The effect of two concentrations of H2S (0.5 and 2.5 ppm), in controlled laboratory conditions (20 °C, 75%RH), on the atmospheric corrosion of pure Ag, Cu and Ni was investigated in this study. The corrosion product morphology and composition were analysed through a multi-technique approach including SEM/EDX, Raman spectroscopy, XPS and XRD. Different corrosion products were identified depending on the type of characterisations providing a better overview of the effect of H2S on the atmospheric corrosion of pure Ag, Cu and Ni. Possible mechanisms involved in the formation of these corrosion products are also discussed in this work. © 2022 The Authors

In the present work, an industrial polyester coil-coated steel was characterized by electrochemical impedance spectroscopy (EIS) during immersion in a 0.5 M NaCl solution for different temperatures (30, 40, 50 and 60 °C). The objective was to propose a methodology to follow the ageing of the coil-coated system, from the first stage of water uptake until the blistering appearance. Relevant parameters were extracted from the EIS diagrams to analyse ageing processes of the polymer and of the metal/polymer interface. Water uptake was determined from the high-frequency part of the impedance diagrams using a linear rule of mixtures. By increasing the temperature, both the water uptake kinetics and the water content in the coating increased. The effect of water uptake on the physical structure of the coating (plasticization) was discussed through the analysis of a time constant corresponding to the dielectric manifestation of the polymer glass transition. At 40, 50 and 60 °C, appearance of corrosion was detected on the impedance spectra by a decrease, at low frequency, of the impedance modulus and of the phase angle. For 60 °C, the corroded surface area as a function of time, was assessed from the EIS data analysis with adapted equivalent circuits. The corroded surface areas followed similar trend as blister surface areas determined from images analysis.

The role of Sn on the atmospheric corrosion performance of binary Cu-Sn bronze alloys (4–6 wt.% Sn) compared with Cu metal used in outdoor architecture is elucidated in terms of microstructure, native surface oxide composition, patina evolution, corrosion rates, appearance and metal release. Results are presented for non-exposed surfaces and surfaces exposed at different urban and marine sites in Europe up to 5 years and based on multi-analytical findings from microscopic, spectroscopic, electrochemical and chemical investigations. Alloying influenced the corrosion, aesthetic appearance and patina evolution, differently for urban and marine sites, whereas no effects were observed on the release pattern. © 2019 The Authors

The development of new metallic coatings to protect steel, as well as the optimization of maintenance operations on site requires obtaining relevant corrosion data as function of the exposure conditions. In atmospheric and aggressive environments such as under accelerated corrosion tests or in coastal zones, electrical resistance (ER) sensors have demonstrated their ability to provide relevant real-time corrosion data. Among the sensors commercially available, only single material such as steel, zinc, copper are proposed. However, even if this allows obtaining interesting corrosion data for such reference materials, these data are not representative of industrial systems, such as galvanized steel. Indeed, zinc-based coatings can contain different alloying elements, e.g., aluminum and magnesium, which impact drastically their resistance to corrosion. In addition, with single material sensors, the influence of the galvanic coupling between the coating and the substrate, in the presence of a defect or a cut edge is not considered. In this study, hot dip galvanized, electrogalvanized, and painted steel ER sensors are exposed in accelerated corrosion tests. The results show that this method is very promising to (i) detect the red rust apparition; (ii) assess the corrosion resistance of industrial zinc and organic coatings; and (iii) obtain relevant data in real-time along the exposure time. 

Hybrid sol–gel coatings are widely used as protective layers for aluminum alloys because of their barrier abilities. This study aims at explaining the barrier properties of a sol–gel coating based on alkyltrimethoxysilane and methacrylate resin by its film structure. This approach was examined by modifying one photopolymerization parameter, e.g., by varying the content of radical photoinitiator. By neutral salt spray test and electrochemical impedance spectroscopy, the barrier properties are highlighted. The film structure is related to thermomechanical properties of films whose glass transition temperature and elastic modulus are measured by dynamic mechanical analysis and nanoindentation, respectively. On a finer scale, conversion of methacrylate functions calculated from Fourier transform infrared spectroscopy has given information on the chemical structure of films. The morphology of these coatings is studied by scanning electron microscopy, transmission electron microscopy, atomic force microscopy operating in tapping mode, and X-ray diffraction. Results revealed that formulations containing between 3 and 9 wt% of radical photoinitiator exhibit the maximal conversion of methacrylate functions and, at a microscopic scale, a homogeneous coating where the two organic and inorganic networks are well interpenetrated. This hybrid sol–gel microstructure corresponds to the highest glass transition temperature and the highest mechanical characteristics (elastic modulus, E and hardness, H) and the highest protection performance. This results in the best barrier properties, and thus the highest corrosion resistance.

