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GEN-33.5 A Novel Method Using Electromagnetic Stirring to Improve Resistance Spot Weld Quality of Advanced High Strength Steel (AHSS)

Wednesday, June 6, 2012: 3:05 PM
Trillium 1 (Hilton Chicago/Indian Lakes Resort)
Dr. Qi Shen , Shanghai Key Laboratory of Digital Autobody Engineering, Shanghai Jiao Tong University, Shanghai, China
Prof. YongBing Li , Shanghai Key Laboratory of Digital Autobody Engineering, Shanghai Jiao Tong University, Shanghai, China
Prof. ZhongQin Lin , Shanghai Key Laboratory of Digital Autobody Engineering, Shanghai Jiao Tong University, Shanghai, China
Prof. GuanLong Chen , Shanghai Key Laboratory of Digital Autobody Engineering, Shanghai Jiao Tong University, Shanghai, China

With the widespread use of the advanced high strength steels (AHSS) in car body manufacturing, the traditional resistance spot welding (RSW) technology has faced big challenges. That is, the risk of welding defects, such as interfacial cracks and shrinkage cavities, has been raised due to the poor weldability of these lightweight materials. In the present study, a novel method aimed on RSW quality improvement of these light weight materials has been proposed through the application of electromagnetic stirring (EMS) technology. During the EMS-RSW process, an external constant magnetic field was applied perpendicular to the welding direction. Molten metal driven by both the induced magnetic field and the external magnetic field will flow in a complicated mode, which will affect the melting, heat transfer and crystallization behaviors during the weld growth. As a typical kind of AHSS, dual-phase steel (DP) DP590 and DP780 were chosen as the workpieces. Metallographic results in Figs.1(a) and (b) showed that, differing from the traditional ellipsoid resistance spot weld (RSW weld), the weld under the EMS effect (EMS-RSW weld) was peanut-shell shaped with the increased nugget diameter. In addition, within the EMS-RSW weld, crystal orientation along the faying surface of workpieces was less directional and the microstructures were refined with slightly higher uniformity in the fusion zone. Furthermore, the EMS-RSW weld exhibited higher ultimate failure load and longer elongation in tensile-shear testing shown in Fig.1(c). Besides, in fatigue testing, the EMS-RSW weld also showed longer fatigue life under dynamic tensile-shear loads. Therefore, it could be concluded that the application of EMS will improve the overall mechanical performance of RSW welds for DP steels through nugget diameter increase and grain refinement. After in-depth studies, EMS is expected to be an effective way to improve the weldability in RSW for AHSS, ultra-HSS, and even light metals.

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