Non-chromate conversion coatings compliant with MIL-DTL-55411 have been demonstrated to provide protection comparable to their chromate counterparts. Repair materials are available to address defects in bath-applied conversion coatings from most manufacturers for these products that have been approved under MIL-DTL-817062, though with significant variations in their application methodology and efficacy. In this work, repair material chemistries from three different vendors were evaluated, working towards a single application method that can be used independent of the selected chemistry. Each coating was then benchmarked against an industry standard chromate conversion coating repair material in terms of both the corrosion performance as well as the capability of each coating to maintain the ability to make low resistance electrical contact to the surface.
Chromate conversion coatings are relied upon to ensure the long-term corrosion performance and surface electrical properties of aluminum alloys, as well as to improve the bond strength and adhesive properties of organic coatings and adhesives. Chromate based chemistries have been all but eliminated in Europe, and it is believed the Environmental Protection Agency (EPA) will stage their elimination in the USA within the next 5 to 10 years. The development of chemistries to replace chromate has been a hot area of research for over 30 years, and now a series of commercial alternatives have become available. These new coatings differ in their chemistry and performance characteristics, as well as their functional limitations, from chromate. Repair materials available from a variety of manufacturers, used to address defects in the conversion coating, have been found to vary in terms of their application methodology and efficacy as will be discussed below. The purpose of this work is to evaluate a variety of application methods and chemistries in an effort to ultimately develop a single procedure that can be used to apply each effectively.
