Micro-arc Oxidation Coatings Research Articles

Microstructure and corrosion performance of Zr–1Nb alloy laser welded joints treated by micro-arc oxidation

The protective coatings on laser-welded joints of Zr–1Nb alloy were prepared by the micro-arc oxidation (MAO) process. The morphology, microstructure and phase composition of MAO coatings at different regions of Zr–1Nb alloy laser-welded joints were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behaviors of the coatings. The MAO coatings at the fusion zone (FZ) and heat-affected zone (HAZ) were smooth with some small holes, while MAO coatings at base metal (BM) were relatively rough with large holes. The cross-sectional topography at FZ coatings was quite dense with less distribution of pores and cracks, which can effectively improve the protective properties of the coatings. HAZ coatings were divided into outer loose layer and inner dense layer. The BM coating layer possessing many holes was a typical sparse layer structure. The phase compositions of welded joints treated by MAO were diverse at different zones of the joints, but all of them consisted of the monoclinic ZrO2 and tetragonal ZrO2 phases. The coatings of FZ had the best corrosion resistance, compared with HAZ and BM. The results of EIS indicated that the thickness and defects of the inner compact layer played a key role in improving the corrosion resistance of the MAO coatings on the surface of the Zr–1Nb alloy laser-welded joints.

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.

Global and Local Corrosion Performance of Nano-SiC Induced Micro-arc Oxidation Coating on Magnesium Alloy

Global and Local Corrosion Performance of Nano-SiC Induced Micro-arc Oxidation Coating on Magnesium Alloy

Preparation and formation mechanism of anodic coatings co-doped with Ga, Si, and P ions on Ti–6Al–4V alloys

In this study, gallium (Ga) ions, known to be effective against both bacteria and cancer, was incorporated into micro-arc oxidation (MAO) coatings on Ti–6Al–4V alloys. In a fixed solution of 5 g/L Na3PO4, the influences of Ga(NO3)3 concentration, Na2SiO3 concentration, Na2SO4 concentration and treatment time on coating properties were studied by using an orthogonal experiment to prepare Ga-Si-P coatings. In addition, the roles of each electrolyte on coating formation were clarified by using signal factor experiments. The results show that the raised Ga(NO3)3 concentration and current density continually increase the Ga content, showing that the Ga ions enter into MAO coatings by both diffusion and electromigration. Ga(NO3)3 is harmful for coating formation, while Na2SO4, Na2SiO3 and Na3PO4 act as film-forming agents. The Si content is negatively related to the P content resulted from the competition between Na2SiO3 and Na3PO4 to take part in the coating formation, while the P content is positively related to the Ga content attributed to the main existence form of Ga ions in MAO coatings as amorphous Ga2O3 and GaPO4.

Influence alloying elements of Al and Y in Mg Li alloy on the corrosion behavior and wear resistance of microarc oxidation coatings

Microarc oxidation (MAO) coatings were performed on different Mg Li alloys (Mg 14Li, Mg-14Li-3Al, Mg-14Li-3Al-1Y) in silicate electrolyte. The morphology, thickness, corrosion behavior and wear resistance of the coatings were characterized and analyzed. Results indicate that, compared to Mg 14Li alloy, adding Al and Y in the substrate refines the grains and forms the AlLi and Al 2 Y phases, contributing to the differences in corrosion behaviors of the Mg Li alloys. The alloying elements and uniformly fine microstructure modify the MAO growth process and promote the formation of thick coatings with fewer defects. The MAO coating on the Mg-14Li-3Al-1Y alloy possesses the best corrosion resistance with the i corr of 7.485 × 10 −6 A/cm 2 , due to the densest coating and the thickest inner layer. The reduced porosity and smoother surface enhance the hardness and wear resistance of the MAO coatings on the Mg-14Li-3Al and Mg-14Li-3Al-1Y alloys. It is worth considering the refinement of microstructure and incorporation of passive elements for preparing compact MAO coatings with excellent performances on Mg Li alloys. • The formation mechanism of MAO coatings was influenced by Al and Y in Mg 14Li alloy. • A compact and thick MAO coating was formed on Mg-14Li-3Al-1Y alloy. • High corrosion and wear resistant MAO coating can be obtained on Mg-14Li-3Al-1Y.

