Chromate Conversion Coating on Aluminum Alloys

Campestrini, P.; Goeminne, G.; Terryn, Herman; Vereecken, Jean; Wit, J.H.W. de

doi:10.1149/1.1637355

Cited by 75 publications

(48 citation statements)

References 42 publications

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“…Very few in situ CCC measurements have been carried out. An example of open-circuit potential measurements is given by Campestrini et al 1 Goeminne et al 2 and Vuillemin et al 3 used electrochemical reduction of chromate on graphite electrodes to monitor chromate that did not react at the Al surface. The former investigators used a rotating ring-disk method with an Al alloy as the disk and graphite ring.…”

mentioning

confidence: 99%

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Isaacs

Sasaki

Jeffcoate

et al. 2005

J. Electrochem. Soc.

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In situ X-ray adsorption near-edge structure ͑XANES͒ has been used to investigate the formation of chromate conversion coatings on pure Al, commercial Al alloys ͑AA 1100, AA2024, and AA7075͒, and a series of binary Al-Cu alloys. The method employed cells designed to determine the growth of the total chromium ͓Cr͑total͔͒ and hexavalent chromate ͓Cr͑VI͔͒ in the chromate conversion coating ͑CCC͒ as a function of exposure time to a chromate solution. Three sets of data were obtained, where ͑i͒ the Al was exposed to only a limited amount of solution; ͑ii͒ the chromate solution was excluded after short periods of repeated exposures to the solution; and ͑iii͒ the Al was exposed continuously to the chromate solution. All the results showed a very rapid initial growth within the first seconds, followed by a continued increase in thickness for exposures up to 1 h. Measurements with Al-Cu binary alloys demonstrated that the difference observed in AA2024 and AA1100 may not be due to Cu alloying. used electrochemical reduction of chromate on graphite electrodes to monitor chromate that did not react at the Al surface. The former investigators used a rotating ring-disk method with an Al alloy as the disk and graphite ring.2 The latter investigators employed a flow system with a graphite electrode downstream to an Al alloy to study CCC growth following laser removal of a thin mask that initially protected the Al. They also employed a quartz crystal microbalance on which the alloy film was sputtered, and coupled the mass variations with chromate consumption. 3 X-ray adsorption offers a powerful method for the in situ study of the kinetics of chemical changes taking place at surfaces, by monitoring the growth and dissolution of the films.3-12 X-ray adsorption near-edge structure ͑XANES͒ has been used to study the products of reactions of chromate conversion coatings ͑CCC͒ adhering to Al surfaces, and the behavior of these products with time and exposure to solutions. [4][5][6][7][8][9][10][11][12][13] CCCs are made up of Cr͑III͒ and Cr͑VI͒ species such as in CrO 4 2− ; the latter is believed to be responsible for CCC's ability to protect scratches on a metal surface from undergoing further electrochemical degradation. A factor that assists in the determination of Cr speciation is a distinct pre-edge peak at 5993 eV in the XANES spectrum when hexavalent chromium Cr͑VI͒ is present. In addition, the ratio of height above the edge arising from all chromium species present ͓Cr͑total͔͒ to the pre-edge height ͓only Cr͑VI͔͒ provides a quantitative measure of Cr͑VI͒ content in the CCC. However, XANES measurements of CCC have generally been made ex situ.In this study, we introduce designs of cells that allow monitoring of a specimen surface exposed to a chromate solution without being removed from the aqueous environment. We present data on aluminum and its alloys ͑i͒ when exposed to a limited volume of solution; ͑ii͒ when subjected to repeated exposure to the chromate solution; and ͑iii͒ when continuously exposed to the CCC solution. Fro...

