SKPFM and SEM study of the deposition mechanism of Zr/Ti based pre-treatment on AA6016 aluminum alloy

Andreatta, F.; Turco, A.; Graeve, Iris De; Terryn, Herman; Wit, J.H.W. de; Fedrizzi, L.

doi:10.1016/j.surfcoat.2007.02.039

Cited by 128 publications

(125 citation statements)

References 14 publications

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“…22 The first plateau can be attributed to the lateral coverage of the aluminum substrate with this layer. 22 Stage III shows the second increase of potential indicates the further growth of the layer. It is known that oxide layers grow in thickness over the general aluminum substrate as a result of the cathodic reactions at the oxide surface via electron tunneling through the growing oxide layer or residual flaws in the layer.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Visser

González-García

Mol

et al. 2018

J. Electrochem. Soc.

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This study focuses on the elucidation of the formation mechanism of passive layers on AA2024-T3 during the exposure to alkaline lithium carbonate solutions in the presence of sodium chloride. Under controlled conditions, in an electrochemical cell, a protective layer was generated comprising an amorphous inner layer and a crystalline outer-layer. In order to resolve the formation mechanism, the layers were characterized using surface analytical techniques to characterize the surface morphology, thickness and elemental composition of the layers at different stages of the formation process. In addition, electrochemical techniques were applied to link the electrochemical properties of the layers with the different stages of formation. The results demonstrate that the formation mechanism of these layers comprises three different stages: (I) oxide thinning, (II) anodic dissolution and film formation, followed by (III) film growth through a competitive growth-dissolution process. The passive properties of the layers are generated in the third stage through the densification of the amorphous layer. The combined results provide an enhanced insight in the formation mechanism and the development of the passive properties of these layers when lithium salts are used as leaching corrosion inhibitor for coated AA2024-T3. Lithium salts gained interest as corrosion inhibitor after the observations of unexpected passivity of aluminum in alkaline lithium solutions by Gui and Devine.1 Aluminum is stable in the range of pH 4 to pH 9 due to the passivity of aluminum oxide.2 However, it is known that aluminum shows a high corrosion rate at pH values higher than 10.3 The corrosion process under these alkaline conditions is dominated by two subsequent sub-processes leading to significant mass loss. First, there is the process of direct (anodic) dissolution of the aluminum metal and the formation of an amorphous aluminum hydroxide gel film on the aluminum substrate, and second, the process of chemical dissolution of the aluminum hydroxide gel film into the bulk solution.4 In contrast, aluminum shows a passive behavior by the formation of a lithium containing film when exposed to alkaline lithium salt solutions. 1,5 This passive behavior was implemented by Buchheit et al. with the development of a hexavalent chromium-free chemical conversion coating from alkaline lithium carbonate solutions (pH 11-13), generating lithium aluminum carbonate hydroxide hydrate (hydrotalcite) layers on aluminum alloys.6 They studied the composition, structure and performance of these conversion coatings in relation to processing parameters and various bath chemistries and demonstrated that these hydrotalcite coatings exhibit similar corrosion protective properties as traditional conversion coatings.7 However, application of these conversion coatings in combination with coatings did not result in an equal performance compared to hexavalent chromium-based conversion coatings. In 2010, it was discovered that lithium salts could be considered as a potential alte...

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Section: Resultsmentioning

confidence: 99%

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Visser

González-García

Mol

et al. 2018

J. Electrochem. Soc.

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“…An increased deposition around the intermetallic particles is observed and is caused by the cathodic nature of these particles. 35 Detailed XPS peak fitting analysis of Zr as the major component of the film showed the presence of ZrO 2 and a bond between Zr and an element more electronegative than O, i.e. Fluorine.…”

Section: Discussionmentioning

confidence: 99%

“…34 Previous studies have shown that intermetallics present on the surface are preferential nucleation sites for coatings because of their cathodic nature and it is clear that these properties vary depending on the exact alloy composition. [34][35][36] Concerning deposition of nanoceramic conversion coatings, direct evidence has been presented that intermetallic particles act as local cathodes, leading to increased pH in the region of the intermetallic particles, and subsequently to increased deposition of TiO 2 /ZrO 2 -based conversion coatings in the absence of Cu. 36,37 The inhomogeneity of the deposition can be affected by stirring (convection).…”

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confidence: 99%

Role of Intermetallics and Copper in the Deposition of ZrO₂Conversion Coatings on AA6014

