Solid State Joining of Thin Hybrid Sandwiches Made of Steel and Polymer: a Feasibility Study

The growing demand for more environmentally friendly vehicles has led to an increased use of light materials in the transportation industry with the aim to reduce structural weight, fuel consumption, and gas emissions, thereby boosting cost-effectiveness and recyclable properties. Complex multi-material steel-based components would allow to improve mechanical properties and minimize weight even further. In particular, new sandwich materials made by steel outer skins and a polymeric internal layer seems very promising for obtaining mechanical performance and lightness at the same time. Unfortunately, traditional welding techniques, like arc welding, laser welding, and resistance spot welding, usually used to join steels and aluminum alloys, cannot be applied for these materials due to their peculiar nature. In this paper, the feasibility of Friction Stir Welding to join thin sandwich components made of two steel outer layers and an internal polymeric layer was assessed. Both a pin and a pinless tool were used to weld the upper and the lower surface of the joint in order to obtain solid state bonding of the metal and fusion welding of the polymer at the same time.