PARTICLE-REINFORCED ALUMINUM AND MAGNESIUM MATRIX COMPOSITES

Particle reinforced metal matrix composites are now being produced com mercially, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together wi th the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into co nsideration to produce a high quality billet. With powder metallurgy p rocessing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing t hey are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The facto rs controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produce d by powder metallurgy, since they are required to consolidate the com posite fully. Other methods, such as spray casting, molten metal infil tration, and molten metal mixing give an essentially fully consolidate d product directly, but extrusion, etc., can improve the properties by modifying the reinforcement distribution. The mechanical properties o btained in metal matrix composites are dependent on a wide range of fa ctors, and the present understanding, and areas requiring further stud y, are discussed. The successful commercial production of metal matrix composites will finally depend on their cost effectiveness for differ ent applications. This requires optimum methods of processing, machini ng, and recycling, and the routes being developed to achieve this are considered.