Micro-arc Oxidation Film Research Articles

Enhancing the self-healing property by adding the synergetic corrosion inhibitors of Na3PO4 and 2-mercaptobenzothiazole into the coating of Mg alloy

Self-healing coatings can inhibit the corrosion of Mg alloys from the damaged areas. In this paper, a duplex self-healing coating, with loading interphase inhibitor into the pores of micro-arc oxidation (MAO) film and doping organic inhibitor into the top paint, is prepared to enhance the self-healing property. The synergistic effect between both inhibitors and the self-healing property of the coating were characterized. The releasing and healing processes were investigated. The results show that 2-mercaptobenzothiazole (MBT) can absorb on the defects of the formed Mg3(PO4)2 and Mg(OH)2 film, which further inhibits the corrosion process by synergistic effect. When the self-healing coating is damaged, phosphate ions can be released from the MAO film quickly while MBT is released from the top paint slowly, then they synergistically inhibit the corrosion of the damaged areas, enhancing the self-healing property greatly in comparison with addition of each inhibitor singly.

Influence of irradiation intensity on corrosion properties of microarc oxidation film on AZ31 magnesium alloy with HIPIB

Purpose The purpose of this paper is to investigate the effect of high-intensity pulsed ion beam (HIPIB) intensity on the structure and corrosive properties of microarc oxidation (MAO) films on AZ31 magnesium alloy and explore the mechanism for modified anti-corrosion properties of irradiated films. Design/methodology/approach The energy deposited on the coating surface influences the remelting process of the MAO coatings significantly, which was closely related to the intensity of HIPIB; therefore, HIPIB with various intensities of 100-350 A/cm2, was selected to modify the MAO films on AZ31 magnesium alloy. The changes in film structure and phase structure of modified films were characterized by scanning electron microscopy and X-ray diffractometry (XRD) with CuKα, respectively. The corrosive behavior of the MAO films was featured with polarization curves and electrochemical impedance spectrum in 3.5 per cent NaCl solution on a PAR 2273 electrochemical workstation. Findings The results clearly show that a dense, continual and remelted layer with a few micrometers in thickness was obtained on the irradiated surface at 200 A/cm2, which are mainly responsible for the modified and optimal anti-corrosion property of MAO films by suppressing/retarding the process of the corrosive electrolyte infiltration into magnesium substrate surface. Originality/value The paper reveals that HIPIB irradiation could modify the corrosion resistance by producing a remelted compact layer on the MAO film surface at a suitable irradiation parameter and explored the modified mechanism of MAO films.

Growth mechanism of micro-arc oxidation film on 6061 aluminum alloy

The 6061 aluminum alloy was disposed using bipolar pulse micro-arc oxidation power supply in Na2SiO3-CH3COONa-Na5P3O10 electrolyte system, where the surface spark discharge of aluminum alloy during micro-arc oxidation was observed by long distance working microscope, and the micro-structure of molten pool in micro-arc oxidation film were studied by 3D video microscope, SEM, XRD, combined with film/substrate separation technology and layer by layer thinning technique. Also, the mechanism of micro-arc oxidation breakdown and discharge of aluminum alloy was investigated thoroughly. The results showed that duration time of spark discharge increased with the progress of micro-arc oxidation reaction, which was 67 ms when oxidation reaction lasted 1 min, however it reached 532 ms when reaction lasted 90 min. With increase of oxide film thickness, the size of spark and weld pool increased, where the size of spark was exponentially related to thickness of film, and size of molten pool was linear to the film thickness, while two sizes were approximately equal. The profile of molten pool was trumped-like shape, and part of the pool was connected with each other in the oxide film, leading to a formation of three-dimensional network structure. At the bottom of oxide film, there were discharge micropores with a diameter of ∼150–200 nm, and α-Al2O3 phase content in the film increased from the surface to bottom. Micro-arc discharge occurred in ‘interlock’ form at bottom of the oxide film, forming ‘fire flower clusters’, which melted and vaporized around metals, such that spraying concurred, while new oxides was formed at the surface and bottom of oxide film, thus making the oxide film thicker.

