Micro-arc Oxidation Technology Research Articles

Recent Patents of Micro-arc Oxidation Technology

Abstract: Micro-arc oxidation (MAO) is a new surface treatment technology that can improve wear resistance, corrosion resistance, high voltage insulation, and other metal properties. Therefore, this technology is widely used in automobile manufacturing, aerospace, ship anti-corrosion, medical equipment, sewage treatment, and other fields. This paper reviews the representative patents of micro-arc oxidation technology at home and abroad. The micro-arc oxidation processing device, the process method of micro-arc oxidation processing, the power supply and electrical parameters of micro-arc oxidation, the preparation of electrolytes, and the methods of anticorrosion and protection of metal surface are analyzed. The development trend of micro-arc oxidation technology in the future is discussed. Micro-arc oxidation is a simple, green, and environment- friendly surface treatment technology, and there will be more patents in the field of micro- arc oxidation in the future.

Study on micro-arc oxidation coating of copper pretreated at high temperature

Micro-arc oxidation (MAO), also known as plasma electrolytic oxidation (PEO), is a surface treatment technology widely used in valve metals. As a widely used non-valve metal, copper is generally not easy to prepare MAO coating on its surface. In this paper, from the principle of MAO, the black coating was successfully prepared on the surface of pure copper by using high temperature pretreatment method and MAO technology, and the surface morphology and composition of the coating are characterised in detail. Friction experiments show that the MAO coatings formed by copper after high-temperature pretreatment at 300 °C have better wear resistance. The water contact angle test and electrochemical experiments show that the 300 °C sample has a higher water contact angle and excellent corrosion resistance. This study expands the surface treatment method of copper and provides a new idea for MAO technology in the surface treatment of other non-valve metals.

Self-assembled Ti3C2Tx membrane driven by Marangoni effect for anti-corrosive and anti-wear applications

The recent rise of Ti3C2Tx has extended the applications in epoxy resin due to its large specific surface area and excellent mechanical properties. Whereas, the synergy between epoxy and Ti3C2Tx restricts properties enhancements when Ti3C2Tx is subjected to random orientation and discontinuous distribution. To optimize the barrier and lubrication characteristics of Ti3C2Tx, we have successfully prepared Ti3C2Tx membrane by using the Marangoni effect self-assembled method to move Ti3C2Tx nanosheets to the same latitude and deposit them on epoxy resin for the first time. Meanwhile, micro-arc oxidation technology was adopted to enhance the bonding strength of the substrate with epoxy. Due to the effective corrosion resistance offered by the Ti3C2Tx membrane, even after 28days of immersion, the pure epoxy coating had completely failed, while the |Z|0.01Hz value of the multilayer coating still increased by 36.5 % compared to MAO/EP/EP. Furthermore, the wear rate and the friction coefficient reduced by 58.2 % and 21.4 % in comparison to the pure epoxy coating. This exceptional lubrication property stems from the interlayer shear sliding of the expansive Ti3C2Tx nanosheets, effectively preventing direct contact between the friction ball and the epoxy.

Polyvinyl alcohol gel/micro-arc oxidation 3D-printed porous structural aluminium for oil-water separation

Traditional oil-water separation membranes still face challenges in designing membrane structures and pore sizes. In this study, we successfully prepared a PVA@MAO 3D-Al material with an internal porous structure using 3D printing technology and micro-arc oxidation (MAO). Compared to the base 3D-Al material, the fabricated PVA@MAO 3D-Al exhibits excellent wear resistance, with an average friction coefficient reduced by 66% in dry friction and 22% in water lubrication. In electrochemical experiments, corrosion current density decreased by an order of magnitude, indicating higher stability of PVA@MAO 3D-Al in corrosive environments. In oil-water separation experiments, PVA@MAO 3D-Al achieved separation efficiencies exceeding 97% for mixtures of white oil, kerosene, liquid paraffin, and cyclohexane with water. Moreover, even after undergoing 600 cycles of reciprocating friction and exposure to various environmental solutions, the separation efficiency of PVA@MAO 3D-Al for white oil/water mixtures remained above 96%, demonstrating outstanding physical and chemical stability. This suggests that PVA@MAO 3D-Al is suitable for use in extremely harsh environments. This study introduces a simple and efficient approach to manufacturing oil-water separation membranes using 3D printing technology, coupled with MAO technology to enhance the base material's performance. The combination of these techniques opens up new avenues in the field of oil-water separation.

