Standard Corrosion Tests Research Articles

Corrosion behavior of dissimilar Al–Mg–Si alloys joint welded under hybrid CMT-laser oscillation welding

As the corrosion behavior of 6xxx series aluminum alloys depends on composition and microstructure, the microstructure and corrosion behavior of 6082 and a new 6xxx aluminum alloy weld joint are investigated under a standard corrosion test in this study. These results show the asymmetrical welding joint structure and a distribution of corrosion severity across the weld joint. Substantial differences were observed in the size and distribution of Mg2Si particles and Fe-bearing intermetallics in various regions of the weld joint. It was found that the equiaxed grain zone on new 6xxx aluminum side is not most susceptible to corrosion, contrary to previous results, but the narrow partially melted line on 6082 side is. Not all corrosion induced by Fe-bearing intermetallics originates from the Al matrix, adjacent Fe-bearing intermetallics and Mg2Si could also form galvanic microcells, resulting in preferential dissolution of Mg2Si over the Al matrix.

The effect of partial recrystallization on the corrosion resistance of EN AW6082 forged components evaluated with different tests

AbstractStructural automotive components are extensively made of aluminum alloy forgings, due to the elevate strength and low weight required. These products are frequently subjected to recrystallization. Recrystallization, often limited to surface or forging portions, is expected to reduce its tensile strength and corrosion resistance, but the literature is scarce on this subject. For a more comprehensive understanding, the present research studied the corrosion behavior of samples collected from EN AW 6082‐T6 forged components, designed to expose both recrystallized and not recrystallized surfaces to the corrosive environment. Several standardized corrosion tests (i.e., PV 1113, ISO 11846, and VW 96380) were applied to assess the most representative with respect to real field exposure. Tensile tests were performed in four different conditions, recrystallized and not recrystallized specimens in an as‐forged state or after corrosion. The recrystallization led to a reduction in tensile properties, but this gap was compensated by a higher corrosion resistance than the not recrystallized samples. Consequently, the mechanical properties became comparable after the corrosion test.

Dual-functional anti-corrosion coatings with surface hydrophobicity and internal smart-releasing Ce3+ loaded in bentonite on carbon steel

Water-based coatings are gradually replacing traditional oil-based coatings for environmentally friendly applications, which creates a new paradigm in corrosion control of metallic components. In this work, water-based ZrO2–SiO2 sol-gel coatings were prepared for corrosion protection of carbon steel. The effects of the sol-gel ZrO2 to SiO2 ratio, coating thickness, corrosion inhibitor content and surface hydrophobicity on the coating physicochemical and anti-corrosion properties were investigated. The results showed that, compared to the pure silica coating, coating with 1/9 wt% ZrO2 in SiO2 matrix and coating thickness of 25 μm provided about 7 times higher corrosion resistance (impedance modulus 1.38 × 108 Ω cm2). A smart-releasing corrosion inhibitor containing Ce3+ ions (0.91 wt%) loaded into the layered structure of bentonite showed ability to delay the corrosion of substrate by 9 orders of magnitude by trapping Cl− ions from the environment and releasing Ce3+ ions at the cracked substrate surface. By applying a hydrophobic top layer, the water contact angle increased from 89° to 115°, which further increased the impedance modulus of the coating from 2.42 × 109 to 3.60 × 109 Ω cm2. The optimized coating passed salt spray standard corrosion test for 720 h (on scribed coating) due to the cathodic protection by corrosion inhibitor and shielding effects of a top hydrophobic layer. This work provides an enhanced strategy of dual-functional anti-corrosion coatings with surface water repellency and internal smart-releasing corrosion inhibitor for steel against environmental corrosion and damages with efficient self-healing functionality.

