Efficient Melt Stirring Using Pulse Sequences of a Rotating Magnetic Field: Part II. Application to Solidification of Al-Si Alloys

Abstract

The present study considers the solidification of an Al-7 wt pct Si alloy under the influence of electromagnetic melt stirring using a rotating magnetic field (RMF). The effect of a continuously applied RMF is compared with an RMF pulse sequence of alternating direction (RMF-PSAD). The resulting flow structure in a cylindrical liquid metal column has been measured by isothermal experiments using the ternary alloy GaInSn. The solidification experiments performed with the Al-7 wt pct Si alloy confirm our numerical predictions concerning the temperature field during solidification and the distribution of primary crystals and eutectic phase in the solidified samples. The application of the RMF-PSAD regime at suitable frequencies of the reversals of the magnetic field direction f P delivers an equiaxed microstructure without macrosegregation.

Flow, heat and mass transfers during solidification under traveling/rotating magnetic field

“…Based on the solidifying benchmark and the multiscale solidifying numerical modeling, it is necessary to experimentally investigate the flow behaviors driven by the socalled modulated magnetic field [6] or pulsed magnetic field [12,13]. An eutectic alloy GaInSn (melting temperature approximately equal to 10.5°C), is used as the experimental metal and is contained in a transparent rectangular cavity with a width of 1 cm, length of 10 cm, and height of 6 cm, respectively.…”

UDV study of a liquid metal vortex flow

“…Stirring provides homogenisation of inclusions and temperature distribution, grain refining and smoothing of the crystallization front (e.g. [16,17,18]). …”

Free dendrite growth under modulated flow in pure substances: two-dimensional phase-field simulations

“…Recent works devoted to the application of rotating magnetic fields (RMF) to solidification processes have shown a marked impact of the RMF onto the micro-structure evolution [1,2], in particular stimulating a grain refinement [3] in combination with an early onset of the columnarto-equiaxed transition [1]. Beside the modification of local undercooling due to an enhanced heat and mass transfer in the melt stopping the columnar front, another important source for the preferred growth of equiaxed grains in the melt is seen in the fragmentation of secondary dendrite arms.…”

“…In view of the recent effort to use temporally modulated RMF's [7,3] and tailoring the flow on the macroscale, an improved understanding is also required of the impact of the flow oscillations on the dendritic microstructure. Theoretical models exist which describe the operating state of the tip [8,9,10,11] (and references therein) under steady-state conditions for the purely diffusive growth of free dendrites, and even to some extent for the presence of flow.…”

“…we consider a thermal dendrite. In analogy to [7,3], where a sequence of Lorentz-force impulses was imposed on the melt, a sequence of velocity impulses is used here to model the periodic velocity variations, which are characteristic for this kind of modulated forced convection. To our knowledge the current work is the first numerical study of the effect of periodic-flow-induced forcing on dendrite morphology that responds qualitatively to phenomena as reported by Bouissou [5].…”