The double-edge effect of second-phase particles on the recrystallization behaviour and associated mechanical properties of metallic materials

Recovery, recrystallization and grain growth are among the most important metallurgical heat treatment processes to soften cold worked metals and design desired microstructures and textures. Specifically the reduction in grain size can be efficiently achieved by recrystallization. While plastic cold working increases the stored energy of metals, mainly through dislocation accumulation, recovery and specifically recrystallization lead to it reduction. While recovery describes the gradual re-ordering and annihilation of the stored dislocations, primary recrystallization proceeds discontinuously by the formation and motion of high angle grain boundaries which discontinuously sweep the deformation substructure. Grain growth describes the process of competitive capillary driven coarsening of the average grain size. This chapter reviews the main mechanisms, lattice defects, and driving forces associated with recovery, recrystallization and grain growth and provides an introduction to the simulation of these phenomena.

Recovery and Recrystallization: Phenomena, Physics, Models, Simulation

The development of microstructure during the deformation and annealing of discontinuously reinforced metal-matrix composites is discussed with particular reference to composites having a pure aluminium matrix. The deformation inhomogeneities induced by the ceramic particles are examined, and the role of the particles in the nucleation and growth of recrystallised grains during subsequent heat treatment is considered. The effect of the ceramic particles on the microstructures developed during multipass hot rolling is shown to be complex, depending on particle size and volume fraction. Superplasticity is shown to occur by several mechanisms in particulate composites. The effect of deformation processing on the ceramic is discussed, with emphasis on the fracture and realignment of ceramic particles, platelets, and whiskers.MST/1299

Microstructural development during thermomechanical processing of particulate metal-matrix composites

Magnesium alloy AZ31 was cold deformed and then subjected to a wide range of annealing conditions to study the annealing response of the material. Recrystallization and grain growth kinetics during annealing were obtained from hardness testing and microstructural analysis. Results show that the annealing response of AZ31 is sensitive to the amount of deformation, temperature and annealing time, producing characteristic microstructures at each stage of the annealing process.

B. Bay

Papers

Initial stages of recrystallization in aluminium containing both large and small particles