Corrosion Resistance Of Aluminum Alloys Research Articles

Unusual Corrosion of Instruments Deployed in the Deep Sea for Indian Tsunami Early Warning System

AbstractUnderwater technology is advancing with the development of instruments capable of measuring continuous data for longer durations for diversified ocean data collection. A bottom pressure recorder is deployed on the seabed to measure the water level for tsunami early warning, thus playing a critical role in saving lives. Recently, many countries have installed their warning systems. Here, we report an unusual corrosion of such an instrument deployed in the deep sea (3,250 m) in the Bay of Bengal, which led to severe damage of the instrument. This paper reports for the first time on the investigation and possible causes for this unusual corrosion of an instrument made from highly marine corrosion-resistant aluminum alloy and duplex stainless steel material.

Hybride Sol-Gel Coatings for Protection of Aluminium Alloys

Aluminum and its alloys are used in a broad spectrum of applications on the basis of their physical characteristics, such as stiffness, low density and high strength-to-weight ratio [1]. While the physical properties of aluminum metal are improved by alloying, its corrosion resistance is reduced. Aluminum alloys are highly susceptible to oxidation and pitting corrosion in aggressive environments. Serial 7xxx wrought alloys contain major additions of zinc, along with magnesium or magnesium and copper in such ratios as to increase their strength [1]. Of the various approaches that have been employed as alternatives to CCCs ‒ electro-polymerization, anodization, conversion coatings and sol-gel synthesis [2] ‒ the last mentioned is considered to be the most promising. It can be applied to a substrate by different methods, most commonly spinning, dipping or spraying.We have investigated a three component system for the preparation of corrosion resistant coatings on 7075-T6 aluminum alloy [3,4]. The sol-gel process allows the introduction of organic molecules into an inorganic network, forming hybrid organic-inorganic coatings, the so-called ormosils (organically modified silica) also known as silanes. Ormosils exhibit a combination of desirable properties of both inorganic (thermal stability, hardness, durability) and polymeric (toughness and flexibility) components within a single network. It was shown that the corrosion resistance of aluminum alloys has been improved by the deposition of two component hybrid coatings [5,6]. Further, combination of ormosil with zirconium-based additives (organically modified ceramics called ormocers) has initiated a new trend in the corrosion protective properties of hybrid sol-gel coatings [7,8].In this work coatings were synthesized by alkoxide sol-gel reaction, using the organically modified siloxane precursors tetraethyl orthosilicate (TEOS) and 3-methacryloxypropyl trimethoxysilane (MAPTMS) (Sol 1), and zirconium tetrapropoxide (ZTP) chelated with methacrylic acid (MAA) (Sol 2). The synthesis was optimized using in situ FTIR spectroscopy. Optimized sols were spin-coated onto aluminum alloy AA7075-T6 substrate and the corrosion properties of deposited coating investigated in dilute Harrison’s solution optimized to simulate aircraft conditions in air. The establishment of Si-O-Si, and especially Si-O-Zr, bonds was shown to be crucial to achieve excellent corrosion protection. An optimal performance resulted in a current density two orders of magnitude lower than that for bare substrate. No susceptibility to localized corrosion was observed up to electrode potentials of 7 V. The coatings were up to 10 mm thick, homogeneous and dense.

Study on dimensional and corrosion properties of thixoformed A356 and AA7075 aluminum bipolar plates for proton exchange membrane fuel cells

