Ultrasonic-assisted soldering of Al alloy using a novel Ni mesh reinforced Sn-9Zn solder

Ultrasonic-assisted soldering technique has gained extensive application for low-temperature bonding of Al alloys. However, using common Sn-based solders restricts the further improvement of the reliability of Al alloy joints due to their poor mechanical properties. In this study, we developed a novel low-temperature composite solder by incorporating the regular Ni mesh into Sn-9Zn solder and soldered 7075 Al alloy by ultrasonic-assisted soldering technique. The microstructure and shear properties of joints were explored with regard to the effects of soldering time and mesh counts. Results illustrated that solder seams were primarily composed of Ni mesh, Sn-Zn eutectic, β-Sn, η-Zn solid solution, and α-Al solid solution. Among them, α-Al solid solutions increased with extending the soldering time. Meanwhile, the enrichment of Zn and O elements was detected at the Al substrate interface. Significantly, the joints using 250#Ni mesh exhibited superior shear properties than those using 100#Ni mesh. The joint showed the highest shear strength of 74.39 MPa under soldering for 5 s. The above findings would broaden the technical approach of Al alloy bonding and promote engineering applications.