Modelling of transport phenomena in laser welding of dissimilar metals

The transport phenomena (heat transfer, fluid flow and species distribution) are numerically modelled for the case of laser welding of dissimilar metals. The model involves convection in the weld pool along with melting and mixing. The associated metallurgical phenomenon is an extremely complex one, and the present work is a preliminary attempt to model the process after making suitable assumptions. The numerical study is performed using a pressure based finite volume technique after making appropriate modifications to the algorithm to include the associated phase change processes and dissimilarity in the metal properties. The phase change process is modelled using an enthalpy-porosity technique, while the dissimilar metal properties are handled using appropriate mixture theories. As a case study, we have used dissimilar couples of copper-nickel. It is observed that the weld pool shape becomes asymmetric evert when the heat source is symmetrically applied on the two metals forming the couple. As the weld pool develops, the side melting earlier is found to experience more convection and better mixing. Corresponding experiments are performed using the same parameters as in the computations, showing a good qualitative agreement between the two results. A scale analysis is performed to predict the time scale of initiation of melting of each metal. The scale-analysis predictions show a good agreement with the numerical results.