Abstract:To enhance the fatigue performance of the central hole specimen of the aviation titanium alloy Ti-4Al-5Mo-5V-6Cr-1Nb, hole extrusion strengthening experiment was conducted on the center hole of its plate using a slotted mandrel. The effects of hole extrusion strengthening on the microstructure and fatigue performance of the alloy were analyzed, and the anti-fatigue enhancement effect and microscopic mechanism of hole extrusion strengthening revealed. The results showed that the hole extrusion strengthened layer with a gradient distribution of deformation degree consisted of a grain refinement zone near the hole edge and a deformation zone away from the hole edge. The depth of the residual stress layer on the inner side of the hole wall was 2000 μm, and the maximum residual stress was -700 MPa. The depth of the strengthened layer was 100 μm, and the highest hardness value was 380 HV0.1, which was 20% higher than the hardness value of the matrix. The fatigue life and fatigue life dispersion of the alloy was significantly improved after hole extrusion strengthening, with the median life and average life increasing by 2.74 times and 2.53 times, respectively, and the coefficient of variation decreasing from 48.7% to 29.6%. The residual stress field and strengthened layer effectively suppressed the initiation of fatigue cracks on the inner surface of the hole wall, shifting the initiation of fatigue cracks from the surface to the subsurface, resulting in finer striations with a striation spacing decreasing from 1.94 μm to 0.92 μm..