Investigation on the Mechanism of Gradient Structure Evolution and Fatigue Performance in 2A12 Aluminum Alloy under Abrasive Water Jet Treatment

This study aims to elucidate the mechanisms by which high-pressure abrasive water jet (AWJ) strengthening influences gradient structural evolution and fatigue performance in 2A12 aluminum alloy. By systematically varying key processing parameters, including jet pressure, impingement angle, and number of peening passes, comprehensive characterizations were conducted in terms of microhardness, three-dimensional surface morphology, residual stress, fatigue life, and fracture behavior. Finite element simulations were further performed to analyze the evolution of residual stress fields.The results demonstrate that AWJ treatment induces the formation of a gradient-structured surface layer characterized by increased hardness, elevated compressive residual stress, and refined substructures, leading to a significant improvement in fatigue performance. The strengthening effectiveness shows a strong dependence on processing parameters. An optimal parameter combination—consisting of a jet pressure of 19 MPa, a normal impingement angle (90°), and two peening passes—yields the best overall performance, with a fatigue life of approximately 4.8 × 10 5 cycles under a stress amplitude of 260 MPa, a peak compressive residual stress exceeding 290 MPa, and a hardened layer thickness greater than 180 μm.Fractographic observations indicate that appropriate AWJ treatment can delay crack initiation, stabilize crack propagation, and promote a transition in fracture characteristics toward more ductile behavior. These findings reveal a synergistic multi-mechanism strengthening pathway governed by gradient structure formation and provide both mechanistic insight and practical guidance for enhancing the service performance of high-strength aluminum alloys.