Advanced chrome-free organic–inorganic hybrid pretreatments for aerospace aluminum alloy 2024-T3—application of novel bis-ureasil sol–gel precursors

Abstract

Effective pretreatment of aluminum alloys is very critical to success of protective coating systems for aerospace applications. While chromate-based pretreatments have been very successful for corrosion protection, they have been a target for replacement due to the increasingly stricter regulatory requirements arising from toxicity and carcinogenic nature of Cr(VI) used in such pretreatments. Among many approaches to develop alternative systems, the organic-inorganic hybrid (OIH) coatings based on sol-gel technology has advanced rapidly. We have successfully developed OIH coating systems by using suitably tailored organosilane precursors and sol-gel processing conditions. A series of novel bis-ureasil precursors have been developed and employed as organic precursor of OIH systems. Statistical design of experimental methodology (DoE) has been used to study and optimize compositional and process parameters using multifactor analysis of variance (ANOVA) analysis method. The corrosion resistance study (Potentiodynamic polarization, salt-spray corrosion test) shows that by proper choice of sol-gel precursors, cross-linkers, and reaction conditions, very dense, adherent and protective hybrid coatings, comparable in performance to chromate-based ones, can be obtained for aerospace aluminum alloy 2024-T3.

Sol–gel route to ceria coatings on AA2024-T3 aluminum alloy

“…[10][11][12][13][14][15] By means of various additives to the coating-forming solution, the coatings with different physical and chemical properties can be obtained. When organic molecules were introduced into an inorganic network, a hybrid organic-inorganic coating could be successfully synthesized.…”

Enhancing the Corrosion Protection of AA2024-T3 Alloy by Surface Treatments Based on Piperazine-Modified Hybrid Sol–Gel Films

“…In this context, numerous researchers are making a considerable effort to look for alternatives to chromate conversion coatings (CCCs) due to the carcinogenic effect of the hexavalent chromium used on these formulations [6,7]. One promising technique to develop eco-friendly and non-toxic coatings consists of applying films based on hybrid organopolysiloxane precursors as surface chemical conversion coatings [8][9][10][11]. The hybrid sol-gel method consists of a combination of hydrolysis and condensation processes of mixtures of organic and inorganic constituents, which makes possible the production of coatings with good flexibility, reduced defects and hydrophobic in nature, keeping the adhesion to the metal substrate and improving the compatibility with polymeric top-coatings [12][13][14][15].…”

Effect of AA2024‐T3 surface pretreatment on the physicochemical properties and the anticorrosion performance of poly(γ‐glycidoxypropyltrimethoxysilane) sol‐gel coating

“…Because of their exceptional mechanical properties and low densities, some aluminum alloys, such as AA2024‐T3, were widely used in the aerospace industry. However, because of many intermetallics formed in AA2024‐T3, particularly the S‐phase, the exposure of the alloy to aggressive conditions increased the corrosion susceptibility …”