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Ce-based conversion coatings on Rheo-HPDC low Si content aluminium alloy
Department of Industrial Engineering, University of Trento, Italy.
Department of Industrial Engineering, University of Trento, Italy.
Department of Industrial Engineering, University of Trento, Italy.
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0003-2924-137X
2017 (English)In: EUROCORR 2017 - The Annual Congress of the European Federation of Corrosion, 20th International Corrosion Congress and Process Safety Congress 2017, Asociace koroznich inzenyru z.s.- AKI - Czech Association of Corrosion Engineers , 2017, p. 777-794Conference paper, Published paper (Refereed)
Abstract [en]

Cerium-based conversion coatings have been considered as an effective alternative to hazardous and carcinogenic chromate-based coatings used in the treatment of metal surfaces such as aluminium alloys. However, there is still considerable debate over the mechanism by which these coatings are formed on different alloys and microstructure features. In the current work, Ce-based conversion coatings were deposited on Rheo-HPDC Al-Si alloys by immersion in water-based solutions of cerium nitrate. Effect of deposition parameters including immersion time and Ce(NO3)3.6H2O concentration on the corrosion resistance and the morphology of coatings was investigated. In addition in some experiments, NaCl was added to the cerium based solution in order to accelerate the deposition of the conversion coating and also to understand the coating formation mechanism. Electrochemical behaviour of the treated aluminium alloys was evaluated in the solution of 0.05 mol/L NaCl using polarization test and electrochemical impedance spectroscopy (EIS) measurements. The morphology and distribution of the cerium-based conversion coatings on the aluminium alloys were studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). Conversion treated substrates in all solutions were shown to possess improved corrosion resistance in comparison to the untreated samples. Immersion time and Ce(NO3)3.6H2O concentration slightly affect the deposition and the passivation capability of the cerium hydroxide/oxide layers. SEM images revealed that the deposition of cerium is more favoured in some cathodic areas including iron-based intermetallics and/or eutectic silicon phase. This phenomenon helps to block the active interfaces between these cathodic sites and the aluminium matrix, which is prone to localized corrosion in chloride ion containing environments. 

Place, publisher, year, edition, pages
Asociace koroznich inzenyru z.s.- AKI - Czech Association of Corrosion Engineers , 2017. p. 777-794
Keywords [en]
Aluminum alloys, Aluminum coatings, Aluminum corrosion, Cerium compounds, Chromate coatings, Chromates, Corrosion resistance, Deposition, Electrochemical corrosion, Electrochemical impedance spectroscopy, Energy dispersive spectroscopy, Localized corrosion, Scanning electron microscopy, Silicon alloys, Sodium chloride, Solution mining, X ray photoelectron spectroscopy, Cerium-based conversion coatings, Conversion coatings, Deposition Parameters, Electrochemical behaviour, Electrochemical impedance spectroscopy measurements, Energy dispersive x-ray spectroscopy, Immersion in waters, Polarization tests, Corrosion resistant coatings
National Category
Corrosion Engineering
Identifiers
URN: urn:nbn:se:hj:diva-41533Scopus ID: 2-s2.0-85052327991OAI: oai:DiVA.org:hj-41533DiVA, id: diva2:1250195
Conference
Joint European Corrosion Congress 2017, EUROCORR 2017 and 20th International Corrosion Congress and Process Safety Congress 2017; Prague ; Czech Republic; 3 - 7 September 2017
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2018-09-21Bibliographically approved

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Zanella, Caterina

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