Solidification of a binary metal alloy in a turbulent melt flow driven by AC fields


Solidification of a binary metal alloy in a turbulent melt flow driven by AC fields

Nikrityuk, P. A.; Eckert, K.; Eckert, S.

The application of an RMF during the solidification of a metal alloy may cause macrosegregations, which are the result of the secondary flow in the form of a double vortex structure appearing in a rotating flow due to the Ekman pumping effect. The aim of this work is to improve the understanding of the influence of turbulent RMF-driven flows on the final macrosegregation during unidirectional columnar and equiaxed solidification of a binary metal alloy. The weakly turbulent flow was modeled by means of direct numerical simulations in an axisymmetric approach, where the transient heat and mass transfer was simulated by means of a standard mixture model. Both types of solidification, columnar and equiaxed, were considered by the application of both a permeability and a hybrid model to treat the fluid flow in the mushy zone. Our analysis shows that the oscillations of the radial flow are damped by the rather high viscosity of the slurry region formed by the mixture of equiaxed dendrites and interdendritic liquid. The transport of the equiaxed dendrites towards the axis of the cylinder results in a faster cooling of the melt and a convex shape of the mushy zone. The final macrosegregation is significantly smaller in comparison with the columnar solidification. An increase of the Taylor number leads to a further decrease of the macrosegregation in the middle of the sample for two reasons. First, the enhancement of turbulent mixing of the rejected solute and floating dendrites with the bulk liquid mediated by the T-G vortices, and second, the transport of floating dendrites by the flow reduces the ‘washing’ effect, given by the convective transport of the rejected solute from the solid interface, in comparison with non-movable dendrites.

Keywords: solidification; melt flow; rotating magnetic field; turbulence; macrosegregation

  • Lecture (Conference)
    6th International Symposium on Turbulence, Heat and Mass Transfer, 14.-18.09.2009, Rome, Italy

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Publ.-Id: 12552