Elke Schaberger-Zimmermann

The impact of melt flow on the grain orientation in solidifying metal alloys

Directional solidification experiments were performed in PbSn and AlSi alloys under the influence of a rotating magnetic field. The solidification process was started without forced melt convection before applying a sudden onset of the electromagnetic force. Just before and after the initiation of the magnetic field the grain structure was analysed. Electrolytic etching was used to identify grains having different orientations and related EBSD measurements provided quantitative values for the crystallographic orientation of the grains. Whereas a distinct asymmetric grain growth or a deflection of the columnar grains becomes obvious in case of forced melt flow, a perceivable modification of the crystal orientation cannot be detected.

Investigations of fluid flow effects on dendritic solidification: Consequences on fragmentation, macrosegregation and the influence of electromagnetic stirring

Solidification experiments and numerical simulations have been performed to improve the understanding of the complex interrelation between melt flow and the formation of dendritic structures during solidification of Al-Cu and Ga-In alloys. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Within this project special interest was focused on fragmentation and segregation phenomena. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. X-ray radioscopy was applied as a powerful tool for the visualization of dendritic growth and coarsening.

Formation of intermetallic phases in AlSi7Fe1 alloy processed onboard the ISS

This paper provides an analysis of the formation of intermetallic phases in AlSi7Fe1 alloy in samples processed onboard the ISS. Based on axial 2D cross-sections obtained from regions of pure diffusive growth and also solidified with forced melt flow, the sizes and distribution of intermetallic β-Al5FeSi phases were determined for different solidification velocities. In diffusive case the phases are larger and more homogeneously distributed than in case of induced melt flow. Additionally, especially for lower solidification velocity, the enrichment of Si and Fe in the centre part of the sample results in a few but rather large β-Al5FeSi particles.