Sol-Gel Derived Surface Treatments for Aircraft Aluminum Alloys

Abstract

Abstract : Technologies for providing enhanced corrosion resistance for 2024-T3 aluminum alloy were investigated. This program investigated: (a) laser processing of metal surfaces to obtain optimum corrosion resistance and (b) the development of sol-gel derived coatings specifically targeted for use on aircraft aluminum alloys. Specifically, a nanosecond excimer laser was used for the surface modification of structure and composition of 2024-T3 aluminum alloy. Environmental scanning electron microscopy (ESEM) was used to characterize the alloy surface structural modification and composition as a function of laser fluence and pulse number. Potentiogynamic scan (PDS) and electrochemical impedance spectroscopy (EIS) were used to analyze corrosion resistance properties of the pre- and post-treated alloys. The ablation process was found to result in the removal of second phase elements, i.e., copper, and growth of the barrier aluminum oxide layer on the surface. These two complementary effects were found to enhance the corrosion resistance properties of the aluminum alloy surface. Additionally, various organically-modified silicate (Ormosil) coatings were investigated and found to provide good corrosion resistance characteristics for 2024-T3 aluminum alloys as determined using potentiodynamic polarization scans and accelerated salt spray testing. Ormosil structures were investigated using solid state NMR. Structure/property relationships were developed based on a correlation of NMR and salt spray/electrochemical data. The incorporation of a curing agent was found to enhance the corrosion resistance characteristics of the Ormosil coating.