Diffuse emissions and dispersion of metals from different sources in the society have lately received an increased concern from an environmental perspective. Large research efforts have been initiated and undertaken by the division of Corrosion Science at KTH to fill knowledge gaps on corrosion-induced metal release from external constructions and buildings. The generation of such data is of paramount importance for the on-going assessment of flows and potential adverse environmental effects caused by released metals. Generated information is also essential for an improved understanding of prevailing atmospheric corrosion processes of importance for the preservation of our cultural heritage, e.g. bronze statues exposed to the atmosphere. This paper summarizes and compares long-term metal release data from pure copper, bronze (6%wt Sn) and brass (20%wt Zn) exposed at unsheltered conditions in five European environments of significantly different climatic and pollutant conditions; three urban sites (Stockholm-Sweden, Milan-Italy and Madrid-Spain) and two marine sites (Brest-France, Cadiz-Spain). Generated data are interpreted with respect to parallel multi-analytical studies of changes in patina characteristics, corrosion rates and differences in prevailing environmental conditions.

Zinc release data from 5 years of unsheltered exposures in a marine and an urban site is compiled for different zinc material types. The thin surface treatment on zinc materials is gradually detached after approximately 2 years at both sites, revealing the pre-weathered zinc surface unprotected. This consequently increased the release rates of zinc from this surface, whereas the zinc runoff rate from the bare zinc sheet remained relatively stable. Raman studies on bare zinc sheet exposed for 5 years at the marine site revealed zinc oxide of varying crystalline nature and hydrozincite to appear localized and separated from each other.

This study investigated the corrosion behavior of AISI 316L produced by direct energy deposition (DED). Microstructural and chemical analysis showed a homogeneous distribution of Si and Si–Mn inclusions of 0.5–1 µm and the Cr and Mo enrichment within interdendritic areas. Scanning Kelvin probe analysis of additively manufactured stainless steel highlighted a regular “striped-like” surface potential feature with a potential gradient of 30 mV for a mean value of 0.320 ± 0.017 V versus standard hydrogen electrode. It can be related to the presence of the residual stress in the oxide film and the complex thermal history due to the fabrication process. A cyclic corrosion test simulating atmospheric conditions revealed the same corrosion properties for stainless steel fabricated by DED compared to cold rolled one. Various surface preparations of 316L were also exposed for corrosion tests. It was found that the “as-received” and “brushed” surfaces exhibited poorer corrosion resistance due to the presence of an as-build defective layer. However, prior passivation of brushed surface, machining, or mechanical grinding down to P1200 improve significantly the corrosion resistance. © 2022 French Corrosion Institute part of RISE Research Institutes of Sweden. Materials and Corrosion published by Wiley-VCH GmbH.

β-Mg17Al12, η-Al8Mn5 and an α-magnesium phase have been synthesized from pure components by controlled solidification procedures. These phases have been studied using different electrochemical techniques including the scanning Kelvin probe (SKP). From the results, it was possible to determine the nobility and the rate of the cathodic reaction of the different phases. Measurements have also been made on an AZ91D Mg-alloy using scanning Kelvin probe force microscopy (SKPFM) and field emission gun scanning electron microscopy (FEG-SEM). The results show that the Volta potentials measured with the scanning Kelvin probe (SKP) on bulk intermetallics are comparable with those recorded with the SKPFM on the AZ91D alloy. It is shown that SKPFM provides information on the local nobility of the different intermetallic particles and phases on the submicron scale. Both the η-Al8Mn5 phase and the β-Mg17Al12 phase in AZ91D showed a more noble potential than the α-magnesium phase. It is also shown that the aluminium-rich coring along the grain boundaries results in measurable changes in the Volta potential. Finally, the role of the β-Mg17Al12 phase and the η-Al8Mn5 phase in the corrosion behaviour of AZ91D is discussed in term of local nobility, surface coverage of the cathode and the cathodic activity of the different phases.

The mechanisms of inhibition of chromate conversion coating on the filiform corrosion of coated aluminum alloy AA6016 was investigated using X-ray absorption near-edge structure (XANES) spectroscopy and Raman microspectroscopy. The results showed that Cr(VI) was preferably leached out at the opening of the filament, whereas Cr(VI) was reduced to Cr(III) at all other locations. The leached out Cr(VI) accumulated mainly in the pitting area, located in the scratch just outside the filament. The chromate released from the CCC was partly reduced to Cr(III) in the pit. The formation of an Al/Cr mixed oxide was observed in the pitting area. The repassivation of pits in the scratch by the chromate leaching from the CCC close to the scratch explains the low propagation of filiform corrosion observed for the chromated surfaces.

