RU2720269C1 - Method of producing corrosion-resistant electrochemical zinc-nickel-cobalt coating - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to electroplating, in particular to processes of electrochemical deposition of coating Zn-Ni-Co, and can be used in production of structural corrosion-resistant materials for operation in aggressive media. Method involves electrodeposition of zinc-nickel-cobalt coating on steel surface subjected to preliminary mechanical treatment, degreasing, etching, removal of oxide films with subsequent washing in water, wherein electrodeposition is carried out using reverse mode from 125 to 155 cycles of electrolysis at cathode current density i=0.5–2.0 A/dm, anode current density i=4.0–5.0 A/dm, at duration of cathode polarization of one cycle τ=15–20 s and duration of anode polarization of one cycle τ=1.0 s, at temperature of electrolyte with graphite anode from 20 °C to 25 °C, pH from 4.5 to 5.5, wherein electrolyte additionally contains salt of sulfuric acid NaSO, as ZnSOcontains ZnSO⋅7HO, as NiSO– NiSO⋅7HO, as CoSO– CoSO⋅7HO with following ratio of components, g/l: ZnSO⋅7HO 60.0–72.0; NiSO⋅7HO 34.0–39.0; CoSO⋅7HO 19.7–33.7; NaSO60.0–72.0; glycine 52.5–70.0; water – rest.EFFECT: reduction of corrosion current, which leads to increase of corrosion resistance and uniformity of microstructure of applied coating, intensification of process of electrochemical deposition and reduction of time of process, as well as improvement of environmental safety and reduction of economic costs of production.1 cl, 16 ex

Description

The invention relates to the field of electroplating, in particular to the processes of electrochemical deposition of Zn-Ni-Co coatings, and can be used in the manufacture of structural corrosion-resistant materials for use in aggressive environments.

A known method of applying a corrosion-resistant coating of Zn-Ni-Co, consisting of the steps of: preparing a metal surface to be coated, including cleaning it in an alkaline solution and washing, chemical etching in HCl for 5 minutes and washing, electrochemical etching in an alkaline solution of NaOH and sodium gluconate in for 2 minutes at a current density of 0.01 A / dm ² and washing, electrodeposition of the coating is carried out in a stationary mode on a previously prepared coated metal surface by immersion in a solution of electrolyte Ava, g / l: NiSO ₄ - 92.8, NiCl ₂ - 12.96, ZnCl ₂ - 13.6, CoSO ₄ from 15.5 to 77.5, H ₃ BO ₃ - 37, MgSO ₄ - 12, brightener - 14 cm ³ / dm ³ and water at a solution pH of 4.5-5.0 and a cathodic current density i _k = 5.0 A / dm ² using a nickel anode. The process time was 16 minutes (0.27 hours). The deposition time was adapted to obtain a coating thickness of about 20 μm (assuming 100% current efficiency of zinc). The metal surface to be coated is St3S steel. The process temperature was 75 ° C. After the final washing and drying, the composition of the obtained zinc-nickel-cobalt coating: Zn - 75.4%, Ni - 12.8%, Co - 11.8% (1).

The disadvantages of this method are the multicomponent electrolyte, the presence in the composition of the electrolyte brightener and heating the electrolyte solution for electrochemical coating. The high working temperature of the electrolyte - 75 ° C causes the evaporation of the solution and the electrolyte vapor has a toxic effect on the personnel of the galvanic section, additional energy consumption is also required to heat the electrolyte, water to replenish the required volume of electrolyte in the galvanic bath, and supply and exhaust ventilation of the room.

A known method of producing an electrochemical coating of zinc-nickel-cobalt, consisting of processing a metal surface to be coated, including mechanical cleaning of dirt, oxides, followed by washing in distilled water; degreasing in an alkaline solution, followed by washing in distilled water; etching in a slightly acidic solution, followed by washing in distilled water; immersion of a pre-prepared metal coated surface in an electrolyte solution of the composition, g / l: ZnSO ₄ - 61.3, Н ₃ ВО ₃ - 14.8, Na ₂ SO ₄ - 14.2, alloying elements: NiSO ₄ - 53.37 and CoSO ₄ - 5.4 and water, s subsequent washing with distilled water and drying. Cathode current density i _k = 1 A / dm ² . The corrosion current of the obtained coatings i _coor = 7.2 μA / cm ² (2).