Relationship between porosity, pore parameters and properties of microarc oxidation film on AZ91D magnesium alloy

Microarc oxidation films on AZ91D magnesium alloy were prepared in sodium silicate-based electrolyte by a high-frequency bipolar pulsing mode. The effects of porosity and pore parameters on the properties of the films were studied. The results show that with the increased current frequency, the relative content of Mg element and the relative content of MgSiO3 phase in the films increase. The bonding strength of the films increases and the film microhardness decreases with the increased porosity respectively. Pore diameter could also affect the film properties to some degree. As the current frequency increases, the pore diameter and the film porosity decrease while the interpore distance and the pore circularity increase. The larger pore diameter and the higher porosity could promote the cracking behavior of the films while the larger interpore distance and the higher pore circularity could hinder the cracking behavior. Crack density is a better parameter than crack width when evaluating heat resistance. With decreased film porosity, the film impedance in 3.5% NaCl solution increases. The lower porosity and the better continuity of the films improve the anti-corrosion ability of the films.

Anti-fracture performance of micro-arc oxidization films on TiNiSi shape memory alloy after elongation, bending and shape recovery

The adhesion of a coating on a shape memory alloy (SMA) as an implant is very crucial, because the coating may break when the implant undergoes shape change and recovery during implantation. This study investigated parameters for micro-arc oxidation (MAO) applied to Ti50Ni49Si1 SMA from the viewpoint of coating adhesion. Four kinds of adhesion tests were utilized to evaluate the adhesion of a coating: pull out, scratch, tension-recovery, and bending-recovery tests. Ti50Ni49Si1 SMA is a martensitic phase alloy, and it has higher transformation temperatures (Ms = 48.83 °C and Af = 112.19 °) than the equiatomic Ti50Ni50 SMA. MAO produced an oxide film with a porous surface. Increasing the anodic voltage caused the pore size, the film thickness, and the surface roughness to increase, while the shape recovery rate was deceased. The oxide film formed by applying an 80 V voltage contained small amounts of nanopores. The application of 120 V or 150 V produced micropores and nanopores that were distributed in the middle of the film and film/substrate interface, respectively. The adhesive strength of the MAO films formed by 80 V, 120 V, and 150 V were 33.8 ± 6.4, 42.6 ± 4.8, and 78.9 ± 4.2 MPa, respectively. The oxide films did not fail in the pull out evaluation. The critical load of the MAO films was increased with the anodic voltage: its values for the oxide films formed at 80 V, 120 V, and 150 V were 71.2 ± 2.3, 90.9 ± 2.8, and 112.7 ± 2.4 mN, respectively, and they were measured by scratch tests. However, the use of a low anodic voltage or short duration is beneficial to MAO film adhesion when plastic deformation is imposed to the substrate. Specimens anodized at 80 V remained unbroken, but the films were detached at 120 V and 150 V after their elongation by tensile force and subsequent recovery by heating. The bending and recovery behaviours caused most of the MAO films to crack, except for the specimens anodized at 80 V for 3 and 5 min.

Effect of micro arc oxidation on micro – structure and electrochemical corrosion performance of cold sprayed aluminum coating

PurposeTo improve the electrochemical corrosion resistance of cold sprayed Al coating.Design/methodology/approachA cold sprayed aluminum (Al) coating fabricated on S355 structural steel was oxidized using a micro arc oxidation (MAO). The electrochemical corrosion and impedance spectroscopy were tested to investigate its corrosion performance.FindingsThe MAO film is primarily α-Al2O3 and γ-Al2O3, which increases its density and surface quality. The corrosion potential is positively shifted by 0.2 V, and the electrochemical impedance is significantly increased.Originality/valueA cold sprayed Al coating on S355 steel was first oxidized using a MAO. The effects of MAO on the microstructure of Al coating were investigated to analyze its electrochemical corrosion behavior.

Zeta potential of microarc oxidation film on zirlo alloy in different aqueous solutions

Zeta potentials of the bare Zirlo alloy and its microarc oxidation (MAO) film in KCl, NaCl, H3BO3 and LiOH solutions were measured. Their corrosion behavior in different solutions were evaluated by electrochemical impedance spectroscopy (EIS). The correlation between zeta potential and corrosion behavior was also analyzed. The MAO treatment shifted the iso-electric point (IEP) to a higher pH value in 1500 ppm B3+ and 2.3 ppm Li+ mixed aqueous solution for simulating normal water chemistry in nuclear reactors. Besides, MAO film with higher zeta potential could reduce the adsorption of lithium ions, which improved the corrosion resistance of Zirlo alloy.

