Low-Cost Aluminum Metal-Matrix Composites

Aluminum metal matrix composites (MMCs) are appealing because of their low density and high specific stiffness. In addition, ceramic-particle reinforcement significantly increases wear resistance. Nevertheless, the high cost relative to conventional aluminum alloys has prevented widespread industrial applications. Two primary factors account for the high cost of MMCs. The first factor is the raw material cost of both the aluminum matrix material and the ceramic reinforcement particles. The second factor is related to the fabrication process. If these two factors could be controlled and reduced, then a wider range of applications becomes possible. Toward this end, Metal Matrix Composites for the 21st Century (MC-21), Inc., in Carson City, Nevada, has developed a novel process in which the particulate is rapidly mixed into the matrix alloy. The process significantly reduces the time required for mixing, and therefore can reduce the labor and, ultimately, the cost. In addition, the mixing system may be placed at a foundry, and the molten material may be transferred directly to the casting floor without the need for remelting of the ingot. Furthermore, the selection of a lower-cost material for the reinforcement, rather than the expensive F-500 grade, would also reduce the expense. The economics of the MC-21 rapid mixing process and lower-cost raw materials show a strong potential for being able to produce a castable 359/SiC/20p aluminum MMC product for close to 2.20 dollars per kg (1 dollar /lb). This article describes current MMC mixing processes. Then the MC-21 process is discussed, with details provided of its operation, showing how it can reduce costs. (CSA)