Filiform Corrosion Research Articles

Heterostructured melamine resin Spheres@GO reinforced epoxy composite achieving robust Corrosion-Resistance of Zn-Al-Mg coated steel for automotive applications

Dual threats of over-film (degradation) and under-film filiform corrosion (FFC) pose a significant challenge to the reliable application of Zn-Al-Mg coated steel (ZAM-steel), necessitating the development of effective protection strategies. This study introduces a novel MRS@GO nanohybrid, integrated within epoxy (EP) coatings, to enhance the corrosion resistance of ZAM-steel in 3.5 wt% NaCl solution. The hierarchical structure of MRS@GO synergistically combines the barrier properties of an insulating material (MRS) with the electrochemical benefits of a conducting material (GO), providing superior protection. This dual functionality significantly improves the overall performance and durability of ZAM-steel, making it a promising candidate as the decorative coating for the automotive industry.

Microstructure-induced anisotropic biocorrosion response of laser additive manufactured WE43 alloy

The microstructure and corrosion of laser-processed WE43 was studied. Results suggest that multi-factors like grain structure, crystallographic defect, and precipitate distribution result in an anisotropic corrosion response. XY plane with high crystal defect densities offers more sites for pitting corrosion. Filiform corrosion is detected on both XY plane and XZ plane, where Zr-rich and RE-rich precipitate distribution plays an essential role in corrosion initiation and propagation. The enrichment of Zr around filament corrosion promotes local micro-galvanic corrosion. Notably, the XY-plane, with continuous distribution and extended scanning trajectory edge, is particularly susceptible to filiform corrosion as compared with XZ-plane.

Designing a high barrier, tough and self-repairing epoxy composite coatings with Ce-MOF decorated 2D α-ZrP smart nanofiller

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.

Cracks propagation mechanism of intergranular corrosion in Al–Cu–Li AA2195 alloys governed by constant relative humidity

Atmospheric corrosion of Al–Cu–Li AA2195 alloys was investigated in constant relative humidity (RH) controlled by saturated salt solutions. Corrosion process was governed by RH, especially for the transformation of corrosion products and crack growth. The deceleration corrosion kinetics and maximum pit depth were found to be in accordance with the power laws. The corrosion products gradually transformed from γ-Al(OH)3 and γ-AlOOH into NaAlCO3(OH)2 and γ-Al(OH)3 affected by RH and exposure time. The localized formation of pitting, filiform and exfoliation corrosion was induced by the presence of Cu/Mg/Li-containing secondary precipitates, including T1(Al2CuLi), θ'(Al2Cu) and S'(Al2CuMg) phases. Secondary precipitates with lower potential were prone to triggering intergranular corrosion. The primary cracks penetrated into the internal matrix along large angular grain boundaires. Secondary cracks propagated along corrosion channels of the stress-concentrated triple grain boundaries with higher schimd factors, larger Kernel average misorientation and higher geometrically necessary dislocation densities. A crack propagation mechanism controlled by RH was proposed.

Effects of mechanical surface pre-treatment on integrity and corrosion of bare and coated AA6082 substrates

In this study, two classes of surface pre-treatment methods, namely three blast-cleaning methods with different abrasive materials (for initial preparation) and three mechanical methods (for repair applications) were applied to study their effects on surface morphology, composition, and corrosion of AA6082 substrates in artificial seawater. Coating adhesion and coating corrosion protection ability were investigated by applying a single-layer epoxy coating (250 μm dry film thickness) onto the substrates.The mechanical methods delivered cleaner surfaces with more regular surface morphologies, whereas the blast-cleaning methods revealed less clean surfaces and more irregular surface morphologies. The latter methods promoted the detrimental embedment of abrasive particles into the substrates. The corrosion performance of the pre-treated substrates was worse after blast-cleaning compared to mechanical treatments. However, all methods met the adhesion requirements for offshore applications. Regarding coating degradation, only the filiform corrosion test delivered meaningful results, whereas the duration of the cyclic corrosion test (3000 h) was too short to distinguish between the different methods because of neglectable degradation. Mechanical interlocking and isotropic surface morphologies are found to be more important for coating performance than a cleaner surface, and the remains of blasting material were neglectable too.

