Plasma Electrolytic Oxidation Layer Research Articles

Electron Donor-Induced Electrochemical Reduction in Vanadate Anions to Enhance the Electrochemical Performance of Plasma Electrolytic Oxidation Layers

Electron Donor-Induced Electrochemical Reduction in Vanadate Anions to Enhance the Electrochemical Performance of Plasma Electrolytic Oxidation Layers

In-situ construction of functional carbon layer on the plasma electrolytic oxidation-pretreated Ti-6Al-4V alloy to enhance anti-static properties

Thermal control coatings prepared by plasma electrolytic oxidation (PEO) have shown broad application potential, especially in the aerospace field. However, the high insulation nature results in charge accumulation during the real application in spacecraft, aggravating the risk of electrostatic discharges and endangering equipment's safety. Herein, a functional anti-static thermal control composite coating on the surface of Ti-6Al-4V alloys was constructed by preparation route involving in-situ polymerization and carbonization of polydopamine (PDA) on the PEO layer. After the introduction of carbonized PDA, the composite coating retained the pristine porous structure of the PEO coating with improved crystallinity. Notably, the consecutive functional carbon layer ingrates the graphite nanocrystals and N-doped graphite to achieve high conductivity and then renders the composite coating with the lowest volume resistivity (6.04 × 104 Ω m) and surface resistance (9.0 × 107 Ω/□). Moreover, the two-step prepared coating showed high absorption (200–2500 nm, 0.929) and emission (2–16.6 μm, 0.921) along with excellent stability at high temperature (∼200 ℃) and low temperature (∼−200 ℃) even over 48 h. This contribution reveals a promising direction to widen the practical application of the PEO thermal control coating.

The Tribological Properties of Plasma Electrolytic Oxidation Layers Synthesized on Arc Spray Coatings on Aluminum Alloys in Contact with Various Friction Materials

Oxide layers on the surface of the aluminum alloys D16 and AMg6 and on arc coatings sprayed with electrode wires made of the alloys D16 and AMg6 were synthesized using plasma electrolytic oxidation (PEO). The microstructure, phase composition and micro-hardness of the PEO layers were studied. In addition to the two main phases (α-Al2O3 and γ-Al2O3), a small amount of a metastable crystalized Al2.427O3.64 phase was found in their structure. A comparison was made of the wear resistance and friction coefficients of the synthesized PEO layers during friction tests in pairs with other PEO layers, a galvanic chromium coating, cast iron, steels and bronze of the BrC30 type. The results of the friction tests for the various PEO layers on aluminum alloys in tribo-contact with high-hardness elements made of hardened or chrome-plated steel justify the possibility of their use in a friction pair. We experimentally showed the influence of glycerin additive in motor oil 15W30 on the change in the friction coefficient of the PEO layers synthesized on the aluminum alloys and on the arc-sprayed coatings on their surfaces in tribocouples with hardened steel.

Mechanism of plasma electrolytic oxidation in Mg3ZnCa implants: a study of double-layer formation and properties through nanoindentation

Plasma electrolytic oxidation (PEO), applied to light metals such as titanium, aluminum, and magnesium, creates a two-layer coating and has become increasingly important in metal coatings. However, due to the high voltage and temperature of the process, no online instrument could monitor the underlying mechanism. This paper presents a new image proving that the surface of PEO-coated Mg3ZnCa boiled during the process and argues that three hypotheses are involved in the PEO mechanism based on boiling caused by tolerating high voltage during the PEO process, which could explain the current‒voltage diagram of the process. Finally, nanoindentation was used to measure the elastic module and hardness of the PEO layers. The nanoindentation test results revealed the similarity of the elastic module of the outer porous layer and the primary alloy, with values of 40.25 GPa and 41.47 GPa, respectively, confirming that the outer porous layer corresponds to the cold plasma-gas phase formed during the PEO process.

