Corrosion Protection Of Aluminum Alloys Research Articles

Incorporation of Anions into Anodic Alumina-A New Track in Cr(VI) Anodizing Substitution?

Aluminum technical alloys are well known for their outstanding mechanical properties, especially after heat treatment. However, quenching and aging, which improve the mechanical properties, by the formation of Cu-rich zones and phases that are coherent with the matrix and block the dislocation motion, cause uneven distribution of the elements in the alloy and consequently make it prone to corrosion. One method providing satisfactory corrosion protection of aluminum alloys is anodizing. On an industrial scale, it is usually carried out in electrolytes containing chromates that were found to be cancerogenic and toxic. Therefore, much effort has been undertaken to find substitutions. Currently, there are many Cr(VI)-free substitutes like tartaric-sulfuric acid anodizing or citric-sulfuric acid anodizing. Despite using such approaches even on the industrial scale, Cr(VI)-based anodizing still seems to be superior; therefore, there is an urge to find more complex but more effective approaches in anodizing. The incorporation of anions into anodic alumina from the electrolytes is a commonly known effect. Researchers used this phenomenon to entrap various other anions and organic compounds into anodic alumina to change their properties. In this review paper, the impact of the incorporation of various corrosion inhibitors into anodic alumina on the corrosion performance of the alloys is discussed. It is shown that Mo compounds are promising, especially when combined with organic acids.

A robust and multifunctional superhydrophobic coating based on natural palygorskite for corrosion protection of aluminum alloys

Biomimetic superhydrophobic surfaces have become an increasingly hot topic in the area of aluminum alloy protection. However, it remains a significant challenge to construct superhydrophobic coatings with reliable durability and multifunction through simple and economical strategies. In this study, we designed a novel superhydrophobic coating with a water contact angle of ∼165.0° and a sliding angle of ∼2.4° on Al alloys by spraying hydrophobically modified natural palygorskite (SH-PAL) on the pre-cured epoxy resin (EP). The resulting superhydrophobic coating (EP@SH-PAL) exhibits good mechanical resistance, UV resistance, hot water repellency, chemical stability, thermal stability, and self-healing capabilities against plasma etching. Corrosion tests reveal that the protection efficiency of the EP@SH-PAL sample is up to 99.98 %, which remains at a high value of 90.30 % even after 20 days of immersion in 3.5 wt% NaCl. This improved corrosion resistance is attributed to the synergistic physical shielding from the SH-PAL topcoat and the EP primer. Meanwhile, molecular dynamics simulations of the mechanical durability and corrosion resistance of the EP@SH-PAL coating were performed to support the experimental results at the microscopic level. In addition, the above-prepared superhydrophobic coating also demonstrates excellent self-cleaning and antifouling characteristics. This research will provide a new method for fabricating low-cost, multifunctional, superhydrophobic anticorrosion coatings on aluminum alloys and other metal substrates.

Hydrocarbon-degrading Shewanella algae shows oxidative deterioration corrosion at the aluminium alloy & coating interface

In this investigation, microbial adhesion expedites formation and alteration of aluminous minerals within aviation fuel tank systems. The corrosion mechanisms of two uncoated aluminium alloys and three types of coating-pretreated aluminium alloys by hydrocarbon-degrading Shewanella algae are examined. NO3- reduction of microorganisms induces corrosion acceleration of LY12 aluminium alloy (1.48 g*m−2*h−1) and corrosion inhibition of 7B04 aluminium alloy. CLSM and SEM observation of coating morphology highlight the microbial deterioration behaviors of coatings (pitting, swelling, and peeling). It inspires material selection and surface coating of microbial corrosion protection of aluminium alloy in marine and aerial environments.

Durable slippery liquid-infused porous surfaces for effective corrosion protection of aluminum alloy in ethylene glycol-water solutions

Aluminum (Al) alloys are extensively utilized in liquid-cooling heat dissipation systems owing to their superior strength-to-weight performance, ease of processing, and high thermal conductivity. However, they are susceptible to corrosion in the cooling medium, such as ethylene glycol-water solutions. This study presents a straightforward and cost-effective method to create a slippery liquid-infused porous surface (SLIPS) designed to effectively prevent corrosion of the 6061 Al alloy in ethylene glycol-water solutions. Micro/nano hierarchical structures were achieved on the SLIPS through plasma electrolytic oxidation and hydrothermal treatment. Following the modification of low-surface-energy materials and the infusion of silicone oil, the SLIPS exhibited an outstanding slippery property, allowing ethylene glycol-water droplets to effortlessly slide down the inclined surface at an angle of 1.1°. Additionally, the SLIPS demonstrated remarkable anti-corrosion performance against ethylene glycol-water solutions, with a minimum corrosion current density (Icorr) of 2.4 × 10−10 A·cm−2. Crucially, long-term immersion test results on corrosion resistance revealed that the SLIPS provided reliable corrosion protection for the 6061 Al alloy, exhibiting an Icorr increased by 4 orders of magnitude compared to a smooth substrate. These findings hold significant potential for advancing the widespread application of SLIPS in liquid-cooling heat dissipation systems.

