Forming mechanism, mechanical properties, and corrosion properties of aluminum alloy sheet with gradient structure processed by plastic flow machining

Plastic flow machining (PFM), a novel severe plastic deformation machining, was proposed to prepare 7075 aluminum alloy sheets with a gradient structure. The forming performance and mechanism of PFM are investigated. Further, the corresponding microstructure was characterized by EBSD. During PFM, the 7075 aluminum alloy sheet was stratified into four obvious layers, whereas the microstructure presents layer-by-layer refinement from top to bottom. The above gradient structure can be controlled by adjusting the extrusion thickness ( t ch ) and extrusion angle ( θ ). As the increased t ch or the deceased θ , the refinement layer proportion could be increased. Meanwhile, the mechanical properties have been investigated by the tensile test and Vickers hardness test. With decreasing t ch or decreasing θ , there is an increase in strength and a decrease in the extension. It is possible to simultaneously elongate the fine and coarse grain layers for gradient structure, which effectively suppresses local strain and presents a different tensile process from homogeneous materials. Therefore, 7075 aluminum alloy sheets have excellent strength-ductility synergy, which higher strength can be obtained by sacrificing only a tiny amount of ductility. The overall hardness of the material was significantly improved. Meanwhile, the gradient structure sheets significantly improve corrosion resistance compared to the ST samples. The insights in this study exhibit that the 7075 aluminum alloy sheets processed by PFM have excellent properties and application prospects and may provide a feasible and efficient one-step machining for green machining lightweight materials with a gradient structure. • An aluminum alloy sheet with a gradient structure was prepared in one step • Explanation of grain refinement and gradient structure formation by the effects of strain and friction factors • The beneficial effects of grain structure gradient distribution on mechanical properties (i.e., strength-ductility relationship and hardness) were analyzed • The effect of grain refinement on the optimization of the corrosion properties of the sheet surface was analyzed