Concurrent formation of two different type precipitation-free zones during the initial stage of homogenization

Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy were used to study the microstructure evolution of Al–Cu–Mg alloy during the initial stage of homogenization. It was found that two types of precipitation-free zones (PFZs) can form concurrently: one near grain boundaries and the other at the grain centres. Depth profile analyses of solute concentrations and dislocation-loop distributions strongly suggested that the formations of the two type of PFZs are different, due solely and exclusively to solute and vacancy depletion, respectively. A mechanism model was proposed to explain the concurrent formation of the two different type of PFZs during the initial stage of homogenization.