A Review on Anodizing of Aerospace Aluminum Alloys for Corrosion Protection

Effect of Citric Acid Hard Anodizing on the Mechanical Properties and Corrosion Resistance of Different Aluminum Alloys

Hard anodizing is used to improve the anodic films' mechanical qualities and aluminum alloys' corrosion resistance. Applications for anodic oxide coatings on aluminum alloys include the space environment. In this work, the aluminum alloys 2024-T3 (Al-Cu), 6061-T6 (Al-Mg-Si), and 7075-T6 (Al-Zn) were prepared by hard anodizing electrochemical treatment using citric and sulfur acid baths at different concentrations. The aim of the work is to observe the effect of citric acid on the microstructure of the substrate, the mechanical properties, the corrosion resistance, and the morphology of the hard anodic layers. Hard anodizing was performed on three different aluminum alloys using three citric-sulfuric acid mixtures for 60 min and using current densities of 3.0 and 4.5 A/dm2. Vickers microhardness (HV) measurements and scanning electron microscopy (SEM) were utilized to determine the mechanical characteristics and microstructure of the hard anodizing material, and electrochemical techniques to understand the corrosion kinetics. The result indicates that the aluminum alloy 6061-T6 (Al-Mg-Si) has the maximum hard-coat thickness and hardness. The oxidation of Zn and Mg during the anodizing process found in the 7075-T6 (Al-Zn) alloy promotes oxide formation. Because of the high copper concentration, the oxide layer that forms on the 2024-T6 (Al-Cu) Al alloy has the lowest thickness, hardness, and corrosion resistance. Citric and sulfuric acid solutions can be used to provide hard anodizing in a variety of aluminum alloys that have corrosion resistance and mechanical qualities on par with or better than traditional sulfuric acid anodizing.

Spray freeze dried cannabidiol with dipalmitoylphosphatidylcholine (DPPC) for inhalation and solubility enhancement

Pulmonary delivery is an efficient route of administration to deliver cannabidiol (CBD) due to the high bioavailability and fast onset of action. The major formulation challenge is the poor aqueous solubility of CBD. This study aimed to produce inhalable CBD powders with enhanced solubility and characterise their solid-state properties. CBD was spray freeze dried with mannitol or trehalose dihydrate with and without dipalmitoylphosphatidylcholine (DPPC). All four powders had acceptable yields at > 70 % with porous and spherical particles. The two crystalline mannitol powders contained less residual solvent than both amorphous trehalose ones. The addition of DPPC did not affect the crystallinity and residual solvent level of the powders. Instead, DPPC made the particles more porous, decreased the particle size from 19-23 µm to 11-13 µm, and increased CBD solubility from 0.36 µg/mL to over 2 µg/mL. The two DPPC powders were dispersed from a low resistance RS01 inhaler, showing acceptable aerosol performance with emitted fractions at 91-93 % and fine particle fractions < 5 µm at 34-43 %. These formulations can be used as a platform to deliver CBD and other cannabinoids by inhalation.

Investigation of metal concentration distribution and corresponding health exposure assessment of fabricated metal product manufacturers

The fabricated metal product industries were identified as producers of variable and heterogeneous pollution. Workers in these manufacturing facilities are exposed to multiple pollutants present at variable concentrations. Specific known adverse health effects include bladder cancer associated with metalworking fluid exposure and lung cancer associated with electroplating processes. To reduce the incidence of these adverse effects, the main challenge is to identify the most hazardous pollutants within this complex exposure environment and evaluate the corresponding health potentials. In this study, exposure indices were formulated to assess multiple metal exposures with the ultimate goal of providing relevant information for exposure reduction and control measures. Fifteen plants, including metal mold manufacturing, metal casting, and surface treatment plants, were investigated in terms of total concentration, summation of corresponding ratio to threshold limit value (STLVr), hazard index (HI), and incremental cancer risk. The results revealed that emissions of aluminum, iron, and manganese were primarily found in the metal mold manufacturing/casting plants, while emissions of chromium, nickel, and zinc were found in surface treatment plants. STLVr and HI were more useful than the total concentration for identifying hazardous metals, which were chromium and nickel, and could specify the facilities that were in need of control measures. As for cancer risk, the metal mold manufacturing/casting plants had lower risk than the surface treatment plants, and the contributing metals for these two plant types were cobalt and chromium, respectively. This study established a useful procedure to evaluate health hazards and cancer risk. The resulting information is useful for prioritizing mitigation control of multiple metal exposures.