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mentioning

confidence: 99%

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Isaacs

Sasaki

Jeffcoate

et al. 2005

J. Electrochem. Soc.

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“…[38] The obtained values during the OCP measurements indicate that in this electrolyte, the CCCs in both substrates can function as a protective film. [1,2,[13][14][15] Forget and Zhang et al [36,39] have also reported similar potentials for galvanized steel and their chromated coatings have a negative potential with respect to bare zinc. They suggested that the chromate coatings can cathodically inhibit the corrosion of zinc in the solution, and when the anodic reaction remains the same, the corrosion current is reduced and the potential shifts negatively, which could explain the behavior of the Fe-Zn substrates here obtained.…”

Section: B Microstructural Characterization Of Cccsmentioning

confidence: 78%

“…[10][11][12] The mechanism by which conventional CCCs inhibit the corrosion of metals is not yet fully understood, although a large number of studies have been performed and some insight has been obtained. [13][14][15] In order to understand the process and the effect of some parameters such as temperature, pH, immersion time, and substrate, a detailed characterization is required.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Chromate Conversion Coatings on GALVALUME and Galvanized Steel Substrates

Domínguez‐Crespo

Onofre-Bustamante

Torres‐Huerta

et al. 2009

Metall Mater Trans A

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The morphology, composition, and corrosion performance of chromate conversion coatings (CCCs) formed on GALVALUME (Fe-Al-Zn) and galvanized steel (Fe-Zn) samples have been studied, and different immersion times (0, 10, 30, and 60 seconds) have been compared. The coated surfaces were analyzed using light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements in a NaCl solution (3 wt pct). The electrochemical measurements were carried out using the polarization resistance, Tafel, and ac impedance methods. A nonuniform growth of the CCCs having a porous morphology and cracks that appear extended to the base metal was observed. The XRD patterns show that the coatings mainly consist of CrO 3 , Cr 2 O 3 , and traces of Cr 2 O 7 À2 . The electrochemical results show that GALVALUME presents a better behavior than that of the galvanized steel alloys at each dipping time. The SEM micrographs show that the galvanized steel treatments resulted in the formation of a more uniform film, but their protection barrier broke down faster than that of the GALVALUME samples in contact with the aggressive media. The samples that underwent the lowest degree of dissolution were those with a dipping time of 30 seconds. The difference in the corrosion protection given by the two substrate types could be attributed to the structural properties, grain size, composition, and roughness, which affect oxygen diffusion.

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“…Radioluminescence of this material has been investigated by lots of experiments, in which particle beams were used giving rise to high ionization and displacement rates. Although quantitative data on the emission band, linearity, thermal and mechanical properties of Al 2 O 3 :Cr 3+ material have been obtained [10][11][12][13][14], the emission characteristics of the luminescence coating in terms of the fabrication process still need further investigation. For the application of proton beam diagnostics at CSNS, works on Al 2 O 3 :Cr 3+ coating fabrication are proceeded.…”

Section: Introductionmentioning

confidence: 99%

Measurements and characteristics of $$\hbox {Al}_{2}\hbox {O}_{3}{:}\hbox {Cr}^{3+}$$ Al 2 O 3 :

Zeng

Wei

et al. 2017

Radiat Detect Technol Methods

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Introduction To set up an online proton beam diagnostic system near the neutron production target of China Spallation Neutron Source (CSNS), a luminescence coating sprayed on the target window and a corresponding optic system were fabricated. In the work, the fabrication of Results The emission spectrum excited by 532-nm laser has two obvious peaks at 692.9 nm and 694.3 nm. The samples by flame spraying process with the powders obtained from melting method show higher luminescence intensity than the samples by plasma spraying process. It is observed that the luminescence intensity has some relationships with the alpha phase in the samples, which is deduced from the XRD and photoluminescence tests results. A lower temperature during the flame spraying process will help to keep more alpha phase in the material. The selected four samples show successful fluoresced results in the radioluminescence experiment. Conclusions The luminescence intensity of the coating is improved greatly by the studies on the fabrication process and the characteristics of the samples. The luminescence coating used in beam diagnostics will be fabricated by the confirmed technical process. More works will be continued to improve the characteristics of the luminescence light by controlling Cr concentration and annealing in 1200 ∼ 2000 • C environment in the future.

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Chromate Conversion Coating on Aluminum Alloys

Cited by 75 publications

References 42 publications

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Synthesis and Characterization of Chromate Conversion Coatings on GALVALUME and Galvanized Steel Substrates

Measurements and characteristics of $$\hbox {Al}_{2}\hbox {O}_{3}{:}\hbox {Cr}^{3+}$$ Al 2 O 3 :

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