Microstructure formation in 6061 aluminum alloy during nano-second pulsed laser processing

Pulsed lasers are a very promising branch of laser material processing in terms of high productivity and quality of the resulting welds. However, laser welding of Al-based alloys is challenging due to their solidification hot cracking susceptibility. In this paper, AA6061 alloy, a widely used engineering material, was processed with a nano-second pulsed welding in keyhole mode. The influence of process parameters, such as the laser power and the pulse duration, on the weld seam microstructure and geometrical characteristics were investigated. It was found that this welding mode produced crack-free welds for all tested processing conditions. Unexpectedly, neither dendritic structures, nor heat affected zones (HAZ), were observed. This was found to be due to extremely high temperature gradients determined from the geometrical analysis of the welds, and confirmed by solidification microstructure modeling.