Control of solidified structures in aluminum–silicon alloys by high magnetic fields

In order to investigate the effects of high magnetic fields on the as-solidified structures of Al alloys, solidification experiments of hypoeutectic and hypereutectic Al–Si alloys under various high magnetic field conditions (up to 12 T) have been conducted. It was found that uniform magnetic fields and gradient magnetic fields affect the solidification process by Lorentz force and magnetization force, respectively. The primary silicon crystals of hypereutectic Al–Si alloys are distributed, relatively, homogeneously under uniform magnetic fields, whereas they congregate near the top surface or bottom of samples by the combined action of buoyancy and magnetization force under gradient magnetic fields. The results indicate that it is possible to control the behaviors of reinforced particles in the metal matrix and improve the material performances by using high magnetic fields in the solidification process of metal matrix composites. The experiments also showed that high magnetic fields decrease the interlamellar spacing of the eutectic structure, while there exists a certain optimum value of magnetic intensity corresponding to the minimum value of interlamellar spacing, and magnetic energy is capable of influencing thermodynamic equilibrium of solidifying system and makes the content of eutectic aluminum in eutectic structures increased.