Analysis of Nugget Formation During Resistance Spot Welding on Dissimilar Metal Sheets of Aluminum and Magnesium Alloys
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INTRODUCTION
IN the automotive industry, lightweight automobiles are in strong demand because of the related fuel consumption reduction and natural resource savings.[1,2] Aluminum and magnesium alloys belong to the structural materials of light alloy. Owing to their low density and significant mechanical properties, aluminum and magnesium alloys were adopted and are expected to be extensively used to replace steel as the primary structural material in automobiles.[3] Resistance spot welding (RSW) is a largely used and important welding process in the automotive industry; RSW has the capacity to assemble thin sheets, such as austenitic stainless steel, zinc-coated steel, titanium alloy, aluminum alloy, and magnesium alloy.[1–8] Owing to the fact that the consumption of light alloy materials in the automobile industry has been gradually increasing, the RSW of different alloys is seeing increased demand. Researchers have conducted many studies regarding the RSW of dissimilar metal materials. Galvanized steel and stainless steel sheet are widely used in the manufacture of automobiles. Marashi and others used RSW to join austenitic stainless steel and galvanized low carbon steel and studied the relationship between the failure mode and weld fusion zone characteristics, including the nugget size and microstructure. As the physical properties of both materials were close, a high welding reliability of weld joints was obtained.[9] Naffakh et al. conducted a study to characterize the welding of AISI 310 austenitic stainless steel to the YI LUO, Professor, is with the School of Material Science and Engineering, Chongqing University of Technology, Chongqing 400054, P.R. China. Contact e-mail:[email protected] JINGLONG LI, Professor, is with the State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, Shaanxi, P.R. China. Manuscript submitted April 5, 2013. Article published online July 19, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
INCONEL 657 nickel-chromium superalloy, especially the fracture mode of the joint and its characteristics.[10] A large number of studies also revealed that the quality of weld joints had a close relationship to the formation process of RSW nugget. Therefore, some researchers paid attention to the process and mechanism of RSW nugget formation. Electrical contact resistance is of critical importance in resistance welding. Feng and others studied the formation characteristics of nugget during RSW on AZ31B magnesium alloy using the numerical simulation method. The results showed that the contact resistance at the interface has a significant effect on nugget formation. The welding process parameters, including welding time and welding current level, are similar to those in Al alloy welding.[11] The contact resistance was experimentally investigated for the welding of mild steel, stainless steel, and aluminum to themselves in the experiments of Song and others. The results showed the influence of interface normal pressure, temperature, and base metal on con
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