Investigations on the diffusion bonding of titanium alloy and aluminum alloy using copper at low bonding pressure

Abstract

This research investigates the diffusion bonding of hybrid aluminum (Al)–titanium (Ti) joints using a copper (Cu) interlayer in a vacuum environment. At 610 °C and 1 MPa pressure, partial melting of Al caused deformation and misalignment, while 520 °C showed no melting of Al–Cu at the interface. A rod-shaped precipitate with primarily Al was observed at 550 °C, and grain coarsening occurred at 580 °C at the interface, accompanied by increased Cu diffusion within the Al matrix for a bonding time of 45 min. A Ti–Al-based intermetallic layer formed on the Ti side, but voids and cracks were present in the Al–Cu diffusion region at 580 °C. Hardness variation resulted from microstructural changes due to bonding temperature, particularly near the bond line due to hard intermetallic compounds. Shear strength averaged 41 MPa at 550 °C and decreased to 33 MPa at 580 °C due to grain growth, voids, and crack propagation, causing brittle joint failure at the interface. X-ray diffraction on the fracture surfaces revealed that the failure of diffusion-bonded joints is attributed to fractures through the Ti–Al-based intermetallic compounds at the interface and unbonded region.