Micro-arc Oxidation Coatings Research Articles

Effects and mechanism of Zn on the structure and corrosion resistance of microarc oxidation coatings on aluminum alloy

A composite Zn coating is prepared on 2024 aluminum alloy by microarc oxidation (MAO) and the corrosion resistance is investigated. During MAO, the addition of an appropriate concentration of Zn2+ regulates the size and intensity of surface sparks on the sample giving rise to a uniform distribution of MAO current and less large discharge channels. The crystal structure of Al2O3 is compressed and the density of the coating increases. The coating has the Zn3Al94O144 phase and electrochemical tests reveal a corrosion current density (icorr) that is 3 orders of magnitude smaller than that of the coating without Zn doping. Density-functional theory calculations show that Zn inhibits the adsorption of Cl- and consequently reduces the damage to the passivation layer.

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.

Superhydrophobic surface on MAO-processed AZ31B alloy with zinc phosphate nanoflower arrays for excellent corrosion resistance in salt and acidic environments

Corrosion caused by the active chemical properties of magnesium (Mg) alloys seriously restricts their applications in aerospace, transportation, biomedicine, and other fields. Although micro-arc oxidation (MAO) coatings can provide some corrosion protection for Mg alloys, their microporous structure is prone to localized corrosion. Herein, nanoflower-shaped zinc phosphate is prepared and hydrophobically modified. The commercial glue is used to bond the nanoflower-shaped zinc phosphate particle arrays to the MAO-coated AZ31B alloy substrate to produce a two-layer composite coating with superhydrophobic properties. The composite coating exhibits obvious repulsive effects in salt and acidic solutions as indicated by contact angles of 160° and 156°, respectively. The composite coating has improved electrochemical properties and immersion corrosion in both the salt and acidic solutions compared to the substrate and MAO-coated sample. Moreover, the composite coating retains the long-term superhydrophobic effects under different conditions such as immersion in salt and acidic solutions, water scouring, and sunlight exposure, which well indicates commercial applications.

Improved Corrosion Properties of Mg-Gd-Zn-Zr Alloy by Micro-Arc Oxidation

In order to improve the corrosion resistance of Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys for biomedical application, the alloy was micro-arc oxidation (MAO)-treated using silicate electrolyte system under various voltages (400 V, 425 V, 450 V, 475 V). The effects of voltage on the microstructure and corrosion properties of MAO coating were investigated via X-ray diffraction (XRD) and a scanning electron microscope (SEM) combined with an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscope (XPS), and electrochemical experiments. The results showed that, with the increase in voltage, the MAO coatings became thicker and the micropores on the MAO coating increased in diameter. The main phase compositions of the MAO coatings were MgO and Mg2SiO4. Potentiodynamic polarization curve results showed that MAO coatings could enhance corrosion resistances, where the corrosion current density decreased by six orders of magnitude and the corrosion potential of the specimens increased by 300 mV for the voltage of 450 V in the MAO treatment; nevertheless, the corrosion resistance rapidly deteriorated due to the creation of large micropores in the MAO coating, which provide a pathway for corrosive media when the voltage is 475 V. The electrochemical impedance spectroscopy results showed that MAO treatments could increase low-frequency modulus resistance and increase the corrosion resistance of Mg alloys. In addition, MAO-treated GZ31K alloys still exhibited uniform corrosion, which is desirable for biomedical applications.

