Effect of a High Static Magnetic Field on the Origin of Stray Grains during Directional Solidification

The formation of stray grains in directionally solidified Al-4.5 mass% Cu alloy under an axial high static magnetic field up to 6 T has been investigated. Electron backscattering diffraction (EBSD) was performed to analysis the orientation of the stray grains. The experimental results suggest that the formation of the stray grains are significantly affected by the external magnetic field. The modification of dendrite morphology demonstrates the existence of thermoelectric magnetic effect on dendrite scale. It is implied that the thermoelectric magnetic force (TEMF) gives rise to the pinch-off of the sidebranches. When the fragments form, they will become the souce of the stray grains. Moreover, free dendritic fragment will rotate in melt and tend to align the (310) crystallographic axis along the direction of the magnetic field. This is because of the magnetic torque induced by the anisotropic susceptibility of alpha-Al crystal.