Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium
Plasma electrolytic oxidation (PEO) is a method to obtain protective coatings on metallic light-weight construction materials. Here, the workpiece receives a strong anodic polarisation in a suitable aqueous electrolyte, which leads to the formation of a passive layer and a gaseous shell. Afterwards,...
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doaj-26cd5aaedf8944cb9964cebc38ceed4c2020-11-25T04:00:23ZengMDPI AGCoatings2079-64122020-10-011096596510.3390/coatings10100965Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of MagnesiumFrank Simchen0Maximilian Sieber1Thomas Mehner2Thomas Lampke3Materials and Surface Engineering Group, Chemnitz University of Technology, D-09107 Chemnitz, GermanyDepartment of Corrosion Protection and Testing, EXCOR Korrosionsforschung GmbH, Magdeburger Straße 58, 01067 Dresden, GermanyMaterials and Surface Engineering Group, Chemnitz University of Technology, D-09107 Chemnitz, GermanyDepartment of Corrosion Protection and Testing, EXCOR Korrosionsforschung GmbH, Magdeburger Straße 58, 01067 Dresden, GermanyPlasma electrolytic oxidation (PEO) is a method to obtain protective coatings on metallic light-weight construction materials. Here, the workpiece receives a strong anodic polarisation in a suitable aqueous electrolyte, which leads to the formation of a passive layer and a gaseous shell. Afterwards, plasma electrolytic discharges appear on the substrate surface and convert it into a ceramic layer. The properties of the passive layer are influenced by the selected substrate/electrolyte combination and are essential for the PEO process-initiation and characteristics. In this work, a new method for the systematic investigation of the substrate/electrolyte interactions during the pre-discharge stage is presented. The procedure is carried out by a polarisation experiment and allows for a quantitative characterisation of the passivation behavior, based on a small electrolyte volume. The method is used to investigate a literature-known electrical conduction mechanism on passive films formed on magnesium, by cross-comparison between different Mg and Al materials. In addition, the influence of phosphate, glycerol, and fluoride on the passivation behaviour of the Mg alloy AZ31 in an alkaline environment is considered and quantified. The results provide an explanatory approach for the positive influence of toxic fluorides within the electrolyte on the morphology of PEO layers on magnesium.https://www.mdpi.com/2079-6412/10/10/965plasma electrolytic oxidationaluminiummagnesiumpassivationfluoride |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Frank Simchen Maximilian Sieber Thomas Mehner Thomas Lampke |
spellingShingle |
Frank Simchen Maximilian Sieber Thomas Mehner Thomas Lampke Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium Coatings plasma electrolytic oxidation aluminium magnesium passivation fluoride |
author_facet |
Frank Simchen Maximilian Sieber Thomas Mehner Thomas Lampke |
author_sort |
Frank Simchen |
title |
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium |
title_short |
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium |
title_full |
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium |
title_fullStr |
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium |
title_full_unstemmed |
Characterisation Method of the Passivation Mechanisms during the pre-discharge Stage of Plasma Electrolytic Oxidation indicating the Mode of Action of Fluorides in PEO of Magnesium |
title_sort |
characterisation method of the passivation mechanisms during the pre-discharge stage of plasma electrolytic oxidation indicating the mode of action of fluorides in peo of magnesium |
publisher |
MDPI AG |
series |
Coatings |
issn |
2079-6412 |
publishDate |
2020-10-01 |
description |
Plasma electrolytic oxidation (PEO) is a method to obtain protective coatings on metallic light-weight construction materials. Here, the workpiece receives a strong anodic polarisation in a suitable aqueous electrolyte, which leads to the formation of a passive layer and a gaseous shell. Afterwards, plasma electrolytic discharges appear on the substrate surface and convert it into a ceramic layer. The properties of the passive layer are influenced by the selected substrate/electrolyte combination and are essential for the PEO process-initiation and characteristics. In this work, a new method for the systematic investigation of the substrate/electrolyte interactions during the pre-discharge stage is presented. The procedure is carried out by a polarisation experiment and allows for a quantitative characterisation of the passivation behavior, based on a small electrolyte volume. The method is used to investigate a literature-known electrical conduction mechanism on passive films formed on magnesium, by cross-comparison between different Mg and Al materials. In addition, the influence of phosphate, glycerol, and fluoride on the passivation behaviour of the Mg alloy AZ31 in an alkaline environment is considered and quantified. The results provide an explanatory approach for the positive influence of toxic fluorides within the electrolyte on the morphology of PEO layers on magnesium. |
topic |
plasma electrolytic oxidation aluminium magnesium passivation fluoride |
url |
https://www.mdpi.com/2079-6412/10/10/965 |
work_keys_str_mv |
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