Abstract: Achieving reliable bonding is critical for low-temperature active soldering in Al alloys. In this study, a novel Ti-Cu-Ni alloy mesh-reinforced SAC305 composite solder was developed for active soldering of 5A06-Al alloy at 350 °C. Effects of soldering time on the microstructure and mechanical properties of joints were investigated, and the interfacial bonding mechanism of joints was analyzed. Results showed that the (Cu, Ni)₆Sn₅ phase was formed between alloy mesh and SAC305 solder in the active composite solder, while Ti atoms were uniformly released from the alloy mesh. Metallurgical products within joints mainly comprised (Cu, Ni)₆Sn₅ and Al₃(Ni, Cu)₂ phases, which developed with increasing soldering time. An amorphous Al₂O₃ layer and a Mg-containing layer were formed at the Al substrate/SAC305 solder interface. Mg atoms could enhance the charge transfer between Ti atoms and oxide film, attracting the diffusion of Ti atoms to oxide film. The oxide film removal processes relied on the synergistic impacts of Ti and Mg. The highest shear strength of joints reached 53.21 ± 0.91 MPa, exceeding previously reported properties for low-temperature active soldering by over 100 %. This exploration may provide insights into developing low-temperature active soldering technologies for Al alloys.

Key words: 5A06-Al alloy, Ti alloy mesh, Active soldering, Interfacial bonding mechanism, Shear strength