The effect of SiC particle reinforcement on the creep behavior of 2080 aluminum
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INTRODUCTION
PARTICLE-REINFORCED aluminum alloys offer significant improvements relative to monolithic alloys in room-temperature mechanical properties such as strength, modulus, fatigue resistance, and wear resistance. However, the use of particle-reinforced aluminum composites for some automotive engine applications will require the ability to withstand temperatures of up to 250 7C. As a result, properties such as creep resistance may play an important role in the materials selection process. The majority of investigations into the creep behavior of particle-reinforced aluminum alloys[1–13] have been performed at temperatures greater than 250 7C. While these studies have shown that particle reinforcement improves the creep resistance of aluminum alloys, the matrix precipitate structure is unstable in this temperature regime. As a result, trends observed at high temperatures cannot be generalized to lower temperatures, where the matrix precipitate structure is more stable. Previous work by the present authors[14,15,16] showed that in the temperature range 150 7C to 250 7C, the creep behavior of particle-reinforced aluminum alloys is strongly dependent on matrix strength and matrix strengthening mechanisms. In matrices with strong, stable microstructures (precipitation strengthened or solid solution strengthened at low temperatures), only modest creep strengthening from the addition of reinforcement is observed. This strengthening could be accurately modeled by continuum mechanics approximations for direct reinforcement strengthening. In weak matrices (e.g., pure aluminum or solid solution alloys at high temperatures), the presence of the reinforcing particles alters the matrix dislocation structure during creep, resulting in significant indirect (matrix) strengthening. P.E. KRAJEWSKI, Senior Research Engineer, is with the General Motors R&D Center, Warren, MI 48090-9055. J.E. ALLISON, Staff Scientist, is with Ford Research Laboratory, Ford Motor Company, Dearborn, MI 48124. J.W. JONES, Professor, Department of Materials Science and Engineering, and Associate Dean for Undergraduate Education, is with the College of Engineering, University of Michigan, Ann Arbor, MI 48109. Manuscript submitted January 12, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
Although indirect strengthening effects are less pronounced in precipitation-hardened composites compared to pure aluminum, particle reinforcement may affect matrix precipitate structure during both heat treatment and deformation. Reinforcing particles have been shown to alter aging kinetics in aluminum alloys, as well as precipitate size and distribution.[17,18,19] In addition, precipitate coarsening during deformation has been observed. Vyletel[20] showed that during fatigue, strain localization decreases in precipitate stability in 2219/TiC/15p. Clearly, the presence of particle reinforcement can affect matrix precipitate structure in aluminum alloys, which may lead to indirect strengthening effects that influence creep resistance. This article examines the
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