Effect of amount of foaming agent added on easy disassembly of steel/aluminum FSW-joint by foaming weld interface

To reduce the weight of structural components, multi-material designs are widely used. However, when products reach the end of their service life, they should be easily disassembled for reuse and recycling. In this study, we attempted to facilitate disassembly by adding a foaming agent to the weld interface during the butt welding of steel (SS400) and aluminum alloy (A4045) plates by friction stir welding (FSW), causing the weld interface to foam during disassembly. By varying the amount of the foaming agent added during FSW, the expansion ratio during foaming was varied, and its effect on the fracture load was investigated. It was found that even when performing FSW between SS400 and A4045 with a foaming agent sheet placed between them, SS400 and A4045 could be firmly welded without defects, and the foaming agent had little effect on the weld strength. In addition, by foaming the weld interface of firmly welded specimens, it was found that fracture load and fracture energy could be significantly reduced, enabling the separation of SS400 and A4045 at low loads and energies. In particular, by adding 0.6 mass% or more of the foaming agent and the expansion ratio exceeds 2.0, the fracture load can be further reduced compared with that resulting from the generation of an intermetallic compound (IMC) layer. In the specimens with high foaming agent content, fractures occurred at the pores, but not at the IMC layer. Therefore, by inducing fracture at the pores, separation could be achieved while preventing the inclusion of steel in aluminum. • Disassembly of butt welded steel and aluminum alloy was attempted. • Foaming agent was added to the weld interface during the butt welding by FSW. • Foaming of weld interface was induced by heating. • Foaming weld interface enabled separation of steel and aluminum alloy at low loads. • Fractures occurred at pores of foamed part, but not at IMC layer.