High Performance Electrolytic Coating Touch-Up Repairs for Aluminum

Corrosion protection for aerospace aluminum primarily relies on two inorganic coatings: chromate conversion coating and anodize coatings. Anodizing provides a superior barrier against corrosion, especially in harsh salt-water environments. In contrast, chromate conversion coatings (e.g., Alodine, Iridite) offer less protection but are significantly easier to apply, requiring a simple, non-electrolytic chemical application. This difference in application creates a maintenance challenge. Anodizing is a complex process generally restricted to depot or Original Equipment Manufacturer (OEM) production facilities. Field repairs on anodized components, which can comprise up to 5% of the surface area under MIL-PRF-8625, often fall back on the use of easier-to-apply chromate conversion coatings. Touch-up pens, in particular, are widely used in aviation maintenance, from large depots to resource-constrained fleet environments. However, when used on an anodized part, these chromate repairs create a point of weakness that is more susceptible to corrosion. A third alternative, electrolytic conversion coating, has been developed to bridge the performance gap between these two methods. Recent studies at NAVAIR demonstrate that applying a small electrical current (several hundred milliamps per square foot) during the conversion coating process significantly enhances corrosion resistance. Currently, the equipment required for this process restricts its use to depot factories where chemical processing shops are available. This creates a need for a field-deployable solution. This topic seeks the development of a portable touch-up method for applying electrolytic conversion coatings. The solution is critical for filling a technology gap for a method to apply, repair, and touch-up aluminum coatings at the fleet level, improving corrosion capabilities across all levels of aircraft manufacturing, maintenance, and rework operations. The ideal solution should meet the following criteria: • The method must prevent chemical spills, environmental release, operator exposure, and contamination of the maintenance area. • The process should be simple, cost-effective, easy to deploy to fleet maintenance sites, and require minimal operator training. • The process should generate minimal hazardous waste, and the equipment should be simplified and miniaturized as much as is practical. • The resulting coating must meet or exceed the corrosion performance requirements of MIL-DTL-81706. • The application method must not damage the underlying aluminum through pitting, fatigue loss, or other undesirable effects. • Primary aerospace aluminum alloys are 2000, 6000, and 7000 series aluminum alloys. However, the application method must perform equally well on all aluminum alloys. • The process must not use hexavalent chromium.