Structural changes during annealing of submicro- and nanocrystalline aluminum alloys

The annealing-induced evolution of the structure and microhardness of submicro-and nanocrystalline Al-3% Mg and Al 1570 alloys produced by torsional severe plastic deformation are studied. Annealing of the Al-3% Mg alloy at 373-423 K and annealing of the Al 1570 alloy at 373-473 K are shown to result in the relaxation of internal stresses and subsequent normal grain growth. As the annealing temperature increases, the microhardness decreases. At higher temperatures (473 K for the Al-3% Mg alloy and 573 K for the Al 1570 alloy), anomalous grain growth takes place. This growth is accompanied by the appearance of numerous grains with a high dislocation density, a high concentration of impurity atoms in grain boundaries, and an increase in the microhardness. These effects are explained.