Due to new constraints in environmental legislation, it is necessary to develop suitable methods for the evaluation and the qualification of new protective paint systems. In particular, the need is high for investigating the protection performance of paint systems used in aggressive environments, such as environments of corrosivity category C5-M. The investigating method should be sensitive and relatively quick, give reproducible results and correctly discriminate paint systems. This paper presents results obtained on paint systems in the accelerated corrosion test according to ISO 20340 [1]. The evaluation technique as well as the criteria used for the acceptance of the aging test is discussed. From the results, it is clear that there is a need to develop or adapt sensitive tools to determine underfilm corrosion at early stages. In this view, the scanning Kelvin probe appears to be a promising tool to study the kinetics of delamination at the paint/metal interface.

Ultra-high-pressure (UHP) waterjetting is becoming more common for coatings on steel structures. An effort was made to design an appropriate welded sample, including a mixed zone at the periphery of the weld seam cleaned by UHP waterjetting to get a cleanliness DHP4. Three different paint systems were applied on the various panel design and roughnesses, and they were exposed to cyclic corrosion tests and natural weathering. Two designs of test panels were considered, flat panels and welded panels. The flat panels were then cleaned by UHP waterjetting on only one side, to treatment degree DHP1, light cleaning according to NF T 35-520 standard. The corrosion performance of the paint systems as a function of surface preparation was carried out in the laboratory. No degradation such as blistering, rusting, cracking, and chalking was observed on any of the paint systems. However, a loss of brightness was seen on S2 paint systems.

Among available standardized test methods for evaluating the performance of marine and offshore coatings, ISO 20340 Annex A is widely used.1 It is well known that tests performed on presumably identical materials in presumably similar circumstances do not in general yield to identical results. Such deviation is attributed to unavoidable random errors inherent in every test procedure and the fact that the parameters that may influence the outcome of a test cannot all be completely controlled. One consequence of such deviation is that different coating selection may be obtained upon where and how the test is performed, as ISO 20340 Annex A includes acceptance criteria for the selection of coating systems. Thus, to establish the precision of ISO 20340 Annex A, six laboratories participated in a round-robin evaluation of ISO 20340 Annex A test method for the first time. The aim was to estimate the repeatability and the reproducibility of this test upon laboratory, and eventually to determine how to improve the test method and the standard for the further revision of the standard. Five different painted systems applied on abrasive blasted steel were selected so that it included good and poor systems. The results of this study in terms of scribe creep and pull-off strength data were analyzed regarding the repeatability within a laboratory and lab-To-lab reproducibility.

Laboratory tests have been performed to determine how climatic parameters, e.g., relative humidity, temperature, and the amount of sodium chloride (NaCl), influence the corrosion rate of magnesium alloys AZ91D (UNS M 11916) and AM50 (UNS M 10500). The effect of the surface state also has been investigated. The exposures were performed at 75%. 85%. and 95% relative humidity (RH) and at 25°C and 35°C. The amount of NaCl ranged from 14 μg cm-2 to 240 μg cm-2 . The corrosion rate of both materials increased as a function of temperature, RH, and amount of NaCl. A strong influence of the surface state, i.e., as-cast or polished, was observed mainly due to the combined effect of an active surface layer and the roughness of as-cast surfaces. © 2004, NACE International.

Laboratory tests have been performed in order to determine how the climatic parameters e.g. relative humidity and temperature, and the amount of NaCl influence the corrosion rate of magnesium alloys AZ91D and AM50. The effect of the surface state has also been investigated. The exposures were performed at 75%, 85% and 95% R.H. and at 25 and 35oC. The amount of sodium chloride ranged from 14 to 240 μg cm-2. The corrosion rate of both materials increased as a function of temperature, relative humidity and NaCl amount. A strong influence of the surface state e.g. as cast or polished was observed mainly due the discontinuity of as cast surfaces.

