Evolution of interfacial structures and mechanical performance of sapphire and Sn–9Zn–2Al joints by ultrasound

A method of ultrasonic-assisted soldering was applied to join sapphire with Sn–9Zn–2Al at 250°C in air. The sapphire samples were hot-dipped in the liquid filler metal under the ultrasonic action before ultrasonic-assisted soldering. The experimental results have shown that the joints dipped for different durations had similar morphologies, while the shear strength was dependent on the dipping duration. The shear strength of the joints increased rapidly from 13 to 22 MPa within the hot-dipping duration of 50 seconds, and increased slowly to 46 MPa at 2000 seconds. The evolution of the interface structure and the fracture mode was analyzed. The interfacial strength was dominated by the deposited Al₂O₃ at the interface in the early stage. After the entire surface of sapphire was covered by deposited Al₂O₃, Zn-rich phases at the interface and the thickening of deposited Al₂O₃ layer enhanced the interfacial strength at the later stage. Our study revealed the evolution of the interface structure and the strengthening mechanism in the joint of sapphire with Sn–Zn–Al alloys.