Anodic film growth on Al–Li–Cu alloy AA2099-T8

Ma, Yan; Zhou, Xiaorong; Thompson, G.E.; Curioni, Michele; Skeldon, P.; Zhang, X.; Sun, Zhenqiu; Luo, Chen; Tang, Zilong; Lü, Fan

doi:10.1016/j.electacta.2012.06.126

Cited by 42 publications

(33 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Cavities and regions of altered film morphology are evident on the surface and associated to the different oxidation behavior of the various metallurgical phases present on the alloy. 23,29,30 After sealing in hot water (Fig. 10b), the surface morphology did not appear substantially different from the one observed on the asanodized specimen.…”

Section: Resultsmentioning

confidence: 98%

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Carangelo

Curioni

Acquesta

et al. 2016

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Chromic acid anodizing has been used for almost a century to enhance corrosion protection of aerospace alloys. For some applications, hydrothermal sealing in hexavalent chromium-containing solution is required to enhance further the corrosion resistance but, due to environmental concerns, the use of hexavalent chromium must be discontinued. Good progress has been made to replace chromates during anodizing but comparatively less effort has focused on the sealing process. In this work, for the first time, electrochemical impedance spectroscopy (EIS) has been used to characterize in-situ the sealing processes occurring during hot water sealing, sodium chromate sealing and cerium sealing. The results suggest that the processes occurring during sodium chromate sealing are significantly different compared to hot water and cerium sealing. In particular, during chromate sealing, the porous skeleton is significantly attacked, suggesting that the anticorrosion performance is likely to arise from the residuals of chromate rather than from the improvement of the barrier properties. In contrast, during hot water sealing, little attack occurs on the porous skeleton, and the improved corrosion protection is due to the enhanced barrier effect. During cerium sealing, precipitation of cerium products occurs, providing an inhibitor reservoir, and little, if any, attack occurs on the pre-existing oxide. Chromic acid anodizing (CAA) is widely used in the aeronautic industry to improve corrosion resistance of aluminum alloys.1 Since the beginning of the 1990s, however, the high toxicity associated with Cr (VI) has imposed restrictions on their use in industrial applications. As a consequence, numerous attempts have been made to find less toxic alternatives. 2,3Anodizing with dilute sulfuric acid (DSA) has been used to obtain thin anodic films (1-5 μm) that provide some protection without excessive deterioration of the fatigue life for specific aerospace alloys. Although the fatigue performance of DSA is acceptable, the corrosion resistance is lower than that of parts anodized in chromic acid (CAA). More recently, a new anodizing procedure, involving the addition of tartaric acid in dilute sulfuric acid electrolyte and called tartaric-sulfuric acid anodizing (TSA), was introduced.4-6 The addition of tartaric acid to sulfuric acid baths improves significantly the anticorrosive properties of the anodic layers compared to those obtained by sulfuric acid anodizing.7 Recent work, 7 however, indicates that the mechanism of porous film growth is not significantly affected by tartaric acid additions and that tartaric acid is not incorporated in significant amounts into the oxide material. Thus the corrosion resistance provided by TSA is likely to be associated with residuals of tartaric acid adsorbed on the porous skeleton. Tartaric acid concentration in the order of ppm, has been proved to be effective in reducing both the oxide dissolution rate in acidic environments and the anodic reaction rate. The effect of tartaric acid on the anodic fi...

show abstract

Section: Resultsmentioning

confidence: 98%

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Carangelo

Curioni

Acquesta

et al. 2016

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…A fine void is shown in the anodic film formed on the alkaline etched specimen (indicated by the arrow in Figure 10b), with an alloy ridge at the film/alloy interface below the void and a protrusion of the film above the void. From previous work, 20,28,29 it is known that this void and voids observed later within the anodic film are oxygen gas-filled voids formed as a consequence of copper enrichment, oxidation and associated oxygen gas generation. This observation suggests that oxygen gas-filled voids have developed in the very early stages of anodizing for the alkaline etched specimen due to the presence of copper enriched layer developed during alkaline etching.…”

Section: Resultsmentioning

confidence: 94%

“…In contrast, the anodic film formed on alkaline etched specimen shows irregular pore morphology, with lateral porosity present in the cell boundary regions of the major pores (indicated by the arrows). According to previous work, 17,18,20,[24][25][26] the lateral porosity originates from oxidation of copper and associated generation of oxygen gas-filled voids during anodizing. Therefore, it is implied that the level of copper in the copper-enriched layer of the mechanically polished specimen is insufficient for oxidation of copper after anodizing for 20 s; conversely, a sufficient level of copper has been established in the copper-enriched layer of alkaline etched specimen and, therefore, oxidation of copper and associated generation of oxygen gas-filled voids occurred.…”

