Fatigue life of AW 7075 Aluminium Alloy after Severe Shot Peening Treatment with Different Intensities

Fatigue life of AW 7075 aluminium alloy in the high and ultra-high cycle region was tested after application of severe shot peening surface treatment with different peening intensities. Severe shot peening with 9.6N Almen intensity and coverage of 650% provides increase of the fatigue life up-to 9%. However, using more severe peening parameters, 14.9A Almen intensity and coverage of 650%, significantly decreases the fatigue life up-to 21%. Study of the surface layer character showed a damage of the surface integrity by shot peening treatment with the more severe parameters. According to fracture surface analysis, in both cases shot peening caused increase of the number of initiated fatigue cracks. The fatigue crack propagation in the strengthened surface layer after treatment with 9.6N/650% parameter has a different orientation and character when compared to not-treated specimens. After treatment with 14.9A/650% parameters, due very strong work hardening, the surface layer started to peel off during propagation of fatigue crack.