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The study investigated the effect of sebacate as a corrosion inhibitor for acrylic-coated steel. Specifically, it examined its impact on mitigating a frequent case of paint delamination, known as filiform corrosion (FFC), through a chosen weathering test designed to stress the degradation of the produced samples. Sebacate was demonstrated to be an efficient organic molecule for enhancing the corrosion resistance of steel. This efficacy was evaluated through electrochemical characterization based on electrochemical impedance spectroscopy measurements and potentiodynamic polarization curves, including the application of an FFC susceptibility prediction methodology based on measurements obtained in FFC-simulated electrolytes. An inhibition efficiency of 98% was measured in near-neutral saline solutions compared to conditions lacking inhibitor presence. During FFC simulation, the primary effect observed was associated with a reduction in cathodic activity evolution. Furthermore, a significant reduction in corrosion creep evolution of 35% was found. These experimental findings aligned closely with the outcomes projected by the simulated investigations. [ABSTRACT FROM AUTHOR]

In this work, corrosion behavior and the concurrent acoustic emission (AE) signals of AZ31 alloy under NaCl and Na2SO4 solution droplets were comparatively investigated in combination with in-situ optical microscopy observations. It was observed that after a short initial corrosion accompanied by the growth and rupture of H2 bubbles, the later corrosion behavior of AZ31 alloy mainly developed into filiform corrosion under NaCl solution droplet and pitting corrosion under Na2SO4 solution droplet. AE signals were detected in both cases. In particular, AE parameters of amplitude and duration were found to well identify filiform and pitting corrosion. AE signals were mainly correlated with the observed evolution of H2 bubbles of different shapes and positions, i.e., regularly round bubbles grew and ruptured at the filament head near the metal surface during filiform corrosion; whereas irregularly-shaped bubbles grew and ruptured at the pit mouth during pitting corrosion. [ABSTRACT FROM AUTHOR]

Sacrificial metallic coatings are an effective strategy for mitigating corrosion in steel operating in industrial environments. This review article focuses on examining the protection mechanism of zinc-aluminum-magnesium (Zn-Al-Mg) coatings on steel substrates. Specifically, it investigates the effects of various elements and their corrosion products on the corrosion resistance of Zn-Al-Mg coatings. Furthermore, this review summarizes the formation mechanisms of various specialized corrosion modes that occur following the corrosion of Zn-Al-Mg coatings, based on previous experimental findings. It also includes suggestions for further research areas that could contribute to the development of highly corrosion-resistant and long-lasting coatings. These suggestions are based on published laboratory and field test results available in literature.

The direct industrial importance of the corrosion resistance in WE43 is best emphasized by its extensive use in the automotive, aerospace and electronic industries where weight reduction is a necessary requirement. In this work, the corrosion especially the filiform corrosion in a 3.5 wt.% NaCl solution and their dependence on the Zr distribution for WE43 were studied by weight loss tests, hydrogen evolution tests, electrochemical measurements and microscopic analyses. The Zr distribution significantly influenced the initiation and propagation of the filiform corrosion, and accordingly significantly influenced the corrosion rate. WE43 with a cluster Zr distribution displayed filiform corrosion throughout the entire surface with an irregular network distribution of filaments. WE43 with a uniform line Zr distribution exhibited only a few examples of linear filiform corrosion. WE43 with a dispersive Zr distribution exhibited no filiform corrosion. The stability of the corrosion film was responsible for the filiform corrosion. Anodic polarisation promoted the initiation and progression of the filiform corrosion, while cathodic polarisation had an inhibiting effect on the filiform corrosion. The serrated interface of the filiform corrosion increased the contact area between the substrate and the corrosive medium, and hence increased the corrosion rate.

It is recently suggested that air-formed film plays an important role in controlling corrosion resistance of Mg-Li alloys. However, the structure of the air-formed film and its effect on corrosion resistance of Mg-Li alloys has not been fully understood. Firstly, the air-formed films formed on α and β phases in a dual-phase LZ91 Mg-Li alloy after exposure to laboratory air for up to 48 h have been examined by SEM under the assistance of ultramicrotomy. Then, the effect of the air-formed film on surface potential and, consequently, corrosion/oxidation behavior of the alloy has been investigated. Finally, in order to exclude the influence from α phase, the structure of the air-formed film on β phase and its effect on corrosion/oxidation behavior of Mg-Li alloys have been studied based on a single-phase LA141 Mg-Li alloy. The results show that the air-formed film is thin and negligible on α phase but thick on β phase after prolonged exposure to laboratory air. The thick air-formed film on β phase has a multilayer structure with an inner layer consisting of MgO/Mg(OH)2 and outer layer consisting of Li2CO3, which greatly elevates the surface potential of β phase in air. Both LZ91 and LA141 Mg-Li alloys firstly undergo uniform corrosion and then filiform corrosion when immersed in NaCl solution and the pre-existed air-formed film on β-Li phase can retard the occurrence of filiform corrosion in the alloys.

