Mechanism of ultrasonic-assisted transient liquid phase bonding of 6061 Al alloy with cladded Zn-Al alloy in air

Abstract Full α-Al solid solution of the 6061 Al alloy joint was successfully achieved using ultrasonic-assisted transient liquid phase (TLP) bonding at 450 °C. The process contained two steps, both assisted by ultrasonic vibration: 1) cladding the bonding material; 2) TLP bonding in air. The molten Zn-Al alloy, with optimized composition, was cladded on the surface of 6061 Al alloy. Ultrasonic assisted TLP bonding using the cladded layer can produce a sound joint with shear strength reaching 95 % of the base metal. The optimized joint consisted of Zn diffusion layer and full α-Al solid solution of interlayer, and the oxide film was completely removed owe to the ultrasonic vibration. The existence of Zn-Al eutectic phase and voids deteriorated the joint strength when the Al content of the interlayer was 20 wt.%. The isothermal solidification completed at 450–480 °C using interlayer of Zn-15Al. Longer ultrasonic time promoted the microstructure homogenization, while residual liquid phase in the interlayer would degrade the joint strength if ultrasonic time was deficient. The ultrasonic vibration accelerated the dissolution of Al into the liquid and Zn into the substrate because of the acoustic cavitation micro-jet and acoustic streaming effects. The isothermal solidification can be finished within a bonding time of 60 s with residual liquid squeezing out during bonding process.