Recently, the welding of dissimilar material using high energy beam has gained greater popularity. During the process of welding, the differences in physical properties of the materials and high concentration of energy have a great influence on the related fluid flow and heat transfer characteristics in the molten pool. For the welding of a similar material, the fluid flow in the molten pool is often assumed to be laminar in nature. However, in the dissimilar material welding, the fluid flow in the molten pool is more intensive and complicated. It is necessary to take into account the effects of turbulence in the numerical model. In this paper, the simulation of laser welding of low carbon steel and stainless steel couple is carried out. A three-dimensional, transient numerical model is developed using computational fluid dynamics (CFD) method. The characteristics of heat, mass and momentum transports in the molten metal pool are investigated using both laminar and turbulent flow models under identical welding conditions of laser power and moving speed. To improve calculation accuracy, the turbulence effects are taken into account by employing a suitably modified kε model. Melting and solidification were simulated not by tracking the solid-liquid interface but using the Enthalpy-Porosity model to save calculation time. Results show that the diffusive transport is enhanced in the turbulent model. This is reflected in the reduction in the maximum values of temperature and velocity magnitude in the turbulent model in comparison to those in the laminar model. The influence of turbulence on the species transport in the molten pool is significant. The phase distribution in the turbulent simulation is found to be more uniform than that obtained in the laminar simulation. Good agreements between the experimental observations and simulation results are obtained by the proposed method. This study has laid a solid foundation for the analysis of welded joint by coupled thermo-hydro-mechanical method.

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