Dehydration-Induced Loss of Corrosion Protection Properties in Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Laget, V.; Jeffcoate, C. S.; Isaacs, H.S.; Buchheit, R. G.

doi:10.1149/1.1593040

Cited by 35 publications

(45 citation statements)

References 22 publications

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“…A crack-mud structure as observed on Figure 7 has already been observed on conversion layers by numerous researchers on a variety of conversion coatings: chromate conversion coating, 33,54 cerium conversion coating 25,55,56 and TCP. 11,19 It is generally accepted that cracks form on conversion coatings because of dehydration, the formation of cracks resulting from stresses induced in the coating during the drying process.…”

Section: 33supporting

confidence: 58%

“…The high vacuum to which a sample is exposed during a SEM experiment can trigger an accelerated drying, which creates these mud-like cracks. The formation of these cracks under vacuum was followed in an environmental SEM by Laget et al 33 on a chromate conversion coating and by Guo et al…”

Section: Discussionmentioning

confidence: 99%

“…Our work does not demonstrate the link between the susceptibility to cracking of the conversion layer under vacuum and its corrosion resistance, as has been established by other researchers. 25,33,65,66 Laget et al 33 studied chromate conversion coating, and concluded that the dehydration of the coatings explains the losses in corrosion resistance observed after aging. Heller et al 65 found that inhibiting cracking improves the corrosion resistance of cerium conversion coatings but that elimination of cracking alone does not guarantee a good corrosion protection.…”

Section: Discussionmentioning

confidence: 99%

“…11,19 It is generally accepted that cracks form on conversion coatings because of dehydration, the formation of cracks resulting from stresses induced in the coating during the drying process. 11,25,33,55,56 The thickness of the coating was reported to have a strong impact on the cracking of conversion layers. 55 We have also observed a more severe cracking on thicker conversion layers (results not detailed here).…”

Section: 33mentioning

confidence: 99%

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Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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The effects of post-treatment applied on Trivalent Chromium Protection (TCP) coatings deposited on aluminum alloy 2024-T3 was studied by electrochemical and surface analytical techniques: X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The aim of the post-treatment was to improve the corrosion resistance of the TCP coating. To understand the influence of the post-treatment, using a bath containing H 2 O 2 and a lanthanum salt as an inhibitor, our approach was to study the effect of these two components separately. It was found that the improved corrosion protection provided by the post-treated TCP was related to a synergetic effect of the two components. XPS and ToF-SIMS analyses showed that (i) the thickness of the TCP coating is not modified by the post-treatment, (ii) lanthanum is present on the surface and in the bulk of the TCP and (iii) is found in very small amount only on the extreme surface. The total concentration of Cr(VI) (oxide/hydroxide) was estimated to be below 0.1 wt% in the post-treated TCP layer. It was concluded that lanthanum plays a significant role in improving the coating density and homogeneity and has a beneficial effect on the TCP coating cracking as observed by Scanning Electron Aluminum alloys are used for aerospace applications for their low weight and good mechanical properties.1-3 To improve the corrosion properties of aluminum alloys and to provide good paint adhesion, the first layer of coating applied on the aluminum alloy surface used to be a chromate conversion coating (CCC).4-6 However, hexavalent chromium used in the CCC coatings is highly toxic, 4,7 its use is very much restricted in Europe 8 and the United States 9 and will be forbidden by 2024 by the European Community with respect to the Registration, Evaluation, Authorization and Restriction of Chemicals (REACh).8 Therefore, new conversion coatings have been developed, and one of the most promising solutions is the Trivalent Chromium Protection coating called also as the Trivalent Chrome Process (TCP).10-14 TCP conversion coatings are formed by immersion in a solution containing Zr 4+ , Cr 3+ and F − ions, at a pH between 3.8 and 4.0. As it has already been widely discussed, the coating formation mechanism occurs by multiple chemical steps. 10,11,13,[15][16][17] The initial step involves dissolution of the aluminum oxide layer by fluorides. The removal of the oxide layer exposes the metal surface where cathodic reactions take place. Oxygen reduction reaction, and possibly hydrogen discharge, which counterbalance aluminum oxidation, consume protons and causes a pH increase at the interface between the metallic substrate and the solution, as measured by Li et al. 15 The high pH favors the precipitation of ions present in the solution, forming a hydrated layer of zirconium and chromium oxide. The thickness of the TCP layer is usually of the order of 100 nm, depending on the nature of the aluminum alloy, the concentration of the solution and the immersion time.11,12,18 ...

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Section: 33supporting

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: 33mentioning

confidence: 99%

See 2 more Smart Citations

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Ely

Światowska

Seyeux

et al. 2017

J. Electrochem. Soc.

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“…[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.…”

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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Corrosion inhibition of pure aluminium and AA2014‐T6 alloy by strontium chromate at low concentration

Liu

Feng

Zhou

et al. 2015

Surface & Interface Analysis

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The influence of a low concentration of strontium chromate on the corrosion inhibition of superpure aluminium and AA2014-T6 aluminium alloy in 0.6 M chloride solution has been investigated to simulate the leaching process of inhibitors from coatings. The potential-time and polarisation behaviour show influences on both the anodic and cathodic kinetics on the superpure aluminium surface. However, predominant cathodic inhibition was observed for the AA2014-T6 aluminium alloy. It was evident that chromium species were reduced at cathodic second phase particles, forming a thin passive film at the cathodic sites, which blocks the oxygen reduction reaction and, consequently, provides effective corrosion inhibition.

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Dehydration-Induced Loss of Corrosion Protection Properties in Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Cited by 35 publications

References 22 publications

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Role of Post-Treatment in Improved Corrosion Behavior of Trivalent Chromium Protection (TCP) Coating Deposited on Aluminum Alloy 2024-T3

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Corrosion inhibition of pure aluminium and AA2014‐T6 alloy by strontium chromate at low concentration

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