Asymmetric Nugget Growth in Aluminum Resistance Spot Welding With Multi-Ring Domed Electrodes: An Experimental Study

Abstract

Resistance spot welding of aluminum alloys (Al RSW) is known to be very challenging, in part due to the undesirable and hard-to-predict asymmetric growth of the weld nugget. In this paper, two 1.2 mm thick AA6022-T4 aluminum alloy sheets were joined by RSW using multi-ring domed (MRD) electrodes to experimentally investigate the effect of sheet surface condition, electrode surface morphology, electrode material, weld schedule, and electrode tip condition on asymmetric nugget growth, as well as the resulting weld microstructure and coach peel strength. It was found that asymmetric nugget growth was most strongly influenced by sheet surface conditions and electrode materials at the positive polarity electrode side. The asymmetric nuggets exhibited a smaller nugget angle in relation to the faying surface and a wider partially melted zone (PMZ) in the sheet adjacent to the negative electrode which reduced weld mechanical strength and toughness. In addition, the asymmetric nugget growth also caused asymmetric electrode/workpiece interaction.