Dissimilar Steel-Aluminium Friction Melt Bonding Investigation of the impact of Ultra-Sounds and Post Welding Pressure on the quality of the joint

The automotive world is constantly evolving, and one of the current objectives is to reduce vehicle fuel consumption. One way of achieving this is to lower the weight of cars by using steel and aluminium for the chassis to combine the strength and lightness of the 2 materials respectively. However welding dissimilar materials is complex, as the process creates a layer of brittle intermetallics (IM) and hot tearing that weaken the strength of the weld. The aim of increasing the mechanical strength of the weld was therefore investigated using the recently developed Friction Melt Bonding (FMB) process. The FMB of S235 and AA6061 with a cemented tungsten carbide with cobalt (WC-Co) tool was analysed for 2 different backing plates, stainless steel and brass, and was investigated under the use of ultrasound (US) emitted into the aluminium plate as well as under the application of post-weld pressure. The tests were then analysed using either SEM or mechanical shear tests. The US have no significant effect on the thickness of the IM, but they did reduce the risk of hot cracking. Post-pressure increased the height of the IM but diminished the risk of hot cracking. It also produced shear-resistant welds with a fracture in one of the materials. The technique is thus promising and deserves further analysis.