Corrosion Resistance Of Micro-arc Oxidation Research Articles

Effect of voltage on microstructure and corrosion resistance of micro-arc oxidation coating on Mg–Zn–Ca biodegradable alloy

This work discussed the influences of voltage on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coating developed on Mg–2Zn-0.3Ca (ZX20) alloys. The MAO coatings on ZX20 alloy surface consist of MgO and Mg2SiO4 compounds. They feature two layers, namely a porous outer layer and a dense inner layer. Higher voltage forms a thicker MAO coating on ZX20 alloy, meanwhile, larger diameter micropores and more thermal micro-cracks are generated in the coating. The MAO coating on ZX20 alloy obtained at 400V has the largest thickness (5.98 ± 0.23 μm), the largest diameter of the micropores (1.02 ± 0.64 μm), the most thermal cracks and the most amount of Mg2SiO4. The MAO coating on ZX20 alloy obtained at 300V has the largest contact angle value and the highest bonding strength. During the immersion corrosion, the corrosive ions such as Cl− can enter the outer layer of the coating and react with MgO to generate Mg(OH)2, resulting in the dissolution of the coating. With the prolong of the immersion time, local corrosion and cracks form at the weak site of the coating, speeding up the corrosion. While, the dense inner layer containing chemically stable Mg2SiO4 has less defect, providing an effective physical barrier for the substrate and enhancing the corrosion resistance of ZX20 alloy. The ZX20 alloy coated at 300V exhibits the lowest degradation rate (PH = 0.13 mm y−1) due to its dense inner layer, as well as having the largest contact angle value and the highest bonding strength.

Effect of SeO2 on corrosion resistance of micro-arc oxidation

ABSTRACT In order to make titanium alloy implants have better corrosion resistance in the human body, selenium-containing coating was added to the surface of Ti6Al7Nb through micro-arc oxidation. The results indicate that the coating has a higher thickness and lower roughness after the addition of selenium element. XRD, SEM, and XPS analysis showed that selenium element was successfully added into the coating. Then the dynamic polarization curve and EIS indicate that the prepared samples have better corrosion resistance in SBF solution compared to the unadded samples, (i corr ) and (E corr ) are 2.695 × 10−8 A·cm−2 and 0.101 V, respectively. The addition of selenium helps to improve the biological corrosion resistance of the sample in body fluids.

Исследование микродугового оксидирования как метода улучшения технических характеристик сплавов алюминия марки AA5086 и титана марки ВТ6

The article presents the promising field of micro-arc oxidation as a surface modification method with the purpose to improve the corrosion resistance of titanium, aluminum, aluminum alloys and composites. Micro-arc oxidation is an electrochemical process that forms a thick, hard and highly adhesive ceramic oxide layer on the metal surfaces, thereby providing excellent protective properties. This method of hardening the metal surface was used in production in the manufacture of parts from AA5086 and VT6 alloys for industrial fans operating in chemically hazardous facilities. When using micro-arc oxidation, the strength and wear resistance of the internal parts of the fan to aggressive medium was increased. By that increased the trouble-free operation time and reduced the likelihood of destruction of the internal parts of the fan, which subsequently made it safer for employees to operate the fans in close proximity to the work area. This work examines the corrosion resistance of aluminum alloys and composites, since the indicated materials are also widely used in various branches of industry. It also considers the role of alloying elements in influencing corrosion behavior, as well as the influence of microstructure and processing methods on corrosion resistance. In addition, the discussion extends to the corrosion behavior and protective measures for aluminum matrix composites, including the inclusion of reinforcing phases such as ceramic particles, fibers or nanoparticles. Throughout the article, the corrosion resistance of micro-arc oxidation treated surfaces, anodized aluminum layers, aluminum alloys and composites are critically assessed, analyzing the factors influencing their protective characteristics, such as the morphology, composition and thickness of the oxide layers, as well as environmental factors.

Study on Corrosion Resistance of LDH/Micro-Arc Oxidation Composite Superhydrophobic Coatings on AZ31 Magnesium Alloy

Because of some defects such as holes and cracks, the corrosion resistance of micro-arc oxidation coating needs to be improved by surface modification. In this paper, LDH/MAO film with a micro-/nano-structure is constructed on the surface of AZ31 magnesium alloy by controlling the composition and concentration of the hydrothermal solution. The superhydrophobic surface is successfully constructed by coating an OTES modifier on the surface of LDH/MAO film by the spin-coating method. The surface morphologies, contact angles, and corrosion resistance of composite coatings are tested. The results show that the OTES-LDH/MAO composite coatings of magnesium alloy can seal the defects in the MAO film well to achieve a superhydrophobic effect and better corrosion resistance. Compared with a MgO ceramic film, the water contact angle of OTES-LDH/MAO composite coatings is increased from 38° to 155°; the corrosion potential increases by 0.7 V, the corrosion current density and polarization resistance decreases and increases by four orders of magnitude, respectively; and the corrosion resistance becomes much higher than that of MAO film.

