Shot peening-induced surface integrity governing fatigue performance of Al alloy in high to very high cycle regime: Synergistic effects of residual stress, roughness and microstructure

Strategic surface modification governs the fatigue performance of metallic materials by engineering critical surface integrity attributes to suppress crack initiation and extend service life in advanced applications. This work elucidates the critical role of shot-peening-induced surface modification in governing the very-high-cycle fatigue (VHCF) life of 7075-T6 aluminum alloy for advanced engineering applications. By systematically varying shot-peening intensities, we demonstrate that surface integrity characteristics—including microstructure refinement, compressive residual stress (CRS), surface roughness, and grain boundary evolution—competitively determine fatigue resistance. Surface treatment significantly enhances VHCF life through synergistic effects of dislocation-mediated microstructure modification and CRS, particularly at lower stress amplitudes. However, excessive peening intensity degrades fatigue performance due to rougher surfaces, randomized texture, and low-angle grain boundaries. Notably, optimized surface modification at lower intensities prolongs fatigue life for interior-initiated failures beyond 10 8 cycles, where gradual CRS release coupled with dislocation structure evolution further improves durability. These findings establish shot peening as a strategic surface engineering approach to tailor VHCF performance in high-strength alloys.