Numerical simulation of thermal flow dynamics in oscillating laser welding of aluminum alloy

Oscillating laser beam has good welding characteristics due to excellent management of molten thermal flow, but the potential mechanism has been still unclear. In order to describe the influences of circular beam oscillation on the thermal flow dynamics accurately, a transient numerical model of oscillating laser welding of 6061 aluminum alloy was established, whose accuracy is higher than 88% according to the verification of weld shape. The results showed that the oscillating induced vortex was the domain driving force to change the melt flow, and the strengthened convective effect was the key factor to homogenize the temperature field. The convection effect increased about 10 times when the oscillation frequency (f) increased from 20 to 200 Hz, decreasing the average temperature gradient from 1518 to 1067 K/mm. With the increase off, the melt flow gradually changed from the competition between vortex effect and convection to the dominated vortex effect. The whole pool presented as a stable vortex at a high-speed (>= 0.18 m/s) when f >= 100 Hz, where the average velocity of molten pool was equivalent to that of the vortex. At given f, the vortex effect was weakened with the increase of oscillation radius because the proportion of oscillation-driven vortex in whole molten pool reduced. It limited the vortex effect within the front fluid region, and separated some small low-speed (<= 0.06 m/s) vortexes in tail fluid region by the convection effect.