Investigation of Recrystallization Kinetics in 1050 Al Alloy by Experimental Evidence and Modeling Approach

Abstract

The recrystallization (RX) kinetics of commercially pure Al alloy is studied under the scope of annealing temperature, time, and degree of deformation. To examine the distribution of recrystallization, Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory is employed, where the path of microstructural transformation from the deformed state to the fully recovered one is studied as a function of the volume fraction of recrystallized grains (XV) and annealing time. The drop in hardness is recorded for the samples at various stages of annealing with a corresponding decrease in stored energy as the annealing time increases. The stored energy obtained from the hardness results and Orientation Imaging Microscopy (OIM)-based method is found to be in good agreement with each other, proving the efficiency of both techniques. To determine the volume fraction of the recrystallized microstructure, data obtained from Vickers hardness measurements are used. Various parameters associated with recrystallization statistics such as the critical radius of nuclei, the incubation period, and the mobility of High-Angle Grain Boundaries (HAGB) were derived from the experimental evidence. The experimental data also suggest a sharp drop in the velocity of HAGB as the RX transformation process approaches its completion, which is found to be a direct result of a drop in stored energy. A softening window between 42 s and 55 s is identified for our experimental data where the hardness, stored energy, and velocity of HAGB drops very sharply, and the maximum fraction of deformed grains is expected to be converted to the recrystallized ones. Along with experimental observations, an analytical model was developed, which helps to approximate the kinetics of RX and corresponding parameters for various annealing temperatures and strains while revealing the characteristic feature of Avrami exponent n. Both experimental evidence and model data reveal a very strong dependency of recrystallization behavior on the stored energy.