Rheological behavior of molten Al-SiC slurries and comparison of their behavior with metallic slurries

Abstract

In this study a new precise rotational viscometer was developed and used to measure the viscosity of molten A356 alloy containing 5, 15, and 25vol.% of 90–106 μm SiC particles at 650 and 690 °C. Three types of typical curves viscosity (η) versus volume fraction of SiC particles, shear time (t), and shear rate (γ) were derived advantage from the results of viscosity measurements. It would present the viscosity got lowered by decreasing particle volume fraction and by increasing the amounts of shear time and shear rate. In the next step, the influence of the number of aggregates on apparent viscosity was studied by the special tests, developed in this research. Also the formation of aggregates in Al-SiC composite slurries was explained and compared with metallic slurries. It concluded that the origin of aggregation in Al-SiC slurries was long range electrical forces while in metallic slurries it was micro welds between particles. it would show the rheological behavior of Al-SiC slurries could be justified according to the nature and the numbers of their aggregates. At the end, the implications of findings in order to predict the gradient of particles in functionally graded Al-SiC composites, produced by casting, were discussed.