Due to its excellent performance, aluminum alloys are frequently used in wheels, but the corrosion of aluminum alloy wheels is still a major problem to be further studied. To understand the corrosion of wheels, it is important to consider the role of the organic coating in the corrosion process. Meanwhile, it is also meaningful to find an effective method to remove the organic coating properly to investigate the corrosion products under the organic coating. In this paper, the corrosion status of the A356 aluminum alloy substrate under an organic coating was observed firstly; lipid solutions such as NMP solution and butyl acrylate solution were used to remove the coating, and comparative experiments were carried out by controlling factors such as the soaking temperature, time, composition of solution etc. To find out the optimized soaking method to remove the organic coating; finally, the morphology of the localized corrosion on the aluminum alloy surface and the composition and structure of the corrosion products on the aluminum alloy substrate were analyzed. Results show that the corrosion products mainly contain ZrO2, Zr3O2F8, AlO(OH), and Al2O3. The corrosion process prefers to initiate at the defects where the coating and the substrate are not tightly bonded. This work shows the corrosion behavior of the aluminum alloy under an organic coating and provides a useful method to remove the organic coating from the aluminum alloy substrate effectively, and the results can be valuable for the understanding and mitigation of metal corrosion under an organic coating.

• Air-formed (AF) film is characterized under assistance of ultramicrotomy. • AF film is negligible on α but thick on β after prolonged air exposure. • AF film on β has a MgO/Mg(OH) 2 inner layer and a Li 2 CO 3 outer layer. • AF film on β elevates surface potential of the phase in air. • AF film on β retards filiform corrosion in LZ91 and LA141 alloys. It is recently suggested that air-formed film plays an important role in controlling corrosion resistance of Mg-Li alloys. However, the structure of the air-formed film and its effect on corrosion resistance of Mg-Li alloys has not been fully understood. Firstly, the air-formed films formed on α and β phases in a dual-phase LZ91 Mg-Li alloy after exposure to laboratory air for up to 48 h have been examined by SEM under the assistance of ultramicrotomy. Then, the effect of the air-formed film on surface potential and, consequently, corrosion/oxidation behavior of the alloy has been investigated. Finally, in order to exclude the influence from α phase, the structure of the air-formed film on β phase and its effect on corrosion/oxidation behavior of Mg-Li alloys have been studied based on a single-phase LA141 Mg-Li alloy. The results show that the air-formed film is thin and negligible on α phase but thick on β phase after prolonged exposure to laboratory air. The thick air-formed film on β phase has a multilayer structure with an inner layer consisting of MgO/Mg(OH) 2 and outer layer consisting of Li 2 CO 3 , which greatly elevates the surface potential of β phase in air. Both LZ91 and LA141 Mg-Li alloys firstly undergo uniform corrosion and then filiform corrosion when immersed in NaCl solution and the pre-existed air-formed film on β-Li phase can retard the occurrence of filiform corrosion in the alloys. [ABSTRACT FROM AUTHOR]

The direct industrial importance of the corrosion resistance in WE43 is best emphasized by its extensive use in the automotive, aerospace and electronic industries where weight reduction is a necessary requirement. In this work, the corrosion especially the filiform corrosion in a 3.5 wt.% NaCl solution and their dependence on the Zr distribution for WE43 were studied by weight loss tests, hydrogen evolution tests, electrochemical measurements and microscopic analyses. The Zr distribution significantly influenced the initiation and propagation of the filiform corrosion, and accordingly significantly influenced the corrosion rate. WE43 with a cluster Zr distribution displayed filiform corrosion throughout the entire surface with an irregular network distribution of filaments. WE43 with a uniform line Zr distribution exhibited only a few examples of linear filiform corrosion. WE43 with a dispersive Zr distribution exhibited no filiform corrosion. The stability of the corrosion film was responsible for the filiform corrosion. Anodic polarisation promoted the initiation and progression of the filiform corrosion, while cathodic polarisation had an inhibiting effect on the filiform corrosion. The serrated interface of the filiform corrosion increased the contact area between the substrate and the corrosive medium, and hence increased the corrosion rate. [ABSTRACT FROM AUTHOR]

The study investigated the effect of sebacate as a corrosion inhibitor for acrylic-coated steel. Specifically, it examined its impact on mitigating a frequent case of paint delamination, known as filiform corrosion (FFC), through a chosen weathering test designed to stress the degradation of the produced samples. Sebacate was demonstrated to be an efficient organic molecule for enhancing the corrosion resistance of steel. This efficacy was evaluated through electrochemical characterization based on electrochemical impedance spectroscopy measurements and potentiodynamic polarization curves, including the application of an FFC susceptibility prediction methodology based on measurements obtained in FFC-simulated electrolytes. An inhibition efficiency of 98% was measured in near-neutral saline solutions compared to conditions lacking inhibitor presence. During FFC simulation, the primary effect observed was associated with a reduction in cathodic activity evolution. Furthermore, a significant reduction in corrosion creep evolution of 35% was found. These experimental findings aligned closely with the outcomes projected by the simulated investigations.

