Accelerated coarsening of Si precipitates in cold-rolled aluminum 359/SiC/20p composites

Abstract

The poor mechanical properties of cast A metal matrix composites (MMCs) have often been attributed to inadequate wetting of SiC particles by molten Al alloy and formation of detrimental reaction products (such as aluminum carbides) at the particle-matrix interface. Duralcan, Inc. recently made big progress in the casting area by preparing Al MMCs with high silicon (7--10 wt.%) containing matrix alloys. The high Si content slows down the reaction between the molten Al and SiC. Such composites still need thermomechanical treatments for improving the homogeneity of the reinforcement and the microstructure of the matrix. The authors have recently improved the ductility of a cast Al MMC from 0.4 to 11% elongation by cold-rolling to 90% reduction in thickness and subsequently heat-treating the composite. However, Al alloys with high Si contents have eutectic Si precipitates. The effects of the thermomechanical treatments on the coarsening characteristics of the Si precipitates need to be understood. Here the authors report that the heat treatment following a large cold rolling causes an accelerated growth of the Si precipitates in the composites.