Effects of laser oscillation on fluid flow in weld pool and macrosegregation mitigation during laser welding of Al-Si coated press-hardened steels

Abstract

For the mitigation of macrosegregations in the weld seams, an oscillating laser was applied in the laser welding of Al-Si coated press-handened steels (PHS) using a Ni foils as a interlayer. As captured by the high-speed camera, the stirring effect of the oscillating laser led to obvious fluctuations of the weld pool liquid, and the weld pool width increased with the oscillation diameter of the laser. The concentration distributions of elements Ni and Al were measured in the weld seams obtained from the laser linear and oscillationn welding. It is indicated that the macrosegregation was migitated through the laser oscillation welding with an increasing diameter. Numerical modeling of the weld pool fluid fields during laser welding was carried out by using a three-dimensional multiphase lattice Boltzmann model. The simulation results for the laser linear welding case showed that the velocity vectors with high magnitudes were symerically perpendicular to the keyhole boundary and pointed to the interior liquid phase in the weld pool. Thus, these forced convections transported the Ni and Al atoms from the weld pool center and surface to the lower part of the weld pool. In the laser oscillation welding case, however, the velocity vectors at the keyhole boundary were asymetrical as the keyhole moves, which were beneficial for efficiently mixing the weld pool liquid. The simulation results provided reasonable explanations for the different patterns of Ni and Al concentration distribuitons in the weld seams obtained from laser linear and oscillation welding.