Elevated Temperature Strength, Aging Response and Creep of Aluminum Matrix Composites

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Abstract
Aluminum matrix composites with reinforcement of planar-random graphite fibers, SiC whiskers, or alumina particulates have been evaluated for their high temperature performance. The composites were aged at 150 and 200°C for up to 500 hours. Microhardness results indicate accelerated aging of the composites in comparison with that of wrought 6061 Al resolutionized and aged under identical conditions. The aging response of the composites depends on the characteristics of the reinforcements. The graphite fiber reinforced composites and the silicon carbide whisker reinforced compos ites retain their tensile strength and stiffness in the overaged condition of the matrix. The composites were tested for their tensile stiffness and strength at temperatures of 150 to 350°C. The Young's modulus of all the composites remain relatively constant up to 350°C. Both the graphite fiber and silicon carbide whisker reinforced composites show substantial strength advantage over that of the wrought 6061 Al at all temperatures. The silicon car bide whisker and alumina particulate composites were evaluated for their creep behavior. These composites were subjected to creep deformation at temperatures of 232 to 350°C under stresses of up to 100 MPa. The whisker reinforced composite shows significant re sistance to creep; about two orders of magnitude lower steady state creep rates than that of the wrought aluminum. The particulate composite had a moderate increase in creep resistance.