Effects of dispersed α-Al2O3 particles into a cold-sprayed aluminium coating on its subsequent oxidation by the PEO process

The present study focused on the use of a duplex surface treatment combining cold-spray deposition and plasma electrolytic oxidation (PEO) to produce an aluminium metal matrix composite coating, including dispersed α-Al2O3 particles, with improved tribological properties. Al/α-Al2O3 composite coatings were first deposited by cold-spray, with various thickness and proportion in α-Al2O3 particles, and, then partially oxidized by PEO under various processing durations and sparking regimes (arcs or soft regime). The feasibility of cold-spraying thick, compact and adherent aluminium coatings containing well-dispersed α-Al2O3 particles (up to 14 vol%) was demonstrated in this work. It was also pointed out that the addition of hard α-Al2O3 particles into the spray composition tends to densify the deposited aluminium coating. This was related to a stronger peening effect which, in turn, decreases the growth kinetic of the subsequent PEO oxide layer. The presence of dispersed α-Al2O3 particles was found to promote the formation of the corundum alumina phase in the PEO oxide layer by triggering the transition to the soft sparking regime earlier. It was also observed that dispersed α-Al2O3 particles remain unaffected throughout the PEO oxide layers formed within the conventional arcs sparking regime while they undergo a morphological transformation within the specific soft sparking regime. This was explained by considering the different type of micro-discharges that initiate during each regime. Finally, sliding wear tests revealed that the incorporation of α-Al2O3 particles into the cold-sprayed coating resulted in a slight decrease in the friction coefficient and the wear rate of the produced PEO layers.

Functionalization of Plasma Electrolytic Oxidation/Sol–Gel Coatings on AZ31 with Organic Corrosion Inhibitors

In this investigation, the sol–gel method is employed along with a corrosion inhibitor to seal a plasma electrolytic oxidation (PEO) coating, aiming to improve the long-term corrosion resistance of the AZ31 Mg alloy. Following an initial screening of corrosion inhibitors, 8-hydroxyquinoline (8HQ) is incorporated into the hybrid PEO/sol–gel system using two methods: (i) post-treatment of the PEO layer through immersion in an inhibitor-containing solution; (ii) loading the inhibitor into the sol–gel precursor. The characterization includes scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), and water drop contact angle measurements. The rheological properties of the inhibitor-loaded sol–gel precursors are assessed by measuring flow curves. The corrosion processes are evaluated in a saline solution through electrochemical impedance spectroscopy (EIS) and immersion tests with unscratched and scratched specimens, respectively. The results demonstrate the successful incorporation of the inhibitor for both loading strategies. Regardless of the loading approach, systems containing 8HQ exhibit the most favourable long-term corrosion resistance.

Effect of electrolyte composition on the formation of PEO coatings on AA2024 aluminium alloy

Since the electrolyte composition plays a crucial role in the plasma electrolytic oxidation (PEO) coating formation process, a systematic and in-depth study was proposed to identify an electrolyte composition for fast PEO coating growth on AA2024 alloy. Different concentration ratios of mixed alkaline electrolytes (hydroxide, silicate and phosphate) were investigated. PEO process was conducted at low constant current density of 50 mA/cm2, which is intended for lowering the energy consumption. Results demonstrated that the breakdown voltage of PEO coatings is directly proportional to the logarithm of electrolyte resistivity. The coating growth mechanism showed two main directions. The thickening of the coating mainly depends on the rapid deposition of electrolyte compounds in Si-based electrolyte, and the coating growth occurs mainly towards the electrolyte/coating interface. Contrary, in OH-, and P-based electrolytes, the inward coating growth was dominating mainly by substrate oxidation. A variety of phases as a function of different electrolyte compositions and final voltages were observed. With high final voltages (over 470 V) for coatings produced in mixed electrolytes with low concentrations of hydroxide, silicate or phosphate (2 and 6 g/L), γ-Al2O3 crystalline phase predominates in the PEO layer composition. However, only a low efficiency of coating growth can be reached. In the electrolytes with high silicate concentrations accompanied by an increase of phosphate concentration, the final voltage is around 455 V and the coating composition is dominated by an amorphous phase in combination with crystalline mullite and γ-Al2O3. High silicate-phosphate contents (18–24 g/L) in mixed electrolytes with low final voltages of about 360 V results in a fully amorphous PEO layer and significantly increases coating thickness. A combination of low content of hydroxide, high silicate with increasing content of phosphate in mixed electrolyte increases the coating thickness, and improves the density and uniformity of the overall PEO layers.

Hierarchical Hybrid Coatings with Drug-Eluting Capacity for Mg Alloy Biomaterials.

