Properties Of Micro-arc Oxidation Coatings Research Articles

Mutual Impact of Four Organic Calcium Salts on the Formation and Properties of Micro-Arc Oxidation Coatings on AZ31B Magnesium Alloys

Calcium phosphate (Ca–P) coatings provide an effective approach in current research and the clinical application of Mg alloys by endowing them with improved corrosion resistance, biocompatibility, and even bioactivity. Ca-containing coatings were prepared on AZ31B magnesium alloys using the micro-arc oxidation (MAO) technique and a combination of ethylenediaminetetraacetic acid calcium disodium (EDTA–Ca), calcium glycerophosphate (GP–Ca), calcium gluconate (CaGlu2), and calcium lactate (CaLac2) as the Ca source in a near-neutral solution. The respective and mutual impacts of the four calcium salts on the formation and properties of the coatings were investigated. Experimental results indicated that GP–Ca was more decisive than EDTA–Ca, CaGlu2, and CaLac2 in the formation, morphology, and, therefore, the corrosion resistance of the coatings. GP–Ca alone could not effectively incorporate Ca2+ ions into the coatings but it could combine with EDTA–Ca, CaGlu2, and CaLac2 to bring a synergistic effect in improving the Ca content of the coatings. The bifunctional structure of CaGlu2 and CaLac2, containing hydroxyl groups and carboxylic groups with anchoring effects, enabled them to enhance the Ca content of the coatings. However, due to minor differences in functional group orientation, CaGlu2 was a little more efficient than CaLac2 in increasing Ca content, while CaLac2 was a little more efficient than CaGlu2 in improving the corrosion resistance of the coatings. Finally, the total concentration of the four calcium salts, [Ca2+]T, should be controlled at a proper level; otherwise, excessively high [Ca2+]T would produce localized microbumps originating from coating ablation, eventually deteriorating the corrosion resistance of the coatings.

Effect of zinc oxide on the electrochemical properties of micro-arc oxidation coatings in seawater

Purpose The purpose of this paper is to explore the effect of ZnO on the structure and properties of micro-arc oxidation (MAO) coating on rare earth magnesium alloy under large concentration gradient. Design/methodology/approach The macroscopic and microscopic morphology, thickness, surface roughness, chemical composition and structure of the coating were characterized by different characterization methods. The corrosion resistance of the film was studied by electrochemical and scanning Kelvin probe force microscopy. The results show that the addition of ZnO can significantly improve the compactness and corrosion resistance of the MAO coating, but the high concentration of ZnO will cause microcracks, which will reduce the corrosion resistance to a certain extent. Findings When the concentration of zinc oxide is 8 g/L, the compactness and corrosion resistance of the coating are the best, and the thickness of the coating is positively correlated with the concentration of ZnO. Research limitations/implications Too high concentration of ZnO reduces the performance of MAO coating. Practical implications The MAO coating prepared by adding ZnO has good corrosion resistance. Combined with organic coatings, it can be applied in corrosive marine environments, such as ship parts and hulls. To a certain extent, it can reduce the economic loss caused by corrosion. Originality/value The effect of ZnO on the corrosion resistance of MAO coating in electrolyte solution was studied systematically, and the conclusion was new to the common knowledge.

The Effect of Yttrium Nitrate Content on the Microstructure and Properties of a Micro-Arc Oxidation Coating Prepared on a ZK61M Magnesium Alloy

To investigate the effect of the content of yttrium nitrate on the microstructure and properties of micro-arc oxidation coatings on a ZK61M magnesium alloy, this study successfully prepared a ZrO2-Y2O3-containing composite ceramic coating on a ZK61M magnesium alloy by using micro-arc oxidation (MAO) technology, adding different amounts of yttrium nitrate (0 g/L, 0.15 g/L, 0.45 g/L, and 0.75 g/L) to a zirconate electrolyte with the main components of 6 g/L of (NH4)2ZrF6, 4 g/L of NaH2PO4, 1 g/L of NaF, and a pH value of 7.5–8.0. The microstructure, phase composition, corrosion resistance, and friction coefficient of the coating were investigated using a scanning electron microscope, an energy spectrometer, an X-ray diffractometer, a photoelectron spectrometer, an electrochemical tester, and a friction and wear tester, respectively. The results showed that the composite ceramic coating was composed of c-ZrO2, t-ZrO2, m-ZrO2, MgO, Y2O3, and MgF2. Among the MAO coatings prepared in this experiment, it was when the concentration of the Y(NO3)3 was 0.75 g/L that the coating exhibited the best corrosion resistance and wear resistance. The corrosion current density (Icorr) was 1.415 × 10−8 A·cm−2, which was four orders of magnitude lower than that of the substrate. The friction coefficient and wear volume of the coating were reduced by 30.77% and 96.55% compared to the substrate, respectively.

