Tailoring the weld microstructure to prevent solidification cracking in remote laser welding of AA6005 aluminium alloys using adjustable ringmode beam

Abstract

Solidification cracking is a prevalent defect in welding aluminium alloys which can be effectively mitigated by employing grain refinement strategies. This paper investigates the feasibility of tailoring the weld zone grain structure of 6xxx series aluminium alloys using an adjustable ring mode (ARM) laser beam to reduce the centreline cracking susceptibility. An in-process monitoring approach, comprising a high-speed camera and an ad-hoc Digital Image Correlation, was adopted to examine the strain development during laser welding on a self-restraint test rig. Results revealed that transverse strain in the weld centre exhibits a parabola-like relationship with the core/ring power ratio, with the minimum strain determined at the power ratio of ∼1.5, regardless of the total power employed. The microstructural analysis demonstrated that increasing the core/ring power ratio can lead to the refinement of columnar and equiaxed grains. Furthermore, the formation of secondary equiaxed grains is promoted when the power ratio increases, and this is proved to be related to the characteristic of the ARM laser by the like-for-like comparison. Overall, a fine-tuned power ratio of 1.5 is determined in the studied material and welding configuration for achieving a centreline crack free weld, benefiting from the improved microstructure and reduced thermal strain.