Passive film formation of wrought and laser powder bed fusion (LPBF) 316L with different heat treatments was investigated. The passive films of the samples were formed after electrochemical passivation in a chloride acidic solution. The electrochemical passivation was monitored thanks to an original approach by electrochemical impedance spectroscopy (EIS). This electrochemical monitoring allows following the formation of the passive layer. Electrochemical results show significant differences between the wrought and LPBF 316L regarding the electrical properties of the metal/electrolyte interface.

The corrosion of carbon steel in aqueous CO2 environments remains a key challenge in oil and gas systems. Despite decades of research, the mechanistic role of CO2 remains a topic of debate. In this study, electrochemical impedance and polarization measurements were systematically performed at pH levels of 3-5 in 0.17 mol L-1 NaCl, under both CO2-Saturated and N2-Purged conditions. The results demonstrate that CO2 corrosion rates are independent of pH, in contrast to N2 systems, where corrosion increases with acidity. Impedance diagrams revealed a characteristic inductive loop whose frequency was invariant with pH under CO2, interpreted as a catalytic effect of hydrated CO2 species. A new electrochemical model was developed, introducing this catalytic role in the hydrogen evolution reaction, in addition to the classical buffer mechanism. This new model quantitatively reproduces both the pH-independent corrosion rate and the impedance response, thereby providing a significant step forward in the mechanistic framework for CO2 corrosion of carbon steel.

To investigate the failure mechanism of AA5052/polyurethane coating system in seawater fluctuation zone, a dynamic corrosion simulation setup for the seawater/atmosphere interface was constructed in this study. Electrochemical impedance spectroscopy (EIS) was employed to systematically investigate the electrochemical behaviors of the coating system under two wet-dry alternating cycles. Based on the non-uniform water absorption behavior of the coating, a bilayer model was proposed to analyze the EIS data, and the early-stage corrosion mechanism was discussed in detail. The results indicated that the EIS spectra exhibited three time constants, which correspond to the impedance contributions from the inner coating layer, the outer coating layer, and the oxide film on the substrate metal, respectively. Long-term water level fluctuations were found to exacerbate the decrease in the resistivity of the coating's outer layer and accelerate the deterioration of the protective performance of the inner layer. In contrast, the salt concentration effect was shown to weaken and delay coating deterioration in the short term. The proposed bilayer model effectively characterizes the internal resistivity distribution of the coating and reveals the penetration patterns of corrosive media. This study provides a theoretical basis for the durability design and service life prediction of coatings in dynamic marine environments.

The water level fluctuation zone (or alternating wet and dry environment) is a typical service condition for marine aluminum alloys (AAs). The mechanism by which cathodic protection affects the corrosion of AAs in this environment remains to be clarified. In this study, the corrosion behavior of AA5083 (connected with an Al-Zn-In-Cd sacrificial anode) in a simulated water level fluctuation zone was investigated using electrochemical impedance spectroscopy (EIS) combined with surface and cross-sectional morphology observation. The localized and uniform corrosion of AA5083 in the water level fluctuation zone is accelerated after coupling with the Al-Zn-In-Cd anode. This is mainly because, under wet conditions, the sacrificial anode causes the protection potential to be excessively negative, and the hydrogen evolution reaction on the electrode surface dominates. This leads to the alkalization of the electrode surface, a reduction in the thickness of the oxide film, and thus accelerates the corrosion of the alloy matrix.

The interpretation of impedance spectroscopy data requires both a physical insight into the chemistry and physics that govern the system under investigation and an assessment of the error structure of the measurement. Our group has recently published a measurement model computer program that enables both assessing the stochastic and bias errors in a measurement and provides for regression of interpretation models. The object of this work is to describe the approach taken by our group for interpretation of impedance data, including error analysis and development of interpretation models.

Under sacrificial anode cathodic protection (SACP), harsh marine environments and non-uniform anode distribution often induce localized overprotection on metals. However, the corrosion behavior and underlying mechanism of AA5083 under such SACP-induced overprotection remain unclear. In this study, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) were employed to investigate the corrosion mechanism of AA5083 under sacrificial anode (Al-Zn-In) protection in the simulated water level fluctuation zone and full immersion zone. A comprehensive kinetic model considering electrochemical dominant reactions (anodic/cathodic reactions) and adsorbed intermediates (Alads+, Hads) was proposed. The results showed that under SACP at the over-negative potential, the cathodic hydrogen evolution reaction (HER) of AA5083 dominated the electrochemical process, leading to localized alkalization. Enhanced micro-galvanic effect between the Al matrix and cathodic intermetallic particles (IMPs), combined with intensified hydrogen-enhanced anodic dissolution, reduced the thickness and compactness of the oxide film, accelerating the corrosion of AA5083 under SACP.