Self-assembled Ti3C2Tx membrane driven by Marangoni effect for anti-corrosive and anti-wear applications

The recent rise of Ti3C2Tx has extended the applications in epoxy resin due to its large specific surface area and excellent mechanical properties. Whereas, the synergy between epoxy and Ti3C2Tx restricts properties enhancements when Ti3C2Tx is subjected to random orientation and discontinuous distribution. To optimize the barrier and lubrication characteristics of Ti3C2Tx, we have successfully prepared Ti3C2Tx membrane by using the Marangoni effect self-assembled method to move Ti3C2Tx nanosheets to the same latitude and deposit them on epoxy resin for the first time. Meanwhile, micro-arc oxidation technology was adopted to enhance the bonding strength of the substrate with epoxy. Due to the effective corrosion resistance offered by the Ti3C2Tx membrane, even after 28days of immersion, the pure epoxy coating had completely failed, while the |Z|0.01Hz value of the multilayer coating still increased by 36.5 % compared to MAO/EP/EP. Furthermore, the wear rate and the friction coefficient reduced by 58.2 % and 21.4 % in comparison to the pure epoxy coating. This exceptional lubrication property stems from the interlayer shear sliding of the expansive Ti3C2Tx nanosheets, effectively preventing direct contact between the friction ball and the epoxy.

Study on the Optimization of the Preparation Process of ZM5 Magnesium Alloy Micro-Arc Oxidation Hard Ceramic Coatings and Coatings Properties

Hard ceramic coatings were successfully prepared on the surface of ZM5 magnesium alloy by micro-arc oxidation (MAO) technology in silicate and aluminate electrolytes, respectively. The optimization of hard ceramic coatings prepared in these electrolyte systems was investigated through an orthogonal experimental design. The microstructure, elemental composition, phase composition, and tribological properties of the coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and tribological testing equipment. The results show that the growth of the hard ceramic coatings is significantly influenced by the different electrolyte systems. Coatings prepared from both systems have shown good wear resistance, with the aluminate electrolyte system being superior to the silicate system in performance. The optimized formulation for the silicate electrolyte solution has been determined to be sodium silicate at 8 g/L, sodium dihydrogen phosphate at 0.2 g/L, sodium tetraborate at 2 g/L, and potassium hydroxide at 1 g/L. The optimized formulation for the aluminate electrolyte solution consists of sodium aluminate at 5 g/L, sodium fluoride at 3 g/L, sodium citrate at 3 g/L, and sodium hydroxide at 0.5 g/L.

Preparation and properties of micro-arc oxidation ceramic coatings using machine vision technology

In this paper, a machine vision system is combined with non-immersion micro-arc oxidation (MAO) technology, using color as a visual feature, and automatically determining the MAO process through a self-developed color image segmentation program for HSV channel. The robotic arm accurately regulates the machining position and duration. Dense ceramic oxide coatings of similar quality to the artificially prepared coatings were successfully prepared on aluminum (Al) surface. The surface morphology and elemental composition of the samples were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The performance of the coatings was tested through thickness tests, hardness tests, and roughness tests. The tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results confirm the effectiveness of a machine vision system for MAO process control, which is capable of preparing high-quality coatings comparable to manual operations. This not only solves the need for precise film formation in different application scenarios, but also provides a more efficient, controllable and innovative solution for the MAO process.

Formation of ceramic coatings on non-valve metal low carbon steel using micro-arc oxidation technology

Valve metals are metals that can undergo surface modification through micro-arc oxidation (MAO). Iron is not considered a valve metal and cannot undergo MAO. Steel is a widely used alloy due to its excellent properties, including high toughness, good workability, and low cost. However, its weak corrosion and abrasion resistance limit its range of application and service life. Al2O3 ceramic coating is formed on the surface of non-valve metal low carbon steel using MAO technology. The surface morphology and composition of the MAO coatings on non-valve metals are investigated through characterization. Tribological experiments show that the coefficient of friction of the samples obtained from the MAO power supply frequency of 1400 Hz is the smallest. After conducting a corrosion resistance test following MAO treatment, the impedance increased by three orders of magnitude and the corrosion rate decreased by one order of magnitude. The use of MAO treatment can expand the use of steel and shows promise for application to other non-valve metals.

