Architectural optimization of an epoxy-based hybrid sol–gel coating for the corrosion protection of a cast Elektron21 magnesium alloy

•A defect-free bilayer hybrid sol–gel coating was successfully produced.•The first deposed layer may provide a nobler surface for the second layer.•The second deposed layer covers the defects observed on the first deposed layer.•A global thickness threshold is observed on the electrochemical results...

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Bibliographic Details
Published in:Applied surface science 2014-08, Vol.309, p.62-73
Main Authors: Murillo-Gutiérrez, N.V., Ansart, F., Bonino, J-P., Kunst, S.R., Malfatti, C.F.
Format: Article
Language:English
Subjects:
Architecture
Coating
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Condensed matter: structure, mechanical and thermal properties
Corrosion
Corrosion prevention
Cross-disciplinary physics: materials science
rheology
Defects
Electrochemical impedance spectroscopy
Elektron21
Engineering Sciences
Exact sciences and technology
Impedance
Magnesium
Magnesium base alloys
Materials
Physics
Sol gel process
Sol–gel
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Summary:•A defect-free bilayer hybrid sol–gel coating was successfully produced.•The first deposed layer may provide a nobler surface for the second layer.•The second deposed layer covers the defects observed on the first deposed layer.•A global thickness threshold is observed on the electrochemical results.•The architecture of the bilayer system has a strong influence on the properties of the coating. An epoxy-based hybrid sol–gel coating was prepared in various architectural configurations has been studied for the corrosion protection of a cast Elektron21 magnesium alloy. The creation of a single layer of this coating presents defects consisting of macro-pores and protuberances, which opens access for corrosive species to reach the metallic substrate. These defects are suspected to result from the high reactivity of the substrate, as well as to the irregular topography of the substrate disrupted by the microstructure of the own magnesium alloy. Hence, a sol–gel coating in bilayer architecture is proposed, where the first layer would “inert” the surface of the magnesium substrate, and the second layer would cover the defects of the first layer and also thickening the coating. The morphological characteristics of the sol–gel coatings were analyzed by scanning electron microscopy (SEM), and their corrosion behavior was evaluated by OCP (open circuit potential) monitoring and electrochemical impedance spectroscopy (EIS) in chloride media. It is shown that both the architectural arrangement and the individual thickness of the first and second layers have an important influence on the anticorrosion performances of the protective system, just as much as its global thickness.
ISSN:0169-4332
1873-5584
DOI:10.1016/j.apsusc.2014.04.169