Corrosion behavior of Shape Memory Alloy in NaCl environment and recovery maintenance in Cu-Zn-Al sysytem

Shape memory effect (SME) and the relation with corrosion behavior of Cu-Zn-Al Smart Memory Alloys (SMAs) were investigated using different techniques: Scanning Electron Microscopy equipped with an Energy Dispersive System, X-Ray Diffraction analysis, Electrochemical Test in NaCl solutions with different concentrations (0.035%, 0.35% and 3.5%), which simulate coastal conditions, mechanical characterization through tensile test and guided bend test. SMAs are an important class of smart materials able to recover after deformation a pre-imposed shape through a temperature modification. These alloys show great potential, finding several applications in medicine and in different types of industry sectors (aerospace, architecture, automotive etc.). Cu-based SMAs, including Cu-Zn-Al alloys, have lower production costs with respect to Ni-Ti alloys as well as good possibility in seismic and architectural applications. A Cu-Zn-Al alloy with a theoretical composition of 25 wt.% Zn and 4 wt.% Al was produced by casting method. The aim of this study is to characterize the microstructure, the mechanical properties and the corrosion behavior through different kind of standard corrosion tests of this alloy and to evaluate the effect of corrosion damage on the shape memory recovery capability through a combination of corrosion and thermos-mechanical cyclic test and SEM observation

Analysis of Failure Causes of 0Cr19Ni9 Blade Crack

In this paper, fracture morphology observation, microstructure analysis, standard corrosion test, and other experimental methods are used to analyze the causes of corrosion and cracking of steam turbine blades (0Cr19Ni9) produced by a certain company. The results showed that cracks appeared during the operation of the blade. A large number of dimples were observed under the scanning electron microscope, almost all of which were shear dimples; at the same time, fatigue bands were also distributed in them. The internal cause of the cracks is the long-term service, which causes the carbon and the alloy to undergo a diffusion reaction to form carbon-rich areas and carbides. They are thermally corroded in the service environment, and the carbon-rich zone is reduced, which reduces the strength of the zone; carbides accumulate at the grain boundary, causing groove-shaped defects at the grain boundary to form a cutting effect. It is easy to form a source of fatigue cracks. The external cause is that the material is subjected to transverse stress for a long time during operation, which leads to the generation of cracks. This article analyzes the failure causes of the blade and proposes related solutions, which have important reference value for production practice.

Hybrid Sol-Gel Coatings Doped with Non-Toxic Corrosion Inhibitors for Corrosion Protection on AZ61 Magnesium Alloy.

Physiological human fluid is a natural corrosive environment and can lead to serious corrosion and mechanical damages to light Mg–Al alloys used in prosthetics for biomedical applications. In this work, organic–inorganic hybrid coatings doped with various environmentally friendly and non-toxic corrosion inhibitors have been prepared by the sol-gel process for the corrosion protection of AZ61 magnesium alloys. Effectiveness has been evaluated by pH measurements, optical microscopy, and SEM during a standard corrosion test in a Hanks’ Balanced Salt Solution. The results showed that the addition of an inhibitor to the sol-gel coating can improve significantly the corrosion performance, being an excellent barrier for the L-cysteine-doped hybrid sol-gel films. The incorporation of TiO2 nanoparticles, 2-Aminopyridine and quinine organic molecules slowed down the corrosion rate of the Mg–Al alloy. Graphene oxide seemed to have the same response to corrosion as the hybrid sol-gel coating without inhibitors.

Влияние антикоррозионных пленкообразующих составов на усталость авиационных конструкций. Обзор исследований

Corrosion of aircraft structures is one of the main factors limiting the duration of their operation, affecting on the economic efficiency and safety of air transport. Corrosion protection is performed at the stage of manufacturing aircraft structures, during their repair and operation. One of the additional measures of anti-corrosion protection is the use of film-forming coatings, which displace moisture from the gaps of structural joints, form a protective film, and also slow down the corrosion process. The protective properties of film-forming coatings are investigated by standard corrosion tests. At the same time, the specifics of aircraft structures and the possible side effects of the use of anti-corrosion compounds require special studies. The article presents an analysis of works in which the effect of film-forming anticorrosive compounds on the fatigue of elements of aircraft structures is considered.The main type of joints in the structure of modern aircraft are riveted joints. The high penetrating ability of film-forming materials ensures their penetration into the gaps of riveted joints, which, in some cases, can affect the frictional forces between the connected elements, which ensure the integrity of the joints. In some experimental investigations, the influence of film-forming compositions on the kinetics of fatigue crack growth is noted as a side effect. A number of possible mechanisms of deceleration and acceleration of the rate of crack propagation are considered. Experimental data concerning the effect of anticorrosive compounds on the fatigue of riveted joints and the process of propagation of fatigue cracks in structural materials, indicate the need to develop a universal methodology for the selection and use of film-forming compositions for the protection of aircraft structures from corrosion, taking into account the minimization or prevention of negative side effects on the service life of aircraft.

