Kinetic analysis of retrogression process for 7075 aluminum alloy

In this paper, the microstructure evolution of retrogression process in the matrix for 7075 aluminum alloy was quantitatively analyzed by a model with the precipitates of dissolution, growth and coarsening. An idealized grain boundary affected zone was established to predict the microstructure evolution of grain boundary. The prediction of precipitates radius is generally agreed with experimental results. The model investigates the influence of retrogression temperatures on microstructure both in the matrix and grain boundary. The kinetic analysis for retrogression shows the minimum volume fractions of precipitates at 240°C and 220°C drop to 2.30% and 2.67%, while it is up to 35.2% at 200°C, which larger than the initial state (T6 temper) for 2.9%. And the grain boundary precipitates at 240°C and 220°C undergoes coarsening stage in the initial of retrogression. However, the pure growth of grain boundary precipitates at 200 °C occurs before the coarsening stage.