MA8 Magnesium Alloy Research Articles

The Influence of Surface Preparation on Corrosion-Protection Properties of Oxide Layers Formed on MA8 Magnesium Alloy by Microarc Oxidation

The Influence of Surface Preparation on Corrosion-Protection Properties of Oxide Layers Formed on MA8 Magnesium Alloy by Microarc Oxidation

Design of self-healing PEO-based protective layers containing in-situ grown LDH loaded with inhibitor on the MA8 magnesium alloy

The high corrosion rate of magnesium and its alloys in chloride-containing solution significantly reduces the potential of this material for diverse applications. Therefore, the formation of a smart protective coating was achieved in this work to prevent degradation of the MA8 magnesium alloy. A porous ceramic-like matrix was obtained on the material by plasma electrolytic oxidation (PEO). Further surface functionalization was performed using layered double hydroxides (LDH) served as nanocontainers for the corrosion inhibitor. Several methods of LDH intercalation with benzotriazole (BTA) were proposed. The composition and morphology of the formed coating were studied using SEM-EDX analysis, XRD, XPS, and Raman microspectroscopy. The corrosion behavior of the coated samples was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization. The corrosion rate was estimated using volumetry and gravimetry methods. The formed composite coating provides the Mg alloy with the lowest corrosion activity (|Z|f = 0.1 Hz = 8.48·105 Ω·cm2, Ic = 1.4·10−8 A/cm2, PH = 0.21 mm/year) and improves the protective properties of the PEO-coated sample (|Z|f = 0.1 Hz = 8.37·103 Ω·cm2, Ic = 4.1·10−7 A/cm2, PH = 0.31 mm/year). The realization of the self-healing effect of the inhibitor-containing LDH/PEO-coated system was studied using localized electrochemical methods (SVET and SIET) with two artificial defects on the surface. A mechanism involving three stages for the active corrosion protection of the alloy was proposed. These findings contribute to the follow-up work of developing modified LDH/PEO-based structures that promote the Mg alloy with high corrosion resistance, superior electrochemical performance for applications in various fields of industry and medicine.

A Superior Corrosion Protection of Mg Alloy via Smart Nontoxic Hybrid Inhibitor-Containing Coatings.

The increase of corrosion resistance of magnesium and its alloys by forming the smart self-healing hybrid coatings was achieved in this work in two steps. In the first step, using the plasma electrolytic oxidation (PEO) treatment, a ceramic-like bioactive coating was synthesized on the surface of biodegradable MA8 magnesium alloy. During the second step, the formed porous PEO layer was impregnated with a corrosion inhibitor 8-hydroxyquinoline (8-HQ) and bioresorbable polymer polycaprolactone (PCL) in different variations to enhance the protective properties of the coating. The composition, anticorrosion, and antifriction properties of the formed coatings were studied. 8-HQ allows controlling the rate of material degradation due to the self-healing effect of the smart coating. PCL treatment of the inhibitor-containing layer significantly improves the corrosion and wear resistance and retains an inhibitor in the pores of the PEO layer. It was revealed that the corrosion inhibitor incorporation method (including the number of steps, impregnation, and the type of solvent) significantly matters to the self-healing mechanism. The hybrid coatings obtained by a 1-step treatment in a dichloromethane solution containing 6 wt.% polycaprolactone and 15 g/L of 8-HQ are characterized by the best corrosion resistance. This coating demonstrates the lowest value of corrosion current density (3.02 × 10-7 A cm-2). The formation of the hybrid coating results in the corrosion rate decrease by 18 times (0.007 mm year-1) as compared to the blank PEO layer (0.128 mm year-1). An inhibitor efficiency was established to be 83.9%. The mechanism of corrosion protection of Mg alloy via smart hybrid coating was revealed.

