Effects of controlled convections on dendritic microstructure and segregation during microgravity solidification

Abstract

The effect of fluid flow on the microstructure formation in Al-cast alloys is studied experimentally: During three sounding rocket missions (TEXUS 39, TEXUS 41 and MAXUS 7) four samples of the composition Al-6wt.% Si were directionally solidified upwards under a medium temperature gradient (4K/mm) at constant solidification velocities (0.06 and 0.12mm/s) without and under the influence of forced fluid flow conditions to compare diffusive solidification conditions with convective ones. The paper shows that experiments under microgravity conditions yield other microstructures as experiments under earth conditions (with and without fluid flow): The secondary dendrite arm spacing was found to decrease, as the convection effects were reduced in microgravity. For high fluid flow velocity a change to pure eutectic solidification at the axis of the samples is observed.