Section: Resultsmentioning

confidence: 98%

“…Barrier-type anodic film formation.-It has been indicated previously that preferential oxidation of intermetallic particles on the mechanically polished alloy in the early stages of anodizing in ammonium pentaborate is responsible for the voltage plateau between 12 and 20 V. 20 Therefore, the absence of such a voltage plateau during anodizing of the alkaline etched specimen to similar voltages ( Figure 9) suggests considerable removal of intermetallic particles from the alloy surface by alkaline etching.…”

Section: Discussionmentioning

confidence: 93%

See 1 more Smart Citation

Microstructural Modification Arising from Alkaline Etching and Its Effect on Anodizing Behavior of Al-Li-Cu Alloy

Zhou

Thompson

et al. 2013

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Surface and near-surface microstructures of alkaline etched AA2099-T8 aluminum alloy have been characterized. The effect of alkaline etching on the anodizing behavior of the alloy in both acidic and neutral electrolytes has been investigated by comparing the electrochemical responses and the resultant anodic films of mechanically polished and alkaline etched alloys. It was revealed that alkaline etching could locally remove intermetallics from the alloy surface, with development of a copper-enriched layer immediately beneath a residual alumina film of about 5 nm thickness. The "footprints" of alkaline etching, i.e. the removal of intermetallics and the formation of copper-enriched layer during alkaline etching, could affect subsequent anodizing behavior of the alloy, particularly in the early stages. The removal of intermetallics from the alloy surface could not only improve anodizing efficiency but also contribute to reduced discontinuities in the resultant anodic films, potentially benefiting corrosion and fatigue resistances of the anodized profiles. The difference in anodizing behavior caused by the copper-enriched layer developed during alkaline etching was considered limited to the early stages of anodizing, since a similar copper-enriched layer could be formed quickly during subsequent anodizing process, regardless of the surface pre-treatment.Alkaline etching has been widely employed as a surface pretreatment for anodizing aluminum and its alloys, providing treated products with clean surface of matte appearance. 1-3 The responses of aluminum and its alloys to alkaline etching have been studied extensively, with a focus on the influence of alkaline etching on surface morphology and near surface microstructure of the treated alloys. 4-14 Surface scallops, gain boundary grooves and etching steps can be formed on surface etched in an alkaline solution, 4-7 due to different etching behavior of intermetallics, grain boundaries and grains of different orientations. In addition, impurities or alloying elements may enrich in the near-surface regions, in forms of impurity ridges, fine intermetallic particles or a thin layer with enriched alloying elements, immediately beneath a residual alumina film of a few nanometer thickness. [8][9][10][11][12][13][14] Despite the recognition of "footprints" left by alkaline etching on aluminum and its alloys, the influence of the "footprints" on the subsequent anodizing behavior has received little attention. Such research is relevant to optimizing the anodizing of aluminum alloys and, consequently, improving the performance of anodized alloys, including the newly developed, high performance, lithium-containing, aerospace aluminum alloys such as AA2099, which have been exploited in recent years. 15 In previous work, the microstructure of an AA2099-T8 aluminum alloy extrusion 16 and the anodizing behavior in acidic [17][18][19] and neutral 20 solutions have been studied. In the present work, following characterization of the surface and near-surface microstructures of the alkal...

show abstract

“…10 shows the theoretical structure of such type of anodic film. A key characteristic of the coating is the presence of an inner oxide layer, which is due to aluminum reaction with the oxygen of the environment, and of an outer oxide layer, which is due to the treatment and is consisted mainly of alumina and embedded anions [27,28].…”

Section: Eis Analysismentioning

confidence: 99%

Electrochemical corrosion evaluation of pure, carbon-coated and anodized Al foams

et al. 2015

View full text Add to dashboard Cite

Anodic film growth on Al–Li–Cu alloy AA2099-T8

Cited by 42 publications

References 33 publications

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Microstructural Modification Arising from Alkaline Etching and Its Effect on Anodizing Behavior of Al-Li-Cu Alloy

Electrochemical corrosion evaluation of pure, carbon-coated and anodized Al foams

Contact Info

Product

Resources

About