Effect of a high axial magnetic field on the microstructure in a directionally solidified Al–Al 2Cu eutectic alloy

Abstract

The effect of a high axial magnetic field (up to 12 T) on the microstructure in a directionally solidified Al–Al 2Cu eutectic alloy has been investigated experimentally. The results show that a high magnetic field decreases the eutectic spacing and degenerates the lamellar structure into a wavy one at a low growth speed. X-ray diffraction, selected-area electron diffraction and high-resolution electron microscopy analyses indicate that the field changes the preferred orientation. The Al 2Cu crystal is oriented with the 〈0 0 1〉-crystal direction along the solidification direction (i.e., the magnetic field direction). At a pulling velocity of 0.5 μm/s, the magnetic field ( B ⩾ 4T) is responsible for the segregation; which consists of Al striations on the longitudinal section and Al-rich zones on the transverse section. The effects of the field may be attributed to the orientation of the Al 2Cu and the Al crystals and the decrease of the diffusion coefficient caused by the magnetic field.