Application of a rotating magnetic field during directional solidification of Pb-Sn alloys: Consequences on the CET


Application of a rotating magnetic field during directional solidification of Pb-Sn alloys: Consequences on the CET

Willers, B.; Eckert, S.; Nikritjuk, P. A.; Eckert, K.; Michel, U.; Zouhar, G.

Many references from the cast metal literature are known discussing the effect of melt convection during the early stages of solidification on the grain structure. The application of mechanical or electromagnetic stirring, ultrasonic or sonic vibrations promotes the formation of fine, equiaxed grains. In this paper experimental and numerical investigations will be presented concerning the influence of a flow driven by a rotating magnetic field (RMF) on the momentum, heat and mass transfer within binary Sn-Pb alloys solidified directionally. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification.
The continuum formulation based model has been adopted for numerical simulations. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution given by for a finite cylinder.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front and a shift of the mixture concentration towards the eutectic concentration on the axis of the ingots. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted downwards by increasing the field strength.

Keywords: solidification; Pb-Sn alloys; convection; rotating magnetic field

  • Lecture (Conference)
    International Conference on Advances in Solidification Processes, 07.-10.06.05, Stockholm, Sweden
  • Materials Science and Engineering A 413-414(2005), 211-216

Permalink: https://www.hzdr.de/publications/Publ-7295
Publ.-Id: 7295