Recrystallization kinetics and final grain size in a cold rolled particulate reinforced Al-based MMC

The recrystallization kinetics and final grain size following cold rolling and annealing of an Al alloy (AA2014) and a particulate reinforced AA2014 composite containing 20 vol% alumina particulates of average diameter 15 μm were investigated. For a given level of strain (5–95% reduction), annealing was carried out at temperatures from 350 to 500 °C and heating rates from 2.5×10 −3 to 30 °C/s. The alumina particles in the composite act as potential sites for particle stimulated nucleation (PSN) of recrystallization. Compared with the alloy, recrystallization in the composite was accelerated, particularly following low levels of cold-work. This was attributed to extensive PSN at low strains in the composite and from an increased stored energy of the matrix thereby increasing the driving force for recrystallization. For a given set of processing conditions, the recrystallized grain size in the composite was finer than in the alloy. This was most notable for material strained to less than 50% reduction and annealed at low temperatures and low heating rates and was attributable to the same factors influencing the recrystallization kinetics. A model is presented for the composite to predict the recrystallized grain size as a function of strain, with respect to the size distribution and number density of alumina particles. This model predicts the strain dependence of the recrystallized grain size and, in particular, the grain size insensitivity to strain at moderate-to-high levels of cold-work.