RU2677388C1 - Method of making protective coatings on valve metals and alloys thereof - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to plasma-electrolytic coating of valve metals and their alloys and may find application in various industries, in engineering, instrumentation for work in friction units and to protect products and structures from atmospheric and electrochemical corrosion. Method includes plasma-electrolytic oxidation for 40–50 minutes in the bipolar mode with an effective current density of 20–180 A/dmin alkaline electrolyte containing, g/l: sodium fluoride NaF 0.6–3.0, potassium tartrate CHOK⋅0.5 HO 25–50, sodium silicate NaSiO⋅2HO 25–50, sodium borate NaBO⋅10HO 10–30, sodium molybdate NaMoO⋅2HO 1–10, and during the first 5 minutes the anode voltage is raised from 30 V to the initial formation voltage, which is 460–470 V for aluminum and its alloys and 260–270 V for titanium and its alloys, form the coating, increasing the voltage to 480–490 V at a speed of 0.6 V/min for aluminum and its alloys and at a speed of 6.0 V/min for titanium and its alloys, after which they complete the formation, reducing the voltage for 6–7 min up to 400–420 V for aluminum and up to 220–230 V for titanium, the density of the cathode current during the formation of the coating is increased to 50–75 A/dmand reduce to 10 A/dmwithin 6–7 minutes at the completion of the formation of the coating simultaneously with a decrease in the anode voltage.EFFECT: increasing the corrosion resistance of the resulting coatings, increasing the hydrophobicity and improving the mechanical properties.3 cl, 4 dwg, 6 ex

Description

The invention relates to plasma-electrolytic coating on valve metals and their alloys, mainly on aluminum and its alloys, on titanium and its alloys, and can find application in various industries, in mechanical engineering, instrumentation for work in friction units and for product protection and structures from atmospheric and electrochemical corrosion, as well as to obtain a sublayer for paint coatings, to give products and structures a decorative look.

A known method of forming AMg-5 aluminum alloy (content, wt.%: Mg 5.3, Mn 0.55, Ti 0.06, Al - the rest) of protective coatings (Electrochemical properties of coatings on aluminum. Vestnik FEB RAS. 2007. No. 2, pp. 158-162), which provides for the oxidation of the mentioned alloy under conditions of anodic-cathodic polarization for 10 min in an aqueous electrolyte containing, g / l: potassium tartrate C ₄ H ₄ O ₆ K ₂ ⋅0.5H ₂ O 10, sodium fluoride NaF 1,5, followed by modification of the obtained coating by sealing the pores of the outer porous layer by boiling in distilled water or application of ultrafine polytetrafluoroethylene to the oxidized surface with its subsequent heat treatment for 1 h at temperatures up to 200 ° C. The disadvantages of this method are the need for additional processing, which complicates the method and increases energy consumption, as well as the limited scope of its application, including a single alloy.

A known method of producing a coating on aluminum alloys by plasma electrolytic oxidation (RU 2547983, publ. 2015.04.10), which is carried out by applying alternating current with an effective density of 5-60 A / dm ² formed by sequences of anode and cathode pulses lasting 100-250 microseconds each with a time interval between sequences, the duration of which is not less than the total duration of the anode and cathode pulses, in an aqueous electrolyte containing, g / l:

sodium tetraborate 10-aq 20-50, sodium hydroxide 1-4, molybdenum sodium 0.5-2.0

boric acid 5-15, and may additionally contain 2-5 g / l sodium phosphate disubstituted,

in this case, a modifying surface treatment is preliminarily carried out in an aqueous solution containing, g / l: nitric acid 450-500 and sodium fluoride 45-50. The disadvantage of this method is the need for additional modifying surface treatment in an extremely aggressive electrolyte based on nitric acid, which complicates the method, makes it environmentally unsafe and requires special protection measures for workers, as well as a limited range of oxidized metals, which includes only aluminum alloys.

