ISSN:
0142-2421
Keywords:
conversion coating
;
aluminium
;
alloy
;
x-ray photoelectron spectroscopy
;
scanning electron microscopy
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Physics
Notes:
X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and potentiodynamic measurements have been made on chromate conversion-coated Al 2024-T3 alloy. X-ray photoelectron spectroscopy measurements indicated that the conversion coating had a surface of CrOOH and Cr(VI), enriched in ferricyanide. The bulk of the coating was an equal mixture of CrOOH and Cr2O3 with significant levels of F- and Fe, the latter implying the presence of ferricyanide throughout the coating. Copper(II) ion was present at the interface between the conversion coating and the alloy, as well as Al3+. During ageing experiments, potentiodynamic measurements indicated that the corrosion current (icorr) decreased from ∽0.4 to ∽0.04 μA cm-2 during the first 40 h after preparation but thereafter slowly increased. No significant changes were observed in the chemistry of the coating by XPS for ageing times longer than 40 h, although morphological changes were observed with SEM. As the coating aged, a network of microcracks developed across the surface. It is believed that Cr6+ is consumed in the process in which plugs of hydrated chromium oxide form at the base of these cracks. © 1997 by John Wiley & Sons, Ltd.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
