Effects of a high-gradient magnetic field on the migratory behavior of primary crystal silicon in hypereutectic Al–Si alloy

Abstract

The migration of primary Si grains during the solidification of Al-18 wt%Si alloy under a high-gradient magnetic field has been investigated experimentally. It was found that under a gradient magnetic field, the primary Si grains migrated toward one end of the specimen, forming a Si-rich layer, and the thickness of the Si-rich layer increased with increasing magnetic flux density. No movement of Si grains was apparent under a magnetic field below 2.3 T. For magnetic fields above 6.6 T, however, the thickness of the Si-rich layer was almost constant. It was shown that the static field also played a role in impeding the movement of the grains. The primary Si grains were refined in the Si layer, even though the primary silicon grains were very dense. The effect of the magnetic flux density on the migratory behavior is discussed.

Magnetic Interaction Between Two Non-Magnetic Particles Migrating in a Conductive Fluid Induced by a Strong Magnetic Field-an Analytical Approach

“…However, the mechanisms of how the magnetic field changes the viscosity are still unclear and the previous equation can only fit a single specific case. According to earlier research [10], the increase of the melt viscosity by the applied magnetic field can be due to the induced restriction force when the particle is moving in the melt. As represented in Fig.…”

“…To elucidate the strong magnetic effect on the feeble magnetic particle-particle interaction, the interaction forces were calculated by using Equations (7) to (10) and the theoretical model in [14]. As illustrated in Fig.…”

“…As well, distinct phenomena can be observed. For instance, the agglomeration of large non-magnetic particles (e.g., several tens of µm) is restricted in a gradient magnetic field with a magnetic field of 10 T, resulting in finer primary crystal sizes in the metal matrix [8][9][10] or peculiar particle alignments [7]. The phenomena become more obvious in stronger magnetic fields [7,10].…”

“…An interparticle interaction due to the conductive fluid flow occurs in parallel with the magnetic dipole-dipole attractive force along the magnetic field direction. Some experimental results have already indicated the presence of this force [10]. However, the magnetic interaction forces are usually in very small magnitudes which make experimental validation difficult.…”

Transformation Inside a Null-Space Region and a Dc Magnetic Funnel for Achieving an Enhanced Magnetic Flux With a Large Gradient

“…The high-gradient magnetic field has been widely used in high-gradient magnetic separation (e.g., beneficiation of minerals) [19,20], micro-fluidic devices [21], biomedicine research (e.g., microchip technology for cell separations [22,23] and cell manipulations [24], as well as drug delivery by nanomagnetic particles [3,4]), wastewater treatment technology [25,26], chemical research (e.g., a high gradient magnetic field that can greatly influence chemical reaction rate [27]), the new generation of materials [28] and so on. Traditionally people obtain a gradient magnetic field simply by using an active magnet, which is an active device and limited by the heat effect.…”