A known method of producing aluminum and its alloys coatings designed to protect against thermal corrosion and abrasive wear using microarc (plasma electrolytic) oxidation (RU 2112087, publ. 1998.05.27) at a formation voltage of 160-170 V and current density 0 , 9-1.2 A / cm ² in an electrolyte containing, g / l: sodium hexafluoroaluminate 2.0-12.0, potassium tartrate 5.0-10.0, sodium fluoride 0.5-2.0 and hydroxide potassium 0.5-0.6. when the pH of the solution is 9.8-10.2. The coatings obtained in a known manner exhibit a certain microhardness and resistance to high temperature corrosion, due to the glass phase based on aluminum oxide modified with fluorine contained in them. However, these coatings do not have sufficient thickness to provide high protective properties and long service life of the coatings, which limits the applicability of the known method. In addition, the known method is intended only for aluminum and its alloys, and experimental verification shows that coatings with sufficiently high protective and mechanical properties are not formed on all aluminum alloys. In the description of the known method, only two specific examples of the preparation of coatings with the declared properties are given: for technical aluminum and a wrought aluminum alloy containing magnesium.

Known (US 5616229, publ. 1997.04.01) is a method for producing a ceramic coating on metals of a valve group, including aluminum, zirconium, titanium, hafnium and alloys of these metals, which immerses the metal as one of the electrodes in an electrolytic bath with an aqueous solution of sodium hydroxide or potassium hydroxide a with a concentration of 0.5-2.0 g / l, transmission using a counter electrode through the aforementioned metal of an alternating electric current with a voltage of at least 700 V, which provides an electrical breakdown with deposition compactly hydroxide on the surface of the metal film. Further, the method involves the introduction of an electrolyte in an amount of 2-200 g / l of an oxygen-containing alkali metal salt, including an element selected from the group Al, Si, Ge, Sn, Pb, As, Sb, Bi, Se, Te, P, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, and Fe, which is accompanied by the formation of a ceramic coating. The known method is energy-intensive, requires special equipment and is carried out with a change of mode and electrolyte. In addition, the wide range of salts and the wide range of their concentrations proposed for use at the stage of forming the ceramic coating create uncertainty in choosing the right option, in the general case they make it difficult to obtain high-quality coatings and complicate the possibility of their intended use.

Known described in patent RU 2534123, publ. 2014.11.27, a method for producing on valve metals and their alloys, mainly on titanium and its alloys, aluminum and its alloys, as well as on magnesium alloys, protective antifriction, wear-resistant and highly corrosion-resistant coatings, which includes electrochemical treatment of a metal surface in an electrolyte containing soluble phosphate, tartrate or silicate at pH values of 8.0-10.5, in bipolar mode with an effective current density of 0.5-1.0 A / cm ² . However, in order to ensure the claimed high protective properties of the coatings, the known method further provides for the deposition of a layer of polytetrafluoroethylene from its suspension followed by heat treatment, which increases the complexity and increases energy consumption, while its implementation requires selection of the composition and regulation of the pH value to obtain the electrolyte in the form of a colloidal a solution forming a suspension during the oxidation process. In addition, the resulting coatings do not have sufficient hardness.

Closest to the claimed is a method of plasma-electrolytic oxidation of valve metals and their alloys (RU 2263163, publ. 2005.10.27), which involves processing in an aqueous electrolyte containing, g / l: trisodium phosphate Na ₃ PO ₄ ⋅ 12Н ₂ О 20- 120, sodium tetraborate Na ₂ B ₄ O ₇ ⋅ 10Н ₂ О⋅ 10-80, sodium tungstate Na ₂ WO ₄ ⋅ 2H ₂ O 1-12, with variable anodic-cathodic polarization of the product with a pulse duration of 0.0033-0.1 seconds and an effective current density of 0.01-0.3 A / cm ² .

The coatings obtained in a known manner exhibit high resistance to atmospheric corrosion, withstand heat up to 250 ° C and a sharp temperature drop, however, the thickness of the coatings, which only reaches 20 microns in some cases, is insufficient to provide long-term reliable protection against electrochemical and chemical corrosion and high mechanical properties.

