Hybrid coatings for corrosion protection of aeronautical parts against runway de-icing chemicals

Sol-gel based inorganic-organic hybrid coatings were developed and coated on aeronautical parts including cadmium plated steel and magnesium alloy. The hybrid coatings were targeted to provide two kinds of solutions. Firstly, the aim was to protect the cadmium-plating against the corrosion initiated especially by runway de-icing chemicals (formiate and acetate based). Secondly, the hybrid coating approach was targeted to provide alternative coating solutions for cadmium plating as well as hexavalent chromium conversion coatings. In order to improve the corrosion resistance of the selected substances, the chemistry of the inorganic backbone of the hybrid coating was varied by using silane and aluminium alkoxides. Furthermore, the organic components of the hybrid coating were also varied. The corrosion performance of the coated specimens were investigated by using standardised runway de-icing corrosion test (AMS G-12) and salt spray test (ISO 9227). Based on the AMS G-12 test results, the use of the hybrid coatings improved the corrosion protection of cadmium plating against runway de-icing corrosion. The salt spray test showed that the corrosion protection performance of the hybrid coating on cadmium-plating was similar to uncoated cadmium plating. In the case of magnesium alloy, the hybrid coating showed also better corrosion protection in the both corrosion tests compared to Cr6 conversion coating.