Filiform corrosion is an active corrosion cell that moves across the metal surface underneath the coating, leaving a tail filled with corrosion products. Filiform corrosion is a main problem on coated aluminium alloys exposed to a humid atmosphere. The corrosion is generally initiated in defects in the coating and propagates in presence of aggressive ions (chloride, sulphate...), oxygen and sufficient relative humidity. The aim of this investigation is to provide more information on the mechanism of filiform corrosion on coated aluminium alloys using complementary localized techniques: the scanning Kelvin probe (SKP), the Fourier Transformed Infra-Red (FTIR) microspectroscopy and X-ray absorption near-edge structure (XANES) technique. SKP can provide information on the potential distribution during corrosion processes on both bare and coated metals with a spatial resolution of approximately 50 μm. Here, SKP measurements have been performed in order to identify the anodic and cathodic sites on filaments formed on coated aluminium during atmospheric exposure. FTIR microspectroscopy permits the identification of thin surface films of corrosion products both under ex-situ and in-situ conditions. As the spatial resolution is similar to the SKP, this technique has provided information on the composition of corrosion products formed in the head and in the tail of the filaments. The initiation and the propagation of filiform corrosion on coated aluminium alloy were investigated using an experimental set-up for in-situ infrared reflection absorption spectroscopy. It consisted of an in-situ cell, where samples were exposed to controlled humid conditions, and an optical microscope linked with a Fourier Transformed Spectrometer. XANES measurements were performed on coated chromated aluminium alloys in order to study the mechanisms of inhibition of chromate on the filiform corrosion. This was performed using a high resolution beam (e.g. 15-35 μm), making possible the establishment of X-ray maps of Cr(VI) and total chromium over the surface including the filament.

We have investigated the initiation and propagation of filiform corrosion on coated aluminium surfaces was using in situ FTIR microspectroscopy and the scanning Kelvin probe. During the initiation partially hydrolysed aluminium chloride was formed in a defect on the coated surface. The conditions in the defect resembled the environment that is found in growing pits with low pH and high chloride concentration close to the coating interface. This weakened the adhesion of the organic coating and initiated the formation of a filament. The movement of the active head was followed with in situ FTIR microspectroscopy in humid air using the characteristic IR band around 2500 cm-1 from Al(H2O)6 3+. This band is present in spectra from partially hydrolysed aluminium chloride, which was found in the head during propagation of the filament. The absorption of water in the hygroscopic corrosion products in the head of the filament was followed by measuring the changes in the intensity of the Al(H2O)6 3+ band during variation in the relative humidity.

We have investigated the initiation and propagation of filiform corrosion on coated aluminum surfaces using a new experimental set-up for in situ Fourier transform infrared (FTIR) microspectroscopy and the scanning Kelvin probe. During the initiation partially hydrolyzed aluminum chloride was formed in a defect on the coated surface. The conditions in the defect resembled the environment that is found in growing pits with low pH and high chloride concentration close to the coating interface. This weakened the adhesion of the organic coating and initiated the formation of a filament. The movement .of the active head was followed with in situ FTIR microspectroscopy in humid air using the characteristic IR band around 2500 cm-1 from Al(H 2O)6 3+. This band is present in spectra from partially hydrolyzed aluminum chloride, which was found in the head during propagation of the filament. The absorption of water in the hygroscopic corrosion products in the head of the filament was followed by measuring the changes in the intensity of the Al(H2O)6 3+ band during variations in the relative humidity. The hygroscopic properties of the aluminum hydroxy chloride salts formed in the head have important consequences for filiform corrosion, especially concerning the influence of climatic parameters such as the relative humidity and the effect of wet/dry transitions on the propagation of filiform corrosion.

The effects of temperature, relative humidity and wet dry transition on initiation and propagation of filiform corrosion on coated aluminium alloys AA6016 have been studied. The aluminium surfaces were tested in both milled and grinded conditions with chromium, phosphate and titanium-zirconium based pretreatment. A full paint system used for automotive applications (ED coat + top-coat) and an electrodeposited coat (ED coat) were investigated for the different combinations of mechanical finish, surface pretreatment and coating system. In the temperature range between 5 to 50°C, filiform corrosion, or underfilm corrosion in general, increased significantly. The effect of relative humidity and wet-dry cycling on the other hand, seems to be strongly influenced by parameters like pretreatment, coating system, and also temperature. Filiform corrosion was the highest in the range 75 to 95 % relative humidity and a distinct maximum was observed at 85% R.H. for some coating systems. However, filiform corrosion propagated at humidity down to 40-50% R.H. For specimens with chromate and phosphate based surface pretreatments, filiform corrosion was lower after exposure to tests with wet-dry cycles. The samples with titanium-zirconium based pretreatments, on the other hand, had a very poor filiform corrosion resistance in the cyclic test compared to exposures at constant relative humidity. © 2003 by NACE International.

