Formation of protective anodic oxides on aluminium by low voltage anodising in sulphuric acid with cerium nitrate and tartaric acid additions

Curioni, Michele; Zuleta, Alejandro; Correa, Esteban; Pan, Xiaoxiao; Baron-Wiechec, A.; Skeldon, P.; Castaño, Juan G.; Echeverría, Félix; Thompson, G.E.

doi:10.1179/0020296712z.00000000059

Cited by 11 publications

(15 citation statements)

References 25 publications

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“…It is likely that the addition of tartaric acid to the anodizing electrolyte decreases the chemical dissolution rate of the alumina oxide film in the acidic environment. 30 Thus, the local pH near the interface between the alumina and post-treatment solution remains lower compared to the pH in proximity of the oxides generated in the absence of tartaric acid. This could result in increased Ce 3+ .…”

Section: +mentioning

confidence: 99%

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

Gordovskaya

Hashimoto

Walton

et al. 2014

J. Electrochem. Soc.

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The development of cerium-rich layers on anodized pure aluminum and AA7075 T6 aluminum alloy has been investigated using scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The surfaces of pure aluminum and AA7075 T6 were pre-treated by alkaline etching and HNO 3 desmutting followed by anodizing in sulfuric acid electrolyte with and without addition of tartaric acid. The outer layer is created by immersion in a cerium (III) nitrate solution containing hydrogen peroxide. It is shown that anodizing in a mixture of sulfuric and tartaric acids prior to the immersion treatment leads to the formation of a thicker and a more uniform cerium-rich layer. The ultramicrotomed sections display the presence of cerium species within the pores of the anodic film. This treatment significantly improves the corrosion resistance of the material. Aluminium alloys are widely used in the aerospace industry because of their high strength to weight ratio. The high strength is achieved by alloying with copper, magnesium, silicon, manganese, and zinc.1,2 However, the resulting microstructure contains intermetallic particles that are more or less noble than the alloy matrix, thereby increasing the corrosion susceptibility of the alloy compared with high purity aluminum. Traditionally, anodizing in chromic acid electrolyte has been used for corrosion protection, with the presence of residual chromate ions within the pores of the anodic film providing corrosion inhibition.3,4 However, the use of chromic acid has associated health issues, as well as having a negative environmental impact.Recently, sulfuric acid (SA) and tartaric/sulfuric acid (TSA) electrolytes have been used as alternatives to chromic acid for anodizing. 5The effect of tartaric acid on the anodic film morphology and corrosion resistance of anodized AA 2024 T3 was studied by Boisier at al. 6 It was found that the addition of tartaric acid to the anodizing electrolyte generates anodic films with reduced porosity and with the pores better distributed over the filmed aluminum surfaces due to the reduced rate of chemical dissolution of the alumina in TSA electrolyte. Several studies have shown that films formed in TSA solution are more resistant to corrosion than films obtained in SA only, but the presence of tartaric acid in the anodizing electrolyte does not change the anodic film morphology. 7,8,9 The protective properties of the anodic oxide films formed in sulfuric acid, with or without tartaric addition, may be enhanced by addition of rare earth compounds (e.g cerium-based compounds) before, during or after anodizing. [10][11][12][13] The main benefits of cerium-based layers are high corrosion resistance, non-toxicity, and a relatively fast deposition process.14,15 Hughes et al., 16 Hinton et al. 17 and Mansfeld et al. 18 achieved enhanced corrosion resistance for AA2024 and 7075 aluminum alloys after spontaneous deposition of conversion coatings in Ce(III) solutions at ambient temperature. Their results have been taken as a ...

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Section: +mentioning

confidence: 99%

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

Gordovskaya

Hashimoto

Walton

et al. 2014

J. Electrochem. Soc.

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“…The concentration of sulfuric acid for the modified TSA cycle was selected on the basis of previous results, [12][13][14]32 such as the steady current attained during anodizing at 7 V (25…”

Section: Methodsmentioning

confidence: 99%

“…Modifications to the TSA cycles, based on lower anodizing potential compared to the traditional TSA, have been previously shown to provide enhanced corrosion protection compared to traditional TSA in the unsealed condition. [12][13][14]32 Typically, for aerospace applications, hydrothermal sealing is performed in sodium chromate solutions, but environmental concerns require the development of more environmentally acceptable alternatives. In this work, the effects of the porous oxide morphology on the sealing response and the anticorrosion performance are investigated.…”

