continuously increased with the rising of Zn content. |
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