The disadvantage of this method of obtaining an electrochemical coating is the use of a highly concentrated solution of alloying components and a high corrosion current.

A known method of producing an electrochemical coating of zinc-nickel-cobalt from an electrolyte composition, g / l: ZnSO ₄ - 50, NiSO ₄ - 100, CoSO ₄ - 25, C ₆ H ₈ O ₇ ⋅H ₂ O - 4, CH ₃ COONa - 60, C ₁₂ H ₁₇ N ₄ OSCl⋅HCl - 0.5 and water, the pH of the solution is 3.0-4.0 at a process temperature of 30 ° C. Cathodic current density i _k = 3 A / dm ² . The metal surface to be coated is steel; zinc is the anode. The resulting alloy contains in its composition Zn - 96.3, Ni - 2.9, Co - 0.8. The corrosion current i _coor = 0.274 mA / cm ^2, the mass is equal to 0.0039 Corrosion rate mm / year (3).

The disadvantages of the known method for producing an electrochemical zinc-nickel-cobalt coating are heating of an electrolyte solution and its multicomponent composition, which complicates the process of wastewater treatment. High concentration of expensive nickel salt in the electrolyte with a low content in the electrodepositable Zn-Ni-Co coating.

Closest to the claimed method is a method for producing a corrosion-resistant electrochemical coating of Zn-Ni-Co by electrodeposition in a stationary mode of electrolysis from an electrolyte composition, g / l: ZnSO ₄ - 3.23, NiSO ₄ - 46.4, CoSO ₄ - 46.5, glycine - NH ₂ CH ₂ COOH - 75.0 and water subjected to preliminary mechanical processing, degreasing, etching, removal of oxide films, the surface became known methods. The cathode current density i _k = 0.075 A / dm ² , the pH of the solution is 6.0; the duration of the deposition process was 4 hours (4). The obtained samples contained Zn - 64%, Ni - 18%, Co - 18%. The corrosion current of the obtained coating was i _coor = 4.28 μA / cm ² .

The disadvantages of this method are the high concentration in the electrolyte of expensive components - salts of nickel and cobalt, the microstructure of the coating is uneven in particle size. The presence of large particles reduces the decorativeness of the coating and increases the possibility of its destruction. The duration of the deposition process contributes to the unevenness of the coating in its composition and causes a constant adjustment of the composition of the electrolyte.

The technical problem of the proposed invention is the need to reduce the corrosion current, leading to increased corrosion resistance and uniformity of the microstructure of the coating, the intensification of the process of electrochemical deposition and the reduction of the time of the process, as well as increased environmental safety and reduced economic costs of production.

The posed problem is solved by the proposed method for producing a corrosion-resistant electrochemical zinc-nickel-cobalt coating, including electrodeposition of zinc-nickel-cobalt coating on pre-machined, degreasing, etching, removing oxide films, followed by washing in water the steel surface in a reverse mode from 125 to 155 cycles of electrolysis of electrolyte containing sulfuric acid salt - ZnSO _4, NiSO _4, CoSO _4, glycine, and water at a cathodic current density i _k = 0.5-2.0 A / dm ^2, ano hydrochloric current density i _a = 4.0-5.0 A / dm ^2, at a duration of one cycle of cathodic polarization τ _k = 15-20 s and the duration of one cycle of anode polarization _and τ = 1.0 sec at a temperature of the electrolyte with a graphite anode from 20 ° C to 25 ° C, pH from 4.5 to 5.5. The electrolyte solution additionally contains sulfuric acid salt - Na ₂ SO ₄ , and as ZnSO ₄ contains ZnSO ₄ ⋅ 7H ₂ O, as NiSO ₄ - NiSO ₄ ⋅ 7H ₂ O, as CoSO ₄ - CoSO ₄ ⋅ 7H ₂ O at the following ratio of components, g / l:

ZnSO ₄ ⋅7H ₂ O 60.0-72.0 NiSO ₄ ⋅7H ₂ O 34.0-39.0 CoSO ₄ ⋅7H ₂ O 19.7-33.7 Na ₂ SO ₄ 60.0-72.0 NH ₂ CH ₂ COOH 52.5-70.0 Water rest

The inventive method is as follows.

