Using electric current to surpass the microstructure breakup limit

Relevance of electrical current distribution to the forced flow and grain refinement in solidified Al-Si hypoeutectic alloy

Significant grain refinement in cast metals can be achieved through the application of electric currents during the solidification process. The present paper investigates the distribution of electric currents on the grain size of solidified Al-7wt.%Si alloy under the application of electric current with constant parameters flowing through two parallel electrodes into the melt within a cylindrical mould. The distribution of electric current was controlled by applying an electrical insulation material coating, boron nitride (NB), to the sidewall of the electrodes. Experimental results showed that the employment of these insulated electrodes can reduce grain size in comparison with the reference case of electrodes without BN coating. Flow measurements were performed in Ga-20wt.%In-12wt.%Sn liquid metal. Higher intensity forced flow occurred when the sidewall of the electrodes was insulated. In order to understand the underlying mechanism behind the stronger forced flow, corresponding numerical simulations were performed to reveal the distributions of the electric current, magnetic field, Lorentz force, and the resultant forced flow. The results achieved indicate that the mechanism of grain refinement driven by electric current is dendrite fragmentation induced by forced flow. In addition, a novel approach to enhance the grain refinement without additional input of current energy was developed.

Electric-field-induced alignment of electrically neutral disk-like particles: modelling and calculation

This work reveals a torque from electric field to electrically neutral flakes that are suspended in a higher electrical conductive matrix. The torque tends to rotate the particles toward an orientation with its long axis parallel to the electric current flow. The alignment enables the anisotropic properties of tiny particles to integrate together and generate desirable macroscale anisotropic properties. The torque was obtained from thermodynamic calculation of electric current free energy at various microstructure configurations. It is significant even when the electrical potential gradient becomes as low as 100 v/m. The changes of electrical, electroplastic and thermal properties during particles alignment were discussed.