Effects of rolling deformation on precipitation behavior and mechanical properties of Al-Zn-Mg-Cu alloy

The effects of cold rolling (CR) with different hot rolling (HR) reductions on the precipitation behavior and mechanical properties of Al-Zn-Mg-Cu (AA7050) alloy are investigated by synchrotron small angle X-ray scattering (SAXS) and transmission electron microscope (TEM). With increasing HR reduction, the refinement degree of recrystallized structure increases, the dissolution and fragmentation of the second phase particles, and ultrafine sub-grains in shear bands occur. The number of spherical strain-induced precipitates (SIP) and ultrafine sub-grains increase due to high dislocation density before T6 heat treatment. After T6 heat treatment, the morphology of nanoprecipitates changes from rod-like to globular, the mean size of nanoprecipitates decreases, and the volume fraction increases with growing HR reduction. The 7050 alloy with 80 % HR reduction presents the highest yield strength of-513 MPa, the tensile strength of-571 MPa and elongation of-13.6 %. The strength increment is mainly ascribed to the contribution of precipitation strengthening and dislocation strengthening relevant to the small mean size and large volume fraction of nanoprecipitates. The improved ductility attributes to the refined recrystallized structure and multi-scale and multi-morphology particles. This investigation can guide further designing novel aluminum alloys by tailoring refined grain, highly dispersed nanoprecipitate structures for a preeminent combination of mechanical properties.