Microstructural and Compositional Characterisation of Chromate Pretreatment on Aluminium

Oki, Makanjuola

doi:10.1155/2013/572379

Cited by 6 publications

(5 citation statements)

References 15 publications

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“…However other researchers believed that in addition to these anchor sites, bonds formation between organic coatings and species in conversion coatings play significant roles in the improvement of paint adhesion properties of conversion coated substrates [21]. Also, in an earlier study it was suggested that roughness at microscopic level imparted on conversion coated surfaces played added significant roles in adhesion improvement properties of conversion coated aluminum substrates [22]. The coating materials as revealed through analysis with the EDX attachment in the SEM are composed of Mn, Al and oxygen compounds, Fig.…”

Section: Surface Morphology and Compositionmentioning

confidence: 99%

Development and performance of hybrid coatings on aluminium alloy

Oki

Adediran

Olayinka

et al. 2017

J. Electrochem. Sci. Eng.

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Section: Surface Morphology and Compositionmentioning

confidence: 99%

Development and performance of hybrid coatings on aluminium alloy

Oki

Adediran

Olayinka

et al. 2017

J. Electrochem. Sci. Eng.

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“…The generally cracked surface morphology is typical of Cr(VI)-based coatings. It has been described by various authors [9][10][11] and is likely the result of shrinkage stresses generated during drying out of the coatings. Cracks in the coatings have been suggested to be beneficial 9 for paint adhesion as they allow for mechanical interlocking between the chromate coatings and subsequently applied organic finishes.…”

Section: Resultsmentioning

confidence: 95%

Alternative corrosion protection pretreatments for aluminum alloys

et al. 2017

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Aluminum alloys are extensively used in space programs for both structural and nonstructural applications. As is well known, the corrosion resistance of these alloys is quite limited and anticorrosion treatment is needed. Currently, the treatment most often used for improving the corrosion resistance of aluminum alloys is chromate (CrVI-based) conversion coatings (CCC). Due to the high environmental impact of these compounds, the REACH Regulation of the European Union decided to limit/restrict the use of hexavalent chromium. A sunset date of mid-2017 has been already set. For the time being, many chromatefree alternative products are available, but they have been found to be significantly inferior in terms of corrosion protection performances with respect to the chromate options. In this regard, there is a great need to develop high-performance hexavalent chromiumfree anticorrosion coatings with low environmental impact and conformity with the EU regulations. The European Space Agency (ESA) is currently involved in a frame contract with Instituto de Soldadura e Qualidade (ISQ) that is currently ongoing. The objective of this study is to evaluate the anticorrosion behavior of the different alternative pretreatments applied to the most used aluminum alloys. The outcome of this activity will be the identification and the optimization of the most promising anticorrosion pretreatment. Several commercial Cr(VI)-free processes were applied onto aluminum alloys (2024-T3 and 2024-T81) used in the construction of ESA spacecraft in order to investigate their anticorrosive properties compared with Alodine 1200, a widely used conventional CCC. One of these commercial processes presented good anticorrosion performance, even better than Alodine 1200, and these results are presented in this paper. Salt spray resistance is included in the testing program as well as metallurgical coating evaluations that include microscopy observations before and after testing and electrochemical impedance spectroscopy in order to evaluate surface and microstructural modifications due to degradation mechanisms. Further studies must be performed with this promising alternative, modifying application parameters in order to achieve improved corrosion protection efficiency.

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“…While the Alodine 1200S coating exposes a typical mud‐cracked pattern, the PreCoat A32 showed a much smoother pattern, with some pores visible on the surface coating. The generally cracked surface morphology is typical of Cr(VI)‐based coatings, and it has been described by various authors as due to the result of shrinkage stresses generated during drying out of the coatings. Cracks in the coatings have been suggested to be beneficial for paint adhesion as they allow for mechanical interlocking between the chromate coatings and subsequently applied organic finishes.…”

Section: Resultsmentioning

confidence: 99%

Trivalent chromium conversion coating on AA2024‐T3 used in aeronautical and aerospace industry

Proença

Pereira

Cabral

et al. 2019

Surface & Interface Analysis

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Significant research has been conducted to replace the chromium(VI)‐based surface treatments, and some commercial substitute systems are now available and needs to be tested to evaluate their performance and to know how they comply with the required specifications. The anticorrosion properties provided by a commercially available trivalent chromium‐based product—PreCoat A32—when applied to AA2024‐T3 aluminium alloy substrates were evaluated in this work and compared with those obtained with a chromium(VI)‐based pretreatment well‐recognized reference (Alodine 1200S). The morphology and elemental composition of the conversion coatings were investigated by high‐resolution microscopy and energy‐dispersive X‐ray analysis, respectively, being the wettability of the modified surface measured by contact angle goniometry. The data obtained reveal that PreCoat A32–treated surfaces are more apt to receive aqueous paint schemes than those healed with Alodine 1200S. The corrosion resistance of the treated samples was monitored by potentiodynamic polarisation assays and electrochemical impedance spectroscopy analysis, revealing that PreCoat A32 coatings provide improved corrosion protection for AA2024‐T3. The corrosion resistance effectiveness of PreCoat A32 was also confirmed in trials realised in salt‐spray chamber, humidity tests, and thermal cycling assays, where more severe exposure conditions were simulated. The gathered data clearly indicate that the PreCoat A32 brings together the mandatory qualities to successfully substitute the conventional and undesirable chromium(VI)‐based treatments, in aeronautical and aerospace industry.

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Microstructural and Compositional Characterisation of Chromate Pretreatment on Aluminium

Cited by 6 publications

References 15 publications

Development and performance of hybrid coatings on aluminium alloy

Development and performance of hybrid coatings on aluminium alloy

Alternative corrosion protection pretreatments for aluminum alloys

Trivalent chromium conversion coating on AA2024‐T3 used in aeronautical and aerospace industry

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