Modelling the anodizing behaviour of aluminium alloys in sulphuric acid through alloy analogues

Miera, M. Saenz de; Curioni, Michele; Skeldon, P.; Thompson, G.E.

doi:10.1016/j.corsci.2008.09.019

Cited by 69 publications

(65 citation statements)

References 11 publications

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“…6, dash-dot lines) show that the current passing through the model IMC rose rapidly, reaching values of ∼80-90% of the total current flowing through the cell. Similar results were found previously for Al 2 Cu/Al-Cu matrix coupled systems, [9] where the times of the voltage transition depended on the area ratios, due to most of the initial current being consumed by the highly alloyed aluminium alloy. The subsequent current decay on the Al 7 Cu 2 Fe alloy also coincided with the time at which the cell voltage increased.…”

Section: Linear Polarisation Behavioursupporting

confidence: 88%

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

Miera

Curioni

Skeldon

et al. 2010

Surface & Interface Analysis

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Model analogues of the metallurgical phases found in 2xxx and 7xxx series aluminium alloys were produced by magnetron sputtering and employed to investigate the local and general anodising behaviour of the alloys. Electrochemical tests, allied with scanning and transmission electron microscopy, enabled insight into the local anodising behaviour of the constituents and related effects on the overall porous oxide morphology. Under potentiodynamic conditions, the observed anodic current peaks of the commercial alloys were related with the anodic oxidation of specific second-phase particles. At 0 V, magnesiumcontaining particles, including S-phase, were preferentially removed from the alloy surface; at 5-6 V SCE , the copper-and/or iron-containing particles, such as θ phase and Al 7 Cu 2 Fe particles were anodically oxidised. The initial voltage transient revealed for the commercial alloys during galvanostatic anodising was related to the previous findings and reproduced by the use of coupled alloy analogues. Transmission electron microscopy revealed that the voltage transient associated with oxidation of second-phase material influence the morphology of the anodic film formed on the aluminium matrix.

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Section: Linear Polarisation Behavioursupporting

confidence: 88%

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

Miera

Curioni

Skeldon

et al. 2010

Surface & Interface Analysis

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“…The current response displayed two peaks during the initial voltage ramp, associated with the oxidation of Al-Mg-Cu and Al-Cu-Fe containing second phase particles, respectively. [23][24][25] During the initial voltage ramp, the current density increased to about 8 mA/cm 2 . As the voltage ramp was interrupted and the constant potential applied, the current decreased slightly, to attain a steady value in the region of 7 mA/cm 2 .…”

Section: Resultsmentioning

confidence: 99%

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.

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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...

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“…The mechanism for the formation of the surface texture during alkaline etching has been reported elsewhere. 18 Anodizing of the alloys of different tempers.-Previous work 8,19 has indicated that intermetallics of different compositions in aluminum alloys are oxidized at specific voltages or voltage ranges. The characteristic voltages/voltage ranges could be determined from the current density-voltage responses of the alloys which were linearly polarized from the OCP to higher voltages.…”

Section: Resultsmentioning

confidence: 99%

Discoloration of Anodized AA6063 Aluminum Alloy

Zhou

Wang

et al. 2014

J. Electrochem. Soc.

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The effect of the anodizing process parameters and the influence of β (Mg 2 Si) phase on the appearance of the anodized AA6063 aluminum alloy have been investigated. It was found that β (Mg 2 Si) phase was preferentially oxidized at low anodizing voltages and the selective oxidation of β (Mg 2 Si) phase resulted in the development of a rough alloy/film interface and the incorporation of silicon into the porous anodic film, which led to the discoloration of the anodized alloy. © The Author Discoloration often appears on extruded AA6063 aluminum alloy after anodizing in sulfuric acid solutions and, to date, achieving reproducible and well-controlled surface appearance of anodized AA6063 alloy profiles is still an intractable issue. Discoloration refers to undesirable changes in the appearance of anodized aluminum alloy profiles (usually darker than the normal appearance), either in specific regions or over the macroscopic alloy surface. The effects of precipitation, surface pre-treatments and anodizing process on discoloration of anodized profiles have been explored by previous investigators.1-6 Nakagawa et al.1 suggested that discoloration was caused by rapid cooling of the extrusions on the run-out-table and reheating the extrusions upon removal from the carbon plates. It was believed that such thermal process accelerated the precipitation of β (Mg 2 Si) phase, 2 which subsequently resulted in discoloration of the anodized extrusions. Further, Nakagawa et al. 3 found that the discoloration became more marked with increase of the time and temperature of the desmutting treatment in sulfuric or nitric acid solutions. Additionally, it was found that the discoloration of the anodized alloys was strongly dependent on the pH of the rinsing water after the desmutting procedure. It was further suggested that the discoloration of anodized alloys originated from reactions between β (Mg 2 Si) precipitates and the acid solution during the desmutting and subsequent water-rinsing treatment. Hayashi et al. 5 anodized Al-Mg-Si alloys that had been heat treated under various conditions initially at 15 V and then at 4 V in sulfuric acid solution. The anodized alloys appeared in colors from gray to black and the degree of coloring increased with the amount of β (Mg 2 Si) precipitates formed during heat-treatment. Based on the roughening of the alloy/oxide interfaces, it was suggested that the coloring might result from the formation of a branched-pore morphology due to the local concentration of the anodizing current on the β (Mg 2 Si) precipitates with consequent uneven dissolution of the barrier layer.Although the literature [1][2][3]5 indicates that the discoloration of the anodic films is related to β (Mg 2 Si) precipitates in the alloy matrix, whether the discoloration is introduced in the surface pre-treatment stage or the anodizing stage remains the subject of discussion. Recent work of the authors on an AA6063 aluminum alloy profile with discolored anodic films 7 suggested that the anodizing process parameters and the statu...

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Modelling the anodizing behaviour of aluminium alloys in sulphuric acid through alloy analogues

Cited by 69 publications

References 11 publications

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

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

Discoloration of Anodized AA6063 Aluminum Alloy

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