Microstructure Development during Hot Deformation of Aluminum to Large Strains

During deformation, the original grains change their shape and the surface area per unit volume increases with strain until a certain critical strain has been reached. The structure of high-angle boundaries has been monitored at increasing strains with the aim of finding the effect of grain breakup and strain-induced boundary migration. It has been found that the distance between the high-angle boundaries does not depend only on geometrical considerations. At high Zener-Hollomon parameters, the distance between the high-angle boundaries was found to be smaller than predicted from geometry, indicating that high-angle boundaries are formed during deformation. In the case of deformation at very low Zener-Hollomon parameters, the distance between the high-angle boundaries was found to be larger than predicted from geometry, which indicates migration of the original grain boundaries in a direction opposite to the one imposed by the deformation. The evolution in grain-boundary structure during deformation has been successfully modeled on the basis of expressions for the grain breakup and restoration reactions. [PUBLICATION ABSTRACT]