There are many factors which influence the incorporation of particulate in metal matrix composites (MMCs). This paper presents work which examines the effect of viscosity during Al–SiC MMC production. Processing periods (up to 65 min), stirring speeds (50– 500 rpm), and re-inforcement sizes (13–100 lm) for two different viscosity levels (1 and 300 mPa s) were investigated. Computer simulations, room temperature analogue fluid simulations, and MMC castings were performed. Volume fraction results of SiC at different locations within the fluids were assessed by each of these methods and compared. From these tests, a stirring speed of 200 rpm for the lower viscosity fluid and 300 rpm for the higher viscosity fluid were found to be best in order to produce uniform distributions of SiC. In order to obtain a uniform re-inforcement distribution in the lower viscosity system, stirring periods were found to range from 14 to 170 s and for the higher viscosity system from 540 to more than 3920 s. Fully uniform suspensions remained for just a couple of seconds in the lower viscosity system compared to about an hour for the higher viscosity system. The modelling approach chosen was found to be useful in predicting settling behaviour in the semi-solid metal.