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

The kinetics of solidification as well as the resulting microstructure are significantly affected by convection occurring in the liquid phase. Therefore, the application of electro-magnetic fields to control solidification processes has received a growing interest. We study the grain growth in various metal alloys under the influence of a rotating magnetic field (RMF) which generates a melt flow aligned mainly perpendicular to the solidification front. Previous investigations showed an inclination of the columnar structure towards the incident flow. The tilting of the columnar grains can be explained by the transport of solute, however, the influence of the flow on the crystal orientation has not been examined so far.
Within the present study directional solidification experiments were performed in PbSn and AlSi alloys applying a sudden onset of the electromagnetic force. Just be-fore and after the initiation of the magnetic field the grain structure was analyzed. Electrolytical 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 by our measurements.