Particle distribution in cast metal matrix composites—Part II

In order to achieve a good distribution of reinforcement particles in a cast metal matrix composite (MMC), the stirring action must be efficient enough to disperse the particles in a homogeneous way. In normal practice stirring takes place in a closed vessel or crucible, where efficiency cannot be seen, and simulation methods are required to inform experimental research. For this research finite element analysis, employing a specialised computational fluid dynamics package, is used to simulate the fluid flow, and thus dispersion of reinforcement material in a molten matrix alloy during stirring. The emphasis is on investigating optimum stirring conditions in order to achieve effective flow patterns to disperse the solid particles in the melt, without breaking the surface layer of the melt. The simulation shows that the stirring parameters such as stirring speed, and impeller position in the crucible have a significant effect on the flow behaviour of the fluid. These parameters interact, with various combinations generating suitable conditions for composite mixing. The model was validated using a visualisation experiment which indicates that, despite some limitations arising from the simplification of the physical situation, the model is a useful tool in specifying process parameter in the production of MMCs.