Low Cost Cast Aluminum Metal Matrix Composites Have Arrived

摘要

Aluminum metal matrix composites (MMC) have found applications in many industries, from aerospace and automotive to sporting goods and electronics packaging. Many of the primary applications have been in military components and structures, where advanced high performance materials are necessary to meet vigorous material challenges. Aluminum MMC are attractive due to their lightweight and high specific stiffness. In addition, the ceramic particle reinforcement significantly increases the wear resistance of these materials. Nevertheless, high materials costs relative to conventional aluminum alloys have been the primary limit to widespread use of such a material family. The use of particulate instead of fiber reinforcement has helped to reduce the overall material cost for those applications that do not require the additional strength obtained from fiber reinforced composites. However, for many cost sensitive industries, such as the on-highway transportation industry, widespread application of particulate reinforced MMC is still limited due to cost and availability. There are two primary components that makeup the cost of metal matrix composite feedstock material. The first is the raw material cost, which is somewhat controlled by the cost of aluminum. However, the raw material used for the reinforcement can play a significant role in the overall MMC material cost. This incurred cost can be affected through the use of alternative and less costly ceramic material options. The other source of cost is related to the compositing processes used to make the aluminum MMC materials. If the cost associated with these two aspects can be controlled and reduced, then this could enable widespread use of particle reinforced aluminum MMC materials. Metal Matrix Composites for the 21st Century (MC-21), Inc., in Carson City, Nevada, has developed a novel rapid mixing process for the production of MMC materials. This is a proprietary process, with the focus of rapidly mixing the particulate into the matrix alloy. The process claims to significantly reduce the time required for mixing, and therefore can reduce the labor and ultimately MMC material costs. In addition, it is proposed to place such a modular mixing system at the site of a foundry, producing the composite material as needed and transferring the molten material directly to the casting floor, without the need for remelting of ingot. This would potentially aid in reducing costs. Further cost savings can be realized with the use of a low cost SiC material for the reinforcement, compared to the standard F-500 grade used in the industry.