Magnesium biodegradable alloys are a promising material for self-dissolving surgical implants. Magnesium is known to be sensitive to electrochemical corrosion due to the galvanic effect between the matrix and particles of secondary phases and inclusions. Another important factor is the pH level. The behavior of certain chemical reactions depends on the pH level, so one can assume that the pH level of a corrosive medium at the material surface is a factor determining what chemical reactions can occur there. Finally, there is evidence that variability of the crystallographic orientation of the grains may be a cause of anisotropy of corrosion properties. The purpose of this work is to reveal the influence of the electrode potential of the microstructural elements, the crystallographic orientation of the grains, and the pH level of the near-surface volume of the corrosion solution on the corrosion process. In the study, sections of 2×1.5 mm were marked on the ZX10 alloy samples, for which maps of the distribution of crystallographic orientations and chemical composition were drawn. To assess the influence of the electrode potential of the particles, the authors carried out a Kelvin probe mapping in the 90×90 µm area. Next, corrosion tests were carried out with video filming of the surface on the marked area. To determine the pH level influence, the solution circulation in the cell was varied. Upon completion of the tests, corrosion products and corrosion damage were examined in detail. According to the results, the pH level in the liquid near-surface micro-volumes has a greater influence than the electrode potential of the particles as it provokes the formation of corrosion products of a different composition, which leads to passivation of the surface areas around the particles. The authors identified two different types of filiform corrosion. For filiform corrosion, a correlation between the corrosion direction and the crystallographic orientation of the grains was established.

The Cheonan, a patrol combat corvette of the South Korean (SK) Navy, sank during a routine patrol mission in the Yellow Sea in March 2010. An SK government report concluded that a North Korean (NK) submarine torpedo attack was responsible for the Cheonan sinking. This report presented a torpedo propulsion section as the conclusive evidence of an NK torpedo attack on the Cheonan. However, a forensic corrosion analysis of this torpedo propulsion section proved it could not have been involved in the Cheonan sinking. Instead, the deformation characteristics of Cheonan's hull plate and main deck are more consistent with damage due to a collision with a submarine than a torpedo explosion. Evidence that led to this conclusion is presented and discussed. [ABSTRACT FROM AUTHOR]

Synergistical passive barrier enhancement and active self-healing has been an emerging tactic for developing prominent anti-corrosion coatings. Herein, a cerium/2-methylimidazole metal-organic framework (Ce-MOF) was that is in-situ grown on ultrathin α-ZrP nanosheets with outstanding dispersibility. The parallel arrangement of α-ZrP-based nanosheets within the epoxy matrix was driven by shear force from blade-coating technology optimizing the coating's physical barrier and self-repairing capability. This advancement may herald a new era in designing smart coatings and offering potent protection against diverse corrosion types such as filiform corrosion. • Ce-MOF was grown in-situ on ultrathin α-ZrP nanosheets using a one-pot co-precipitation method. • The compatibility and dispersity of CeMOF@PDA-ZrP provided strong adhesion and toughness for the epoxy coating. • The coating offers long-term physical barrier protection and effectively inhibits filiform corrosion of carbon steel. • Local electrochemical impedance spectroscopy showed the strong barrier of the nanosheets and pH-sensitive release of inhibitors. [ABSTRACT FROM AUTHOR]

Organic coatings delamination and corrosion pose an ongoing challenge in materials science. This review explores the knowledge of corrosion mechanisms in painted steel structures up to date, focusing on filiform corrosion (FFC) investigating its mechanisms, and discussing available prevention strategies alongside their suitability. First reported in the 1940s, FFC garnered significant attention in the subsequent decades, particularly in the study of coated aluminum, and very recently magnesium alloys. However, its consideration as a component of steel degradation remained comparatively limited during this period. Despite advancements, comprehensive analysis of FFC has been infrequent, prompting a call for an updated critical analysis. This survey emphasizes the necessity for organized FFC mitigation strategies, discussing alternatives and emerging trends. It underscores FFC's potential role as a precursor to general corrosion, emphasizing the economic implications of aesthetic damage. This review aims to fill gaps, assess current knowledge, and pave the way for future research in the realm of organic-coated steel corrosion. [Display omitted] • Filiform corrosion is a dramatic failure mechanism in organic-coated steel. • The coating delamination is verified to be driven by the anodic corrosion reactions. • The metal-paint interface is subjected to a harsh chemical environment discernible between anodic and cathodic sites. [ABSTRACT FROM AUTHOR]

