Enhanced recovery in a particulate-reinforced aluminium composite

The microstructural development during cold rolling and static recovery of an Al alloy (AA 2014) and an AA 2014 particulate-reinforced metal matrix composite (PMMC) was investigated. The composite contained 20 vol.% of 15 μm diameter Al2O3 particulates. Both materials were rolled at room temperature and subsequently annealed to determine the effect of the reinforcement on static recovery. The addition of the ceramic reinforcement affected the matrix deformation microstructure by refining the cellular substructure near Al2O3 particles and generating shear bands and complex deformation zones in the vicinity of particle clusters. Following deformation, room temperature storage was sufficient to decrease the hardness of the composite, and annealing at 200 °C resulted in a more rapid rate of recovery compared with the alloy. This enhanced recovery was attributable to a larger driving force brought about by the finer cell size near the particles, but internal stress relaxation and interfacial diffusion may also be important factors, particularly at ambient temperature. The Al2O3 particles, particularly those in clusters, enhanced considerably the rate of subgrain growth of the matrix. Based on models of various stages of recovery, the enhanced rate of softening in the composite is not likely to be associated with a particular mechanism but involves a number of separate, but overlapping mechanisms.