Investigation on the formation mechanism of irregular dendrite during directional solidification of Al-Cu alloys under a high magnetic field

Al-4.5 wt%Cu alloy is directionally solidified under an axial high magnetic field and the experimental results show that the application of the magnetic field has caused the formation of complex dendrite morphology at moderate growth speeds (10-50 μm/s). Further, the EBSD technology is used to investigate the dendrite morphology and the crystallogeny orientation. The EBSD analysis reveals that the twinning and slip of dendrites have occurred during directional solidification under the magnetic field. Moreover, numerical results reveal that a unidirectional the thermoelectric magnetic force (TEMF) acts on tilted dendrites. This force may cause the dendrite fragmentation and induce the twinning and slip of dendrites. Therefore, the formation of the complex dendrite morphology during directional solidification under the high magnetic field should be attributed to the occurrence of the fragmentation, twinning and slip of dendrites.