Joining performance and thermal mechanism of stainless steel/GFRP bonding joints via single-side resistance spot welding process

As an important way of lightweight, the hybrid structure of metal and plastic has a good application prospect in the automotive field. However, traditional resistance spot welding (RSW) which was used in transportation fields could not join metal and plastic. Here, this challenge was addressed by designing the single-side resistance spot welding equipment with flexible element. The joint between 304 stainless steel (SUS304) and glass fiber reinforced plastics (GFRP) was realized. The results indicated that the flexible element ensured the stability of joining process. Mechanical interlocking and element diffusion generated at the interface. The instantaneous heat input increased with the increase of welding current, the heat accumulation increased with the increase of the welding time and the contact resistance increased with the decrease of the welding pressure, which caused increase of resistance heat. The tensile-shear force increased firstly and then decreased as the resistance heat increased. The optimum tensile-shear force was 732N and the maximum ratio of resin and glass fiber mixture was 54.4% in case of 3000-A welding current, 1.0-s welding time, and 0.3-MPa welding pressure. Fracture consisted of three parts: the decomposed molten zone (DMZ), the effective molten zone (EMZ), and squeezed bonding zone (SBZ). The area of EMZ region in which fracture mode was cohesive failure mode determined the joint strength.