Protection Of Aluminum Alloys Research Articles

An Intelligent Environmental Self-Healing Coating Based on Ph-Stimulated Responsive Dual Nanocontainers for Corrosion Protection of Aluminum Alloy

An Intelligent Environmental Self-Healing Coating Based on Ph-Stimulated Responsive Dual Nanocontainers for Corrosion Protection of Aluminum Alloy

Противокоррозионная защита алюминиевого сплава 1441 бесхроматными конверсионными покрытиями в условиях городской атмосферы

Новые технологии, Химическая промышленность, Химическая технология, Научные журналы, Защита от коррозии, Технология металлов, Свойства материалов, Технические журналы, Наука и технологии, Справочная литература, Научные разработки

Conversion Coatings Based on Rare Earth Nitrates and Chlorides for Corrosion Protection of Aluminum Alloy 7075-T6

Conversion coatings are expected to provide high corrosion protection and to be environmentally friendly at the same time. The aim of this study was to investigate rare earth (cerium and lanthanum) nitrate and chloride conversion coatings deposited on aluminum alloy AA7075-T6. Individual Ce and La nitrate and chloride coatings and their mixtures (Ce(NO3)3:La(NO3)3 and CeCl3:LaCl3) in the ratio 1:3 and 3:1 were studied. The properties of the coatings were investigated as a function of conversion bath parameters: conversion time (from 1 min to 12 h) and conversion temperature (room temperature and 60°C) at constant salt concentration of 0.01 M in the presence of 0.13 M hydrogen peroxide. The morphology and composition of the conversion coatings were analyzed using scanning electron microscopy and energy dispersive x-ray spectroscopy. The corrosion properties of uncoated and coated AA7075-T6 substrates were studied in 0.1 M NaCl using electrochemical potentiodynamic polarization method and salt spray testing...

Protection of aluminium alloys from atmospheric corrosion by thin films of inhibitors

Protection of aluminium alloys from atmospheric corrosion by thin films of inhibitors

Characterization of the Protective Properties of Hydrotalcite on Hybrid Organic-Inorganic Sol-Gel Coatings

The effect of hydrotalcite (HT) on the protection of aluminum alloy by sol-gel films was investigated by electrochemical impedance spectroscopy (EIS) and electrochemical noise measurements (ENM). S...

Influence of anodic coatings on stress corrosion behaviour of 7017 aluminium alloy

Purpose – The purpose of this work was to study the cracking susceptibility of a 7017 aluminium alloy, after anodising under various conditions. Design/methodology/approach – Slow strain tests in dry air, laboratory air and sodium chloride solution were employed. Anodic oxide films were produced with various applied current densities and thicknesses, in horizontal or vertical orientation of the coatings, at the free corrosion potential and also at various anodic or cathodic potentials. For the interpretation of the results, a metallographic study of the specimens before and after straining to failure was carried out using a scanning electron microscope. Findings – The behaviour of anodic coatings was found to depend very much on the anodising conditions. The coatings reduced the ductility of the alloy in dry air but can actually increase the ductility in laboratory air and in 3.5 per cent sodium chloride solution. In most cases, the ductility of coated specimens was greater in 3.5 per cent NaCl solution than in dry air, possibly due to crack blunting by the aggressive environment. Anodic coatings moved the free corrosion potential of the alloy in the noble direction and both the anodised and the bare alloy generally suffered a reduction in ductility at potentials anodic or cathodic to the free corrosion potential, the fall being more rapid for the anodised alloy. Research limitations/implications – The mechanism causing the increased ductility of coated specimens in 3.5 per cent NaCl solution than in dry air remains yet to be confirmed. Practical implications – The selection of suitable anodic coatings for the protection of aluminium alloys against stress corrosion cracking depends on the anodising conditions. Originality/value – The paper provides information regarding the influence of anodising conditions on the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

