Investigation on the corrosion behavior of clad free Aluminium alloys

Within this study the risk of a clad-free concept for future metallic fuselage applications was investigated for AA2024 and AA5028. Also two pre-treatment processes were applied (Phosphoric Sulphuric Acid (PSA) and Tartaric Sulpuric Acid Anodising (TSA)) to evaluate the different performance in terms of corrosion. To investigate the corrosion behavior of clad-free material in comparison to clad material different corrosion tests (Alternate Immersion Emersion Test (AIE), Filiform Corrosion Test (FFT) and Cyclic Corrosion Test were carried out with and without titanium fastener. Finally the corrosion phenomena were assessed by microscopic investigations accompanied with cross-sections.
The corrosion results of the AIE showed no preferred dissolution of the clad layer under galvanic conditions (coupling with Titanium) or without. Mostly the test leads to pitting corrosion of the base material (all tested materials). By applying a cyclic corrosion test a different corrosion phenomena was observed compared to the other corrosion tests. Beside the pitting corrosion on the different materials the test reveals a preferred dissolution of the clad layer on AA2024. However in the same countersunk both pitting corrosion as well as preferred dissolution of the clad was present. Moreover the results of the different tests showed no significant difference between the PSA and TSA treatment. In general the AA5028 showed with all pre-treatments a better corrosion performance than AA2024.