The goal of this project is to develop and refine a two-layer anodization method for aluminum alloys to form:

1. A dense inner aluminum oxide layer that creates an insulating band gap for electrical conduction.
2. A porous outer aluminum oxide layer that facilitates structural adhesion.

The approach for this work focuses on laboratory and benchtop experiments to optimize an anodization process for aluminum alloys used on aircraft. Improvements in the anodization method result in a higher technology readiness level process that provides the most protective inner layer while still maintaining good coating or bonding adhesion properties in the outer layer. The outcomes of the anodization method are evaluated using laboratory and accelerated exposure testing as well as 3 to 6-month outdoor exposures.

Carbon fiber reinforced polymer (CFRP), in thermoset or thermoplastic form, has high specific strength and is finding more applications in more lighter weight air mobility platforms. CFRP/aluminum alloy joints exist in different application scenarios as CFRP components are designed piecewise to replace some conventional aluminum alloy parts. Even for completely new thermoplastic design, however, aluminum alloy inserts are still used for composite manufacturability. CFRP/aluminum alloy joints have galvanic corrosion related stress corrosion cracking risks. An improved joining process for aluminum aircraft alloys to more noble materials like carbon fiber reinforced polymers would suppress galvanic corrosion arising from the dissimilar material couple. This reduction in galvanic corrosion provides direct environmental benefits. The aluminum anodization process reduces the use of toxic or harmful chemicals that are included in legacy aircraft coatings as corrosion inhibitors because corrosion damage would be decreased. In addition, the rate of damage accumulation, that can lead to crack nucleation, from galvanic corrosion would be slowed, thereby extending the service life of some components on the aircraft.