Comparative study of different environmentally friendly (Chromium-free) methods for surface modification of pure magnesium

In this work, three different chromium-free methods of surface modification of pure magnesium were studied; namely, a cerium conversion coating, a carbonated coating and an anodic film. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), micro Raman spectrosco...

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Bibliographic Details
Published in:Surface & coatings technology 2011-09, Vol.205 (23), p.5254-5259
Main Authors: Zuleta, A.A., Correa, E., Villada, C., Sepúlveda, M., Castaño, J.G., Echeverría, F.
Format: Article
Language:English
Subjects:
Anodizing
Applied sciences
Calcium carbonate
Carbonation
Cerium
Chromium-free treatment
Coatings
Conversion coating
Cross-disciplinary physics: materials science
rheology
Electrochemical impedance spectroscopy
Exact sciences and technology
Magnesium
Materials science
Metals. Metallurgy
Morphology
Other surface treatments
Physics
Production techniques
Protective coatings
Surface treatment
Surface treatments
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Summary:In this work, three different chromium-free methods of surface modification of pure magnesium were studied; namely, a cerium conversion coating, a carbonated coating and an anodic film. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), micro Raman spectroscopy (MRS) and X-ray diffraction (XRD) were employed to study the morphology and composition of the surface after treatments. The corrosion resistance of the treated surfaces was evaluated by means of electrochemical impedance spectroscopy (EIS). XRD and MRS showed that conversion coatings obtained from cerium salts consisted of cerium oxides and hydroxides and the major component of the layer was CeO 2. The morphology of the cerium conversion coating consisted of a fiber-like structure that exhibited several network-like cracks. The carbonated coating was mainly composed of aragonitic CaCO 3, whereas the oxide layer formed in the anodizing process was a porous film made of MgO and some phosphate species compounds. The results of EIS tests indicated that calcium carbonated coating provided higher corrosion protection. ► 3 different Chromium-free methods of surface modification on pure Mg. ► All the alternatives, non-toxic methods, improve corrosion behavior of Mg. ► Coating obtained from carbonated treatment exhibits better corrosion protection. ► Compact, stable and adherent layers of CaCO 3 are formed in this method.
ISSN:0257-8972
1879-3347
DOI:10.1016/j.surfcoat.2011.05.048