Microstructure and texture evolution during annealing a cryogenic-SPD processed Al-alloy with a nanoscale lamellar HAGB grain structure

The grain structure and texture evolution during annealing a Al-0.13% Mg submicron-grained alloy, deformed by plane-strain compression (PSC) at cryogenic temperatures, has been investigated by transmission electron microscopy and electron backscatter diffraction. After deformation the alloy contained a lamellar grain structure with a high-angle grain boundary (HAGB) spacing of 190nm and an area fraction of similar to 80%, Oil annealing the grain structure coarsened and transformed from lamellar to equiaxed. Remarkably, the Fraction of low-angle grain boundaries (LAGBs) progressively increased during annealing, to similar to 50% above 300 degrees C, leading to instability and discontinuous recrystallization at higher temperatures. This resulted in a "bimodal grain structure" comprised of bands of coarser grains and fine subgrains, arising Lis a result of the increase in proportion of lower-mobility LAGBs. The surprisingly large increase in LAGB fraction oil annealing is shown to be related to orientation impingement, originating from the strong texture present after PSC in liquid nitrogen. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.