Density functional theory study of the corrosion inhibition performance of 6-mercaptopurine and 6-thioguanine expired drugs toward the aluminium (111) surface

The potentiality of the 6-mercaptopurine (MP) and 6-thioguanine (TG) expired drugs toward the corrosion inhibition of the aluminium (Al) (111) surface was widely investigated using a series of density functional theory (DFT) calculations. A competition between the anti-corrosive features of the studied drugs in the gas and aqueous phases was conducted on both neutral and protonated forms by means of quantum mechanical descriptors. The results of the electrostatic potential analysis demonstrated the prominent nucleophilic nature of the sulfur and nitrogen atoms over the structures of the examined drugs. The frontier molecular orbital theory findings outlined the higher preferability of TG over MP as a corrosion inhibitor. Upon determining the most beneficial configurations of the MP/TG⋯Al (111) complexes, first-principles molecular dynamics simulations were executed. Interestingly, the competence of the TG drug in the corrosion inhibition process of Al (111) was more extensive than that of the MP one, which was confirmed by the interaction energy values of -1.79 and -1.64 eV, respectively. Upon obtaining the relaxed complexes, the effect of the presence of water solvent on the adsorption process was studied. These findings provide a foundation for developing green anti-corrosive inhibitors for the aluminium surface.

Study on the Influence of Surface Treatment Process on the Corrosion Resistance of Aluminum Alloy Profile Coating

This work focuses on different surface treatment processes of the 6061 aluminum alloy profile coatings in the construction industry, mainly including the sand powder film coating, the flat powder coating, the hard anodized film, and the ordinary heat-sealing oxidized coating. The corrosion resistance of the coated aluminum alloy in a 3.5 wt.% NaCl solution (pH 6.5-7.5) and the influence of different surface treatment processes on the corrosion resistance of different samples were studied by scanning electron microscope (SEM) and electrochemical workstation. The result shows that with the increase in corrosion time, the corrosion inhibition performance of the four coated aluminum alloy materials decreased significantly, and the order of decline is: sand powder film coating > hard anodized film > flat powder coating > ordinary heat-sealing oxidized coating. When corroded in a 3.5 wt.% NaCl solution for 2 h, the corrosion inhibition performances of the flat powder coating and ordinary heat-sealing oxidized coating are poor, while the inhibition performances of the sand powder film coating and hard anodized film are good, and the inhibition performance follows the following sequence: the sand powder film coating > hard anodized film> the flat powder coating > ordinary heat-sealing oxidized coating. When corroded in a 3.5 wt.% NaCl solution for 200 h, the corrosion inhibition performances of the sand powder film coating and the flat powder coating are poor, while the inhibition performances of hard anodized film and ordinary heat-sealing oxidized coating are good, and the inhibition performance follows the following sequence: hard anodized film > ordinary heat-sealing oxidized coating > the sand powder film coating > the flat powder coating.

Study of the anticorrosive behavior of samarium as a corrosion inhibitor in multilayer systems for aluminum alloy

This study shows a multilayer system based on samarium compounds as a corrosion inhibitor and a continuous SiO₂ layer by atmospheric pressure plasma jet (APPJ) as a protective barrier for aluminim alloy AA3003. One of the main advantages of this new coating is that it does not require vacuum chambers, which makes it easy to incorporate into production lines for automotive and aeronautical components, etc. The deposit of samarium corrosion inhibitor was carried out by two methods for comparison, the immersion method and a novel method to deposit corrosion inhibitor by APPJ. The multilayer system generated was homogeneous, continuous, adherent, and dense. The electrochemical behavior shows that the samarium compound was completely oxidized on coatings by the immersion method and favors corrosion. The APPJ deposition method shows a protective behavior against corrosion by both samarium compounds and silica depositions. XPS analyses show that the amount of Sm(OH)³ increases by the APPJ method compared with the immersion method since the spectrum of O1s is mainly controlled by OH. It was determined that the best processing times for the electrochemical study of the multilayer system were 40 min for the immersion method and 30 s for the APPJ method for the layer of corrosion inhibitor. In the case of the SiO₂ barrier layer by APPJ, the best time was 60 s of exposure to the plasma jet and this coating could reduce the corrosion of AA3003 by 31.42%.

