Numerical study of thermal fluid dynamics in laser welding of Al alloy with powder feeding

A numerical modeling approach is proposed for the process of powder feeding-based laser welding occurring in joining similar and dissimilar materials. For this reason, a three-dimensional computational model is developed to describe the complex physical phenomena of powder transport, laser heating, and thermal fluid dynamics in the molten pool. The VOF method in conjunction with the continuum theory is employed to study the effects of powder particles on molten pool dynamics. It is found that the addition of powder with an average temperature of 1850 K results in a lot of local low- and high-temperature zones, and small vortexes in the shallow areas of the molten pool with a depth of no more than 0.3 mm. The increasing laser power causes the smaller average depth oscillation amplitude, which visually reflects the higher keyhole stability under partial penetration welding. Note that two vortexes in the opposite direction behind the keyhole exist in full penetration welding, which are mainly driven by surface tension. The increasing average impact velocity of powder particles above 2 m/s leads to the more significant fluctuation of free surface profile, which again results in the smaller keyhole entrance size and more frequent keyhole collapses. Also, the corresponding experimental tests are carried out as verification. The findings from the study provide fundamental insights into the mechanism of melt flow and guidance in process optimization during powder feeding-based laser welding.