Prepare a coated metal surface (steel grade St. 45) for coating by mechanical grinding with sandpaper (GOST 10054-80), washing in running tap water; washing in distilled water; degreasing with an organic solvent: acetone, alcohol or alkaline solution; washing in running tap water; washing in distilled water; etching in 0.1 N hydrochloric acid solution for 30-35 s; washing in running tap water; washing in distilled water.

The quality of the metal surface to be coated is estimated by the value of the immersion potential in the working solution of the electrolyte of the composition, g / l: ZnSO ₄ ⋅ 7H ₂ O - 60-72, NiSO ₄ ⋅ 7H ₂ O - 34-39, CoSO ₄ ⋅ 7H ₂ O - 19.7- 33.7, NaSO - 60-72, glycine - 52.5-70 at pH 4.5-5.5.

An electrolyte solution is prepared based on distilled water at room temperature and reagents: ZnSO ₄ ⋅7H ₂ O (GOST 4174-77), NiSO ₄ ⋅7H ₂ O (GOST 4465-74), CoSO ₄ ⋅7H ₂ O (GOST 4462-78) , NaSO ₄ (GOST 4166-76), glycine - NH ₂ CH ₂ COOH (GOST 61-75 (ST SEV 5375-85), which are dissolved in separate containers per 1 liter of water. Then, the solution is poured into the main tank. Zinc sulfate, nickel sulfate, cobalt sulfate, sodium sulfate, glycine was added to this solution with stirring, the resulting electrolyte was thoroughly mixed. In this electrolyte zinc sulfate, nickel sulfate, sulfate t cobalt ions are sources of zinc, nickel and cobalt, respectively, of sodium sulfate - an electrically conductive additive, the effect of glycine stabilizes the pH value of 4.5-5.5.

Immerse the metal coating surface in the prepared electrolyte.

Electrodeposition is carried out at an electrolyte temperature of 20-25 ° C. Polarization was carried out using a P-8S potentiostat in the reverse electrolysis mode. Used graphite anodes grade EC01 (GOST 3518-95). The coating thickness of zinc-nickel-cobalt was 9-11 microns, which corresponds to the use of this coating in aggressive environments (GOST 9.303-84). The electrolysis is carried out in a reverse mode from 125 to 155 cycles with a cathodic current density i _k = 0.5-2.0 A / dm ² , anodic current density i _a = 4.0-5.0 A / dm ² , with a cathodic polarization duration of one cycle τ _k = 15 -20 s and the duration of the anodic polarization of one cycle τ _a = 1.0 s at an electrolyte temperature with a graphite anode from 20 ° C to 25 ° C, pH from 4.5 to 5.5, the electrolyte solution additionally contains a sulfuric acid salt - Na ₂ SO ₄ , and as ZnSO ₄ contains ZnSO ₄ ⋅ 7H ₂ O, as NiSO ₄ - NiSO ₄ ⋅ 7H ₂ O, as CoSO ₄ - CoSO ₄ ⋅ 7H ₂ O in the following ratio of components, g / l: ZnSO ₄ ⋅ 7H ₂ O: 60.0-72.0; NiSO ₄ ⋅ 7H ₂ O: 34.0-39.0; CoSO ₄ ⋅ 7H ₂ O: 19.7-33.7; Na ₂ SO ₄ : 0.0-72.0; glycine: 52.5-70.0; water: rest.

Washed in distilled water and dried.