Section: C908mentioning

confidence: 99%

“…[12][13][14]32 Previous works have shown that in the unsealed condition finer pores, generated at low anodizing potential, provide a much better anticorrosion performance compared to coarser pores, generated at high potential. [12][13][14]32 However, when anodizing is undertaken at low potential, care must be taken so that the anodizing potential does not fall below the critical value that is necessary for the oxidation of the intermetallics on the alloy surface and for the co-oxidation of alloying elements in solid solution in the matrix. Any residuals of unoxidized noble alloying elements have detrimental effects on the corrosion resistance.…”

mentioning

confidence: 99%

“…13,14 Thus, the approach of tailoring the oxide morphology by controlled variation of the anodizing potential during the anodizing cycle to enhance the corrosion protection performance can also be applied to practical alloys, and it has been followed previously with success. [12][13][14]32 Previous works have shown that in the unsealed condition finer pores, generated at low anodizing potential, provide a much better anticorrosion performance compared to coarser pores, generated at high potential. [12][13][14]32 However, when anodizing is undertaken at low potential, care must be taken so that the anodizing potential does not fall below the critical value that is necessary for the oxidation of the intermetallics on the alloy surface and for the co-oxidation of alloying elements in solid solution in the matrix.…”

mentioning

confidence: 99%

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Cerium-Based Sealing of Anodic Films on AA2024T3: Effect of Pore Morphology on Anticorrosion Performance

Carangelo

Curioni

Acquesta

et al. 2016

J. Electrochem. Soc.

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In this work, porous anodic oxides were produced by traditional and modified tartaric sulfuric anodizing (TSA) processes and sealed in hot water, chromate and cerium based solutions. The sealing behavior of a film with relatively coarse porosity, generated at high voltage (traditional TSA), was compared to the sealing behavior of a film with finer porosity and generated at reduced potential (modified TSA). After sodium chromate sealing, the two anodizing cycles produced film with similar anticorrosion performance. Conversely, after hot water or cerium sealing, the finer oxides generated at low voltage (modified TSA) provided much better corrosion resistance. EIS performed in-situ during sealing revealed that chromate sealing is very aggressive to the porous skeleton compared to the other sealing treatments. Therefore, the original morphology has little effect on the final performance, since both fine and coarse oxides are substantially attacked. In contrast, the oxide morphology has a substantial effect when sealing is performed in hot water or cerium-based solution. Overall, it is possible to obtain films with anticorrosion performance equivalent or improved compared to that obtained by traditional TSA anodizing cycle sealed with chromate by combining the low voltage anodizing cycle with the cerium-based sealing. Aerospace aluminum alloys display outstanding mechanical properties but require specific protection measures in order to meet the requirements of durability and corrosion resistance. Anodizing in acidic electrolytes is one of the methods that are most widely employed for this purpose, since it produces porous oxides that improve corrosion resistance and adhesion with organic coatings.The porous anodic oxide morphology generated on high copper alloys is significantly different from that generated on high purity aluminium.1-3 Specifically, on aluminum, anodizing in phosphoric, sulfuric, or oxalic acid, results in the generation of a well-ordered oxide morphology, comprising closely-packed hexagonal cells with a central cylindrical pore, and having a diameter that is proportional to the applied potential.4-10 Under these conditions, the pore walls are generally straight and uniform (provided that anodizing is conducted under steady applied potential or current). At the bottom of the pores, close to the metal, a barrier layer is observed with thickness proportional to the applied potential. On the other hand, the thickness of the porous oxide is proportional to the charge passed. Due to the dependence of barrier layer thickness and pore diameter on the applied potential, and to the dependence of the film thickness on charge, porous morphologies can be tailored by controlling the electrical regime (potential-time or current-time), and complex morphologies can be achieved to enhance specific properties.11-14 It has been shown that fine pores and thick films are beneficial for corrosion protection.13 However fatigue life can be an issue for aerospace alloys 15 and therefore film thickness should be limited to...

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An alternative to the use of a zero resistance ammeter for electrochemical noise measurement: Theoretical analysis, experimental validation and evaluation of electrode asymmetry

Curioni¹,

Balaskas²,

Thompson³

2013

Corrosion Science

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Formation of protective anodic oxides on aluminium by low voltage anodising in sulphuric acid with cerium nitrate and tartaric acid additions

Cited by 11 publications

References 25 publications

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

Cerium-Based Sealing of Anodic Films on AA2024T3: Effect of Pore Morphology on Anticorrosion Performance

An alternative to the use of a zero resistance ammeter for electrochemical noise measurement: Theoretical analysis, experimental validation and evaluation of electrode asymmetry

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