Passive behavior of magnesium alloys (Mg–Zr) containing rare-earth elements in alkaline media

The passive behavior of magnesium alloys ZK31, EZ33 and WE54 was studied in alkaline media (NaOH – pH 13) in the presence and absence of chloride ions. The electrochemical properties were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measu...

Full description

Saved in:
Bibliographic Details
Published in:Electrochimica acta 2010-02, Vol.55 (7), p.2482-2489
Main Authors: Pinto, R., Ferreira, M.G.S., Carmezim, M.J., Montemor, M.F.
Format: Article
Language:English
Subjects:
Alloys
Applied sciences
Atomic force microscopy
Chlorides
Corrosion
Corrosion mechanisms
Electrochemical impedance spectroscopy
Exact sciences and technology
Impedance
Magnesium base alloys
Metals. Metallurgy
Mg–Zr alloys
Morphology
Passivity
Rare earth metals
Rare earths
X-ray photoelectron spectroscopy
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The passive behavior of magnesium alloys ZK31, EZ33 and WE54 was studied in alkaline media (NaOH – pH 13) in the presence and absence of chloride ions. The electrochemical properties were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the study of the chemical composition and surface morphology of the surface films, respectively. The electrochemical impedance results revealed that the film formed on the surface of the three alloys is characterized by an increasing resistance, which stabilized with time. In the absence of chloride the film resistance was identical for all the three alloys. However, in the presence of chloride, the resistance of the film formed on the EZ33 alloy dropped nearly one order of magnitude comparatively to the other alloys. Generally, in the presence of chloride there was a decrease of the conductive character of the film. The films are homogeneous and, according to the XPS results, the outer layer seemed mainly composed of Mg(OH) 2 and the internal layer composed of MgO, independently of the presence of chloride. The AFM study revealed that the presence of chloride affected film morphology, namely nano-crystallites dimensions and aggregates size that increased.
ISSN:0013-4686
1873-3859
DOI:10.1016/j.electacta.2009.12.012