FLUIDITY AND MICROSTRUCTURE FORMATION DURING FLOW OF AL-SIC PARTICLE COMPOSITES

This article presents the results of casting and spiral fluidity in a Al-7 wt% Si alloy reinforced with 10, 15, and 20 vol% SiC particles in permanent molds. The fluidity of the Al-SiC slurry increases linearly with temperature up to about 760-degrees-C. Above this temperature, t he casting fluidity of the Al-SiC particle slurry does not change sign ificantly with an increase in temperature. In several cases, the fluid ity decreased at temperatures above 760-degrees-C. The fluidity of Al- SiC melts containing 9-mum SiC particles decreased with an increase in volume percentage of SiC up to 15 vol % (the range studied), presumab ly due to an increase in the viscosity of the melt with increasing vol ume percentage of dispersoid and changes in thermophysical properties of the composite. However, the fluidity of Al-20 vol % SiC of 14-mum p article size is higher than the fluidity of Al-15 vol% SiC 9-mum parti cles, indicating the role of particle size and surface area in decreas ing fluidity. Composite slurries travel farther in a channel of larger cross sections compared to channels of smaller cross sections under s imilar conditions. Casting fluidity increases linearly with an increas e in cross section of the channel. A model has been proposed to calcul ate the values of fluidity of the composite as a function of particle volume percent. superheat, flow velocity of the melt, and the cross se ction of the flow channel. Experimental observations have been compare d with the predictions of the model, and some deviations have been att ributed to settling and segregation of SiC particles observed through microstructural examination.