Segregation behavior and microstructure evolution of Cu–Fe alloy under pulsed electric current

The analysis on solidification segregation of Cu-20Fe alloys under pulsed current conditions were performed. The results demonstrate that the liquid-solid phase transition dominates in the absence of pulsed current, with liquid-liquid phase separation restricted to localized or inter-dendritic regions. This predominance originates from the larger nucleation driving force of the Fe-rich phase and the limited time/atomic mobility for liquid–liquid coarsening under the applied cooling conditions. In contrast, the growth and coalescence of minority phases following liquid-liquid phase separation were enhanced markedly with pulsed current application. In the Fe-rich phase, the segregation at grain boundaries increased with pulse current rising, which originates from both the lowered thermodynamic barrier for segregation and the substantially accelerated diffusion kinetics. Current-driven segregation demonstrates greater prominence, compared to thermally activated diffusion-induced segregation. The velocity of Marangoni motion (V_m) is one order of magnitude smaller than the velocity of Stokes motion (V_s) under the action of the electric pulse. Suppressed Stokesian motion under pulsed current conditions, the settling velocity of the droplets decreased, which contributed to the spheroidisation of the dendrites. As the radius of separated droplets increasing, stokes motion dominates the coalescence and merging processes of droplets. In addition, the bubbles in the Cu-20Fe alloy melt under the action of the electric pulse are subjected to migrating upward and overflowing from the liquid surface, which suppressed the pore formation on the surface of the ingot or insides.