CN111206240A

CN111206240A - Method for obtaining passivation region of amorphous Ni-Mo-P coating in salt solution and application thereof

Info

Publication number: CN111206240A
Application number: CN202010054683.4A
Authority: CN
Inventors: 赵冠琳; 张敏; 刘树帅; 邹勇; 王新洪
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2020-01-17
Filing date: 2020-01-17
Publication date: 2020-05-29

Abstract

The invention relates to the technical field of amorphous Ni-Mo-P coating preparation, in particular to a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution and application thereof. The method comprises the following steps: 1) polishing, deoiling and derusting the base material, and then carrying out sensitization treatment; 2) putting the base material subjected to the sensitization treatment in the step 1) into a plating solution for chemical plating; 4) carrying out heat treatment on the substrate material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step 3) in a protective atmosphere: the temperature is 100-300 ℃, and the heat preservation is carried out for 1-36 h; and cooling along with the furnace after the completion to obtain the product. After the special selected process treatment, the corrosion process is changed, the perforation corrosion capability of chloride ions to the coating is reduced, a passivation interval appears on a polarization curve in salt solution, and the excellent chloride ion corrosion resistance is shown.

Description

Method for obtaining passivation region of amorphous Ni-Mo-P coating in salt solution and application thereof

Technical Field

The invention relates to the technical field of amorphous Ni-Mo-P coating preparation, in particular to a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution and application thereof.

Background

The information disclosed in this background of the invention is only for enhancement of understanding of the general background of the invention and is not necessarily to be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

The corrosion problem of metal materials is an important problem which is urgently needed to be solved in the fields of modern industry, national defense engineering construction, human production and life and the like. The appearance of surface engineering technology provides a good solution for improving the surface performance of materials. The chemical plating process is a surface treatment technology with simple and convenient process, energy conservation and environmental protection, wherein the chemical nickel plating process is the most widely applied chemical plating process at present because the plating layer has unique performance, especially excellent corrosion resistance. For chemical nickel and phosphorus plating series coatings, when the coating is in an amorphous state, the corrosion resistance of the coating is better. The amorphous coating is a long-range disordered structure, and the structural uniformity enables the amorphous coating to have better corrosion resistance than coatings of other structural types.

The ternary Ni-Mo-P coating is obtained by adding corresponding molybdenum salt into a plating solution on the basis of the binary Ni-P coating. The addition of the molybdenum salt has certain toxicity to the whole plating solution, so that the preparation of the ternary amorphous Ni-Mo-P plating layer has certain difficulty. The preparation of the amorphous Ni-Mo-P coating with high P content by using a chemical plating method is still a technical difficulty at present.

The radius of chloride ions in the NaCl solution is small, and the penetration capacity is strong. It is easily adsorbed by the metal surface and corrosion spots appear there. When the concentration of the chloride ions reaches a certain value, the anodic dissolution rate of the area is accelerated, and the metal matrix is dug downwards to corrode deeply to form pitting pits. The dissolution of the metal forming the pitting pits can accelerate the aggregation of chloride ions, and when the concentration of the chloride ions reaches a certain critical value, the anode metal is always in an activated state and cannot be passivated, and the formed pitting pits can be continuously enlarged and deepened.

Disclosure of Invention

In view of the above problems, the present inventors have further studied and found that: the passivation layer is prepared on the surface of the amorphous Ni-Mo-P coating, and the coating still keeps an amorphous structure state, so that a passivation interval appears in a salt solution on the Ni-Mo-P coating, and the method is a good method for improving the corrosion resistance of the coating in the salt solution. Therefore, the invention provides a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution and application thereof. After the amorphous Ni-Mo-P chemical plating layer prepared by the invention is subjected to subsequent treatment, the corrosion process of the amorphous Ni-Mo-P chemical plating layer is changed, and the amorphous Ni-Mo-P chemical plating layer has good chloride ion corrosion resistance.

The invention aims at providing a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution.

The second purpose of the invention is to provide the application of the method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution.