Effects of Micro-Shot Peening on the Fatigue Strength of Anodized 7075-T6 Alloy

Micro-shot peening under two Almen intensities was performed to increase the fatigue endurance limit of anodized AA 7075 alloy in T6 condition. Compressive residual stress (CRS) and a nano-grained structure were present in the outermost as-peened layer. Microcracks in the anodized layer obviously abbreviated the fatigue strength/life of the substrate. The endurance limit of the anodized AA 7075 was lowered to less than 200 MPa. By contrast, micro-shot peening increased the endurance limit of the anodized AA 7075 to above that of the substrate (about 300 MPa). Without anodization, the fatigue strength of the high peened (HP) specimen fluctuated; this was the result of high surface roughness of the specimen, as compared to that of the low peened (LP) one. Pickling before anodizing was found to erode the outermost peened layer, which caused a decrease in the positive effect of peening. After anodization, the HP sample had a greater fatigue strength/endurance limit than that of the LP one. The fracture appearance of an anodized fatigued sample showed an observable ring of brittle fracture. Fatigue cracks present in the brittle coating propagated directly into the substrate, significantly damaging the fatigue performance of the anodized sample. The CRS and the nano-grained structure beneath the anodized layer accounted for a noticeable increase in resistance to fatigue failure of the anodized micro-shot peened specimen.

Enhanced corrosion resistance of epoxy-films on ultra-thin SiOx PECVD film coated laser surface melted Al-alloys

The influence of ultra-thin SiOx plasma deposited films on the corrosion resistance of adhesive films on a laser surface melted 7075 aluminium alloy was investigated by means of complementary techniques in comparison to the just laser surface melted state. Laser surface melting (LSM) was performed using a continuous wave mode at a wavelength of 1064 nm. Ultra-thin plasma polymer films were deposited from a mixture of hexamethyldisilane (HMDSO), oxygen, and argon by means of an audio-frequency glow discharge. The surface morphology and surface chemistry compositions were investigated by employing field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), diffuse reflection infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. The corrosion resistance of plasma polymer coated LSM Al-7075 alloy was studied using linear sweep voltammetry and electrochemical impedance spectroscopy in a chloride-containing electrolyte. The electrochemical studies showed an improved corrosion resistance for plasma film-coated alloys compared to the just laser surface melted state. To study the corresponding surface adhesive properties, the samples were coated with an epoxy amine adhesive. 90°-peel test under humid conditions confirmed the improvement of interfacial wet-adhesion corrosion tests showed a strong improvement of the delamination resistance of adhesives caused by the ultra-thin interfacial SiOx-films.

Changes in the Structure and Corrosion Protection Ability of Porous Anodic Oxide Films on Pure Al and Al Alloys by Pore Sealing Treatment

It is well known that corrosion protection of pure Al is enormously improved by the formation of porous anodic oxide films and by pore sealing treatment. However, the effects of anodizing and pore sealing on corrosion protection for Al alloys are unclear, because the alloying elements included in Al alloys affect the structure of anodic oxide films. In the present study, porous anodic oxide films are formed on pure Al, 1050-, 3003- and 5052-Al alloys, and pore sealing was carried out in boiling water. Changes in the structure and corrosion protection ability of porous anodic oxide films on pure Al and the Al alloys by pore sealing, were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). SEM observation showed that anodic oxide films formed on pure Al have a smooth surface after pore sealing, and that cracks are formed in anodic oxide films on 1050-, 3003- and 5052-aluminum alloys, after pore sealing. Corrosion protection after pore sealing increased with anodizing time on pure Al, but only slightly increased with anodizing time on the Al alloys.