Improved wear and corrosion resistance of alumina alloy by MAO and PECVD

Aluminum alloys, which are vital in various industries, are susceptible to corrosion and wear. Although the micro-arc oxidation (MAO) method addresses these issues, it introduces microporosity, which undermines the integrity of the alloy. In this study, MAO coatings are enriched via plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisilane, specifically SiCOx and SiOx. The assessment of the mechanical, tribological, and corrosion-resistant characteristics of these composite coatings reveals substantial enhancements in the aluminum alloy properties post-PECVD treatment. Surface morphology observations highlight the reduced pore size and area of the PECVD-coated surfaces, particularly in SiCOx coatings, which are known for their superior gap-filling properties. Scratch tests demonstrate superior adhesion of SiCOx coatings, showed a higher scratch resistance of approximately 17.8 N compared to 15.9 N for SiOx coatings. The wear rate of the SiCOx coating significantly decreased compared to the MAO coating owing to higher hardness, dropping from 3.57 × 10−5 mm3/N·m to 2.04 × 10−5 mm3/N·m. SiCOx-coated surfaces show higher corrosion potential (−0.0078 V) than MAO-only coating (−0.0212 V), indicating enhanced corrosion resistance. These innovative coatings provide an advanced surface treatment strategy and are suitable for a wide range of industrial applications owing to their enhanced surface attributes.

Corrosion resistance and antibacterial properties of hydrophobic modified Ce-doped micro-arc oxidation coating

Aluminium (Al) alloys with high corrosion resistance and bactericidal capability will have significant potential for broader utilization in marine applications. To achieve this, a layer of cerium (Ce)-doped anodic oxidation (AO) film was prepared on the surface of the Al alloy to modify the pore structure of the micro-arc oxidation (MAO) coating. This not only improved its corrosion resistance but also imparted certain antibacterial properties to the coating. Then, 1H, 1H, 2H, 2H- perfluoroalkyltriethyloxy-silane (PFOTES) was used to hydrophobically modify the coating, which more effectively obstructed corrosive ions and bacteria, further elevating its corrosion resistance and antibacterial properties. Electrochemical tests demonstrated that |Z|0.01Hz of the modified coating was 2.86 × 109 Ω·cm2 which was two orders of magnitude higher than before. Furthermore, it remained above 109 Ω·cm2 even after 288 h of immersion. Moreover, the antibacterial effectiveness of the modified coating against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) increased by 5.89% and 19.53%, respectively, to 98.58% and 97.34%. These findings indicate a promising direction for improving the corrosion resistance of MAO coatings on metallic materials, paving the way for large-scale industrialization.

Silver Containing Antimicrobial Coatings on Innovative Ti-30Nb-5Mo β-Alloy Prepared by Micro-Arc Oxidation for Biomedical Implant Applications

Micro-arc oxidation (MAO) is a versatile surface-modification method that promotes higher wear and corrosion resistance, osseointegration, and biological activity to titanium alloys’ surfaces. This study aimed to modify the surface of a recently developed metastable β Ti alloy, which exhibits more favorable mechanical properties for implant applications compared to some commercial Ti alloys, by incorporating Ag into the coatings to introduce a bactericidal function to the surface. The Ti-30Nb-5Mo alloy, with lower elastic modulus, was treated by the MAO method using electrolyte solutions containing calcium acetate, magnesium acetate, β-glycerol phosphate, and varied concentrations of silver nitrate (1.5 mM, 2.5 mM, and 3.5 mM). With an increase in the concentration of silver ions in the electrolyte, the galvanostatic period during the MAO process decreased from 1.7 s to 0.5 s. The Ca/P ratio increased from 0.72 up to 1.36. X-ray diffraction showed that the MAO coatings were formed by rutile and anatase TiO2 main phases and calcium phosphates. X-ray photoelectron spectroscopy analysis detected the presence of amorphous Nb2O5, CaCO3, and MgCO3, and metallic and oxide forms of Ag. The increase in Ag in the electrolyte decreased the coating thickness (from 14.2 μm down to 10.0 μm), increased the contact angle (from 37.6° up to 57.4°), and slightly increased roughness (from 0.64 μm up to 0.79 μm). The maximum inhibition of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans strains growth was of 43%, 43%, and 61%, respectively. The Ag did not negatively affect the differentiation of adipose-tissue-derived mesenchymal stem cells. Therefore, the treatment of the surface of the innovative Ti-30Nb-5Mo alloy by the MAO method was effective in producing a noncytotoxic porous coating with bactericidal properties and improved osseointegration capabilities.

