Evolution of directional solidification microstructure of Pb-80wt%Sn alloy under medium-density direct current

The effect of a medium-density DC-current and its direction on the directional solidification microstructure and cooling behavior of Pb-80wt%Sn alloy were studied. Experimental results indicated that the microstructure was refined with DC compared to the one without. With the increase of DC density, the primary (λ ₁) and secondary (λ ₂) dendrite arm spacing of the primary phase decrease clearly. It is also found that not only the intensity of the DC current but also its direction affects the microstructure. The size of λ ₁ and λ ₂, in samples treated with positive DC, decreases more clearly than in those with negative DC. The interface morphology in samples processed without and with DC is different when the current direction is changed. Finally, the mechanism of microstructure evolution is discussed.