Resistance and friction stir spot welding of dual-phase (DP 780)—a comparative study

Abstract

Among the AHSS, the dual-phase (DP) steels have been the subject of particular attention owing to their good combination of high strength and ductility and recent study focus on the weldability of these alloys. Resistance spot welding (RSW) is the primary sheet metal lap joining process in the manufacture of automotive assemblies. However, AHSS in RSW has revealed a number of problems that are a concern to the increased adoption of this range of alloys. Friction stir spot welding (FSSW) has been developed as an extension of friction stir welding (FSW). During FSSW, the rotating tool penetrates the sheets being weld and is then retracted producing a stir zone region that comprises a fine dynamically recrystallized microstructure. Solid-state metallurgical bonding was produced using a range of plunge rate, plunge depth, and tool rotational speed. The objective of this work is to compare the microstructure and mechanical properties on DP780 AHSS (1.6 mm thick) spot welds conducted using both process. The hardness, microstructure, failure mode, and bound area were examined. The results show that RSW has higher strength and bound area: the FSSW with decolorized advantage. Based on these results, we can provide the direction to choose the appropriate weld method.