Comparative Study of the Effects of Nano ZnO and CuO on the Biodegradation, Biocompatibility, and Antibacterial Properties of Micro-arc Oxidation Coating of Magnesium Alloy

Comparative Study of the Effects of Nano ZnO and CuO on the Biodegradation, Biocompatibility, and Antibacterial Properties of Micro-arc Oxidation Coating of Magnesium Alloy

Effect of the chemical composition of aluminium alloys on the structure and properties of micro-arc oxidation coatings

Effect of the chemical composition of aluminium alloys on the structure and properties of micro-arc oxidation coatings

Effect of TiO2 nanoparticles on the corrosion resistance, wear, and antibacterial properties of microarc oxidation coatings applied on AZ31 magnesium alloy

Microarc oxidation (MAO) is a surface modification process that is often adopted to produce a hard oxide layer on magnesium alloys to improve their corrosion resistance and wear resistance. However, under continual corrosion, the characteristic porous microstructure of MAO coatings provides diffusion paths that allow corrosive species to penetrate the coatings and react with the substrate underneath. Therefore, the present study investigated the modification of the microstructure of MAO coatings when adding TiO2 nanoparticles to a fluoride-containing silicate electrolyte system under the bipolar current mode. The results indicate that as the concentration of TiO2 nanoparticles increased, the quantity of rutile (TiO2) incorporated in the MAO coating increased, which led to the coating exhibiting an elevated hardness and a color change from white to gray-black. When the TiO2 concentration in the electrolyte was increased from 2.5 to 7.5 g/L, the total impedance of the MAO coating in electrochemical impedance spectroscopy analysis increased from 107 to >600 kΩcm2, which indicates that the corrosion resistance of the coating increased with the number of defects on it decreased. The addition of TiO2 enhances the photocatalytic properties of MAO coatings. However, excessive addition of TiO2 can lead to an adverse effect on the wear resistance of MAO coatings.

Effects of Graphene Oxide on Tribological Properties of Micro-Arc Oxidation Coatings on Ti-6Al-4V

This paper investigates the effect of graphene oxide (GO) particles on the friction reduction and wear resistance of coatings on a Ti-6Al-4V alloy generated using the micro-arc oxidation (MAO) technique. Different concentrations of GO were added in aluminate–phosphate electrolyte. The composition of the MAO coatings was investigated using X-ray diffraction and the energy dispersive spectrum. Measurements of the coating’s thickness, hardness, and roughness have also been conducted. Ball-on-disk friction tests under dry conditions were carried out to reveal the tribological behavior of the MAO coating. The results showed that the coating consisted of Al2TiO5 and γ-Al2O3. The addition of GO greatly reduced the friction coefficient by 25%. The coating with 5 g/L of GO particles exhibited the lowest friction coefficient (reduced from 0.47 to 0.35). Moreover, the coating thickness become thicker (from 10 to 20 μm) with an increase in GO concentration from 0 to 10 g/L. The wear mechanism was revealed via worn surface analysis. This study provides a helpful way to improve the surface wear resistance of titanium alloys.

Effect of h-BN nanoparticles incorporation on the anti-corrosion and anti-wear properties of micro-arc oxidation coatings on 2024 aluminum alloy

Micro-arc oxidation (MAO) coatings are recognized for their protective capabilities, yet their inherent porosity and defects limit broader applications. In this study, we aimed to rectify these limitations and enhance their performance by integrating hexagonal boron nitride (h-BN) nanoparticles into the MAO coatings. This work investigates the influence of h-BN concentration on the structure and properties of MAO coatings on 2024 aluminum alloy substrate. The results indicate that h-BN integration diminishes porosity and roughness, while improving hardness, adhesion, and corrosion and wear resistance. The corrosion current density (Icorr) of the most effective composite coatings is approximately 1% of the 2024 aluminum alloy substrate and 10% of undoped MAO coatings. Wear tests demonstrate the significant self-lubricating effect of the h-BN distributed in the coating, with the coefficient of friction (COF) of the most abrasion-resistant coating after h-BN doping being 67% of the undoped coating. During MAO, h-BN is uniformly incorporated into the coatings via diffusion and electrophoretic migration. The two-dimensional structure of h-BN in the coatings effectively blocks micro-defects, delays corrosive substance penetration, and enables self-lubrication. Conversely, excessive h-BN concentrations can instigate agglomeration and performance degradation. Optimum corrosion resistance is achieved with an h-BN concentration of 2.5 g/L, while the best wear resistance is attained at 10 g/L. The study suggests that h-BN-doped MAO coatings present substantial potential for applications necessitating high corrosion and wear resistance in aluminum alloys.