Analysis of the Extrusion Process of Aluminium Alloy Profiles

The paper presents an analysis of the results of numerical tests of the extrusion process of structural panels made of the 5xxx and 6xxx series aluminium alloys in a designed split die. The obtained products are intended for innovative superstructures of special car bodies. The main purpose of the research was the designed split die and numerical simulations and analysis of test results to determine the parameters of the extrusion process. The distribution of stress intensity, strain, strain rate, and temperature in the extruded metal was analysed for two different speeds of the punch movement. On the basis of the analysis of the distribution of stress values occurring in the extrusion process, the conditions enabling the real process of extrusion of the panel profile in industrial conditions in the designed split die were determined. It was shown that panel sections can be produced from ingots with a length of 770 mm on a press with a pressure of 35 MN (12").

Layered double hydroxides for corrosion-related applications—Main developments from 20 years of research at CICECO

This work describes the main advances carried out in the field of corrosion protection using layered double hydroxides (LDH), both as additive/pigment-based systems in organic coatings and as conversion films/pre-treatments. In the context of the research topic “Celebrating 20 years of CICECO”, the main works reported herein are based on SECOP’s group (CICECO) main advances over the years. More specifically, this review describes structure and properties of LDH, delving into the corrosion field with description of pioneering works, use of LDH as additives to organic coatings, conversion layers, application in reinforced concrete and corrosion detection, and environmental impact of these materials. Moreover, the use of computational tools for the design of LDH materials and understanding of ion-exchange reactions is also presented. The review ends with a critical analysis of the field and future perspectives on the use of LDH for corrosion protection. From the work carried out LDH seem very tenable, versatile, and advantageous for corrosion protection applications, although several obstacles will have to be overcome before their use become commonplace.

Incorporation of Phase Change Materials into the Surface of Aluminum Structures for Thermal Management

This article explores the concept of generating a porous anodic layer on the surface of a metallic component to host a phase change material (PCM) aiming to reduce the peak temperatures that the host structure will experience. The conditions to fabricate a porous anodic layer on top of an aluminum substrate were determined through varying anodization conditions: solution concentration, voltage employed, and anodization times. Pore sizes were characterized using scanning electron microscopy. The alkane n-eicosane was selected as PCM, introduced within the porous anodic annealed layer using vacuum impregnation and the thin film composite structure sealed. Epoxy resin and a metallic paste were tested as sealants. Thermal tests were performed to compare the behavior of aluminum alloy substrates anodized and sealed with and without PCM. The results showed pores with diameters in the 5-85 nm range, with average values that increased as the time of anodization was extended. The aluminum alloy impregnated with n-eicosane presents lowered surface peak temperatures during heating cycles than the samples that were only anodized or than the base alloy, demonstrating the potential of PCM incorporated in the superficial microstructure of anodic structures to manage, to a certain extent, peak transient thermal loads.

Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm2. After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm2 was the best, with corrosion current densities of 2 × 10-8 and 2 × 10-9 A/cm2. Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.

Comparison of 2D and 3D Plasma Electrolytic Oxidation (PEO)-Based Coating Porosity Data Obtained by X-ray Tomography Rendering and a Classical Metallographic Approach

In this work, the porosity of plasma electrolytic oxidation (PEO)-based coatings on Al- and Mg-based substrates was studied by two imaging techniques-namely, SEM and computer microtomography. Two approaches for porosity determination were chosen; relatively simple and fast SEM surface and cross-sectional imaging was compared with X-ray micro computed tomography (microCT) rendering. Differences between 2D and 3D porosity were demonstrated and explained. A more compact PEO coating was found on the Al substrate, with a lower porosity compared to Mg substrates under the same processing parameters. Furthermore, huge pore clusters were detected with microCT. Overall, 2D surface porosity calculations did not show sufficient accuracy for them to become the recommended method for the exact evaluation of the porosity of PEO coatings; microCT is a more appropriate method for porosity evaluation compared to SEM imaging. Moreover, the advantage of 3D microCT images clearly lies in the detection of closed and open porosity, which are important for coating properties.