A New Theoretical Model Study on the Cover Cracking Mechanism of RC Structures Due to Rebar Corrosion

Based on elastoplastic and damage mechanics theory, a new theoretical model of damage cracking on the cover of reinforced concrete structures caused by non-uniform rust expansion is established. The parameter sensitivity analysis indicates that the critical corrosion rate of the structure increases sharply with the increase of the thickness of the concrete cover. The critical corrosion rate decreases when the non-uniform coefficient of the corrosion expansion becomes larger, indicating that the uneven corrosion expansion is disadvantageous for durability. When the rust expands more unevenly, the allowable corrosion amount of the reinforcement becomes smaller. While the concrete grade changes from C15 to C60(concrete design standard in China), the critical corrosion rate modifies between 3.05‰ and 4.1‰. To further verify the rationality of the new theoretical model, the model was conducted to predict the standard corrosion tests. Results show that the scatter points predicted by the new model are small-amplitude oscillation near the test line. Thus, it has been proved the new theoretical model proposed in this paper can be used to predict the critical corrosion rate of RC structures.

Corrosion of cast iron pipelines buried in Fraser River silt subject to climate-induced moisture variations

Experiments were carried out to characterise the influence of soil water retention properties on the corrosion of a cast iron specimen buried in Fraser River silt. The corrosion rates were measured at different degrees of saturation using standard corrosion tests, along with separate water retention tests for the Fraser River silt. Building on previous work on this topic, a numerical model solving moisture flow, oxygen diffusion, electrical conductivity and their coupled influence on metallic corrosion in unsaturated soil was developed. The experimental data and preliminary numerical modelling results were then used as inputs to a field-scale numerical model to examine climate-induced moisture migration around a pipeline and the resulting levels of corrosion. The time-dependent corrosion mass loss and the resulting loss in pipe wall thickness of a buried pipeline were modelled, and it was demonstrated that the cyclic climatic variations predominantly perturb the corrosion rates during the initial cycles, and subsequently a gradual corrosion rate arises depending on general climatic conditions. Further analysis of the influence of electrical resistivity on the levels of corrosion revealed that a decrease in resistivity due to effects such as seawater intrusion or naturally saline soils may result in a significant increase in the levels of localised corrosion.

Structural aspects of decreasing the corrosion resistance of zinc coating obtained in baths with Al, Ni, and Pb additives.

The article presented the results of tests determining the synergistic effect of Al, Ni, and Pb additions on a zinc bath on the structure and corrosion resistance of coatings obtained on low silicon steel. Analyzed coatings were produced on S235JRG2 steel with Si content of 0.02 mass%. The corrosion resistance of the coatings was compared with the corrosion resistance of the coating obtained in the "pure" zinc bath. Structure at high magnifications (SEM) was determined, as well as coating thickness and chemical composition in microspheres. The corrosion resistance of the coatings was established comparatively in standard corrosion tests in neutral salt spray and a humid atmosphere containing SO2. It was found that the addition of Pb to the zinc bath reduced the corrosion resistance of the coatings. In the coating structure obtained in the Zn-AlNiPb bath, lead precipitation was observed in both the outer layer and the intermediate layer of the coating. Grain boundaries were the preferred site for lead precipitation. The presence of Pb precipitates favored conditions for the creation of additional corrosion cells, which led to a decrease in the corrosion resistance of the coatings.