The effects of temperature, relative humidity, and wet-dry transition on initiation and propagation of filiform, corrosion on coated aluminum alloy 6016 (AA6016 [UNS A96016]) have been studied. Corrosion products formed in the filament were analyzed using Fourier transform infrared (FTIR)- microspectroscopy. The aluminum surfaces were tested in both milled finish and grinded conditions with chromium, phosphate, and titanium-zirconium-based pretreatment. An electrodeposited coat (ED coat) and a full paint system used for automotive applications (ED coat + topcoat) were investigated for the different combinations of mechanical finish, surface pretreatment, and coating system. In the temperature range between 5°C and 50°C, filiform corrosion, or underfilm corrosion in general, increased significantly. The effect of relative humidity and wet-dry cycling, on the other hand, seems to be strongly influenced by parameters like pretreatment, coating system, and temperature. Filiform corrosion was the highest in the range from 75% to 95% relative humidity (RH), and a distinct maximum was observed at 85% RH for some coating systems. However, filiform. corrosion propagated at humidity down to 40% to 50% RH. For specimens with chromate- and phosphate-based surface pretreatments, filiform, corrosion was lower after exposure to tests with wet-dry cycles. The samples with titanium-zirconium-based pretreatments, on the other hand, had a very poor filiform corrosion resistance in the cyclic test compared to exposures at constant relative humidity. © 2004, NACE International.

Several studies sponsored by the French Naval Authorities have been conducted during the last 10 years aiming to develop more reliable testing conditions than the conventional neutral salt spray test that should not be used for prediction of material performance. A satisfying correlation to atmospheric field exposure on a ship in service was observed using a 6 months cyclic test from the automotive industry (e.g., Volvo STD23-0014) with a deviation inferior to 25% and an acceleration factor of 4. The possibility to shorten the test duration with a target of 3 months without losing correlation to field exposures is investigated in the present study. A design of experiment is used to study key parameters such as NaCl concentration, the mode of salt application and its frequency as well as the temperature. Ten different marine paint systems used for shipbuilding have been selected. The results indicate an enhancement of the aggressiveness of the test when doubling the salt concentration from 1 to 2 wt%, increasing the number of salt spray per week (from 2 to 3), and the temperature from 35 to 45 °C. The data are compared to marine field exposures in tropical and temperate climates. The most reliable testing conditions to field exposure in marine sites of severity from low C5M to CX on steel include cyclic corrosion tests using 2 wt% of NaCl.

Model hot-dip Zn-Al-Mg coatings with various microstructures were produced in a galvanising simulator by changing the cooling rate. Full characterization of the coatings was performed to identify the chemical composition of the different phases, the size of the grains and their distribution. The corrosion properties of the model microstructures were investigated in outdoor marine atmosphere up to 2 years. Weight loss measurements and cross section observations revealed a tendency for fine microstructures enriched in eutectic phases to be the most corrosion resistant. This was connected to a lower size of cathodic areas at the surface (zinc dendrites), the preferential dissolution of Mg-rich phase (eutectic) and the formation of a stable layered double hydroxide on the surface.

NaCl induced corrosion of Zn-0.2Al, Zn-5Al and Zn-55Al coated steel was investigated at low and ambient CO2 levels.Weight loss measurements revealed an enhancement of the corrosion of Zn-0.2Al and particularly Zn-5Al in low CO2. This was connected to an increase of surface pH in a low CO2 atmosphere promoting the formation of ZnO and layered double hydroxide for Zn-5Al. For Zn-55Al, CO2 depletion did not affect the surface pH due to the acidification effect of Al3+. Preferential dissolution of zinc rich phase was observed on cross-sections, particularly in depleted CO2 experiments. Different sequences of corrosion product formation were proposed for the different Zn-Al coatings. © The Author(s) 2018. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/),

The atmospheric corrosion of line hot dip ZnMgAl coating was investigated at low and ambient concentration of CO2 as a function surface chloride concentration and temperature and compared to conventional hot dip galvanised (GI) and Galfan coatings. The corrosion of zinc coatings was enhanced in low CO2 conditions and ZnMgAl material was more affected than GI, and in the range of the Galfan coating. An obvious pH effect was underlined in low CO2 conditions. Layered double hydroxide (LDH) and simonkolleite were mainly formed on ZnMgAl coating in the absence of CO2 while hydroxycarbonate and simonkolleite were dominating in ambient air.

