Gravity and temperature effects on particle distribution in Al–Si/SiC composites

During the EuroMIR’95 space flight four hypo-eutectic Al–Si alloy matrix composites with a SiC dispersion were made molten at different thermal gradients and solidified with a different cooling rate in the TITUS (Tubular furnace with Integrated Thermal analysis Under Space conditions) tube furnace. On comparison with the ground processed reference samples, it appears that the distribution of the particles in the molten zone is much more homogeneous in the zero gravity cast specimens. Also additional tests were performed in a high gradient furnace (ASPF — advanced solidification processing facility) and in a low gradient furnace to complement the results of the space processed samples. A higher temperature gradient, where the gradient is parallel to the direction of solidification and opposite to the gravity, gives less convection. A decrease in the cooling rate leads to larger dendrites and cells, and to a decrease of the homogeneity of the SiC particle distribution. The SiC particles settle in the terrestrial experiments, but the distribution differs as a function of the thermal profile. The SiC particles form a network in the liquid state but will, during resolidification, be pushed to the last solidified zone, between the α-Al dendrites, into the Al–Si eutectic zone.