In the present study, the effect of varying Zn additions (0.93–3.16 wt%) on the corrosion resistance of wrought Mg-5Al alloys was studied and related to the microstructure changes. Three secondary phases were found: Al–Mn, β-Mg17Al12 enriched with Zn, and Φ-Mg21(Al, Zn)17; the latter observed only in alloys with relatively high Zn content. The corrosion behavior in short periods of immersion is related to pitting corrosion, and strongly influenced by micro-galvanic effects between the secondary phase particles and the α-Mg matrix. In long periods of immersion, a protective layer is formed, and filiform corrosion observed for alloys with Zn content above 1 wt%. However, the micro-galvanic effects still play a crucial role in deterioration of corrosion resistance in alloys with relatively high Zn content. These effects depend on the cathodic behavior of the particles, and on the total number of the particles presented on the alloy's surface. [ABSTRACT FROM AUTHOR]

The symmetrical and asymmetrical electrodes made of Mg were studied in 0.1‐M NaCl electrolyte adjusted at pH 12. The statistical and wavelet methods were employed for analyzing the electrochemical current noise (ECN) signals. The asymmetric configuration was used for electrochemical detection of filiform corrosion on Mg electrode. The real time scale of the dominant transients of the asymmetric electrodes was detected on the basis of the maximum peak in the SDPS plots. The SDPS values of the real time scale crystals of the ECN signals resulting from asymmetrical electrodes increased with the increase in immersion time due to the onset of filiform corrosion. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of conversion coatings (CCs) in mitigating filiform corrosion (FFC) on acrylic-coated steel substrates, with a specific focus on iron phosphatizing and trivalent chromium conversion coatings. Aiming to evaluate the effectiveness of a simulated electrochemical approach introduced in a previous publication, several parameters are determined through an approach involving potentiodynamic polarization curves and zero resistance ammeter on bare CCs. These experiments are conducted in test solutions designed to replicate the electrolytic conditions the substrate encounters undergoing FFC. Similar measurements are collected in neutral testing solutions and the outcomes of the two approaches are discussed regarding the performances of the organic coated sample. The electrochemical evaluation of CCs highlights their potential to reduce the driving forces and nucleation tendency. However, for the steel coated with acrylic paint, while CCs reduce the initiation sites for delamination, they have limited impact on filament propagation. • Employing conversion coatings shows promise as an effective strategy to mitigate filiform corrosion on painted steel. • An electrochemical simulation approach can be applied to anticipate the performance of inorganic coatings. • Simulated quantitative data are deliberated in reference to the actual corrosion resistance. [ABSTRACT FROM AUTHOR]

Zirconium oxide-based conversion coatings (CCs) were prepared from hexafluorozirconic acid, H 2 ZrF 6 , with and without CuII as an additive. The CCs were prepared on primary and recycled AA6060. The deposition mechanism, structure, electrochemical properties and effectiveness in protection against filiform corrosion (FFC) have been explored. In presence of CuII additives, a two step deposition mechanism is observed, evidenced by open circuit potential measurements and in situ dynamic electrochemical impedance spectroscopy. Copper deposits predominantly as copper(II) hydroxyfluoride on the top surface, and metallic Cu 0 at the metal/CC interface, as evidenced by x-ray photoelectron spectroscopy and glow-discharge optical emission spectroscopy. The presence of a CuII additive induces a different distribution of the ZrO 2 -based products. After deposition of a weak organic model coating, aluminium pretreated with the CuII-containing system shows a 10%–30% lower maximum filament length compared to the CuII-free system in FFC tests, despite a ca. one order of magnitude higher cathodic activity of the former. [Display omitted] • Deposition of ZrO 2 based conversion coatings is assisted by CuII additives. • Copper hydroxide deposits in the top regions of such conversion coatings. • Presence of CuII in the conversion bath influences the distribution of ZrO 2 • Higher cathodic activity does not induce faster filiform corrosion. • Comparable filiform corrosion performance between primary and recycled alloys. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis and use of multifunctional methacrylic monomers, which contain basic (amine) functional groups, including an example in which an acid-labile tert -butylcarbamate-protected glycine is used to form a novel methacrylic monomer. The "protected" amino acid-derived functional monomer (BOC-Gly-MA) is copolymerized with an epoxide functional methacrylic monomer (GMA), to deliver novel multifunctional polymers, which are processed into powder coatings and used to study filiform corrosion at the surface of an aluminum substrate. The BOC-Gly-MA-containing copolymers were shown to improve a coating's anticorrosion performance, presenting the lowest average filiform corrosion (FFC) track length, total FFC number, and total corroded surface area (CSA) of the coatings investigated. Further to this, a mode of action for the role of BOC-Gly functional polymers in corrosion protection is proposed, supported by both solution and polymer-aluminum interface studies, delivering new insights into the mode of action of pH-responsive polymer coatings.