Unlocking the Potential of Sebacate: Investigating Its Role in the Inhibition of Filiform Corrosion on Organic Coated Steel

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.

PH-Responsive, Thermoset Polymer Coatings for Active Protection against Aluminum Corrosion.

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.

Study of ZnAl Hydroxides-Based Thin Films to Enhance the Filiform Corrosion Resistance of Acrylic-Coated AA5005

In recent years, the imperative to adopt a sustainable approach to aluminum coating pre-treatments due to environmental concerns has engaged researchers in corrosion studies. This work investigates Zn-Al hydroxides-based conversion coatings developed on AA5005 to enhance filiform corrosion (FFC) resistance. The conversion coatings were applied as a pre-treatment (200 nm–800 nm thick, depending on synthesis conditions) prior to coating with acrylic paint. The synthesis of the Zn-Al hydroxides conversion coating involves a rapid hydrothermal method at near-neutral pH. Electrochemical tests performed on the ZnAl hydroxides conversion coatings onto AA5005 revealed a substantial improvement in localized corrosion resistance. FFC tests in a climatic chamber exhibit a significant decrease (about 50%) in rust creep filament propagation compared to bare AA5005 after 1000 h. Those results were obtained employing Zn and Al salts at neutral pH for ten minutes at 95 °C. The findings obtained suggest that the synthesis process is of potential interest within the context of chemical surface conversion treatments for aluminum. In fact, eco-friendly metallic salts contribute to a more economical and environmentally friendly waste disposal process, making this treatment a potential solution for industrial applications, considering its simplicity, time efficiency, and use of non-toxic products.

Effect of Cu2+ on deposition mechanism and structure of ZrO2-based conversion coatings on AA6060 aluminium alloys and their susceptibility to filiform corrosion

Zirconium oxide-based conversion coatings (CCs) were prepared from hexafluorozirconic acid, H2ZrF6, 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 Cu0 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 ZrO2-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.

Filiform Corrosion on Polyester Powder-Coated Aluminum

Filiform corrosion initiates and grows locally at macroscopic defects in coatings on metal substrates. While typically not detrimental to the bulk metal properties, the filiform corrosion results in threadlike filaments that propagate parallel to the surface underneath the coating. Herein, we present a study correlating the electrochemical and structural properties of polyester powder coatings onto 6022 aluminum to their associated resistance to filiform corrosion. Filiforms are propagated using a modified EN 3665 method and tracked temporally via bright field microscopy. Results including electrochemical impedance spectroscopy, open-circuit potential tracking, and potentiostatic experiments were used to evaluate coating barrier properties. Coating morphologies of pre- and post-corrosion samples are evaluated using SEM and EDX. Mechanical properties of free-standing polyester films are also characterized. The combined electrochemical and mechanical data are used to derive polyester coating design criterion to maximize resistance to filiform corrosion.

Deposition Mechanism, Structure and Corrosion Protection of ZrO2-Based Conversion Coatings on AA6060 Primary and Recycled Aluminum Alloys

Chemical conversion coatings (CC) are amongst the most common surface pretreatments for aluminium alloys before further organic coating steps. The presence of a conversion layer can increase the resistance towards underpaint corrosion such as filiform corrosion (FFC). Here we explore the deposition mechanism, structure and protective properties against FFC of a ZrO2-based CC on AA6060 aluminium alloy by means of electrochemical techniques as open circuit potential measurements, potentiodynamic polarization and dynamic electrochemical impedance spectroscopy (dEIS). Surface composition and elemental distribution are characterized by X-ray photoelectron spectroscopy (XPS), Glow Discharge Optical Emission Spectroscopy (GD-OES) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The variation of important parameters such as charge transfer resistance and capacitance during the conversion layer deposition gives insight into the deposition mechanism. GD-OES and XPS shed light into the structure and composition of the formed CC layer constituted of a mixture of Zr (hydr)oxides based products, redistribution of alloy elements and the nature of deposited additives. Finally, FFC tests reveal a comparable performance between primary and recycled alloys.

