Formation of cube recrystallized grains in high-purity Al

In high-purity 4 N (99.99 wt.%) Al containing 50 wt.ppm Cu, very strong {100} recrystallization textures are developed after 98% cold rolling and annealing at 500 °C. They are about three times stronger than those observed in standard high-purity 4 N Al without Cu addition. In this paper, the mechanism of the formation of such strong {100} recrystallization textures were investigated in detail by using the EBSP (electron backscatter pattern) analysis. It was found that, at the earliest stage of recrystallization, {100} -recrystallized grains were nucleated by forming a row lying parallel to the rolling direction and growing preferentially within the elongated deformed grain in which they were nucleated. Most of these {100} -recrystallized grains had orientations very near to the exact cube orientations. {100} -recrystallized grains in this materials were characterized by their rapid growth, which was observed at the later stages of recrystallization. Since they were surrounded by deformed regions having very strong -fiber rolling textures formed by heavy cold rolling, their grain boundaries were high-angle grain boundaries with high mobility. Assisted further by high stored energy introduced by heavy rolling reductions, {100} -recrystallized grains could grow very rapidly, traversing readily several deformed grains. In this material, {100} -recrystallized grains were not nucleated so abundantly. However, {100} -recrystallized grains were nucleated much earlier and grew much faster than recrystallized grains with other orientations. They were, therefore, always larger than recrystallized grains with other orientations. Due to such size advantages, {100} -recrystallized grains could rapidly consume fine-recrystallized grains with other orientations during the subsequent grain growth process. As a result, microstructures observed after annealing at 500 °C for 2 h consisted mostly of coarse {100} -recrystallized grains slightly misoriented with each other. It is, thus, rapid growth of few {100} -recrystallized grains during recrystallization, and their preferential grain growth, that enhance the development of very strong {100} recrystallization textures in this high-purity Al. Cu seems to suppress nucleation of recrystallized grains with other orientations.