Effect of thermal cycles on interface evolution of vacuum diffusion bonded aluminum alloy 2A14

Wrought aluminum alloy 2A14 samples were diffusion bonded at 500℃, 530℃ and 560℃ respectively for 60 min under the bonding pressure of 4 MPa and a vacuum pressure lower than 3.4×10^-3 Pa.The bonding ratio, the morphologies of the interface and the microstructures of the base metal were examined by scanning electron microscope.The results showed that at 500℃ lower than the solid solution line, the interface after welding remained straight as original in which only a little metallurgical bonding points were presented leading to a very low bonding ratio.At 530℃ above the solid solution line but below the Al-Cu eutectic point, CuAl₂ phase joining additionally contributed to the bonding mechanism hence the bonding ratio increased apparently.When the temperature was further raised to 560℃ above the eutectic point, CuAl₂ phase dissolved and the eutectic liquid formed at the crystal boundaries. The liquid was then extruded into the interface which crashed the oxidation film and filled the interface voids so that the bonding ratio increased remarkably.Therefore, a wavy bonded interface, composed of crystal boundaries, substituted the original straight interface. Based on the analyses, a model was proposed for liquid phase formation at the cry stal boundaries and oxidation film crash.