Influence of voltage modes on microstructure and corrosion resistance of micro-arc oxidation coating on magnesium alloy

Micro-arc oxidation (MAO) technology, as an efficient and widely used technology, can fabricate a ceramic film on magnesium (Mg) alloys in situ to significantly improve corrosion resistance. The study aims to investigate the effect of voltage modes on the preparation and performance of MAO coating on Mg alloys. The scanning electron microscope, X-ray diffractometer, potential dynamic polarization, and electrochemical impedance spectroscopy measurements were applied for characterizing the microstructure, composition, and corrosion resistance of the MAO film, respectively. The results revealed that employed 300/350 V step-up mode, the MAO film showed a more uniform distribution of surface micro-pores, fewer micro-cracks and denser inner layer, lower corrosion current density (1.871 × 10−3 mA·cm−2), and higher electrochemical impedance value, compared to other voltage treated parameters. Therefore, it could be concluded that the step-up voltage parameters are conducive to the optimization of microstructure, improvement of corrosion resistance of MAO coating, and reduction of the energy consumption during processing.

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.

Growth characteristics and corrosion resistance of micro-arc oxidation coating on Al–Mg composite plate

To investigate the growth characteristics and corrosion resistance of Micro-arc oxidation (MAO) coatings prepared from Al–Mg composite plates under sodium silicate electrolyte, comparative experiments were performed using single plate Al and Mg. The results showed that the breakdown of the Mg plate (P–Mg) in the Al–Mg composite plate occurred first than the Al plate (P–Al). The coating thickness of P–Al and P–Mg gradually converged with time. Because after the Al and Mg plates composite, the increased energy consumption of the P–Al made its discharge more intense and accelerated the growth of its coating, while the situation of the P–Mg was opposite. The SEM observation discovered that the coating defects in P–Al and P–Mg coatings showed a gradually increasing trend as time passed. The corrosion resistance tests showed that MAO could effectively improve the corrosion resistance of the Al–Mg composite plate. Compared with the substrate, the corrosion rate of the P–Al coatings was reduced by more than one order of magnitude, while that of the P–Mg coatings was reduced even more. After soaking in 3.5 wt% NaCl solution for 36 h, the corrosion mass loss of Al–Mg composite plate treated by MAO was reduced by at least two orders of magnitude.

Improvement on corrosion resistance of micro-arc oxidized AZ91D magnesium alloy by a pore-sealing coating

Micro-arc oxidation is a low-cost and environmentally friendly technology for improving the corrosion resistance of magnesium alloys. However, the inherent porous structure limits the application of magnesium alloy micro-arc oxidation coatings in corrosion resistance. Herein, we investigated the corrosion resistance and friction resistance of the magnesium alloy micro-arc oxidation coating after being sealed by hydrothermal treatment and heat treatment. SEM, FTIR, XRD and XPS were performed to investigate the surface morphology and chemical composition of the prepared coating. The potentiodynamic polarization curve and electrochemical impedance spectroscopy confirmed that the prepared sample has good corrosion resistance in 3.5 wt% NaCl aqueous solution. In addition, the samples with coating also exhibit good friction resistance. After friction test, the samples still maintain good corrosion resistance. This method not only promotes the application of magnesium alloys in corrosive environments, but also has great potential for industrial production.

Optimized Micro-Arc Oxidation Coating Thickness on ALZ Magnesium Lithium Alloy

Micro-arc oxidation (MAO) is known as a novel technique to use for the modifying the surface of valve metal, which improve mechanical and corrosion resistance properties. In this study, MAO coatings are fabricated on ALZ magnesium lithium alloy to protect the substrate from corrosion using environmentally friendly electrolytes under a high voltage power supply. The Taguchi method is used to identify the effects of current density, coating time and electrical frequency on the thickest coating uniformity. The optimum coating properties are characterized by coating thickness measurement, Scanning electron microscopy (SEM), Potentiodynamic polarization analysis. It was found that the processing time is the main factor affecting the thickest coating uniformity (tu). Coatings fabricated under optimum conditions are in close agreement with the predicted values of Taguchi analysis. The corrosion resistance of MAO coated on ALZ magnesium lithium alloy are greatly improved compare to the bare alloy in corrosive environments.

Improving the corrosion resistance of micro-arc oxidation coated Mg-Zn-Ca alloy.

