Chromate Conversion Coatings Formed on Intermetallic Constituents of AA2024-T3

 

Surface chemical data have been developed to refine an existing model for the Chromate Conversion Coatings (CCC) formed on the AA2024-T3 surface. It was necessary to develop samples of large areas containing compositional homogenous thin films of the various IMCs found on the AA2024-T3 surface in a two-step process. First, disks of IMC compositions were formed by Reactive Arc Melting (RAM). SEM/EDAX and XRD results revealed that these RAM analogs were very close to the desired compositions, exhibiting local areas of compositional variation only at grain boundaries. In the second stage, femtosecond laser ablation of the RAM IMCs disks was found to produce homogenous thin films. These thin films were used to analyze the behavior and formation of CCC on IMCs and sanchem treated AA2024-T3. Figure 1 shows SIMS depth profile revealing significant variations of CCC film formation and minor constituent composition derived from underlying IMCs. The SIMS results also indicated that the CCC formed on the q phase was about 9% and S phase was about 15 % of the average thickness of the CCC formed on the AA2024-T3 surface. The CCC thickness on the Al20Cu2(MnFe)3 was found to be variable having thin and thick islanded structure. These results indicate that the thickness of the CCC appears to diminish with the increasing Cu content of the substrate (Figure 2). Fe(CN)63- retention increased with copper content of the substrate inhibiting the Al3+ production for CCC formation. A comprehensive model for this is shown in fig 2.

 

References:
  1. "Composition of Surface Treated Thin Film Analogs of Intermetallic Constituents in AA2024-T3", M. J. Vasquez, G. P. Halada, C. R. Clayton and J. P. Longtin, in Corrosion and Corrosion Prevention of Low Density Metals and Alloys, B.A. Shaw, R.G. Buchheit and J.P. Moran, Eds, PV 2000-23, p57, The ECS Proceedings Series, Pennington, NJ (2001).

  2. "Studies on the Structure and Formation of Chromate Conversion Coatings on Thin Films of Copper-Containing Intermermetallic Constituents in AA2024-T3", M. J. Vasquez, G. P. Halada, C. R. Clayton", M. J. Vasquez, G. P. Halada and C. R. Clayton, in State-of-the-Art Application of Surface and Interface Analysis Methods to Environmental Material, Interactions: In Honor of James E. Castle's 65th Year, D.R. Baer, C.R. Clayton, G.P. Halada, and G.D. Davis, Eds, PV 2001-01, The ECS Proceedings Series, Pennington, NJ (2001). Accepted for publication.

  3. "Composition of Chromate Conversion Coatings Formed on Multi-layered Thin Films of AA2024-T3 Matrix and Al2Cu, Al2CuMg and Al20Cu2(MnFe)3", M. J. Vasquez, G. P. Halada, and C. R. Clayton, in Corrosion and Corrosion Protection, J. D. Sinclair, E. Kalman, M. W. Kendig, W. Plieth, W. H. Smyrl, Eds, PV 2001-22, The ECS Proceedings Series, Pennington, NJ (2001). Accepted for publication.

  4. "On the Nature Chromate Conversion Coatings Formed on Intermetallic Constituents of AA2024-T3" M. Jaime Vasquez, G. P. Halada, C. R. Clayton and J. P. Longtin, Surface and Interface Analysis (2002). (Accepted)

 



 

Materials Science Department June-2005