Investigation of the jointability of shape memory and superelastic alloy nitinol and twip steels by electric resistance spot welding method

Technological advancements and diversified consumer demands have led manufacturers to use new-generation materials in various production areas. This study aimed to weld a Ni- and Ti-based NITINOL alloy, which has shape memory and superelastic properties and the ability to return to its original form with appropriate thermal and mechanical treatments, with TWIP steel, which is widely used in many areas, especially in the automotive industry. This aimed to combine the superior properties of both materials. Within the scope of the study, NITINOL and TWIP1000 steel samples prepared in specific dimensions were welded using a 120 kVA electric resistance spot welding machine with an electric current-controlled pneumatic system. The electrode force was kept constant at 4 kN during the welding processes; the welding duration was determined as 10, 15, 20, and 25 periods (1 period = 0.02 s), and the welding current was gradually increased between 4300 A and 13000 A. The results were evaluated by tensile shear test, microhardness measurement, electrode immersion depths, core diameters, heights and size ratios, fracture surface examinations, scanning electron microscope (SEM) and X-ray diffractometer (XRD) examinations on the obtained welded joints and in the light of the obtained mechanical and microstructural data, it was concluded that the optimum parameter was 20P cycle time and 6.5 kA current intensity.