Chapter C.6 - Corrosion fatigue

Abstract

Corrosion fatigue is a complex process of material damage resulting from the interaction of two different mechanisms: cyclic mechanical stress and the influence of a corrosive environment. After a certain number of cycles, disturbances in the crystalline network lead to the formation of major defects, generally located in the immediate vicinity of the surface, facilitating the appearance of microscopic cracks. The mechanism of corrosion fatigue is different from that of stress corrosion. On aluminium alloys, fatigue cracks propagate by the formation of striations, which are quasi-cleavages. Propagation rarely occurs along grain boundaries. Three mechanisms are possible to explain corrosion fatigue: hydrogen embrittlement, anodic dissolution due to plastic deformation, and repassivation of the surface behind the crack front by the formation of an oxide film. Generally speaking, corrosion fatigue of aluminium alloys occurs at a lower stress level than stress corrosion cracking. There is no well-established relationship between susceptibility to stress corrosion cracking and corrosion fatigue. Corrosion products can block the progress of corrosion at the crack base. There is therefore competition between two antagonistic processes: progression of hydrogen embrittlement cracking and deceleration due to the effect of corrosion products.