Effect of Magnetic Stirring on the Microstructure of Eutectic Al-Si Alloys

This study focuses on the detailed investigation of the eutectic Aluminium Silicon (Al-12.6 wt% Si) alloy, which was solidified without and with a 10 mT induction rotating magnetic field (RMF). The experiments were conducted as part of the MICAST Hungary project, as the mirror experiments were solidified in the Solidification and Quenching Furnace (SQF) at the International Space Station (ISS). The mirror samples were solidified using solidification parameters similar to the ISS experiments. This study examined the meso-structure of the samples and the eutectic microstructure in both stirred (RMF-applied) and non-stirred (RMF-free) samples. Special attention was given to the influence of magnetic stirring on key microstructural features, such as the eutectic lamellae distance, the length of the lamellae, and the spatial orientation of the lamellae were investigated. Measuring and analysing these parameters gives us an overall picture of the microstructure of the eutectics. The 10 mT low-intensity RMF used in the experiment has a demonstrable effect on the formation of the eutectic structure; short aluminium dendrites concentrate at both edges of the stirred sample, and their proportion decreases as the sample approaches its end. In contrast, in the non-stirred sample, long, elongated Al dendrites solidify parallel to the direction of heat removal, and their proportion and size continuously increase as the sample progresses. Furthermore, a possible relationship was found between the decrease in the eutectic lamella length and the lamellae’s average distance.