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- Electrochemical noise (1)
- Korrosion (1)
- Korrosionsprüfung (1)
- Magnesium (1)
- Nichtrostender Stahl (1)
- Pickling (1)
- Pre-treatment (1)
- Prüfverfahren (1)
- Schneidwaren (1)
Evaluation and Screening of the pre-treatment states of Mg-alloys using Electrochemical Noise
(2009)
A successful application of magnesium alloys as light structural materials and for special applications,
such as in the medical sector, depends significantly on their corrosion properties. Since the use of
well-chosen surface coating systems can optimize these properties, many efforts are going in this
direction. In general, any coating process must be seen in a close connection to the pre-treatment of
the alloy surface, particularly for magnesium alloys.
The pre-treatment is required to prepare the optimal surface for a coating system, in which adhesion
and dissolution behaviour are the central properties. In the case of magnesium alloys this means a
well-controlled removal of the casting or rolling skin, which would be prone to corrosion and poor
adhesion. Additionally, in most cases the surface morphology should be smooth. An investigation of
different pickling solutions and pickling parameters showed a wide range of effectiveness (i.e., the
resulting mass loss and surface morphology). Another important and often underestimated fact is the
comparatively strong tendency of magnesium to react with the atmosphere. For that reason, after a
completed pickling and cleaning treatment the condition of the surrounding atmosphere and the time
prior to coating of the surface should be taken into account because of the formation of different
reaction layers. These layers have an effect on adhesion and the corrosion properties of the coating
system as a whole. For a documentation of the influence of different atmospheres and the timedependence
of the surface activity the measurement of the electrochemical noise is the preferred
technique. This is because it shows instantaneously the actual activity, even in the absence of external
excitation. The influence of different pre-treatments as well as exposure conditions and duration was
investigated using electrochemical noise measurements as a screening method. As a result the pretreatment
which is an important part of the coating process could be considerably improved.
Die Korrosionsbeständigkeit von Schneidwaren wird derzeit noch in einem zyklischen Auslagerungsversuch mit anschließender visueller Bewertung geprüft. Neben der langen Versuchsdauer und unspezifischen Prüfung kommt es teilweise auch zu falschen Prüfaussagen. Durch die Anwendung und Weiterentwicklung einer elektrochemischen Untersuchungsmethodik, die speziell den Beginn von Lochkorrosion in sehr kurzer Zeit detektiert, steht ein neues Kurzzeit-Korrosionsprüfverfahren zur Verfügung, das gegenüber den bisherigen Prüfverfahren erhebliche Vorteile bietet.