Effect of micro-arc oxidation coatings with graphene oxide and graphite on osseointegration of titanium implants-an in vivo study

BackgroundThis in vivo study evaluated the effect of graphene oxide and graphite coatings, coupled with the micro-arc oxidation (MAO) surface roughening technique, known for their mechanical strength, chemical stability, and antibacterial properties. The main objective was to assess the degree of improvement in osseointegration of titanium implants resulting from these interventions. Materials and methodsIn this study, 32 female rats were utilized and randomly allocated into four groups (n = 8 each): machined surface titanium implants (control), those roughened by the MAO method, those coated with graphene oxide-doped MAO, and those with a graphite-doped MAO coating. Titanium implants were surgically placed in the right tibia of the rats. Rats undergoing no additional procedures during the 4-week experimental period were sacrificed at the end. Then, the implants and surrounding bone tissues were separated and embedded in acrylic blocks for reverse torque analysis. Using a digital torque device, the rotational force was applied to all samples using a hex driver and racquet until implant separation from the bone occurred, with the corresponding values recorded on the digital display. Then, statistical analysis was performed to analyze the data. ResultsNo statistically significant difference between the groups was observed in the biomechanical bone–implant connection levels (N/cm) (P = 0.268). Post-hoc tests were not required because no discernible differences were identified between the groups. ConclusionWithin the scope of this study, implants treated with the MAO method, along with those coated with graphene oxide- and graphite-doped MAO method, did not exhibit significant superiority in terms of osseointegration compared to machined surface titanium implants.

The effect of Nb on the formation of TiO2 anodic coating oxide on Ti–Nb alloys through MAO treatment

This study aims to promote the growth of a porous oxidized coating of TiO2 due to oxidation of the surface of the Ti–Nb alloy substrates (Nb = 5, 10, and 25 wt%) using the micro-arc oxidation (MAO) technique. Using structural (x-ray diffraction) and microstructural (optical, confocal, and scanning electron microscopy) characterization techniques, it was observed that Nb promotes the formation of the β phase in Ti alloys, reducing Vickers microhardness and elastic modulus values. Regarding the MAO coating, the results showed that the TiO2 coatings are in the form of anatase and rutile, where Nb promotes the formation of the rutile phase, increasing the hardness of the coatings. MAO coatings have high roughness values due to the formation of porous structures characteristic of MAO surfaces. Adhesion results show that MAO coatings have low adhesion with the substrate.

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.

Effects of Additives on the Microstructure and Tribology Performance of Ta-12W Alloy Micro-Arc Oxidation Coating

Effects of Additives on the Microstructure and Tribology Performance of Ta-12W Alloy Micro-Arc Oxidation Coating

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

PurposeThe 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/approachThe 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.FindingsWhen 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/implicationsToo high concentration of ZnO reduces the performance of MAO coating.Practical implicationsThe 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/valueThe 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.

Effect of Pr(NO3)3 doping on the characteristics of TC4 micro-arc oxidation coatings

Micro-arc oxidation coatings were prepared on the surface of TC4 by adding different contents of rare-earth compound Pr(NO3)3 to the aluminate and phosphate-based electrolyte. The results showed that the change in oxidation voltage increased at first and then decreased with the raised of Pr(NO3)3 addition. At 0.05 g L−1, the oxidation voltage reached the maximum, the number of discharge micropores decreased, while the size increased, the thickness and hardness of the coatings reached the peak values. The coatings mainly included Al2TiO5, anatase, γ-Al2O3 and a little of Pr2O3. Pr(NO3)3-doped coatings showed excellent corrosion resistance in 3.5% NaCl electrochemical workstation and oilfield simulation fluid containing 5% NaCl, and the corrosion resistance of the coatings reached the best at 0.05 g L−1.

