Abstract
The effect of controlled 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). The application of rotating magnetic fields (RMF) during solidification offers the possibility to create defined flow conditions in solidification processing in microgravity 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. The forced fluid flow conditions result in pronounced macrosegregation effects. For high fluid flow velocity a change to pure eutectic solidification at the axis of the samples is observed.
