The Microstructure Response to Fluid Flow Fields in Al-cast Alloys

Abstract

The effect of controlled fluid flow conditions on the microstructure formation in cast Al-alloys was studied experimentally. A pure ternary Al-6wt.%Si-4wt.%Cu alloy has been directionally solidified upwards under a medium temperature gradient (3K/mm) in an aerogel-based furnace facility over a wide range of constant solidification velocities (0.015-0.15mm/s). A coil system around the sample induces a homogeneous rotating magnetic field being able to generate a controlled fluid flow in the melt close to the growing solid-liquid interface. The application of rotating magnetic fields during directional solidification results in pronounced segregation effects. For high magnetic induction and therefore high fluid flow velocity a change to pure eutectic solidification at the axis of the sample is observed. The investigations show that the microstructural features like the primary dendrite and the secondary dendrite arm spacing change in a unique manner with solidification speed and rotating magnetic induction, clearly revealing the dramatic effects of fluid flow on the solidification kinetics.