Effect of a high magnetic field on the morphological instability and irregularity of the interface of a binary alloy during directional solidification

The influence of an axial high magnetic field (tip to 12 T) on the stability and morphology of the liquid-solid interface of a binary alloy has been investigated experimentally during the directional solidification of the Al-0.85 wt.% Cu and Zn-2.0 wt.% Cu alloys. Experimental results indicate that the hi.-h magnetic field caused the breakdown of a planar interface into Cellular undulations and the formation of an irregular shape. Specifically. for the Zn-2.0 wt.% Cu peritectic alloy, it wavy band-like structure appears Under a high magnetic field. Moreover. the high magnetic field promoted the enrichment of the Solute Cu element in the diffusion boundary layer. A theory about the magnetization and Solute build-Up in the diffusion boundary layer Under a high magnetic field for a binary alloy has been proposed. This magnetization and solute build-up could be partly responsible for the breakdown of the planar interface and the formation of the band-like structure in it peritectic alloy. Moreover. the stresses in the solid near the interface Under a high magnetic I field were analyzed measured and simulated numerically. It is suggested that they are responsible to the interface irregularity, and are also capable of inducing the interface instability. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.