Enrichment, incorporation and oxidation of copper during anodising of aluminium–copper alloys

Curioni, Michele; Roeth, F.; Garcia-Vergara, S.J.; Hashimoto, Teruo; Skeldon, P.; Thompson, G.E.; Ferguson, John F.

doi:10.1002/sia.3139

Cited by 25 publications

(31 citation statements)

References 12 publications

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“…This is caused by the higher growth rate of coating and the release of gas during microdischarges. 46 Meanwhile, high temperature at the locations of microdischarges supported the deposition of Si, which was originated from the electrolyte (Fig. 16).…”

Section: Discussionmentioning

confidence: 99%

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Zhu

Zhang

et al. 2018

J. Electrochem. Soc.

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In this study, scanning electron microscopy and electrochemical techniques were used to investigate the effect of the Cu content on the microstructure and corrosion resistance of plasma electrolytic oxidation (PEO) coatings on Al-xCu alloys. The results showed that Cu in the substrate alloy was used to promote the intensity and the transformation process of the microdischarges, which led to the undulating-ribbon feature of cross-sectional morphologies. The formation of pores and cracks in the coatings was facilitated by the oxygen release due to the oxidation of O 2− and the dissolution of copper oxide. Meanwhile, the average porosity of PEO coatings distinctly increased with the increase in the Cu content, which is the key factor causing the decreased corrosion resistance of PEO coatings. Due to their high strength to weight ratio, Cu-containing aluminum alloys are one of the most promising materials for use in aerospace and automobile applications. However, their application is limited by low corrosion resistance. Therefore, plasma electrolytic oxidation (PEO) is considered to be a well-known process for the in situ production of oxide coatings on Al and its alloys, which can offer better corrosion protection as compared to the other surface modification processes for substrate alloys. [1][2][3][4] In general, many processing factors, such as the composition of electrolyte, 5-7 additives, 8-10 applied power modes, 11-13 electrical parameters, 14,15 temperature, 16 and oxidation time, 17 are used to control the PEO process. These parameters not only affect the PEO process but also the performance of the prepared coatings. The characteristics of the formed PEO coatings could also be affected by the alloying elements in substrate alloys. However, this has not been studied in much detail. To the best of our knowledge, the literature contains several papers that describe the effect of multiple elements (such as Si, Mg, Cu, Li, and Fe) on the properties of the formed PEO coatings for commercial aluminum alloys.18-20 While, only a few studies focused on the effect of single alloying element in substrate. Among others, Ali et al. studied the PEO treatment of simple binary Al-Si alloys and reported that the thickness of PEO coatings significantly decreased, whereas their porosity increased with the increase in the Si content. The decomposition of volatile silicon oxides, such as SiO in the formed coatings during the PEO process, contributed to the high porosity. Furthermore, Si exhibits low electrical conductivity, which adversely affects the formation of microdischarges and the oxidation kinetics of the alloy. 21 Meanwhile, Oh et al. studied the effect of Mg on the properties of PEO coatings on Al-Mg alloys and demonstrated that when the amount of Mg was higher than 3 wt% the formation of α-Al 2 O 3 was inhibited.22 It is also reported that Zn is the primary alloying element for the 7××× series Al alloys, and the peculiar function of Zn during the formation of PEO coatings on binary Al-Zn alloys has also been investig...

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Section: Discussionmentioning

confidence: 99%

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Zhu

Zhang

et al. 2018

J. Electrochem. Soc.

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“…1,18,[23][24][25][26][27] The presence of copper ions increases significantly the electronic conductivity within the barrier layer, triggering oxygen evolution within the oxide. 2,18,23,25,[28][29][30][31] Such oxygen evolution disrupts the well-ordered growth of the aluminum oxide, and induces the formation of a spongelike morphology. 1,2,18 The geometrical features of such morphology are still dependent on the anodizing potential and charge, i.e.…”

mentioning

confidence: 99%

“…2,18,23,25,[28][29][30][31] Such oxygen evolution disrupts the well-ordered growth of the aluminum oxide, and induces the formation of a spongelike morphology. 1,2,18 The geometrical features of such morphology are still dependent on the anodizing potential and charge, i.e. higher anodizing potential produces a coarser morphology, whereas the overall oxide thickness is proportional to the charge passed.…”

mentioning

confidence: 99%

“…2,[16][17][18][19][20][21][22] In particular, oxidation of copper at the metal-oxide interface results in injection of copper ions into the oxide. 1,18,[23][24][25][26][27] The presence of copper ions increases significantly the electronic conductivity within the barrier layer, triggering oxygen evolution within the oxide. 2,18,23,25,[28][29][30][31] Such oxygen evolution disrupts the well-ordered growth of the aluminum oxide, and induces the formation of a spongelike morphology.…”

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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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Anodizing—The pore makes the difference

Schneider

Fürbeth

2022

Materials & Corrosion

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The presentation gives an insight into the fascinating world of anodizing as corrosion protection but also goes far beyond. Starting with an introduction to the formation of anodic oxide films and their characteristic features, the authors briefly outline the subject of pore nucleation and growth. The number, size, and shape of the pores essentially determine the properties and play a crucial role in the final application of the anodizing layers. The tailoring of pore design, considering the final application as well as the use of the porous oxide layers for subsequent functional modifications, is demonstrated by examples, exclusively developed in the working groups of the respective authors or in joint research projects, which were in part professionally accompanied and supported by the German Corrosion Society GfKORR e.V.

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Enrichment, incorporation and oxidation of copper during anodising of aluminium–copper alloys

Cited by 25 publications

References 12 publications

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

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

Anodizing—The pore makes the difference

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