Effect of second phase precipitates on recovery and recrystallization behaviour of cold-worked Al2024-SiCp composites

The restoration behaviour of SiC particle reinforced 2024-aluminium composite has been studied under conditions where recrystallization-grain growth and precipitation occur concurrently. An emphasis has been given to understanding the recrystallization-precipitation interaction, in the presence of SiC_p, during annealing. The composite was fabricated by a casting route followed by hot extrusion. Samples were cold deformed to a reduction in height of either 30 or 42 per cent following a heat treatment. The kinetics of recrystallization has been studied in the temperature range 100–485°C. Recrystallization has been monitored by optical microscopy, coupled with hardness measurements. It has been observed that the composite has a lower recrystallization temperature compared to that of an unreinforced alloy under identical annealing conditions. Following recrystallization, grain growth has been noticed in the composite. Although the degree of cold deformation showed some effect on the recrystallization temperature of the composite, it was found to be a weak controlling factor for average recrystallized grain size. Results showed that, in spite of the hardness reduction due to recrystallization-grain growth, the hardness of a composite can be partially restored by concurrent solid solution hardening (dissolution of precipitates) and also by the generation of dislocations during quenching to a low temperature.