Metallic bipolar plates for polymer exchange membrane (PEM) fuel cells are currently manufactured by stamping of thin sheets. However, there are dimensional and shape errors of microchannels because of forming limitation such as spring back of thin sheets after stamping. On the other hand, stamping process is limited to commercially available sheet alloys, which restricts the development of a high corrosion resistant substrate aluminum alloy. Here, thixoforming (a commercial semisolid route) that is applicable to a wide range of aluminum alloys is proposed for net-shape micromanufacturing of aluminum bipolar plates with high dimensional stability. High corrosion resistance cast A356 (Cu-free) and wrought AA7075 (∼2% Cu) aluminum billets are used for this study. Initial billets are heated at different semisolid temperatures. Subsequently, the semisolid slurries are injected into the die cavity. A356 and AA7075 aluminum bipolar plates are successfully fabricated by thixoforming with very small deviation of 0.7% and 1.5% from the nominal value of 0.300 mm in the microchannel depth, respectively. A multilayer coating of TiN/CrN is deposited on the surface of thixoformed bipolar plates through a commercially available magnetron sputtering technique. Electrochemical corrosion tests show that coated-thixoformed A356 (Cu-free) bipolar plates have significantly lower corrosion current densities than coated-thixoformed AA7075 (∼2% Cu) bipolar plates. This seems to be due to the deleterious effect of Cu alloying element on the corrosion resistance of aluminum alloys that clearly confirms the importance of substrate material development for corrosive PEM fuel cell environment. It is suggested that specific high corrosion resistance aluminum alloy for PEM fuel cell application can be simply designed and then thixoforming can be efficiently and cost effectively employed to fabricate net-shape aluminum bipolar plates.

Evaluation of corrosion characteristics of aluminum alloys in the bio-ethanol gasoline blended fuel by 2-electrode electrochemical impedance spectroscopy

The corrosion characteristics of aluminum alloys were investigated in the bio-ethanol gasoline blended fuel at 100°C. The corrosion property of aluminum alloys was evaluated by an in situ 2-electrode electrochemical impedance spectroscopy (EIS), weight loss test and pressure–time measurement. Surface analysis was carried out after immersion test. The polarization resistance of aluminum alloys was increased at initial immersion time due to the formation of boehemite film (γ-AlOOH); after that, it was decreased due to the initiation of aluminum alkoxide reaction. The pressure of autoclave was increased because of the hydrogen gas from the aluminum–ethanol alkoxide reaction. It was verified that a 2-electrode EIS and pressure–time measurements were able to evaluate the corrosion resistance of aluminum alloys in the bio-ethanol gasoline blended solution.

Fabrication of biomimetic super-hydrophobic surface on aluminum alloy

Inspired by microstructure characteristics of surfaces of typical plant leaves such as petal of red rose, the biomimetic super-hydrophobic surface of aluminum alloy has been successfully fabricated by laser processing and surface modification by DTS (CH3(CH2)11Si(OCH3)3). The morphological features, chemical composition, and super-hydrophobicity of resultant surfaces were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle measurements. The super-hydrophobic surface exhibited a microstructure consisting of myriad micro-scale crater-like pits. It is found that the super-hydrophobicity is synchronously governed by both the surface chemical composition and geometrical microstructure structures. The highest water contact angle of resultant surface reaches as high as 161.0°. Moreover, corrosion resistance property of these prepared films against NaCl solution is elucidated using electrochemical measurements; it is found that the corrosion resistance of aluminum alloy is also considerably improved.

Full-scale accelerated tests of aluminum alloys under exposure to marine atmosphere

Dynamics of corrosion of aluminum alloys D16T, V95T2, and 1424TG1 is studied in marine atmosphere at corrosion stations of three climatic zones as dependent on the surface concentration of chlorides. The amount of chlorides on the sample surface depends on the alloy grade: the highest value was characteristic for alloy D16T, and the lowest value was observed on alloy 1424TG1. A predictive estimate is given for corrosion resistance of aluminum alloys as regards the sample weight loss.

Self-Healing of Layered Double Hydroxide Film by Dissolution/Recrystallization for Corrosion Protection of Aluminum

The development of smart corrosion protection systems for aluminum and aluminum alloys is a subject of prime importance. Self-healing materials with longer lifetime and lower production costs have received extensive attention. Herein we report an intrinsic self-healing coating of in situ-grown inorganic zinc, aluminum-containing layered double hydroxide (ZnAl-LDH) film with improved corrosion-resistant performance in chloride-containing solution. An artificial defect roughly 30 μm in width, which penetrated to the aluminum substrate, was made by a razor blade to show the process of self-healing. After immersion in the solution of 3.5 wt% NaCl for a period of time, new LDH crystallites on the aluminum substrate at the site of the artificial defect were observed by scanning electron microscope (SEM). Electrochemical impedance spectroscopy (EIS) and dc polarization curves were monitored in artificial seawater at room temperature to further demonstrate the self-healing process. A possible dissolution/recrystallization mechanism was proposed and confirmed to illustrate the phenomenon of self-healing. The ZnAl-LDH film with self-healing ability can reduce the corrosion of aluminum dramatically. Also, the concept of self-healing via dissolution/recrystallization was extended to improve the corrosion resistance of aluminum alloy.

