The effect of reverse MHD stirring regimes on the structure of a crystallizing aluminum alloy

The effect of reverse MHD stirring regimes on the ingot structure and the hydrodynamics processes occurred during the crystallization of the aluminum alloy Ak7 in a cylindrical crucible was studied both experimentally and numerically. Physical experiments showed that with increasing intensity of the rotating magnetic field generating the toroidal flow of the metal the size of grains in the crystallized ingot decreases. The functional relation exhibiting a pronounced extremum between the grain size in the ingot structure and the reverse period of the rotating magnetic field was determined. Addition of the poloidal flow first causes the grain size to increase, but then this effect decreases because of the increased velocity of the poloidal flow. It was found that the relation between the grain size and the ingot hardness is rather weak. Hydrodynamic parameters that influence the ingot structure in the reverse MHD stirring regime were determined through numerical simulations. Analysis of the results indicates that the reversals have a strong effect on heat and mass transfer processes. In the range of 2 to 5 C, the energy of the vertical flow increases sharply, whereas in the experimentally studied period of reverse pulsations of the rotating magnetic field it decreases in monotone way. As this period increases, the kinetic energy of large-scale flows and the energy of turbulent pulsations increase monotonically.