Interface microstructure and formation mechanism of ultrasonic spot welding for Al-Ti dissimilar metals

The AA6061 Al and commercial pure Ti were welded by ultrasonic spot welding (USW). The focus of this investigation is the interface microstructure and joint formation. The Al-Ti USW joints were welded at the welding energy of 1100 J~ 3200 J. The joint appearance and interface microstructure were observed mainly by Optical microscope (OM) and field emission scanning electron microscope (SEM) The results indicated that good joint only can be achieved with proper welding energy of 2150 J. No significant intermetallic compound (IMC) was found under all conditions. The high energy barriers of Al-Ti and difficulties in diffusion were the main reasons for the absence of IMC according to kinetic analysis. The heat input is crucial for the material plastic flow and bonding area which plays an important role in the joint formation.