Instationäre Erstarrung eutektischer Al-Si-Legierungen

Solidification research has supplied an increasing contribution in the understanding of the relation between process-based solidification parameters (e.g. velocity, temperature gradient) and microstructure parameters in cast alloys (e.g. lamella distance, dendrite spacing). This is due to the solidification experiments under stationary conditions which were performed in Bridgman type furnaces and due to numeric models for temperature and concentration fields, which explain the observed structures in cast alloys like cells or dendrites. In contrast the solidification is not stationary in real casting processes. The velocity, the temperature gradient and the alloy composition change with time and position. These effects lead to the question whether models for microstructure predictions based on stationary investigations describe correctly the structure in cast alloys. Therefore the aim of this work is to compare the microstructure of eutectic and close-eutectic Al-SI alloys, which solidified under stationary conditions, with the microstructure of alloys, which solidified under non stationary conditions. It will be shown whether the classical eutectic solidification theory of Jackson and Hunt and newer theories that based on it can describe an accelerated solidification process or not. Contrary to the usual furnaces, the facility ARTEMIS used for this work (AeRogel TEchnique for MIcrogravity Solidification) posses the capability an accelerated solidification process to control in such a way that the remaining parameters (above all the temperature gradient before the solidification front) remain constant and the entire solidification process can be tracked in-situ. Together with a large quantitative analysis of the structure new results are gained for eutectic and close-eutectic solidification, which were not possible with the usual systems and differ clearly from earlier experiments of other groups. Together with a large quantitative analysis of the microstructure new results are gained for eutectic and close-eutectic solidification, which were not possible with the usual systems and differ clearly from earlier experiments of other groups