The Role of Anodising Parameters in the Performance of Bare and Coated Aerospace Anodic Oxide Films

The anodising process parameters (voltage, temperature, and electrolyte) control the morphology and the chemical composition of the resulting anodic oxide film by altering the balance between oxide growth and oxide dissolution reactions. The porosity of the oxide film is reduced by the addition of tartaric acid to a sulfuric acid electrolyte, while anodising at elevated temperatures enhances oxide dissolution, leading to wider pores and rougher surfaces. No significant changes in the oxide chemical composition as a function of anodising parameters was found; in particular, no tartrate incorporation took place. The resistance of uncoated anodic oxide films against aggressive media and galvanic stress as a function of anodising parameters has been studied by electrochemical methods. Anodising in a mixed tartaric and sulfuric acid electrolyte improves the resistance of the anodic oxide against galvanic stress and aggressive media in comparison to sulfuric acid anodising processes. However, the corrosion protection performance of the anodic oxide films in combination with a corrosion-inhibitor loaded organic coating is not governed by the blank oxide properties but by the adhesion-enhancing morphological features formed during anodising at elevated temperatures at the oxide/coating interface.

Corrosion of Metal Alloys in Potassium Acetate Solutions for Liquid Desiccant Dehumidification and Air Conditioning

For commercial buildings, liquid desiccant air conditioners (LDACs) could provide up to 80% energy savings compared to high-efficiency vapor compression AC, but commonly utilized liquid desiccants are highly corrosive. This precludes the use of metallic components, necessitating specialized plastics and thereby driving up cost, weight, and limiting operational temperature and pressure ranges. Less corrosive alternatives are sought. Here, potassium acetate solutions are investigated as less-corrosive alternatives to the chloride salt solutions that are typically used in LDAC systems. Corrosion evaluations for a Cu alloy (C12200) and two Al alloys (Al3003 and Al1100) in both potassium acetate and chloride salt solutions are presented. We show that yearly corrosion rates are lower in potassium acetate solutions by up to three orders of magnitude. Active corrosion behavior is largely absent in potassium acetate solutions but is present in chloride salt solutions. Furthermore, solid corrosion products are observed in chloride salt solutions. Thus, we conclude that potassium acetate is a promising candidate as a less corrosive alternative liquid desiccant for LDAC systems with metallic components.

Effects of the Shot Peening Process on Corrosion Resistance of Aluminum Alloy: A Review

The high humidity of marine atmosphere and the existence of corrosive chloride ions lead to the premature corrosion failure of aluminum alloy components. The development of surface-strengthening technology provides an opportunity to prolong their service life spans. As a mature surface-strengthening technology, the shot peening process is widely used, owing to its advantages over other strengthening technologies, including its easy operation and high production rate. The shot-peened surface integrity depends on shot peening variables that introduces the thermomechanical effect to the deformed surface layer. When the inappropriate shot peening parameters are adopted, the shot-peened surface integrity could be deteriorated, which further weakens the corrosion performance of the surface. Therefore, it is essential to optimize shot peening process variables with the consideration of the material and its application. In this paper, the strengthening mechanism of the shot peening process was firstly elaborated, and then the effects of process parameters on the surface integrity of aluminum alloy were reviewed. The relationship between the surface integrity and corrosion resistance was also revealed. Two directions, including the application of the surface temperature rise during the shot peening process and the shot-peened surface roughening, are proposed.

Effect of Current Density Ramping on the Growth Rate and Structure of AA2024-T3

The presented study successfully demonstrated advantages of multistep anodization of AA2024—T3. Coating properties and morphology were studied in detail for five anodization processes: a conventional Base process with a constant applied current density and processes with current density applied in one (OS1 and OS2) and five (MS1 and MS2) steps at different magnitudes during the ramp period. Due to lower oxygen infusion, processes MS1 and MS2 produced a more intact coating with reduced porosity and enhanced abrasion resistance and hardness. The presented results clearly demonstrate that starting anodization at a low voltage and then slowly ramping current density will form coatings with a higher aluminum/oxygen ratio and enhanced properties over a shorter period of processing.

