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.
Highlights
The use of advanced high-strength steels (AHSS), such as dual-phase and transformation-induced plasticity (TRIP) steels, has been steadily increasing over the past few years in automotive applications [1, 2,3,4].This is due to the advantages that AHSS grades offer, in terms of higher strength that enables the automakers to decrease the vehicle weight for improved fuel economy and improved crash energy absorption for better occupant protection
To realize the microstructure change, the resistance spot welding was performed on the DP780 base metal
Based on the theory of Resistance spot welding (RSW), the heat can influence the microstructure of alloy with weld process
Summary
The use of advanced high-strength steels (AHSS), such as dual-phase and transformation-induced plasticity (TRIP) steels, has been steadily increasing over the past few years in automotive applications [1, 2,3,4].This is due to the advantages that AHSS grades offer, in terms of higher strength that enables the automakers to decrease the vehicle weight for improved fuel economy and improved crash energy absorption for better occupant protection. Management, Kaohsiung 821, Taiwan 3 Welding Division, Metal Industries Research and Development. Centre (MIRDC), Kaohsiung 811, Taiwan 4 Casting Division, Metal Industries Research and Development. Centre (MIRDC), Kaohsiung 811, Taiwan have seen increased use in automobiles steel grades that are used commercially in automotive bodies at present are those with minimum strength levels of 590 and 780 MPa. Resistance spot welding (RSW) is the predominant mode of fabrication in automotive production with a typical vehicle in North America containing about 4000 to 5000 welds. The feasibility of automotive joining of AHSS using friction stir spot welding has been recently considered [5, 6]. Comparison of resistance spot welding and friction stir spot welding for DP 600 has been reported [7], but the performance of DP 780 welded joints is still generally unknown
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