Low cycle fatigue behaviour of an aluminium alloy with small shearable precipitates: Effect of surface coating

This work shows that the origin of premature Low Cycle Fatigue (LCF) fracture of an underaged Al–Li–Mg–Cu 8090 alloy is a consequence of severe strain localisation mode in the planar slip bands. It is known that an aggressive gaseous environment (even air) can be a major component in the damage process by fatigue. LCF tests are conducted in air and after surface protection of samples by gold coating (deposited under vacuum). The results obtained on coated samples exhibit the extension of fatigue life (Nf) to a value of 200% Nf. This result is discussed in terms of strain irreversibility in slip bands, emergence of these bands at the surface and the surface defect/gaseous environment reaction.