Synthesis and characterization of modified iron oxide hydrophobic corrosion-resistant pigment for aluminum alloy coating

A hydrophobic coating containing modified iron oxides was prepared for corrosion protection of aluminum alloy. The modified iron oxide particles were synthesized using the annealing method and the evaluation of the corrosion-resistant benefits of modified iron oxides as additive in the epoxy resin coating was conducted. The raw FeOOH phase can be transformed into the α-Fe2O3 phase by increasing the annealing temperature. The morphology, colors, and pore size of the modified iron oxide are controllably evolved via finely adjusting the annealing temperature, which is beneficial for the compatibility, dispersion, and stability with epoxy resin. Besides, modified α-Fe2O3 annealed at 700 °C exhibited elliptical morphology and good solubility in epoxy resin solvents to form a hydrophobic corrosion inhibition layer (TP700), which further improves the corrosion resistance. Findings of corrosion electrochemical measurements and salt spray test confirmed the existence of TP700 composite coating resulted in the best corrosion protective properties on aluminum alloy during the corrosion process with the minimum corrosion current of 7.75 × 10−10 A cm−2 and the maximum |Z|0.01Hz value of 1.80 × 108 Ω cm2, which both are about two orders of magnitude higher than the commercial Fe2O3. Our results suggest a new venue for preparing modified iron oxide pigment on the surface of aluminum alloy materials for enhanced anti-corrosion applications.

An Inhibitor-Loaded LDH- and MOF-Based Bilayer Hybrid System for Active Corrosion Protection of Aluminum Alloys.

A novel inhibitor-loaded bilayer hybrid system based on the LDH inner layer and MOF outer layer is designed on an aluminum alloy 2A12 surface to improve corrosion performance. The hybrid film system covers the inherent cavities and intercrystalline defects of the LDH film using the affinity between the LDH and the MOF compounds. The results demonstrate that the LDH-inhI precursor film is entirely covered by new Zn-based MOF microrods. The LDH-inhI precursor film is partially dissolved and recrystallized in favor of MOF crystal growth to strengthen the binding adhesion between LDH and MOF films. The LDH-inhI/MOF-inhII bilayer film shows significantly enhanced corrosion resistance through the synergistic action of LDH and MOF nanocontainers doped with different corrosion inhibitors (vanadates, 2,5-furandicarboxylic acid, and benzotriazoles). Due to the multiple loadings of the MOF film and the sustained-release of the LDH film, this method provides an effective approach to developing new anticorrosion systems and enhancing both the barrier ability and active corrosion protection performance of LDH-based conversion treatments.

Fabrication of dual self-healing silane nanocomposite for efficient corrosion protection of aluminum alloy

1,5-naphthalenediol (ND) inhibitor loaded hollow CeO2 nanoparticles were incorporated into superhydrophobic silane coating on aluminum alloy for corrosion protection. The hollow CeO2 nano-carrier exhibited a large loading amount of 23.5 wt%. The corrosion protection and self-healing performance was investigated by using electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) in 3.5 wt% NaCl solution. EIS result indicated that the constructed silane/CeO2@ND composite coating significantly enhanced the corrosion resistance and the inhibition efficiency was 97.9%. Meanwhile, the localized corrosion was remarkably suppressed from EN measurements. Moreover, the silane/CeO2@ND composite coating exhibited an excellent chemical and mechanical stability and self-healing ability due to the synergistic effect of incorporated inhibitive CeO2 nanoparticles and the loaded effective ND inhibitor.

