Control of Heat Balance Characteristics in Aluminum Resistance Spot Welds using Electrode Surface Patterning

This study aims to clarify the effects of electrode surface patterning and upper-lower electrode combinations on nugget morphology, heat balance, and electrode contamination behavior in aluminum resistance spot welding (RSW). As the use of aluminum increases with the growing demand for electric vehicles and lightweight body structures, issues such as heat imbalance, asymmetric nugget formation, and rapid electrode degradation arise due to its low electrical resistivity and high thermal conductivity. To address these challenges, the influence of electrode patterning on heat balance was analyzed through both SORPAS simulations and experimental evaluations. Simulation results showed that electrode patterning altered the initial current density distribution and reduced early-stage heat generation, leading to delayed nugget initiation and decreased nugget growth. When identical patterns were applied to both electrodes, the reduction in nugget height was more pronounced on the upper sheet with lower bulk resistance. Experimental cross-sectional analysis confirmed the same tendency, and the asymmetric patterning combination with a weak pattern applied to the upper electrode and a strong pattern applied to the lower electrode produced the most balanced nugget geometry. In addition, consecutive spot welding tests and dynamic resistance measurements revealed that the asymmetric patterning combination exhibited the slowest progression of electrode contamination and the latest onset of sticking, maintaining stable resistance behavior during repeated welds. These results demonstrate that applying asymmetric electrode patterning, considering material properties and bulk resistance differences, is more effective for improving heat balance and extending electrode life in aluminum RSW than symmetric pattern application.