Effects of Ni content on microstructure and performance of MAO coatings on binary Al–Ni alloys

In this study, the pure Al and binary Al–Ni alloys with Ni addition of 1, 3, 6, and 10 wt % were coated via micro arc oxidation (MAO) in a tetraborate and phosphate based electrolyte for 60 min. With increased Ni content, the color of MAO coating became darker due to increased Ni-containing compounds on the surface. The Ni played a negative effect on the coating growth, decreasing both the coating thickness and surface roughness. The coatings on the Al–Ni alloys were mainly composed of γ-Al2O3 and α-Al2O3, and the Ni facilitated the formation of α-Al2O3 in the coating. Nanoparticles of NiO were generated around the edge of discharge channels for Al–6Ni and Al–10Ni alloys after a certain oxidation time. All coatings exhibited a uniform and dense surface structure, with the outer layer being more compact than the inner layer. Many tiny pores were found in the inner layer. Despite the corrosion resistance was decreased, the anti-wear performance of MAO treated samples was improved with the increased Ni content in the matrix. While, the corrosion resistance of the coated samples decreased with the adding of Ni content in the matrix.

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.

Investigation of In Vitro Cytocompatibility of Zinc-Containing Coatings Developed on Medical Magnesium Alloys.

In a neutral solution, we investigated the effects of Na2[ZnEDTA] concentrations at 0, 6, 12, 18, and 24 g/L on surface morphology, chemical composition, degradation resistance, and in vitro cytocompatibility of micro-arc oxidation (MAO) coatings developed on WE43 (Mg-Y-Nd-Zr) magnesium alloys. The results show that the enhanced Na2[ZnEDTA] concentration increased the Zn amount but slightly decreased the degradation resistance of MAO-treated coatings. Among the zinc-containing MAO samples, the fabricated sample in the base solution added 6 g/L Na2[ZnEDTA] exhibits the smallest corrosion current density (6.84 × 10-7 A·cm-2), while the sample developed in the solution added 24 g/L Na2[ZnEDTA] and contains the highest Zn content (3.64 wt.%) but exhibits the largest corrosion current density (1.39 × 10-6 A·cm-2). Compared to untreated WE43 magnesium alloys, zinc-containing MAO samples promote initial cell adhesion and spreading and reveal enhanced cell viability. Coating degradation resistance plays a more important role in osseogenic ability than Zn content. Among the untreated WE43 magnesium alloys and the treated MAO samples, the sample developed in the base solution with 6 g/L Na2[ZnEDTA] reveals the highest ALP expression at 14 d. Our results indicate that the MAO samples formed in the solution with Na2[ZnEDTA] promoted degradation resistance and osseogenesis differentiation of the WE43 magnesium alloys, suggesting potential clinic applications.

Effect of graphene additive on microstructure and properties of MAO coatings on 6063 aluminum alloy

Abstract The micro-arc oxidation process is used to improve the properties of 6063 aluminum alloy by forming coatings on the surface of the alloy, in order to further enhance the features of the basic micro-arc oxidation coatings, graphene was added into the silicate alkaline electrolyte. The addition of the graphene influences the surface morphologies, thickness, element distributions, phase compositions, wear resistance and corrosion resistance of the formed coatings. They were studied by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, friction and wear testing and an electrochemical workstation. The results show that the microstructure and properties of the coating were modified with the increase of graphene concentration. However, when too much graphene was added, the performance of the coating became worse.

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.

Adhesion Strength and Anti-Corrosion Performance of Ceramic Coating on Laser-Textured Aluminum Alloy

Laser surface texturing and micro-arc oxidation provide excellent approaches to enhance the adhesion strength and anti-corrosion performance of adhesive bonding interfaces in aluminum alloys, which can be applied in the field of automotive light weighting. Herein, micro-arc oxidation coatings were fabricated on the laser-textured aluminum surface under the voltage of 500 V for various treatment times (5 min, 15 min, 30 min, 60 min). The anti-corrosion performance of ceramic coatings on the laser-textured surface was analyzed using electrochemical measurements. The results of electrochemical measurement indicate that the coating on the sample surface presents two time constants corresponding to a dual-layer structure. The sample grown under 500 V for 60 min exhibits excellent protective performance with a value of 1.3 × 107 ohm·cm2. The adhesion strength of laser-textured ceramic coating is improved compared with the as-received substrate. The sample treated with 500 V for 30 min exhibits the highest bonding strength with a value of 52 MPa. The wider pores and bulges for the sample grown in 60 min would introduce microcracks and consequently reduce the adhesion strength.

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