Influence of surface coverage on the fatigue behavior of a shot peened AA7B50-T7751 alloy

Abstract

Shot peening treatments with coverages of 100%, 300%, 600%, and 1000% were performed to investigate the effects of shot peening coverage on the fatigue behavior of a 7B75-T7751 alloy. Microhardness and residual stress were measured along with the depth from the treated surface to investigate the mechanical properties. The grain refinement obtained with each shot peening condition was characterized and analyzed by using scanning electron microscopy (SEM) observations and x-ray diffraction (XRD) measurements. Fatigue tests of samples shot peening with different coverages were carried out under maximum stress of 225 MPa and 242 MPa respectively, with a stress ratio (R) of 0.06 to evaluate fatigue life. The results indicated that the increase of coverage will not lead to any significant improvement of the residual stress level when the coverage is more than 300%. Additionally, the surface grain refinement caused by shot peening slows down significantly when the coverage increases to 600%. Therefore, the fatigue life can increase with the increase of shot peening coverage, however, when the coverage exceeds 300%, fatigue life significantly drops because of the micro-cracks generated on the surface. It is concluded that the coverage of 300% seems to be the most optimal condition in terms of fatigue life improvement among the different investigated coverages.