Resistance Spot Welding of Galvanized Advanced High Strength DP800 Steel

Abstract

The aim of the study is to investigate the effect of welding current on weld quality of DP800 joints obtained using resistance spot welding method. Electrogalvanized 1 mm thick DP800 steel sheets were used as the workpiece. Resistance spot welding method was applied using welding current varying between 6.5 kA and 12.0 kA with a step size of 0.5 kA. Electrode force and weld time kept constant at 3.1 kN and 14 cycle, respectively. Welded samples were subjected to several tests in order to analyze the weld quality and mechanical performance of the joints in each welding current level. Microstructure, microhardness and nugget geometry on the weld cross sectioning was examined. Afterwards, weld joints were exposed to tensile-shear test. Mechanical properties and failure modes of the fractured joints in tensile loading were analyzed. As a result, it was observed the welding current has a great impact on weld quality. Increase in welding current up to expulsion limit (9.0 kA) resulted in an increase in nugget size and an improvement in the mechanical properties of the joints. However, welding current usage beyond the expulsion limit resulted in inconsistent nugget formation and therefore deviation in the mechanical properties of the joints. As a result, it was found the optimum nugget geometry and the mechanical properties in the DP800 joints are obtained using 9.0 kA welding current.