Innovative projection-assisted resistance line welding (PA-RLW) of aluminium alloys for automobile short-flange applications

Modern automobiles require lightweight yet structurally robust joining solutions for dissimilar thick short flange aluminum components, which present unique challenges due to limited bonding area and load bearing capacity. A new method called projection-assisted resistance line welding (PA-RLW) was introduced to create projection weld connections for dissimilar thick aluminum short flanges used in modern automobiles. This study employs dual optimized projections and an upslope current profile, using FEA simulations, high-speed imaging, infrared thermography, EBSD, and electrode force–time data to analyze weld behavior. Results reveal that PA-RLW reduces the G/R solidification parameter, thereby promoting a transition from columnar to equiaxed grains in the fusion zone. The characteristic force-time curve was analyzed and correlated with interrupted joints obtained at different welding times to understand the physical events that occur during PA-RLW. The PA-RLW process follows a four-stage mechanism, beginning with the collapse of projections under electrode force, followed by localized melting, nugget initiation, and lateral coalescence to form a continuous line weld. The PA-RLW mechanism was validated with Finite element analysis, Infrared (IR) thermography and high speed camera observations. Subsequently, an improved load-bearing capacity has been obtained with PA-RLW welds (∼2.85 kN ± 0.12 mm) when compared with regular Resistance Spot Welded (RSW) and Laser welded samples of similar weld length. This work demonstrates a physical relationship between the electrode-force time characteristics and weld metal evolution, offering a novel monitoring metric applicable across all RSW processes beyond PA-RLW.