Study of steel-aluminium joining under the influence of current waveforms using advanced CMT process variants

In the conventional GMAW process, increasing weld deposition increases the heat input, which adversely affects the steel-aluminum joint performance due to the brittle IMC layer growth. In the present work, advanced CMT variants in AA6061-T6 and galvannealed steel joining were investigated. All Fe-Al joints are made at a constant joining speed and wire feed rate with CMT process variants, viz. CMT-Standard, CMT-Advanced, CMT-Pulsed, and CMT-Pulsed-Advanced. The influence of current and voltage characteristics of process variants on the thermal profile, joint profile, IMC layer morphology, and mechanical properties of the joint was studied. The welding arc and molten droplet transfer phenomena were explained using recorded welding current and voltage waveforms synchronized with welding arc images. The FE-SEM, EDS, and XRD analyses were performed to confirm the phases and morphology of the IMC layer. The results show that the localized heating due to positive current pulses in CMT-Pulsed and CMT-Pulsed-Advanced processes affects the IMC layer morphology and induces cracks at the Fe-Al joints' root, leading to low shear tensile strength. The crack-free joints were observed with the CMT-Standard and CMT-Advanced processes. Also, with an increase in the positive CMT cycle in the CMT-Advanced process, heat input decreases and shear tensile strength increases.