Localized corrosion caused by oxide film breakdown significantly shortens the service life of aluminum alloys in marine environments. However, there are few detailed data available for longer-term field exposures of Al-Mg alloys, especially for the properties of the oxide film. Here, the surface films formed on an unsensitized and a sensitized 5083 Al-Mg alloy samples after 2 years of exposure in the splash zone and the tidal zone are investigated. Pitting corrosion was observed on the samples exposed to the splash zone, whereas the samples in the tidal zone exhibited a characteristic of uniform corrosion. A near-surface deformed layer (NSDL) composed of nanocrystalline grains was found to inhibit intergranular corrosion (IGC) in the sensitized Al-Mg alloy. From the high splash zone to the tidal zone, the corrosion resistance of the surface film that consists of an outer loose corrosion products layer and an inner oxide film decreased. Longer drying time and sufficient oxygen supply in the high splash zone facilitated the formation of a complete oxide film with high Al2O3 content. Under prolonged wetting time and limited oxygen supply in the tidal zone, a defective oxide film enriched in Mg and Si formed on the alloy surface. Our findings provide insights into the corrosion evolution mechanism and oxide film formation of Al-Mg alloys in marine splash and tidal zones.

Chromate passivation treatment is a commonly used surface treatment method for aluminum alloys (AAs) applied in marine engineering. In this study, the electrochemical behaviors of untreated AA5052, chromatepassivated AA5052, and passivated sample subjected to 4-year natural seawater corrosion were investigated by using scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and inductively coupled plasma optical emission spectrometry. The results demonstrate that chromate passivation significantly enhances the corrosion resistance of AA, while the passive film almost completely loses its protective efficacy after 4 years of exposure to natural seawater. The passivated surface exhibits a golden-yellow appearance, which is primarily attributed to the presence of hexavalent chromium (Cr6+) in the surface layer. The passive film presents a bilayer structure, consisting of a dense inner layer (composed of aluminium oxides) homogenous in chemical composition with high constant resistivity and an outer layer presenting a chemical gradient (composed of chromium/aluminium oxides and hydroxides) as well as a gradient in defect concentration with a resistivity variation. The resistivity distribution of the passive film conforms to the power-law model. Localized corrosion of the passivated samples initiates at the cracks of the passive film, whereas localized corrosion of the untreated samples originates around the Fe-rich second-phase particles, subsequently inducing the anodic dissolution of the aluminum (Al) matrix. The dissolution mechanism of the activated regions can be explained by a two-step dissolution mechanism of Al involving adsorbate Al+ads.

This work aims to investigate the corrosion electrochemical behavior of 316L stainless steel (SS) exposed to the seawater-air interfacial environment in China's Bohai Sea for 2.5 years. A floating platform was established for a 2.5 year on-site exposure test of large-scale 316L SS specimens (200 mm x 1000 mm x 3 mm) in the Bohai Strait, with the exposed surface divided into splash, waterline, and full immersion zones. Corrosion behaviors were analyzed via morphology observation and electrochemical tests. Results showed the full immersion zone had the severest corrosion (deepest pits, thickest rust, heaviest biofouling), followed by the splash zone, while the waterline zone was mildest. Electrochemically, the waterline zone exhibited the highest corrosion potential, polarization resistance, and oxide film thickness, indicating optimal corrosion resistance. Barnacles accelerated corrosion in the full immersion zone via synergistic mechanical damage and biochemical effects. This study provides references for marine engineering material selection and corrosion protection of SS.

