Improvement of strength and ductility of an Al–Zn–Mg alloy by controlling grain size and precipitate microstructure with Mn and Ag addition

Both Mn and Ag were added to the Al–Zn–Mg alloy in order to improve both strength and ductility by controlling the grain size and the precipitate microstructure with precipitate-free zones (PFZs). Although adding Mn significantly refined the grains in the Al–Zn–Mg alloy, it decreased the age-hardenability. Adding a combination of Mn and Ag to the Al–Zn–Mg alloy, on the other hand, improved both grain refinement and age-hardenability with a very narrow PFZ in the Al–Zn–Mg alloy. The results strongly suggest that Ag atoms preferentially trap vacancies migrating to not only grain boundaries but also dispersoids and then form fine precipitates in grain interiors and in the vicinity of grain boundaries. Such changes in the microstructure of the Al–Zn–Mg alloy due to adding a combination of Mn and Ag significantly increased both the strength and ductility of the alloy through uniform deformation.