Characterization of the Isothermal Precipitation Kinetics of an Al-Zn-Mg-Cu Alloy

The isothermal precipitation kinetics of an Al-Zn-Mg-Cu alloy was characterized over a wide range of temperatures by means of in situ electrical resistivity measurements, hardness testing, scanning, and transmission electron microscopy. During low temperature isothermal holding, behavior consistent with classical precipitate nucleation, growth, and coarsening was observed. At higher temperatures, the Ostwald coarsening process was characterized and was shown ultimately to result in widely dispersed, incoherent coarse particles. Isothermal temperature–time–precipitate–fraction curves were estimated based on evaluations of in situ electrical resistivity results. Isothermal treatments were observed to influence precipitation during subsequent heating but had little effect on precipitates dissolution.