Channel segregation during solidification and the effects of an alternating traveling magnetic field

Abstract

The model proposed by Felicelli, Heinrich, and Poirier is used to simulate the solidification of a small two-dimensional domain of Pb-10 wt pct Sn alloy in the presence of electromagnetic stirring by different traveling fields, with or without gravity. Results show (a) enrichment of the bulk liquid by mush solute draining; (b) spontaneous formation of vertical channels, acting as ducts, significantly modified by the electromagnetic flow; and possibly (c) a finer periodic structure of subchannels. Only the last feature is sensitive to the mesh size and permeability value. Scaling analysis is used to balance Darcy, buoyancy, and electromagnetic phenomena. Attention is focused on the gradient zone at the solidification front. Electromagnetic forces can change the flow structure in the bulk liquid. In this way, they modify the pressure differences at the solidification front, changing the channel segregation pattern. Although they cannot eliminate the channels, they can control their positions and partly prevent the unsteadiness of buoyancy effects.

Studies on Decarburisation and Desiliconisation of Levitated Fe–C–Si Alloy Droplets

“…Bojarevics and Pericleous 19) have also modeled the EML droplets to show that not only intense fluid flow is generated within the droplet but the droplet can oscillate and that an additional DC field has to be used to stabilize the oscillations and turbulent velocity field. Even in the field of solidification, Medina et al 20) have shown recently that electromagnetic forces can alter the bulk flow structure altering the pressure distribution along the solidification front thereby altering solute gradients within a component.…”

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

“…Both the term ''conduction-dominated solidification'' and Eq. [7] come from the rapid solidification process where the progress of solidification depends only on the temperature profile. [19] The material properties of the alloy were calculated from a linear dependence on the mass concentration of its components and are given in Table I.…”

“…In addition, various kinds of magnetic fields can in principle be combined at random, providing the possibility to create different flow pattern as required. Previous studies particularly concerned with applications exclusively of a rotating magnetic field (RMF) [1][2][3][4] or a traveling magnetic field (TMF) [5][6][7] to solidification processes in order to achieve a purposeful alteration of the microstructure of casting ingots. Generally, the electromagnetically-driven convection promotes a transition from a columnar to an equiaxed, dendritic growth (CET) and provokes a distinct grain refining effect.…”

“…[8,9] Additional melt stirring using electromagnetic forces modifies the melt flow and hence, influences the development of such segregation defects. Medina et al [7] studied the impact of different configurations of an AC traveling magnetic field on the segregation pattern originating from thermosolutal convection. The authors found that the electromagnetic forces can control the size and the location of the channel segregates; however, segregation effects cannot be eliminated.…”

Dynamic melting and impurity particle tracking in continuously adjustable AC magnetic field

“…It is well known that forced stirring of the melt by electromagnetic forces can significantly promote the detachment of dendrite arms and transporting the crystal fragments in a disperse fashion due to the presence of high turbulence [1]. However, a unidirectional stirring in laminar conditions could induce undesirable channel segregation in the solidifying material [2]. Therefore the electromagnetic stirring must be applied in an optimized way, specifically designed for a particular solidification process.…”