Very high-cycle fatigue resistance of shot peened high-strength aluminium alloys

The present paper is aimed at investigating the effect of shot peening on the very-high cycle fatigue resistance of the Al-7075-T651 alloy. Pulsating bending fatigue tests (R = 0.05) were carried out on smooth samples exploring fatigue lives comprised between 105 and 108 cycles. Three peening treatments with different intensity were considered to explore different initial residual stress profiles and surface microstructural conditions. An extensive analysis of the residual stress field was carried out by measuring with the X-ray diffraction (XRD) technique the residual stress profile before and at the end of the fatigue tests, so as to investigate the onset of a stabilized residual stress field. Fatigue crack initiation sites have been investigated through scanning electron microscopy (SEM) fractography. The surface morphology modifications induced by shot peening were evaluated using an optical profilometer. The influence of surface finishing on the fatigue resistance was quantified by eliminating the surface roughness in some peened specimens through a tribofinishing treatment.