Dynamic recrystallization in Al–7Mg alloy

Abstract

The microstructural changes which occur during the extrusion of an Al–7Mg alloy have been investigated using optical and electron microscopy. Light microscopy has shown that recrystallized grains are present both at the original grain boundaries and within the grains, even at the breakthrough pressure. Electron microscopy has shown that a large percentage of recrystallized grains contain a substructure and are thus dynamically recrystallized. The grain size of these dynamically recrystallized grains is usually less than 5 μm. Some hot rolling, and cold rolling followed by annealing, experiments have also been performed to substantiate the evidence for dynamic recrystallization. A large number of recrystallized grains were observed, although the bulk of the material deformed with dynamic recovery as the operative mechanism. It is finally concluded that the high solute content hinders dislocation motion, and nucleation of dynamic recrystallization occurs at dislocation clusters and/or at small particles adjacent to a particle free zone: the dislocation clusters or the row of particles pin the dislocations until a sufficiently high density is generated and the boundary thus formed migrates into the particle free region.