Formation of composite coatings: morphology and composition studies

In this work, composite fluoropolymer-containing coatings were obtained on samples of AMg3 aluminium alloy, MA8 magnesium alloy, and VT1-0 commercially pure titanium treated by plasma electrolytic oxidation (PEO). Superdispersed polytetrafluoroethylene (SPTFE) and a solution of tetrafluoroethylene (TFE) telomers in acetone were applied onto preliminarily formed PEO layers by the spray-coating method. The obtained coatings contained a large amount of crystalline polytetrafluoroethylene embedded in the outer porous layer of the PEO coating and did not have visible defects, which indirectly indicates high protective properties.

Physicochemical studies of composite coatings during accelerated tests for atmospheric corrosion

In the present paper, the formation of protective coatings on the MA8 magnesium alloy by plasma electrolytic oxidation (PEO) with subsequent treatment of fluoropolymer is considered. The morphology of coatings after accelerated climatic tests was investigated and the elemental composition of coatings was studied after tests in a salt spray chamber (SSC). The analysis of the obtained results demonstrated a higher corrosion resistance of the fluoropolymer-containing layers in comparison with the base PEO coating.

Effect of carbon nanotubes incorporation on the properties of the PEO coatings formed on MgMn-Ce alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing multi-walled carbon nanotubes in concentrations of 2, 4 and 6 g/l have been investigated. It was found that the introduction of multi-walled carbon nanotubes leads to an increase in the adhesive strength, microhardness and Young’s modulus of the obtained layers.

Influence of Surface Preparation on Corrosion Resistance Properties of Oxide Layers Formed on Mag-nesium Alloy МА8 by Microarc Oxidation

The article presents the findings on the effect of the substrate pre-impregnation in the ceri-um (III) nitrate and glycerin aqueous solutions on the corrosion-protective properties of the coatings generated on the magnesium alloy MA8 surface by microarc oxidation. The coat-ings were formed in the A-K mode from a silicate-alkaline base electrolyte solution contain-ing compounds with fluoride ions. The corrosion resistance of the magnesium alloy ensured by oxide-ceramic coatings and without them was evaluated by the electrochemical corrosion parameters: corrosion potential, corrosion current density, and polarization resistance. The study has shown that the coatings formed on the surface of the magnesium alloy MA8 provide effective anticorrosive properties of the substrate of MA8 in the solutions containing chloride ions. It was established that the preliminary impregnation of a substrate made of magnesium alloy MA8 in aqueous solutions of cerium (III) nitrate and glycerin affects the mechanism of the resulting corrosion damage.

Changes in Wettability and Corrosion Properties of Coatings Obtained on MA8 Magnesium Alloy after Accelerated Climatic Tests

In the presented study, changes in the wettability and corrosion properties of composite coatings formed on the MA8 magnesium alloy by plasma electrolytic oxidation (PEO) with subsequent treatment with organofluorine polymers were investigated after accelerated climatic tests in a salt spray chamber. It was found by the sessile drop method that after accelerated climatic tests the contact angle decreases by 2.5 times for PEO coatings, and by 15o for composite coatings. Evaluation of the electrochemical properties of the composite layers revealed an insignificant decrease in the value of the corrosion current density after 40 days of holding samples in a salt spray chamber.

Influence of ZrO2/SiO2 nanomaterial incorporation on the properties of PEO layers on Mg-Mn-Ce alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2, 4 and 6 g/l have been investigated. It has been established by SEM, EDS, and XPS that ZrO 2 /SiO 2 nanoparticles successfully were incorporated into the coatings. Micro-Raman spectroscopy showed the presence of ZrO 2 in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg 2 SiO 4 in tetrahedral configuration uniformly distributed in the outer part of coatings. Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEO-layer (from 2.4 × 10 –7 A/cm 2 for base PEO layer to 0.7 × 10 –7 A/cm 2 for coatings with nanoparticles). It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness (this parameter was increased from 2.1 ± 0.3 GPa to 3.1 ± 0.4 GPa) and wearproof (the wear was reduced from (4.3 ± 0.4)×10 –5 mm 3 /( N × m ) to (3.5 ± 0.2)×10 –5 mm 3 /( N × m )).

