Micro-arc Oxidation Film Research Articles

Fabrication and Characterization of Micro-Arc Oxidation Films on β-Titanium Alloy in Silicate and Silicate/Glycerin Electrolyte

Micro-arc oxidation (MAO) films were fabricated on the Ti-39Nb-6Zr alloy at different voltages in the silicate and silicate/glycerin electrolyte. Their morphology, phase structure and composition were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the glycerin additive in the silicate electrolyte improved the compactness of the MAO film. The corrosion resistance was evaluated, and the influence of glycerin additive in electrolyte on the growth of micro-arc oxidized film was revealed by optical emission spectra.

Long-term superhydrophobic, antibacterial, and corrosion-resistant Ag-loaded LiAl-LDH composite coating grown in-situ on MAO coating

This study successfully prepared long-term superhydrophobic, antibacterial, and corrosion-resistant lithium aluminum layered double hydroxide (LiAl-LDH) modified with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) through a hydrothermal reaction. The LiAl-LDH was in situ grown on the micro-arc oxidation (MAO) film and loaded with Ag nanoparticles. The results showed that at a hydrothermal reaction temperature of 150 °C, LiAl-LDH effectively filled the microscopic defects of the MAO coating, significantly enhancing its hydrophobicity. After PFOTES treatment, the water contact angle remained above 150° even after 75 days of immersion in simulated seawater. Additionally, the introduction of Ag+ notably improved the antibacterial properties of the coating. Electrochemical tests indicated that the corrosion resistance of the coating increased with higher hydrothermal temperatures. The corrosion current density of the coating obtained at 150 °C was measured at 2.30 × 10−9 A∙cm−2, which is two orders of magnitude lower than that obtained at 100 °C. Following hydrophobic modification, the corrosion current density decreased further, and after 50 days of immersion in simulated seawater, the |Z|0.01Hz value remained above 108 Ω·cm2, demonstrating excellent corrosion resistance. This study provides important experimental and theoretical foundations for developing metal surface protective coatings with broad application prospects.

Effect of Aluminum by Magnetron Sputtering on the Micro-Arc Oxide Film Layer of Titanium Alloy

Effect of Aluminum by Magnetron Sputtering on the Micro-Arc Oxide Film Layer of Titanium Alloy

Improving the Corrosion Resistance of Micro-Arc Oxidization Film on AZ91D Mg Alloy through Silanization

Improving the Corrosion Resistance of Micro-Arc Oxidization Film on AZ91D Mg Alloy through Silanization

Hardness Distribution and Growth Behavior of Micro-Arc Oxide Ceramic Film with Positive and Negative Pulse Coordination.

Micro-arc oxidation (MAO) is a promising technology for enhancing the wear resistance of engine cylinders by growing a high hardness alumina ceramic film on the surface of light aluminum engine cylinders. However, the positive and negative pulse coordination, voltage characteristic signal, hardness distribution characteristics of the ceramic film, and their internal mechanism during the growth process are still unclear. This paper investigates the synergistic effect mechanism of cathodic and anodic current on the growth behaviour of alumina, dynamic voltage signal, and hardness distribution of micro-arc oxidation film. Ceramic film samples were fabricated under various conditions, including current densities of 10, 12, 14, and 16 A/dm2, and current density ratios of cathode and anode of 1.1, 1.2, and 1.3, respectively. Based on the observed characteristics of the process voltage curve and the spark signal changes, the growth of the ceramic film can be divided into five stages. The influence of positive and negative current density parameters on the segmented growth process of the ceramic film is mainly reflected in the transition time, voltage variation rate, and the voltage value of different growth stages. Enhancing the cathode pulse effect or increasing the current density level can effectively shorten the transition time and accelerate the voltage drop rate. The microhardness of the ceramic film cross-section presents a discontinuous soft-hard-soft regional distribution. Multiple thermal cycles lead to a gradient differentiation of the Al2O3 crystal phase transition ratio along the thickness direction of the layer. The layer grown on the outer surface of the initial substrate exhibits the highest hardness, with a small gradient change in hardness, forming a high hardness zone approximately 20-30 μm wide. This high hardness zone extends to both sides, with hardness decreasing rapidly.

