Oxide formation on aluminum alloys in boiling deionised water and NaCl, CeCl3 and CrCl3 solutions

Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy have been employed to provide depth, surface chemical and morphological information respectively for a range of Al-alloys treated for 2 h at 90-100 °C in either deionised water (DIW), 30 mM NaCl, 10 mM CeCl3 or 10 mM CrCl3 solutions. Alloys included Al sheet 1100-O, 2024-T3, 3004-H19, 5005-O, 6061-T6 and 7075-T6. In DIW all alloys developed the same oxide thickness with a boehmite-like appearance. In NaCl and CeCl3 solutions the oxide thickness varied with alloy composition but was considerably thicker than the deionised case and maintained a boehmite-like appearance. Ce was distributed throughout the oxide but at low levels. In all cases some CeIV was detected on the surface of the oxide, the remainder being CeIII. In CrCl3 solution, the oxide thickness was extremely thin with the appearance of a dense oxide rather than a boehmite-type structure.