This paper presents a short review of the literature data and the newest studies of filiform corrosion (FFC) testing of profiles extruded using a recycling‐friendly AA 6xxx aluminium alloy, with Cu content up to 0.09 wt%. As the pretreatment plays a significant role in avoiding FFC on powder‐coated aluminium profiles, the profiles were pretreated and coated at three different production sites. They have been tested at 40°C, 82% RH for 1000 hours (according to modified ISO 4623‐2). It was observed that differences in FFC behaviour of the same type of profile coated at different plants were more significant than differences between samples with increasing Cu content. In order to understand the differences between profiles coated at different sites, GDOES analysis of samples was performed, specially focusing on surface enrichment of copper through the pretreatment. [ABSTRACT FROM AUTHOR]

Abstract The effect of Sn additions on the microstructure and corrosion behavior of new wrought Mg-5Al-xSn (x = 0.71, 1.47, 2.44, and 3.09 wt%) was studied through optical and electron microscopy, XRD, hydrogen evolution test, and electrochemical measurements. Increasing of the Sn content was followed an increase in the quantity of Sn dissolved in the Mg matrix and precipitation of Mg 2 Sn intermetallics when Sn content exceeded 1.47 wt%. The corrosion mode in a short immersion period was pitting corrosion; presence of cathodic sites (i.e., Mg 2 Sn intermetallics) deteriorated the alloys' corrosion resistance. However, with a long immersion period the corrosion mode of the alloys with Sn content above 0.71 wt% was mixed pitting and filiform corrosion, indicating that a passivation layer was formed on the alloys' surface and increased their corrosion resistance. Highlights • Increasing Sn above 1.5 wt% results in precipitation of Mg 2 Sn intermetallics. • Sn content above 0.7 wt% changes the corrosion mode from pitting to pitting + filiform corrosion. • High Sn content (>1.5 wt%) promotes formation of corrosion products and improves long-period corrosion resistance. [ABSTRACT FROM AUTHOR]

In this work, two rare earth carboxylate compounds, lanthanum 4-hydroxycinnamate (La(4-OHcin) 3) and yttrium 3-(4-methylbenzoyl)propanoate (Y(mbp) 3), were incorporated into bisphenol-based epoxy resin to investigate their effectiveness in coating barrier properties and active corrosion inhibition. EIS results showed that the incorporation of rare earth carboxylate inhibitors significantly improved corrosion resistance compared to the inhibitor free coating, with the global impedance modulus remaining at a level higher than 1 GΩ cm2 after 219 days immersion. Following EIS experiments, cross-sectional views of the coatings exhibited a pore-plugging behavior by rare earth containing precipitates, which reinforced the coating barrier properties and delayed the electrolyte diffusion process. These effects were also reflected from the electrochemical parameters extracted from breakpoint frequency analysis and equivalent circuit modelling. Filiform corrosion experiments for artificially scratched coatings suggest that the addition of rare earth carboxylates effectively suppressed the initiation and growth of filaments as well as the development of the coating delamination front. The active corrosion inhibition is possibly related to the formation of a surface protective film consisting of bimetallic complexes and rare earth metal rich precipitates. The electrochemical measurements and surface analyses evidence the dual function of rare earth carboxylate species for enhancing coating barrier properties against electrolyte penetration and providing active corrosion inhibition for the underlying AS1020 mild steel. • Rare earth carboxylates in coating enhanced the corrosion protection of mild steel. • The pore-plugging effect was observed to improve the coating barrier properties. • Active corrosion inhibition was confirmed using artificially scratched coatings. • Inhibition mechanism of rare earth carboxylates in coatings has been discussed. [ABSTRACT FROM AUTHOR]

Abstract Electroless nickel/nickel-boron (Ni/Ni-B), Ni/alkaline Ni-P and Ni/acidic Ni-P double-layer coatings were deposited on AZ31 magnesium (Mg) alloy prepared by environmental fluoride-free solution under low temperatures. The morphologies, compositions, and crystal structures of three different double-layer coatings were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistance of the different double-layer coatings on Mg alloy surface was studied by electrochemical polarization and electrochemical impedance spectroscopic (EIS) tests, which indicated that the Ni/Ni-B coating presented the more superior corrosion resistance than the Ni/alkaline Ni-P and Ni/acidic Ni-P coatings. Meanwhile, the Ni/Ni-B coating exhibited good repeatability through the electrochemical polarization tests for three Ni/Ni-B samples that prepared under the same processing conditions. In addition, the optimal plating time for the Ni-B coating was further determined by electrochemical polarization tests of samples with different plating times. Highlights • The double-layer Ni/Ni-B coating on AZ31 Mg alloy is prepared by electroless method under relatively lower temperatures. • The pretreatment, activation and plating solutions completely remove fluoride. • The Ni/Ni-B coating exhibits good repeatability. • The optimal plating time of the outer Ni-B coating is obtained. [ABSTRACT FROM AUTHOR]