Influence of seawater composition on SCC behavior of anodized 1050 Al‐alloy

PurposeThe purpose of this paper is to study the stress corrosion cracking (SCC) behaviour of anodized 1050 Al‐alloy in marine environments at different concentrations of sulphate ions.Design/methodology/approachThe SCC experiments were performed by measuring the time to failure in 3.5% NaCl solution, or in the presence of three different concentrations of sulphate ions under conditions of applied anodic current. For the interpretation of the results, changes in potential during SCC tests and optical microscope micrographs of stress corrosion tested specimens at various periods of time, were obtained.FindingsThe influence of seawater composition on the SCC behaviour of the anodized 1050 Al‐alloy depends on the concentration of sulphate ions, the oxide thickness and the stress level. At the higher stress levels and low concentrations of sulphate ions, increased times to failure were observed. These results were attributed to the inhibitory action of sulphate ions. At a low stress level and higher concentration of sulphate ions, the increased times of exposure and the more intensive corrosive environment led to partial destruction of the anodic coatings and a decrease in the time to failure. Better protective properties were observed at an oxide thickness of 10 μm. The thicker oxides did not protect so well because they were more brittle, cracking under strain and allowing corrosive species to reach the metal surface.Research limitations/implicationsThe hypothesised mechanism of the effect of seawater composition on the SCC behaviour of anodized Al‐alloys depended on the concentration of sulphate ions and the stress level remains yet to be confirmed.Practical implicationsThe selection of suitable anodic coatings for the protection of aluminium alloys against stress corrosion cracking depends on the composition of the marine environment.Originality/valueThe paper provides information regarding the influence of sulphate ions on the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

The effect of additions of carboxylic acids to the anodising bath on the corrosion and SCC of anodised aluminium

PurposeThe purpose of this paper is to study of the effect of carboxylic acids additions to the anodising bath on the subsequent corrosion and stress corrosion cracking (SCC) tendencies of anodised 1050 Al‐Alloy in 3M NaCl solution.Design/methodology/approachThe study was carried out using SCC tests and electrochemical cyclic potentiodynamic measurements at a high or a slow scan rates. The anodic coatings were prepared electrolytically in a bath of 4 M H2SO4, with and without additions of 0.015 M oxalic, malonic, tartaric, maleic, or citric acids. The consequent thicknesses and packing densities of the coatings were measured.FindingsThe SCC behaviour was found to vary with both anodising conditions and stress level. The addition of carboxylic acids in the anodising bath increased the protective properties of the coating. In corrosion conditions without stress, the addition of the carboxylic acids decreased the susceptibility to pitting corrosion, the effect depending on the presence or absence of corrosion products. The addition of the carboxylic acids during anodising leads to the formation of less porous and more compact oxide layers and increases the anticorrosive properties of the coatings. The benefits were most pronounced for the coating prepared in the presence of maleic acid.Research limitations/implicationsThe belief that the effect of carboxylic acids on the corrosion and SCC behaviour of Al‐Alloys is due to the absorption of these compounds on the metal surface and the formation of complexes on it, depending on the structure and carbonic chain of these compounds, remains yet to be confirmed.Practical implicationsAnodic coatings prepared in an electrolytic bath containing carboxylic acids can be used for the protection of aluminium alloys against corrosion.Originality/valueThe paper provides information regarding the improvement of the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

Silane Films Modified with Yttrium Oxide Nanoparticles for Improved Corrosion Resistance of AA6061-T6

The present work strives to evaluate the corrosion resistance of aluminum alloy (AA)6061-T6 (UNS A96061) pretreated with bis-1,2-[triethoxysiyl]ethane silane (BTSE) solution containing different contents of yttrium oxide (Y2O3) nanoparticles. The corrosion resistance of the pretreated AA6061-T6 substrates was investigated with potentiodynamic polarization curves and the neutral salt spray (NSS) test. The morphologies of the silane film were observed using scanning electron microscopy (SEM). The results indicated that the presence of small amounts of Y2O3 nanoparticles in BTSE solutions can increase the corrosion resistance of the silane films in 3.5% sodium chloride (NaCl) solution. Y2O3 nanoparticles do not change the behavior of the electrode reaction. The formed silane film acts as a physical barrier for the protection of aluminum alloy. The SEM images indicated that the surface morphologies of silane films formed were flat and compact, when the contents of the Y2O3 nanoparticles in BTSE solutions were between 10 ppm and 20 ppm.

Novel totally chrome free corrosion inhibiting coating technology for protection of aluminium alloys

A totally chrome free coating technology for the protection of aluminium alloys has been developed. This novel technology is a significant step forward in the field of chrome free corrosion inhibition and provides a sustainable and eco-efficient coating solution for both exterior and structural applications in aerospace coatings.