Crevice corrosion – A newly observed mechanism of degradation in biomedical magnesium

Crevice-induced corrosion is not desirable to occur in metallic magnesium (Mg) during many industrial applications. However, orthopedic implants made of Mg alloys have been demonstrated to degrade faster between the joining surface of bone plates and screws after implantation, suggesting the crevice corrosion may occur in the physiological environment. In this paper, a resin device is designed to parallel high purity magnesium (HP-Mg) plates with closely spaced slits. After a standard corrosion test in the phosphate-buffered saline (PBS) solution, the paralleled HP-Mg samples embedded in the custom-made resin device corrode faster than those without the resin device. The corrosion morphology of Mg with the resin device exhibits features of crevice corrosion with many deep holes and river-like texture. Moreover, implantation of the bone plate and screws in vivo demonstrates similar corrosion morphology as that of the in vitro test, suggesting the occurrence of crevice-enhanced corrosion in the bone–bone plate interface, as well as the contact area between the bone plate and the screws. Statement of SignificanceUnderstanding the corrosion behavior of Mg and Mg alloys after implantation is one of the main challenges for developing desirable biodegradable Mg alloys or effective methods to adjust the corrosion rate of Mg-based implants. In this paper, we attempted to understand the corrosion behaviors of HP-Mg at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues after implantation. We designed an in vitro setup to mimic the crevice environment of the in vivo joining surface and found that the crevices existing on the HP-Mg would significantly accelerate the corrosion rate and change the corrosion morphology of HP-Mg plates. The in vivo implantation also showed similar corrosion morphology caused by crevice corrosion, which appeared at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues. Then, we proposed a new corrosion mechanism of Mg-based alloys inside the crevice. The findings of this study can help us broaden our cognition on the corrosion behavior of Mg and Mg alloy-based orthopedic implants.

Mechanical effects on the corrosion resistance of ferritic stainless steels during microabrasion-corrosion

Mechanical events affect the corrosion behaviour of metals in a wide range of industrial applications, but the synergy between corrosion and mechanical events do not allow them to be studied individually. For ferritic stainless steels in H2SO4 corrosive media, a negative synergy between microabrasion and corrosion has been reported, where low friction passive layers reduce wear rates. However, for the abrasion-corrosion of ferritic stainless steels, little attention has been paid to mechanical effects on their corrosion resistance. To investigate this, potentiodynamic curves were obtained for ferritic stainless steels during standard corrosion tests, which were compared to potentiodynamic curves obtained in two other conditions: i) aerated corrosion tests (non-static electrolyte); and ii) microabrasion-corrosion tests using silica + H2SO4 solution slurries. The specimens were ferritic stainless steels with different chemical compositions (11 wt%Cr with and without Ti stabilization; 16 wt%Cr with and without Nb stabilization, 17.5 wt%Cr with Nb + Ti stabilization) and, for comparison, one austenitic stainless steel (18 wt%Cr-8 wt%Ni) and one carbon steel (0.2 wt%C). The results showed that the use of aerated conditions increased passivation current, which was further increased for microabrasion-corrosion conditions. Moreover, although the potentiodynamic curves for all the stainless steel specimens presented a clear passive region under standard corrosion test conditions, only the austenitic stainless steel showed a classic passive region when mechanical effects were present. For the low Cr ferritic stainless steel under microabrasion conditions, the potentiodynamic curves showed a region where the current increased little with potential increased, but this was called a pseudopassivation, since current increased steadily, although little, with potential increase. For higher Cr contents, after the pseudopassive region, a real passive region was present at higher potentials. The potentials for achieving real passive regions were higher under microabrasion conditions than under non-static condition, evidencing a contribution of both mechanical effects (fluid flow and mechanical wear) on their corrosion resistance.