The amount of alloying components in the alloy composition is: nickel from 13.8% to 16.7%, cobalt from 1.3% to 2.4% at cathodic current densities, respectively, i _k from 0.50 A / dm ² to 2.00 A / dm ² . The current efficiency is 85-90%. The corrosion current of the Zn-Ni-Co coating obtained by this method was i _coor = 2.7-3.7 ± 0.1 μA / cm ² with a coating thickness of δ = 9-11 μm.

The cathode current output is determined by the gain - an increase in the mass of the sample. The weight gain (m _practical ) was measured with an accuracy of 0.0005 g on an analytical balance of the VLR-200g-M brand.

Examples of specific implementation of the proposed method.

Example 1

The method of obtaining a corrosion-resistant coating of Zn-Ni-Co prepared metal coated surface was carried out by electrochemical deposition of the coating from an electrolyte composition, g / l:

ZnSO ₄ ⋅7H ₂ O 66.00 NiSO ₄ ⋅7H ₂ O 36.50 CoSO ₄ ⋅7H ₂ O 26.70 NaSO ₄ 66.00 NH ₂ CH ₂ COOH 61.25 Water rest

In this case, the pH of the solution was 5.0 in a reverse mode of 140 cycles of electrolysis at a cathodic current density i _k = 1.0 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a = 4.50 A / dm ² , the duration anodic polarization τ _a = 1.0 s, electrolyte temperature 22 ° С.

This electrolysis mode allows you to get uniform, fine crystalline precipitation, forming a coating. The corrosion current, which determines the rate of corrosion failure of the Zn-Ni-Co coating obtained by this method, i _coor = 3.20 ± 0.1 μA / cm ² . The process takes 3248 s (0.9 hours). The obtained coating sample contains Zn - 82.9%, Ni - 15.3%, Co - 1.85%. The current efficiency of the alloy is 90%. Coating thickness 10 microns.

Example 2

The method was carried out as in example 1 in the reverse mode of conducting from the electrolyte composition, g / l:

ZnSO ₄ ⋅7H ₂ O 72.0 NiSO ₄ ⋅7H ₂ O 39.0 CoSO ₄ ⋅7H ₂ O 33.7 NaSO ₄ 72.0 NH ₂ CH ₂ COOH 70.0 Water rest

The resulting coating has a uniform fine crystalline structure. The process time is 3878 s. Coating thickness 11 microns. Corrosion current i _coor = 2.7 ± 0.1 μA / cm ² . An increase in the claimed limit value of cobalt salt leads to an increase in the cost of electrolyte, to a decrease in the solubility of cobalt salt, which makes it difficult to introduce this electrolyte into production. The current efficiency is 90%.

Example 3

The method was carried out as in example 1 in a reverse mode of conducting 125 cycles of electrolysis from an electrolyte composition, g / l:

ZnSO ₄ ⋅7H ₂ O 60.0 NiSO ₄ ⋅7H ₂ O 34.0 CoSO ₄ ⋅7H ₂ O 19.7 NaSO ₄ 60.0 NH ₂ CH ₂ COOH 52.5 Water rest

The resulting coating has a uniform fine crystalline structure. The process time is 2618 s. Coating thickness 9 microns. Corrosion current i _coor = 3.7 ± 0.1 μA / cm ² .

At a given concentration of cobalt salt in the electrolyte, the amount of cobalt in the coating composition is 0.8-1.0%. With a decrease in the claimed limit value of cobalt salt, a low cobalt content in the coating is observed (less than 0.5%), which negatively affects the protective ability of the coating. The current efficiency is within 90%.

Example 4

The method was carried out as in example 1 at pH = 4.5 and an electrolyte temperature of 22 ° C. Coating thickness 10 microns. The corrosion current, which determines the rate of corrosion failure of the Zn-Ni-Co coating obtained by this method, i _coor = 3.20 ± 0.1 μA / cm ² . A uniform fine crystalline coating is obtained. The current efficiency is 83%.