Method to improve corrosion resistance of AA 5083 by cerium based conversion coating and anodic polarisation in molybdate solution

The corrosion resistance of aluminium alloys can be improved by the formation of chemical conversion coatings. Usually, chromate pretreatment processes are used. However, because of their high toxicity, alternative methods have been studied in the last years. In the present paper, a process to improve the corrosion resistance of AA 5083 was investigated. The main process consisted of serial immersion in two solutions containing two different cerium salts, followed by a further step involving anodisation in Na2MoO4. The corrosion resistance was investigated by potentiodynamic anodic polarisation tests and electrochemical impedance spectroscopy. The morphology and composition of the oxide layers were characterised by scanning electronic microscopy equipped with an energy dispersive X-ray detector. Serial treatment in the two solutions with different cerium salts and H2O2 produced a more uniform and thicker layer with a larger amount of deposits above the alloy cathodic areas than the single two treatments. In this way, the alloy corrosion resistance in chloride environments was improved and decreased the anodic reaction rate. When anodisation in molybdate salts was added, even better results were found. The corrosion resistance was higher due to a thicker and less conductive passive layer.

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.

In situ fabrication of blue ceramic coatings on wrought Al Alloy 2024 by plasma electrolytic oxidation

In situ formation of ceramic coatings on 2024 Al alloy with a blue color was successfully achieved using a plasma electrolytic oxidation process working at atmospheric pressure. This novel blue ceramic coating overcomes the shortcomings of surface treatments resulting from conventional dyeing processes by depositing organic dyes into the porous structure of anodic film, which has poor resistance to abrasion and rapid fading when exposed to sunlight. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize the microstructure of the blue ceramic coating. The fabricated ceramic coating was composed of CoAl2O4, α-Al2O3, and γ-Al2O3. By controlling the working parameters, the distribution of the CoAl2O4 phase on the surface can be adjusted, and plays a key role in the appearance of the coating. Electrochemical testing, thermal cycling method, and pin-on-disk sliding wear testing were employed to evaluate corrosion, thermal cycling, and wear resistance of the ceramic coatings. The results indicate that the blue ceramic coating has a similar polarization resistance to that of conventional anodic film and can significantly enhance the corrosion resistance of aluminum alloy. There are no destructive horizontal cracks observed within the blue ceramic coating when subjected to 120 times of thermal cycling, which heats the samples up to 573 K and followed by submersion in water at room temperature for 10 min. Compared with the aluminum substrate as well as a conventional anodic film coated aluminum sample, the wear resistance of the blue ceramic coating coated sample was significantly increased while the coefficient of friction was decreased from 0.34 to 0.14.

Alumina Sol-Gel Films and Alodine Films on Al 2024 Alloy

Development of the sol-gel films for painting pretreatment of aluminium alloy is to replace bichromate conversion films such as Alodine. Corrosion resistance of Alodine film and sol-gel film were evaluated through potentiodynamic polarization curves, electrochemical impedance spectroscopy, salt spraying and acidic dropping solution. Sol-gel film is almost the same as Alodine film at the film surface density, salt spraying resistance and adhesion with painting coating. Changing color times of dropping solution on sol-gel film is shorter than Alodine film. But the corrosion current of sol-gel film is lower than Alodine and the impedance value is higher than Alodine in 35g/L NaCl solution. Mechanism of corrosion resistance of alumina sol-gel film is that the cathode reaction and anodic reactions are restrained by sol-gel film in the Cl- corrosive medium. The EIS of sol-gel film consisted of only a single capacitive arc with one time constant. Sol-gel coating can prevent or delay the corrosive solution from infiltrating the substrate for its better isolation function, thus protecting 2024 aluminium alloy from corrosion. Sol-gel films can improve corrosion resistance of aluminum alloy and have the same adhesion as Alodine film. It will be a promising alternative pretreatment for aluminum alloys prior to painting.

