Process design of one-step deformation to fabricate double-sided gradient structures: Principle, microstructure and mechanical properties

Double-sided gradient structures, as a method to avoid the strength-ductility dilemma, face the problem of low processing efficiency in manufacturing processes. To address this issue, this work describes a severe plastic deformation process, called plastic flow machining with array sawteeth, which enables the fabrication of double-sided gradient-structured (GS) sheets in one-step deformation. The experimental material in this work was AA1060. In this work, the principle of the process, the microstructure and the mechanical properties of the formed sheet were investigated using simulations and experiments. This process created a significant strain gradient within the sheet (strain differentials of up to 5.5). The surface of the sheet was effectively refined to ultrafine grains (average grain size of 0.819 μm). The Vickers hardness of the sheet's surface was increased by 62 %–71 %. There were significant grain size gradients and hardness gradients in the thickness direction of the sheet. The ultimate tensile strength (UTS) of the sheet could reach 166 MPa while still having reasonable ductility (elongation to failure of 20.8 %). The sheet was annealed at 350 °C for 25 min yielding a uniform elongation (27.5 %) similar to that of the initial coarse-grained sample, while the UTS was 45 % greater than that of the initial sample. These findings provide an efficient method for fabricating double-sided GS sheets with excellent properties and have promising industrial potential.