AVS 58th Annual International Symposium and Exhibition
    Surface Science Division Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM12
Microscale Corrosion of an Aerospace Al 2024 Alloy with Low Mg and the Effect of Chromate and Cerium Based Conversion Coatings

Wednesday, November 2, 2011, 11:40 am, Room 107

Session: Atomistic Control of Structure & Evolution
Presenter: James DeRose, EMPA, Switzerland
Authors: J.A. DeRose, EMPA, Switzerland
T. Suter, EMPA, Switzerland
A. Bałkowiec, Warsaw University of Technology, Poland
J. Michalski, Warsaw University of Technology, Poland
K.J. Kurzydlowski, Warsaw University of Technology, Poland
I. De Graeve, Vrije Universiteit Brussel, Belgium
H. Terryn, Vrije Universiteit Brussel, Belgium
P. Schmutz, EMPA, Switzerland
Correspondent: Click to Email
An aluminum alloy, AA2024-T351 (Al 2024), with a composition having a higher proportion of Cu to Mg (Cu/Mg = 3.7), which is used in the aerospace industry, has been studied for corrosion simulation development. Results show that the Al 2024 alloy’s microstructure and corrosion behavior is quite different from that reported for Al 2024 alloy with higher Mg, a more common composition (normally Cu/Mg = 2.9) [1]. Characterization of the Al 2024 indicates a dominant presence of 2nd phase (AlCuFeMnSi) intermetallic particles (>70%), but that the S phase (Al2CuMg) and θ phase (Al2Cu) precipitate particles are much smaller in population (<30%). Microscale corrosion studies show that open circuit (OCP) and pitting potential (PP) values extracted from micropolarization curves [2] measured for Al 2024 (Cu/Mg = 3.7) 2nd, S, or matrix phase have a large variation within a similar range of values. These results are in contrast to those already reported for Al 2024 with a more common composition (Cu/Mg = 2.9) where the electrochemical potential values separate with respect to the alloy phase and the microstructure shows S phase particles to be in the majority (>60%) [2]. Nanoscale dispersoid particles and, to a much lesser degree, nanoscale 2nd phase particles were also found present throughout the matrix of the Al 2024 studied. The impact of chromate and cerium based conversion coatings, which inhibit corrosion, on the microscale corrosion properties of the Al 2024 alloy has been studied. Electrochemical current density data extracted from micropolarization curves measured for Al 2024 2nd, S, and matrix phase exposed to electrolytic solutions containing chromate (Na2Cr2O7) or cerium based (Ce(NO3)3) molecules show the chromate coating to be more efficient as an corrosion inhibitor. However, other cerium based molecules, such as cerium dibutylphosphate (Ce(dbp)3) and cerium chloride (CeCl3), which have shown more promising results [3], deserve further investigation. [1] R.G. Buchheit, R.P: Grant, P.F. Hlava, B. Mckenzie, G.L. Zender, J. Electrochem. Soc. 144 (1997) 2621. [2] T. Suter, R.C. Alkire, J. Electrochem. Soc. 148 (2001) B36. [3] S.J. Garcíaa, T.H. Muster, Ö. Özkanata, N. Sherman, A.E. Hughes, H. Terryn, J.H.W. de Wita, J.M.C. Mol, Electrochim. Acta 55 (2010) 2457.