Lightweight hybrid materials are important for future developments in transport and aerospace industries. To realize the potential of these multi material systems, we need appropriate and effective joining technologies.

This project investigated ultrasonic metal welding to develop aluminum-titanium hybrid joints in the solid state. We chose important structural aluminum and titanium alloys to produce high strength joints using advanced process control and new welding tools. The project directly compared ultrasonic spot and torsion welding techniques in order to identify the best process for structural applications. A central part of the research involved detailed experiments on the kinematics during ultrasonic welding using online laser vibrometry. The process parameters, welding force, oscillation amplitude and welding energy were determined by modern statistical methods. We investigated closely the bonding phenomena that were related to the process variant and its specific parameters. Using electron microscopy and high resolution spectroscopy we examined possible interfacial reactions like diffusion, formation of mixed crystals, and removal of passivation layers.