A novel diffusion bonding of 6063Al based on a mode of diffusion-migrating and suspension-broken of surface oxide film

The breaking of surface oxide film in a technology area of ultrasonic-assisted diffusion joining manufacturing of large-size structure components is a challenge. In this work, a novel method of breaking surface oxide film of Al alloys based on first diffusion-migrating and then suspension-broken was investigated. Diffusion bonding of 6063Al alloys was performed by Zn interlayer at temperature below 400 °C. The oxide film migrated away from the Al alloy base metal by solid phase diffusion at 360 °C, and remained in the joint as a nanoscale oxide film. When temperature increased to 390 °C, the oxide film suspended in the Zn-Al eutectic liquid phase were rapidly broken up into small fragments through an instantaneous ultrasonic action (only 0.3 s). The change of sound pressure in the liquid metal proved that the suspended continuous oxide film was broken by the micro-jet acted simultaneously on both sides of oxide film induced by the ultrasonic cavitation effect. Finally, the inter-diffusion between Zn and Al at 360 °C was promoted by a longer holding time to obtain the homogeneous joint composed by Zn-Al eutectoid phase containing oxide fragments, and had a higher strength than the base metal. The breaking of oxide film and joint homogenization were performed under pressure-less condition, which effectively avoided the squeezed-out of the liquid phase. This technology shows a great potential for manufacturing large-size joint of industrial products.