Multi-droplet Marangoni motion in immiscible AlSiBi alloys — Results of a D-2 experiment

In the Isothermal Heating Facility (IHF) of the Werkstofflabor on board the D2-mission we performed directional melting and solidification experiments with liquid immiscible AlSiBi alloys. Their main objective was to investigate the Marangoni motion of a large number of Bi droplets within a well defined temperature field ahead of the solid-liquid interface, their hydrodynamic interaction and thus the collision and coagulation processes between them. Two experiment runs were performed successfully, i.e. two samples with a Bi-content of 7 wt.% and two different melting velocities were melted and solidified. Their microstructures clearly show that the Bi droplets moved by Marangoni motion as anticipated. The mean size of the droplets increased by a factor of two and the droplet size distribution was shifted to larger sizes with a long tail showing that coagulation events dominated the coarsening of the dispersion. The results are analysed with a new kind of numerical simulation, the Discrete Multi-Particle Approach (DMPA), developed especially for the decomposition and microstructure evolution in liquid immiscible systems.