Review of Cr-Free Coatings for the Corrosion Protection of Aluminum Aerospace Alloys

Aluminum alloys are known to have many advantages (e.g., light weight and low cost) but they are not immune to corrosion. So, it is important to assess their corrosion behavior, in particular under atmospheric conditions. To protect aluminum alloys against corrosion, paints are generally applied onto the materials. Corrosion protection in the aerospace industry consists of a conversion or anodized coating, an inhibited primer, and a top-coat. Chromate conversion coating (CCC) and primers containing chromate pigments have been widely used in the aerospace industry over the last decades. However, new environmental regulations have led to major changes for aluminum corrosion protection. By limiting or prohibiting some chemicals, for instance Cr(VI), the European regulation REACH (Regulation on Registration Evaluation, Authorization and Restriction of Chemicals) has induced major changes to some of the finishing processes of aluminum alloys (e.g., chromate conversion, chromic acid anodizing, and chromate sealing). Interesting results have been obtained while seeking replacements for Cr(VI), for example, with the incorporation of cerium, lithium salt, or nanocontainers loaded with corrosion inhibitors in organic coatings. For several years, hybrid sol–gel coatings able to replace the pre-treatment and primer steps have been under development, showing interesting results. New prospects for the future involve the use of photopolymerization to reduce the energy-intensive heat treatment needed in sol–gel technology. It will also be necessary to test these new technologies in service conditions or in accelerated corrosion tests before being able to conclude on the real effectiveness of these coatings. This review summarizes the recent developments in Cr-free coatings for aluminum alloys. Their advantages and drawbacks are also discussed.

Growth of Anodic Layers on 304L Stainless Steel Using Fluoride Free Electrolytes and Their Electrochemical Behavior in Chloride Solution

Anodic layers have been grown on 304L stainless steel (304L SS) using two kinds of fluoride-free organic electrolytes. The replacement of NH₄F for NaAlO₂ or Na₂SiO₃ in the glycerol solution and the influence of the H₂O concentration have been examined. The obtained anodic layers were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and potentiodynamic polarization tests. Here, it was found that, although the anodic layers fabricated within the NaAlO₂-electrolyte and high H₂O concentrations presented limited adherence to the substrate, the anodizing in the Na₂SiO₃-electrolyte and low H₂O concentrations allowed the growth oxide layers, and even a type of ordered morphology was observed. Furthermore, the electrochemical tests in chloride solution determined low chemical stability and active behavior of oxide layers grown in NaAlO₂-electrolyte. In contrast, the corrosion resistance was improved approximately one order of magnitude compared to the non-anodized 304L SS substrate for the anodizing treatment in glycerol, 0.05 M Na₂SiO₃, and 1.7 vol% H₂O at 20 mA/cm² for 6 min. Thus, this anodizing condition offers insight into the sustainable growth of oxide layers with potential anti-corrosion properties.

Improving the Anti-Corrosion and Anti-Wear Performance of Anodic Coating on the Surface of AA 5052 via Hydro-Thermal Treatment

Hydro-thermal technology had been used to improve the anti-corrosion and anti-wear performance of anodizing coating on the surface of aluminium alloys. The micromorphology of the coating has been studied by SEM and results proved the coating had a compact structure. The element in the substrate had been characterized by EDS and results proved Fe had redissolved to the Al substrate. The crystalline structure of the coating had been studied by XRD and results proved the anodic coating could be transformed into η-, p- and γ-alumina. The electrochemical properties had been researched using an electrochemical workstation; results proved after the coating had been treated by hydro-thermal technology, its anti-corrosion properties could be improved. At the hydro-thermal temperature of 400 ℃, its open circuit voltage and impedance reached -0.46 V and 160 kΩ × cm2, respectively. The hardness of the coating had to be measured with an HVS-100 micro-hardness tester, with results proving that, after the hydro-thermal treatment, the hardness of the coating increased to 150 HV. The friction coefficient of the coating had been studied using a ball-on-disk tester, and the results proved it decreased to 0.46. The MMW-2 scratch tester had been used to measure the adhesion between the coating and substrate; results proved the coating had better adhesion with the substrate. The thermal conductivity of the coating had been studied by a heat conduction coefficient measurement device; results proved that it reached 11.2 W/m × K at a hydro-thermal temperature of 400 ℃, far higher than that of organic coating.

