Local Electrochemical Impedance Spectroscopy Research Articles

Understanding the Effect of Corrosion Resistance in Welded AA2198‐T8 Alloy: Microstructural‐Electrochemical Insights

ABSTRACTIn this study, we explore the corrosion resistance of AA2198‐T8 alloy in friction stir‐welded zones, focusing on microstructure changes and resulting corrosion susceptibility. Macrogalvanic coupling effects are observed in weldment under corrosive conditions, particularly in the welding joint (WJ), heat‐affected zones, and base metal (BM). Severe localized corrosion is prevalent in anodic zones, revealing intricate trenching patterns around micrometric particles in cathodic domains. Investigating isolated zones exposes SLC across all welding‐affected regions and BM, underscoring the involvement of microgalvanic cells in corrosion. The novel utilization of a syringe cell as an electrochemical tool proves to be instrumental in delineating the electrochemical characteristics of welding testing zones. Notably, stir zone within WJ emerges as the region depicting the lowest corrosion resistance, a critical finding substantiated by localized electrochemical impedance spectroscopy. These insights into the interplay of electrochemical phenomena and microstructural attributes have implications for advancing corrosion mitigation strategies and alloy engineering in materials science.

Multifunctional epoxy coatings reinforced with LDHs-modified silica microspheres: Synergistic effects on corrosion resistance, thermal insulation, and flame retardancy

This research encapsulated hollow silica microspheres with Mg-Al layered double hydroxides (LDHs) via in-situ solution deposition, integrating them into an epoxy matrix to enhance its properties. Electrochemical impedance spectroscopy revealed that SiO2@Mg-Al-NO2-LDHs-EP maintained a high impedance of 1.42×109 Ω·cm2 after a 50-day immersion period, significantly outperforming the base epoxy. The impedance change in the scratch area in the local electrochemical impedance spectroscopy demonstrates the self-healing property of the coating. According to the thermal conductivity meter test results, adding SiO2-LDHs to the coating can reduce the thermal conductivity of the coating by about 20 %. Furthermore, microcalorimeter and cone calorimeter tests show that SiO2@Mg-Al-NO2-LDHs can significantly improve the flame retardancy properties of the coating. This study demonstrates the potential advantages of LDHs-coated silica microspheres in functional coatings.

A distributed constant equivalent circuit model and a method for estimating parameters for paper-based lactate biofuel cells

In this study, a distributed constant-type equivalent circuit model for paper-based lactate biofuel cells (PBFCs) where the anode and cathode are formed on the same plane was constructed, and a method of determining parameter values in the equivalent circuit model was proposed. When PBFC were prepared and the electrochemical impedance of the entire cell was measured, the Nyquist diagram produced a spectrum due to the current line distribution. Parameters, such as charge transfer and solution resistances, were calculated from the obtained spectrum using theoretical impedance equations derived from the proposed equivalent circuit model proposed. In addition, the behavior of the current distribution in the battery was evaluated in detail by moving the reference electrode on and performing local electrochemical impedance spectroscopy at multiple points on the electrode. The models and methods proposed in this study are good for evaluating systems affected by distributed current lines, such as flat batteries, and for determining cell design, electrode areas, and arrangements.

Constructing PANI@CF hybrids enhanced epoxy coatings with integrated functionalities of interfacial enhancement, erosion wear resistance and anti-corrosion

Factors such as sediment erosion and diffusion of corrosive ions in the splash zone result in a serious decrease in the protective performance of organic coatings. Carbon fiber (CF) reinforced polymer coatings have attracted much attention due to the impressive high mechanical strength and reliable chemical stability, but their protection period for steel structures is usually limited by the surface inertness and poor interfacial compatibility of the original CF. Herein, we created a composite coating with excellent erosion and wear resistance and corrosion resistance through simple self-polymerization of polyaniline on carbon fibers. The PANI layer not only helped to improve the interfacial compatibility between fibers/resin, but also exerted its corrosion inhibition effect. The interfacial shear strength (IFSS) value of the modified PANI4@CF monofilament and resin (60.63 MPa) was 46.73 % larger than that of the unmodified CF monofilament. In the simulated splash zone, PANI4@CF5/EP composite coating showed the best erosion resistance and corrosion resistance, and the mass loss and volume loss after erosion test were reduced by 53.39 % and 50.10 %, respectively, compared with pure epoxy coating. The local electrochemical impedance spectroscopy (LEIS) value of PANI4@CF5/EP coating with artificial defect was one order of magnitude higher than the epoxy coating after 48 h immersion. Finally, the environmental conditions of the splash zone were simulated to evaluate the anti-corrosion performance and erosion resistance of the CF reinforced composite coatings, and the protective mechanism was discussed in depth, which has great significance to the development of protective coatings for the splash zone under extreme marine environments.