A hierarchical hybrid coating (HHC) comprising a ceramic oxide layer and two biodegradable polymeric (polycaprolactone, PCL) layers has been developed on Mg3Zn0.4Ca cast alloy in order to provide a controlled degradation rate and functionality by creating a favorable porous surface topography for cell adhesion. The inner, ceramic layer formed by plasma electrolytic oxidation (PEO) has been enriched in bioactive elements (Ca, P, Si). The intermediate PCL layer sealed the defect in the PEO layer and the outer microporous PCL layer loaded with the appropriate active molecule, thus providing drug-eluting capacity. Morphological, chemical, and biological characterizations of the manufactured coatings loaded with ciprofloxacin (CIP) and paracetamol (PAR) have been carried out. In vitro assays with cell lines relevant for cardiovascular implants and bone prosthesis (endothelial cells and premyoblasts) showed that the drug-loaded coating allows for cell proliferation and viability. The study of CIP and PAR cytotoxicity and release rate indicated that the porous PCL layer does not release concentrations detrimental to the cells. However, complete system assays revealed that corrosion behavior and increase of the pH negatively affects cell viability. H2 evolution during corrosion of Mg alloy substrate generates blisters in PCL layer that accelerate the corrosion locally in crevice microenvironment. A detailed mechanism of the system degradation is disclosed. The accelerated degradation of the developed system may present interest for its further adaptation to new cancer therapy strategies.

Evaluating the energy consumption, structural, and corrosion resistance properties of photocatalytic TiO2-based PEO coatings on pre-anodized AA2024-Al

In this work, a thorough investigation is carried out to develop plasma electrolytic oxidation (PEO) coatings on pre-anodized AA2024-Al at various concentrations of TiO2 dispersed in a water base electrolyte of sodium silicate, sodium phosphate dodecahydrate, and potassium hydroxide in order to determine the effect of TiO2 incorporation on energy consumption, coating growth, surface morphology, photocatalytic behavior, and associated long-term corrosion resistance properties. The pre-anodization time is controlled to develop a 20.0 ± 1.6 µm thick anodic film, where a reduction of ∼66 % in the energy consumption (kW h m2 µm−1) is observed compared to the PEO developed without pre-anodic precursors, while the addition of TiO2 nanoparticles (Degusa-P25) into the base electrolyte results in reductions of ∼68 %, 64 %, and 51 % for the PEO coatings developed at 2, 5 and 10 g/L TiO2-based electrolyte, respectively. TiO2-based PEO process is found to improve growth rate, coating microstructure with lower porosity and defects, and reduce energy consumption (for a coating of a given thickness). The photocatalytic activity of TiO2 was investigated by photodegrading phenol under simulated sunlight conditions, where the higher concentration of TiO2 nanoparticles affected the phenol photodegradation efficiency, whereas the effectiveness of TiO2 concentration on the corrosion resistance properties of PEO coatings was observed with nearly one-order higher impedance magnitude (after 336 h) than the PEO layer without TiO2.

Effect of PEO interlayer on oxidation behavior of PEO/Cr composite coating on Zr–1 Nb alloy in 1200 °C steam

The PEO/Cr composite coating on Zr–1 Nb alloy prepared by plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) technologies exhibited good oxidation resistance in 1200 °C steam. The PEO interlayer was gradually dissolved by Zr substrate, and M-ZrO2 to Zr3O phase transformation occurred, but it still moderated the inward oxygen diffusion and the inter-diffusion of Cr and Zr to some extent. Moreover, the PEO interlayer suppressed the formation of ZrCr2 in Zr substrate and ZrCr2O5 secondary phases in its steam oxide layer. The PEO layer and steam oxide layer could prevent from hydrogen permeation into the Zr substrate.

Morphology-Dependent Immunomodulatory Coating of Hydroxyapatite/PEO for Magnesium-Based Bone Implants.