In order to achieve the purpose, the invention adopts the following technical means:

the invention discloses a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution, which comprises the following steps:

(1) polishing, deoiling and derusting the base material, and then carrying out activation treatment for later use;

(2) placing the substrate material subjected to the activation treatment in the step (1) into a plating solution for chemical plating, wherein the plating solution comprises the following components: 25-27 g/L of nickel sulfate, 0.3-0.5 g/L of sodium molybdate, 30-33 g/L of sodium citrate, 12-16 g/L of sodium acetate, 20-28 g/L of sodium hypophosphite and 1.0-1.2 mg/L of thiourea.

(4) Carrying out heat treatment on the base material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step (3) in a protective atmosphere: the temperature is 100-300 ℃, and the heat preservation is carried out for 1-36 h; and cooling along with the furnace after the completion to obtain the product.

Further, in the step (1), the polishing method comprises the following steps: and sequentially selecting 200-mesh, 400-mesh, 600-mesh, 800-mesh and 1000-mesh silicon carbide sand paper to polish the base material to enable the surface of the base material to be flat and bright, and then washing the base material by using deionized water.

Further, in the step (1), the oil removing method is alkaline cleaning oil removing; the method specifically comprises the following steps:the alkaline washing solution comprises the following components: NaOH 25-30g/L (saponification), Na₂CO₃20-25g/L (buffer action), Na₄PO₄·12H₂O7-10 g/L (increased water-washability), Na₂SiO₃·9H₂O10-13 g/L (emulsifier), OP-102-4 g/L (emulsifier). The alkali washing temperature is 75-85 ℃; the alkali washing time is 30-40 min; gas explosion stirring; and (4) washing with deionized water after alkali washing is finished.

Further, in the step (1), the rust removal method comprises the steps of acid pickling rust removal; the method specifically comprises the following steps: the pickling solution is HCl solution with the mass concentration of 25-30%, and the pickling temperature is 25-30 ℃; the pickling time is 15-25 min. And (4) washing with deionized water after pickling is finished.

Further, in the step (1), in order to remove a thin oxide film or residual substances on the surface of the substrate, sensitization treatment of the substrate is required. The sensitization treatment method comprises the following steps: the sensitizing solution is H with the mass concentration of 5-8%₂SO₄Sensitizing the solution at 25-30 ℃ for 30-60 s; and (5) washing with deionized water after finishing the process.

Further, in the step (2), the plating temperature is 80-90 ℃, and the plating time is not less than 3.8 h.

Further, in the step (2), in the plating process, the pH value of the plating solution is controlled to be 8.5-8.8, and the pH value of the plating solution is regulated to be always within the range by using alkaline solutions such as ammonia water/sodium hydroxide and the like during plating, so that the stability of the plating solution is ensured, and the requirement of long-time plating is met. Alternatively, an alkaline solution such as ammonia/sodium hydroxide is added to the plating solution every half hour to control the pH within the above range.

Further, the mass concentration of the alkaline solution is 3-5%, the alkaline solution has the main function of adjusting the pH value of the plating solution in the reaction process, and the effectiveness of the adjustment must be guaranteed on the basis that the balance of the alkaline environment of the plating solution is not damaged.

Further, in the step (4), the protective atmosphere is argon or nitrogen, and the main function of the protective atmosphere is to prevent the coating from being oxidized during the heating process.

Further, in the step (4), when the heat treatment temperature is lower, the corresponding longest heat treatment time is longer; similarly, a higher heat treatment temperature corresponds to a shorter maximum heat treatment time. Thus, the recommended maximum heat treatment time at a temperature of 100 ℃ is 36 h; the recommended maximum heat treatment time at the temperature of 200 ℃ is 24 hours; the recommended maximum heat treatment time at the temperature of 250 ℃ is 16 h; the recommended maximum heat treatment time at a temperature of 300 ℃ is 1 h.

Finally, the invention discloses application of the method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution in material surface treatment.

One of the characteristics of the invention is as follows: in the plating solution, nickel sulfate and sodium molybdate are used as main salts, sodium citrate and sodium acetate are used as complexing agents, sodium hypophosphite is used as a reducing agent, and thiourea is used as a stabilizing agent. A large number of screening tests prove that when the content of each component in the plating solution containing Mo and P elements is in the range, the content of P in the plating layer is up to more than 12 wt.% while the addition of the Mo element in the plating layer is reasonably controlled, the non-crystallization degree of the plating layer is obviously improved, and the plating layer has good thermal stability and corrosion resistance.

