Unusual secondary precipitation within the primary precipitation free zone substantially enhances the ductility of Al–Zn–Mg–Cu alloy

Abstract

The formation of unusual secondary precipitation zones (SPZ) within the primary precipitation free zones (PFZ) effectively reduces the PFZ width, associated with finer grain boundary precipitates (GBP) and precipitates in the matrix. Such a microstructure remarkably facilitates the uniform distribution of dislocations within the matrix during the deformation process, and inhibits the strain concentration due to the dislocation tangle within the PFZ. These result in a significant improvement in the ductility of Al–Zn–Mg–Cu alloys, while retain comparable ultimate tensile strength as if treated in T6 temper.