Formation of chromate conversion coatings on Al-Cu-Mg intermetallic compounds and alloys

• Published in: Journal of the Electrochemical Society 2000-12, Vol.147 (12), p.4494-4501
• Main Authors: MCGOVERN, W. R, SCHMUTZ, P, BUCHHEIT, R. G, MCCREERY, R. L
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Metals. Metallurgy; Nonmetallic coatings; Production techniques; Surface treatment
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1394091

Chromium conversion coating (CCC) formation was monitored on copper-containing aluminum alloys AA2024-T3 and a specially cast Al sub x Cu sub y Mg sub z ingot using Raman spectroscopy of the 860 cm exp -1 band. The Al sub x Cu sub y Mg sub z ingot's different phases were compositionally analyzed with energy-dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) before and after treatments using commercial Alodine 1200S chromium solution. Profilometry and Raman intensity of the 860 cm exp -1 band were used to gauge CCC film thickness on AA-2024-T3 alloy. A linear relationship between CCC thickness and the integrated 860 cm exp -1 band was shown to exist on AA-2024 alloy. Raman intensity of the 860 cm exp -1 band was also integrated and spatially mapped using commercially available software. These results were verified with AES depth profiling using an Ar exp + ion sputter. CCC formation was found to be slower on the Al sub x Cu sub y Mg sub z phases with higher copper content. Similarly, in 2024-T3, CCC formation was suppressed on S-phase Al sub 2 CuMg and depressed Al sub 20 Cu sub 2 FeMn intermetallics of 2024 aluminum alloy. Fe(CN) sub 6 exp 3-/4- adsorption on the Al sub x Cu sub y Mg sub z ingot phases, Cu, Al, Mg, and AA2024-T3 were characterized by Raman in the 2100 cm exp -1 range.