Corrosion fatigue mechanisms of an 8090 AlLiCu alloy

Abstract

The corrosion fatigue behaviour of a commercial 8090 AlLi alloy has been analysed in a 3.5% NaCl solution at pH 6. At applied low plastic strain amplitudes, the effect of strain rate ϵ dot is shown to be very significant on the fatigue lives and on the crack initiation modes. This effect is related to the different corrosion processes which can take place at free corrosion potential. The analysis of the crack initiation modes by scanning electron microscopy as a function of ϵ dot allows us to emphasize the role of pitting on the corrosion fatigue behaviour of the 8090 alloy. Complementary tests are performed to separate the role of pitting from the role of other electrochemical processes. According to the value of the strain rate, four different corrosion fatigue mechanisms are proposed. The role of pitting is shown to be very different according to the strain rate range. Finally an interaction between stress corrosion and corrosion fatigue is observed at very low strain rates and related to the crack initiation process.