Research on the growth behavior of scanning microarc oxide film

Research on the growth behavior of scanning microarc oxide film

Effects of Electrolyte Compositions and Electrical Parameters on Micro-Arc Oxidation Coatings on 7075 Aluminum Alloy

Aluminum alloys are widely used in a variety of industries nowadays for their high strength-to-weight ratio, good formability, low density, and recyclability. However, their poor corrosion and wear resistance properties restrict their applications. This study investigated the effects of electrical parameters and electrolyte compositions on the microstructures of micro-arc oxidation (MAO) film on a 7075 Al alloy substrate. The morphology, microstructure, and compositions of the MAO coatings were characterized using a scanning electron microscope (SEM), X-ray diffraction (XRD), and an electron probe micro-analyzer (EPMA). Furthermore, measurements of microhardness, corrosion resistance, and wear resistance were also conducted. The cathodic current and duty ratio are proportional to film thickness, which consequently improves the wear and corrosion resistance. The microstructural observations of the aluminate-based coatings revealed that increasing cathodic current reduces the pancake-like structures, and a lot of small pores appear on the top of the coatings, which makes the surface smoother. Moreover, the aluminate-based coatings are mainly composed of α-Al2O3 and γ-Al2O3, while the silicate-based coatings mainly consist of γ-Al2O3 and a small amount of α-Al2O3 phase. Due to the phase compositions, the microhardness of the aluminate-based coatings can reach 1300~1500 HV and exhibit better wear resistance than silicate-based coatings.

Growth pattern of soft-spark micro-arc oxide coating on titanium alloy in silicon anion electrolyte

Soft-spark micro-arc oxidation (MAO) is considered a potential solution for eliminating the porosity on the surface coating of titanium alloys during the MAO process. However, the mechanisms behind soft-sparking and the growth of coatings on Ti alloys are not yet fully understood. This study aimed to investigate the growth pattern of soft-spark MAO coating on titanium alloys by using sodium silicate as the electrolyte and manipulating the soft-sparking duration. The research focused on analyzing the positive and negative pulse voltage-time response curves, surface micromorphology, surface composition, cross-sectional structure, phase composition, dynamic potential polarization curve, microhardness, and thickness growth curve during the soft-spark process. The research findings revealed that soft spark discharges occurred in the plasma atmosphere near the surface of the external porous layer. The sparks penetrated the weak points of the amorphous interface layer (existing between the MAO coating and the substrate), forming filamentary discharges within the coating. This phenomenon led to the formation of a significant amount of rutile phases and bubble pores within the soft-spark coating, promoting the expansion of soft-sparks into the coating and facilitating the growth of the soft-spark coating. While the inner hardness of the soft-spark MAO film reached 1146 HV, the plasma atmosphere discharge also led to the formation of numerous filamentary channels and gas pores within the coating. Consequently, the coating's corrosion resistance did not show any improvement.

Effect of oxidation time on the structure and properties of Ti–25Nb–3Zr–2Sn–3Mo titanium alloy microarc oxide film layer

In order to improve various properties of medical titanium alloys, Ti–3Zr–2Sn–3Mo–25Nb titanium alloy specimens were subjected to microarc oxidation (BMAO) in 0.1 mol/l sodium tetraborate electrolyte to cover the substrate with a micro-nano double-graded structured coating. The effect of oxidation time on the microstructure, physical phase, hardness, corrosion resistance, and wettability of the micro-nano film layer was investigated. The results show that the microporous size of the film increases with the increase in oxidation time, and the hardness of the BMAO film increases with the increase in oxidation time; the corrosion resistance of the BMAO film is better than that of the substrate, and the self-corrosion potential is the largest at 14 min of oxidation time, reaching −0.1349 V, which is 65% higher than that of the substrate, and the self-corrosion current is the lowest, at 1.1376 × 10−9 A cm−2, which is one order of magnitude lower than that of the substrate; the micro-nano film layer exhibits superhydrophilicity, which increases and then decreases with time, and the contact angle is the smallest at 6 min of oxidation time, 4.4°, which is one order of magnitude lower than that of the substrate, 73.75°.

