Strain-based investigation on solidification crack susceptibility of 6005 aluminium using adjustable ring mode (ARM) laser welding

Remote Laser Welding (RLW) of dissimilar metallic thin foils (below 500 µm) has fundamental importance in battery pack manufacturing where high repeatability is a strict requirement. Since the welding process is very sensitive to part-to-part gaps, it is critical to understand the physical phenomena during melting, formation of the keyhole and solidification. This study has been designed to investigate the underlying physics of the welding process and understand the influence of the laser beam wobbling and part-to-part gap on temperature fields and metal mixing. A CFD multi-physics model has been implemented and then calibrated with experimental data. Two scenarios with part-to-part gap (0 and 100 µm) have been considered during lap welding of 300 µm copper to 300 µm nickel-plated steel, with circular beam wobbling. The study has highlighted that the part-to-part gap leads to uncontrolled metal mixing. Potential strategies for weld optimization are discussed throughout the paper. Solidification cracks are among the most deteriorating defects observed in Remote Laser Welding (RLW) of 6xxx aluminium alloys. This research has been designed to study the solidification crack susceptibility during RLW of AA6005 alloy using Adjustable Ring mode (ARM) laser technology. The experimental setup included a high-speed camera on the self-restraint test rig, and the strains near the root of the solidification front were identified with a Finite Element based Digital Image Correlation (DIC) technique. This DIC technique allows the precise measurement of displacements and evaluates the strains at the root of the melt pool, and further correlates the critical strains formed near the root with the power ratios of the core and ring beam. A process window relating the total laser power and the power ratio to the cracking susceptibility was identified. Although a linear dependency exists between power ratio and weld penetration depth, the same does not apply to the crack sensitivity since a parabola-like relationship was observed. Findings suggested that the transition from coarse to fine equiaxed grains at increasing power ratios reduces the crack sensitivity to the threshold power ratio of 1.5. It reveals that the cracking susceptibility is determined by the combined effect of the grain refinement (predominant at power ratios below 1.5) and the permeability in the fusion zone (predominant at power ratios above 1.5)