The stress corrosion cracking (SCC) susceptibility of sensitized 5083 aluminum alloy (AA) in the water level fluctuation zone is greatly affected by the immersed-exposed alternating time. Here, a novel device was established to simulate the SCC in the water level fluctuation zone with varying immersed-exposed alternating time. The SCC mechanism of sensitized AA5083 was investigated using slow strain rate tensile (SSRT) tests and electrochemical impedance spectroscopy (EIS) analysis combined with constant load tests. With the prolongation of the immersed-exposed alternating time from 1-1 to 120-120min, the corrosion extent gradually increased and became stable due to the water evaporation, salt concentration, and abundant oxygen supplement in the thin electrolyte layer (TEL) on the alloy surface during the exposed process, which promoted the anodic dissolution of Mg-rich phase at the grain boundaries (GBs). Thus, the tendency of intergranular fracture increased under the stress, resulting in high SCC susceptibility. Combined effect of corrosion and stress led to the formation of more defective surface oxide film with double-layer structure in the water level fluctuation zone than that in the full immersion environment.

This paper aims to investigate the influence mechanism of silicon (Si) network morphology on the localized corrosion behavior of AlSi10Mg alloy prepared by selective laser melting (SLM) in 3.5 wt% NaCl solution. Four different Si microstructures, i.e., coarse Si network, fine Si network, broken Si network, and isolated Si particles, were regulated through stress relief annealing at 200 degrees C and 300 degrees C (designated as SR200 and SR300 respectively), and T6 heat treatment. Microstructure observation, electrochemical testing, corrosion morphology characterization, and scanning Kelvin probe force microscopy (SKPFM) are used to identify the corrosion mechanism. The results show that heat treatment significantly changes the morphology of Si microstructure. The SLM-AlSi10Mg alloy mainly undergoes pitting corrosion in NaCl solution, and pitting preferentially occurs at the molt pool boundary (MPB). The oxide film on the alloy surface has a bilayer structure: inner dense Al2O3 layer and outer porous Al(OH)3 layer. A more uniform and dense oxide film with stronger protectiveness is formed on Al matrix with networked Si. The inner dense layer on Al matrix with the particulate Si is thinner than with the Si network, resulting in weakened protectiveness. SKPFM analysis reveals that the potential difference between Si and Al matrix increases with the coarsening of the Si network, and the MPB becomes a preferential corrosion area due to the larger potential difference. This study provides a theoretical basis for optimizing the corrosion resistance of SLM-AlSi10Mg alloy.

The oxide film is crucial for the cavitation erosion resistance of passive metals, such as aluminum (Al) alloys. However, the properties of the oxide film and the way cavitation intensity impacts its dissolution mechanism remain unclear. In this study, electrochemical impedance spectroscopy (EIS) was employed to investigate the corrosion mechanism of an AA7050 Al alloy under cavitation erosion-corrosion (CEC) conditions. Morphological alterations, the degree of surface lattice distortion, and the composition of the oxide film were characterized. The influence of the gap width between the vibratory horn and the stationary samples on the CEC mechanism was also discussed. A comprehensive model that is independent of the gap width and considers the presence of one adsorbed intermediate, Al+, for anodic dissolution is proposed to elucidate the corrosion of Al under CEC conditions.

The steam generator (SG) tubes of pressurized water reactors are manufactured with Ni-based alloys; their corrosion behavior in the simulated primary water environment largely depends on the properties of the oxides formed during the exposure to this environment. Ex-situ experiments, in particular electrochemical impedance spectroscopy (EIS) measurements at room temperature, were performed to characterize the electrical properties of the oxides. The analyses were conducted on two industrial samples, in their as-received state to study the native oxide films, and after exposure to the simulated primary water environment to analyze the oxide layers formed in this environment. A physical model was proposed based on the EIS data and previous TEM and XPS characterizations. For both conditions, EIS showed a capacitive behavior of the oxide films in relation with their passive properties: the passive contribution of the film was modelled using the power law model. The data acquired for the oxide films formed in simulated primary water environment also showed a porous behavior that was considered using a De Levie impedance. The data were successfully fitted and the parameters of the model determined. The values of these parameters were discussed according to previous TEM observations and XPS chemical analyses of the films formed on the two SG tubes. A good correlation was evidenced between the results obtained from the electrochemical measurements of this work and the chemical and structural analyses of the oxide films formed in the simulated primary water environment.

The remanufacture of damaged conversion coatings requires a dry-in-place, no rinsing process. This work reports a novel brushing conversion treatment method. The SEM and TEM analyses demonstrate a porous but more compact structure, whereas electrochemical measurements prove an enhanced corrosion resistance of brushing conversion coatings, as compared with the conventional immersion coatings. The more compact structure was ascribed to the accelerated coating growth kinetics under the continuous brushing, and the enhanced corrosion resistance was attributed to the retard of the penetration of corrosive ions in the maze-like porous structure.