Review of the state of art of Li-based inhibitors and coating technology for the corrosion protection of aluminium alloys

The quest for novel alternatives to hexavalent-chromium-based corrosion inhibitors is of utmost significance and urgency. Strict international health and safety regulations, due to growing concerns regarding the impact of hexavalent chromium on human health and the environment, have pushed the commercial introduction of many alternative inhibitor types, but the implementation of alternative active protective primers for structural parts in the aerospace industry is still pending. This endeavour has proven to be remarkably challenging, as the potential replacement coating types must meet numerous functional requirements encompassing cost-effectiveness and exceptional corrosion protection for intrinsically corrosion susceptible aerospace aluminium alloys. In recent years, considerable attention has been drawn to lithium salts as environmentally friendly corrosion inhibitors forming the basis for a novel active protective coating technology. The involvement of lithium ions has been shown to play a pivotal role in the conversion process of aluminium alloy surfaces by stabilizing the reaction products, thereby facilitating the gradual development of a protective layer with a multi-layered configuration, which exhibits considerable variability in morphology, depending on local chemical and electrochemical conditions. The versatility of the lithium-based corrosion protection extends to their application as corrosion inhibiting pigments in organic coatings or as a pre-treatment, directly forming conversion layers, thereby enhancing their practical implementation. However, previous chromate replacement reviews only introduced the promising outcomes provided by the lithium technology, omitting key details of its development and formation mechanism. This paper critically reviews and summarizes the studies conducted to date on lithium-based inhibitor technologies for the corrosion protection of aluminium alloys as well as topics to be investigated in the future.

Biofouling and Corrosion Protection of Aluminum Alloys Through Ultrafast Laser Surface Texturing for Marine Applications

AbstractSurface biofouling, corrosion, and wettability are important parameters to understand and characterize aluminum alloys to prevent the failure in marine environments. Antifouling technologies predominantly encompass chemical and biocidal approaches with negative environmental consequences. Therefore, this study focuses on a new method of producing non‐toxic and effective antifouling and corrosion‐resistant surfaces. In this study, ultrafast laser texturing is used to modify the surface of an aluminum alloy using a femtosecond laser system. Five different unique texture patterns are designed and fabricated using 3 W laser power, 100 kHz pulse repetition rate, and 4 mm s−1 scanning speed in order to make the aluminum surface antifouling and corrosion resistant. The non‐textured sample has a contact angle of 85° while the textured samples have contact angles of up to 157°. The contact angle increased with time up to 90 days of aging. Biofouling assessment is conducted using marine algae Nitzschia ovalis as a marine fouling test organism. A reduction of biofilm coverage of 79% is recorded from the laser‐produced star pattern texture. This study demonstrates that laser‐textured surfaces have the potential to mitigate the formation of biofilms on the surfaces while also providing a mechanism to control the relative level of corrosion.

Chromate (Cr6+)-free surface treatments for active corrosion protection of aluminum alloys: a review

Chromate (Cr6+)-free surface treatments for active corrosion protection of aluminum alloys: a review

Effectiveness of Mesoporous Silica Nanoparticles Functionalized with Benzoyl Chloride in pH-Responsive Anticorrosion Polymer Coatings.

Smart polymer coatings embedding stimuli-responsive corrosion inhibitor nanocarriers are commonly exploited, in the literature, for the development of high-performance active coatings. In this work, high-surface-area amino-functionalized mesoporous silica nanoparticles (MSN-NH2) were developed with a one-step synthesis process and then functionalized with benzoyl chloride (MSN-BC) through a reaction with amino groups. MSN-BC are able to release benzoic acid (BA) in acid and alkaline conditions as a result of the hydrolysis of the pH-sensitive amide bond. MSN-BC were embedded in polymer coatings to exploit the pH-dependent release of corrosion-inhibiting BA. After an in-depth characterization of the developed functional nanoparticles and of their pH-dependent release kinetics of BA, MSN-BC were embedded in an acrylic matrix, realizing coatings for the corrosion protection of aluminum AA2024 alloys. Results demonstrate the effectiveness of the nanoparticles' porous structure for a high loading of the anticorrosive active agent BA and the long-lasting efficiency of the coating for the corrosion protection of aluminum alloys, as validated by morphological and electrochemical impedance spectroscopy (EIS) measurements. EIS experiments were carried out with up to 21 days of exposure to a corrosive environment, revealing the potentialities of the acrylic coatings embedding MSN-BC for the protection of aluminum alloys.

