Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review

Abrahami, Shoshan Tamar; Kok, John M. M. de; Terryn, Herman; Mol, J.M.C.

doi:10.1007/s11705-017-1641-3

Cited by 61 publications

(35 citation statements)

References 89 publications

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“…Chromate conversion coatings have been used as common protection or primer coatings for aluminium alloys. Their use is nowadays limited and is expected to be replaced completely by other types of protective coating which are environmentally acceptable and not toxic like hexavalent chromium [1]. To achieve complete withdrawal of chromate coatings from the market, numerous studies have been dedicated to the development of alternative coatings that would exhibit comparable anti-corrosion characteristics and add further functionalities, including self-healing, improved mechanical strength, adhesion, hydrophobicity, etc.…”

Section: Introductionmentioning

confidence: 99%

The Effect of the Methyl and Ethyl Group of the Acrylate Precursor in Hybrid Silane Coatings Used for Corrosion Protection of Aluminium Alloy 7075-T6

et al. 2020

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This study investigated polysiloxane hybrid sol-gel coatings synthesized from tetraethyl orthosilicate (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MAPTMS) and two different precursors, i.e., methyl- or ethyl- methacrylate (MMA or EMA), as corrosion protection of aluminium alloy 7075-T6. The hypothesis was that the additional alkyl group might affect the chemical properties and, consequently, the corrosion properties. Synthesis of the sols proceeded in two steps, each involving either MMA or EMA in the same molar ratio. The resulting sols, siloxane-(poly(methyl methacrylate-co-MAPTMS)) or siloxane-(poly(ethyl methacrylate-co-MAPTMS)), were applied on aluminium alloy followed by characterization in terms of chemical structure and composition, topography, wettability, adhesion and corrosion resistance in 0.1 M sodium chloride solution. The chemical properties of sols, monoliths and coatings were investigated using Fourier transform infrared spectrometry, solid state nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Coatings were similar in terms of surface topography, while the wettability of the coating with EMA showed 6° greater water contact angle compared to the coating with MMA. Both coatings were shown, by electrochemical impedance spectroscopy in 0.1 M NaCl solution, to act as barriers to protect the underlying substrate in which coating with EMA exhibits better protection properties after 2 months of immersion. Adhesion tests confirmed the highest grade of adhesion to the substrate for both coatings. Testing in a salt-spray chamber demonstrated excellent corrosion protection, where coatings remaining intact after more than 600 h of exposure.

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Section: Introductionmentioning

confidence: 99%

The Effect of the Methyl and Ethyl Group of the Acrylate Precursor in Hybrid Silane Coatings Used for Corrosion Protection of Aluminium Alloy 7075-T6

et al. 2020

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“…When performed in acidic solution, anodizing results in a duplex layer composed of a very thin barrier layer with high resistance to corrosion and a thicker porous layer, whose microstructure is ideal for increasing adhesion between the substrate and protective coatings . In the aerospace industry, for more than 60 years, anodizing has been performed in acidic baths containing chromate ions, mainly for structural components . In a bid to increase the corrosion resistance, the anodized alloy is then subjected to the commercial alodine treatment (which also contains chromates) and by the application of a primer (generally containing chromate‐base inhibitors) and a topcoat .…”

Section: Introductionmentioning

confidence: 99%

“…With specific reference to anodizing, various alternative bath compositions are being employed by commercial aviation. Among them, the anodizing in boric‐sulfuric acid patented by Boeing, in tartaric sulfuric acid (TSA) used by Airbus, and in phosphoric and sulfuric acid bath, which, according to Abrahami et al, should be used by Fokker in the near future. The TSA anodizing procedure, used in this study, is considered environmentally friendly and results in anodized layers with corrosion resistance similar to those produced in chromic acid electrolytes .…”

Section: Introductionmentioning

confidence: 99%

“…2,10 In the aerospace industry, for more than 60 years, anodizing has been performed in acidic baths containing chromate ions, mainly for structural components. 11 In a bid to increase the corrosion resistance, the anodized alloy is then subjected to the commercial alodine treatment (which also contains chromates) and by the application of a primer (generally containing chromate-base inhibitors) and a topcoat. 8,9 To ensure good adhesion of the primer, the porous layer cannot be sealed.…”

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confidence: 99%

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EIS investigation of a Ce‐based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA

Ramirez

Queiroz

Terada

et al. 2019

Surface & Interface Analysis

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In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self‐healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self‐healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024‐T3 alloy anodized in tartaric‐sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM‐EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H2O2 solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM‐EDS analysis of the samples posttreated in the H2O2 containing solution, prior and after the corrosion test, showed the presence of Ce oxy‐hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.

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“…Plasma electrolytic oxidation (PEO) is a plasma-assisted electrochemical surface treatment characterized by the utilization of high voltages (100-600 V) in alkaline electrolytes to produce ceramic-like coatings on light alloys such as aluminium [1], magnesium [2] and titanium [3]. This technology may become a potential alternative to conventional toxic and highly carcinogenic chromic acid anodizing (CAA) for niche applications [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

LDH Post-Treatment of Flash PEO Coatings

et al. 2019

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This work investigates environmentally friendly alternatives to toxic and carcinogenic Cr (VI)-based surface treatments for aluminium alloys. It is focused on multifunctional thin or flash plasma electrolytic oxidation (PEO)-layered double hydroxides (LDH) coatings. Three PEO coatings developed under a current-controlled mode based on aluminate, silicate and phosphate were selected from 31 processes (with different combinations of electrolytes, electrical conditions and time) according to corrosive behavior and energy consumption. In situ Zn-Al LDH was optimized in terms of chemical composition and exposure time on the bulk material, then applied to the selected PEO coatings. The structure, morphology and composition of PEO coatings with and without Zn-Al-LDH were characterized using XRD, SEM and EDS. Thicker and more porous PEO coatings revealed higher amounts of LDH flakes on their surfaces. The corrosive behavior of the coatings was studied by electrochemical impedance spectroscopy (EIS). The corrosion resistance was enhanced considerably after the PEO coatings formation in comparison with bulk material. Corrosion resistance was not affected after the LDH treatment, which can be considered as a first step in achieving active protection systems by posterior incorporation of green corrosion inhibitors.

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Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review

Abstract: Important note To cite this publication, please use the final published version (if applicable). Please check the document version above.

Cited by 61 publications

References 89 publications

The Effect of the Methyl and Ethyl Group of the Acrylate Precursor in Hybrid Silane Coatings Used for Corrosion Protection of Aluminium Alloy 7075-T6

The Effect of the Methyl and Ethyl Group of the Acrylate Precursor in Hybrid Silane Coatings Used for Corrosion Protection of Aluminium Alloy 7075-T6

EIS investigation of a Ce‐based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA

LDH Post-Treatment of Flash PEO Coatings

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