Use of cerium-based inhibitors in electrochemically deposited coatings for the corrosion protection of aluminum alloys

Corrosion is a common problem in military aircraft and structural components made from high strength aluminum alloys such as 7075 T-6 and 2024 T-3 are particularly susceptible. Chromating is the most commercially used surface pre-treatment for the corrosion protection of aluminum alloys in the aircraft and the aerospace industries. Major reasons for the widespread use of chromium-based protective coatings are their self-healing nature, excellent corrosion resistance and their ease of application. However, current environmental legislation is moving towards total exclusion of hexavalent chromium, Cr6+ due to its toxic nature. Regulatory pressure to reduce the hazardous waste of chromium supports development of non-toxic alternative methods of corrosion protection.; The degree and type of corrosion protection provided by these alternative coatings are also of importance. ASTM standards are used to evaluate coating performance, but these methods are time consuming and not particularly quantitative nor reproducible. Some ASTM methods require from 336 to 2000 hours, so it is clear that the development of an accelerated test method for the evaluation of new corrosion inhibitive systems which successfully correlates with the ASTM B-117 Salt Spray test is necessary.; The purpose of this study was the incorporation and evaluation of promising cerium-based corrosion inhibitors into cathodically deposited electrocoat primers for the replacement of toxic chromium in military and aerospace applications. Classical ASTM methods, as well as short term electrochemical tests, were used to evaluate the corrosion protection provided by the inhibitor containing primer formulations. SEM/EDX and Auger spectroscopies were used to characterize the morphology and elemental composition of the resulting coatings.