Effect of dispersion parameters and cold deformation on recrystallisation of Al–SiC composites

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Abstract
The effect of SiC whisker concentration (1–4 vol.-%), Al2O3 fine particle size and concentration (f/r=0·25–0·5 μm−1f volume concentrationr radius of particles), and degree of deformation by cold rolling (50–90%) on the recrystallisation behaviour and grain size in Al–SiC composites was studied. The result is of general interest as the Al–Al2O3–SiC composite is an alloy system with stable coarse and fine particles, the parameters of which can be varied independently over a wide range. The microstructure in the cold rolled state and initial stages of recrystallisation was examined using transmission electron microscopy. The recrystallisation temperature in different composites was determined by microhardness measurement after an isochronal heat treatment. The average grain size and grain size distribution in fully recrystallised composites were measured. It was found that the SiC whiskers act as strong nucleation sites and also enhance dynamic recovery, whereas the Al2O3 fine particles have the opposite effect. The number density of nuclei and the recrystallisation temperature were greatly affected by Al2O3 concentration and degree of cold deformation. The average grain size and the width of the grain size distribution decreased with increasing SiC content and decreasing f/r ratio of Al2O3 particles. These results were discussed and related to the effect of the parameters studied on critical nuclei size, nucleation rate, nuclei-whisker interaction, and grain growth. MST/1270