Cleaner flotation separation of chalcopyrite from pyrite at low alkalinity: Based on calcium hypochlorite oxidative modification in acid mine drainage system

Efficient and clean flotation separation of copper-sulfur has attracted soaring interest in the beneficiation of sulfide ore. The objective of this work was to examine the influence of calcium hypochlorite (Ca(ClO)2) oxidative modification on the flotation separation of chalcopyrite from pyrite in acid mine drainage (AMD) system. A maximum recovery difference of 69.70 % between both minerals was observed under the recommended conditions (initial pH = 8.5 ± 0.2, [Ca(ClO)2] = 100 mg/L, [EX] = 32 mg/L, and the volume ratio of AMD to pure water = 1:1). A high-grade concentrate with 77.35 % Cu recovery and 29.01 % Cu grade was obtained, demonstrated by mixed-mineral micro-flotation experiments. Analysis of Cu and Fe ions influence indicated that low concentrations of Fe3+ and Cu2+ favored the selective separation of pyrite and chalcopyrite. Moreover, analysis of the pulp ion concentrations showed that Ca(ClO)2 promoted the dissolution of iron ions on the pyrite surface compared to chalcopyrite, thereby enhancing pyrite oxidation. The Ca(ClO)2 interacted more intensively with the pyrite surface, forming a passivated layer that impeded the adsorption of collector, as demonstrated by Zeta potential and contact angle results. The generation of hydrophilic products caused by oxidation on the pyrite surface, such as CaSO4, CaOH+, Fe(Ⅲ)–OOH, and/or Fe2(SO4)3 was confirmed by XPS analysis, further reducing the floatability of pyrite. Furthermore, local electrochemical impedance spectroscopy and scanning electron microscopy analyses further afforded favorable evidence for selective inhibition of pyrite by Ca(ClO)2 in the AMD system. This study provides a new approach to achieve cleaner separation of pyrite and chalcopyrite and offers new perspectives for AMD treatment solutions.

Design and Development of Flow Fields with Multiple Inlets or Outlets in Vanadium Redox Flow Batteries

In vanadium redox flow batteries, the flow field geometry plays a dramatic role on the distribution of the electrolyte and its design results from the trade-off between high battery performance and low pressure drops. In the literature, it was demonstrated that electrolyte permeation through the porous electrode is mainly regulated by pressure difference between adjacent channels, leading to the presence of under-the-rib fluxes. With the support of a 3D computational fluid dynamic model, this work presents two novel flow field geometries that are designed to tune the direction of the pressure gradients between channels in order to promote the under-the-rib fluxes mechanism. The first geometry is named Two Outlets and exploits the splitting of the electrolyte flow into two adjacent interdigitated layouts with the aim to give to the pressure gradient a more transverse direction with respect to the channels, raising the intensity of under-the-rib fluxes and making their distribution more uniform throughout the electrode area. The second geometry is named Four Inlets and presents four inlets located at the corners of the distributor, with an interdigitated-like layout radially oriented from each inlet to one single central outlet, with the concept of reducing the heterogeneity of the flow velocity within the electrode. Subsequently, flow fields performance is verified experimentally adopting a segmented hardware in symmetric cell configuration with positive electrolyte, which permits the measurement of local current distribution and local electrochemical impedance spectroscopy. Compared to a conventional interdigitated geometry, both the developed configurations permit a significant decrease in the pressure drops without any reduction in battery performance. In the Four Inlets flow field the pressure drop reduction is more evident (up to 50%) due to the lower electrolyte velocities in the feeding channels, while the Two Outlets configuration guarantees a more homogeneous current density distribution.

