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

Abstract

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).