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Plasma Electrolytic Oxidation of High-Strength Aluminium Alloys—Substrate Effect on Wear and Corrosion Performance

1
Department of Corrosion Protection and Testing, EXCOR Korrosionsforschung GmbH, Magdeburger Straße 58, 01067 Dresden, Germany
2
Materials and Surface Engineering Group, Chemnitz University of Technology, D-09107 Chemnitz, Germany
*
Author to whom correspondence should be addressed.
Metals 2018, 8(5), 356; https://doi.org/10.3390/met8050356
Received: 12 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 15 May 2018
(This article belongs to the Special Issue Plasma Electrolytic Oxidation)
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Abstract

With the progress in materials science and production technology and the establishment of light-weight design in many fields of the industry, the application of light metals no longer requires only mechanical strength, but also a significant protection of the material against wear and corrosion. Hard and wear-resistant oxide coatings on aluminium are produced by plasma electrolytic oxidation (PEO). During PEO, a conversion of the aluminium substrate to a ceramic oxide takes place. While the role of strength-giving alloying elements like Cu, Mg/Si, Zn, and Zn/Cu on the PEO process has selectively been subject of investigation in the past, the significance of the alloy composition for the service properties of the coatings is still unknown. Therefore, the performance of PEO coatings produced on the widely used commercial high-strength alloys AlCu4Mg1 (EN AW-2024), AlMgSi1 (EN AW-6082), and AlZn5.5MgCu (EN AW-7075) is examined with regard to their behaviour in the rubber-wheel test according to ASTM G65 and the current density-potential behaviour of the substrates with undamaged and worn coatings in dilute NaCl solution. To give a reference to the unalloyed material the testings were carried out also on Al 99.5 (EN AW-1050) which was treated in an adjusted PEO process. Although differences in the conversion of intermetallic phases during PEO and the phase composition of the coatings on the various substrates are determined, the service properties are hardly depending on the alloying elements of the investigated aluminium materials. The wear rates in the rubber-wheel test are low for all the alloyed samples. The current density-potential curves show a decrease of the corrosion current density by approximately one order of magnitude compared to the bare substrate. Eventually, previous wear of the coatings does not deteriorate the corrosion behaviour. PEO layers on technically pure aluminum can resist the testing regimes if they are prepared in an electrolyte with an elevated silicate content and without additional hydroxide ions, during a longer process time. View Full-Text
Keywords: plasma electrolytic oxidation; wear; rubber-wheel test ASTM G65; corrosion; current density-potential characterization; high-strength aluminium plasma electrolytic oxidation; wear; rubber-wheel test ASTM G65; corrosion; current density-potential characterization; high-strength aluminium
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Sieber, M.; Simchen, F.; Morgenstern, R.; Scharf, I.; Lampke, T. Plasma Electrolytic Oxidation of High-Strength Aluminium Alloys—Substrate Effect on Wear and Corrosion Performance. Metals 2018, 8, 356.

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