Investigation of the Characteristics of MAO Coatings Formed on Ti6Al4V Titanium Alloy in Electrolytes with Graphene Oxide Additives

Coatings with a thickness from ~40 to ~50 µm on Ti6Al4V titanium alloy were formed by micro-arc oxidation in a silicate-hypophosphite electrolyte with additions of graphene oxide. Micro-arc oxidation treatment was carried out in the anode–cathode mode (50 Hz) with a ratio of anode to cathode currents of 1:1, a total density of 20 A/dm2, and a treatment duration of 30 min. The effect of the graphene oxide concentration in electrolytes on the thickness, roughness, hardness, surface morphology, structure, composition of micro-arc oxidation coatings, and its electrochemical corrosion behavior in 3.5% NaCl solution was studied. The input of graphene oxide additives into the base silicate hypophosphite electrolyte led to an increase in the hardness of micro-arc oxidation coatings. Electrochemical polarization studies and impedance data showed that the best characteristics in terms of corrosion-protective ability among coatings formed in electrolytes with graphene oxide additives were those formed in the electrolyte with a graphene oxide concentration of 0.1 g·L−l. A further increase in the graphene oxide concentration in the electrolyte did not improve the protective properties of micro-arc oxidation coatings.

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.

Effect of Pulse Duty Cycle and Oxidation Time on Microstructure and Properties of Micro-arc Oxidation Coatings on Ti6Al4V Alloy

Micro-arc oxidation (MAO) technology can in-suit generate coatings with high hardness and strong adhesion on the surface of titanium alloy, thereby greatly improve the application range of titanium alloy. The morphology and properties of coatings are controlled by changing electrical parameters such as duty cycle and oxidation time. This work mainly aims to study the influence of different duty cycles and oxidation times on MAO coatings microstructures and properties of Ti6Al4V alloy under the condition of constant voltage and pulse frequency. The scanning electron microscopy (SEM) and X-ray Diffractometer (XRD) were used to investigate into MAO coatings microstructure and phase composition. The roughness, porosity, thickness, and microhardness of MAO coatings were evaluated respectively by roughness tester, thickness gauge, and microhardness tester. The results show that surface morphology of the MAO coatings change from crater-like micropores to foam-like protrusions with the enhancement of duty cycle and oxidation time. When duty cycle is 50% and oxidation time is 30 min respectively, the ejection of the molten material made the MAO coating surface appear foam-like protrusions, and the surface morphology is seriously damaged. When the oxidation time and the duty cycle are 30 min and 10% respectively, the rutile phase intensity is the maximum, and further increasing the duty cycle will lead to a rutile phase decrease. In a limit range, the hardness rise with increase of oxidation time and duty cycle. The highest hardness is 668.85 HV.

Increasing the compact density and its consistency in the cross-section for enhancing the anti-corrosion and mechanical properties of micro-arc oxidation coatings

The micro-arc oxidation coatings (MAO) coatings formed on the magnesium (Mg) matrix usually have various porosity in the cross-section due to the uneven thermal stress, resulting in the non-consistent compact density in the external and inner layer. However, the consistency of the compact density in the cross-section is less concerned, and its effect on the surficial anti-corrosion and mechanical properties is still unclear. Herein, we employed the Zirconium Oxide particles as a heat-absorbing agent to tune the temperature gradient and achieved the in situ growth of MAO coatings on Mg alloy with a tunable compact density in the external layer and inner layer separately. It is found that compact density plays a key role in corrosion resistance, while the consistency of compact density along the cross-section is very crucial for the mechanical properties. Increasing the compact density and reducing its gradual difference could significantly enhance both the anti-corrosion and mechanical properties. The effect of the inconsistent compact density on the anti-corrosion property could be weakened by reducing the porosity on the external layer, but the simulation results demonstrate its effect on the mechanical properties would be strengthened due to the stress concentration. MAO coatings with homogeneous and compact structures in the cross-section present superior anti-corrosion properties and excellent mechanical properties.

