Abstract: In recent years, ultrafine-grained gradient structures have received wide attention owing to their excellent strength-plasticity balance. Plastic flow machining, as a special process of severe plastic deformation, can prepare ultrafine-grained unilateral gradient sheets in one step at room temperature without cumbersome equipment. However, research on the preparation process of bilateral gradient metal sheets and their performance optimization is still insufficient, and the existing methods face challenges such as complex principles, high consumption and low efficiency. To realize the efficient preparation of bilateral gradient sheets and the synergistic optimization of strength and ductility, a new process of plastic flow machining based on multiple shearing induced by arrayed sawteeth is proposed. Combining the experiments and finite element analysis, the aluminum alloy sheets with bilateral gradient structure prepared under different sawteeth angles are investigated, and their forming mechanism, microstructure and mechanical properties are analyzed in detail. The results show that the sheets prepared by this process exhibit significant bilateral gradients in equivalent strain, grain size and microhardness. This is attributed to the multiple shearing induced by arrayed sawteeth and the intense deformation triggered by tool extrusion friction, leading to the formation of high strain zones on both sides of the sheet, respectively. The strain distribution inside the sheet can be effectively altered by adjusting the sawteeth angle, which in turn controls the proportion of fine-grained layers. This process opens up a feasible path for efficiently preparing sheets with bilateral gradient structure and provides a practical reference for applying the multiple shear mechanism in modulation of material microstructures.

Key words: arrayed sawteeth, plastic flow machining, bilateral gradient structure, multiple shearing