Effects of aging and passivation on corrosion fatigue crack propagation of an Al-Li-Zr alloy

Abstract

Fatigue cracking of an Al-Li-Zr alloy has been investigated by measuring crack closure as a function of ageing stage and applied anodic potential in 0.5 M Na2SO4 and 3.5 wt% NaCl solutions with an unloading elastic compliance technique. The present work involves complementary anodic behaviour of the Al-Li-Zr alloy in both solutions by the parentiodynamic polarization and potentiostatic current transient experiments. The Na2SO4 solution raised more the intrinsic fatigue crack propagation (FCP) rate for the overaged specimen than that for the peak-aged one. The higher intrinsic FCP rate of the overaged specimen is due to the higher anodic dissolution rate at the crack tip region as compared to the peak-aged one. The intrinsic FCP rates under unstable passivation potentials in both solutions were significantly larger than those obtained under stable passivation potentials. The difference between the intrinsic FCP rates under stable and unstable passivation potentials is discussed in terms of environment-assisted crack-tip damage processes based on the repassivation behaviour.