Improved corrosion and wear resistance of micro-arc oxidation coatings on the 2024 aluminum alloy by incorporation of quasi-two-dimensional sericite microplates

Although aluminum alloys are widely used in the aerospace and automotive industry, they are susceptible to local corrosion and wear during long-term service in harsh environment. In this work, micro-arc oxidation (MAO) coatings containing quasi-2D sericite microplates are prepared on the 2024 aluminum alloy, and their corrosion and wear resistance are investigated. The results reveal that the sericite-incorporated MAO sample prepared in the 15 g/L sericite electrolyte (M−15) possesses the best corrosion resistance in 3.5 wt% NaCl solution, as manifested by a corrosion current density of 2.93 × 10−10 A ∗ cm−2 that is 4 orders of magnitude less than that of the 2024 Al alloy substrate. The wear resistance of MAO coating is also improved by the addition of sericite microplates, which is shown by the low wear rate and reduced coefficient of friction (∼0.3) of M−15 against steel ball. Our mechanistic study reveals that the quasi-2D sericite microplates in the coatings can prevent the penetration of the corrosive media and facilitate the formation of the tribo-transfer film. The sericite-containing MAO coatings providing excellent protection to aluminum alloys under corrosion and wear conditions possess great application prospects and large commercial potential.

Effect of micro-arc oxidation coatings with different thickness on high cycle fatigue performance of Ti-6Al-4V titanium alloy

Micro-arc oxidation (MAO) coatings with 2 μm, 5 μm and 10 μm in thickness were produced on Ti-6Al-4V titanium alloy by MAO treatment, and the effect of coating thickness on the high cycle fatigue property was investigated. The microscopies and phases of coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The results indicated that the coatings were mainly composed of anatase TiO2. The MAO process generated micro pits at the substrate surface. The micro pits played a role of the notches, which induced the crack initiation during fatigue loading. The fatigue life of samples decreased with the increase of coating thickness. The micro pits were the main factor for the decrease of the fatigue life.

Corrosion and wear properties of h-BN-modified TC4 titanium alloy micro-arc oxide coatings

In this study, ceramic coatings were prepared on the surface of TC4 titanium (Ti) alloy by micro-arc oxidation (MAO). The morphology, element distribution and phase composition of MAO coatings were analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and other analytical methods. The effect of hexagonal boron nitride (h-BN) doping on the wear resistance and corrosion resistance of the MAO layer was studied. The results showed that the coating was mainly composed of rutile titanium dioxide (TiO2), anatase titanium dioxide and a small amount of h-BN. Furthermore, the composite coating containing h-BN was less porous than the particle-free coating. The test results showed that h-BN doping slightly affected the hardness of the MAO coating, and it was helpful in improving the thickness, corrosion resistance and wear resistance of the coatings. When the amount of h-BN was 3 g/l, the corrosion current density of the coating was the smallest. When the addition of h-BN was 1.5 g/l, the friction coefficient of the coating was the smallest. The wear mechanism was adhesive wear, accompanied by slight abrasive wear.

Effect of thermal conductivity on micro-arc oxidation coatings

ABSTRACT Ceramic layers were deposited on Al–xCu (x = 1, 3, and 4.5 wt-%) alloys by micro-arc oxidation (MAO) at oxidation times of 10 and 24 min. Effects of changes in electrical conductivity (EC) and thermal conductivity (TC) of the substrate on microstructure, phase composition, residual stress (RS), and thermal shock resistance (TSR) of the layers were studied. The low EC was not conducive to the formation of α-Al2O3 at the 10 min oxidation. The low TC contributed to the increasing coating thickness and residual compressive stress (RCS) formation. Coatings on the alloy with 1 wt-% Cu exhibited residual tensile stress (RTS). The cavity formation induced by Al2Cu phase affected the current and RS. The results of thermal shock tests showed that the high TC and RTS in the ceramic layers impaired the TSR. The RCS together with the high TC caused the significant cohesive failure.

