Low-melting glasses in Bi₂O₃-B₂O₃-SiO₂-CuO system for sealing Al-50Si alloy and YSZ ceramic

The rapid advancement of hypersonic vehicles and space probes has set even more rigorous demands on the heterogeneous bonding technology between infrared window materials and their supporting structures. The application of lead-free low-melting glass solder in the Bi₂O₃-B₂O₃-SiO₂-CuO system for joining Al-50Si alloy and YSZ ceramic is investigated. The glass-forming ability, thermal properties, structural characteristics, and their impact on sealing performance were investigated by systematically adjusting the molar ratio of SiO₂ to CuO. Based on characterization results obtained from XRD, DSC, Dilatometry, FTIR, and high-temperature wettability testing, the glass composition 50Bi₂O₃-30B₂O₃-15SiO₂-5CuO was determined to be optimal for the dissimilar joining of Al-50Si alloy and YSZ ceramic. 50Bi₂O₃-30B₂O₃-15SiO₂-5CuO glass exhibited favorable wettability on both Al-50Si alloy and YSZ ceramic within the temperature range of 400-500 °C, with the optimum wetting temperature being 480 °C. Under the soldering conditions of 480 °C for 20 min, a reliable glass seal was successfully achieved between Al-50Si alloy and YSZ ceramic. Characterized by a uniform, crack-free interface, the joint's microstructure was primarily comprised of a glassy matrix containing precipitated Bi₄B₂O₉ and Bi₂O₃ phases, which contributed to an average joint shear strength of 20.9 MPa. The research provides a feasible glass solder solution for the low-temperature, non-vacuum joining of YSZ ceramics and hypereutectic Al-50Si alloy.