Effects of electrode degradation on electrode life in resistance spot welding of aluminum alloy 5182

Electrode endurance tests were conducted to investigate the effects of electrode degradation on electrode life in resistance spot welding of 1.5-mm-thick sheet aluminum Alloy 5182 using a medium-frequency direct-current welding machine and electrodes with tip-face diameter of 10 mm and radius of curvature of 50 mm. The observed electrode life ranged from about 400 to 900 welds even though all the process conditions were intentionally kept constant. However, despite the large variation, distinct patterns were found to correlate electrode life to electrode degradation in terms of the change in nominal electrode tip-face area and contact areas at both electrode/sheet (E/S) and sheet/sheet (S/S) interfaces. The reduction in joint strength occurred because of undersized nugget formation due to increased contact areas and hence reduced current density. The electrode degradation may be monitored by the increase in all three areas (nominal tip-face area, and E/S and S/S contact areas), but the E/S contact area is believed to be the most suitable because a minimum of extra work is needed to measure it. The button diameter, measured from peel testing, is affected by nugget diameter (current density) and possibly other factors, such as weld expulsion and porosity distribution as well.