Study of the Marangoni effect by FEM and AFM on microstructure properties and morphology of laser-treated Al-Fe alloy

Historically several authors have discussed the Marangoni effect. This effect is a phenomenon of interfacial turbulence provoked by surface tension gradients that might be induced by gradients in temperature, concentration and surface charge through the interface, still, it is known that this effect effectively enhances the rate of mass transfer across the interface. This phenomenon takes into consideration thermophysical and metallurgical properties of the remelting Al-alloy, laser beam parameters and boundary conditions of the process. As a result of heating the material, in the area of laser beam operation a weld pool was created, whose shape and size depends on convection caused by the Marangoni force. Numerical simulation, in general, is a powerful tool to obtain complete understanding of the physical phenomena and the underlying mechanisms of welding processes.

A 3D thermal FEM model has been built to calculate the temperature field and fluid flow field in the molten pool cross-section. Results of numerical simulation, experimental of the micrographs and morphologies were presented, discussed and checked. By FEM the fluid flow due to the Marangoni effect presents two symmetric vortices corresponding to the molten pool center line. The Marangoni effect can lead to mass transfer and interfacial turbulence, when this phenomenon is considered, maximum values of the flow velocity and as well as thermal gradient occur around on the workpiece surface, smaller velocity and thermal gradient occur in the melt pool-substrate interface, thus, the Marangoni effect was more noticeable in lower than in high laser beam velocities. This phenomenon influences and controls the quality, such as, properties of the microstructure, morphological characteristic and as well as quality of laser-treated workpiece tracks, therefore, at low laser beam velocities the morphology is higher and quality of track presents many defects than at high laser beam velocities. Simulation results were assessed with the experimental data, their results were fairly coherent. Numerical simulation is a powerful tool to obtain complete understanding of physical phenomena and underlying mechanisms of LSR-treated processes, therefore, to better use this innovative technology, for thorough physical understanding associated to molten pool phenomena.