Effects of Nickel Additive on Micro-Arc Oxidation Coating of AZ63B Magnesium Alloy

Based on environmentally friendly and green manufacturing of magnesium alloys, micro-arc oxidation coatings were prepared in optimized metasilicate solutions on AZ63B magnesium alloys surfaces. Effect of nickel additive on working voltage, surface morphology, thickness, hardness, composition and corrosion resistance of micro-arc oxidation coating of magnesium alloys was studied. The surface morphology, composition, microstructure and corrosion resistance of conversion coatings were investigated by using scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray diffraction (XRD) and electrochemical tests respectively. The results show that brown coating was prepared in electrolyte with the addition of nickel acetate, which can accelerate growth of micro-arc oxide film layer and make the smaller hole on the surface. The micro-arc oxide coating mainly consists of Mg2SiO4, MgSiO3, MgAl2O4, Ni2SiO4. Potentiodynamic measurements and electrochemical impedance spectroscopy (EIS) testify that the corrosion resistant of micro-arc oxidation film adding nickel acetate electrolyte increases significantly.

High temperature tribological behavior of microarc oxidation film on Ti-39Nb-6Zr alloy

The TiO2-Nb2O5-ZrO2 composite film on Ti-39Nb-6Zr alloy was in-situ synthesized by microarc oxidation (MAO) process in potassium hydroxide electrolyte. Morphology, composition and hardness of MAO film were characterized. The tribological behavior of bare and coated Ti-39Nb-6Zr alloy under dry sliding against ZrO2 ceramic ball were studied by a ball-on-disk friction tester at the ambient temperature, 200 °C and 400 °C. Their friction coefficient and wear rate were obtained and wear mechanism analyzed. The MAO surface treatment significantly decreased friction coefficient and wear rate of Ti-39Nb-6Zr alloy at the ambient temperature and 200 °C, but the friction coefficient showed a periodical fluctuation at 400 °C while the wear rate clearly decreased. The MAO film has excellent wear resistance at different temperatures due to the formation of TiO2, Nb2O5, and ZrO2 ceramic phases. The wear mechanism of Ti-39Nb-6Zr alloy was mainly the abrasive wear at ambient temperature, but was transformed to abrasive, adhesive and oxidation wear at high temperature. The MAO treated alloy mainly displayed the adhesive wear at ambient temperature, 200 °C and 400 °C. Furthermore, the polished treatment for MAO film could obviously reduce its low friction coefficient and wear rate at the ambient temperature and 200 °C.

Experimental Parameter Effect on Ceramic Coating Film on LY12 Alloy by Micro-arc Oxidation

Ceramic coatings were fabricated on the surface of LY12 aluminum alloy by micro-arc oxidation (MAO) method in NaSiO3-NaOH solution. Effect of experimental parameter on the MAO film was investigated. The results show that the ceramic layers formed on the surface of the alloy show different surface morphologies, and thickness of MAO film increases with the increase of voltage and oxidation time. These films contain two layers, an outer porous layer and an inner barrier layer, which consists mainly of γ-Al2O3 phase and a small amount of α-Al2O3 phase..

Friction-wear behaviours of micro-arc oxidation films in situ grown on 7475 aluminium alloys

An oxide film was prepared on 7475 aluminium alloy using a micro-arc oxidation (MAO). The surface–interface morphologies, chemical compositions and phases of the obtained MAO films were analysed using a field emission scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer, respectively, and the friction-wear properties of the MAO film under the different loads and wear speeds were investigated using a wear test. The results show that there are a large number of convexes and concave features on the MAO film, which are primarily composed of Al and O, and the phases of MAO film are composed of α-Al2O3 and γ-Al2O3. The MAO film is in situ produced on the 7475 aluminium alloy, forming a metallurgical bonding with the substrate. The average coefficients of friction (COFs) and wear depths before and after MAO decreased by 40, and 26·5%, respectively. The COFs of MAO films decrease with the wear loads and speeds, while the wear volumes increase with the wear loads and speeds. The oxides in the MAO film play a role of reducing friction and decreasing wear, the wear mechanism is primarily composed of abrasive wear.