One of the most critical issues concerning orthopedic implants is the risk of chronic inflammation, which poses a threat to the bone healing process. Osteo-immunomodulation plays a pivotal role in implant technology by influencing proinflammatory and anti-inflammatory responses, ultimately promoting bone healing. This study aims to investigate the morphology-dependent osteo-immunomodulatory properties of a hydroxyapatite (HA)/plasma electrolytic oxidation (PEO)-coated WE43 alloy. In this context, following the PEO process with various operational parameters (duty cycles of 50-40, 50-20, 70-40%, and frequencies of 0.5, 0.8, and 1 kHz), a layer of HA was applied as the top coating using a straightforward hot-dip process. The results revealed the formation of the PEO layer with distinct morphologies and pore sizes, depending on the operational parameters. Specifically, a uniform PEO coating with small pore sizes (5.2-5.3 μm) led to the creation of plate-like HA particles, while a random-like HA structure formed on nonuniform surfaces with large pores (7.0-11.1 μm) of PEO. Moreover, it was observed that the plate-like HA coating exhibited higher adhesion strength than the random one (classified as class 2 vs class 3 based on cross-cut standards). Furthermore, electrochemical impedance spectroscopy (EIS) and polarization studies confirmed a substantial increase in the polarization resistance (680 kΩ) and total impedance (48 559.6 Ω) for the plate-like HA/PEO as compared to the substrate (an increase of 1511-fold and 311-fold, respectively) and the random HA/PEO samples (an increase of 85-fold and 18-fold, respectively). In addition, compared to random HA coatings, there was a significant enhancement in the viability (150% control vs 96% control), proliferation, and differentiation of MG63 cells when exposed to plate-like HA coatings. Moreover, surface morphology and chemistry pronouncedly impacted macrophages' viability, morphology, and phenotype. Notably, plate-like HA coatings resulted in a higher upregulation of BMP-2 and TGF-β than proinflammatory cytokines (IL-6 and M-CSF), indicating a polarization of macrophage type 1 (M1) toward type 2 (M2). In summary, the bilayer HA/PEO coating exhibited remarkable osteo-immunomodulatory activity, making it highly appealing for use in bone implant applications.

Self-healing plasma electrolytic oxidation (PEO) coating developed by an assembly of corrosion inhibitive layer and sol-gel sealing on AA2024

The inherent porous structure of PEO coatings is regarded as a drawback for long-term protection. In this investigation, the presence of pores and defects in the PEO coating was exploited as reservoirs for corrosion inhibitors to generate self-healing properties on AA2024. Smart coating systems were fabricated on the PEO layer in which 8-hydroxyquinoline (8-HQ) and benzotriazole (BTA) were employed as corrosion inhibitive layers followed by a sol-gel sealing. The protective performance relies on the mechanical interlocking between the sol-gel coating and the sublayer plus the sealing ability of the sol-gel in the presence of the intermediate layer.

TiO2-CoFe2O4 and TiO2-CuFe2O4 Composite Films: A New Approach to Synthesis, Characterization, and Optical and Photocatalytic Properties

Here, we report a new simple and fast method of cobalt and copper ferrites film fabrication on the Ti/TiO2 surface. The approach is based on the deposition of gelatin gel containing copper and cobalt nitrates on the surface of porous oxide-silicon coatings on titanium obtained by plasma electrolytic oxidation (PEO) followed by two-stage annealing at 300 °C and 800 °C to yield ferrite films with good adhesion to PEO layer. The presence of Co/Cu ferrite phases was confirmed by EDX analysis, XRD, and Mössbauer spectroscopy. TiO2-CoFe2O4 and TiO2-CuFe2O4 composite films have excellent performance in the photocatalytic degradation of indigo carmine as a model dye at pH 3 under UV and visible irradiation. The suggested approach to obtain ferrite/TiO2 composite films is promising for the development of magnetic materials, sensors, catalysts, and photocatalysts for various applications.

Optimization of the PEO process for in-situ synthesis of SiO2 and hydroxyapatite on Mg alloy and assessment of biodegradation and bioactivity

In the current study, a MgO-based bioactive coating consisting of silicon dioxide (SiO2) and hydroxyapatite (HA) was fabricated on the surface of AZ31 magnesium alloy through the plasma electrolytic oxidation (PEO) method. To achieve the goal, the process conditions were optimized in an electrolyte containing 5 g/L Na3PO4.12H2O, 15 g/L Na2SiO3.9H2O, and 10 g/L C3H7O6CaP with a pH of 12.5 and an electrical conductivity of 30 mS.cm−1. Thereafter, silicon dioxide and hydroxyapatite were simultaneously synthesized in-situ over the PEO process for 10min at an operating voltage of 370 V. The percentage of surficial open porosity of the relevant PEO layer was estimated to be approximately 10.30 % using the ImageJ software. Furthermore, in-vitro corrosion and bioactivity assessments of PEO layer were conducted in the simulated body fluid (SBF) at 37 °C with immersion intervals of up to 10 days. The results of electrochemical impedance spectroscopy (EIS) indicated that the PEO coating containing both SiO2 and HA maintained its protective performance against corrosion over the entire 7 days of immersion in the SBF, whereas the corrosion resistance of the PEO layer with only the synthesized SiO2 experienced a significant decline after 3 days of immersion. Assessment of in-vitro bioactivity over 10 days of immersion in the SBF revealed that the sample with synthesized SiO2 and hydroxyapatite in its PEO layer exhibited a higher potential for hydroxyapatite deposition on the surface compared to SiO2-containing PEO coating.

