Composition, Structure, and Protective Properties of Air-Formed Oxide Films on Magnesium Alloys. Magnesium and Its Alloys (2019), 2019
In spite of the growing interest in the corrosion mechanisms of magnesium (Mg) and its alloys, ke... more In spite of the growing interest in the corrosion mechanisms of magnesium (Mg) and its alloys, key aspects have not been sufficiently clarified to date. Considerable recent research has addressed the relationships among the chemical composition, the presence and quantity of precipitates, inclusions or impurities and the microstructure of magnesium alloys and their corrosion resistance. However, the precise nature and properties of the thin, air-formed oxide film, which is approximately 3 nm thick, that spontaneously grows on the outermost surface in contact with the atmosphere and its effect on the corrosion of commercial magnesium alloys is still subject to debate. Differences in the thickness, uniformity and chemical composition of these films associated with the alloying element content or the surface conditions of the bulk material may provide basic corrosion-related information that is expected to increase the protective properties for Mg alloys. This entry provides an overview of our current understanding of air-formed oxide films on the surface of magnesium alloys and the possible relationship between the surface composition and degradation of the material. The protective capacity of certain of these thin surface films in different corrosive environments is critically discussed.
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Papers by S Feliu Jr
good castability, which makes them promising lightweight structural materials.
However, since magnesium is one of the most chemically active metals, its corrosion
resistance is one of the key points that limit its use in real conditions.
This thesis is divided into three chapters. The first focuses on the corrosion mechanism
of pure magnesium and the negative difference effect (NDE). The second is formed by
an in-depth study of the native oxide surface films and the corrosion products layers
formed on the AZ31 and AZ61 magnesium alloys, along with their influence on
corrosion. The third chapter comprises several studies where different strategies to
reduce the corrosion rate of magnesium and its alloys were analyzed.
Chapter I: Corrosion Mechanisms of Magnesium and the Negative Dif
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interest, but their insufficient corrosion resistance is sometimes an impediment to their
widespread use. This explains why much current research is focused on better understanding
and improving the corrosion behaviour of these alloys.
Such research often relies on the results of immersion tests in aqueous chloride solutions, which
have generally proven to be highly appropriate for a quick characterisation and classification
of the corrosion resistance of the different magnesium alloys. Corrosion tests in chloridecontaining
media may, however, be subject to a serious problem as has been noted by several
authors [1-3], in that important discrepancies are sometimes seen between the magnitude of
the experimental values and expected values based on available information on the typical
behaviour of these alloys. In this respect it is a well known fact that much lower electrochemical
corrosion rate values may be obtained with magnesium alloys immersed in some corrosive
media than the real values determined gravimetrically. In the literature, this behaviour has
tentatively been associated with several phenomena such as material disintegration, the
participation of monovalent Mg+
ions in the corrosion process, and anomalous chemical
dissolution, although the true causes of such discrepancies remains to be fully clarified.