Effect of bonding parameters on microstructure development during TGTLP bonding of Al7075 alloy

The effect of temperature, pressure and bonding time on microstructure of temperature gradient transient liquid phase (TGTLP) diffusion bonded Al7075 alloy using liquid gallium interlayer was investigated. The selected bonding method relies on using the minimum amount of liquid gallium on faying surfaces, using a very fast heating rate to reach the joining temperature and imposing a temperature gradient across the bond region. The microstructure of the diffusion bonded joints was evaluated by light optical microscopy, scanning electron microscopy and energy dispersive spectroscopy (EDS). Results show that by increasing the temperature, pressure and time of joining, a more uniform microstructure can be obtained at the joint area. The best joint microstructure was achieved at a temperature of 460 degrees C, pressure of 10 MPa and time of 10 min. EDS spot analysis indicates that brittle silicon-rich precipitates form at the joint line during TGTLP bonding.