Passivation of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys in 1 M H2SO4 and 1 M NaOH solutions

The corrosion mechanisms of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al–Cr–Fe surface is exhibited from 1 M H2SO4 to 1 M NaOH solutions, which was confirmed by ICP-OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy-hydroxide film. Although Al–Cu–Fe–Cr showed passivation during potentiodynamic polarization, heavy active corrosion at OCP was revealed by ICP-OES. For the Al–Cu–Fe–Cr alloy, the 10% content of Cr is insufficient to maintain a protective “chemically stable” Cr oxide/hydroxide.

Research highlights
► Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys are passive in pH 0 and 14 upon polarization.
► High “chemical” stability of passive over long exposure to 1 M H2SO4 and 1 M NaOH only found for Al–Cr–Fe alloy.
► Chromium cations enrichment is found in the outermost part of passive film on Al–Cr–Fe.
► Very thin mixed Al–Cr oxy-hydroxide is sufficient to efficiently stabilize the passive film/solution interface.