Achieving superior strength and ductility in 7075 aluminum alloy through the design of multi-gradient nanostructure by ultrasonic surface rolling and aging

Abstract

Aluminum alloys were used in various fields due to their high specific strength and low density. However, the disadvantage of low strength limits its wider application. In this work, the effect of ultrasonic surface rolling process (USRP) and artificial aging on microstructure and mechanical properties of 7075 aluminum alloy were investigated in detail. The results indicated that a multi-gradient nanostructure (MGNS) layer, i.e., grain gradient and precipitation gradient, was generated on the surface of the alloy. The tensile strength of the aged-USRP sample (692 MPa) was about 63 % higher than that of the coarse-grained sample (425 MPa), and the plasticity was comparable to that of the coarse-grained specimen. The underlying mechanisms of grain refinements, precipitation behavior and their effects on tensile properties were quantitatively analyzed. The high strength of the aged-USRP sample originated from grain boundary strengthening, precipitation strengthening, dislocation strengthening and synergistic strengthening. The activation of geometrically necessary dislocations (GNDs) during tensile deformation improved the plastic coordination ability of different microstructures. Thus, excellent strength-ductility synergy of 7075 aluminum alloy was obtained. • Multi-gradient nanostructure was formed on the surface of 7075 Aluminum Alloy. • Gradient nanostructure of type and number density of precipitates formed. • The multi-gradient nanostructure enhanced strength-ductility synergy of the alloy.