A facile method for fabrication of superhydrophobic coating on aluminum alloy

A superhydrophobic coating applied in corrosion protection was successfully fabricated on the surface of aluminum alloy by chemical etching and surface modification. The water contact angle on the surface was measured to be 161.2° ± 1.7° with sliding angle smaller than 8°, and the superhydrophobic coating showed a long service life. The surface structure and composition were then characterized by means of SEM and XPS. The electrochemical measurements showed that the superhydrophobic coating significantly improved the corrosion resistance of aluminum alloy. The superhydrophobic phenomenon of the prepared surface was analyzed with Cassie theory, and it was found that only about 6% of the water surface is in contact with the metal substrate and 94% is in contact with the air cushion. Copyright © 2011 John Wiley & Sons, Ltd.

EFFECT OF COLD DEFORMATION ON THE CORROSION BEHAVIOUR OF Mn–CONTAINING ALUMINIUM ALLOY TUBE

Aluminium alloys are extensively employed as heat transfer tube materials in heat exchangers.Previous work has focused on the corrosion behaviour of tube materials in brazed heat exchangers.However,very little attention has been devoted to corrosion of tubes in mechanically-expanded heat exchangers despite the observation of some instances of early corrosion failure in bent region of aluminium alloy tube.The effects of cold deformation on the corrosion behaviour of aluminium tube materials have been studied in 0.6 mol/L NaCl and SWAAT solutions by SEM,TEM, potentiodynamic polarizations and immersion test.The results show that high Mn content(0.22%, mass fraction) can experience preferential corrosion and early failure in the bent region,but not for one with a lower Mn content(0.08%).SEM/TEM observations of the microstructure of the alloys show that each alloy has one main type of coarse intermetallic particle.However,TEM observations show that there is a distinct difference in particle morphology between the bent and straight regions of the high Mn alloy tube,the bent region has more nano-scale Mn-rich particles than the straight region, and no such effects are observed on the low Mn alloy.The microelectrochemical polarisation measurements show that the straight region of high Mn has highest pitting potential,but cold deformation can decrease the pitting potential of bent region of high Mn tube,but no such effects on low Mn tube. The immersion test shows that the bent region of high Mn alloy has highest attack;this is associated with precipitation of 20—100 nm Mn-rich particles,which cause increased anodic reactivity as they provide further pit initiation sites and cause solute depletion in the matrix.In addition,the Mn-rich particles are also sites for enhanced cathodic reactivity.The relationship between the microstructure and electrochemical properties of tube materials before and after cold deformation is established.The results indicate Mn can improve the corrosion resistance of aluminium alloy,but the mechanical cold deformation will weaken the effect.

Al 5052 합금의 저입열 Pulse MIG 최적 현장 용접조건 산정에 관한 실험적 연구

The weight reduction of the transportations has become an important technical subject Al and Al alloys, especially Al 5052 alloys have been being applied as door materials for automobile. One of the most widely known car weight-reduction methods is to use light and corrosion-resistant aluminum alloys. However, because of high electrical and thermal conductivity and a low melting point, it is difficult to obtain good weld quality when working with the aluminum alloys. Also, Pulse MIG welding is the typical aluminum welding process, but it is difficult to apply to the thin plate, because of melt-through and humping-bead. In order to enhance weld quality, welding parameters should be considered in optimizing the welding process. In this experiment, Al 5052 sheets were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) pulse process. The proper welding conditions such as welding current, welding speed, torch angle <TEX>$50^{\circ}$</TEX> and gap 0~1mm are determined by tensile test and bead shape. Through this study, range of welding current are confirmed from 100A to 120A. And, the range of welding speed is confirmed from 1.2m/min to 1.5m/min.