The objective of the invention is to provide a method for producing valve metals, mainly aluminum and its alloys, titanium and its alloys, coatings with high protective and mechanical properties.

The technical result of the method is to increase the corrosion resistance of the formed coatings, improve their mechanical properties, increase hydrophobicity.

The specified technical result is achieved by the method of producing protective coatings on valve metals and their alloys by plasma-electrolytic oxidation for 40-50 minutes in a bipolar mode in an alkaline electrolyte containing sodium tetraborate Na ₂ B ₄ O ₇ ⋅ 10 N ₂ O and sodium salt of oxometallic acid, in which, unlike the known one, during the first 5 minutes the anode voltage is raised from 30 V to the initial formation voltage and forms a coating, increasing the voltage at a speed of 0.6-6.0 V / min to 480-490 V, after what head rshayut forming, within 6-7 minutes, reduces the voltage to 220-420 V, the maximum current density the cathode during coating formation is set to 50-75 A / dm ^2, reducing its value to 10 A / dm ² while decreasing the anode voltage, the electrolyte as an oxometallic sodium salt contains sodium molybdate Na ₂ MoO ₄ ⋅ 2H ₂ O and additionally includes potassium tartrate C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H2O, sodium silicate Na ₂ SiO ₃ ⋅ 2H ₂ O and fluoride sodium NaF in the following components, g / l:

NaF 0.6-3.0 C ₄ H ₄ ObK2 0.5 N ₂ 0 25-50 Na ₂ MoO ₄ 1-10 Na ₂ B ₄ O ₇ ⋅ 10H ₂ O 10-30 Na ₂ SiO ₃ ⋅2 H ₂ O 25-50.

Upon receipt of coatings on aluminum and its alloys, the voltage during coating formation is raised from 460-470 V to 480-490 at a speed of 0.6 V / min and complete the formation, reducing the voltage to 400-420 V for 6-7 minutes.

Upon receipt of the coating on titanium and its alloys, the voltage during coating formation is raised from 260-270 V to 470-480 V at a speed of 6 V / min and the formation is completed, reducing the voltage to 220-230 V for 6-7 minutes.

The method is as follows.

An electrolyte is prepared by successively dissolving the constituent components in distilled water at room temperature with thorough stirring for 25-30 minutes. The electrolyte thus prepared is held for another 30 minutes before use.

The product to be coated is placed in a container filled with electrolyte (in an electrolytic bath under industrial conditions), while the product is one of the electrodes, and the counter electrode is made of titanium. To cool the electrolyte, a hollow refrigerator is used in the form of a coil cooled by running water, placed around the perimeter of the tank with electrolyte. Thus, the temperature of the electrolyte during the oxidation process is maintained within 10 ° C, which ensures its stability and an increase in its working life.

In the process of oxidation, voltage is applied to the electrodes, realizing a bipolar mode, while the polarizing signal supplied to the oxidized sample is generated by sequences of anode and cathode pulses with a duration of 3300 μs each without a time interval between them.

The oxidation process is carried out for 40-50 minutes at an effective value of the density of the unregulated anode current, increasing with increasing voltage from 20 to 180 A / dm ² , while the nature of the change in the density of the anode current for different aluminum alloys is the same, the spread in magnitude does not exceed 5 % A similar picture is observed for titanium alloys.

During the first 5 minutes, the anode voltage is increased from 30 V to a value that provides the beginning of coating formation: 460-470 V for aluminum and its alloys and 260-270 V for titanium and its alloys. A quick increase in voltage during the initial processing period avoids unnecessary energy consumption and saves time.