Hybrid PEO/sol-gel coatings loaded with Ce for corrosion protection of AA2024-T3

Plasma electrolytic oxidation (PEO) has been targeted as an eco-friendly alternative technology to conventional chromic acid anodizing (CAA) for corrosion protection of aluminium alloys in the aircraft industry. However, conventional PEO technology implies high energy consumption. Flash-PEO coatings (≤10 μm) produced in short treatment times (≤ 5 min) constitute a feasible way to overcome this limitation. Nevertheless, the long-term corrosion resistance is compromised, thus requiring novel sealing post-treatments. The present work studies the effect of stand-alone hybrid sol-gel (HSG) and Ce-doped hybrid sol-gel (HSGCe) coatings as a sealing post-treatment to evaluate the long-term corrosion resistance of Flash-PEO coatings on aluminium alloy (AA) 2024-T3. The characterization of the PEO, HSG, and HSG-Ce coatings was performed by scanning electron microscopy, X-ray diffraction, water contact angle, dry adhesion tests (ISO 2409), optical profilometry and Fourier transform infrared spectroscopy. The corrosion behaviour was assessed by electrochemical impedance spectroscopy up to 21 days (3.5 wt% NaCl). Active corrosion protection was assessed by immersion tests of artificially scratched coatings. Present findings reveal that low-energy-cost Flash-PEO coatings were successfully formed on AA2024-T3 alloy. Both HSG and HSG-Ce coatings were homogeneously formed on Flash PEO coating. Regarding the corrosion resistance, HSG-Ce showed significant scratch protection during 21 days of immersion in 3.5 wt% NaCl. The results suggest that, while the release of Si and Ce from the coating provided corrosion protection, NO3−release promoted localized corrosion phenomena in the scribe. This was associated with the preferential pitting corrosion phenomena at the Cu-rich intermetallic compounds instead of forming a thick and stableNO3−-rich passive layer.

LDH-Based "Smart" Films for Corrosion Sensing and Protection.

In a "smart" corrosion-protective coating system, both the active anti-corrosion and the early corrosion detection of underlying metals are highly required. It is practical significant to develop materials that possess self-detecting of the early local corrosion and self-healing of coating defects simultaneously. The organic compound 8-hydroxyquinoline (8HQ) is an effective inhibitor and a fluorescent sensor probe for corrosion of aluminum alloy. Therefore, a layer double hydroxide (LDH) nanocontainer film loaded with the 8HQ was developed for the active corrosion protection purpose of aluminum alloy AA2024. In corrosive environments, the 8HQ are released from LDH film to inhibit the corrosion process, leading to the loss of the complexation with Al3+ ions in LDH laminates, thus turning off fluorescence. Results show that the LDH film loaded with 8HQ composites can improve the anti-corrosion performance of the film by releasing corrosion inhibitors on demand. Simultaneously, due to the complexation of 8HQ and Al3+ ions, the LDH film is fluorescent at the initial stage under ultraviolet light, and then becomes non-fluorescent at the corrosion sites, indicating the corrosion evolution process of the coating. The 8HQ-loaded LDH film with self-healing and self-detecting dual functions provides promising opportunities for the effective corrosion protection of aluminum alloy due to its "smart" and multifunctional properties.

Mechanistic origins of corrosion protection of aluminum alloys by graphene/polyetherimide nanocomposite coatings

Light-weighting vehicular components through adoption of light-metal structural alloys holds promise for reducing the fuel consumption of internal combustion engine vehicles and increasing the range of battery electric vehicles. However, the alloyed microstructure and surface precipitates of aluminum alloys render these materials susceptible to corrosion under modest excursions from neutral pH. Traditional chromium-based anodic passivation layers are subject to increasingly stringent environmental regulations, whereas options for sacrificial cathodic films are sparse for electropositive metals. While hybrid nanocomposite coatings have shown initial promise, mechanistic underpinnings remain poorly understood. Here, a fully imidized polyetherimide (PEI) resin is utilized as the continuous phase with inclusion of unfunctionalized exfoliated graphite (UFG). A comprehensive investigation of the mechanisms of corrosion protection reveals key fundamental design principles underpinning corrosion inhibition. First, strong interfacial adhesion, which for PEI is facilitated by binding of imide carbonyl moieties to Lewis acidic sites on Al surfaces. Second, the miscibility of ion-impervious nanoscopic UFG fillers and stabilization of a substantial interphase region at UFG/PEI boundaries that result in minimizing the free volume at the filler/polymer interface. Finally, extended tortuosity of ion diffusion pathways imbued by the below-percolation-threshold 2D fillers. These three design principles help govern and modulate ion transport from electrolyte/coating interfaces to the coating/metal interface and are crucial for the extended preservation of barrier properties. The results suggest an approach to systematically activate multiple modes of corrosion inhibition through rational design of hybrid nanocomposite coatings across hard-to-abate sectors where light metal alloys are likely to play an increasingly prominent role.

