Influences of cold-sprayed steel interlayer on mechanical properties of laser welded steel/Al lap joints

Multi-material body designs have been utilized in order to achieve lightweight automobiles, though there are only a few choices in joining ultra-high strength steel to aluminum extrusions, requiring a single-side access. For this reason, the authors have developed a laser lap-joining method, using a cold-sprayed steel coating as an interlayer, though the effects of the coating's properties on the joint strength have not been investigated sys-tematically up to now. In order to improve weld performance, these influences are needed to be clarified. In this study, therefore, the influences of the coating's characteristics on joint strengths were investigated. The tensile-shear strength (TSS) and cross-tension strength (CTS) of the welds with the coating were higher than those without it, and both strengths increased as the coating became thicker. When a 2.0 mm-thick interlayer was used, the TSS and CTS reached 10.5 and 4.5 kN, which were 2.3 and 5.8 times greater, respectively, than those without the coating. It was also found that the cold-spray conditions, connected to a particle velocity, greatly influenced adhesive strengths, which were strongly associated with the joint properties. The higher the adhesive shear and peel strengths grew, the greater the TSS and CTS became, respectively. Substantial improvement in the weld performance was observed when the particle velocity in the cold-spray process was 778 m/s and above, indi-cating that the spray conditions such as types of gases, pressure and temperature, where this speed can be achieved, should be chosen.