Simulation and Optimization of the Auxiliary Cathode for Inter-Electrode Discharge Electric Field in Microarc Oxidation.

Currently, research on the edge effect issue in the micro-arc oxidation process primarily focuses on investigating process conditions and enhancing additives. However, some scholars have utilized finite element analysis software to simulate the edge effect during the simulation process, overlooking the investigation of the morphology of the auxiliary cathode. This study analyzes the growth characteristics of the oxide film on aluminum alloy 2A12 during micro-arc oxidation. Additionally, the inter-electrode discharge electric field is simulated using the finite element analysis method. The auxiliary cathode is optimized to mitigate the influence of the edge effect on the film layer. The findings indicate that employing a cylindrical shape as the auxiliary cathode instead of a rectangular groove leads to an increased thickness of the micro-arc oxidation film. However, it also results in an augmented length of the film layer affected by the edge effect at both ends of the workpiece. Decreasing the distance between the auxiliary cathode and the workpiece surface leads to a higher thickness of the obtained micro-arc oxidation film. Decreasing the length of the auxiliary cathode results in a reduction in both the thickness of the film layer on the workpiece surface and the area affected by the edge effect. Increasing the eccentric cone ratio of the auxiliary cathode enhances the uniformity of the micro-arc oxidation film layer. In this study, we present a novel auxiliary cathode model that incorporates a smaller cylindrical shell at the center and eccentric cone shells on each side. This model has the potential to enhance the optimization rate of the micro-arc oxidation film layer on cylindrical workpieces by 17.77%.

Effect of electrical parameters on the growth and properties of 7075 aluminum alloy film based on scanning micro-arc oxidation with mesh electrode

The effect of electrical parameters on the properties of 7075 aluminum alloy films under scanning micro-arc oxidation was studied. The process of micro-arc oxidation is simulated in this paper. This method greatly reduces the experimental cost of micro-arc oxidation research and provides a new idea for the subsequent research of micro-arc oxidation. The micro-arc oxidation process was simulated by COMSOL Multiphysics. The film thickness, hardness and corrosion resistance are used as indexes, and forward voltage, positive duty cycle and pulse frequency are used as design factors to carry out orthogonal experiments with three factors and three indexes. Vega XMU scanning electron microscope is used to observe the surface and section morphology of the micro-arc oxidation film. VERSA STAT 3 F electrochemical workstation is used to detect the potentiodynamic polarization curve of the film and Tafel fitting is performed to obtain the self-corrosion potential (Ecorr). The thickness and hardness of the film are tested by Nix coating thickness tester and HV-1000 Vickers hardness tester. The results show that the film uniformity of the network electrode is better than that of the tube electrode under the condition of scanning micro-arc oxidation. The order of electrical parameters affecting film thickness and hardness is forward voltage > forward duty cycle > pulse frequency. The order of the electrical parameters affecting the corrosion resistance of the film is pulse frequency > forward voltage > forward duty cycle. The best combination of electrical parameters is: forward voltage 500 V, forward duty ratio 30%, pulse frequency 200 Hz.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

Effects of K2TiF6 and Electrolyte Temperatures on Energy Consumption and Properties of MAO Coatings on 6063 Aluminum Alloy

