CASTING' FLUIDITY OF MELT-PARTICLE SLURRY IN CAST COMPOSITES

Abstract

Casting of melt-particle slurry or suspension into composite components often creates a problem of particle segregation due to settling under dynamic conditions of flow in the mould channels. The present study has aimed to devise a set-up for investigating this phenomenon. A slurry of 10 wt% of - 325 mesh size alumina particles in molten aluminium is sucked into a channel of pipes under different levels of vacuum resulting in different flow velocities of the slurry in the pipe. The flow velocity has been measured with the help of two thermocouples by noting the time interval when the slurry reaches two predetermined points. The microstructures of the slurry solidified in the pipe while under flow at velocities of 28 cm/sec. and 40 cm/sec. have been investigated at different flow distances. It has been observed that at higher flow velocities larger clusters of particles are sucked into the pipe as compared to that at lower flow velocities. Settling during flow has resulted in an increase in particle content at the bottom of the pipe but a decrease in particle content at the top in the pipe with increasing distance of flow. It has been attributed to longer settling time available in the slurry segment which flows a longer distance. However, the particle content in the middle of the pipe is relatively uniform. It is evident that the flow velocities used in the present investigation is not sufficient to overcome the effect of particle settling which is enhanced in larger particle clusters sucked at higher flow velocities.