The experiments showed that, given constant cooling conditions, the proportion of the globulitic structure volume depends directly on the type and intensity of the electromagnetically driven flow and can be controlled by a defined setting of the magnetic field parameters. For instance, a distinct grain refinement was detected in the microstructure after electromagnetic stirring (Figures 2 and 3). At the same time, however, undesirable flow-specific segregations were observed. The Dresden scientists are therefore looking for a specific flow pattern that leads to a fine-grained globulitic structure, but not to any segregation of the phase components.
Results from the numerical simulations show that a controlled modulation of the magnetic field amplitude may generate a suitable flow pattern that significantly reduces the degree of segregation. This was taken as the basis for developing concepts for optimising the time functions for the magnetic field parameters amplitude and frequency which are examined in the solidification experiments. This approach has already brought the first clear success [1, 2].
To obtain a better understanding of correlations between the flow field ahead of the solidification front and the features of the solidification structure, the ultrasound Doppler technique was further developed at the FZD for applications in metal melts. Using this technique, flow speeds can be measured during solidification in the liquid phase for the first time .