Microstructural path and temperature dependence of recrystallization in commercial aluminum

The isothermal recrystallization of 90% cold-rolled commercial purity alumi num alloy AA1050 was studied by means of quantitative microscopy at four te mperatures from 245 degreesC to 280 degreesC. The microstructural-propertie s, V,, the volume fraction recrystallized, S-v, the interfacial area densit y separating recrystallized grains from deformed grains and (lambda), the m ean recrystallized grain free length, were measured stereologically as a fu nction of time. The kinetics, microstructural path, grain boundary migratio n rates and temperature dependence of recrystallization were quantified exp erimentally. Based on analysis of all data and microstructural path modelli ng, recrystallization was determined to be growth (boundary migration rate) controlled; all nucleation occurred in time periods short compared to the earliest annealing times. The activation energy for grain boundary migratio n was calculated to be 172-183 kJ/mole suggesting that a solute-limited gra in boundary migration rate mechanism was operative in the alloy. The recrys tallization microstructural path was found to be isokinetic, i.e, identical at all the annealing temperatures studied. Two stages of recrystallization kinetics were observed; an early transient-like stage characterized by dec reasing growth rates and a later stage in which the kinetics approached Avr ami behavior and the growth rates were approximately constant The transient -like behavior is attributed to the steep, deformation-induced stored energ y gradients surrounding precipitate particles where the recrystallized grai ns are nucleated. (C) 2001 Published by Elsevier Science Ltd on behalf of A cta Materialia Inc.