Corrosion behaviour of a quaternary Al–Li–Cu–Mg alloy in 3·5% NaCl solution

Abstract

The corrosion resistance of a quaternary Al–Li–Cu–Mg 8090 alloy in the peak aged condition was evaluated in aqueous environments over a range of aggressiveness. The corrosion rate was established through weight loss measurements obtained in total immersion tests. These measurements show a steady loss of material in the aqueous solutions: corrosion rates were observed to decrease with time of immersion. The pH of solutions changed during the period of testing. Analytical study of the surfaces of samples by optical microscopy and SEM revealed rapid corrosion during the initial hours of immersion, followed by a period dominated by pitting. In all environments, pitting occurred at the second phase particles dispersed in the matrix, and at the grain boundary precipitate particles. The number, density, and size of pits increased with immersion time. In the highly aggressive acidic environments, rapid degradation of the surface was noted, and corrosion was severe along the grain boundaries. The results of the total immersion tests suggest the operation of several concurrent and competing processes, involving intrinsic microstructural features, alloy composition, and chemistry of the aqueous environment.