Recrystallization in fibrous and particulate metal matrix composites

Abstract

Recrystallization behaviour has been explored for several metal matrix composites produced by powder blending followed by extrusion. Commercial purity aluminium was used as the matrix material. The composites contain a fine dispersion of Al 2O 3 (inherited from the original oxide film on the aluminium powder) in addition to the reinforcement. Both the large reinforcement particles and the fine oxide dispersion influence recrystallization. Nucleation may be stimulated by the large particles, while subsequent growth of these nuclei is inhibited by the fine dispersion as a result of Zener pinning effects. In the current study, recrystallization has been monitored by optical microscopy, coupled with hardness measurements. Increasing the reinforcement content from 10 vol.% to 20 vol.% was found to increase the nucleation efficiency at the reinforcing particles, resulting in a much finer recrystallized grain size. Short fibres were found to nucleate recrystallization more efficiently than equiaxed particles.