To decrease energy consumption and improve the performance of micro-arc oxidation (MAO) films on 6063 Al alloy, a policy of K2TiF6 additive and electrolyte temperature control was adapted. The specific energy consumption relied on the K2TiF6 additive and more particularly on the electrolyte temperatures. Scanning electron microscopy demonstrates that electrolytes with 5 g/L K2TiF6 can effectively seal the surface pores and increase the thickness of the compact inner layer. Spectral analysis shows that the surface oxide coating consists of γ-Al2O3 phase. Following 336 h of the total immersion process, the impedance modulus of the oxidation film, prepared at 25 °C (Ti5-25), remained 1.08 × 106 Ω·cm2. Moreover, Ti5-25 has the best performance/energy-consumption ratio with a compact inner layer (2.5 ± 0.3 μm). This research found that the time of the big arc stage increased with the temperature, resulting in producing more internal defects in the film. In this work, we employ a dual-track strategy of additive and temperature providing an avenue to reduce the energy consumption of MAO on alloys.

Growth behavior and corrosion resistance of graphene oxide/MgAl Layered double hydroxide coating grown on micro-arc oxidation film of magnesium alloys

The MgAl Layered double hydroxides (LDHs)/graphene oxide (GO) composite film was fabricated in situ on the micro-arc oxidation (MAO) film (MAO/LG) of AZ31 magnesium alloy in one step by hydrothermal chemical conversion method. The growth behavior and corrosion properties of LG films were investigated. The results show that the chemical structure, composition and morphology of the LG film will gradually change with the extension of the hydrothermal treatment time based on using the self-dissolved cation (Mg2+ and Al3+) in the MAO film as the source of growing LDHs without introducing any external metal cations. The potentiodynamic polarization showed that the MAO/LG-12 h coating (1.28 × 10−9 A/cm2) after in situ growth for 12 h was more corrosion resistant than the MAO coating (8.49 × 10−6 A/cm2). The synergistic effect of GO and LDHs can significantly improve the corrosion protection ability of MAO coating. In addition, the transition process of the growth behavior of the LG film layer on the MAO coating is explained in detail.

Influence of voltage modes on microstructure and corrosion resistance of micro-arc oxidation coating on magnesium alloy

Micro-arc oxidation (MAO) technology, as an efficient and widely used technology, can fabricate a ceramic film on magnesium (Mg) alloys in situ to significantly improve corrosion resistance. The study aims to investigate the effect of voltage modes on the preparation and performance of MAO coating on Mg alloys. The scanning electron microscope, X-ray diffractometer, potential dynamic polarization, and electrochemical impedance spectroscopy measurements were applied for characterizing the microstructure, composition, and corrosion resistance of the MAO film, respectively. The results revealed that employed 300/350 V step-up mode, the MAO film showed a more uniform distribution of surface micro-pores, fewer micro-cracks and denser inner layer, lower corrosion current density (1.871 × 10−3 mA·cm−2), and higher electrochemical impedance value, compared to other voltage treated parameters. Therefore, it could be concluded that the step-up voltage parameters are conducive to the optimization of microstructure, improvement of corrosion resistance of MAO coating, and reduction of the energy consumption during processing.

Improved corrosion resistance of MAO coating on Mg-Li alloy by RGO modified silanization

The inherent micropores and microcracks in the micro-arc oxidation (MAO) film on the surface of Mg-Li alloy limit the corrosion resistance of the film in corrosive environments. In this work, the double-layer micro-arc oxidation/3-glycidoxypropyltrimethoxysilane (KH560) composite film was prepared on the surface of the LA103Z Mg-Li alloy by MAO and silanization treatments. Based on this, the modification with reduced graphene oxide (RGO) to the KH560 film was studied and the corrosion resistance of the film was investigated. The results show that the silane film prepared is uniform and complete which fills up the micropores and microcracks of the MAO film, enhancing the shielding effect of the film. Moreover, the RGO modification increases the thickness of the KH560 film and the corrosion resistance of the composite film significantly in 3.5 wt% NaCl solution.