RESEARCH AND APPLICATION OF MICROARC OXIDATION TECHNOLOGY FOR RESTORATION OF WORKING PISTON SURFACES OF FREIGHT VEHICLES

The scientific article is devoted to the study and application of micro-arc oxidation technology for the restoration of the working surfaces of truck pistons. The study includes an analysis of the physical and chemical processes occurring during microarc oxidation of aluminum alloys from which the pistons are made. The physical impact of MAO promotes the formation of a strong and stable oxide layer, leading to improved surface morphology and closure of microcracks. The results obtained confirm that this technology promotes the formation of hard coatings. The presence of microcracks and surface defects on the original surface of the aluminum alloy caused by operation is noted. After applying the micro-arc oxidation procedure, significant improved surface morphology, reduction of microcracks and removal of defects are visible, indicating the high efficiency of the process. The use of micro-arc oxidized coatings in mechanical engineering promises to increase the durability and efficiency of freight vehicles, as well as reduce repair and maintenance costs. This research represents an important contribution to the field of technological solutions for the remanufacturing of vehicle parts, providing promising prospects for industrial applications.

Preparation and Performance of Micro-Arc Oxidation Coatings for Corrosion Protection of LaFe11.6Si1.4 Alloy.

The microstructure, corrosion resistance, and phase-transition process of micro-arc oxidation (MAO) coatings prepared on LaFe11.6Si1.4 alloy surfaces in different electrolyte systems were systematically investigated. Research has demonstrated that various electrolyte systems do not alter the main components of the coatings. However, the synergistic action of Na2CO3 and Na2B4O7 more effectively modulated the ionization and chemical reactions of the MAO process and accelerated the formation of α-Al2O3. Moreover, the addition of Na2CO3 and Na2B4O7 improved the micromorphology of the coating, resulting in a uniform coating thickness and good bonding with the LaFe11.6Si1.4 substrate. The dynamic potential polarization analysis was performed in a three-electrode system consisting of a LaFe11.6Si1.4 working electrode, a saturated calomel reference electrode, and a platinum auxiliary electrode. The results showed that the self-corrosion potential of the LaFe11.6Si1.4 alloy without surface treatment was -0.68 V, with a current density of 8.96 × 10-6 A/cm2. In contrast, the presence of a micro-arc electrolytic oxidation coating significantly improved the corrosion resistance of the LaFe11.6Si1.4 substrate, where the minimum corrosion current density was 1.32 × 10-7 A/cm2 and the corrosion potential was -0.50 V. Similarly, after optimizing the MAO electrolyte with Na2CO3 and Na2B4O7, the corrosion resistance of the material further improved. Simultaneously, the effect of the coatings on the order of the phase transition, latent heat, and temperature is negligible. Therefore, micro-arc oxidation technology based on the in situ growth coating of the material surface effectively improves the working life and stability of La(Fe, Si)13 materials in the refrigeration cycle, which is an excellent alternative as a protection technology to promote the practical process of magnetic refrigeration technology.

Preparation of HA-MAO coatings on β-type alloys and its corrosion resistance in high glucose environments.

Aim to provide practical clinical guidance for the treatment of implants in diabetic patients, this study investigated the corrosion mechanism of bionic coatings containing different Ca/P ratios in diabetic environments. The bionic coatings were prepared in β-titanium alloys using micro-arc oxidation (MAO) technology and evaluated for corrosion mechanism, biocompatibility, and safety by cytotoxicity, electrochemical corrosion, and coating bonding force experiments. Ca and P from the electrolyte were integrated into the coating during MAO discharge process to form hydroxyapatite. The coating Ca/P ratio initially increased and then decreased with the electrolyte Ca/P ratio. In vitro cellular experiments demonstrated that increasing the porosity of HA-containing coatings would be beneficial to the growth of cells adhering to their surfaces. Corrosion tests revealed that the corrosion tendency of the coating at higher sugar content was more severe, and a proper elevation of the Ca/P ratio was better for the corrosion resistance of the coating. The bonding analysis of the coatings before and after corrosion showed that an increase in the Ca/P ratio would improve the bonding of the MAO coatings in higher glucose content environments, thus improving the safety of the implants in diabetic patients.

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.

Micro-arc oxidation (MAO) and its potential for improving the performance of titanium implants in biomedical applications.

Titanium (Ti) and its alloys have good biocompatibility, mechanical properties and corrosion resistance, making them attractive for biomedical applications. However, their biological inertness and lack of antimicrobial properties may compromise the success of implants. In this review, the potential of micro-arc oxidation (MAO) technology to create bioactive coatings on Ti implants is discussed. The review covers the following aspects: 1) different factors, such as electrolyte, voltage and current, affect the properties of MAO coatings; 2) MAO coatings affect biocompatibility, including cytocompatibility, hemocompatibility, angiogenic activity, corrosion resistance, osteogenic activity and osseointegration; 3) antibacterial properties can be achieved by adding copper (Cu), silver (Ag), zinc (Zn) and other elements to achieve antimicrobial properties; and 4) MAO can be combined with other physical and chemical techniques to enhance the performance of MAO coatings. It is concluded that MAO coatings offer new opportunities for improving the use of Ti and its alloys in biomedical applications, and some suggestions for future research are provided.

