The effect of exposure conditions on performance evaluation of post-treated anodic oxides on an aerospace aluminium alloy: Comparison between salt spray and immersion testing

In this work, the effect of the corrosion testing methodology on the degradation of anodized and post-treated AA-2024T3 specimens is considered. Two post-treatments are selected for the anodized layers, namely hydrothermal sealing and cerium-based post treatment. The two post-treatments are selected such that in one case corrosion protection mainly arises from a barrier effect (hydrothermal sealing) and in the other it arises from active inhibition (cerium-based treatment). It is found that salt spray and immersion testing provide similar results for the hydrothermally sealed oxides, but differ substantially for the cerium-treated oxides. The discrepancy is due to the fact that the continuously refreshing electrolyte layer during salt-spray testing promotes film dissolution and hinders precipitation of aluminium hydroxide and cerium compounds, unlike in stagnant bulk electrolyte. Hence, salt-spray testing is likely to be more aggressive than immersion testing for those systems that rely on active inhibition. •The effects of exposure condition on anticorrosion performance were investigated.•Anodized AA2024T3 specimens were post-treated by a cerium-based solution and hot water sealing.•EIS was used to assess corrosion progress as a function of time during salt spray testing and immersion testing.•Salt spray test is more aggressive than immersion test when active inhibition provides corrosion resistance.•Salt spray test and immersion test are similar when corrosion resistance is provided by barrier effect.