Fabrication and characterization of microarc oxidation films on Ti-39Nb-6Zr alloy at different voltages in KOH electrolyte

The TiO2/Nb2O5/ZrO2 ceramic films were successfully prepared on Ti-39Nb-6Zr alloy by microarc oxidation (MAO) at different voltages in KOH electrolyte. Their morphology, phase structure and composition were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Their conducting properties were analyzed by impedance spectroscopy and Mott–Schottky test. Meanwhile, their corrosion behaviors were evaluated by electrochemical impedance spectroscopy (EIS). The MAO films as n-type materials were 8 μm–15.8 μm thick with fine micropores on the surface. These films consisted of anatase TiO2, rutile TiO2, Nb2O5, monoclinic ZrO2 (m-ZrO2) and ZrTiO4 phases. Their conductivity gradually increased with the frequency from 4.07 × 10−15 S cm−1 at 0.01 Hz to 1.61 × 10−6 S cm−1 at 107 Hz. Their flat band potential was in the range of 0.34 V–0.77 V, and doping density varied between 3.50 × 1017 cm−3 and 5.25 × 1018 cm−3 which decreased with increasing positive voltage of MAO process. The Ti-39Nb-6Zr alloy coated at +400 V/−60 V had good corrosion resistance with lower corrosion current density and higher impedance.

The micro-arc oxidation (MAO) behaviors of in-situ TiB2/A201 composite

The Micro-arc oxidation (MAO) treatment on the in-situ TiB2/A201 composites was performed using the aluminate-based electrolyte, and the corresponding MAO behavior was discussed in this work. In connection with the film thickness-time curve, the voltage-time for the MAO process on the TiB2/A201 composite can be divided into two periods, namely the initial period (Stage I and II) and linear growth period (Stage III and IV). The phase and morphologies evolutions of the composite experienced these stages have been characterized by X-Ray diffraction, scanning electron microscopy and Micro-Raman spectroscopy. It is found the TiB2 particles have played a dual role in the MAO process. Firstly, the external current can leak through conductive TiB2 particles in the initial period. However, this leaking way has been quickly cut off by the oxidation of TiB2 to TiO2. Secondly, the TiB2 particles beneath the metal-oxide interface can impede MAO film from growing inward. Nevertheless, these TiB2 particles should be oxidized and then melted gradually, and finally dissolved into the oxide film.

Anodic dyeing of micro-arc oxidized aluminum with a cathodic pretreatment

Conventional anodized aluminum with diverse colors by surface dyeing has recently become widespread for consumer electronic appliances. Satisfactory performance, though, it failed to present good enough protection purpose. On the contrary, micro-arc oxidation (MAO) is a relatively new anodizing surface treatment to provide very high surface hardness and thus protection purpose but is incompatible with the dyeing process. In this study, we investigated a dyeing method for the MAO treated aluminum alloy by using a cathodic pretreatment to produce micropores over the MAO layer, as a result to absorb the anionic dye in a subsequent anodic treatment, thereby dyeing the MAO layer. The research results showed that the dyed MAO film achieved the optimal color saturation (L* a* b*)=(53.55, 1.17, −29.16) when the specimen was immersed in a blue dye to undergo a dyeing process with an applied anodic current of 1 A subsequent to the pretreatment at an applied cathodic voltage of 30V. Additionally, red and green dyes were also demonstrated to be feasible. Mechanism to make the MAO layer dyeable is proposed.

PREPARATION OF GRAYISH BLACK FILM ON AM50 MAGNESIUM ALLOY BY CHEMICAL CONVERSION–MICRO-ARC OXIDATION

The grayish black film was prepared on AM50 magnesium alloy with a new method which combined chemical conversion with micro-arc oxidation (MAO). The optimum formula of chemical conversion was obtained by L9(34) orthogonal test. Meanwhile, the morphology, structure, composition and corrosion resistance of films were analyzed by scanning electron microscopy (SEM), energy spectrum analysis (energy dispersive X-ray spectroscopy (EDS)), X-ray diffraction (XRD), electrochemical tests and CuSO4 drip experiment. The results indicated that Mo element was introduced into the MAO film by chemical conversion pretreatment. The surface of composite film was smooth and compact. The main phase composition of the composite film were SiO2, Mo9O[Formula: see text], MgSiO[Formula: see text] Mg2SiO4 and Mo9O[Formula: see text] was identified to be responsible for giving color to the film. The corrosion resistance of the grayish black film was improved obviously.

