Schedule and electrode design for resistance spot weld bonding Al to steels

A 2-step schedule, consisting of a pre-cleaning step followed by a welding step, and an electrode design incorporating a multistep face geometry were developed to address issues of inclusions in the aluminum fusion zone and over thickening of intermetallic compound (IMC) layer in weld bonding of aluminum to steel. The pre cleaning phase used a multi-pulse current to expel the adhesive from the contacting faces. The subsequent welding phase created a sound joint by growing aluminum nugget diameter while limiting IMC thickening and breaking down remaining inclusions. The multistep electrode contributed to effectiveness of the cleaning by boosting expulsion in the pre-cleaning stage. It also reduced reaction between the electrode and the outer surface of the aluminum via breaking down the oxide film of the aluminum and hence reducing contact resistance. The uncured RSWB joints, generated from the 2-step schedule together with the multistep electrode, had approximately 95% improvement in lap shear peak load compared to joints fabricated using the conventional 1-step welding schedule with a dome electrode. The cured RSWB joints achieved approximately 20% and 80% improvement in the peak load and energy absorption, respectively, in coach peel tests.