Spent nuclear fuel in the U.K. is stored within ponds dosed with NaOH in order to inhibit corrosion and, to ensure the efficiency of storage regimes, there is a need to define and quantify the corrosion processes involved during immersion of fuel cladding. In this project, state-of-the-art characterisation techniques were employed to image the corroding surfaces of two nuclear fuel cladding materials: stainless steel and Magnox. Advanced gas-cooled reactor fuel cladding consists of 20Cr-25Ni-Nb stabilised stainless steel and during irradiation the microstructure of the cladding undergoes significant changes, including grain boundary element depletion and segregation. High-speed atomic force microscopy with nanoscale resolution, enabled precipitates and pit initiation in stainless steel to be imaged. Magnox is a magnesium–aluminium alloy and during irradiation in a reactor the outer metal surface oxidises, forming an adherent passive layer which subsequently hydrates when exposed to water. Corrosion processes encompass breakdown of passivity and filiform-like corrosion, both of which were imaged in situ using the scanning vibrating electrode technique. [ABSTRACT FROM AUTHOR]

The filiform corrosion mechanism on acrylic-coated steel is investigated through potentiodynamic curves collecting anodic and cathodic branches in two different electrolytes simulating the liquid environments at the metal-paint interface. Zero resistance amperometry was chosen as an additional tool to achieve numerical results. The potential difference and the current density between the anodic and cathodic portions of the filament tip were estimated using a simplified setup. The role of oxygen availability on the corrosion mechanisms was also investigated by modifying the amount of dissolved oxygen in the simulating electrolytes and the humidostatic chamber employed for FFC propagation. [Display omitted] • Acrylic-coated carbon steel is susceptible to filiform corrosion. • The leading head is characterized by a typical "V-shape". • The morphology and the corrosion rate are determined by the oxygen available. • Electrochemical analyses are able to assess the driving force of the mechanism. • Anode and Cathode reactive sites have comparable areas. [ABSTRACT FROM AUTHOR]

The effect of precipitates on filiform corrosion (FFC) growth of coated Al-Mg-Si-Cu alloys with different coolings and chemical components was investigated using a cyclic corrosion test and dynamic polarization in an acid solution. Total FFC growth was accelerated by air cooling, while being suppressed by water quenching for high Cu containing Al alloy. Comparison of water quenching with air cooling showed that the cathodic current densities and number of precipitates including Cu were lower after water quenching at high Cu containing Al alloy. These results suggest that suppression of precipitates including Cu improves the FFC growth resistance of Al-Mg-Si-Cu alloys. [ABSTRACT FROM AUTHOR]

This work aims at studying by electrochemical impedance spectroscopy (EIS) the susceptibility to filiform corrosion of low carbon steel covered by cataphoretic coating. The determination of the exposed metallic area variations of scratched samples during ageing test is an estimation of the disbonding of the coating and/or the filiform corrosion. This area can be evaluated by electrochemical impedance spectroscopy (EIS). A simplified electrical equivalent model used to estimate the exposed metallic area is valid if the corrosion products are correctly dissolved before characterization. Furthermore the steel is a very complex substrate and thus many parameters must be optimized in order to remove the corrosion products before EIS measurements. [ABSTRACT FROM AUTHOR]

Surface treatment of aluminium alloys using steam with oxidative chemistries, namely KMnO 4 and HNO 3 resulted in accelerated growth of oxide on aluminium alloys. Detailed investigation of the corrosion performance of the treated surfaces was carried out using potentiodynamic polarisation and standard industrial test methods such as acetic acid salt spray (AASS) and filiform corrosion on commercial AA6060 alloy. Barrier properties of the film including adhesion were evaluated using tape test under wet and dry conditions. Electrochemical results showed reduced cathodic and anodic activity, while the protection provided by steam treatment with HNO 3 was a function of the concentration of NO 3 − ions. The coating generated by inclusion of KMnO 4 showed highest resistance to filiform corrosion. Overall, the performance of the steam treated surfaces under filiform corrosion and AASS test was a result of the local coverage of the alloy microstructure resulting from steam containing with KMnO 4 and HNO 3 . [ABSTRACT FROM AUTHOR]

The steam treatment of aluminium alloys with varying vapour pressure of steam resulted in the growth of aluminium oxyhydroxide films of thickness range between 450 and 825 nm. The surface composition, corrosion resistance, and adhesion of the produced films were characterised by XPS, potentiodynamic polarisation, acetic acid salt spray, filiform corrosion test, and tape test. The oxide films formed by steam treatment showed good corrosion resistance in NaCl solution by significantly reducing anodic and cathodic activities. The pitting potential of the surface treated with steam was a function of the vapour pressure of the steam. The accelerated corrosion and adhesion tests on steam generated oxide films with commercial powder coating verified that the performance of the oxide coating is highly dependent on the vapour pressure of the steam. [ABSTRACT FROM AUTHOR]

