This paper investigates the influence of surface ultrasonic rolling treatment on the fatigue performance of Mg-3Al-1Zn extruded alloy and systematically analyzes the evolution laws of fatigue life and mechanical properties with the thickness of the surface removed layer. The results show that after ultrasonic rolling treatment, the fatigue life of the alloy at a stress amplitude of 240 MPa changes significantly and reaches a peak at a specific removal thickness: when the 80 μm surface layer is removed, the fatigue life reaches 7.79 × 10⁶ cycles, which is much higher than that of the untreated sample (3.87 × 10⁴) and the sample only subjected to ultrasonic surface rolling processing (1.8 × 10⁴). With the increase in the removal thickness, the fatigue life shows a trend of first increasing and then decreasing, and a second increase occurs within the range of 400–500 μm. Microstructure analysis indicates that at a depth of 80 μm from the surface, the strength is enhanced due to grain refinement and the peak hardness, thereby inhibiting the initiation of fatigue cracks, while within the depth range of 400–500 μm, there exist high-density dislocations and deformation layers, which also effectively hinder crack propagation. This study reveals the key role of surface state and subsurface microstructure in the fatigue behavior of magnesium alloys, providing a theoretical basis for improving the fatigue performance of magnesium alloys through surface modification.

In this study, a three-dimensional thermo-mechanical coupled finite element framework for orthogonal cutting with coated tools was established in ABAQUS/Explicit. The framework incorporated the Johnson-Cook constitutive model and a temperature-dependent modified Coulomb friction model. The transient mechanical and thermal responses of uncoated WC-Co, TiN-coated, and TiAlN-coated tools were evaluated at cutting speeds of 50, 100, and 150 m/min. Long-term wear evolution was then predicted by integrating the Usui wear equation with three-stage nonlinear wear theory. Prediction errors for cutting force and cutting temperature remained within 10% across the tested cutting speeds. The TiAlN coating reduced friction and restricted heat conduction into the tool substrate under high strain-rate conditions. The near-field tool temperature decreased by 4.0% to 9.5%, with an 8.2% reduction at 150 m/min. Compared with uncoated WC-Co, TiAlN reduced the simulated main cutting force by 6.0%, 5.6%, and 4.4% at 50, 100, and 150 m/min, respectively. Cutting experiments yielded force reductions of 5.0% to 7.1%. After 30 min of dry cutting at 150 m/min, the model predicted flank wear depths of 0.398 mm for uncoated WC-Co, 0.261 mm for TiN, and 0.235 mm for TiAlN. Relative errors against the measured flank wear depths ranged from 3.4% to 4.7%. The small error between the predicted wear evolution and the experimental data demonstrated that the established model achieved a high level of predictive accuracy.