Fabrication and photocatalytic activity of MAO–TiO2 films formed on titanium doped with cations

The microarc oxidation (MAO) TiO2 films were fabricated in phosphate based electrolyte under different voltages on titanium to study the optimum voltage for photocatalysis, and then the doping process was carried out under the optimum condition above. The surface morphology and composition of MAO films were examined by scanning electron microscopy and X-ray diffraction. The photocatalytic activities of MAO films with and without cation dopant were evaluated by photocatalytic decolourisation of methylene blue in aqueous solution as a model pollutant under simulated sunlight irradiation. The results showed that the photocatalytic activity of MAO–TiO2 films first increased and then decreased with increasing the voltage, and the cation dopant enhanced the photocatalytic activity of MAO–TiO2 films. Moreover, the transition metal cation Cu2+ was more suitable for dope than the rare earth metal cation Ce4+ to some extent.

Growth Behaviors of Layered Double Hydroxide on Microarc Oxidation Film and Anti-Corrosion Performances of the Composite Film

Microarc oxidation (MAO) film has been widely used as an anti-corrosive film for Al alloys. However, it is still a big challenge to further improve its anti-corrosion performance due to the defects that form during the MAO process. In this study, for the first time, Ni-Al layered double hydroxide (LDH) was in-situ synthesized on the MAO film to seal its defects, which contributes to the corrosion resistance enhancement of MAO treated 6061 Al alloy. The growth of the LDH on MAO film is largely determined by the specific area, chemical composition, and crystalline structures of the alumina phase of the MAO film. More importantly, LDH nanoplates can grow into the micropores and microcracks in MAO film, and then gradually seal these structural defects. The anti-corrosion performance of MAO film during long-term immersion in NaCl solution also can be improved greatly via LDH treating because the defect-sealing effects of LDH can enhance the barrier property of both the porous and dense layers of MAO film, and then restrain the penetration of corrosive agents through the MAO film to the metal substrate.

Preparation and Characterization of Black Micro-Arc Oxidation Films

Preparation and Characterization of Black Micro-Arc Oxidation Films

Effects of Acidic MAO Electrolytes on the Coatings of Ti Alloy and the Proliferation of Osteoblast

Titanium oxide coatings are prepared by using Micro-arc oxidation method on the Ti-6Al-4V in 5% H2SO4 and 10% H3PO4 electrolytes. MG63 cells are grown in coculture on oxide films for different times to evaluate the cell proliferation ability of various films. The morphologies, phase component and roughness of coatings are characterized by means of SEM, XRD and roughness instrument. The results show that the pore diameter of micro-arc oxidation films increase with the increment of voltage and the biggest pore diameters are 239.2 nm and 2.398 μm in H2SO4 and H3PO4 respectively. The films consist of rutile and / or anatase phases with porous structures are formed on Ti-6Al-4V after oxidizing in H2SO4, while amorphous titanium with matrix phase is produced in H3PO4. The samples treated in H2SO4 solution exhibit a more significant effect on the cell proliferation compared with H3PO4 as the OD value of the samples treated in H2SO4 increase with voltage represents the greater quantity of cells, but in H3PO4 the OD value is the highest under the lowest voltage at the same time.

The influence of Ac parameters in the process of micro-arc oxidation film electric breakdown

This paper studies the electric breakdown discharge process of micro-arc oxidation film on the surface of aluminum alloy. Based on the analysis of the AC parameters variation in the micro-arc oxidation process, the following conclusions can be drawn: The growth of oxide film can be divided into three stages, and Oxide film breakdown discharge occurs twice in the micro-arc oxidation process. The first stage is the formation and disruptive discharge of amorphous oxide film, producing the ceramic oxide granules, which belong to solid dielectric breakdown. In this stage the membrane voltage of the oxide film plays a key role; the second stage is the formation of ceramic oxide film, the ceramic oxide granules turns into porous structure oxide film in this stage; the third stage is the growth of ceramic oxide film, the gas film that forms in the oxide film’s porous structure is electric broken-down, which is the second breakdown discharge process, the current density on the oxide film surface could affect the breakdown process significantly.