The main coating formation process is carried out with a smooth increase in the anode voltage to 480-490 V with an average voltage change rate of 0.6 V / min for aluminum and its alloys and with an average voltage change rate of 6 V / min for titanium and its alloys. Then within 6-7 minutes the voltage is reduced to 400-420 V for aluminum and to 220-230 V for titanium. In the course of a gradual decrease in the voltage and, accordingly, the density of the anode current, the surface of the formed coating is compacted, open pores and defects formed during the growth of the coating are “healed”.

The presence of the cathode component, in principle, creates favorable conditions for the formation of the coating during its anodic polarization, and also leads to the heating of the inner part of the oxide layer, to the formation of high-temperature phases of oxides in this region and the melting of the surface of the oxide layer. As a result, the porosity decreases, and the mechanical and corrosion resistance of the formed coatings increases.

However, a high cathode current density can lead to a deterioration in the adhesion of the formed coating up to its separation from the substrate.

According to the proposed method, the maximum value of the cathodic current density is used, not exceeding 50-75 A / dm ² , which best ensures the formation of defect-free, finely porous dense coatings, while its density is controlled in such a way that at the same time as the anode voltage decreases at the final stage of formation coating its value decreases to 10 A / DM ² .

The multicomponent composition of the electrolyte is universal, provides optimal and approximate conditions for the oxidation process for various aluminum alloys and titanium alloys, and, ultimately, largely determines the composition and properties of the resulting coatings.

Silicate and molybdate present in the electrolyte contribute to the formation of high-quality coatings due to the fact that they are sources of polymerizable anions that form anionic complexes that interact with cations of the oxidized material.

In addition, sodium molybdate is necessary for the formation of molybdenum carbide in the coating composition, which increases the microhardness of coatings, and sodium silicate is one of the main components that ensure the formation of a dense coating.

The introduction of soluble sodium salts into the electrolyte, in particular sodium fluoride, which reduces the viscosity of the solution and facilitates the flow of electrochemical processes during microplasma discharges, leads to an intensification of the oxidation process.

In addition, the presence of sodium fluoride in the solution leads to an increase in its electrical conductivity, and, consequently, increases the scattering capacity of the electrolyte.

The introduction of a salt of tartaric acid, potassium tartrate, into the electrolyte gives the effect of increasing the duration of microplasma discharges during thermolysis of the electrolyte at the anode and, therefore, increases the duration of the temperature effect on the formed coating. Due to this, a high coating growth rate is achieved at lower voltage values compared to an electrolyte not containing potassium tartrate.

Sodium tetraborate is designed to buffer electrolyte to avoid lowering the pH of the solution, which can lead to the destruction of complex anions. In addition, it provides a decrease in the porosity of the formed coatings.

Thus, the proposed method provides the formation by plasma electrolytic oxidation on the surface of valve metals and their alloys, mainly aluminum and titanium alloys, protective PEO coatings exhibiting high corrosion resistance, high mechanical properties, namely, microhardness high enough for use for industrial purposes and good adhesion to the substrate. In addition, the resulting coatings exhibit thickness and hydrophobicity, which give a significant contribution to their protective properties. Examples of specific implementation of the method

For the formation of protective coatings were used samples with a size of 30 mm × 30 mm × 2.0 mm Their surface was treated with sandpaper of various grain sizes (320-400, 600, 800, 1000), washed and dried under a stream of warm air.

To conduct plasma electrolytic oxidation, a TER4-100 / 460N-2-2UHL4 thyristor current source with a nominal power of 29 kW with program control was used, which provided polarized pulses with a duration of 0.0033 s to the sample being processed.

The thickness of the formed oxide films was measured using an eddy current coating thickness gauge VT-201 (OOO KID, Russia) with a basic measurement error of 3%.

The morphology of PEO coatings was studied using an Evex Mini-SEM SX-3000 benchtop electron microscope (Evex Analytical Instruments Inc., USA) at an accelerating voltage of 20 kV.

Coating porosity was determined by analyzing SEM images obtained at the same magnification using Image J 1.50g software (National Institutes of Health, USA).