Four additives (Na2WO4, nano-hydroxyapatite, K2TiF6 and NaF) were added into the Na5P3O10 + NaOH + C3H8O3 base electrolyte according to the orthogonal design of four factors three levels (L9 (34)). Nine different micro-arc oxidation (MAO) coatings were fabricated on Mg–2Zn–0.5Ca alloys through orthogonal experiments. The effects of four additives on the microstructure, mechanical properties, corrosion resistance and biocompatibility of MAO coatings were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), electrochemical corrosion test and in vitro degradation test. The addition of nano-hydroxyapatite and K2TiF6 showed self-sealing effects and contributed to the corrosion resistance of the samples significantly. The addition of 0.5 g L−1 Na2WO4 markedly elevated the bonding strength of the coatings with the substrate. The optimal combination of factors and levels considering both mechanical properties and corrosion resistance was: 0.5 g L−1 Na2WO4, 0 g L−1 NaF, 5 g L−1 n-HAp, 5 g L−1 K2TiF6. The growth mechanism of MAO coatings combining with the visual phenomenon was discussed as well.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg−Al layered double hydroxide coating

Abstract To further enhance the corrosion resistance of the porous micro-arc oxidation (MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg−Al layered double hydroxide (LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.

Microstructure and Corrosion Behavior of Composite Coating on Pure Mg Acquired by Sliding Friction Treatment and Micro-Arc Oxidation.

For the purpose of detecting the influence of grain structure of a Mg matrix on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coating, prior to MAO processing, sliding friction treatment (SFT) was adopted to generate a fine-grained (FG) layer on coarse-grained (CG) pure Mg surface. It showed that the FG layer had superior corrosion resistance, as compared to the CG matrix, owing to the grain refinement; furthermore, it successfully survived after MAO treatment. Thus, an excellent FG-MAO coating was gained by combining SFT and MAO. The surface morphology and element composition of FG-MAO and CG-MAO samples did not show significant changes. However, the FG layer favorably facilitated the formation of an excellent MAO coating, which possessed a superior bonding property and greater thickness. Consequently, the modified FG-MAO sample possessed enhanced corrosion resistance, since a lower hydrogen evolution rate, a larger impedance modulus and a lower corrosion current were observed on the FG-MAO sample.

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.

Effect of organic additives on structure and corrosion resistance of MAO coating

In order to improve the corrosion resistance of micro-arc oxidation (MAO) coated Mg alloys, some organic additives (3-aminopropyltrimethoxysilane (APTMS), glycerol, triethanolamine (TEA)) were doped in the silicate-based electrolyte and the microstructure and corrosion resistance were investigated. The surface and cross-section morphology feature, phase composition, elemental composition, and functional groups were examined by SEM, XRD, EDX, and FT-IR, respectively. The corrosion resistance was evaluated by electrochemical tests in 3.5% NaCl solution. The results showed that the addition of organic additives had little effect on the phase composition, while it influenced the thickness and microstructure of the coating and so improved the corrosion resistance. After the addition of APTMS, the coating thickness was increased, and the corrosion resistance became the best due to the smallest pore size, relatively dense microstructure and the formation of Mg-O-Si chemical bond with the long organic alkyl chains. The addition of TEA or glycerol makes the coating microstructure loose. Although the addition of TEA reveals larger pore size and micro-crack than addition of glycerol, its corrosion resistance was higher due to the largest thickness.

Microstructure and degradation properties of C-containing composite coatings on magnesium alloy wires treated with micro-arc oxidation

Abstract To improve the corrosion resistance of micro-arc oxidation (MAO) treated Mg alloy wires, carbon (C) nanoparticles were added to the silicate electrolyte to fabricate C-containing composite coatings. Comparisons of microstructure, corrosion resistance and mechanical properties of uncoated wires, MAO-C-free coated wires and MAO-C coated wires were performed. The results indicated that the surface layers of Mg alloy wires treated with MAO were primarily composed of MgO and Mg 2 SiO 4 phases and demonstrated porous morphologies. The C nanoparticles in the electrolyte were capable of incorporating into composite coatings, forming a dense composite coating microstructure and resulting in the formation of a small amount of MgAlO 4 and Mg 3 SiO 4 F 2 , which improve corrosion resistance in static and dynamic immersion environments. Measurements of mechanical properties demonstrated that the MAO-C coated wires retained a high tensile strength of 180 MPa, even after dynamic immersion for 50 days, and possessed better corrosion resistance than the wires coated with MAO-C-free coating. The effects of shear stress and localized environment changes resulting from the flowing corrosive media were proposed as two mechanisms that accelerated corrosion in a dynamic immersion environment.

