Investigation of microstructure and mechanical properties of DC04-HRP6222 steels joined by resistance spot welding method

In this study, point resistance welded joints made using DC04 and HRP6222 steel sheets, which are used in the automotive industry, were examined. Experimental studies have been carried out on the microstructural properties of point resistance welded joints made with different electrode pressures and welding currents and the effects of these properties on mechanical properties such as hardness and tensile shear. As a result of the data obtained from the experimental studies, ITAB and weld metal microstructure in the point resistance welded samples showed that the microstructure of the weld metal changed significantly compared to the base metal as a result of rapid cooling and heat input factors. After spot resistance welding, an increase in hardness occurred in the heat-affected and weld metal regions. It has been determined that the hardness strength value of HRP6222 steel is higher than that of DC04 steel. As the electrode pressure and welding current parameter values increased, hardness values, core diameter values and tensile shear load capacity increased as a result of the increase in heat input. It has been determined that the tensile shear strength properties are directly proportional to the core size. Core diameter values and tensile shear strength values were measured in B6 welded joints in HRP6222-HRP6222 junction group, where the values of. 2,4 kN electrode pressure and 8 kA welding current were the highest. During the tensile shear tests, interface, button and full button (tear) type fractures occurred in the point resistance welded samples. It has been observed that banded surfaces and hollow structures are formed in the fracture regions of the point resistance welded samples, where the rupture has started. As a result of the formation of banded surfaces in the fracture regions, brittle fracture and ductile fracture were determined in the hollow structures.