Particle Dispersion and Fluid-Particle Interaction in a Slurry of Liquid Al–Mg Alloy and Al2O3 Particles

Abstract

The influence of process parameters such as the temperature, stirring speed and position of the impeller and its size on the flow pattern of molten Al-4 mass% Mg alloy controlling the retention of Al₂O₃ particles in it has been analysed. The analysis of the mixing process was carried out with the help of a model expression for the various parameters of a concentrically agitated fluid system influencing the fluid profile at the top of the crucible. The results show that in all the choices of process parameters in this work the impeller surface has been exposed except during mixing at the holding temperature of 883 K. The exposing of the impeller has been found to play a significant role in retaining the particles in the agitated slurry. However, the retention of particles has been found to be controlled by the radius of the cylindrically rotating zone, r_c, which increases with the increase in the stirring speed and size of the impeller at a given holding temperature. The retention of particles in the slurry increases so long as r_c remains below r₃, the radius of the central region of the impeller excluding the blades. In case of low holding temperature of 883 K a large retention of alumina inside the melt without any exposure of the impeller may have been possible due to the mechanical entrapment of the particles. The observations of cold model experiments have been found to be in qualitative agreement with the results obtained in the cast composites.