Nanostructured surface pre‐treatment based on self‐assembled molecules for corrosion protection of Alclad 7475‐T761 aluminum alloy

Coatings based on self‐assembled molecules (SAMs) for corrosion protection of aircraft aluminum alloys have been studied to evaluate their potentialities as replacements to yellow chromate conversion coatings (CCC), due to the toxicity of these leading to environmental problems. In this work, the influence of alkane diphosphonates self‐assembling molecules on the corrosion resistance of the AA7475‐T761 cladded with AA7072 was investigated by electrochemical impedance spectroscopy and cathodic and anodic polarization curves, in naturally aerated 0.5 mol/L Na₂SO₄ aqueous solution, with pH adjusted to 4. Corrosion accelerated experiments (salt spray tests) were also carried out to examine the resistance of the SAM treated samples against corrosion. The results suggested that the development of boehmite (aluminum oxide) layer with incorporation of SAM was beneficial to the corrosion resistance of the tested aluminum alloy. Samples surface treated with SAM or aluminum oxide/SAM (without and with subsequent polyester layer) showed better corrosion resistance results than samples with CCC, indicating that this last type of coating containing hexavalent chromium could be replaced by the environmentally friendly pre‐treatment corresponding to boehmite growth followed by incorporation of SAM.