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

Wint, Natalie; Eaves, D.; Williams, Geraint; McMurray, H. N.

doi:10.1016/j.corsci.2020.109168

Cited by 13 publications

(2 citation statements)

References 74 publications

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“…Thus far limited investigations have been conducted to study the effects of process conditions. Investigations on the influence of cooling rate on surface corrosion 21,23 and coating thickness on filiform corrosion 24 of ZMA coatings have been conducted. However, limited published studies have been conducted to investigate the influence of coating thickness (coating weights) on the cut-edge and surface corrosion of ZMA coatings.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic investigation on the influence of coating weights on the corrosion behaviour of hot-dip-galvanised Zn-Mg-Al coatings.

Malla,

Sullivan,

Penney

et al. 2024

Preprint

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Time-lapse Microscopy, scanning vibrating electrode technique and potentiodynamic methods were used to study the influence of increasing coating weight (80-310 gm-2) on microstructure, cut-edge and surface corrosion of Zn-Mg-Al coatings in 0.17 M NaCl. Cut-edge corrosion was similar for all coating weights due to the ORR becoming diffusion-limited. A 64% reduction in surface corrosion was observed for high coating weights through increases in eutectic volume fraction. Spatial and temporal corrosion mechanisms were controlled by microstructural morphological differences as coating weight varied. 80 g.m-2 coatings demonstrated lateral anodic spreading potentially reducing coating penetration rates despite their higher surface corrosion rate.

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Section: Introductionmentioning

confidence: 99%

Mechanistic investigation on the influence of coating weights on the corrosion behaviour of hot-dip-galvanised Zn-Mg-Al coatings.

Malla,

Sullivan,

Penney

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…Sacrificial alloy coatings have previously been coated with model organic coatings, such as PVB, to assess their corrosion performance. PVB coated HDG fails according to a cathodic disbondment mechanism, yet zinc-magnesium-aluminium alloys (116,117) and aluminium alloys (118,119) fail via a filiform corrosion (anodic) disbondment mechanism.…”

Section: Introductionmentioning

confidence: 99%

The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel

Gallagher¹

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This work set out to elucidate the microstructural corrosion mechanisms of sacrificial corrosion coating, Galvalloy® (Zn-4.8wt.%Al), which is used extensively in the strip steel industry. Corrosion of Galvalloy® occurs at the surface, where only Galvalloy® is exposed, and the cut edge, where Galvalloy® and steel are coupled, which increases the corrosion rate of Galvalloy®. Chapter 3 demonstrates the time-lapse microscopy (TLM) technique being used to analyse, in-situ, the microstructural mechanism of surface and cut-edge corrosion of Galvalloy® immersed in pH 7 1 wt.% NaCl. Rotating disk electrode (RDE) and potentiodynamic polarisation (PD) tests were performed on the individual phases of Galvalloy® to identify their anodic and cathodic activity in 1 wt.% NaCl. TLM showed that surface corrosion initiates and propagates through the binary eutectic Zn-Al phase, whereas cut-edge corrosion initiates within the primary zinc dendrite phase and proceeding through the entire microstructure. The electrochemical data validated this as the RDE showed that the Al containing phases could not support cathodic activity as well as the primary zinc phases and PD showed that the zinc phases are more susceptible to anodic dissolution when polarised. Chapter 4 investigated, using TLM and PD, the corrosion rate and mechanism of the Galvalloy® surface across pH 3, 7, 10 and 13 in 1 wt. % NaCl. At pH 3 and 13, D showed a maxima of corrosion rate was seen and TLM illustrated no precipitation of corrosion product. PD showed pH 7 having the lowest icorr, however, the precipitated corrosion product formed at a smaller radius relative to active anodes during TLM experiments of pH 10 compared to pH 7. Chapter 5 utilized ZRA and TLM to investigate the rate and mechanism of the corrosion of Galvalloy® next to a steel ‘cut-edge’ across pH 3, 7, 10 and 13 in 1 wt. % NaCl. The corrosion rate of Galvalloy® was greater compared to the surface corrosion, due to the polarisation imposed by the connection to the steel substrate and the same corrosion rate to pH trend in Chapter 4 was see. At pH 7, 10 and 13, corrosion initiation occurs in the zinc dendrites, whereas at pH 3 the corrosion is generalised. Chapter 6 investigated the effect of increasing steel to Galvalloy® on the corrosion rate of Galvalloy® at pH 7 in 1 wt.% NaCl using ZRA and TLM. ZRA demonstrated a linear trend, whereas TLM showed a non-linear trend which is suggested to be due to the increased ease of precipitation in the experimental set-up. Chapter 7 is an example of a real-world corrosion problem involving organically coated Galvalloy®. 2 µL of HCl, FeCl2, NaCl and Acetic acid (CH3OOH) were administered to a scribed region of PVB coated Galvalloy® and exposed to a high relative-humidity environment for a month to induce under-film corrosion in order to compare the results to deduce which salt was responsible for the real-world corrosion. NaCl was the salt that posed the greatest similarity and cathodic delamination is the postulated corrosion mechanism.

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Principal investigation on the surface chemistry of phosphated zinc coatings treated by hot active plasma

Duchoslav,

Himmelbauer,

Kürnsteiner

et al. 2024

Applied Surface Science

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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

Cited by 13 publications

References 74 publications

Mechanistic investigation on the influence of coating weights on the corrosion behaviour of hot-dip-galvanised Zn-Mg-Al coatings.

Mechanistic investigation on the influence of coating weights on the corrosion behaviour of hot-dip-galvanised Zn-Mg-Al coatings.

The corrosion of Zn-4.8%Al sacrificial coatings used for the protection of steel

Principal investigation on the surface chemistry of phosphated zinc coatings treated by hot active plasma

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