Marine paints are complex polymeric systems containing layers of different nature that significantly delay the corrosion failures. In order to obtain a rapid ranking in the corrosion protection provided by the paints, it is important to apply sensitive and non-invasive methods for early detection of under paint corrosion. Scanning Kelvin Probe (SKP) was used to determine the mechanism(s) of corrosion and paint de-adhesion. This technique is sensitive to the metal-polymer interface and gives a quick assessment of cathodic delamination or anodic undermining. Depending on the type of exposure the mode of corrosion de-adhesion was evaluated and compared with SKP data obtained under polarization experiments by impressed current in aqueous electrolyte. After exposure, pull off test and Scanning Electron Microscopy – Energy Dispersive X ray Spectrometry (SEM-EDX technique) were applied to determine the paint adhesion stability around the defect and to analyse the steel-paint interface. 

Zinc rich primers provide corrosion protection of steel constructions under heavy corrosive conditions such as offshore environments. In general, the paint contains different polymeric layers including the zinc-rich primer with a total thickness larger than 00 μm that significantly delays the degradation of the paint and the observation of corrosion failures. For prediction of corrosion failure and a quick ranking of paint systems, a new sensitive and non-invasive method for assessment has to be developed. Two commercial coatings with different corrosion protection ability were selected for the study. Scanning Kelvin Probe (SKP) was used to determine the sacrificial protection of steel by multilayer paint systems containing zinc rich primer during exposure to accelerated corrosion tests under atmospheric or under immersed conditions. Scanning Electron Microscopy - Energy Dispersive X-Ray Spectrometer (SEM-EDX) techniques were applied to analyse the cross sections after exposure. It is shown that SKP could quickly access the level of cathodic protection of the steel substrate underneath of industrial thick marine paints.

The scanning Kelvin probe (SKP) is a non-destructive technique for measuring the surface distribution of the Volta potential with a high spatial resolution of a few tens of micrometers. The SKP technique allows in situ studies of the localized corrosion processes under atmospheric weathering conditions, on metal surfaces, or underneath organic coatings. In the present study, the SKP technique was used to follow the kinetics of underpaint corrosion from a defect applied on steel coated with thick marine paint systems (0.4 mm to 0.5 mm) as a function of exposure time in an accelerated corrosion test. Three different paint systems were investigated. In addition, the influence of surface cleanliness in terms of salt concentration on a steel substrate prior to paint application was investigated using the SKP technique. The results showed the high efficiency of the SKP technique for early corrosion evaluation under thick paints on steel substrate.

The kinetics of vanadate release from an organic coating and the stability and protective ability of the newly formed vanadate-based films on zinc surfaces have been studied with respect to self-healing ability of vanadate-pigmented organic coatings. The results were compared with those obtained with chromate. The kinetics of vanadate release from a polyester coating was comparable to that of chromate. The methods of X-ray absorption near edge spectroscopy (XANES) and scanning Kelvin probe were used for studying the mechanism of inhibition and the kinetics of vanadate reduction on bare zinc. XANES proved to be a powerful tool for determination of the oxidation state of vanadium in surface films. The experiments showed that vanadate was reduced more rapidly than chromate under the same atmospheric conditions. However, addition of magnesium phosphate resulted in a significantly lower reduction rate of vanadate. The results are discussed in light of the increased adsorption ability of the more negatively charged vanadium(V) species at higher pH, while the oxygen reduction process on zinc is inhibited due to the presence of phosphate. Thus, vanadate in combination with another inhibitor could provide corrosion protection at defects of organic coatings on zinc comparable to that of chromate.

The initial atmospheric corrosion of ZnAl2Mg2 coated steel in humid air with 80ppb SO2 was studied using in situ Infrared Reflection Absorption Spectroscopy, XRD and SEM. Corrosion products formed in SO2- and SO2 and NaCl containing environments on ZnAl2Mg2 (ZM) were dominated by Mg-containing sulphite and sulphates with sulphite formed mainly initially. The sulphite formation is connected with dissolution of the Mg-containing oxide layer present initially. This is followed by a localised corrosion process where Mg rich phase in the binary eutectic microstructure is dissolved anodically while the Zn-rich phase is the site for the cathodic oxygen reduction.