Surface Protection for Aircraft Maintenance by Means of Zinc Rich Primers

The aerospace industry urgently needs environmentally friendly materials and processes for corrosion protection of aluminium alloys in aircraft structures. Until now this has been achieved by hexavalent chromium based compounds in either surface pre-treatments or primers. Due to its carcinogenic properties the use of chromates is restricted and a ban is expected soon. Up to now an all over recognized replacement of chromates is not available for aircraft maintenance, although a lot of research has been done and promising results also exist for some chromium-free conversion coatings and for magnesium rich primers. WIWeB found out in laboratory scale and by flight trials that thin layers of zinc rich primers, if applied with dry film thickness of 10 – 20 µm, can be used successfully to prevent corrosion on aluminium for aircraft. Solvent based as well as water based zinc rich primers have been tested. The major part of the work presented is from further investigations which show, that another great improvement can be achieved, when thin layers of organic adhesion inhibitors like 2-aminopropyltriethoxysilane and 4-t-butylbenzoic acid are applied on the unclad Al 2024 panels, which had been scrubbed with abrasive pads before. This process is followed by the application of the thin film of zinc rich epoxy primer before the usual 2-pack epoxy primer is applied.

Constraints Based Modeling for Innovative Product & Process Designs

An innovative, constraints based modeling (CBM) approach proved successful for product developments and process improvements. The product developments involved specifying the chemical composition range for a set of chromium-free, high-performance consumable electrodes intended for gas-metal arc welding (GMAW) of high-strength steels used in hull constructions while significantly reducing energy costs. The process improvements involved selecting appropriate non-carcinogenic chemicals for a non-chromate conversion coating bath used with corrosion protection of aluminum alloys. In both cases, successful application of the CBM approach also led to the award of U.S. Patents.

Protection of Aluminium Alloys via Hybrid Sol-Gel Coatings with Encapsulated Organic Corrosion Inhibitors

Several heterocyclic organic corrosion inhibitors that contain ionazible functional group were encapsulated into nano-structural hybrid organo-silicate coating to improve its corrosion protection performance on aluminum alloy 2024-T3 substrate. When the coating is formed on the substrate surface, it serves simultaneously as protective barrier and as a reservoir for leachable corrosion inhibitor that is stored and released through the mechanism of reversible ionic interaction with the matrix material. The efficiency of active corrosion protection for these coating systems was examined by electrochemical methods including potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS). The effects of chemical structure and the loading concentration of the inhibitor within the coating were determined.

Modified Means for Corrosion Protection of Aluminum Alloys. 1. Estimates of Effectiveness of R-3b and EP-060tsb Compositions

Accelerated corrosion and outdoor climatic (Cuba) testing of standard and newly developed agents and systems designed for the purpose of preventing the development of exfoliation and microbiological corrosion types on metal samples and structural parts were carried out. Recommendations on using most effective agents are given, which include procedures of aluminum alloy surface treatment involving the removal of corrosion products.

Marine Corrosion and Protection of Aluminum Alloys According to Their Composition and Structure

Based on long-term tests of aluminum alloys in seawater of various climatic zones from the Arctic to the tropics, the peculiarities of their corrosion behavior are revealed. In contrast to other alloys, hydrogen sulfide has a beneficial effect on their corrosion resistance due to the passivation. However, deep in the Black Sea, the alloys, which are susceptible to structural types of corrosion, were subjected to strong exfoliation corrosion, because hydrogen sulfide excluded fouling with microorganisms that inhibits exfoliation corrosion. Alloys of the Al-Mg system exhibit the highest corrosion resistance in seawater. Alloy of an AMr61 type (σul = 340 MPa, σ0.2 = 180–210 MPa, δ = 11–15%) has shown a good performance. Alloying with scandium and thermomechanical treatment make possible further simultaneous improvement of mechanical properties and corrosion resistance. It is shown that crevice corrosion is more typical of corrosion-resistant low aluminum alloys possessing lower free-corrosion and pitting potentials compared to high alloys, which are susceptible to structural types of corrosion, in particular, exfoliation corrosion. The methods of the aluminum alloys protection against marine corrosion are considered. It is shown that, in contrast to carbon steels, the anodic-cathodic protection is used for aluminum alloys.

Protection of aluminum alloys from filiform corrosion by low-temperature plasma interface engineering

This study investigates the filiform corrosion resistance of chromate-free coating systems fabricated on aluminum alloys by low-temperature plasma interface engineering. The aluminum alloys investigated include AA2024-T3 ([2B]), AA7075-T6 ([7B]), Alclad AA2024-T3 ([2A]), plate stock AA2124-T851([2P]), plate stock AA7050-T7451 ([7P]), and ion vapor deposition (IVD) Al-coated AA2024-T3 ([2I]), IVD Al-coated plate stock AA2124-T851([2PI]), IVD Al-coated plate stock AA7050-T7451 ([7PI]). Direct current (DC) cathodic plasma processes including plasma treatment and plasma deposition were used to create the water-insensitive adhesion of organic coatings to aluminum alloys. With appropriate application to aluminum alloys, DC cathodic plasma coatings of trimethylsilane (TMS) combined with argon plasma post-treatment provided tenacious and water-insensitive adhesion between the water-borne, chromate-free spray primers and aluminum substrates. These chromate-free coating systems, when tested by filiform corrosion test, showed superb resistance to filiform corrosion. Filiform corrosion test was found to be a good measure of water sensitivity of the coating interfaces.

