The effect of nucleus size on mechanical properties in electrical resistance spot welding of sheets used in automotive industry

In this study, the effects of welding current and time on the tensile-peel strength and tensile-shear strength of welding joint in electrical resistance spot welding of chromided micro-alloyed steel sheets having 0.8 mm thickness and galvanized chromided micro-alloyed steel sheets having 1.0 mm thickness were investigated. A timer and current controlled electrical resistance spot welding machine having 120 kVA capacity and pneumatic application mechanism with a single lever was used to prepare the specimens. Welding current periods of 5, 10, 15, 20 and 25 were selected and it was adjusted by increasing 1 kA from 3.5 to 10 kA during welding process. The electrode pressure was fixed at 6 kN. The obtained welding joints were exposed to tensile-peel and tensile-shear tests and their core sizes, heights and nucleus size ratios were calculated by means of an optical microscope. The effect of nucleus size ratios on tensile-peel strength and tensile-shear strength were researched by using related diagrams and the optimum welding currents and times were advised.