Olga Kachurina

Comparison of single and multilayer coatings based on ormosil and conversion layers for aluminum alloy corrosion inhibition

Corrosion resistance behavior of single and multilayer coatings based on ormosil, trivalent chromium conversion coating (tccc) and hexavalent chromium conversion coatings (hccc) on the surface of 2024-T3 aluminum alloy (AA) was investigated using potentiodynamic polarization curves and accelerated salt spray testing. The magnitude of the corrosion resistance for single layer coatings increased tccc < ormosil < hccc. Multilayer ormosil/ormosil coatings are subject to phase separation, leading to poor performance in the electrochemical and accelerated salt spray testing. The presence of either hccc or tccc in the multilayer film was found to augment the inherent corrosion resistance of the ormosil barrier film. Multilayer coatings composed of either tccc/ormosil or hccc/ormosil were found to exhibit Rcorr values in the range 158–177 kΘcm2. This implies that the environmentally-benign and nontoxic trivalent chromium conversion coating used in combination with an ormosil film may be a potential alternative for hexavalent chromium conversion coatings.

Electrochemical and salt spray analysis of multilayer ormosil/conversion coating systems for the corrosion resistance of 2024-T3 aluminum alloys

The corrosion resistance characteristics of multilayer coating systems comprised of a conversion coating base layer and an organically modified silicate (ormosil) topcoat have been analyzed using salt spray and potentiodynamic polarization curve analyses. The effectiveness of the multilayer coating systems was found to depend on the presence of an electrochemically active species in the conversion coating and on the presence of a curing agent in the ormosil system. Multilayer coatings systems comprised of conversion coatings that contain active corrosion inhibitors were found to provide high degrees of corrosion protection. In all cases, the presence of the ormosil was found to enhance the corrosion resistance of the underlying conversion coating. The use of multilayer ormosil/conversion coating systems enhances the corrosion protection of 2024-T3 aluminum alloy by combining previously developed corrosion protection methods with emerging sol-gel technology.

Laser-induced electrochemical characteristics of aluminum alloy 2024-T3

Laser-induced surface modification of aluminum alloy 2024-T3 was investigated as laser intensity dependence of surface composition and patterning related to electrochemical characteristics using techniques of environmental scanning electron microscopy (ESEM), potentiodynamic scan, and electrochemical impedance spectroscopy (EIS). Analysis of surface composition using ESEM and EIS indicated that laser fluences in a range of 1.1–1.3 J/cm2 were found to preferentially reduce the copper concentration in the alloy surface to approximately 0.1 wt % and grow the oxidized layer on the surface. Surface composition and patterning were accordingly correlated to electrochemical characteristics of corrosion resistance, capacitance, and potential, which were subsequently used to calculate the corresponding thickness of the formed oxide layer. An enhancement of corrosion resistance characteristics of the 2024-T3 aluminum alloy was attributed to the combination of laser-induced copper removal and oxide layer formation on...

Technique for the removal of organic–inorganic hybrid coatings from 2024-T3 aluminum alloy

Organically modified silicate (Ormosil) films have been found to provide good corrosion protection for aerospace aluminum alloys (AAs) as they form a dense, mechanically stable, highly adherent, barrier layer on the metal surface. In order to be considered for large-scale applications, a suitable, low-cost, environmentally benign coating removal method is necessary. In this study, the effectiveness of various acidic, basic, and organic solvents for Ormosil coating removal from 2024-T3 AA substrates was investigated. Results presented herein indicate that a dilute zincate solution, of the type commonly used as a pretreatment for electroless and electroplated nickel deposition on AAs, effectively removed the Ormosil coating at room temperature. This coating removal technique leaves a thin zincate layer on the AA surface, slowing dissolution of the metal in the basic solution, hence, maintaining the integrity of the AA substrate. The residual zincate layer may be easily removed using dilute phosphoric acid.