Numerical and experimental study on melt-pool heat transfer and weld characteristics in dual-mode fiber laser welding of aluminum alloy

A dual-mode fiber laser consisting of center and ring beams has attracted significant attention in the laser welding field owing to its ability to stabilize melt pools and reduce defect formation. In this study, a dual-mode fiber laser was adopted for butt welding of an aluminum alloy. Experimental and numerical investigations were conducted to analyze the weld characteristics and heat transfer phenomena during the process. The use of both the center and ring beams produced a funnel-like weld shape because of the low ring beam intensity, resulting only in the melting of the upper part of the workpiece. As the ring beam power increased, the temperature gradient near the solidification front, acting as a driving force for fluid flow, decreased. This contributed to the relatively gentle fluid flow and the smooth bead surface. It was also found that an increase in ring power lowered the cooling rate of the melt zone near the weld edge. Therefore, the average grain size of the weld zone increased with an increase in the ring power. The results of this study provide fundamental insights into the mechanism of dual-mode fiber laser welding.