Anodization and Plasma Electrolytic Oxidation Treatments of AZ91D Mg Alloy in Alkaline Aqueous Solutions

Mg alloys, such as AZ91 (Mg-9mass%Al-1mass%Zn), are lightweight materials with excellent mechanical properties. The applications of Mg alloys in automobiles could significantly contribute to reducing carbon dioxide emissions. Mg alloys are fully recyclable and abundantly available, which increases their desirability in light of rising environmental consciousness. However, the low corrosion resistance of Mg alloys is one of the major limitations to further applications.In Mg alloys, corrosion behavior is known to be related to the microstructure. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β phase (in lamellar α + β microstructure and along the α-mother phase 1. Furthermore, the β phase exhibited a higher potential in the OCPs of each phase and a small area with the boundary in 0.1 M NaCl at pH 8.0 2. Thus, the surface films of β phases was thought to suppress the corrosion of Mg alloys. Mg alloys can be treated by anodic oxidation or plasma electrolytic oxidation to obtain excellent corrosion resistance. The latter is similar to anodic oxidation but applies a higher voltage, which causes a discharge on the electrode surface and the resulting plasma modifies the oxide film significantly.In this study, anodic oxidation and plasma electrolytic oxidation were performed on AZ91D Mg alloy in alkaline solutions such as sodium phosphate. This study aims to compare the two methods in the same solution and to produce an Al-rich surface film with excellent corrosion resistance.In anodic oxidation, the size of the electrode area was approximately 1 cm2. The surface of the specimen was coated with epoxy resin, followed by paraffin. The reference electrode was Ag / AgCl (3.33 M KCl). The experiments were performed at 25 ℃. The scan rate of potentiodynamic polarization was set at 23 mV min-1. The starting potential was set at 20 mV lower than the open-circuit potential. The anodic oxidation treatments were terminated at 0 V, 3 V, and 5 V. Plasma electrolytic oxidation was performed with a liquid volume of 500 mL. The sample was mounted on a resin holder. The electrode surface was approximately 50 mm2. A Pt plate was used as the counter electrode. The sample and the counter electrode were fixed at a distance of 0.5 cm. A plasma-generating power supply was used. The solution was cooled down to 20 ℃ while the voltage was applied. The frequency and the pulse interval were adjusted. The voltage and type of solution were changed to produce the film. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Journal of Magnesium and Alloys, 11, 137-153 (2023).

In-situ measurement of electrochemical activity related to filiform corrosion in organic coated steel by scanning vibrating electrode technique and scanning micropotentiometry

A new approach to studying the mechanism of filiform corrosion in organic coated steel based on the scanning vibrating electrode technique (SVET) and micropotentiometry (potentiometric SECM) is presented. The electrochemical activity of the process under the coating is evaluated by mapping the ionic current densities emanating from some artificial defects made in specific locations of the filament identifiable thanks to the transparency of the coating. In addition, antimony tips are employed to investigate the pH changes associated to the different corrosion reactions at the metal-paint interface. Local pH levels associated to anodic and cathodic regions are determined along the filament.

Dynamic Electrochemical Impedance Spectroscopy for the Evaluation of Localised Corrosion on Aluminium Alloys

AbstractDynamic electrochemical impedance spectroscopy (dEIS), an extension of conventional EIS, was used for rapid measurements of initiation of localised corrosion on 3005 aluminium alloys with different Mn (1.08–1.39 wt. %) and Cu (0.15–0.22 wt. %) content by evaluating the onset and evolution of a Faradaic process observed in 0.5 M Na2SO4+0.1 M NaCl. Differences between samples were detected with highest sensitivity from the charge transfer resistance during chronoamperometry at ca. 120 mV above the corrosion potential. These differences were caused by differences in pitting initiation, and correlated well with filament density from a filiform corrosion (FFC) test of samples coated with a 20 μm epoxy topcoat. The observation can be explained by the role of pitting in FFC initiation and the similarity in FFC propagation with pit growth. The results suggest that dEIS is an efficient method for screening alloys for their FFC susceptibility.

