The kinetics and mechanism of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

Wint, Natalie; Eaves, D.; Michailidou, E.; Bennett, Andrew; Searle, Justin; Williams, Geraint; McMurray, H. N.

doi:10.1016/j.corsci.2019.06.028

Cited by 27 publications

(27 citation statements)

References 79 publications

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“…% Al, 1.5 wt. % Mg coatings were found to exhibit a high resistance to corrosion driven delamination of an organic (PVB) overcoat film [18]. This finding was believed to be a result from the presence of Mg-Zn and Mg-Al-Zn eutectic phases in the coating microstructure.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of eutectic therefore renders the principle O2 reduction cathode (primary zinc) discontinuous and inhibits the movement of the cathodic disbondment front [18].…”

Section: Introductionmentioning

confidence: 99%

“…In comparison, acetic acid, CH3COOH (which will from this point be referred to as HAc) induced FFC has recently been shown to be an important mode of the corrosion driven organic coating failure on ZAM [18]. FFC is a form of anodic disbondment which occurs when an aggressive electrolyte comes into contact with the metal substrate at defects in the organic coating [2].…”

Section: Introductionmentioning

confidence: 99%

“…FFC then propagates via differential aeration [19][20][21][22][23][24]. Although FeCl2, NaCl and HCl have been shown to act as initiators of FFC on iron [22][23]25] and aluminium [24,[26][27][28][29][30][31][32], and magnesium [33], only HAc has been found to reliably and reproducibility produce FFC on ZAM coatings [18]. HAc is known to be one of the most ubiquitous initiators of atmospheric corrosion which occurs on materials exposed to indoor environments and it is emitted during several important technological and biological processes [34][35][36][37][38][39][40][41][42].…”

Section: Introductionmentioning

confidence: 99%

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The effect of composition and thickness on the mechanism and kinetics of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

et al. 2021

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Section: Introductionmentioning

confidence: 99%

“…The presence of eutectic therefore renders the principle O2 reduction cathode (primary zinc) discontinuous and inhibits the movement of the cathodic disbondment front [18].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The effect of composition and thickness on the mechanism and kinetics of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

et al. 2021

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“…Filiform corrosion, FFC, is a type of anodic undermining and is considered the primary mechanism for coating failure on multiple organically coated metal systems [100]. Most relevant to this work is the occurrence of FFC on magnesium [101] and magnesium-containing zinc coatings [19,102] following the exposure of penetrative defects in the organic coating to particularly aggressive electrolytes, such as HCl. It is generally presumed that a droplet of aggressive electrolyte propagates beneath an organic coating via anodic attack of the metal substrate at the head of the droplet, coupled with cathodic oxygen reduction at the tail of the droplet (Figure 1…”

Section: Failurementioning

confidence: 99%

Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel

Bolton¹

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Physical vapour deposition (PVD) of zinc alloy coatings was investigated as a potential substitute process for commercially available hot dip galvanising (HDG) of strip steel. Therefore, zinc alloy coatings deposited by PVD were systematically compared with traditional sacrificial HDG zinc alloy coatings, in terms of bare metal corrosion resistance and resistance to corrosion-driven delamination of an organic overcoat, to establish the effects of magnesium content, microstructure and surface treatment. The effectiveness of modern corrosion inhibitor pigments, of known volume fraction, on HDG and PVD zinc coatings was also explored. All PVD coatings and commercially available HDG coatings were characterised using microscopy techniques and x-ray diffraction to identify the microstructure and phases present as a function of magnesium content. It was confirmed that the PVD coatings were significantly thinner than the HDG coatings. The pure zinc PVD coating was comprised of hexagonal microplates, whereas the HDG counterpart contained grains 5-10 time larger. The PVD coating containing 4 wt% magnesium exhibited a discrete structure, a binary system of zinc-rich and Mg2Zn11-rich phases, much finer than the HDG Zn-Mg-Al (ZMA) coating. The PVD coatings containing 10 wt% and 20 wt% magnesium were studied using transmission electron microscopy as they possessed nanostructures containing Mg2Zn11 and MgZn2 phases respectively. Open circuit potential (OCP) measurements in chloride-containing solution established that an increase in magnesium content in PVD coating resulted in a decrease in the initial immersion open circuit potential. Additionally, increased magnesium content in the PVD layers also correlated with an increase in corrosion resistance, as made evident by reduced Ecorr and Icorr values during potentiodynamic studies. Electrochemical impedance spectroscopy (EIS) comparative studies suggested an improvement in corrosion resistance exhibited by PVD0 compared to HDG, both zinc-only coatings, attributed to the finer and more compact surface morphology. Bare metal corrosion response for all coatings was studied using a novel augmentation of the scanning vibrating electrode technique (SVET), known as SVET-TLI (time-lapse imaging). The combination of electrochemical mapping and photographic imagery revealed a potential optimum magnesium content within the PVD coatings. PVD4 exhibited the lowest anodic current density over a 24 hour study compared to the HDG, ZMA and other PVD coatings. Furthermore, the characteristic black staining attributed to magnesium corrosion was observed on the magnesium-containing PVD coatings. However, on the PVD Zn-Mg coatings the staining was observed in the regions established as net cathodes, which is contrary to association of staining with magnesium dissolution which takes place in local anodes. Using the scanning vibrating kelvin probe (SKP) method, PVD4 was identified as the optimum magnesium composition as it was found to be resistant of both corrosion-driven cathodic delamination and anodic undermining. Cathodic delamination was observed on the zinc-only coatings, PVD0 and HDG, as well as PVD10 (although at a much slower rate). ZMA and PVD20, both MgZn2-containing systems, showed resistance to cathodic delamination and evidence of anodic undermining. Exploring several modern inhibitive pigments incorporated in the organic overcoat allowed the identification of a commercial pigment “PAM” to provide the greatest improvement in delamination resistance for the zinc-only metallic coatings.

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Unsupervised Analysis of Optical Imaging Data for the Discovery of Reactivity Patterns in Metal Alloy

Makogon

Galochkina

et al. 2023

Small Methods

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Operando wide‐field optical microscopy imaging yields a wealth of information about the reactivity of metal interfaces, yet the data are often unstructured and challenging to process. In this study, the power of unsupervised machine learning (ML) algorithms is harnessed to analyze chemical reactivity images obtained dynamically by reflectivity microscopy in combination with ex situ scanning electron microscopy to identify and cluster the chemical reactivity of particles in Al alloy. The ML analysis uncovers three distinct clusters of reactivity from unlabeled datasets. A detailed examination of representative reactivity patterns confirms the chemical communication of generated OH− fluxes within particles, as supported by statistical analysis of size distribution and finite element modelling (FEM). The ML procedures also reveal statistically significant patterns of reactivity under dynamic conditions, such as pH acidification. The results align well with a numerical model of chemical communication, underscoring the synergy between data‐driven ML and physics‐driven FEM approaches.

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The kinetics and mechanism of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

Cited by 27 publications

References 79 publications

The effect of composition and thickness on the mechanism and kinetics of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

The effect of composition and thickness on the mechanism and kinetics of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

Improved organic coating delamination resistance using physical vapour deposited Zn-Mg layers on strip steel

Unsupervised Analysis of Optical Imaging Data for the Discovery of Reactivity Patterns in Metal Alloy

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