Surface and Tribological Properties of Oxide Films on Aluminium Alloy through Fly-Ash Reinforcement

Hard anodizing has proven to be a helpful surface treatment for aluminium alloy and typically accompanied by the growth of a porous and highly flawed oxide layer. The presence of pores on the oxide surface can be taken as an advantage in improving the surface properties. Fly-ash particles are high in SiO2 and Al2O3 content and can be utilized as inexpensive strengthening particles, which can increase the wear resistance and microhardness of composite material. It was noticed that limited research had been carried out in utilizing fly-ash as reinforcement on composite oxide coating as a wear resistance candidate. Thus, this study focused on reinforcing fly-ash on oxide coating and investigating its tribological performance. The composite oxide coating was grown on AA2017 aluminium alloy through anodizing process. To understand the effect of anodizing time and fly-ash content, the parameters were varied from 5–60 min and 0–50 g/L, respectively. The findings suggested that 60 min of anodizing time provides the highest thickness and surface roughness at 35 µm and 6.5 µm, respectively. Interestingly, composite oxide coating with 50 g/L fly-ash provides the highest coating thickness but has the lowest roughness at 52 μm and 8.2 μm, respectively. The composite oxide coatings are observed to reduce friction only for a limited time, despite their potential in significantly reducing the wear rate. The wear mechanism observed was adhesion, micro-crack, and delamination. The findings of this study are believed to provide insight on the potential of fly-ash to be a reinforcement for wear-reduction materials.

Effect of Chemical Surface Texturing on the Superhydrophobic Behavior of Micro-Nano-Roughened AA6082 Surfaces

Superhydrophobic surfaces on 6082 aluminum alloy substrates are tailored by low-cost chemical surface treatments coupled to a fluorine-free alkyl-silane coating deposition. In particular, three different surface treatments are investigated: boiling water, HF/HCl, and HNO3/HCl etching. The results show that the micro-nano structure and the wetting behavior are greatly influenced by the applied surface texturing treatment. After silanization, all the textured surfaces exhibit a superhydrophobic behavior. The highest water contact angle (WCA, ≈180°) is obtained by HF/HCl etching. Interestingly, the water sliding angle (WSA) is affected by the anisotropic surface characteristics. Indeed, for the HF/HCl and the HNO3/HCl samples, the WSA in the longitudinal direction is lower than the transversal one, which slightly affects the self-cleaning capacity. The results point out that the superhydrophobic behavior of the aluminum alloys surface can be easily tailored by performing a two-step procedure: (i) roughening treatment and (ii) surface chemical silanization. Considering these promising results, the aim of further studies will be to improve the knowledge and optimize the process parameters in order to tailor a superhydrophobic surface with an effective performance in terms of stability and durability.

Influence of Alloying Elements on the Mechanical Properties of Anodized Aluminum and on the Adhesion of Copper Metallization

The active development of the power electronics market and a constant increase in the prices of components require new materials and approaches, including a power module packaging technology. The use of aluminum instead of copper in the power module baseplate is an interesting and promising solution. The insulated metal baseplate is one of the most extensively developed technologies nowadays. The object of this study is an insulated metal substrate based on anodized aluminum. The main goal of the article is the comparison of copper topology adhesion to an anodized aluminum oxide layer formed on different aluminum alloys with aluminum content of at least 99.3 wt %. Peel test and pull-off adhesions showed a twofold difference for both aluminum alloys. The high ordered defect-free anodized alumina formed on alloys with copper content of 0.06 wt % had a mean pull-off adhesion of 27 N/mm² and hardness of 489 HV. In the case of the alloy with copper content of around 0.15 wt %, it had hardness of 295 HV and a mean pull-off adhesion of 12 N/mm². The results of our microstructure investigation showed that anodized alumina based on alloys with copper content of around 0.15 wt % is fragile due to spherical holes. Summing up the results, it can be concluded that not all initial impurities are critical for anodized alumina, but some, specifically copper, dramatically decreased the mechanical properties of anodized alumina.