Electrochemical studies to establish the corrosion resistance of the obtained coatings were carried out by potentiodynamic polarization in a 3% NaCl solution using VersaSTAT MS (Princeton Applied Research, USA). The polarization dependences were recorded during the potential sweep from the value of E ₁ = E _k - 250 mV to the value of E ₂ = E _k + 1000 mV at a potential sweep speed of 1 mV / s for aluminum alloys and from E ₁ = E _k - 250 mV to the value of E ₂ = E _to + 250 mV at a potential sweep speed of 0.1667 mV / s.

In addition, the corrosion resistance of the obtained coatings on aluminum alloys to an atmosphere containing chloride ions was evaluated by the drop method according to GOST 9302-88 (250 cm ³ / hydrochloric acid with a density of 1.19 g / cm ³ and 30 g of potassium dichromate per 1 dm ³ solutions).

To measure contact angles (wetting angles), we used the method of digital image processing of a sitting drop of deionized water on the surface of the formed PEO coatings. To measure contact angles and obtain optical images of sessile droplets with a volume of 10 μl, Kruss DSA100 was used. The initial contact angles were measured at 10 different positions on the surface of each sample after a 60 second drop exposure.

The microhardness of the coating material was determined on a DUH-W201 dynamic ultramicrohardness meter (Shimadzu, Japan). The measurements were carried out at a load of 300 mN using a Vickers indenter with an angle at the apex of 110 °. The values obtained from 10 points were averaged and the error was calculated. Evaluation and comparative analysis of the elastoplastic properties of the coatings was performed using the Shimadzu DUH Analysis Application v software. 2.10.

The strength properties of the obtained coatings were investigated by sclerometry (scratch testing) using a Revetest Scratch Tester (CSM Instrument, Switzerland). With a uniform increase in load from 1 N to 180 N with a loading speed of 15.5 N / min. critical loads were determined at which the first traces of failure appeared on the coating.

Example 1

AMg3 aluminum alloy plates (wt.%: Mg 2.6-3.6; Mn 0.5; Si 0.4; Fe 0.4; Cr 0.3; Zn 0.2; Ti 0.15; Cu 0 , 1; the rest of Al) was treated for 45 minutes in bipolar mode in an electrolyte of the following composition, g / l:

NaF 0.6 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O 25 Na ₂ MoO ₄ 3 Na ₂ B ₄ O ₇ ⋅ 10 H ₂ O twenty Na ₂ SiO ₃ ⋅2 H ₂ O 25.

During the first 5 min of treatment, the anode voltage was increased from 30 V to 470 V (initial formation voltage), then a coating was formed by increasing the voltage to 480 V and the mode was completed by decreasing the voltage from 480 V to 420 V at a speed of about 10 V / min (6 -7 min). The cathode current density during coating formation is raised to 50 A / dm ² and simultaneously with a decrease in the anode voltage is reduced to 10 A / dm ² . Unregulated density of the anode current during oxidation varies from 20-30 to 180 A / DM ² .

As a result, a uniform defect-free brown coating with a thickness of 85 ± 4 μm was obtained. Corrosive current density for the resulting coating is (2.3 ± 1.5) × 10 ^-8 A / cm ² , microhardness 10500-11900 MPa. The coating withstands a load of 155.6 ± 3.9 N during scratch testing. The wetting angle of deionized water was (48 ± 2) °. The corrosion resistance measured by the drop method was 55-60 minutes.

Example 2

AMg6 aluminum alloy plates (wt.%: Mg 5.8-6.8; Mn 0.5-0.8; Si 0.4; Fe 0.4; Zn 0.2; Cu 0.1; Ti 0.02- 0.1; the rest of Al) was treated under the conditions of example 1 in an electrolyte of the following composition, g / l:

NaF 0.6 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O thirty Na ₂ MoO ₄ one Na ₂ B ₄ O ₇ ⋅ 10 H ₂ O twenty Na ₂ SiO ₃ ⋅2 H ₂ O thirty.

