Study of mass transport in autogenous GTA welding of dissimilar metals

The transport processes associated with mixing of two dissimilar alloys in a gas-tungsten arc weld pool are investigated numerically and experimentally. The numerical model includes the electromagnetic, velocity, temperature, and concentration fields. The model is solved fully coupled using the finite element software COMSOL Multiphysics®. The simulation shows that at early times surface tension drives a toroidal vortex flow around the circumference of the weld pool. At these times, the distribution of metals in the weld pool is not uniform since the fluid flow within the melt is not fully developed. At later times, the weld pool expands and deepens, and a secondary flow develops that circulates the flow along the bottom of the weld pool and then back along its edges where it is coupled with a toroidal vortex. This flow causes the melt to quickly become homogeneous. The numerical predictions of the concentration distribution were verified by comparison with experimental results obtained from electron dispersive spectroscopy (EDS). The predicted weld-pool geometry was also in reasonable agreement with the experimental result. In examining the surface tension effects, it was found that, except at early times, the temperature driven Marangoni forces dominate the surfactant driven effects (sulfur). However, the surfactant still has an important role because it modifies the temperature sensitivity of the surface tension.