Corrosion and wear behaviour of nano Al2O3 reinforced copper metal matrix composites synthesized by high energy ball milling

Copper alloys and composites find a variety of applications where wear and corrosion resistance are of paramount importance. An attempt has been made to study the behavior of copper alumina composites made through powder metallurgy. Microcrystalline Alumina (Al2O3) and Copper (Cu) powders were synthesized by high energy planetary ball milling to reduce their particle size to nano scale. In the present work, corrosion and wear behavior of copper MMC reinforced with different weight percentages (5, 10, 15%) of Alumina were examined and the results are presented. Powders were characterized by X-ray diffraction (XRD) to obtain the particle size of the composite powders and scanning electron microscopy (SEM) was also used to know the dominant process during each cycle of milling. Green compacts were obtained by compressing the powders into solid by placing them in a rectangular die using a universal testing machine (UTM), sintered in electric furnace and cooled. Wear and corrosion properties of the compacts were studied using Pin-on-Disc apparatus and Standard corrosion test using linear potentiodynamic polarization tester with 3.5% NaCl as per ASTM G99 standards. Best wear and corrosion values were obtained at 15% wt. % of alumina and 10% wt. % of alumina respectively.

Core-shell structured mZVI/Ca(OH)2 particle: Morphology, aggregation and corrosion

A calcium hydroxide shell was coated onto the surface of micro-sized zero valent iron (mZVI) particles by hydrothermal approach in oversaturated Ca(OH)2 solution. The heterogeneous nucleation of nano-scale Ca(OH)2 particle on micro-scale spherical ZVI surface was clearly observed by scanning electronic microscope (SEM). The moderate solubility of Ca(OH)2 was demonstrated as the crucial factor in inducing slow nucleation rate and in facilitating the abundant growth of Ca(OH)2 nuclei on mZVI surface. The growth of shell thickness was found to obey the zero order kinetics with the rate constant at about 15nm/h. The Ca(OH)2 shell was demonstrated to be anticorrosive to protect reactive Fe0 from oxidation based on standard corrosion test. In addition, the instant aggregation process of mZVI within 120s was slowed down after Ca(OH)2 shell coating. The saturation magnetization of mZVI, measured by a vibrating sample magnetometer (VSM), was gradually diminished along with the shell formation with a 32% reduction after excluding the Fe0 content change effect. This indicated that Ca(OH)2 shell coating can partially eliminated particle-particle or cluster-cluster magnetic attraction force to enhance the dispersion stability and resultantly facilitate the transportation. The dissolution of Ca(OH)2 shell was greatly dependent on the pH value of the background water environment. The pH gradient change resulted from the Ca(OH)2 shell dissolution along mZVI particle transport was illustrated by a conceptual model.

Corrosion resistance of high‐alloyed stainless steel membrane supports under flue gas conditions of a lignite‐fueled power plant

Metal‐supported silica membranes are attractive candidates for CO2 capture from the exhaust of coal‐fueled power plants. Compared to their full ceramic counterparts, the introduction of the metal support facilitates sealing of the membrane by established technologies, such as welding, and enhances the robustness of the membrane in the harsh environment of the power plant. As well‐known from other steel components in flue gas desulfurization units, long‐term corrosion resistance of the metal support is mandatory for the success of this new membrane concept. In the present work, a research concept is introduced enabling a systematic benchmark of stainless steels regarding their suitability to be used for the metal support of the CO2 selective silica membranes. The study combines field tests of porous samples in direct contact with the exhaust gas of a lignite‐fueled power plant and standardized corrosion tests of dense and porous samples in the laboratory according to DIN 50918 using exhaust gas condensate as the corrosive medium. Preliminary results are achieved on austenitic steel (AISI 316L) as well as on two ferritic steels (Crofer22APU, Plansee ITM). Ferritic steels are chosen due to their availability as substrates with well‐defined porosity and with adapted thermal expansion coefficient enabling successful coating of the CO2 selective silica membrane.

Non-corrosive and Biomaterials Protic Ionic Liquids with High Lubricating Performance

Achieving non-corrosive and green ionic liquids is a big challenge for the tribologist. A kind of biomaterials-based protic ionic liquids (PILs) was synthesized in this paper. Rapeseed oil, group 1 mineral oil and one commercially available fully formulated gear oil were as used reference to study the property of the synthesized PILs. The copper strip standard corrosion test was employed to study the anti-corrosion property. The boundary lubrication and elastohydrodynamic lubrication performance of the lubricants was studied on an Optimol SRV-III oscillating friction and wear tester, and a WAM (model 11) ball-on-disk test rig, respectively. The lubricating mechanism of the synthesized PILs was also discussed in this paper.

