Forming of Metal Matrix Composites

Metal matrix composites (MMCs), through a proper selection of matrix and reinforcement, offer unusual combinations of physical and mechanical properties such as high specific strength and stiffness, high thermal and electrical conductivity, high wear resistance, good corrosion resistance, and good impact and fatigue properties, together with superior thermal stability when compared to the unreinforced matrix alloys. Near net shape forming and improvements in microstructure, strength, and ductility can be achieved in discontinuously reinforced MMCs through the application of primary or secondary plastic deformation processes such as extrusion, rolling, forging, superplastic forming, or friction processing. Thermomechanical processing can be directly a part of the production process or follow a primary stage of fabrication or consolidation. Processing can be mainly divided in hot and cold working, the latter often followed by annealing. The set of processing conditions (e.g., temperature, total deformation, deformation rate) is of crucial importance with respect to the resultant microstructural and consequently mechanical properties, and must be optimized with respect to the system to be processed (matrix alloy, reinforcing hard phase, reinforcement size, and volume content).Several research groups have dedicated considerable efforts to study hot and cold forming of MMCs and their effects on microstructural and mechanical properties. In this review, the latest research findings in mechanical forming processes for MMCs are illustrated. The main emphasis is dedicated to particulate-reinforced, Al-based MMCs, due to their widespread use, although references to other significant systems, and in particular to other light metal matrices, are also given. For each treated forming process, the current advances in processing optimization and enhancement in mechanical properties and microstructure are described and discussed.