As a result of processing, a uniform brown-free, defect-free coating was formed with a thickness of 73 ± 3 μm with the following characteristics: corrosion current density (2.9 ± 1.1) × 10 ^-8 A / cm ² , microhardness 8700-11000 MPa; the maximum load during scratch testing was 148.3 ± 5.2 N. The angle of wetting with deionized water was (57 ± 3) °. The corrosion resistance measured by the drop method was 55-60 minutes.

The graph of changes in the anode and cathode voltage and the anode and cathode currents of Examples 1-2 is shown in FIG. one.

Example 3

Plates of Sc-containing aluminum alloy B-1579 (wt.%: Mg 6.78; Zn 0.62; Si 0.51; Cr 0.17; Fe 0.15; Cu 0.14; Zr 0.13; Sc 0.13; Ni 0.1; Ti 0.02; Al balance). The anode voltage during the formation of the coating was raised from 460 to 490 V and after 35 minutes of oxidation was reduced to 400 V. The cathode current during the formation of the coating was raised to 60 A / dm ² and reduced simultaneously with a decrease in the anode voltage to 10 A / dm ² . The treatment was carried out in an electrolyte containing, g / l:

NaF 0.6 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O 25 Na ₂ MoO ₄ 3 Na ₂ B ₄ O ₇ ⋅ 10 H ₂ O twenty Na ₂ SiO ₃ ⋅2 H ₂ O thirty.

An even, defect-free coating of dark brown color with a thickness of 61 ± 3 μm was obtained with the following characteristics: density of corrosion current (3.1 ± 1.6) × 10 ^-8 A / cm ² , microhardness 8700-10000 MPa; the maximum load during scratch testing was 121.7 ± 5.4 N. The angle of wetting with deionized water was (97 ± 2) °. The corrosion resistance measured by the drop method was 45-50 minutes.

Example 4

Plates of a Cu-containing aluminum alloy D16 (wt.%: Cu 3.8-4.9; Mg 1.2-1.8; Mn 0.3-0.9; Si 0.5; Fe 0.5; Zn 0, 25; Ti 0.15; Cr 0.1; the rest Al) was oxidized under the conditions of example 3 in an electrolyte containing, g / l:

NaF 1,0 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O fifty Na ₂ MoO ₄ 10 Na ₂ B ₄ O ₇ ⋅ 10H ₂ O thirty Na ₂ SiO ₃ ⋅2 H ₂ O fifty.

A rough, defect-free coating of dark brown color with a thickness of 69 ± 4 μm was obtained with the following characteristics: corrosion current density (5.9 ± 1.6) × 010 ^-8 A / cm ² , microhardness 11500-12000 MPa; the maximum load during scratch testing was 157.1 ± 2.1 N. The angle of wetting with deionized water was (44 ± 5) °. The corrosion resistance measured by the drop method was 25-30 minutes. Example 5

Plates of technical titanium VT1-0 grade (wt.%, Fe 0.2; Si 0.1; C 0.07; other impurities 0.3, the rest Ti) were oxidized in bipolar mode for 45 minutes in an electrolyte of the following composition g / l;

NaF 0.9 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O thirty Na ₂ MoO ₄ 3 Na ₂ B ₄ O ₇ ⋅ 10H ₂ O 10 Na ₂ SiO ₃ ⋅2 H ₂ O 40.

During the first 5 minutes, the anode voltage was increased from 30 V to 270 V, then it was raised to 470 V at a speed of 6 V / min and the mode was completed by reducing the anode voltage from 470 V to 220 V for about 7 minutes. The cathode current density was raised during coating formation to 75 A / dm ² and decreased to 10 A / dm ² simultaneously with a decrease in the anode voltage.

