Corrosion Resistant Silica-Based Conversion Coatings

Illinois Applied Research Institute (ARI) researchers Dr. Dan Krogstad (co-PI) and Dr. Maryam Eslami, along with Prof. Mohan Sankaran (PI) from the Department of Nuclear, Plasma, and Radiological Engineering (NPRE) and Interim Director of ARI, have successfully completed a project focused on the development of environmentally friendly corrosion prevention on aluminum surfaces for naval aviation by atmospheric-pressure microwave plasma-based cleaning and deposition. This two-year project was funded by the Naval Air Warfare Center Aircraft Division (NAWCAD).

The Department of Defense and the US Navy increasingly rely on aluminum alloys due to their high strength-to-weight ratio and corrosion resistance, particularly in marine environments, where reducing weight and improving fuel efficiency are critical. However, while aluminum alloys are more corrosion-resistant than carbon steel, they are still susceptible to pitting and intergranular corrosion, especially in sea water. Effective corrosion management is essential to prevent structural degradation. By focusing on advanced protective coatings, the US Navy enhances asset durability, reduces lifecycle costs, and ensures that critical vessels and equipment remain mission ready.

In this project, using an atmospheric plasma process, silica-based conversion coatings were fabricated on different aluminum alloys, including AA1100-H14, AA2024-T3, and AA7075-T6. The fabricated conversion coatings showed homogenous thickness and composition across the surface, regardless of the composition of the substrate and the presence of secondary phases, such as intermetallic particles. The results of electrochemical corrosion characterization and post-corrosion microscopy investigations showed that the conversion coatings were effective in decreasing the corrosion rate and protecting the alloy surfaces in NaCl solution (sea water).

This project demonstrated the effectiveness of using atmospheric-pressure plasmas to deposit silica-based conversion coatings on aluminum alloys. Atmospheric-pressure plasmas can reduce the costs and hazards associated with traditional immersion-based application methods by minimizing use of chemicals and solvents. Additionally, the work has shown that the quality of the coatings can be improved compared to immersion methods, because plasma deposition is substrate-agnostic and avoids preferential nucleation and growth on intermetallic particles.

Figure. (a) Surface and (b) cross-sectional SEM images of the atmospheric plasma fabricated Si-based conversion coating on AA2024-T3.