As the Department of Defense transitions away from the use of hexavalent chromium due to health concerns and increasing regulations, new corrosion protection technologies must be developed and validated. In order to more quickly and reliably evaluate these technologies, accelerated corrosion tests that more accurately mimic operational environments are needed. The development of a new accelerated corrosion test method is discussed in this work. Six test methods were designed to explore the effect of relative humidity cycling, electrolyte deposition duration & frequency, and test assembly design on the resulting corrosion damage of coated metallic assemblies. After exposure to each method, assemblies were analyzed for corrosion damage using optical and laser profilometry along with cross sectioning across fastener holes. An optimal method was identified based on the degree to which the performance of various chromated and non-chromated coating stack ups could be distinguished after exposure to the method for 1,250 hours.
Hexavalent chromium is utilized for the purpose of providing corrosion inhibition on many DoD assets in the form of surface treatments and primers. However, hexavalent chromium is also a known carcinogen and environmental toxin. As a result, processes which involve the application of hexavalent chromium will likely face increased regulation in the future. Currently, there are few other compounds that provide the level of corrosion resistance provided by hexavalent chromium, so the need for accelerated and relevant research, test, and development of alternative corrosion preventative compounds is becoming more important and urgent.
The best way to replicate the mode and severity of corrosion-induced damage is through outdoor field exposure. Typically, new formulations are first tested under laboratory conditions, and the most promising are advanced to outdoor coupon exposures. Coatings or technologies that perform well during these two tests are then advanced to trial applications on fielded assets. This is time consuming and therefore restricts the rate at which new coating technologies can be tested and qualified. There are many accelerated corrosion test (ACT) methods (e.g., ASTM B117, ASTM G85, GMW14872, etc.)[2-4], but these test methods are unreliable in their ability to reliably replicate corrosion severity and failure mechanisms seen in outdoor exposures. In addition, it is well known that the chambers used for these test methods can vary greatly from test to test and from lab to lab. Recent studies indicate the shortfall of many of these ACT methods lay in their lack of control of relative humidity[1]. To address these issues, a new method with strict control over relative humidity needs to be developed.