Comparison of Tribological Characteristics of AA2024 Coated by Plasma Electrolytic Oxidation (PEO) Sealed by Different sol–gel Layers

The application of sol–gel on plasma electrolytic oxidation (PEO) coatings can increase wear resistance by sealing the surface defects such as pores and cracks in the outer layer of the PEO layer and strengthen the coating. Four different sol–gel formulations based on precursors—(3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltriethoxysilane (MTES), methacryloxypropyltrimethoxysilane (MAPTMS), (3-aminopropyl)triethoxysilane (APTES), and zirconium(IV) propoxide (ZTP) along with tetraethoxysilane (TEOS)—were used to seal PEO pores, and the samples were tested tribologically. A sliding reciprocating tribometer was used to carry out a wear test with an alumina ball as the counter body in two different conditions: (a) 2.5 N load for 20 min, and (b) 3 N load for 40 min. The coefficient of friction and wear rate as volume loss per unit sliding length were obtained for all sol–gel-sealed specimens and unsealed PEO-coated and bare AA2024 substrate. 3D mechanical profilometer surface scans were used to compare the depth of wear traces. The elemental color mapping using SEM and EDS revealed that silicon remains present in the wear tracks of PEO coatings sealed with sol–gel layers containing GPTMS (PSG) and ZTP (PSG-ZT). GPTMS (PSG) was able to fill the pores of the PEO layer efficiently due to its cross-linked network. Moreover, sol–gel containing ZTP (PSG-ZT) was deposited as a thick layer on top of the PEO layer which provided good lubrication and resistance to wear. However, other sol–gel formulations (PSG-MT and PSG-AP) were worn out during tests at a higher load (3 N). The most stable friction coefficient (COF) and specific wear rates were observed with sol–gels with GPTMS and ZTP.

Mechanical and corrosion-resistant coatings prepared on AZ63 Mg alloy by plasma electrolytic oxidation

Using the plasma electrolytic oxidation (PEO) process conducted in galvanostatic mode at a constant current density of 0.2 A/cm2 in aqueous aluminate, silicate, and phosphate electrolytic solutions, we successfully produced magnesium oxide coatings (up to 182 μm) on AZ63 alloy. Structural, chemical composition, and morphological evaluations of the coatings were investigated by XRD, XPS, and SEM. The results indicated that mixed-crystalline magnesium oxide grown on pure AZ63 alloy forms porous 8–30 μm PEO layers with increased hardness and improved corrosion resistance. At the same time, values of 26.9 GPa and 2.0 μA/cm2 yield noticeable performance characteristics.

Influence of Plasma Electrolytic Oxidation of Cast Al-Si Alloys on Their Phase Composition and Abrasive Wear Resistance

The microhardness and abrasive wear resistance of cast Al-Si alloys after plasma-electrolytic oxidation (PEO) in a weakly alkaline basic electrolyte (3 g/L KOH + 2 g/L Na2SiO3), as well as with the addition of H2O2, were determined. X-ray analysis showed that the PEO layer comprises two oxide phases, namely α-Al2O3 and γ-Al2O3, as well as sillimanite -Al2O3 · SiO2 and a small percentage of mullite -3 Al2O3 · 2SiO2. Silicon is present in the structure of the oxide layer, and its percentage is greater than that of the alloys in their initial state. It has been shown that the characteristics of PEO layers on AK9 and AK12 silumins synthesized in an electrolyte of basic composition increase (microhardness up to 900–1000 HV and abrasive wear resistance by 14–57 times). The formation of PEO layers in the base electrolyte with the addition of 3 g/L of hydrogen peroxide intensifies the synthesis process and promotes the formation of high-temperature oxide phases (in particular, corundum). The abrasive wear resistance of both silumins with PEO layers synthesized in such an electrolyte increases by 30–70%.