Corrosion protection of aluminum alloy 7075 using functionalized micro- silica based epoxy coatings

Composite coatings were prepared by using epoxy-hardener having a 2:1 composition and functionalized SiO2 having 0, 0.01, 0.03, and 0.05 proportion/s accordingly. Curing of the coatings on aluminium alloy 7075 substrates was performed at a temperature of 60 ± 5 °C. Moreover, corrosion assessment was carried out in 0.6M NaCl solution at room temperature. The outcome of Fourier Transform Infrared Spectroscopy (FT-IR) confirmed the presence of Si-O bond and epoxide peaks. XRD spectra depict that the intensity of AA-7075 peaks was substantially effected possibly due to more x-rays absorption in composite coatings as a result of increasing silica content. Electrochemical Impedance Spectroscopy (EIS) analysis depicted 116, 284, 620, and 1309% increase in charge transfer resistance (Rct) for 0, 1, 3, and 5% silica composition relative to bare AA-7075 samples. Moreover, potentiodynamic plots were used to estimate corrosion rate which depicted decline of 20, 55, 40, 90 and 97% when compared with pure AA-7075 substrate.

Robust superhydrophobic SiO2/epoxy composite coating prepared by one-step spraying method for corrosion protection of aluminum alloy: Experimental and theoretical studies

In this work, a robust epoxy adhesive (EP) @ superhydrophobic SiO2 (SH-SiO2)-based superhydrophobic coating was prepared on the aluminum substrate by a simple one-step spraying strategy. The prepared EP@SH-SiO2 coating exhibits hierarchical micro/nanostructures and is capable of maintaining a contact angle of more than 150° after 1000 cm of abrasion length and 80 tape-peeling repetitions. Molecular dynamics (MD) simulations and quantum mechanics calculations show that the improved mechanical resistance is attributed to the enhanced interfacial interaction between the EP@SH-SiO2 coating and the underlying substrate induced by the epoxy adhesive. Electrochemical measurements in 3.5 wt% NaCl solution show the corrosion inhibition efficiency of the EP@SH-SiO2 coating reaches up to 99.99%, and even after 8 days of immersion, the low frequency impedance modulus of the EP@SH-SiO2 sample is still ∼1 order of magnitude higher than that bare aluminum, demonstrating excellent long-term corrosion protection. The diffusion behavior of the corrosive medium in the EP@SH-SiO2 coating was revealed by MD simulation to support the experimental results. Additionally, the EP@SH-SiO2 coating exhibits good chemical stability and hydrophobic repair properties. This work will provide a new perspective for the preparation and study of robust superhydrophobic aluminum for corrosion protection properties.

Self-Healing Coatings with Double-Layered Structure for Corrosion Protection of Aluminum Alloys

Self-Healing Coatings with Double-Layered Structure for Corrosion Protection of Aluminum Alloys

Corrosion protection of aluminum alloys with chromate-free inhibited conversion coatings in a tropical climate

Corrosion protection of aluminum alloys with chromate-free inhibited conversion coatings in a tropical climate

In-situ preparation of superhydrophobic Zn-Al layered double hydroxide coatings for corrosion protection of aluminum alloy

• The superhydrophobic Zn-Al LDHs coatings were fabricated on the aluminium alloy; • The superhydrophobic coatings significantly enhance metal corrosion resistance; • The anti-corrosion performance of coatings was dramatically affected by dopants. The superhydrophobic Zn-Al layered double hydroxides (LDHs) coatings were successfully in-situ fabricated on surface of 3003 aluminum alloy using hydrothermal and impregnation methods. The anti-corrosion performance of the superhydrophobic Zn-Al LDHs coatings was investigated using electrochemical tests as well as some surface characterizations. Results indicate that the superhydrophobic Zn-Al LDHs coatings can dramatically enhance the corrosion resistance of aluminum alloy. The different dopants can dramatically impact the anti-corrosion performance. It was attributed to the blocking effect and the capture capability of Cl - by the LDH films. Relevant mechanisms for corrosion protection of the superhydrophobic Zn-Al LDHs coatings have been proposed.

The effect of pH on the corrosion protection of aluminum alloys in lithium-carbonate-containing NaCl solutions

The corrosion inhibiting effect of lithium carbonate has been studied over the pH range relevant for atmospheric corrosion conditions at the polymer/metal interface. It is demonstrated that lithium carbonate offers optimum corrosion protection under moderately alkaline conditions attributed to the formation of a protective layer identified as aluminum-lithium layered double hydroxide. It is proposed that an active-to-passive transition occurs in the presence of lithium carbonate under moderately alkaline conditions where anodic dissolution of the aluminum matrix is an important step prior to the formation of the protective layer. After prolonged exposure, the protective layer is uniformly formed on the surface of AA2024-T3 and lithium containing AA2198-T8 covering both the matrix and active intermetallic particles thus hindering further corrosion reactions.