Characterization of resistance spot welded joints between aluminum alloy and mild steel with composite electrodes

To enhance the performance of resistance spot welded joints between aluminum alloy (AA) and mild steel (MS), a specific electrode termed embedded composite electrode was used for welding. The microstructure and properties of the joints obtained under different welding parameters were characterized. The observation results on the cross-section of the joints showed an acetabuliform nugget and ring nugget formed on the AA and MS sides of the joints, respectively, and a reaction layer with bimodal thickness distribution was found at the welding interface. The maximum tensile shear of the joints reached 5.86 kN at the welding current of 26 kA. This study reveals that the resistance spot welding with composite electrodes is a promising approach for restraining the intermetallic compounds growth in the welding central region.