PNNL

Abstract

The mechanical properties of Metal Matrix Composites (MMCs) are strongly affected by the quality of the bond between the matrix and the reinforcing particle. In aluminum MMCs reinforced with SiC particles, the particle/matrix interface can be degraded at high temperature by the formation of aluminum carbide and aluminum/magnesium oxides. The temperature that these reactions occur at is an important process limit during melting, casting, and eventual product recycling. Recently, lower cost Al/SiC MMCs have become available that utilize less well-graded particulate and a unique rapid-mixing technique. However, as a result of the relaxed control on the particle size fraction, a significantly larger percentage of the particulate is found in the finer size ranges. This leads to an increase in the interface area between the SiC particles and the aluminum melt, and raises the possibility that detrimental aluminum carbide and oxide reactions could occur at lower temperatures, or lower time-at-temperature, than in current commercial products. In this study, we quantify by conventional, and in-situ liquid metal XRD, the time-temperature relationship for interfacial carbide/oxide formation, and compare commercially available MMC materials to MMC material produced from less well-graded SiC particulate.