Electroless Plating of Ni-P and Ni-P-PTFE on Micro-Arc Oxidation Coatings for Improved Tribological Performance

Although micro-arc oxidation (MAO) coatings are widely used for anti-wear protection of metals, they usually contain lots of pores and exhibit high coefficient of friction. In this work, porous MAO coatings consisting of Al2TiO5 were fabricated on the titanium substrate, and then Ni-P and Ni-P-polytetrafluoroethylene (PTFE) were deposited via electroless plating to fill MAO pores and improve the tribological performance. Electroless deposited Ni-P has high wear resistance and the incorporated PTFE particles have self-lubricating property. Results show that the micro-pores of the MAO coating were completely filled by deposited Ni-P and Ni-P-PTFE, and the self-lubricating PTFE particles distributed uniformly in the coating. For the MAO-Ni-P-PTFE coating, the MAO and Ni-P components mechanically interlocked and played a load-carrying role during the tribological test, and the dispersed PTFE particles produced low friction. Compared with the MAO and MAO-Ni-P coatings, the MAO-Ni-P-PTFE coating exhibited much lower coefficient of friction and wear rate.

Effect of Pulse Frequency on Phase Composition and Properties of Amorphous Zirconium Alloy Micro-arc Oxidation Coating

The micro-arc oxidation coating was prepared on the surface of the amorphous zirconium sheet, and the influence of frequency on the micro-arc oxidation coating of the Zr-based amorphous alloy was studied. The results show that the change of the frequency of the electrical parameters of the micro-arc oxidation in the silicate micro-arc oxidation bath will promote the transformation of the t-ZrO2 phase to the m-ZrO2 phase in the coating; the frequency affects the gap, uniformity and thickness of the coating. When the frequency is 400 Hz, the coating surface has small voids and no cracks, and the thickness reaches a maximum of 15 μm. With the increase of frequency, the weight loss of the amorphous zirconium micro-arc oxidation coating first decreases and then increases. The wear resistance can be improved.

Исследование защитных свойств покрытий, полученных методом микродугового оксидирования в щелочных растворах электролитов

The article presents the results of a study of the corrosion properties of oxide coatings compacted with polymers and without compaction. Oxide coatings were obtained on VT1-0 and VT5 titanium alloys under the influence of fast pulsed actions of the micro-arc oxidation (MAO) process. To form MAO coatings, a pulsed mode of the process was used with an anodic current pulse duration of 250 ± 25 μs; the cathodic current pulse duration of 5 ± 0.5 ms; pause between anodic and cathodic current pulses 250 ± 25 μs; repetition rate of anodic and cathodic pulses 50 ± 0.5 Hz. Alkaline solutions were used as electrolytes. Fluoroplastic and epoxy resin solutions were used to seal the oxide coatings. The obtained MAO coatings have 4.4 – 7.5 % porosity on the VT1-0 alloy and 5.4 – 12.1 % on the VT5 alloy. The average diameter of oxide coating pores varies from 0.1 to 0,5 µm. X-ray phase analysis showed titanium dioxide in anatase and rutile modification in the oxide coatings composition. Tests performed in a 24 % solution of sulfuric acid at 40 and 75°C showed that the coatings on the VT1-0 alloy, both oxide and oxide-polymer, are more corrosion resistant than similar coatings on the VT5 alloy. All types of coatings produced on VT1-0 alloy are corrosion-resistant at a test temperature of 40 °C. Consolidation of MAO coatings with polymeric materials improves corrosion properties.

Microstructure and elemental composition of UMAO calcium phosphate coatings

The influence of the employing ultrasound (US) with different powers and waveforms during the micro-arc oxidation (MAO) on the formation of elemental composition and microstructure of the CaP coatings was studied. The energy-dispersive X-ray spectroscopy (EDX) revealed the following quantitative elemental composition of both the MAO and US-assisted MAO (UMAO) coatings: O (66-70 аt.%); P (14-16 at.%); Ti (11-13 аt.%); Ca (4-5 аt.%). The transmission electron microscopy (TEM) revealed the amorphous-crystalline microstructure in both the coatings regardless of the application of US during the MAO. The nanocrystallites of the CаHPO4, β-Cа2P2O7, and TiO2 (anatase) phases were observed in the coatings. In addition to these phases, a high-temperature metastable phase α-Ca2P2O7 was detected in the UMAO coatings.