Effect of ultrasonic cold forging technology as the pretreatment on the corrosion resistance of MAO Ca/P coating on AZ31B Mg alloy

A calcium phosphate contained (Ca/P) coating was obtained on AZ31B Mg alloy by micro-arc oxidation (MAO) process under the pretreatment of ultrasonic cold forging technology (UCFT). The surface nanograins were introduced after UCFT pretreatment on AZ31B Mg alloy. Optical microscope (OM) was employed to observe the microstructures of the untreated and UCFT treated samples. Transmission electron microscopy (TEM) and atomic force microscope (AFM) were employed to observe the microstructures of nanograins and the surface roughness of the UCFT treated Mg alloys. The grain size of the UCFT treated Mg alloy is 48.67nm and the surface roughness is 17.03nm. The microstructures and the phase compositions of MAO samples were observed and analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The XRD results show that the coating include Ca/P phase, including hydroxyapatite (Ca10(PO4)6(OH)2), HA), tertiary calcium phosphate (Ca3(PO4)2, TCP) and calcium phosphate dehydrate (CaHPO4⋅2H2O, DCPD). The hardness of the samples was measured by the micro-hardness tester under the loads of 10g, 25g and 50g. 3D topographies of hardness indenter were characterized by 3D profiler. The immersion tests and potentiodynamic polarization tests were used to evaluate the weight loss rate and corrosion current density in simulated body fluid (SBF). The results show that the corrosion resistance of Ca/P MAO coating on Mg alloy was improved greatly by the pretreatment of UCFT.

Preparation and corrosion resistance of MAO layer/Yb2SiO5 composite coating on Mg alloy

Microarc oxidation (MAO) layer and atmospheric plasma spraying (APS) Yb2SiO5 coat were successfully prepared on Mg alloy to improve the corrosion resistance of the substrate. Bond stability and protection of the composite coating were investigated. The results show that thermal sprayed Yb2SiO5 coat has good compatibility with MAO layer. The composite coating is well bonded with Mg alloy. MAO layer provides a stable interface and high hardness for Mg alloy to bond with Yb2SiO5 coat. The composite coating shows excellent thermal shock resistance. Porous MAO coating is effectively sealed by the melted Yb2SiO5. The MAO layer/Yb2SiO5 composite coating significantly improves the corrosion resistance of Mg alloy.

Improvement to corrosion resistance of MAO coated 2519 aluminum alloy by formation of polypropylene film on its surface

In order to improve the corrosion resistance of micro arc oxidized coating on 2519 aluminum alloy, a thin layer of polypropylene (PP) film was prepared on its surface. The structure and corrosion protection properties of the coatings were investigated. The corrosion resistance of micro-arc oxidation (MAO) coating can be improved effectively by forming of this kind of thin film due to the physical barrier effect of PP film and the sealing effect of the micro defects in MAO coating by PP. PP film on MAO coating is deteriorated by micro cracks during immersion. The EIS plots were fitted by appropriate equivalent circuits.

Effect of chloride ion level on the corrosion performance of MAO modified AZ31 alloy in NaCl solutions

Microarc oxidation coatings were fabricated on AZ31 magnesium alloy in the electrolyte of sodium phosphate. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were employed to investigate the electrochemical corrosion behavior. The corroded surface was characterized by an optical microscope and X-ray diffraction. The influence of chloride ion concentration on the corrosion resistance of microarc oxidation coated AZ31 alloy is discussed. The corrosion current density enlarged ratio and the charge transfer resistance reduced ratio indicated that the extent of the corrosion damage of microarc oxidation coated AZ31 alloy is much higher when chloride ion concentration is greater than 5%. A corrosion mechanism related to the effect of chloride ion concentrations on the corrosion behavior is proposed.

Growth process and corrosion resistance of micro-arc oxidation coating on Mg-Zn-Gd magnesium alloys

A Mg-6Zn-3Gd (mass fraction, %) alloy, noted as ZG63, was coated by different micro-arc oxidation (MAO) processes, and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy (SEM), glancing angle X-ray diffractometry (GAXRD) and various electrochemical methods. The micro-arc oxidation process consists of three stages and corresponds with different coating structures. In the initial stage, the coating thickness is linearly increased and is controlled by electrochemical polarization. In the second stage, the coating grows mainly inward and accords with parabolic regularity. In the third stage, the loose coating forms and is controlled by local arc light. The looser coating is mainly composed of MgSiO 3 and the compact coating is mainly composed of MgO. From micro-arc oxidation stage to local arc light stage, the corrosion resistance of the coated alloy firstly increases and then decreases. The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.