Study of the matching performance of a microarc oxidation film/electrophoresis composite coating on magnesium alloys

AbstractThe combination of a microarc oxidation (MAO) film and water‐based electrophoresis painting (EP) technology is a promising surface treatment for magnesium alloys, but the matching performance between them has not been investigated systematically. For fabricating the optimal composite coating, the influence of the MAO film condition and electrophoresis parameters on the overall performance of the composite coating was investigated by scanning electron microscopy, finite element modeling, electrochemical impedance spectroscopy, and immersion tests. The results indicate that the composite coating with an MAO voltage of 330 V and an EP voltage of 120 V shows the best corrosion resistance. Its excellent anticorrosion performance is attributed to the suitable thickness ratio of the MAO/EP coating and the excellent mechanical interlock effect of the MAO/EP interface. The microstructure of the MAO coating plays a key role; the uniform micropore size promotes a uniform electric field distribution in the initial electrophoresis process, which can considerably improve the sealing pore quality of the EP resin and further maximize the interfacial adhesion strength.

Study on Preparation of Micro-Arc Oxidation Film on TC4 Alloy with Titanium Dioxide Colloid in Electrolyte

The micro-arc oxidation film on TC4 alloy was prepared using a multifunctional micro-arc oxidation (MAO) power source. The effect of nano-titania colloid addition on the growth process, microstructure, and comprehensive mechanical properties of titanium alloy micro-arc oxidation films was studied by gradient concentration. The results show that, with the increase in titanium dioxide colloid content, the intensity of the discharge phenomenon during the MAO process increases, and the average current density gradually increases. The film thickness is gradually increased from 111.06 μm to 159.8 μm, and the roughness first decreases and then increases. The XRD results show that the rutile content in the film layer is increased with titanium dioxide colloid in the electrolyte. This resulted in an increase in the density of the film, and lead to the corrosion resistance of film improved. When the concentration of titanium dioxide colloid is 1.5 g/L, the comprehensive performance of the film is the best.

Wound-Healing on Minimally Invasive Systems with Micro-Arc Oxidized (MAO) and Acid-Etched (SLA) Surface Modifications in Finite Element Liver Model

The purpose of this research is to study micro-arc oxidation (MAO) and acid etching (SLA) in the liver after minimally invasive treatment. The three-dimensional (3D) liver model is rebuilt by magnetic resonance imaging (MRI) to simulate the clinical process. The processing layer is an important factor in clinical applications. Several studies have investigated the finite element model of the liver; however, few people have studied the equipment model with treated layers. The results revealed that temperature was significantly decreased when devices using MAO and SLA thin films. In addition, the SLA treatment group showed a relatively low temperature, which was 12.88% lower. It is an effective means to reduce abnormally thermal injury and lateral thermal area. The present study reveals that the novel nanostructured thin film on electrosurgery devices is an effective means of improving the performance of reducing over thermal injury and uniformly distributing temperature in livers.

Properties of Micro-Arc Oxidation Coatings on 5052 Al Alloy Sealed by SiO2 Nanoparticles

Micro-arc oxidation (MAO) treatment can effectively improve the wear resistance, corrosion resistance, and mechanical strength of aluminum alloy substrates. Improving the porous structure of MAO film and effectively sealing the pores is a significant research issue. In this study, the MAO treatment of 5052 aluminum alloy was carried out in silicate electrolytes. The MAO films were sealed with different concentrations of SiO2 nanoparticles. The effects of SiO2 nanoparticle content on the MAO films’ microstructure, mechanical properties, and corrosion performance were systematically investigated. When adding SiO2 nanoparticles to electrolytes, the particles were deposited at the micropores of the film, which could effectively seal the porous MAO film and significantly improve its corrosion and wear resistance. The corrosion resistance and wear resistance properties were optimal with 5.0 g/L SiO2 addition. Compared to the unsealed film, the corrosion current density and corrosion rate decreased from 1.24 × 10−9 A/cm2 and 1.47 × 10−5 mm/a to 7.78 × 10−10 A/cm2 and 9.15 × 10−6 mm/a, respectively. Moreover, the average friction coefficient of the sealed film was 0.606, which was ~19.3% lower than that of the substrate and 3.3% lower than for the unsealed film.