Effect of Si3N4/TaC Particles on the Structure and Properties of Microarc Oxidation Coatings on TC4 Alloy

Si3N4/TaC composite MAO coatings were fabricated by microarc oxidation (MAO) on a Ti–6Al–4V (TC4) alloy in a phosphate-based electrolyte containing Si3N4/TaC mixed particles. The influence of the amount of Si3N4/TaC particles on the microstructure, composition, tribological behavior, and corrosion properties of the MAO coatings has been investigated. Morphological research of the MAO coatings was carried out using scanning electron microscopy (SEM), with the surface porosity analyzed by ImageJ software. X-ray diffraction (XRD) was used for the detection of the phase characteristic of the MAO coatings, and an abrasive wear test and electrochemical measurements were conducted in the artificial seawater solution by the ball-on-disc friction tester and the electrochemical workstation, respectively. The results showed that Si3N4/TaC particles could be successfully incorporated into the composite coatings, and the addition of Si3N4/TaC particles greatly reduced the porosity of the coatings, thus improving both tribological and corrosion properties of the composite MAO coatings. The composite MAO coating with the addition of 1 g/L Si3N4 + 0.5 g/L TaC particles showed the best tribological property and the optimum corrosion properties.

Influence of combined B4C/C particles on the properties of microarc oxidation coatings on Mg-Li alloy

Microarc oxidation coatings incorporated with B4C and C particles were prepared on Mg-Li alloy. The influence of combined B4C/C particles on the microstructure and properties of microarc oxidation coatings was investigated. Results show that B4C and C particles are successfully integrated into the coating where B4C partially blocks the micropores and C particles form bulges on the surface. The composite B4C/C particles contribute to increasing the thickness and decreasing the porosity of the coating, thus maintaining the corrosion resistance together with a significant increase in the wear resistance of the coating. It is mainly attributed to the high hardness of B4C particles and the lubrication of C particles in the coating. The composite addition of particles to the microarc oxidation electrolyte is an effective method to enhance the coating properties.

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.

The properties of microarc oxidation coatings installed on AlSi10Mg specimens produced by selective laser melting

This paper examines the properties of coatings produced by microarc oxidation (MAO) on AlSi10Mg alloy specimens, which were obtained by selective laser melting. Two different electrolytes were used to install the coatings: silicate and silicate-phosphate. Modes were used that are recommended for the microarc oxidation of high-silicon aluminium casting alloys. As a result, double-layer coatings of different thicknesses were produced in relatively close timeframes of the MAO process. The thickness, roughness and wear spots were analyzed with the help of a laser interference microscope; the hardness was measured on a microhardness tester; the morphology and the elemental composition of the MAO coatings were analyzed by means of scanning electron microscopy (SEM); an X-ray diffractometer was used for phase analysis. The measurements showed that the coatings produced in the silicate-phosphate electrolyte have higher microhardness, corrosion resistance and specific electrical strength. Based on the results of friction tests and having analyzed the Ffr – Dr hysteresis loops obtained for reciprocating wear of the specimens, with the friction force Ffr and the travel D being simultaneously measured, the authors established that the wear resistance of the coatings produced in silicate-phosphate electrolyte is ~1.4 times higher than in the case of silicate electrolyte. The conducted study confirmed the efficiency of using silicate-phosphate electrolyte for producing high-quality protective coatings, which applies to almost all parameters. The paper shows that MAO coatings installed on AlSi10Mg alloy specimens produced by selective laser melting offer high performance. Thus, they can be recommended for pilot production of spacecraft components.This research was carried out as part of an assignment of the Ministry of Education and Science of Russia, Subject No.: FSFF-2020-0014.

Growth characteristics and properties of micro-arc oxidation coatings on AlSi10Mg selective laser-melted components

Micro-arc oxidation (MAO) ceramic coatings were prepared on porous AlSi10Mg selective laser-melted components to improve their corrosion property. The microstructure and composition of the coatings at different processing times were characterized via scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. Results showed that the diameter of micro-pores increased with an extension of treatment time, the porosity of coatings decreased from 6.24% to 0.85%. Thickness increased from 4.45 ± 0.01 μm to 15.20 ± 0.01 μm and surface roughness increased from 0.76 ± 0.01 μm to 5.41 ± 0.01 μm with increasing processing time. Meanwhile, the coatings were mostly composed of γ-Al2O3 and trace amounts of α-Al2O3, Al2SiO5, AlPO4 and WO3, the content of α-Al2O3 was increased from 0.51% to 4.12%. Corrosion current density decreased from 2.213 e−5 A·cm−2 to 1.088 e−7 A·cm−2. The polarization resistances Rb were increased from 4.8 × 103 Ω·cm2 to 2.6 × 105 Ω·cm2. The long term EIS results show that Rb was 7.7 × 103 Ω·cm2 after 3 weeks immersion, which show that the MAO coatings could provide good protection on AlSi10Mg alloy. The gas holes and defects of the SLM components were treated via MAO to form uniform MAO coatings on the surface of a sample, expanding the application range of selective laser-melted components in corrosive environments.

