Investigation on Resistance Spot Welding of TWIP Steel Sheets

A widespread usage of new advanced high strength TWIP steels in the automotive industry is conditional on proper assembly operations by welding. Therefore, the effects of the main important process parameters on the mechanical and microstructural properties of resistance spot welded TWIP sheets are examined here. The welding parameters used were welding current, clamping force, and welding time. An L-9(33) orthogonally array was used to design the experimental tests. The mechanical response of the welded joints was assessed by tensile shear tests and Vickers microhardness measurements. The effect of the welding parameters on the fracture mode of the tensile shear specimens was also investigated. Some combinations of the welding process parameters guaranteed acceptable tensile shear strengths for the automotive industry. The tensile shear samples mainly failed by interfacial fracture mode, while partial thickness with pull out fractures were observed in the samples welded with the highest welding current and clamping force. Improper clamping force and welding current promoted excessive metal expulsions and, in turn, the formation of welding defects in the weld spots.