Computational Modeling of GMAW Process for Joining Dissimilar Aluminum Alloys

A three-dimensional transient model is developed to solve for heat transfer, fluid flow, and species distribution during a continuous gas metal arc welding (GMAW) process for joining dissimilar aluminum alloys. The phase-change process during melting and solidification is modeled using a fixed-grid enthalpy-porositytechnique, and Scheil's model is used to determine coupling among composition, temperature, and the liquid fraction. The effect of molten droplet addition to the weld pool is simulated using a “cavity” model, in which the droplet heat and species addition to the molten pool are considered as volumetric heat and species sources, respectively, distributed in an imaginary cylindrical cavity within the molten pool. To establish the model for joining dissimilar alloys, results for joining two pieces of a similar alloy are also presented. The dissimilar welding model is demonstrated using a case study in which a plate of wrought aluminum alloy (with approximately 0.5 wt% Si) is butt-welded to an aluminum cast alloy plate (with approximately 10 wt% Si) of equal thickness using a GMAW process. Macrosegregation, along with the associated heat transfer and fluid flow phenomena and their role in the weld pool development, are discussed. The model is able to capture some of the key features of the process, such as differential heating of the two alloys, asymmetric weld pool development, mixing of the molten alloys, and the final composition after solidification.