Example 5

The method was carried out as in example 1 at pH = 5.5 and an electrolyte temperature of 25 ° C. Coating thickness 10 microns. The corrosion current, which determines the rate of corrosion failure of the Zn-Ni-Co coating obtained by this method, i _coor = 3.20 ± 0.1 μA / cm ² . A uniform fine crystalline coating is obtained. The current efficiency is 85%.

Example 6

The method was carried out as in example 1 at pH = 5.5 and an electrolyte temperature of 18 ° C. Coating thickness 10 microns. In the composition of the obtained coating, a decrease in the nickel content was observed, which slightly reduces the corrosion resistance.

Example 7

The method was carried out as in example 1 at pH = 5.5 and an electrolyte temperature of 30 ° C. Coating thickness 10 microns. During the process, an increase in hydrogen evolution was observed. Also, the presence of heating requires additional equipment and entails additional economic costs. Nickel content decreased by 2%.

Example 8

The method was carried out as in example 1 at pH = 4.0.

During the process of electrolytic deposition, intense hydrogen evolution is observed, which leads to a decrease in current efficiency to 75.0-79.0%, the formation of a porous coating.

Example 9

The method was carried out as in example 1 at pH = 6.0. Coating thickness 10 microns.

The formation of a powdery precipitate and the inclusion of hydroxides in the coating composition, as well as a decrease in the nickel content in the coating composition to 7%, were observed.

Example 10

The method was carried out as in example 1 in a reverse electrolysis mode at a cathodic current density i _k = 0.5 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a = 4.0 A / dm ² , the duration of the anodic polarization τ _a = 1 with. Coating thickness 10 microns.

Corrosion current i _coor = 3.2 ± 0.1 μA / cm ² . The composition of the obtained coatings: Zn - 80.85%, Ni - 13.80%, Co - 1.30%. The current efficiency is 90%.

Example 11

The method was carried out as in example 1 in a reverse electrolysis mode at a cathodic current density i _k = 2.0 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a = 4.0 A / dm ² , the duration of the anodic polarization τ _a = 1.0 with. Coating thickness 10 microns.

Corrosion current i _coor = 3.2 ± 0.1 μA / cm ² . The composition of the obtained coatings Zn - 84.9%, Ni - 16.75%, Co - 2.40%. The current efficiency is 90%.

Example 12

The method was carried out as in example 1 with a cathodic current density i _k = 1.0 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a = 4.0 A / dm ² , the duration of the anodic polarization τ _a = 1 s. Coating thickness 10 microns.

Corrosion current i _coor = 3.2 ± 0.1 μA / cm ² . The composition of the obtained coatings Zn - 82.9%, Ni - 15.28%, Co - 1.85%. The current efficiency is 90%.

Example 13

The method was carried out as in example 1 in a reverse electrolysis mode at a cathodic current density i _k = 0.2 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a - 4.0 A / dm ² , the duration of the anodic polarization τ _a = 1 with. Coating thickness 10 microns.

At a given cathodic current density, a long deposition time is necessary to obtain the required coating thickness.

Example 14

The method was carried out as in example 1 in the reverse mode of electrolysis at a cathodic current density i _k = 3.0 A / dm ² , the duration of the cathodic polarization τ _k = 20 s, the anodic current density i _a = 4.5 A / dm ² , the duration of the anodic polarization τ _a = 1 with. Coating thickness 10 microns.

The coating obtained at this cathodic current density is darker, which negatively affects the decorative properties of the coating, and a powdery precipitate has formed on the surface, and an increase in hydrogen evolution has been observed.

Example 15

The method was carried out as in example 1 with a content of NH ₂ CH ₂ COOH - 37.50 g / L. Coating thickness 10 microns.

This amount of glycine in the electrolyte is not enough to provide complexing and buffering properties - the current efficiency decreases by 8%, and a powdery precipitate forms.

Example 16

The method was carried out as in example 1 with a content of NH ₂ CH ₂ COOH - 75.00 g / L. Coating thickness 10 microns.