Effect of Titanium-Fine-Particle Bombarding Treatment on Corrosion Resistance of Aluminium Alloy and Carbon Steel

This study investigated effect of titanium-fine-particle bombarding (Ti-FPB) treatment on corrosion resistance of A7075-T6 aluminum alloy and S45C carbon steel. Ti-FPB treatment is a surface-modification method to bombard countless titanium-fine-particles accelerated to high speed to the materials. After the treatment was conducted on the materials, the characteristics of the formed surface layers were examined in detail. As a result, it was shown that titanium composing the fine-particles was diffused over the surfaces because kinetic energy of the fine-particles was converted to thermal energy and the surface temperature was rapidly increased. At the same time, the surface hardness was remarkably increased and compressive residual stress was introduced. Further, the Ti-FPBed materials were immersed in 5 mass% salt-water maintained at 353 K. In this test, the specimens were fixed under stress of 80% of the yield strength. The results showed that the diffused titanium through Ti-FPB treatment improved the corrosion resistance of A7075-T6 alloy and S45C steel and the reduction in the tensile strength and elongation was suppressed.

Anodic behavior of Al–Bi and Al–Sb alloys in 3% NaCl solution

The methods of polarization curves and scanning electron microscopy are used to study the pitting corrosion resistance of Al-Bi (up to 4 wt.% Bi) and Al-Sb (up to 20 wt.% Sb) binary alloys in a 3% NaCl solution. With concentration of the alloying element to 0.1 wt.%, current density decreases and corrosion slows down. With higher concentrations of antimony and bismuth, the early passivation current density increases and the active region reduces on potentiodynamic curves. This indicates that the corrosion resistance of aluminum alloys decreases with greater content of the other phase (Bi or Sb).

Metallurgical aspects of corrosion resistance of aluminium alloys

AbstractAluminium is the second most often used metal after steel. In this paper, the most current uses of aluminium alloys are first summarised. Then, their different corrosion modes, i.e. pitting, crevice, filiform, galvanic and structural corrosion (including inter‐granular, exfoliation and stress corrosion cracking) are reviewed, with particular attention paid to metallurgical factors controlling the corrosion process. For each mode, some instances of possible in‐service failure are given, followed by the discussion of the involved mechanisms and the presentation of appropriate solutions to prevent corrosion. Last, passivity and polarisation behaviour are discussed with reference to stainless steels.

Role of nanostructure in pitting of Al–Cu–Mg alloys

Aluminium alloys possess a unique combination of strength and low density, which historically have made these alloys ideal for many structural applications. However, addition of alloying elements in appreciable concentrations, in particular Cu and Mg, make Al-alloys inherently susceptible to localised corrosion. In this work, we adopt a bottom-up approach in an attempt to quantify the critical microstructural feature size (viz. precipitate size) that is capable of triggering a cascade of pitting events and eventual degradation of corrosion resistance. This is accomplished by exploiting the well characterised hardening response in a model alloy, Al–1.1Cu–1.7Mg (at.%), for which pitting resistance of the alloy was tracked with aging time and hence microstructural evolution. Corrosion performance and microstructural characterisation were carried out using a combination of electrochemical testing, coupled with high-resolution scanning transmission electron microscopy (HRSTEM) and atom probe tomography (APT). Results indicate, at least for this particular alloy, that second phase features below a critical width of approximately 3 nm can be tolerated from a corrosion perspective. This study has potentially wide consequences in the understanding of aluminium alloy corrosion initiation and the development of highly corrosion resistant aluminium alloys.

Growth mechanism and corrosion behavior of ceramic coatings on aluminum produced by autocontrol AC pulse PEO

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate.

Corrosion resistance of aluminium alloy pretreated based on bis-sulphur silane with rare earth salt

Pretreatment for the Al alloy based on bis-[triethoxysilylpropyl]tetrasulphide (BTSPS) with Ce(NO3)3 is put forward in order to improve corrosion resistance of AA2024-T3 alloy in the present paper. The coating is formed by one step dip coating. The cross-linked pretreated coating on Al alloy is characterised with reflection absorption infrared spectroscopy. The chemical composition and the in depth distribution of different elements present in the coating are analysed by Auger electron spectroscopy. Corrosion resistance and hydrophobicity of pretreated coating on the Al alloy is respectively assessed by salt spray test, electrochemical tests and thermogravimetric analysis. The role of Ce3+ ion and sulphur present in one of the BTSPS solutions in the formation of the surface film is discussed. The results show that the one step pretreatment coating of BTSPS with Ce(NO3)3 provides excellent corrosion protection with the Al alloy compared with that of BTSPS without Ce(NO3)3.