Investigation on the effect and growth mechanism of two-stage MAO coating

As a more popular surface treatment method, micro-arc oxidation technology can well solve the problems of insufficient strength and poor corrosion resistance of aluminum alloy surface. In this paper, a composite coating was obtained by using a two-stage micro-arc oxidation method different from the conventional micro-arc oxidation treatment, which solved the problem of incompatibility between the two types of electrolytes and obtained a coating with superior effect. The microscopic morphology and elemental composition were characterized by using Energy Dispersive Spectrometer (EDS)/X-ray Diffraction (XRD)/Scanning Electron Microscopy (SEM). The coating thickness was tested using a coating thickness gauge, its tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results show that the coating has the advantages of large thickness, dense, good anti-wear performance, small friction coefficient and excellent corrosion resistance, which enhanced the performance of MAO coating and was an important guide for further work.

Friction mechanism of DLC/MAO wear-resistant coatings with porous surface texture constructed in-situ by micro-arc oxidation

A porous textured DLC/MAO multilayer coating was constructed in-situ on Al alloy by depositing a diamond-like carbon (DLC) film onto a micro-arc oxidation (MAO) layer. The morphology, composition and tribological properties were investigated. The wear mechanism of the coating and the effect of load on wear were studied in detail under dry and oil-lubricated conditions. The results showed that DLC/MAO coating had excellent load-bearing capacity and wear resistance. The porous texture was generated in-situ on the aluminum alloy substrate by micro-arc oxidation technology, which played a mechanical interlocking effect in making the multi-layer coating tightly bonded. It can also capture wear debris to reduce abrasive wear under dry conditions while storing lubricating oil to supplement the lubricating film under oil-lubrication. DLC top film optimized the frictional resistance induced by the porous texture through graphitization and low-shear transfer film formation, reducing up to 70.7 % and 54.9 % in friction coefficient and wear track width under dry conditions. Under oil lubrication, the solid-liquid synergy between the graphitized layer and the liquid lubricating film can reduce the friction coefficient and wear track width by up to 20.9 % and 52.1 %. Hence, the combination of DLC top film and MAO tie layer realizes excellent anti-friction/wear and durability.

Construction of superhydrophobic film on the titanium alloy welded joint and its corrosion resistance study

PurposeThis study aims to improve the corrosion resistance of TA2-welded joints by superhydrophobic surface modification using micro-arc oxidation technology and low surface energy substance modification.Design/methodology/approachThe microstructure and chemical state of the superhydrophobic film layer were analyzed using scanning electron microscopy, energy dispersive X-ray spectroscopy, three-dimensional morphology, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. The influence of the superhydrophobic film layer on the corrosion resistance of TA2-welded joints was investigated using classical electrochemical testing methods.FindingsThe characterization results showed that the super hydrophobic TiO2 ceramic membrane was successfully constructed on the surface of the TA2-welded joint, and the construction of the super hydrophobic film greatly improved the corrosion resistance of the TA2-welded joint.Originality/valueThe superhydrophobic TiO2 ceramic membrane has excellent corrosion resistance. The micro nanostructure in the superhydrophobic film can intercept air to form an air layer to prevent the corrosion medium from contacting the surface, thus, improving the corrosion resistance of the sample.

Probing photothermal superhydrophobic behaviors of graphene&SiO2 hybrid coating for anti-freeze application

An active @ passive anti-icing surface coating was successfully prepared using graphene&SiO2 hybrid structure toward photothermal superhydrophobic performance. The coating consists of polydimethylsiloxane (PDMS) with E51 epoxy resin linked to fumed silica (nano-SiO2) to provide a multistage rough structure and graphene as the primary photothermal nanoparticle for various surface anti-freeze application. The surface morphology of this photothermal superhydrophobic coating is validated to be as a uniformly rough cauliflower structure with a large number of “air valley”. More importantly, the addition of 0.2 g graphene could exhibit the best photothermal effect (2 sun (≈ 200 mW/cm2), stable average temperature of 49.56 °C) along with superhydrophobic effect (162.2°), excellent chemical stability properties. In order to improve the organic-inorganic interfacial bonding and the mechanical durability of photothermal superhydrophobic coatings, using micro-arc oxidation technology to establish the microporous structure on the surface of substrate for exerting interlocking effect, after pushing and pulling under applied load of 300 g for 200 cm, the outstanding wear resistance of the composite coating was verified. Thanks to the interlocking effect, the excellent superhydrophobic properties provided by the construction of the typical Cassie-Baxter model of the surface and the use of multiple layers of graphene increasing the probability of π-π* electron leap, the multi-stage photothermal superhydrophobic composite coating is able to show a long-lasting anti-icing and de-icing effect.