The initial atmospheric corrosion of ZM (ZnAlMg)-coated steel in humid air (85% RH) and humid argon (85% RH) containing 320 ppb SO2 was studied using in situ infrared reflection absorption spectroscopy (IRRAS), FTIR-ATR focal plane array (FPA) imaging and SEM-EDS. The corrosion products formed in humid air containing SO2 are mainly composed of magnesium sulphites and sulphates, with sulphite-containing corrosion products formed initially while the contribution from sulphates increased with exposure time. The results from FTIR-FPA imaging and SEM-EDS showed that the magnesium sulphite and sulphate are formed mainly on eutectic phases with a higher quantity of corrosion products formed on the binary eutectic (Zn-MgZn2 ) phases. This is due to presence of microgalvanic elements with the zinc-rich phases as the main sites for the cathodic oxygen reduction while the anodic reactions take place on the eutectic areas. Sulphate content is the highest on the binary eutectic phases, due to the microgalvanic effects and the production of oxidants by the cathodic reaction, which increases the oxidation of sulphite to sulphate.

The formation of corrosion products on Zn55Al coated steel has been investigated upon field exposures in a marine environment. The corrosion products consisted mainly of zinc aluminium hydroxy carbonate, Zn0.71Al0.29(OH)2(CO3)0.145·xH2O, zinc chloro sulfate (NaZn4(SO4)Cl(OH)6·6H2O), zinc hydroxy chloride, Zn5(OH)8Cl2·H2O and zinc hydroxy carbonate, Zn5(OH)6(CO3)2 were the first three phases were formed initially while zinc hydroxy carbonate Zn5(OH)6(CO3)2 was formed after prolonged exposure in more corrosive conditions. The initial corrosion product formation was due to selective corrosion of the zinc rich interdendritic areas of the coating resulting in a mixture of zinc and zinc aluminium corrosion products. © 2010 Elsevier Ltd.

NaCl induced atmospheric corrosion of ZnAl2Mg2 coated, electrogalvanised (EG) and hot dipped galvanised (HDG) steel was studied using in situ infrared reflection absorption spectroscopy, XRD and SEM. Initial corrosion leads to the formation of Mg/Al and Zn/Al layered double hydroxides (LDHs) on ZnAl2Mg2, due to the anodic dissolution of Zn-MgZn2 phases and cathodic oxygen reduction on Zn-Al-MgZn2, Al-phases and on zinc dendrites. In contrast to EG and HDG, were no ZnO and Zn5(OH)8Cl2{dot operator}H2O detected. This is explained by the buffering effect of Mg and Al which inhibit the ZnO formation, reduce the cathodic reaction and corrosion rate on ZnAl2Mg2.

Anticorrosive coatings are widely used to protect steel against corrosion. Different standards exist to access the corrosion performance of anticorrosive paints. Among them, the so-called neutral salt spray test (NSST-ISO 9227) or cycling corrosion tests ISO 12944-6, ISO 12944-9, NACE TM0304, or NACE TM0404 can be named. It is well-known that some accelerated corrosion tests are not fully representative of the field exposure results. However, a lack in the literature exists correlating accelerated tests to field exposure, especially when long-term durations are considered. In this study, 11 different organic coatings have been investigated in terms of coating resistance to corrosion creep in two types of field exposure sites, namely a stationary site and an operating ship, and their performance was compared to two accelerated tests (ISO 12944-9 and modified ASTM D5894 standard). The results showed differences in the sites’ corrosivity and the coating systems’ performance as a function of the exposure sites. A lack of correlation exists between the ISO 12944-9 standard and the stationary site, due to the latter’s high corrosivity, while, to the contrary, a satisfying correlation with the operating ship was demonstrated; whereas, the modified ASTM D5894 standard showed a satisfying correlation with both types of sites.

For indoor conditions, risks of corrosion are more easily and more reliably estimated by exposing reference metals, as compared to by analysing climatic conditions and air pollutants. Corrosion of the reference metals can be evaluated as metal loss or metal gain, by electrolytic reduction or by methods permitting more or less continuous corrosion monitoring. Sensitive and continuous monitoring methods would be useful for classifying conditions in permanent or temporary museum displays, for selecting between storage facilities for corrosion sensitive artefacts, for evaluating effects of visitors or effects of air conditioning etc. Commercially available instruments for on-line corrosion monitoring of atmospheres indoors, the quartz crystal microbalance and electrical resistance sensors, have been evaluated for sensitivity, reliability and fitness for use. Additionally, performance of laboratory manufactured electrical resistance sensors is evaluated. These sensors are to be used with a small battery operated corrosion logger currently under development. The corrosion logger is intended for permanent or temporary use, such as in display cases, in cabinets intended for storage of sensitive objects or even in transport packages. A quartz crystal microbalance measures the resonance frequency of a metal-coated quartz crystal. Corrosion of the metal coating leads to the formation of a corrosion film on the surface, increasing the weight of the crystal, decreasing its resonance frequency. Drawbacks of the method are that the readings are slightly temperature dependent and affected by particles and other contaminants on the surface, as well as by moisture films, thus by the relative humidity. With electrical resistance sensors, corrosion is measured as changes in resistance of a thin metal track. The resistance increases when the metal thickness is reduced from corrosion. Since this method measures corrosion directly it is not affected by particles or by the humidity. Common for both methods is that only metals attacked by uniform corrosion are suitable, not metals susceptible to local corrosion such as pitting corrosion. In this investigation, copper and silver coatings have been employed. For both methods the sensitivity was found to be sufficient for monitoring atmospheric conditions in rooms requiring low corrosion rates, such as instrument rooms and museums. Electrical resistance sensors seem to be the sensor type best suited for use under indoors atmospheric conditions. Further development, optimizing sensitivity and variation in response for use with the corrosion logger under development, is needed as well as expanding the range of metals used.

