Abstract
Chromate coatings used as corrosion protection technologies for aluminum alloys are environmentally harmful and extremely toxic. This paper presents an investigation on the deposition of environmentally friendly cerium oxide-based anticorrosive coatings on aluminum alloy 2024 substrates by the sol - gel method. The influence of the calcination temperature on both the microstructural characteristics and the electrochemical corrosion performance was tested using scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), before and after, periods of immersion in saline corrosive solutions. The ceramic coatings synthesized at 200, 300 and 400 °C showed very resistive behaviors leading to both an efficient passivation of the alloy surfaces and good corrosion protection. This passivation was maintained for 30 days of immersion in saline solutions, as well as, when aggressive electrochemical polarization experiments (until 2.0 V versus saturated calomel electrode) were used. Very high resistances for the charge transfer (0.14-0.28 GΩ) and very low current density values (5 × 10- 14 -5 × 10- 11 A cm- 2) were estimated by EIS and potentiodynamic polarization, respectively, for coatings prepared at 200-400 °C. Thus, the coatings prepared in this study by the sol - gel method appear as an efficient treatment for the corrosion protection of aluminum alloys.
Highlights
The aluminum alloy 2024 (AA2024) is widely used for structural applications in the aerospace industry due to its good combination of high strength, fatigue resistance and low density
These patterns reveal the presence of crystalline cerium dioxide (CeO2) deposits (Joint Committee of Power Diffraction Standards-JCPDS #43-1002) with characteristic peaks in the 2θ values of 28.6, 33.0, 47.5, 56.3, 69.4 and 88.4° corresponding to the reflection planes of the cerianite structure (111), (200), (222), (311), (400) and (422), respectively
This preferential deposition is expected for the sol–gel method and is in agreement with previous reports that observed the same 2θ values for crystalline CeO2 coatings prepared by the sol–gel method, using ammonium cerium nitrate as precursor[7,19]
Summary
The aluminum alloy 2024 (AA2024) is widely used for structural applications in the aerospace industry due to its good combination of high strength, fatigue resistance and low density. The deposition of cerium oxide coatings on AA7075-T6 surfaces by sol–gel method at 300 and 400 °C of calcination temperature produced very efficient active barrier against corrosion[7]. This study presents the development of anticorrosive cerium oxide coatings prepared by the sol–gel method using a broad range of deposition temperatures (100, 200, 300 and 400 °C) on AA2024 substrates. Their microstructural characterization and electrochemical corrosion testing was carried out by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The anticorrosive performance of the coatings was tested, showing that the calcination temperature used in the synthesis has considerable influence on the efficiency of the protective coating
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