Ultrasonic-assisted liquid phase diffusion bonding of Al alloys under low temperature and pressure for high-temperature resistance applications

A joint obtained at relatively low temperatures and serving under high temperatures has been a longstanding goal for aluminum alloy heat sinks used in extreme environments. In this work, 6063Al alloy joints were fabricated in the air by ultrasonic-assisted liquid phase diffusion bonding with an Sn-9Zn interlayer at 300 °C. The Sn element provided the possibility of diffusion bonding of Al alloys at low temperatures, and the Zn element and ultrasonic vibration could accelerate the diffusion of Sn in Al alloys. Ultrasonic vibration induced co-diffusion of the Sn and Zn elements through the grain boundary into the Al parent alloy during bonding, and the bonding interfaces of Al/Al and Al/Al₂O₃/Sn/Al₂O₃/Al were dominated by the Sn-embedded ceramic-shell structures, ensuring high joint strength at high working temperatures. A joint with a strength coefficient of 89.9 % was obtained at the lowest bonding temperature among all the current diffusion bonding processes for Al alloys. Subsequently, the formation mechanism of the joints, the co-diffusion behaviors of the Sn and Zn elements, and the evolution of the interface structure at different test temperatures were discussed.