DESIGN,PROCESSING AND EVALUATION OF FUNCTIONALLY GRADIENT MATERIALS BY MEANS OF CENTRIFUGAL CASTING METHOD

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When the centrifugal casting method is employed in the production process of metal matrix composite, it is possible to control the distribution of reinforcement in radial direction. The present research project is intended to clarify the effect of casting conditions on the mechanical properties of the metal matrix composite from both experimental and theoretical points of view. The following results are obtained through the project.1.Experimental results : A metal matrix composite, which is composed of Al-alloy as the matrix and SiC-particles as the reinforcement, is produced by means of a centrifugal casting apparatus. The matrix is too rapidly solidified around the casting mold and so the reinforcement is not sufficiently distributed over the thickness, although the volume fraction of the reinforcement in general increases with radius. This can be improved by heating the surrounding mold. The casting pressure due to centrifugal force strengthens the bonding resistance between the matrix and reinforcement. Therefore the casting conditions, such as the casting speed as well as the mold temperature, have a predominant influence on the mechanical property of the products.2.Numerical results : A numerical simulation is carried out in order to evaluate both the distribution of reinforcement and the residual stresses, based on the finite element method. The simulated results of the SiC-particle distribution show good agreement with the experimental data. And higher casting speed is needed in order to obtain a final product with highly gradient content of the reinforcement. It is shown that larger residual stress is induced through the processing when including higher volume fraction of the reinforcement in the metal matrix composite.