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 AlxCuyMg, ingot using Raman spectroscopy of the 860 cm(-1) band. The AlxCuyMgz ingot's different phases were compositionally analyzed with energy-dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) before and after treatments using commercial Alodine(TM) 1200S chromium solution. Profilometry and Raman intensity of the 860 sm(-1) band were used to gauge CCC film thickness on AA2024-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 be slower on the AlxCuyMgz phases with higher copper content. Similarly. in 2024-T3, CCC formation was suppressed on S-phase Al2CuMg and "depressed" Al20Cu2FeMn intermetallics of 2024 aluminum alloy. Fe(CN)(6)(3-/4-) adsorption on the Al-x-CuyMgz ingot phases, Cu, Al, Mg, and AA2024-T3 were characterized by Raman in the 2100 um-l range. (C) 2000 The Electrochemical Society. S0013-4651(00)04-023-4. All rights reserved.