Intergranular corrosion (IGC) significantly damages the strength of Al-Mg alloys with a Mg content > 3 wt% when these alloys are serviced in marine environments. Although a dense oxide film can prevent the degradation of Al alloys, the influence of tensile stress on the properties of the oxide film is unclear. Here, the oxide films formed on a sensitized 5083 Al-Mg alloy under constant elastic and plastic tensile stresses are investigated. Pitting corrosion and intergranular corrosion occurred on the alloy surface. Tensile stress accelerated the anodic dissolution on the alloy surface and promoted intergranular corrosion, weakening the corrosion resistance of the oxide film. A heterogeneous oxide film was found on sensitized Al-Mg alloy, with the oxide film formed on the IGC region was thicker than that on the alloy matrix due to local alkalization. Tensile stress caused dislocations near the grain boundaries, but did not change the composition of the oxide film in the region subjected to intergranular corrosion. Density-functional theory calculations suggest that tensile stress destroyed the oxide film and weakened the electronic interactions between the oxide film and the alloy matrix, fostering the propagation of intergranular corrosion. Our findings clarify the mechanisms of oxide film formation on Al-Mg alloys under constant tensile stress in aqueous solution.

This study explores the influence of aging on hydrogen embrittlement (HE) susceptibility and corrosion resistance of AA7050 via microstructural characterization, slow strain rate tensile testing, thermal desorption spectroscopy, and electrochemical measurements. Prolonging aging (2-72 h) transforms grain boundary eta-phase (MgZn2) from continuous to discontinuous distribution, widens precipitate-free zones), and increases the HE susceptibility index from 13.69% to 55.80%. Short-aged samples (2 h) exhibit dimple fractures dominated by hydrogen-enhanced decohesion, while long-aged samples (24-72 h) show mixed intergranular/quasi-cleavage fractures via synergistic HEDE and hydrogen-enhanced localized plasticity. Hydrogen accumulates at Al/Al(7)Cu2Fe interfaces, weakening cohesion. H-charged samples display reduced oxide film thickness and degraded corrosion resistance, confirming a corrosion-HE feedback mechanism. This work provides insights for optimizing aging processes to enhance AA7050 performance. Longer aging time in 7050 Al alloy boosts HESI from 13.69% to 55.8% by altering microstructure.Hydrogen embrittlement mechanisms vary with aging: HEDE at 2 h, HEDE + HELP at 24 h and 72 h.Hydrogen charging deteriorates 7050 Al alloy's corrosion resistance, thinning the oxide film.Al(7)Cu2Fe traps hydrogen, facilitating crack propagation; Si - rich phase doesn't.

Barrier properties of innovative epoxy coatings containing 10 or 20 phr of phosphate/phosphonium ionic liquid (IL) were investigated using mainly electrochemical impedance spectroscopy. The impedance diagrams revealed quasi-pure capacitive behavior and the impedance modulus at low frequency, related to corrosion resistance, remains at around 1012 omega cm2 during immersion time in 0.1 M NaCl solution. The capacitances were graphically extracted from Cole-Cole representations, and the resistances were determined using R//C electric equivalent circuits. Both epoxy-IL coatings were free of porosity and impeded the hydration of the matrix. The results were also compared to those of conventional epoxy coatings, for which hydration occurs owing to their porosity. Results indicate that this new epoxy-IL coating system would offer excellent anticorrosion protection for metallic substrates.

In this study, the impedance response of a passive material is investigated, attributing it to a normal time constant distribution caused by resistivity variations within the passive film. Two models, namely the Power Law Model (PLM) and the recently developed Dielectric Bi-Layer Model (DBLM), are employed to express the impedance data. The PLM considers an oxide film as a single layer with a power-law distribution of resistivity, while the DBLM incorporates two distinct layers: an inner layer with constant resistivity (ρ0) and an outer layer with resistivity following Young's theory. Application of both models to 316L stainless steel immersed in a borate buffer solution exhibit that PLM and DBLM fitting results are in good agreement with experimental data. While the models differ mainly in resistivity profiles at the vicinity of the outer interface, the results suggest that deviations in regressed parameters indicate similar ranges for resistivity profiles calculated by both models. DBLM, in particular, is highlighted as promising for interpreting impedance data of passive materials due to its reliance on physical concepts.