Synergistic effect of “double pores” texture on tribological properties of AZ31 Mg alloy micro-arc oxide ceramic coatings

Micro-arc oxidation (MAO) technology for the generation of ceramic coatings on metal surfaces have been gradually used for protecting metal components from the severe wear and corrosion attack. In this study, laser texturing was applied to ameliorate the MAO ceramic coating. The scalability of ceramic coated samples by laser texturing technology was scrutinized in terms of microstructure, coefficient of friction (COF) and corrosion resistance. It turns out that the “Double pores” system generated by laser structuring of the substrate before MAO treatment has the capacity to enhance the tribological properties of the ceramic coating. After laser structuring, the proportion of magnesium oxide in the ceramic coating generated by the Mg alloy substrate increases, which is due to the oxidation of the magnesium substrate by the high temperature laser. At the same time, it also accounts for the increase in cracks on the surface of the coating. In addition, the presence of cracks has an impact on the corrosion resistance of the ceramic coating. Interestingly, the COF of the treated ceramic coating becomes lower and the heat from the texturing process has a “Quenching effect” on the substrate. In general, the COF of the ceramic coating on the surface of the laser texturing Mg substrate is reduced by 31 % compared to the original ceramic coating, at the expense of some corrosion resistance.

Preparation and mechanical and biological performance of the Sr-containing microarc oxidation layer on titanium implants

A Strontium-doped titanium oxide coating was successfully prepared on a TA4 substrate with one-step microarc oxidation (MAO) technology. Then bioactivity of the coating was performed with the inducation test of bone-like apatite formation immersed in simulated body fluid (SBF). The biological activity of the coating was evaluated with cell culture experiments, and its corrosion resistance was characterized with electrochemical tests in the SBF. The composition and morphology of the coatings before and after SBF immersion were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results showed that the coating had a rough porous structure, which was mainly composed of anatase, rutile and Ti phases. The SBF immersion test showed that abundant 3D micro nanopore structures were formed on the surface of the porous titanium oxide coatings, which enabled the coatings to exhibit good apatite nucleation ability. Faster precipitation of bone-like apatite by MAO-Sr coatings in SBF. Finally, in the biological compatibility test, compared with TA4, the contact angle between the MAO-Sr coating and SBF solution was lower, and the proliferation ability of bone marrow stromal cells (BMSCs) in the biological coating was stronger, indicating the good biocompatibility of the coating.

Effect of zinc or copper doping on corrosion resistance and anti-oxidative stress of strontium-based micro-arc oxidation coatings on titanium

In osteoporosis, the osteogenic microenvironment maintains a high level of oxidative stress (OS) due to the overaccumulation of reactive oxygen species (ROS). It not only significantly destroys the bioactivity of titanium (Ti) implants, but also enhances Ti implant corrosion, which has a significant impact on the early osteointegration of Ti implants. In this study, using microarc oxidation (MAO) technology, we constructed strontium/zinc (Sr/Zn)- and strontium/copper (Sr/Cu)-doped MAO coatings on the surface of the Ti implant and studied their corrosion resistance and osteoinductive properties under normal and OS conditions. Apart from their chemical compositions, their physical and chemical properties (roughness, hydrophilicity, morphology, and crystal structure) were similar. In the anti-corrosion test, the MAO-Sr/Zn groups (especially MAO-Sr/Zn3) exhibited perfect performance in both normal and OS microenvironments, whereas MAO-Sr/Cu showed poor corrosion resistance. In terms of biological behavior, based on the perfect osteogenesis and anti-OS properties of Sr and Zn, MAO-Sr/Zn3 exhibited the best performance in terms of cell viability, mineralization, and anti-OS ability, followed by MAO-Sr/Cu2, due to a suitable proportion of Sr/Cu. Therefore the excellent comprehensive performance of MAO-Sr/Zn3 showed that it has broad potential for implant repair in patients with osteoporosis.