Effect of Coating Damage on the Micro Area Corrosion Performance of HDR Duplex Stainless Steel

In order to determine the effect of damaged insulating enamel on the corrosion of high-chromium (H), duplex (D), and corrosion-resistant (R) duplex stainless steel, the corrosion characteristics of HDR duplex stainless steel in 3.5% NaCl solution were studied by means of local electrochemical impedance spectroscopy (LEIS) and micro-morphology analysis. It was shown that the LEIS impedance was stable at about 7.0 × 103 Ω within 10 days when the HDR duplex stainless steel was not coated. The minimum LEIS impedance of exposed HDR at the damaged area fluctuated around 6.5 × 103 Ω within 15 days when the coating of the self-control insulating enamel damaged area was 1 mm × 10 mm. The coating-damaged area from 1 mm × 10 mm reduced to a circular hole with a diameter of φ1 mm, and the LEIS impedance of the exposed HDR increased at the damaged coating. When extending along the damaged coating to the intact coating area, the impedance rapidly increased, and the further the distance from the damage, the greater the increase in impedance. The impedance of coated HDR increased with the prolongation of immersion time and ultimately stabilized. The thicker the coating, the longer the impedance took to reach a stable state. The stabilized coating had a better effect on improving the corrosion resistance of HDR duplex stainless steel. Within 15 days, the HDR ferrite structure at different areas of coating damage prioritized corrosion. Cl− mainly comes from the solution, and Si and S elements mainly come from elements of the collective itself, with Cl− adsorption, S, and Si element inclusion being the main factors influencing the corrosion of the ferrite structure.

Smart self-healing coating based on the covalent organic frameworks (COF LZU-1) for corrosion protection of steel

COF LZU-1 has the characteristics of a porous structure, a large specific surface area, and good chemical stability. In recent decades, extensive research has been conducted on its use as a nanomaterial for drug loading and separation. Here, we report a new corrosion inhibitor encapsulated nanostructure (LZU-1 @BTA). We synthesized LZU-1 via a hydrothermal method and loaded benzotriazole (BTA) corrosion inhibitor into LZU-1. The results show that loaded BTA can achieve effective pH-responsive release under acidic and alkaline conditions. The amino group present in the LZU-1 molecule can cross-link with epoxy resin, and its compatibility allows for good dispersion in epoxy resin without any further modification. The LZU-1 @BTA modified epoxy coating has shown remarkable anti-corrosion properties and excellent self-healing capabilities, which have been evaluated through various techniques such as potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), local electrochemical impedance spectroscopy (LEIS), scanning Kelvin probe (SKP) and salt spray testing. The high-quality dispersion of LZU-1 @BTA in the resin, the high cross-linking density, and the pH-responsive release of BTA in the epoxy resin are some of the key factors that contribute to the excellent anti-corrosion performance of the epoxy resin composite coating. This research has opened up new possibilities for designing anti-corrosion coatings with significantly better corrosion resistance.

Integrated scanning electrochemical cell microscopy platform with local electrochemical impedance spectroscopy using a preamplifier.

Local electrochemical impedance spectroscopy (LEIS) has emerged as a technique to characterize local electrochemical processes on heterogeneous surfaces. However, current LEIS heavily relies on lock-in amplifiers that have a poor gain effect for weak currents, limiting the achievements of high-spatial imaging. Herein, an integrated scanning electrochemical cell microscopy is developed by directly collecting the alternating current (AC) signal through a preamplifier. The recorded local current (sub nA-level) is compared with the initial excitation signal to get the parameters for Nyquist plotting. By integrating this method into scanning electrochemical cell microscopy (SECCM), an image of LEIS at the Indium Tin Oxide/gold (ITO/Au) electrode is obtained with a spatial resolution of 180 nm. The established SECCM platform is integrated such that it could be positioned into the limited space (e.g. glove box) for real characterization of electrodes.

