This study investigates the effects of surface treatments on the mechanical properties of 4 mm thick flat test specimens made from annealed AA 7075 alloy in three conditions: as-received, shot-peened, and electropolished. Experimental investigations, including cyclic stress response, fatigue life, microstructural observations, and mechanical properties, are conducted to provide insights into the fatigue behaviour of the alloy. The surface roughness (Ra) values were measured at 546 nm for as-received, 830 nm for shot-peened, and 72 nm for electropolished samples. Push–pull fatigue tests conducted at a stress amplitude of 500 MPa with a load ratio (R) of -1 yielded average fatigue lives of 1200 cycles for as-received, 990 cycles for shot-peened, and 2700 cycles for electropolished samples. These results align with the general observation that smoother surfaces yield better fatigue life, which can be explained by the influence of surface conditions on stress–strain behaviour, microstructure, and fracture mechanisms. The smoother surfaces have lower stress concentration points, so the propensity for crack nucleation and propagation is lower in these samples, leading to improved mechanical properties.
