Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Journal Article · Sat Jan 01 04:00:00 EST 2005 · J. Electrochem. Soc.

DOI:https://doi.org/10.1149/1.2041027· OSTI ID:913764

Isaacs, H; Sasaki, K; Jeffcoate, C; Laget, V; Buchheit, R

We used in situ X-ray adsorption near-edge structure (XANES) to investigate the formation of chromate conversion coatings on pure Al, commercial Al alloys (AA 1100, AA2024, and AA7075), and a series of binary A1-Cu alloys. The method employed a new electrochemical cell that can determine the ratio of hexavalent chromium (Cr(VI)) to total chromium (Cr(total)) speciation in conversion coatings as a fraction of exposure time to a chromate solution. The spectra showed that the initial Cr(VI)/Cr(total) ratios are greater than later ones for pure Al and AAl 100, but not for AA2024 and AA7075. Measurements with Al-Cu alloys demonstrated that the difference observed in AA2024 and AA7075 may not be due to Cu alloying. The proportion of Cr(VI) in the coatings becomes approximately constant after 180 s of exposure for all the specimens examined even though the coatings continue to grow.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 913764
• Report Number(s): BNL--78332-2007-JA
• Journal Information: J. Electrochem. Soc., Journal Name: J. Electrochem. Soc. Vol. 152; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM
ALUMINIUM BASE ALLOYS
CHROMATES
CHROMIUM
COATINGS
COPPER ALLOYS
ELECTROCHEMICAL CELLS
KINETICS
national synchrotron light source