The Air Force and the Army currently spend about $1 billion and $10 billion per year respectively in developing a corrosion protection strategy. Most of this corrosion protection strategy is based on the use of barrier coatings and paints that contain chromates. Chromate corrosion protection technologies will be replaced only when environmentally friendly corrosion protection technologies achieve acceptable levels of performance. Currently, chromate-free conversion coatings do not match the level of corrosion protection provided by chromate conversion coatings. To a large extent, coating formulators do not know what attributes of chromate coatings result in their superior performance.

This project attempts to acquire a fundamental understanding of the chemical and physical processes and mechanisms of corrosion protection provided by chromate-based coatings applied to metal surfaces. A specific focus will be placed on corrosion protection of aluminum alloys.

Concept of Surface Conversion Coatings. The Prototypical Classes of Chromate-Free Conversion Coating Technology Proposed To Be Examined Are on the Right Hand Portion of the Diagram.

This program comprises a multi-year fundamental research effort. The first research activity will focus on the role of microstructural heterogeneity in the alloy substrate on chromate conversion coating formation and breakdown. The second research activity will study the relationship between coating structure and chemistry and coating properties and performance. This relationship will be evaluated for non-ideal conditions to which the coatings may be subjected. These conditions include advanced age, exposure to conditions that subsequently impair coating corrosion resistance mechanisms, and less than ideal application methods. The third research activity will focus on the development of rapid, quantitative, and predictive tests to measure corrosion protection.

Electrochemical measurements (cyclic voltametry) on bulk intermetallics were initiated to characterize the effect of Alodine solution chemistry on the formation of chromate conversion coatings. Observations were made of chemical heterogeneity on intermetalic phases using Raman and Infrared spectroscopy to determine variations in composition. The spectroscopic characterization of chromate/epoxy 828 coatings was completed providing baseline data involving aging and the release of chromate.

This program will allow for the elimination of the toxic hazard that chromates pose to human health through the replacement of chromate corrosion protection technologies throughout the Department of Defense and the Department of Energy. An understanding of the attributes that give chromate coatings their superior performance also will be evaluated.