Multiphase and multiphysics modeling of dendrite growth and gas porosity evolution during solidification

Gas porosity is one of the most detrimental defects that can considerably deteriorate mechanical properties of casting parts. Simulating the interaction between gas porosity and solidifying microstructure is challenging due to multiphase and multiphysical characteristics. In this work, a solid-liquid-gas multiphase-field lattice-Boltzmann model is developed to describe the complex multiphase interaction during solidification. The model relaxes the assumption of pure metal system, simplified bubble shape and pure diffusion condition. It can consider solid growth, bubble motion, interface deformation, component transport, melt flow, and partition of both alloy solute and dissolved gas species. The model is validated in terms of mass conservation, mapping operation to the two-phase model, Laplace pressure condition, and bubble dynamics. The effectiveness of the model is further evaluated by comparing with other four models and experiments. The model is successfully used to describe the interaction between gas porosity and magnesium dendrite. The dependence of phase fractions on the characteristic parameters including melt undercooling, interface mobility coefficient and internal bubble pressure is quantified to explore the multiphase equilibrium. The proposed model can be regarded as complementary to the previous models and it is suitable for addressing the problems involving the solid-liquid-gas multiphase and multiphysical characteristics.