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.

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 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 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

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.

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.

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.

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.

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.

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.