Incorporation of Ions into Nanostructured Anodic Oxides-Mechanism and Functionalities

Anodic oxidation of metals leads to the formation of ordered nanoporous or nanotubular oxide layers that contribute to numerous existing and emerging applications. However, there are still numerous fundamental aspects of anodizing that have to be well understood and require deeper understanding. Anodization of metals is accompanied by the inevitable phenomenon of anion incorporation, which is discussed in detail in this review. Additionally, the influence of anion incorporation into anodic alumina and its impact on various properties is elaborated. The literature reports on the impact of the incorporated electrolyte anions on photoluminescence, galvanoluminescence and refractive index of anodic alumina are analyzed. Additionally, the influence of the type and amount of the incorporated anions on the chemical properties of anodic alumina, based on the literature data, was also shown to be important. The role of fluoride anions in d-electronic metal anodizing is shown to be important in the formation of nanostructured morphology. Additionally, the impact of incorporated anionic species, such as ruthenites, and their influence on anodic oxides formation, such as titania, reveals how the phenomenon of anion incorporation can be beneficial.

Corrosion Behavior of AA2055 Aluminum-Lithium Alloys Anodized in the Presence of Sulfuric Acid Solution

The aim of this work was to evaluate the corrosion behavior of the AA2055 Aluminum-lithium alloy anodized in a sulfuric acid (H2SO4) bath, varying the current density of 0.19 and 1 A·cm−2 and why the sealing solution was water (H2O) and sodium dichromate (Na2Cr2O7). Anodized samples were exposed to a 10 vol.% H2SO4 solution and the electrochemical technique used was electrochemical impedance spectroscopy. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to characterization of the anodizing layer, determinate morphology and thickness of coatings. The Na2Cr2O7 sealing solution tends to increase the charge transfer resistance and produces a more homogeneous and compact passive oxide layer, and imparts a corrosion inhibition protection to the AA2055. SEM observations indicated that the morphology and thickness of the anodic films formed on AA2055 aluminum-lithium alloy anodized have the best results for both current densities.

Effect of Various Forms of Aluminum 6082 on the Mechanical Properties, Microstructure and Surface Modification of the Profile after Extrusion Process

This article presents a method of reusing aluminum scrap from alloy 6082 using the hot extrusion process. Aluminum chips from milling and turning processes, having different sizes and morphologies, were cold pressed into briquettes prior to hot pressing at 400 °C at a ram speed of 2 mm/s. The study of mechanical properties combined with observations of the microstructures, as well as tests of density, hardness and electrical conductivity were carried out. On the basis of the results, the possibility of using the plastic consolidation method and obtaining materials with similar to a solid ingot mechanical properties, density and electrical conductivity was proven. The possibility of modifying the surface of consolidated aluminum scrap was tested in processes examples: polishing, anodizing and coloring. For this purpose, a number of analyses and tests were carried out: comparison of colors on color histograms, roughness determination, SEM and chemical composition analysis. It has been proven there are differences in the surface treatment of the solid material and that of scrap consolidation, and as such, these differences may significantly affect the final quality.

Corrosion Behavior of AA 1100 Anodized in Gallic-Sulfuric Acid Solution

Sulfuric acid anodization is one of the common methods used to improve corrosion resistance of aluminum alloys. Organic acids can be added to the sulfuric acid electrolyte in order to improve the properties of the anodized aluminum produced. In this study, the use of gallic acid as an additive to the sulfuric acid anodization of AA1100 was explored. The effect of varying anodization current density and gallic acid concentration on the properties of anodized aluminum samples was observed using electrochemical impedance spectroscopy, linear polarization, and scanning electron microscopy. It was observed that the corrosion resistance of samples anodized in gallic-sulfuric acid solution at 10 mA·cm−2 is lower than samples anodized in sulfuric acid. It was also observed that higher anodization current density can lead to lower corrosion resistances for aluminum samples anodized in gallic-sulfuric acid solution. However, samples anodized at 5 mA·cm−2 and at a gallic acid concentration of 5 g·L−1 showed better corrosion performance than the samples anodized in sulfuric acid only. This suggests that the use of low amounts of gallic acid as an additive for sulfuric acid anodization can lead to better corrosion resistances for anodized aluminum.

Green Nanocoatings Based on the Deposition of Zirconium Oxide: The Role of the Substrate

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO₂ film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO₂ films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.