A rough dark gray coating was obtained with a thickness of 47 ± 5 μm with the following characteristics: density of corrosion current (9.7 ± 4.5) × 10 ^-9 A / cm ² , microhardness 5900-7000 MPa; maximum load during scratch testing 38.4 ± 2.9 N. The angle of wetting with deionized water was (99 ± 4) °

Example 6

VT6 grade titanium alloy plates (wt.%, Fe up to 0.6; C up to 0.1; Si up to 0.1; V 3.5-5.3; N up to 0.5; Al 5.3-6, 8; Zr to 0.3; O to 0.2; Ti 86.45-90.9) were oxidized in bipolar mode for 45 minutes in an electrolyte of the following composition g / l;

NaF 3.0 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O fifty Na ₂ MoO ₄ 5 Na ₂ B ₄ O ₇ ⋅ 10H ₂ O 10 Na ₂ SiO ₃ ⋅2 H ₂ O 40.

During the first 5 minutes, the anode voltage was increased from 30 V to 260 V, then it was raised to 480 V at a speed of 6 V / min and the mode was completed by reducing the anode voltage from 480 V to 230 V for about 6 minutes. The cathode current density was raised during the coating formation to 50 A / dm ² and decreased to 10 A / dm ² simultaneously with a decrease in the anode voltage.

An even defect-free black coating was obtained with a thickness of 39 ± 5 μm with the following characteristics: density of corrosion current (9.9 ± 1.8) × 10 ^-9 A / cm ² , microhardness 5100-6500 MPa; the maximum load during scratch testing was 28.4 ± 3.9 N. The angle of wetting with deionized water was (104 ± 3) °.

The graph of changes in the anode and cathode voltage and the anode and cathode currents of Examples 5-6 is shown in FIG. 2.

In FIG. 3 shows SEM images of the surface of coatings formed on aluminum alloys according to Examples 1-4 at two different magnifications: a-AMg3; b-AMg6; bb = 1579; g-D16 at magnification × 100; d, f, g, h - the same coatings at a magnification of × 300.

In FIG. 4 shows SEM images of the surface of coatings formed on titanium and its alloy according to Examples 5-6; (a-VT1-0; b-VT6) with an increase of × 100 and c, d - the same coatings with an increase of × 300.

Claims (4)

1. The method of producing protective coatings on products from valve metals and their alloys, including plasma-electrolytic oxidation in bipolar mode in an alkaline electrolyte containing sodium tetraborate Na ₂ B ₄ O ₇ ⋅ 10H ₂ O, sodium salt of oxometallic acid, characterized in that during the first 5 minutes, the anode voltage is raised from 30 V to the initial formation voltage, then a coating is formed within 30-35 min with an increase in voltage at a speed of 0.6-6.0 V / min to 480-490 V, after which the formation is completed with a decrease apryazheniya to 220-420 volts for 6-7 min, maximum cathode current density during the formation of the coating is set at 50-75 A / dm ^2, the current density is reduced to a value of 10 A / dm ² while decreasing the anode voltage, the electrolyte contains sodium molybdate Na ₂ MoO ₄ ⋅ 2H ₂ O as an oxometallic salt of sodium and additionally includes potassium tartrate C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 N ₂ O, sodium silicate Na ₂ SiO ₃ ⋅ 2H ₂ O and sodium fluoride NaF in the following components, g / l: NaF                       0.6-3.0 C ₄ H ₄ O ₆ K ₂ ⋅ 0.5 H ₂ O 25-50 Na ₂ MoO ₄               1-10 Na ₂ B ₄ O ₇ ⋅ 10 H ₂ O 10-30 Na ₂ SiO ₃ ⋅2 H ₂ O 25-50 2. The method according to p. 1, characterized in that when receiving coatings on products from aluminum and its alloys, the voltage during the formation of the coating is raised from 460-470 V to 480-490 V at a speed of 0.6 V / min, and complete the formation with a decrease in voltage to 400-420 V for 6-7 minutes 3. The method according to p. 1, characterized in that when receiving coatings on products made of titanium and its alloys, the voltage during coating formation is raised from 260-270 V to 470-480 V at a speed of 6 V / min, and the formation is completed when reduced voltage up to 220-230 V for 6-7 minutes.

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