In this study, oxide layers generated on aluminum alloy 6060 (UVS A96060) using a steam-based process were compared with conventional chromate and chromate-phosphate conversion coatings. Chemical composition and microstructure of the conversion coatings were investigated and their corrosion performance was evaluated using potentiodynamic polarization, acetic acid salt spray, and filiform corrosion testing of powder coated specimens. The steam-based process resulted in homogenous growth of oxide layer and superior coverage over intermetallic particles when compared to chromate-based conversion coatings. The coating formed by steam showed improved corrosion resistance, while adhesion to powder coating and filiform corrosion was comparable with chromate conversion coatings. [ABSTRACT FROM AUTHOR]

The filiform corrosion (FFC) of organic coated magnesium alloys is investigated using in-situ scanning Kelvin probe and time-lapse photography. FFC is initiated by injecting MgCl 2 , HCl and FeCl 2 into a coating defect and ensuing FFC propagation rates are shown to increase as a logarithmic function of the chloride ion concentration and are strongly dependent on relative humidity. Post-corrosion surface analysis shows chloride abundance near the filament leading edge and evidence of sequestration within corroded regions behind. The FFC mechanism is consistent with chloride-induced anodic dissolution at the front coupling with water reduction on a cathodically-activated corroded surface behind. • Organic coated Mg alloys (E717, AZ31 & AZ91) are susceptible to filiform corrosion. • The filiform corrosion propagation rate is dependent on the Cl- concentration. • Increasing relative humidity produces higher rates of filiform corrosion propagation. • Chloride-induced anodic dissolution at the filament leading edge. • Progressive depletion of Cl- via entrapment within the corrosion product. [ABSTRACT FROM AUTHOR]

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The atmospheric corrosion of coated steel samples with artificial defects was characterized to determine the environmental variables that are important in the corrosion process. Coated steel samples were exposed to different climates in Hawaii, Florida, and Ohio. The iron oxides formed under the coating were identified with Raman spectroscopy, which allowed the corrosion mechanisms to be deduced. Those mechanisms were influenced by the time of wetness (TOW) and the deposition rate of chloride and sulfur that were measured at the different sites. Two corrosion morphologies were observed: bead-like corrosion was formed in the defect vicinity and filiform corrosion (FFC) was initiated from the bead-like corrosion. Bead-like corrosion was influenced by the TOW and the salt deposition, whereas FFC grew in the humid environment, but its mechanism was independent of the salt deposition. At almost all of the sites tested, chloride was the only salt that participated in the corrosion process. [ABSTRACT FROM AUTHOR]

Filiform corrosion (FFC) has been shown to occur during field exposure of scribed organic-coated steel. In this paper, the FFC filament morphologies formed under polyvinyl butyral (PVB) and bisphenol A based epoxy coatings after initiation with hydrochloric acid (HCl) solution were compared. Under the epoxy coating, secondary filaments were observed at right angles from the main filament. These secondary filaments suggested that chloride had migrated perpendicular to the filament direction. This perpendicular chloride migration may be driven by the straight (more open) head/tail boundaries, which were noticeable on the filaments growing under the epoxy coating. Under PVB, the filament depth increased with the number of moles of chloride and the filament head radius. These tendencies were not measured under the epoxy coating because the filament head changed shape during propagation, which may have been associated with anisotropic coating properties. The effects of prior exposure to ASTM G85 and ASTM G154 environments on FFC initiation and propagation were investigated. Pre-exposutes affected the initial stage ofFCC, but, once initiated, the filament propagation only depended on the filament head size. Degradation of the coating/ steel interface during ASTM G85 exposure reduced FCC incubation time and increased the number of initial sites. Improvement in interface stability during exposure to ASTM G154 for PVB-coated steel increased FCC incubation time and reduced the size and the number of initial sites. [ABSTRACT FROM AUTHOR]

The role on filiform corrosion (FFC), after an automotive painting process with a phosphate treatment, of the near surface deformed layer (NSDL) formed during mechanical processing on AA8006 aluminium alloys is investigated. Samples subjected to specific surface pretreatments are examined before and after different steps of the phosphating process in order to identify the characteristics of the NSDL that are responsible for the susceptibility to FFC. The thickness, the structure and the composition of this NSDL are determined by SEM, RBS, XPS and transmission electron microscopy. The presence of a 200-nm thick NSDL which is not completely eliminated during the degreasing step of the phosphating process increases dramatically the FFC susceptibility of AA8006 aluminium alloys compared with beforehand etched samples. The influence of Pb and Mg segregation on top of the surface is found to be negligible whereas the specific microstructure of the NSDL characterised by nanograins with boundaries decorated by nano-sized oxide intermetallic particles seems to play a major role on FFC. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Development of smart composite coatings combining nanocontainers with fluorescent dye and inhibitor. • Detection by fluorescence of the initial stage of the degradation in FFC. • Inhibition of cathodic delamination during the FFC. Filiform corrosion (FFC) is a degradation affecting coated steel in atmospheric conditions. For industrial application the corrosion detection at the early stage is important to apply the reliable protection. Investigation on the use of nanocontainers for the detection and protection of organic layer is described. Fluorescent dye was used to detect the active corrosion and to evaluate the efficiency of inhibitors encapsulated inside PVB model organic coating. Active dissolution is located at the filament head whereas the cathodic reaction occurs along the tail where the oxygen concentration is higher. The fluorescent dye use is a relevant technique for the detection of corrosion early stages and inhibition efficiency. [ABSTRACT FROM AUTHOR]