Improvement of Steam Oxidation Resistance of the Γ-Tial Alloy with Microarc Oxidation Coatings at 900 - 1200°C

Improvement of Steam Oxidation Resistance of the Γ-Tial Alloy with Microarc Oxidation Coatings at 900 - 1200°C

Corrosion Behavior of Micro-Arc Oxidation Coating on Zirconium Alloy in Superheated Steam Condition

Corrosion Behavior of Micro-Arc Oxidation Coating on Zirconium Alloy in Superheated Steam Condition

Study of microarc oxidation coatings friction and wearing under base oils greasing conditions

The presented paper is considered the issues of coatings wear resistance formed by the microarc oxidation method (MAO-coatings) on aluminum alloys. To form coatings, the aluminum alloys D16 (2024) and V95 (7075) in base weakly alkaline electrolyte and its modification by the way introduction into it such components like sodium aluminate, suspension of fluoroplastic and their combination with carbon nanoparticles were used. Tribotests of the friction couple "MAO-coating — steel ShKh15" by the scheme "Ring—Ring" under greasing condition performed an improvement of MAO-coatings tribological characteristics in the electrolyte modified by the fluoroplastic suspension.

Corrosion Resistance and Biocompatibility of Micro-Arc Oxidation Coatings with the Variable Sodium Fluoride Concentration on Zm21 Magnesium Alloys

Corrosion Resistance and Biocompatibility of Micro-Arc Oxidation Coatings with the Variable Sodium Fluoride Concentration on Zm21 Magnesium Alloys

Effects of Graphene on the Wear and Corrosion Resistance of Micro-Arc Oxidation Coating on a Titanium Alloy

In order to improve the wear and corrosion resistance of micro-arc oxidation (MAO) coating on a Ti-5Al-1V-1Sn-1Zr-0.8Mo alloy, 0–0.20 g/L graphene was added to the electrolyte to prepare micro-arc oxidation coating. The thickness, roughness, micro-morphology, and composition of the MAO coating were characterized, and the wear and corrosion resistance of the coating was tested and analyzed. The results show that with 0.05 g/L of graphene in the electrolyte, the roughness of the coating decreased from 56.76 μm to 31.81 μm. With the increase in the addition of graphene, the microstructure of the coating became more compact, the diameter of micro-holes and micro-cracks decreased, and the corrosion resistance of the coating improved. The wear tests showed that the mass loss of the coating at the early wear stage (0~100 revolutions) was greater than that at the later stage (100~250 revolutions), and the wear resistance of the coating obtained by the addition of 0.10 g/L of graphene was the highest. With 0.10 g/L of graphene, the adhesion force between the coating and the substrate alloy is the largest, reaching 57.1 N, which is 9.98 N higher than that without graphene. After salt spray corrosion for 480 h, the coating with graphene has better corrosion resistance than that of a graphene-free coating.

In situ preparation of MAO/TiO2 composite coating on WE43 alloy for anti-corrosion protection

Microarc oxidation (MAO) coatings have attracted a lot of researchers because of their excellent adhesion to the substrate alloys. However, the porous structure of the MAO coating allows aggressive ions to invade the MAO/substrate interface and deteriorates the anti-corrosion of the coating. Herein, to seal the micropores and improve corrosion protection, a dense and biocompatible TiO2 layer was successfully developed on the MAO coating of the biodegradable WE43 alloy. Characteristics of the composite coating were analyzed, and then the degradation behavior of the samples was investigated. Results demonstrated that the micro-defects in MAO coating were effectively sealed by TiO2. Compared with WE43 alloy, the corrosion current density of the sample coated with MAO/TiO2 was reduced by three orders of magnitude, indicating that the composite coating has an excellent anti-corrosion behavior. In addition, the anti-corrosion mechanism of MAO/TiO2 composite coating was also suggested.

Effect of (NH4)2ZrF6, Voltage and Treating Time on Corrosion Resistance of Micro-Arc Oxidation Coatings Applied on ZK61M Magnesium Alloys.

The effects of (NH4)2ZrF6 concentration, voltage and treating time on the corrosion resistance of ZK61M magnesium alloy micro-arc oxidation coatings were studied by orthogonal experiments. The SEM result shows that the surface roughness and porosity of MAO coatings increased with (NH4)2ZrF6 concentration, voltage and treating time as a whole, except the porosity decreased with treating time. EDS, XRD and XPS analysis show that (NH4)2ZrF6 was successfully incorporated into coatings by reactive incorporation, coatings are dominantly composed of ZrO2, MgO, MgF2 and amorphous phase Mg phosphate. Potentiodynamic polarization was used to evaluate the corrosion property of coatings. When the concentration of (NH4)2ZrF6 is 6 g/L, the voltage is 450 V, and the treating time is 15 min, the coating exhibits the best corrosion resistance which corrosion current density is four magnitudes lower than substrate attributed to the incorporation of ZrO2 and the deposition of MgF2 in the micropores.