Institute of Continuous Media Mechanics, Ural Branch of the Russian Academy of Sciences, Perm, Russia:

S. Yu. Khripchenko, Leading Researcher, Doctor of Technical Sciences, professor, e-mail: khripch@icmm.ru
V. M. Dolgikh, Senior Researcher, Candidate of Technical Sciences

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.

1. Timofeev V., Khatsayuk M. Theoretical Design Fundamentals for MHD Stirrers for Molten Metals. Magnetohydrodynamics. 2016. Vol. 52, No. 4. pp. 495–506.
2. Borisov V. G. Technology for production of shaped products from aluminum alloys by thixoforming. Problems and solutions. Tekhnologiya legkikh splavov. 2016. No. 2. pp. 71–79.
3. Protokovilov I. V. MHD technologies in metallurgy. Sovremennaya elektrometallurgiya. 2011. Vol. 105, No. 4. pp. 32–41.
4. Borisov V. Aluminum-Dased Cmposite Billets Produced by Plasma Injectin and Thixocasting. Light metal Age. 2017. pp. 48–51.
5. Borisov V. G., Yudakov A. A., Khripchenko S. Yu., Denisov S. A., Zaytsev V. N. Device for introduction of finely divided components into matrix metal melt. Patent RF, No. 2144573. Applied: 27.06.1995. Published: 20.01.2000.

6. Grants I., Räbiger D., Vogt T., Eckert S., Gerbeth G. Application of magnetically driven tornado-like vortex for stirring floating particles into liquid metal. Magnetohydrodynamics. 2015. Vol. 51, No. 3. pp. 419–424.
7. Cramer A., Pal J., Gerbeth G. Experimental investigation of a ow driven by a combination of a rotating and a traveling magnetic eld. Phys. Fluids. 2007. No. 19. pp. 109–118.
8. Khripchenko S. Yu., Dolgikh V. М., Denisov S. А., Kolesnichenko I. V., Nikulin L. V. Formation of structure and properties of aluminum ingots under the magnetohydrodynamic conditions. Tsvetnye Metally. 2013. No. 4. pp. 70–73.
9. Eckert S., Nikrityuk P. A., Willers B., Räbiger D., Shevchenko N. et al. Electromagnetic melt flow control during solidification of metallic alloys. Eur. Phys. Journal Special Topics. 2013. Vol. 220. pp. 123–137. DOI: 10.1140/epjst/e2013-01802-7.
10. Khripchenko S. Yu., Siraev R. R. Influence of toroidal mhd stirring on liquid metal crystallization front motion and heat transfer in a cylindrical crucible. Magnetohydrodynamics. 2019. Vol. 55, No. 4. pp. 271–278. DOI: 10.22364/mhd.55.4.4.
11. Räbiger D., Leonhardt M., Eckert S., Gerbeth G. Flow control during solidification of SnPb-alloys using time-modulated AC magnetic fields. IOP Conference Series: Materials Science and Engineering. 2011. Vol. 27. DOI: 10.1088/1757-899X/27/1/012053.
12. Stiller J., Koal K., Nagel W. E., Pal J., Cramer A. Liquid metal flows driven by rotating and traveling magnetic fields. Eur. Phys. Journal Special Topics. 2013. Vol. 220. pp. 111–122.
13. Khripchenko S. Yu., Siraev R. R., Denisov S. A., Dolgikh V. M., Kolesnichenko I. V. Liquid metal flow exposed to modulated travelling and rotating magnetic fields in a cylindrical crucible. Magnetohydrodynamics. 2018. Vol. 54, No. 4. pp. 373–381. DOI: 10.22364/mhd.54.4.5.