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Conjugated polymers (CPs) continue to be of interest for use as components of corrosion control coatings. For aluminum alloys, however, there is controversy and uncertainty regarding the protection mechanism(s), or indeed even whether corrosion protection by a CP is possible. Recent results from our laboratory indicate that, for an aluminum alloy coated with the oxidized form of polypyrrole (PPy), a passivation mechanism is not likely and that the dopant release mechanism may not be effective, especially in the presence of oxygen. An alternative approach is to utilize the neutral or reduced (n-doped) form of a conjugated polymer to cathodically protect the alloy and/or to serve as an oxygen scavenging coating. The CP coatings and alloy studied were neutral PPy and neutral or n-doped poly(2,3-dihexylthieno[3,4-b]pyrazine) on AA 2024-T3. Results from the scanning vibrating electrode technique and galvanic coupling measurements are presented to demonstrate the efficacy of this approach. [ABSTRACT FROM AUTHOR]

As an alternative to toxic chromate coating, Mg-rich primers have been designed to protect Al alloys (in particular AA2024-T3 [UNS A92024]) and developed in analogy to Zn-rich primers for steel substrate. The Mg pigment present in the primer can provide cathodic protection to Al substrates and significantly deter Al alloy corrosion when damage occurs. To determine how much the pigment metal alloy composition can be varied without sacrificing corrosion protection. three different primers based on Mg alloy powders as pigments were formulated with an epoxy-polyamide polymer binder at different pigment volume concentrations (PVC). Their behaviors were studied after cyclic exposure in a Prohesion chamber using electrochemical methods. Testing results from electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) showed that the metal-rich primers with Mg alloys as pigments could provide cathodic protection. and precipitates formed from oxidation of Mg alloy particles were similar to the ones found in the pure Mg-rich primer system. Furthermore, the investigation of the properties of the three alloy pigments gave a good understanding of the effects of particle shape, particle size, particle size distribution, and metal alloy chemical composition. [ABSTRACT FROM AUTHOR]