| Due to the drive for weight reduction in the automobile industry, near net shape parts produced by semi-solid processing of aluminum alloys are increasingly replacing traditional steel parts. Magnetohydrodynamic direct chill casting (MHD-DC) process, developed in the mid-eighties, is the method of choice to produce rheocast metal alloys for semi-solid applications. In spite of commercial applicability of the MHD-DC process there is no integrated process model available for this process. In the present work we use an experimental setup that combines directional solidification with magnetic stirring to develop a numerical model for the MHD-DC process.; We use the finite element method to solve the coupled equations of turbulent fluid flow, species transport and heat transfer with solidification on a fixed grid. Effects of the rotating magnetic field are incorporated through a body-force term which is determined a priori based on a detailed analytical study and experimental data. Due to the nature of temperature-solute coupling and the advection dominated evolution of the liquid fraction, special numerical procedures had to be implemented in the present work.; The numerical procedure used in the present work is validated against two validation problems. In the first validation problem, we apply the two-phase methodology to solve the classical problem of diffusion-dominated solidification. The good agreement between the finite element solution and the analytical solution establishes soundness of the two-phase formulation developed in this work. In the second validation problem, a finite element prediction of the flow induced in a cylindrical cavity due to a rotating magnetic field is compared with an independent spectral solution. The close agreement between two radically different solution procedures establishes the accuracy in the formulation and implementation of the both procedures.; We then simulate the experiments using the numerical model. The numerical model predicts macrosegregation effects similar to those observed in the experiments. The temperature traces obtained from experiments and predicted by the numerical calculations also agree very well. We extend the numerical framework to make microstructural predictions by generalizing existing literature in grain coarsening. |