Local electrochemical and thermal investigation of a segmented reversible solid oxide fuel cell and electrolyzer

A novel setup has been designed and mounted to investigate the local electrochemical and thermal behavior of a cell from a 4-cell short stack under reversible operation solid oxide fuel cell/solid oxide electrolyzer (SOFC/SOE). It consists in the partition of the cell's oxygen electrode into 20 segments, where each segment is controlled by a specific electronic load. This allows to control the segments independently in galvanostatic or potentiostatic mode. The configuration also enables local electrochemical impedance spectroscopy (EIS) measurements of each segment. 20 thermocouples were added to measure the local temperature of the segments in order to gain a deeper insight into the cell thermal distribution. This helps correlating the local thermal and electrochemical responses to the operating parameters. This specific setup allowed mapping the cell's local behavior based on a multidimensional operating conditions matrix, including current density, temperature, feed gas composition, sweep gas flow and polarization. Moreover, a durability test of more than 1,000 h helped investigating the local long-term degradation in a reversible (day SOE, night SOFC) configuration. These results are of significant importance towards optimal operation of a reversible SOC with enhanced durability.

Local Electrochemical Corrosion of 6061 Aluminum Alloy with Nano-SiO2/MAO Composite Coating.

To improve the corrosion resistance of 6061 Al in electric vehicle battery packs, a composite coating of nano-SiO2/Micro-Arc oxidation (MAO) ceramic structure was prepared on its surface. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves (PDP) were used to evaluate the corrosion resistance of the specimens after 7 days immersion in a 3.5% NaCl solution. The corrosion resistance of the prefabricated coatings was measured via local electrochemical impedance spectroscopy (LEIS). Confocal microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure and phase composition of the specimens. An energy dispersive spectrometer (EDS) was used to detect the elemental composition of the surface of the specimen. The results showed that the specimen with nano-SiO2/MAO composite coating had the least amount of micropores and superior corrosion resistance. The global electrochemical impedance of nano-SiO2/MAO composite coating was 1.1 times higher than that of the MAO coating and 8.4 times higher than that of the 6061 Al. When the coating was defective, the local electrochemical impedance of the nano-SiO2/MAO composite coating was still two times higher than that of the MAO coating. In the presence of scratches, the nano-SiO2/MAO composite coating still showed high corrosion resistance. The collapse corrosion mechanism of the nano-SiO2/MAO composite coating was proposed.

Effect of regulating dissolved oxygen concentration in pulp with aerated gas on pyrite flotation

Moderate oxidation is beneficial to the flotation of sulfide ores, but the exact dissolved oxygen (DO) concentration suitable for flotation is still unclear. In this work, a self–made vacuum aeration flotation equipment was designed and assembled to accurately control the DO concentration in pulp by adjusting the relative proportion of O2/N2 during aeration, and the effect of DO concentration on the floatability and surface properties of pyrite as well as the interaction between pyrite and xanthate was studied. Microflotation experiments, contact angle, time–of–flight secondary ion mass spectrometry, X–ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, electrochemical and localized electrochemical impedance spectroscopy measurements were conducted in this investigation. The results showed that the flotation recovery of pyrite could be remarkably affected by DO concentration in pulp; it increased first and then decreased with the increase of DO concentration; an optimal DO concentration (DO = 3.3 mg/L) was helpful for pyrite flotation recovery; both the formation of dixanthogen and the avoidance of excessive iron oxide/hydroxide formed on pyrite surface were the key to improve the pyrite recovery. This research is expected to be applied in optimizing the flotation separation by DO-pH combined detection and regulation, strengthening the green flotation of sulfide ore with low collectors, and the design and manufacture of new closed and efficient sulfide ore flotation equipment.