In this work, the corrosion performance of stainless steel materials for application in the automotive industry has been evaluated by means of on-vehicle testing and laboratory cyclic corrosion tests. Additional laboratory measurements have also been performed in well defined exposure conditions. The results indicate that no cosmetic corrosion was observed upon on-vehicle exposures after 2 years exposure in Sweden and Germany and 5 years exposure in France. Cyclic corrosion tests were also performed in order to assess the corrosion resistance of different stainless steel grades. The results indicate large discrepancies in corrosion resistance when comparing the different cycles. This is explained by differences in chloride deposition, wet/dry cycle condition and way of deposition of the pollution on the samples. From the results it is obvious that cyclic accelerated corrosion tests that have been developed for assessing the performance of precoated materials cannot directly be used to assess the corrosion resistance of stainless steel. Hence, there is a need to develop or to adapt cyclic corrosion tests in order to evaluate the corrosion resistance of stainless steel. Copyright © 2004 SAE International.

There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments.

A compact and autonomous corrosion sensor using the principle of electrical resistance variations of its metallic sensitive tracks has been used for different applications under atmospheric corrosion conditions. The measurements of the corrosion rate are performed in-situ both under laboratory and field exposures. From the results, it is possible to better understand the atmospheric corrosion of steel and zinc under various exposure conditions. The technique should also allow the design of reliable and realistic corrosion tests for different industrial applications. 

Zn coated steel (Z) and ZnAlMg coated steel (ZM3.7/3 = Zn–Al (3.7 wt.%)-Mg (3.0 wt.%)) have been exposed for 6 years at twelve different weathering sites world wide. The mass loss of the coatings have been measured after 1, 2, 4, and 6 years exposure. From the results, it is shown that ZM3.7/3 had always a better corrosion performance compared to Z. The ratio of performance after 6 years of exposure varied from about 1.4 to 4.4 with a mean value of 2.8. At temperate marine sites (e.g., temperature between 9–20°C) with low to moderate SO 2 pollution a good relationship was observed between the relative performance of ZM3.7/3 and the corrosion rate of Z. It was thus concluded that ZM3.7/3 has a better relative performance in harsh environments. The corrosion performance of ZM3.7/3 was shown to be connected to the formation of protective corrosion products.

Hot-dip Zn55Al-coated steel samples have been exposed for up to 6 years at 11 different weathering sites, including marine, marine-industrial, acid-rain and dry atmospheres. From the mass loss measurements, Zn55Al metallic coating showed globally long-term good corrosion resistance in all weathering conditions compared with hot-dip Zn-0.2Al-coated steel (Z). Yet, weaker performance was observed on Zn55Al in high SO2 polluted atmosphere, particularly when combined with seawater aerosols. This is explained by a more acidic surface condition linked to high SO2. Although the extent of corrosion in this phase was different at the different sites, the final corrosion products formed after 6 years were rather similar at all sites. This consists of hydrous aluminium sulphate or hydrous aluminium hydroxy sulphate and, probably also a smaller amount of sulphate-containing zinc corrosion products or Al/Zn products.

The aim of this study is to evaluate fatigue performance of joined assemblies (spot weld and/or adhesive bonding) in corrosive environment. Various assemblies have been tested in alternated and simultaneous fatigue-corrosion modes. Adhesive joints are strongly affected by simultaneous fatigue-corrosion with a large drop of the fatigue life compared to results in air. By alternating fatigue and corrosion, the reduction of fatigue life is important. For spot welding, fatigue life is decreased at higher load amplitudes and increased at lower amplitudes. These results are strongly linked to the opening of the gap near the spot weld at high load amplitudes. At low amplitudes, corrosion might limit the local stress at the notch root of the weld.