Sarfraz

Posner

Lange

et al. 2014

J. Electrochem. Soc.

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Zirconium oxide based conversion coatings are nickel-free alternatives to trication phosphate coatings. Here, the role of intermetallic inclusions in aluminum alloy AA6014 on the formation of Cu-rich particles inside ZrO 2 -based conversion layers with a film thickness of 25-30 nm was investigated. The role of the intermetallic inclusions on the deposition mechanism was characterized by varying the immersion time of the substrate and analyzing the coatings by electron microscopy and atomic force microscopy. Statistical analysis on the growth of the copper rich particles showed instantaneous nucleation of these particles, with a subsequent homogeneous inplane growth at constant height. A strong preferential nucleation of the Cu-rich particles on the intermetallic particles was observed, and was attributed to the cathodic nature of the intermetallics. Raman spectroscopy indicated the presence of crystalline CuO and amorphous ZrO 2 in the film. Enhanced layer formation in the vicinity of intermetallic particles was observed. Conversion coatings are widely used to protect metal surfaces from corrosion and to promote the adhesion of subsequently applied organic paints.1 While phosphate-based conversion coatings still have a large range of applications and some aspects of their formation are subject to more recent work, 2,3 current efforts focus on the replacement of conventional, μm thick phosphate and chromate containing systems by thin coatings that results in layers with an average thickness of just few tens of nm, without toxic ingredients. [4][5][6][7] One class of candidates are rare-earth based coatings. 4,6,[8][9][10] Other candidates are nanoceramic conversion coatings, typically containing zirconium or titanium oxides. Such coatings are either deposited on the surface by sol-gel chemistry, or by immersion into a fluoric acidic of Zr/Ti. Nanoceramic coatings have been shown to provide good multi-metal corrosion protection for various substrates including steel, zinc, and Al alloys, [11][12][13][14][15][16][17] and combine good corrosion performance with excellent adhesion properties. 5,[18][19][20][21][22] A lot of work has been specifically focused on investigation of zirconium or titanium based pretreatment on Al alloys. Their basic film formation mechanism is (i) fluoride etching of the oxide layer (which can be replaced by alkaline treatment), 23 (ii) onset of hydrogen evolution reaction, i.e. water reduction with a consequent increase in pH near the interface, and (iii) subsequent precipitation of oxyhydroxides as oxide precursors.24-27 Inclusion of Cu II salts (or alternatively, Fe salts) in the bath has been shown to lead to higher overall growth rate of the film on cold rolled steel compared to the solutions without Cu II . 25,28 Coatings prepared by including copper in the solution were also shown to be thicker and showed enrichment of copper within the conversion film. 25,28 Painted cold-rolled steel pretreated with a Cu-containing ZrO 2 -based coating shows low frequency impedance moduli comparabl...

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“…The immersion time is an important parameter that can modify the formation of the converted coating and its microstructure. Depending on the sample, the treatment time, the performance of the coating and its morphology changes, as well as the composition of the converted layer [8,21]. Although the Nyquist diagrams present a single semicircle for all samples (which is indicative of a reaction between the electrolyte and coatings), the Bode diagrams have at least two semicircles.…”

Section: Resultsmentioning

confidence: 99%

Corrosion Behavior of a Conversion Coating Based on Zirconium and Colorants on Galvanized Steel by Electrodeposition

Costa¹,

Agnoli²,

Ferreira³

2015

TMM

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Corrosion performance of Zr-based coating on substrates obtained by zinc electrodeposition in an alkaline bath is compared to chromate coatings (Cr III and Cr VI). The "nano Zr" is a conversion coating formed by immersion in a hexafluorozirconic acid solution. Since the "nano Zr" coating is transparent, the addiction of a colorant provides color to the surface. In this case, the colorant, when applied after the conversion coating, conferred the yellow color to the surface. The coating produced improves the corrosion protection of the substrate. For this study the samples were analyzed by electrochemical impedance spectroscopy (EIS) and accelerated corrosion test in a humidity chamber. The results showed similar behaviors between the "nano Zr", colorant and the chromate (Cr III) coating. Therefore this kind of conversion coating is a promising substitute for chromate coatings. Keywords: Nano Zr; Immersion process; Electrodeposited zinc; Hexafluorozirconic alkaline solution. COMPORTAMENTO DA CORROSÃO DE UM REVESTIMENTO DE CONVERSÃO À BASE DE ZIRCÔNIO E CORANTES NO AÇO ZINCADO POR ELETRODEPOSIÇÃO ResumoNo presente estudo, avaliou-se o desempenho de revestimentos à base de zircônio e corante sobre substratos de zinco obtidos por eletrodeposição em meio alcalino, em relação aos revestimentos de cromato (CrIII e CrVI). O revestimento "nano Zr" é obtido através da imersão em solução de conversão à base de ácido hexafluorzircônio. Uma vez que o revestimento "nano Zr" é transparente, a adição de um corante proporciona cor à superfície. Neste caso, o corante, quando aplicado depois do revestimento de conversão, confere cor amarela à superfície. O revestimento produzido melhora a proteção contra a corrosão do substrato. Para este estudo ensaios de espectroscopia de impedância eletroquímica (EIS) e testes em câmara úmida foram feitos. Os resultados mostraram comportamentos semelhantes entre o "Zr nano" e corante e o revestimento cromato (CrIII). Por conseguinte, este tipo de revestimento de conversão é um promissor substituto para os revestimentos de cromatização. Palavras-chave: Nano Zr; Processo de imersão; Zinco eletrodepositado; Solução ácida de hexaflúorzircônio.

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SKPFM and SEM study of the deposition mechanism of Zr/Ti based pre-treatment on AA6016 aluminum alloy

Cited by 128 publications

References 14 publications

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Role of Intermetallics and Copper in the Deposition of ZrO₂Conversion Coatings on AA6014

Corrosion Behavior of a Conversion Coating Based on Zirconium and Colorants on Galvanized Steel by Electrodeposition

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SKPFM and SEM study of the deposition mechanism of Zr/Ti based pre-treatment on AA6016 aluminum alloy

Cited by 128 publications

References 14 publications

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride

Role of Intermetallics and Copper in the Deposition of ZrO2Conversion Coatings on AA6014

Corrosion Behavior of a Conversion Coating Based on Zirconium and Colorants on Galvanized Steel by Electrodeposition

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Role of Intermetallics and Copper in the Deposition of ZrO₂Conversion Coatings on AA6014