Metallurgical Effects of Shunting Current on Resistance Spot-Welded Joints of AA2219 Sheets M. Jafari Vardanjani, A. Araee, J. Senkara, J. Jakubowski, and J. Godek (Submitted March 17, 2016; in revised form May 9, 2016; published online June 13, 2016) Shunting effect is the loss of electrical current via the secondary circuit provided due to the existence of previous nugget in a series of welding spots. This phenomenon influences on metallurgical aspects of resistance spot-welded (RSW) joints in terms of quality and performance. In this paper RSW joints of AA2219 sheets with 1 mm thickness are investigated metallurgically for shunted and single spots. An electro- thermal finite element analysis is performed on the RSW process of shunted spot and temperature distri- bution and variation are obtained. These predictions are then compared with experimental micrographs. Three values of 5 mm, 20 mm, and infinite (i.e., single spot) are assumed for welding distance. Numerical and experimental results are matching each other in terms of nugget and HAZ geometry as increasing distance raised nugget size and symmetry of HAZ. In addition, important effect of shunting current on nugget thickness, microstructure, and Copper segregation on HAZ grain boundaries were discovered. A quanti- tative analysis is also performed about the influence of welding distance on important properties including ratio of nugget thickness and diameter (r t ), ratio of HAZ area on shunted and free side of nugget (r HA ), and ratio of equivalent segregated and total amount of Copper, measured in sample (r Cu ) on HAZ. Increasing distance from 5 mm to infinite, indicated a gain of 111.04, 245.55, and 275.15% in r t , r HA , and r Cu , respectively, while obtained ratios for 20 mm welding distance was suitable compared to single spot. Keywords electron microscopy, modeling and simulation, optical metallography, resistance spot welding, shunting effect 1. Introduction Shunting effect is the result of current loss due to passing electrical current via the circuit established by previous welding spot(s). This phenomenon alternates electrical and temperature distribution while metallurgical performance of shunted nugget downgrades comparing to normal spot. This is a common phenomenon for a variety of products encompassing a series of welding spots. Of the most important products are aircrafts with usage of AA2219 for different parts in the product. Since final mechanical and metallurgical performance of welding spots in these products are necessary, it is important to make sure about the quality of intermittent spots. This is a noticeable reason for experimental and/or analytical investigation of shunting phe- nomenon to find solutions for optimization of the involved parameters such as welding distance between spots. This way it will be possible to reduce the negative effects of such phe- nomenon on mechanical and metallurgical quality of final nugget. 2. Literature Review One of the primitive experimental studies was performed by Hard et al. (Ref 1) who provided a method for detecting shunting path. Blair (Ref 2) and Ando et al. (Ref 3) added more parameters such as size of sheet, welding distance, geometry of electrode, and electrode force to find minimum required distance to minimize shunting effect. In different experimental studies, Senkara (Ref 4) and Zhang (Ref 5) considered shunting current on crack generation in RSW of AA5754. Although side effects of shunting current was proved on the appearance of cracks around shunted nugget, deeper investigation is required to check the precise influence of shunting current on mechan- ical aspects of shunted spots. In another experimental study, relationship of shunting intensity with surface quality was observed by Howe (Ref 6) and Wang et al. (Ref 7). Metallurgical microstructure of nugget is also considered in different aspects such as effect of microstructure on failure type by Pouranvari (Ref 8, 9). In other study, micrographs were checked to ensure about the effect of isotropy of grains of base metal on final quality of RSW joint (Ref 10) while metallographic results showed better quality of RSW spot for the sheet with isotropic grains. Although these studies tried to find a better mechanism of RSW on metallurgical quality of nuggets, wider consideration seems required to investigate microstructural alternations in nugget and HAZ after RSW process. Analytical studies of RSW are usually classified into two types. Earlier analytical studies focused on electro-thermal aspect of the process while mechanical aspect was added in the next researches. Although arithmetic part of analysis of RSW process in terms of electrical, thermal, and mechanical aspects of the process are similar for both single and shunted RSW, 3D or 2D axisymmetric finite element models used to analyze single welding spot are not appropriate to solve the problem of M. Jafari Vardanjani is on Sabbatical leave from Department of Mechanical Engineering, University of Tehran. M. Jafari Vardanjani, Department of Welding Engineering, Warsaw University of Technology, Poland, A. Araee, Department of Mechanical Engineering, University of Tehran, Iran, Postal address: Kuy-e-Daneshgah, 14395-515 Tehran, Iran; and J. Senkara, J. Jakubowski, and J. Godek, Department of Welding Engineering, Warsaw University of Technology, Poland, Postal address: Narbutta 85 St., 02-524 Warsaw, Poland. Contact e-mail: mehdijafari@ut.ac.ir. JMEPEG (2016) 25:3506–3517 ÓASM International DOI: 10.1007/s11665-016-2168-3 1059-9495/$19.00 3506—Volume 25(8) August 2016 Journal of Materials Engineering and Performance