Preferential surface aging: New processes for the improvement of the fatigue properties of components exposed to mechanical loads

Certain age-hardenable alloys, for example, selected aluminum and titanium alloys as well as precipitation hardening steels, are amenable to a novel method for improving fatigue behavior called preferential surface aging. First, a mechanical surface treatment such as shot peening or surface rolling is applied to induce cold work in the `skin'. Then, an aging treatment is carried out such that the age hardening reaction is much more pronounced in the skin than in the bulk. Advantages of this method are that it can offer higher ductilities than a high strength conventionally aged condition, while endurance limits are even higher than after conventional mechanical surface treatments.