Effect of a low axial magnetic field on the primary Al2Cu phase growth in a directionally solidified Al–Cu hypereutectic alloy

Effect of a low axial magnetic field on the growth behavior of the primary Al2Cu phase in the Al-40 wt% Cu hypereutectic alloy during directional solidification at a low growth speed has been investigated experimentally. The results show that the application of a low magnetic field (≤1 T) causes the primary Al2Cu phase to become deformed and irregular opposed to the well developed strip-like primary phase in the absence of the field. The deformation of the primary phase is maximum when a 0.5 T magnetic field is applied. Moreover, it has been found that the magnetic field promotes a transition of the primary phase morphology from faceted growth to irregular cellular structure and makes the primary phase spacing decrease with the increase of the magnetic field intensity. From the macroscopic scale, the magnetic field causes the occurrence of a considerable radial macrosegregation. These experimental results may be attributed to the effects of thermoelectric magnetic force (TEMF) in the solid and thermoelectromagnetic convection (TEMC) in the liquid. Further, the model of these effects is presented and evaluated numerically. The results indicate that the numerical magnitude of the TEMF during directional solidification under a 0.5 T low axial magnetic field can be of the order of 103 N/m3. The force causes TEMC at different scales to modify the distribution of solute at the interface and should be responsible for the deformation, fracture and deflection of the primary phase.

► We firstly investigate the primary Al2Cu phase growth under the magnetic field.
► Magnetic field changes the primary Al2Cu phase growth behavior dramatically.
► Faceted–non-faceted transition of the primary Al2Cu phase has been found.
► Application of magnetic field causes a considerable radial macro-segregation.
► Quantitative and qualitative analyses are firstly presented to the evaluation.