Effect of a high axial magnetic field on the structure of directionally solidified Al-Si alloys

The effects of an axial high magnetic field on the growth of the alpha-Al dendrites and the alignment of the iron-intermetallics (beta-AlSiFe phases) in directionally solidified Al-7 wt% Si and Al-7 wt% Si-1 wt% Fe alloys were investigated experimentally. The results showed that the application of a high magnetic field changed the alpha-Al dendrite morphology significantly. Indeed, a high magnetic field caused the deformation of the alpha-Al dendrites and induced the occurrence of the columnar-to-equiaxed transition (CET). It was also found that a high magnetic field was capable of aligning the beta-AlSiFe phases with the < 001 >-crystal direction along the solidification direction. Further, the Seebeck thermoelectric signal at the liquid/solid interface in the Al-7 wt% Si alloys was measured in situ and the results indicated that the value of the Seebeck signal was of the order of 10 mu V. The modification of the alpha-Al dendrite morphology under the magnetic field should be attributed to the thermoelectric magnetic force acting on the alpha-Al dendrites. The magnetization force may be responsible for the alignment of the beta-AlSiFe phases under the magnetic field.