Metallurgical Effects of Shunting Current on Resistance Spot-Welded Joints of AA2219 Sheets

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 distribution 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 quantitative 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, −45.55, and −75.15% in r _t, r _HA, and r _Cu, respectively, while obtained ratios for 20 mm welding distance was suitable compared to single spot.