Plasmachemical Conservation of Corroded Metallic Objects

Plasmachemical process for conservation of metallic objects is a new way of effective and fast treatment of corroded objects. This process consists of two main steps: corrosion removal and deposition of a protecting film. Removal of corrosion products is based on plasmachemical reduction of corrosion layers by radio-frequency (RF) low pressure hydrogen plasma. Chosen barrier films are parylene (poly-para-xylylene) coatings and SiO2- like high density films. Parylene coatings are prepared by a standard chemical vapor deposition (CVD) method. Plasma enhanced chemical vapour deposition (PECVD) enables preparation of SiOx based thin films with higher flexibility due to variable incorporated organics groups. The coatings were characterized by various methods in order to obtain information about their chemical structure (FTIR) and barrier properties (OTR). The results from standard corrosion test were compared with those on samples treated by conventional conservation procedures.

Corrosion Resistance of ZnAlMg Alloys for Batch Hot Dip Galvanizing

In the paper the results of corrosion resistance tests on ZnAlMg alloys used as batch hot dip galvanizing baths are presented. The tests were carried out on ZnAl alloys with 7 wt.% Al with the addition of 3 wt.% and 6 wt.% Mg. Corrosion resistance of tested alloys was compared with corrosion resistance of the traditional zinc bath alloy. Corrosion resistance of the alloys was defined by comparative methods in two standard corrosion tests in neutral salt spray and in moist atmosphere containing SO2. Electrochemical parameters of the corrosion process were determined on the basis of potentiodynamic tests. It was determined that the alloy of ZnAl7 has better corrosion resistance than the corrosion resistance of the alloy of a traditional zinc bath and that the addition of Mg to the alloy increases the corrosion resistance.

The Influence of the Chemical Composition of a Zinc Bath upon Corrosion Resistance of Coatings Obtained on Sebisty Steel

In the paper the results of tests defining the influence of the chemical composition of a zinc bath on the corrosion resistance of coatings obtained on Sebisty steel are presented. The coatings for the tests were produced on Sebisty steel with the content of silicon of 0.18 wt. % in Zn-AlNi, Zn-AlNiPb and Zn-AlNiBiSn baths. Corrosion resistance of coatings obtained in alloy baths was compared with the corrosion resistance of a coating obtained in a bath of pure Zn. The structure of coatings has been developed, the chemical composition of structural components of the coating and the coating thickness have be established. Corrosion resistance of the coatings was defined by comparative methods in a standard corrosion test in neutral salt spray. The tests were carried out in accordance with the EN ISO 9227 standard. It has been established that alloy additions to a zinc bath have impact upon corrosion resistance of obtained coatings. The addition of Pb results in a decrease in corrosion resistance of a coating obtained on Sebisty steel.

The Influence of N<sub>2</sub> Partial Pressure on Color, Mechanical, and Corrosion Properties of TiN Thin Films Deposited by DC Reactive Magnetron Sputtering

Multi-functional thin films have gained increasing importance in a decorative application. Among the available material, titanium nitride (TiN) thin film is interesting due to its golden color and mechanical resistance. Beside their properties, the corrosion property of TiN films is mainly considered in order to extend the life time. In this work, the TiN thin films were deposited on 3x3 cm2 Si(100) substrates by dc reactive magnetron sputtering technique. The effects of N2 partial pressure (PN2) on deposited film properties such as microstructure, surface morphology, color, mechanical and corrosion properties were investigated. We found that the crystal structure of the TiN films exhibit the (200) preferred orientation. The color of TiN films change from gold-yellow to gold-red colors by increasing of N2 partial pressure that could be explained by Drude model. The TiN films have smoother surface when the N2 partial pressure increases. Standard corrosion tests in artificial sweat solution show the corrosion current density (icorr) in the range between 0.25 to 4.25 mA/cm2 and the polarization resistance increases with increasing of N2 partial pressure. The highest hardness of the film is approximately 40 GPa with elastic modulus of 340 GPa. We conclude that N2 partial pressure corelates with color, mechanical property and corrosion resistance of TiN films, which were optimized to use in decorative application.