Herein, the characterization of microstructures and mechanical properties of Al–Zn alloys ultrafine-grained (UFG) by using high pressure torsion (HPT) is surveyed. Emphasis is placed on the decomposition of the solid solution structures due to the HPT process, leading to unique mechanical and plastic properties of the UFG alloys. The decomposed microstructures, the grain boundaries wetted by Zn-rich layers, as well as the softening, grain boundary sliding (GBS) with usually high strain rate sensitivity and super-ductility of the HPT-processed samples are described and discussed. Furthermore, the innovation potential of intensive GBS at room temperature is briefly considered.