A Superior Corrosion Protection of Mg Alloy via Smart Nontoxic Hybrid Inhibitor-Containing Coatings.

The increase of corrosion resistance of magnesium and its alloys by forming the smart self-healing hybrid coatings was achieved in this work in two steps. In the first step, using the plasma electrolytic oxidation (PEO) treatment, a ceramic-like bioactive coating was synthesized on the surface of biodegradable MA8 magnesium alloy. During the second step, the formed porous PEO layer was impregnated with a corrosion inhibitor 8-hydroxyquinoline (8-HQ) and bioresorbable polymer polycaprolactone (PCL) in different variations to enhance the protective properties of the coating. The composition, anticorrosion, and antifriction properties of the formed coatings were studied. 8-HQ allows controlling the rate of material degradation due to the self-healing effect of the smart coating. PCL treatment of the inhibitor-containing layer significantly improves the corrosion and wear resistance and retains an inhibitor in the pores of the PEO layer. It was revealed that the corrosion inhibitor incorporation method (including the number of steps, impregnation, and the type of solvent) significantly matters to the self-healing mechanism. The hybrid coatings obtained by a 1-step treatment in a dichloromethane solution containing 6 wt.% polycaprolactone and 15 g/L of 8-HQ are characterized by the best corrosion resistance. This coating demonstrates the lowest value of corrosion current density (3.02 × 10-7 A cm-2). The formation of the hybrid coating results in the corrosion rate decrease by 18 times (0.007 mm year-1) as compared to the blank PEO layer (0.128 mm year-1). An inhibitor efficiency was established to be 83.9%. The mechanism of corrosion protection of Mg alloy via smart hybrid coating was revealed.

Plasma electrolytic oxidation treatments for bimetallic substrates enabling sustainable procedures for automotive painting

Magnesium- or Aluminium based lightweight alloys are increasingly utilized in the automotive sector. To ensure corrosion protection of these lightweight alloys, plasma electrolytic oxidation (PEO) can be utilized to from protective layers in an efficient manner on those lightweight alloy materials. In real vehicles often a blend of joined materials is used and it must be evaluated if the joined material combinations can be subjected directly to corrosion protection treatments or if separated treatments are necessary for different materials, which would significantly enhance production costs. In this study we investigate the feasibility of the PEO process for already joined Al-alloy and Mg-alloy materials. Special focus is put on the compatibility with subsequent cathodic dip coating (CDC) processes and the corrosion resistance of the coated materials was evaluated, which is highly relevant for applications in vehicles. We provide characterization of the formed PEO layers and could demonstrate different layer formation behaviour and composition, depending on the alloy material. It could be also shown that Mg-alloy and Al-alloy materials joined by gluing and riveting can be subjected to the PEO process, resulting in effective, simultaneous protective layer formation on both materials. Finally, it is demonstrated that the joined and PEO treated materials exhibit excellent compatibility with the cathodic dip coating process and that previous PEO treatment results in better corrosion resistance also for cathodic dip coated samples.

A comparative study of different sol-gel coatings for sealing the plasma electrolytic oxidation (PEO) layer on AA2024 alloy

Owing to the inherent porosity of the coatings produced through the PEO process, the application of sol-gel coatings as a post-treatment has drawn immense attention thanks to their eco-friendly and reliable protective characteristics. Various parameters affect their performance, and the type of sol-gel precursors plays a significant role. In this study, various sol-gel precursors were used to prepare four types of PEO/sol-gel coating systems followed by an investigation of their sealing ability and corrosion resistance properties on AA2024 alloy. The corrosion prevention performance of the coatings was studied by electrochemical impedance spectroscopy (EIS) along with Scanning Vibrating Electrode Technique (SVET) analyzes. Some chemical characterization tests, such as Fourier Transform Infrared Spectroscopy (FT-IR) and rheology measurement, affirmed the influence of the sol-gel chemical composition on its compactness and the network viscosity. The distinctive sealing ability of different sol-gel coatings for the defects and pore filling of the PEO layer was visualized by Scanning Electron Microscope (SEM). To this end, different sol-gel formulations and various sol-gel network properties accordingly caused dissimilar sealing features for the PEO pores and, subsequently, the corrosion resistance of the duplex PEO/sol-gel coating is widely dependent on the used sol-gel precursors.