The Potential of the Superhydrophobic State to Protect Magnesium Alloy against Corrosion

We describe the technologically simple route for the fabrication of the superhydrophobic coatings on top of wrought magnesium alloy MA8 based on nanosecond laser processing followed by the chemical vapor deposition of fluorosilane. The chemical and phase composition, surface morphologies, and variation of the coating wettability during prolonged contact with 0.5 NaCl solution or with salt aerosol were characterized using X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy measurements, and the wettability analysis. The as-prepared coatings demonstrate corrosion current of more than eight orders of magnitude lower, while after 30 days of sample immersion into corrosive solution, the current was four orders of magnitude lower than that obtained for a polished sample which was for only 2 h in contact with electrolyte. The mechanisms of the protective activity of fabricated coatings were discussed.

Composite stearate-containing coatings to control the resorption rate of biomedical items made of magnesium alloy MA8

Composite stearate-containing coatings to control the resorption rate of biomedical items made of magnesium alloy MA8

Localized corrosion of magnesium alloys potentially applicable for medical implants: fundamental aspects

A comparative analysis of the corrosion activity of bioresorbable MA8 magnesium alloy (Mg– Mn – Ce system) in a medium for cultivation of mammalian cells (minimum essential medium, MEM) and 0.83 wt. % aqueous NaCl solution was performed. The development of the corrosion process on the surface of a magnesium alloy in two media was established using local scanning electrochemical methods (scanning vibrating electrode technique and scanning ion-selective electrode technique), traditional electrochemical methods (potentiodynamic polarization, electrochemical impedance spectroscopy) and hydrogen evolution measurements. The protective properties of the corrosion film formed on the alloy in MEM, as well as during exposure to NaCl solution, were established. The composition of the layer of corrosion products formed on the magnesium alloy in MEM was studied using confocal Raman spectroscopy, X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-Ray analysis. Calcium-phosphate compounds are the main products formed on the surface of a magnesium alloy during immersion in MEM. The model of corrosion mechanism of magnesium alloy in MEM, which includes three stages of the development of surface film, is proposed. The formation on the magnesium alloy in MEM of corrosion product layer, including magnesium-substituted hydroxyapatite, stabilizes the local pH below 9.0, which along with the presence of organic acids, does not allow increasing the pH during corrosion. A diagram that allows one to determine the possible reactions occurring on the surface of a magnesium alloy in MEM and the thermodynamic probability of the formation of chemical compounds based on the values of the local pH is designed. The obtained results indicate the prospect of using bioresorbable magnesium implants in surgery.

Composite Coatings Formed on PEO Pretreated MA8 Magnesium Alloy in Aqueous Suspension of PTFE

The paper presents results of the composite polymer-containing layers formation by plasma electrolytic oxidation (PEO) with subsequent application of the superdispersed polytetrafluoroethylene (SPTFE) aqueous suspension. The corrosion properties and adhesion of coatings have been investigated using potentiodynamic polarization and scratch tests. Incorporation of SPTFE decreased the corrosion current density for composite layers by more than 3 orders of magnitude in comparison with the base PEO-coating and increased the coatings adhesion by 30 %.

Formation of PEO Coatings Modified by SiC Nanoparticles on the MA8 Magnesium Alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing silicon carbide nanoparticles in concentrations of 2, 4 and 6 g/l have been investigated. It has been shown that coatings, which contain nanoparticles, have a significant advantage in microhardenss and adhesive strength in comparison with the surface layers obtained without their use.

Влияние электротоковых характеристик процесса формирования на свойства ПЭО-покрытий, получаемых на магниевом сплаве МА8 в потенциодинамическом режиме

