Numerical Study on the Effects of Thermo-Electromagnetic Force on Solute Transport and Microstructural Evolution in a Directionally Solidified Al-2.5 wt.% Cu Alloy

Thermo-electromagnetic force plays a crucial role in tailoring the solidification microstructure by altering thermal-solutal buoyancy. However, while in situ synchrotron experiments offer some observations of microstructural evolution, their restricted spatial resolution and beam intensity prevent the full characterization of fluid flow and solute transport during solidification. To address this limitation, a calibrated model of a cellular automaton method coupled with a Eulerian multiphase approach is employed in this study to comprehensively investigate the impact of solute distribution on grain evolution during the directional solidification of an Al-2.5 wt.% Cu alloy under varying steady magnetic fields from 0.5 T to 4.0 T. The model incorporates heat and solute transport, nucleation, grain growth, and complex melt flows driven by thermal-solutal buoyancy, alongside thermo-electromagnetic effects and induced Lorentz forces. Simulations reveal that under a steady 0.5 T magnetic field, an elliptical copper-rich region forms near the solidification front. This solute redistribution significantly influences the development of a tilted solid–liquid interface, consistent with experimental observations. As the magnetic field strength increases, this copper-rich region transitions from an elliptical to a circular morphology. Notably, under a 4.0 T magnetic field, the tilted interface is effectively stabilized due to the suppression of grain growth. Furthermore, significant grain refinement is observed under a steady magnetic field, as the average grain size decreases from 209.3 μm without magnetic field to 122.5 μm of 0.5 T. This refinement is driven by redistribution of the copper concentration, which increases the undercooling from 1.4 K to 3.7 K and generates new nucleation zones. This solute-driven mechanism is identified as the primary cause of grain refinement under steady magnetic fields and is successfully validated by experimental results. These results shed new light on the mechanism of grain growth evolution under a steady magnetic field.