Probing passivity of corroding metals using scanning electrochemical probe microscopy

AbstractPassive films are essential for the longevity of metals and alloys in corrosive environments. A great deal of research has been devoted to understanding and characterizing passive films, including their chemical composition, uniformity, thickness, porosity, and conductivity. Many characterization techniques are conducted under vacuum, which do not portray the true in‐service environments passive films will endure. Scanning electrochemical probe microscopy (SEPM) techniques have emerged as necessary tools to complement research on characterizing passive films to enable the in situ extraction of passive film parameters and monitoring of local breakdown events of compromised films. Herein, we review the current research efforts using scanning electrochemical microscopy, scanning electrochemical cell microscopy (or droplet cell measurements), and local electrochemical impedance spectroscopy techniques to advance the knowledge of local properties of passivated metals. The future use of SEPM for quantitative extraction of local film characteristics within in‐service environments (i.e., with varying pH, solution composition, and applied potential) is promising, which can be correlated to nanostructural and microstructural features of the passive film and underlying metal using complementary microscopy and spectroscopy methods. The outlook on this topic is highlighted, including exciting avenues and challenges of these methods in characterizing advanced alloy systems and protective surface films.

Bioinspired polydopamine nanosheets for the enhancement in anti-corrosion performance of water-borne epoxy coatings

The utilization of two-dimensional (2D) inorganic nanomaterials as nanofillers in the anticorrosion fields has garnered significant attention due to their exceptional barrier properties. However, uniform dispersion of nanofillers and good interfacial compatibility with organic coatings still remain a substantial challenge. Consequently, there is a need to explore novel and eco-friendly 2D nanomaterials for anticorrosive applications. In this study, two-dimensional polydopamine nanosheets (PDANS) were synthesized through a facile template method, and incorporated into water-borne epoxy (WEP) coating as green anticorrosive additives. Compared to WEP coating, the prepared PDANS/WEP coatings exhibited significantly enhanced corrosion protection performance, with a nearly 50% reduction in water uptake and a 22-fold increase in the |Z|f=0.01Hz value at a 0.5 wt% PDANS loading. These improvements can be attributed to the favorable interfacial compatibility between PDANS and WEP matrix, as well as the superior barrier properties of PDANS. Furthermore, local electrochemical impedance spectroscopy (LEIS) results demonstrated that the damaged PDANS/WEP coating provided enhanced corrosion protection by inhibiting steel corrosion through the chelating interaction between PDANS and steel, thereby reducing the coating delamination. Based on these findings, it can be inferred that PDANS hold great promise for the development of innovative anticorrosive coatings.

Novel application of depressant sodium mercaptoacetate in flotation separation of chalcopyrite and pyrite

The development of flotation reagents with high selectivity and strong depression ability is of great significance in the efficient enrichment of copper sulfide ores. In this work, a new depressant, sodium mercaptoacetate (SMA) has been explored for the flotation separation of chalcopyrite and pyrite, and the depression mechanism of SMA was studied by Fourier Transform Infrared spectrometer (FTIR), adsorption tests, local electrochemical impedance spectroscopy test (LEIS), Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). Micro-flotation tests showed that SMA strongly depresses pyrite in the pH range of 6–10. When the dosage of SMA is 2.5 × 10−5 mol/L, the dosage of SBX is 1 × 10−5 mol/L, and pH = 6.5, the concentrate with a Cu grade of 31.93% and chalcopyrite recovery of 85.97% can be obtained, in which the pyrite recovery was only 4.18%, respectively. The strong chemical adsorption between SMA and Fe atomic sites exposed on the surface of pyrite reduces the hydrophobicity of pyrite and hinders the adsorption of SBX. In comparison, SMA has less adsorption on the surface of chalcopyrite and hardly affects the further adsorption of SBX. It was shown that SMA could be used as an effective depressant for pyrite in the flotation separation of chalcopyrite and pyrite.

Effect of Redox Switch, Coupling, and Continuous Polarization on the Anti-Corrosion Properties of PEDOT Film in NaCl Solution

Conjugated poly(3,4-ethylenedioxythiophene) (PEDOT) film was electrochemically synthesized on stainless steel (SS). Redox interactions between the PEDOT film and the SS substrate were examined in 3.5 wt.% NaCl aqueous solution with the aid of electrochemical and spectroscopic analyses. The results show that the PEDOT film exhibited a barrier effect and mediated the oxygen reduction reaction, thus hindering ion diffusion to the steel substrate. Localized electrochemical impedance spectroscopy (LEIS) of the scratched area on the polymer film shows that PEDOT healed the defect by coupling with redox reactions on the steel surface to prevent charge localization and concentration. The electroactivity of the polymer film declined when PEDOT was polarized at potentials >−0.7 V. Prolonged exposure of the PEDOT film to dissolved oxygen in NaCl solution resulted in the polymer’s over-oxidation (degradation), evidenced by the formation of a carbonyl group in the spectroscopic result. The degradation of PEDOT was attributed to chain scissoring due to hydroxide ion attacks on the polymer chain.

