RHEOLOGICAL MODEL OF SEMISOLID A356-SIC COMPOSITE ALLOYS .2. RECONSTITUTION OF AGGLOMERATE STRUCTURES AT REST

This study is complementary to the previous paper on the dissociation of the particulate structure during shear of semi-solid A356 alloy rei nforced with SIC particles and focuses on the reconstitution of the st ructure at rest. Semi-solid composite alloys with 26% primary solid fr action are initially sheared under specific conditions in order to est ablish a dynamic equilibrium state and viscosities were then measured after varying periods of rest. The kinetics of reconstitution are pres ented using an analogous model to the dissociation of the particulate structure by defining a reconstitution parameter. The model was applie d successfully to the results of this study as well as to the data of similar studies in the literature. The kinetic reconstitution constant was observed to be about 4-9 times smaller than the dissociation cons tant and was found to increase with a decrease in the solid fraction o f primary particles, an increase in the shear rate prior to rest and a decrease in content of SIC particles. The presence of the SiC particl es was also found to oppose the tendency for the primary particles to agglomerate thus slowing down the reconstitution kinetics.