The author has studied on the secondary recrystallization of Al polycrystal with the purities of 99.996% and 99.6% comparing the results with those of Al single crystals. The following results were obtained: (1) The coarsening did not occur in 99.996%Al, but it occured, in 99.6%Al at a certain range of rolling reduction, which seemed to be the higher the thickness of specimen was the larger, that is, the range was30∼50%in 0.4 mm, 40∼50% in 1 mm, 40∼60% in 5 mm and 70∼95% reduction in 10 mm thickness. (2) Even in the case of specimens cross-rolled or preheated at a lower temperature than 600° after rolling, the coarsening range of rolling reduction was almost unchanged. (3) The coarsening temperature of 1 mm thickness specimen was 600° in 40% red., 590° in 50% red. and 580° in 60% red and for 10 mm thickness specimen it was about 550° in 95% red., but it was 490°, in the 96% rolled specimens sampled from commercial products. (4) The orientations of secondarily recrystallized grain were for the most part nearly (111) or (100), regardless of the rolling method or the heat treatment.
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