Effect of SiC addition in electrolyte on the microstructure and tribological properties of micro-arc oxidation coatings on Al-Mg-Sc alloy

sHard and wear-resistant ceramic coatings with SiC nanoparticles were in situ fabricated on Al-Mg-Sc alloy using micro-arc oxidation (MAO) method in alkaline silicate electrolyte. The microstructure, roughness, and composition of the MAO coatings were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser scanning confocal microscopy (LSCM), respectively. The microhardness of the MAO coatings was obtained microhardness tester. The wear resistance of the MAO coatings was evaluated by ball-on-disc reciprocating tribo-tester. The results showed that the phase composition of the obtained coatings with the typical pancake-like stacking structures was mainly composed of α-Al2O3 and γ-Al2O3. the porosity and roughness gradually decreased with the increment of SiC nanoparticles concentration. Al content gradually decreased from the matrix to the outside, while the Si content gradually increased. The incorporation of SiC nanoparticles further increased the microhardness of the MAO coating. Especially in alkaline silicate electrolyte with 1.5g l−1 SiC nanoparticles, the microhardness could reach 1270 HV0.5. The friction coefficient of the MAO coatings prepared in electrolyte solution with SiC addition varied from 0.4 to 0.55, and the ceramic coating with 1.5g l−1 SiC nanoparticles exhibited the best wear resistance. The wear mechanism was attributed to be the combination of abrasive wear, adhesive wear and oxidation wear.

Effect of zinc content on the microstructure, in vitro bioactivity, and corrosion behavior of the microarc oxidized Mg-xZn-0.6Ca (x = 3.0, 4.5, 6.0) alloy.

Bioceramic calcium phosphorus (CaP) coatings were prepared on self-designed Mg-xZn-0.6Ca (x = 3.0, 4.5, 6.0 wt. %) alloy by microarc oxidation (MAO). The corrosion resistance, bioactivity, and biodegradability of the CaP coatings prepared on alloys with different zinc (Zn) contents were systematically studied and discussed by potentiodynamic polarization and in vitro immersion tests in the simulated body fluid solution. The CaP coatings and corrosion products were characterized by scanning electron microscopy, energy dispersive spectrometry, x-ray diffraction, and Fourier transform infrared spectroscopy. Based on the difference of microstructure caused by zinc content, the effect of microstructure on the properties of MAO coatings was analyzed by taking grain boundary and second phase defects as examples. Results showed that the CaP coatings could be prepared on the surface of the self-designed Mg-Zn-0.6Ca alloy by MAO. The CaP coatings have good bioactivity. Meanwhile, the Zn content has a significant effect on the microstructure of the CaP coatings. When the Zn content is 3.0 wt. %, the corrosion resistance and biocompatibility of the CaP coatings are obviously improved with good biological properties.

Properties of Micro-Arc Oxidation Coating Fabricated on Magnesium Under Two Steps Current-Decreasing Mode

A concept of two steps current-decreasing mode derived from constant current mode was developed to fabricate micro-arc oxidation (MAO) coatings on ZK60 Magnesium (Mg) alloy in a dual electrolyte system. The growth characteristics of coatings were analyzed by voltage-time curves, and the coating microstructures were characterized by scanning electron microscopy (SEM). Meanwhile, the roughness, corrosion behavior and microhardness of MAO coatings were investigated. The results showed that the MAO coatings exhibit a smooth and compact surface and have improved hardness and thickness, smaller roughness, uneven distribution of holes and even low electrical energy consumption. Such positive characteristics results in an improved corrosion resistance of MAO coatings. The coating produced under the two steps current mode of “1.2-0.6A” showed a smaller corrosion rate of 0.1559 g/m2h as compared to the counterpart produced under the other modes. The nanoscratch tests results showed that the coating fabricated by “1.2-0.6A” mode has strong bond strength with the substrate. Under this optimized mode, the MAO process also had the lowest energy consumption of 49.8 W·(dm2·μm)-1.