An increase in the glycine content practically does not affect the composition of the resulting coating, but the electrolyte rises in price.

The proposed method uses an electrolyte containing a predominant amount of ZnSO ₄ , and the introduction of Na ₂ SO ₄ as an electrically conductive additive increases the efficiency of the reverse electrolysis mode, thereby increasing the conductivity of the solution and, therefore, increasing the dissipation capacity of the electrolyte, which makes it possible to coat Details of complex configuration.

An increase in the rate of metal electroreduction when applying a reverse deposition mode helps to reduce hydrogen evolution and increase current efficiency.

The use of an insoluble graphite anode does not lead to a change in the concentration of one of the components of the electrolyte, allows the process of adjusting the composition of the electrolyte based on the results of a chemical analysis of the claimed components, in contrast to the prototype with a zinc anode, the dissolution of which reduces the stability of the composition of the electrolyte.

The use of a less concentrated electrolyte according to NiSO ₄ ⋅ 7H ₂ O, CoSO ₄ ⋅ 7H ₂ O, NH ₂ CH ₂ COOH and the absence of heating of the electrolyte solution reduces the cost of the electrolyte, and therefore, the coating itself.

The use of an electrolyte containing salts of one acid simplifies and cheapens the process of wastewater treatment.

An increase in corrosion resistance was revealed with a lower concentration of alloying components in the electrolyte composition and a smaller coating thickness. The process time is reduced by more than 4 times.

During the entire period of operation of the electrolyte of the electrochemical coating, spontaneous precipitation of components in the volume of the electrolyte and on the walls of the bath was not observed. Therefore, we can conclude that the proposed electrolyte is highly stable during its use and storage.

Sources of information:

1. Wykpis K. Influence of Co ²⁺ ions concentration in a galvanic bath on properties of electrolytic Zn-Ni-Co coatings / K. Wykpis // Surface and Interface Analysis. - 2014. - V. 46. - No. 10-11. - P. 746-749. DOI: 10.1002 / sia. 5463

Milorad V. The comparative study of the corrosion stability of Zn-Ni-Co alloy coatings deposited from chloride and sulphate baths / M.V.

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Milorad V. The comparative study of the corrosion stability of Zn-Ni-Co alloy coatings deposited from chloride and sulphate baths / MV

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JB Bajat // Zastita materijala. - 2017. - V. 58. - Broj. 2. - P. 198-203. DOI: 10.5937 / ZasMat 1702198T

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Claims (2)

A method of obtaining a corrosion-resistant electrochemical zinc-nickel-cobalt coating on a steel surface, including preliminary machining, degreasing, etching, removal of oxide films, followed by washing in water of a coated steel surface and subsequent electrodeposition of a zinc-nickel-cobalt coating in an electrolysis mode from an electrolyte containing salts of sulfuric acid ZnSO ₄ , NiSO ₄ , CoSO ₄ , glycine and water, characterized in that the electrolysis is carried out in a reverse mode from 125 to 155 cycles when cat one current density i _k = 0.5-2.0 A / dm ² , anodic current density i _a = 4.0-5.0 A / dm ² , with the duration of the cathodic polarization of one cycle τ _k = 15-20 s and the duration of the anode polarization of one cycle τ _a = 1.0 s, at an electrolyte temperature with a graphite anode from 20 ° C to 25 ° C, pH from 4.5 to 5.5, while the electrolyte solution additionally contains a salt of sulfuric acid Na ₂ SO ₄ , as ZnSO ₄ contains ZnSO ₄ ⋅ 7H ₂ O, as NiSO ₄ - NiSO ₄ ⋅ 7H ₂ O, as CoSO ₄ - CoSO ₄ ⋅ 7H ₂ O, in the following ratio of components, g / l: ZnSO ₄ ⋅7H ₂ O  60.0-72.0 NiSO ₄ ⋅7H ₂ O  34.0-39.0 CoSO ₄ ⋅7H ₂ O  19.7-33.7 Na ₂ SO ₄  60.0-72.0 glycine  52.5-70.0 water  rest