On the Occurrence of Filiform Corrosion on Organic-Coated Carbon Steel Exposed to Cyclic Aging Test

Filiform corrosion (FFC) is one of the possible failure mechanisms of organic-coated steel. Beyond cathodic delamination, FFC causes paint detachment and the dramatic loss of the protective properties given by the applied paint. As both failure mechanisms occur during in-field exposure (depending on the environment), when assessing the performance of the protective paint by lab scale tests, we must be aware of the failure mechanism we induce with different accelerated aging cabinets. In this study, we investigate the effect of the prohesion test on the initiation and propagation of FFC. We highlight the concurrent development of FFC and cathodic blistering, which includes the change between the cathodic and anodic delamination front, during an accelerated aging procedure that cycles between saturated humidity and dry stages. The role of the presence of aggressive contaminants (Cl− and ) is discussed. According to our findings, cyclic aging tests seem to better stick to the failure mechanism occurring during in-field exposure, particularly due to the wet/dry cycles.

Multisine impedimetric monitoring with an in-depth distribution of relaxation times analysis of WE43 and AZ31 magnesium alloys corrosion

This research aims to develop and utilize an impedance-based tool for monitoring non-stationary electrochemical processes, coupling the multisinusoidal perturbation signal approach and distribution of relaxation times (DRT) analysis for the first time. The approach was used to distinguish independent processes occurring at the surface of AZ31 and WE43 Mg alloys undergoing corrosion in Hank’s Balanced Salt Solution at 37 °C. We highlighted two common processes related to corrosion product layer formation. Detailed DEIS-DRT analysis was capable of real-time identification of a unique third process for the WE43 alloy, resulting from a spatially localized filiform corrosion attack in the vicinity of intermetallic particles. The proposed tool proved to be highly efficient in terms of studying non-stationary processes, while the DRT analysis allowed for an in-depth and precise localization of the number and the kinetics of the ongoing processes. The corrosion mechanism description was supported by numerous microscopic and spectroscopic tools.

Probing corrosion using a simple and versatile in situ multimodal corrosion measurement system

In this work, we have developed a unique in situ multimodal corrosion system that is capable of acquiring electrochemical data, sample imaging/visualization and hydrogen collection, simultaneously. Each of these modalities yield valuable information pertaining to the ongoing corrosion process. Combining them can yield holistic information on the role of microstructure, processing history, presence of coatings, etc., on the sequence of steps occurring during the corrosion process, and how they correlate with the acquired electrochemical data. Four materials systems, namely AA6061-T6 aluminum alloy, AZ91 magnesium alloy, galvanized DP590 steel, and pure Zn, were investigated under open circuit potential and under potentiodynamic polarization. The multimodal corrosion system was utilized to observe processes such as surface passivation and dissolution, pit and filiform corrosion initiation and propagation, and was correlated with location and magnitude of hydrogen evolution. This approach is shown to yield a truly multimodal understanding of the ongoing corrosion processes.

Pioneering Enhanced Corrosion Resistance along the Normal Plane of an Ultra-Light Mg-Li Extruded Sheet.

The microstructure and corrosion anisotropy of the Mg-5Li extruded sheet were investigated in this work. Three distinct samples cut from the normal plane (A), longitudinal plane (B), and cross-sectional plane (C) of the as-extruded sheet were prepared. The microstructure was analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The corrosion resistance and behaviors of the three samples in a 0.1 mol/L NaCl solution were evaluated by employing hydrogen evolution, mass loss testing, electrochemical assessments, and corrosion morphology analyses. The results revealed that sample A displayed a distinctive bimodal (0002) basal texture, along with clearly distinguishably larger grain sizes than the other samples. The effect of grain size and crystallographic orientation on the corrosion resistance was highlighted, indicating the pioneering corrosion resistance of sample A and the lowest corrosion resistance of sample C. Furthermore, all three samples exhibited the characteristic filiform corrosion during the initial stages of corrosion, progressing into the formation of corrosion pits, with sample C displaying pronounced susceptibility.

Wild avalanches and mild fluctuations during filiform corrosion of Mg in NaCl solution

Wild avalanches and mild fluctuations during filiform corrosion of Mg in NaCl solution

Study on filiform corrosion of A356 aluminum alloy under an organic coating

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.