Increasing the efficiency of modifying ingots made of aluminum alloy AK7 by alternately acting running and rotating magnetic fields

In recent years, to improve the quality and structure of ingots produced from aluminum alloys by semi-continuous casting, it has been suggested to use the so-called bidirectional MHD stirring. In this case, the metal poured into the hot top section of the mold is under permanent action of the traveling and rotating magnetic fields, which generate in the liquid metal a vertical and azimuthal mixing flow, respectively. However, with the application of this technique it is impossible to obtain a symmetric flow (which is important for the process of ingot formation) consisting of a poloidal and a toroidal mode due to cross coupling between the traveling and rotating magnetic fields. The article discusses the possibility of symmetrizing the flow of crystallizing metal which is in turn exposed to the rotating and traveling magnetic fields. Owing to applied in turn of the running and rotating fields, coupling between them is unfeasible. The article describes the experiments, in which the crystallizing aluminum alloy Ak7 is continuously exposed to simultaneously applied traveling and rotating magnetic fields, and the experiments, in which the traveling and rotating fields are applied in turn. The experiments have shown that the refinement of the grain structure of the crystallized alloy is mainly due to a toroidal flow generated by a rotating magnetic field. Grain coarsening is achieved by the addition of the poloidal flow driven by the traveling magnetic field to the toroidal flow. The experiments have also shown that alternatively applied traveling and rotating magnetic fields acting on the crystallizing alloy, can give rise to the flow regimes, in which the grain size (in the structure of the resulting ingot) is smaller than in the case of continuously applied magnetic fields. Moreover, in the regime of alternatively applied traveling and rotating magnetic fields, energy consumption is twice as low as in the regime of continuously operating magnetic fields. This work was supported by the RFBR grant no. 19-48-590001 r_a.