Numerical study of alloying element distribution in CO2 laser-GMA hybrid welding

This article addresses the physical assumptions and mathematical models required to precisely predict molten metal flow in CO2 laser-GMA hybrid welding and assesses that welding phenomena can be explained by the consequent simulation results. To this end, three-dimensional transient simulations of CO2 laser-GMA hybrid welding for the laser trailing the arc are conducted by combining the arc welding model and the laser welding model without any interactive effect between the two. Additionally, based on the hypothesis that fluid flow inside a molten pool might affect the alloying element distributions, an additional conservation equation is newly suggested and united with the aforementioned models to examine the hypothesis and the validity of the models. It is found that similar fusion zones and alloying element distributions are predicted by numerical simulations, although for a laser- and material-dependant quantity epsilon, which is the function of material properties and laser wavelength and decides the reflectivity together with incident angle in the simplified Fresnel's reflection model, the theoretical value of 0.08 rather than the compensated value of 0.2 is used in the simplified Fresnel's reflection model for steel and CO2 laser. It is thought that these are not only strongly affected by molten metal flow but also the assumptions and models used in the flow calculation are appropriate. However, in spite of the good prediction results, it is deemed that many effects overlooked in this study should be investigated in further studies. (C) 2010 Elsevier B.V. All rights reserved.