The in situ formation of I-phase improves the corrosion resistance of the duplex structured Mg–6% Li alloy. Corrosion attack on the surfaces of Mg–6% Li alloy is very inhomogeneous and severe pits and filiform corrosion clearly occur on the surfaces after immersion in 0.1M NaCl solution. For the I-phase-containing Mg–6% Li–6% Zn–1.2% Y alloy, the corrosion attack is homogeneous and no severe pits and filiform corrosion can be observed. [ABSTRACT FROM AUTHOR]

The filiform corrosion behaviour of hot-rolled AA3104 aluminium alloy was investigated in the presence of a near-surface deformed layer produced by hot rolling. Through detailed examination of microstructure of the near-surface deformed layer and observation of the propagation behaviour of filiform corrosion, it was found that lateral development of surface-active filiform corrosion in the deformed layer was promoted by magnesium oxide in bands and manganese-containing dispersoids. Further, successive-pitting filiform corrosion was observed along the underlying grain boundaries of the bulk alloy, which develops into crystallographic corrosion of the grain interiors. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Recently thin film metallic glass represents a class of promising engineering materials for structural applications. In this work, the Zr-based thin film metallic glass (TFMG) was fabricated on the Si and AISI 420 substrates using a Zr–Cu–Ni–Al alloy and pure Zr metal targets by a pulsed DC magnetron sputtering system. The chemical compositions, crystalline structures, microstructures and corrosion behavior in hydrochloric (HCl) aqueous solutions of Zr-based TFMGs were investigated. The results showed that the surface morphologies of Zr-based TFMG were very smooth. A compact and dense structure without columnar structure was observed. The amorphous structure of Zr-based TFMG was characterized by the X-ray diffractometer and transmission electron microscopy analyses. After the potentiodynamic polarization test, the better corrosion resistance was achieved for the Zr-based TFMG coated AISI 420 in 1mM HCl aqueous solution. Based on the surface morphologies and chemical analysis results of the corroded surfaces, the pitting, crevice corrosion and filiform corrosion were found. The corrosion mechanisms of the Zr-based TFMG were discussed in this work. [Copyright &y& Elsevier]

Abstract: In-coating cation and anion exchange pigments are studied with respect to their ability to inhibit chloride-induced filiform corrosion (FFC) on organic-coated AA2024-T3 aluminium alloy substrates. In-situ scanning Kelvin probe potentiometry is used to quantify both underfilm potentials associated with populations of propagating corrosion filaments and the kinetics of coating disbondment. Smart-release bentonite pigments containing exchangeable cerium (III) and yttrium (III) cations are shown to be largely ineffective in reducing rates of FFC propagation. The reasons for this are discussed in terms of the chemistry of the electrolyte-filled corrosion filament head. In contrast, anion-exchange hydrotalcite (HT) based pigments are highly effective inhibitors of FFC. A comparison of the extent of FFC observed for various inorganic exchangeable anions is made with as-received HT comprising carbonate anions. Of the anions evaluated, exchangeable chromate unsurprisingly provides the highest FFC inhibition efficiency. It is also demonstrated that exchanging the native carbonate ions for certain organic species which act as complexing agents for copper ions, gives rise to an equivalent level of FFC inhibition. The implication of these findings with respect to the mechanism of FFC on copper containing aluminium alloys is considered. [Copyright &y& Elsevier]

Abstract: The aim of this study is to develop a newly silane sol–gel pretreatment on the barrier properties and filiform corrosion resistance of 6016 aluminium alloy covered by cataphoretic coating. The sol–gel coatings are used as coupling agent between aluminium substrate and cataphoretic paint. The pretreatment is an aqueous solution of three different silane compounds (glycidyloxypropyltrimethoxysilane (GPS), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES)) hydrolysed at two different pH (2 and 3.5). A system without pretreatment was studied as reference. The electrocoatings were cured between 155°C and 195°C in order to modify their mechanical properties. Polarisation curves, EIS and FT-IR measurements were used in order to characterize the silane layers. EIS measurements were used to follow the barrier properties and the water uptake evolution on intact coatings. The filiform corrosion protection of the coating was also evaluated by a normalized filiform corrosion test. [Copyright &y& Elsevier]