Установлено, что в потенциодинамическом режиме формирования покрытий методом плазменного электролитического оксидирования (ПЭО) электрохимические и морфологические свойства получаемых поверхностей можно регулировать, используя максимальную плотность тока. Получены зависимости данной величины от таких параметров, как максимальное значение и скорость изменения напряжения, а также от размеров оксидируемого изделия. Исследована зависимость защитных свойств ПЭО-покрытий, получаемых на магниевом сплаве МА8, от максимальной плотности тока формирования. Проведены морфологические и электрохимические исследования полученных гетерооксидных слоев с целью выявления корреляции свойств покрытий с плотностью тока формирования. Методами сканирующей электронной микроскопии и потенциодинамической поляризации изучены основные защитные свойства ПЭО-покрытий. Результаты свидетельствуют об увеличении толщины и пористости покрытий при росте значений плотности тока формирования. Показано, что при переходе от низких (2 мА/мм2) к высоким (до 12 мА/мм2) максимальным значениям плотности тока поляризационное сопротивление имеет максимум в области значения 4 мА/мм2, что свидетельствует об оптимальном режиме формирования ПЭО-покрытий с высокими барьерными свойствами. It is established that in the potentiodynamic coating-formation mode by plasma electrolytic oxidation (PEO), the electrochemical and morphological properties of the resulting surfaces can be adjusted using the maximum current density. In this paper, the dependences of this value on such parameters as the maximum value and the rate of voltage change, as well as on the size of the oxidized product are obtained. The dependence of the protective properties of PEO-coatings obtained on magnesium alloy MA8 on the maximum density of the formation current is studied. Morphological and electrochemical studies of the obtained heteroxide layers were performed in order to identify the correlation of the coating properties with the density of the formation current. The main protective properties of PEO-coatings have been studied using scanning electron microscopy and potentiodynamic polarization. The results obtained indicate an increase in the thickness and porosity of coatings with an increase in the values of density of the formation current. It is shown that during the transition from low (2 mA/mm2) to high (up to 12 mA/mm2) maximum values of the current density, the polarization resistance has a maximum in range of 4 mA/mm2, which indicates the optimal mode of formation of PEO coatings with high barrier properties.

Incorporation of TiO<sub>2</sub>(B) Nanoparticles into PEO Coatings on MA8 Magnesium Alloy

The way of protective coatings formation on MA8 magnesium alloy by plasma electrolytic oxidation (PEO) in the electrolyte containing TiO2(B) nanoparticles has been developed. It is shown that the coatings, which contain nanoparticles, have a significant advantage in microhardenss and adhesive strength in comparison with the surface layers obtained without their use.

Correlation between the Properties of PEO-Layer and Coating Formation Current Density

Presented paper considers the formation of protective coatings on MA8 magnesium alloy by plasma-electrolytic oxidation (PEO). The influence of current densities formation on the structure, corrosion properties of PEO-coatings was studied. Electrochemical and scanning electron microscopy of the surface and cross-section of the samples were carried out. The effect of changing the formation current density on the functional parameters of coatings, such as corrosion resistance, thickness and porosity was investigated.

5-хлор-1,2,3-бензотриазол как камерный ингибитор коррозии магниевого сплава МА8

Новые технологии, Химическая промышленность, Химическая технология, Научные журналы, Защита от коррозии, Технология металлов, Свойства материалов, Технические журналы, Наука и технологии, Справочная литература, Научные разработки

Localized currents and pH distribution studied during corrosion of MA8 Mg alloy in the cell culture medium

Electrochemical behaviour of MA8 magnesium alloy in minimum essential medium (MEM) and 0.83 wt. % NaCl solution is compared using SVET, local pH measurements and hydrogen evolution tests. Corrosion products formed on the alloy surfaces are characterized using XRD and SEM-EDX analysis. Potential by-products of cells and bacteria activities increase the sample activity in MEM at the initial stage of material immersion. Hydrogen evolution rate is higher for samples in NaCl solution in comparison with MEM. Formation of partially protective magnesium-substituted hydroxyapatite stabilizes the local pH of MEM below 9.0 and does not allow to increase the pH during corrosion.

Characterization of PEO-Coatings on the MA8 Magnesium Alloy Formed in Electrolyte Containing ZrO2/SiO2 Nanoparticles

The properties of coatings obtained by plasma electrolytic oxidation on the MA8 magnesium alloy in electrolytes containing zirconia-silica nanoparticles at a concentration of 2, 4 and 6 g/l are studied. Coating formed in electrolyte containing particles in concentration 4 g/l possesses the impedance modulus by an one order of magnitude higher compared to the base PEO-coating. The protective properties are retained after a 24-h exposure to a corrosive environment.