Predictions of solute mixing in a weld pool and macrosegregation formation during dissimilar-filler welding of aluminum alloys: Modeling and experiments

The solute mixing phenomena of filler and base metal melts during dissimilar-filler metal-inert gas (MIG) welding are simulated by a multi-phase lattice Boltzmann (LB) model for predicting macrosegregation formation in the weld joint. The LB models incorporates the calculations of fluid field and solute transport, and the quantitative capalibity is validated through the problem of one-dimensional liquid diffusion. For the MIG welding of AA6063 sheets with an ER5183 filler wire, the simulation results reveal that the periodic impingement of heterogeneous filler metal droplets leads to symmetrical vortex flows accompanied by the unmixed zones formed in the center. These unmixed zones locate in the bulk weld pool and would develop into macrosegregation in the weld joint. In addition, the fluid flow near the fusion boundary remains almost stagnant, which gives rise to the appearance of the thereby continuous unmixed zone. The predicted distribution of unmixed zone in the weld pool agree well with the macrosegregation patterns in the weld joint observed in the experiments. For partially mimicking the effect of external magnetic field on droplet movement recorded by a high-speed camera, random droplet flight directions are arranged in the LB simulations. With the increase of droplet impact speed (Weber number) and the arrangement of random droplet flight direction, the simulated Mg concentration in the weld pool becomes more uniform, implying that the risk of macrosegregation formation is reduced. The LB simulations provides insight for better understanding the formation of weld defects during MIG welding with a dissimilar filler metal.