Revealing the Influential Mechanism of the Direct Current on Columnar-to-Equiaxed Transition in Directionally Solidified Al–15Sn–1Cu Alloy Under 10 T Magnetic Field

The effect of the direct current (DC) on the solidification structure in the directional solidification of Al–15Sn–1Cu alloy under 10 T magnetic field was investigated experimentally and numerically. The experimental results show that coarse columnar grains are observed when no DC is applied. However, the microstructure transforms from columnar dendrites to irregular dendrites, and the columnar-to-equiaxed transition (CET) occurs with the application of DC. The numerical results show that the Lorentz force acting on the dendrites can be increased by the application of DC. Additionally, the torque created by the Lorentz force results in the stress concentration at the roots of dendrites arms. The stress increases with the DC when it is larger than the thermoelectric current. Consequently, the dendrites break into fragments when the stress exceeds a certain value and CET occurs. The results indicate that the application of DC facilitates CET at higher withdrawal speeds. Furthermore, this work may initiate a novel method for CET via applying the DC in directional solidification under 10 T magnetic field.