Formation of Chromate Conversion Coatings on Al-Cu-Mg Intermetallic Compounds and Alloys

Chromium conversion coating (CCC) formation was monitored on copper-containing aluminum alloys AA2024-T3 and a specially cast Al x Cu y Mg z ingot using Raman spectroscopy of the 860 cm -1 band. The Al x Cu y Mg 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 -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 -1 band was shown to exist on AA-2024 alloy. Raman intensity of the 860 cm -1 band was also integrated and spatially mapped using commercially available software. These results were verified with AES depth profiling using an Ar + ion sputter. CCC formation was found to he slower on the Al x Cu y Mg z phases with higher copper content. Similarly, in 2024-T3, CCC formation was suppressed on S-phase Al 2 CuMg and depressed Al 20 Cu 2 FeMn intermetallics of 2024 aluminum alloy. Fe(CN) 3-/4- 6 adsorption on the Al x- Cu v Mg z ingot phases, Cu, Al, Mg, and AA2024-T3 were characterized by Raman in the 2100 cm -1 range.