Aluminum alloys corrosion organic coatings

Twite R. L. and Bierwagen G. P. (1998), Review of alternatives to chromate for corrosion protection of aluminum aerospace alloys . Prog. Organic Coatings, 33,91-100. 

Metroke, T. L. Kachurina, O. Knobbe, E. T. "Spectroscopic and Corrosion Resistance Characterization of GLYMOTEOS Ormosil Coatings for Aluminum Alloy Corrosion Inhibition," Progress in Organic Coatings, 2002,44,295-305. 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

XPS Cls/Si2p ratio steadily increases with the reaction time (film thickness) by a closed-system plasma polymerization, while the ratio more or less stays at a constant level by a flow system cathodic polymerization, as shown in Figure 4.10. Such a graded ultrathin film was found to provide an excellent corrosion protection of aluminum alloy when an organic coating was applied on top of the ultrathin film [8]. 

Filiform corrosion is observed under thin organic coatings (typically 0.1 mm) on aluminum and steel exposed to a humid atmosphere. It has been observed in aircraft structures, beverage cans, flanges, gaskets, and weld zones [111—113]. Corrosion-resistant alloys of stainless steel, copper, and titanium are not susceptible to fihform corrosion. Metals with thin organic coatings are in contact with water from the humid atmosphere. 

Williams G., McMuiray H.N. (2003), Anion-exchange inhibition of filiform corrosion on organic coated AA2024-T3 aluminum alloy by hydrotalcite-like pigments , Electrochem. Solid Slate Lett., 6, B9-B11. 

For this reason, corrosion inhibitors such as cerium salts or organic biocides are successfully added to the silane sol-gel layer. Akid and coworkers, for example, have developed a broad range of chromate-free xerogel coatings based on doped Ormosil formulations with very high corrosion resistance and with little evidence of change after extensive salt spray tests for a variety of different metal substrates (aluminum alloys, steel, magnesium, etc.). 

Aluminum and its alloys should be anodized and painted, except in areas of electrical bonding. In such areas and where anodizing is not possible, a ehemical film treatment may be used, although it does not afford corrosion protection equivalent to anodizing. When possible, chemical films should be given the additional protection of organic coatings. 

Ooij, W, J. Corrosion Protection of Aluminum Alloys by Conversion Systems and Organic Coatings, Chemtech, 1998,26-63. 

Metroke, T. L. Gandhi, J. S. Apblett, A. "Corrosion Resistance of Ormosil Coatings on 2024-T3 Aluminum Alloy," Progress In Organic Coatings, 2004,504,231-246. 

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