Adherence of Electrodeposited Zn–Ni Coatings on EN AW2024 T3 Aluminium Alloy

The use of hexavalent chromium in surface treatments will be reduced in the future, as it is suspected to be carcinogenic. Electrodeposition of Zn–Ni, which is currently used on steel, represents a non-chromate alternative surface treatment for the corrosion protection of aluminium alloys. Zn–Ni coatings were electrodeposited onto an EN AW2024 T3 aluminium alloy sheet in a laboratory flow cell. To obtain several percentages of Ni in the coatings, solutions with different Ni2+ concentrations were used. The influence of a specific pretreatment to promote adherence, such as zincate immersion (109 g L–1 ZnO, 525 g L–1 NaOH) or phosphoric anodisation (36 wt-%H3PO4, 20°C) prior to electrodeposition was also investigated. The smoothness of the coating, measured on a three-dimensional roughness tester, increased when the percentage of Ni increased. This can be explained by a microstructural refinement observed using SEM and AFM. These microstructural changes are due to the evolution of the crystal structure of the coatings and can be observed by X-ray diffraction. The mechanical properties of the coatings (hardness and Young's modulus) were measured by microindentation and nanoindentation. The adherence of the coatings was tested by a scratch test and a three point bending test dedicated to coatings. The scratch behaviour of the coatings was a function of the percentage of Ni. The scratches observed indicate a ductile fracture for coatings with a low percentage of Ni and a brittle fracture for a high percentage of Ni. Bending tests demonstrated the favourable effect of pretreatments such as zincate immersion or phosphoric anodisation as well as adhesion enhancement as a function of increasing percentage of Ni. SE/503

PAni as Prospective Replacement of Chromium Conversion Coating in the Protection of Steels and Aluminum Alloys

Corrosion inhibition properties of chemical and electrochemically synthesized polyaniline(PAni), poly-o-methoxianiline(POMA)and their copolymers, in form of coatings of stainless steel AISI 304 and aluminum alloy 6061-T6 are studied in 3%and 0.1 M NaCl solutions, respectively. Polarization curves showed that the protection of steels by PAni is of anodic nature by setting the redox potential in the passive potential of the substrate. However, the protection of aluminum alloys after separation of both the corrosion and pitting potential is also anodic.

“Barrier-Adhesion” Principle for Corrosion Protection

Abstract The “barrier-adhesion” principle for corrosion protection of aluminum alloys is presented. Corrosion that occurs in a coated aluminum alloy can be viewed as pertaining to one of the two following corrosion modes: corrosion that occurs at and in the vicinity of a damaged coating (damaged surface corrosion, such as that associated with scribed corrosion testing) and corrosion that occurs under an undamaged coating, which often appears as many small pits (pitting corrosion). The damaged surface corrosion has been found to be a consequence of corrosion-induced delamination of the coating, which enhances the propagation of corrosion from the damaged site. With a coating system that contains corrosion inhibitors, the corrosion at the damaged site is suppressed to prevent delamination. It was found that if a good barrier is adhered to the metal surface by the tenacious water-insensitive adhesion, the corrosion-induced delamination can be prevented without corrosion inhibitors in the primer. Pitting corr...

Improved Corrosion Protection of Aluminum Alloys by System Approach Interface Engineering: Part 1—Alclad 2024-T3

Abstract This study investigated the development of chromate-free corrosion protection systems for Alclad 2024-T3 (UNS A92024) aluminum alloy ([2A]) based on the concept of system approach interface engineering (SAIE) by chemical and plasma techniques. Anode magnetron enhanced direct current (DC) cathodic plasmas were used to treat [2A] surface and to create interface engineered systems of cathodic electrocoat (E-coat)/plasma polymer/plasma-treated [2A]. Plasma polymer coatings provided not only a corrosion-resistant layer on [2A] surface but also an excellent adhesion base for subsequent cathodic E-coat. When tested by sulfur dioxide (SO2) and Prohesion salt spray tests, these plasma-modified systems showed excellent corrosion protection characteristics. The corrosion test results of SO2 and Prohesion salt spray tests showed that most of these plasma polymer-coated systems outperformed or performed comparably to the two types of controls used in this study (i.e., chromate conversion-coated and E-coated o...