Dodecylbenzene sulfonate isopropanolamine as an eco-friendly collector for selective separation of cassiterite from quartz

The effective separation of fine cassiterite from quartz requires the addition of inhibitors and activators. Dodecylbenzene sulfonate isopropanolamine (DBIA) is a selective collector that separates cassiterite from quartz. At pH 6.5, using a reagent system of 1.25 × 10−4 mol/L DBIA, the flotation recoveries of quartz and cassiterite were less than 10% and 94.25%, respectively. The flotation indices of cassiterite concentrate with a recovery of 88.06% and a grade of 74.02% were achieved during the same flotation test of artificially mixed minerals. Zeta potential, Total organic carbon (TOC) test, localized electrochemical impedance spectroscopy scanning (LEIS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to investigate the selective collection mechanism of DBAI on the mineral surfaces. The results demonstrated that DBIA was poorly physically adsorbed on quartz but strongly chemically adsorbed on the tin sites of the cassiterite surface. These findings provide a theoretical foundation for cassiterite and quartz flotation separation and a fresh, fruitful approach.

Determination of Surface Intrinsic Resilience against Bubble Coverage Using Localized Electrochemical Impedance Spectroscopy Time Domain Information

Bubble coverage on electrode surfaces presents challenges for the wide application of water electrolysis technology. Earlier experimental studies on superaerophobic electrode surfaces indicated that surface roughness of microscale morphologies can greatly increase the surface’s resilience against bubble coverage at high current densities. Localized electrochemical impedance spectroscopy (LEIS) is used in this paper to assess this surface conductance under bubbles. The local impedance of the bubble-shielded area and the contour around the bubble were investigated on polished nickel and dynamic hydrogen bubble templating (DHBT) nickel surfaces with different porosities and pore distributions. This study demonstrated that porosity could reduce the resistivity caused by bubble coverage, and an evenly distributed porous surface is more resilient to bubble coverage.

Insight into selective depression of sodium thioglycallate on arsenopyrite flotation: Adsorption mechanism and constructure

Arsenopyrite is a hazardous substance exist in copper concentrate, thus causing serious environmental pollution during the smelting process. However, the selective depression of arsenopyrite remains a challenge to flotation. This study aims to analyze the depression mechanism of sodium thioglycallate (STG) towards arsenopyrite in the Cu-As separation flotation. Micro-flotation tests confirmed that STG was able to selectively depress arsenopyrite in chalcopyrite flotation and lowered As content in copper concentrate. Local electrochemical impedance spectroscopy (LEIS) demonstrated that STG preferred to adsorb on arsenopyrite than on chalcopyrite, which enhanced electrochemical impedance and reduced surface reactivity. Furthermore, surface adsorption test and contact angle measurement illustrated that STG hindered butyl xanthate (BX) adsorption on arsenopyrite surface, thus the wettability of arsenopyrite was further enhanced. The results of fourier transform infrared spectroscopy (FTIR), DFT caculation and Molecular dynamics simulations (MDS) revealed that STG chemically bond with Fe and As sites on the surface of arsenopyrite through its -SH group, and it formed a hydrogen bond with water molecules via its -COO- group at the top of molecule. Ultimately, a bridge-similar constructure was generated among arsenopyrite, STG and water molecules. This constructure resulted in a stable hydrophilic film covered on arsenopyrite surface, thus its flotability was severely deteriorated.

INVESTIGAÇÃO DA ATIVIDADE ELETROQUÍMICA DE LIGA Al-Cu-Li APÓS PROCESSO DE SOLDAGEM POR FRICÇÃO E MISTURA

INVESTIGATION OF THE ELECTROCHEMICAL ACTIVITY OF AN Al-Cu-Li ALLOY AFTER FRICTION STIR WELDING PROCESS. In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).