The second characteristic of the invention is: the pH value of the plating solution is regulated to be always in a set range by using alkaline solutions such as ammonia water/sodium hydroxide and the like in the plating process, so that the plating rate is not too high in the plating process of the plating solution, the long-time stability of the plating solution is further ensured by controlling the plating rate, the requirement of long-time plating is met, and the high-phosphorus amorphous Ni-Mo-P plating layer with large thickness (more than 37 mu m) is ensured to be obtained by keeping the stability of the plating solution for a long time. This is because the present inventors found that: in the chemical plating codeposition process, the reaction process of separating out one Mo atom consumes more atomic hydrogen than the reaction process of separating out one P atom, and the separation of the atomic hydrogen has a great relationship with the pH value of the plating solution, which shows that the influence of the pH value on the separation rate of the Mo element is larger than that of the P element. If the pH value is smaller, the precipitation rate of Mo is increased, sodium molybdate has a poisoning effect on the whole plating solution, and the stability of the whole plating solution is damaged when the precipitation of Mo is accelerated, so that the control of a reasonable pH value range and the maintenance of the reasonable pH value range are the key for maintaining the stability of the plating solution and ensuring the long-time plating.

The invention is characterized in that: the amorphous Ni-Mo-P plating layer prepared by chemical plating is ensured to be still kept in an amorphous structure state after being subjected to a heat treatment process. This is an important factor in the occurrence of passive zones of the coating in the salt bath. The heat treatment means of the present invention can achieve the above object because: when the temperature is in the range of 100-300 ℃, heating the amorphous coating can help the structural relaxation of atoms in the coating and the uniformity of components, which are both important factors for forming a passivation interval on the surface of the coating in a salt solution at a later stage. When the temperature is higher than 300 ℃, the amorphous plating layer can quickly generate structural transformation, the amorphous state is transformed into a crystal structure state, atoms already form stable compounds at the moment, and oxides or compounds with protection effect can not be formed in a corrosive solution, so that a passivation region can not be formed; when the temperature is too low, the atoms in the amorphous coating layer move too slowly, and the change of the structure, the components and the like can occur only after a long heat preservation time, so that a large amount of resources are wasted.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

(1) by screening and optimizing the composition of the plating solution and improving the plating method, the invention can prepare a large-thickness high-P (more than 12 wt.%) amorphous Ni-Mo-P plating layer on the surface of a common carbon steel substrate, no obvious holes are found in the plating layer, and the plating layer is well combined with the substrate.

(2) Experiments prove that the original amorphous Ni-Mo-P coating (which is not subjected to subsequent heat treatment) prepared by the chemical plating process does not have an obvious passivation region on the polarization curve in a salt solution, which indicates that the amorphous Ni-Mo-P coating which is not subjected to subsequent heat treatment cannot well resist the perforation corrosion of chlorine ions. After the special selected process treatment, the corrosion process is changed, the perforation corrosion capability of chloride ions to the plating layer is reduced, a passivation interval appears on a polarization curve in salt solution, and the excellent chloride ion corrosion resistance is shown.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 shows XRD results of Ni-Mo-P coatings prepared according to the first embodiment of the present invention after heat treatment for 200-16 h.

FIG. 2 is an XRD result of the Ni-Mo-P coating prepared by the second embodiment of the invention after heat treatment for 250-4 h.

FIG. 3 is a graph showing the polarization of Ni-Mo-P coatings prepared in accordance with the first embodiment of the present invention in a 3.5 wt.% NaCl solution after heat treatment for 200-16 h.

FIG. 4 is a graph showing the polarization of a Ni-Mo-P coating prepared in accordance with a second embodiment of the present invention in a 3.5 wt.% NaCl solution after heat treatment for 250-4 hours.

FIG. 5 is a graph showing polarization curves of Ni-Mo-P coatings prepared in a 3.5 wt.% NaCl solution according to a first experimental example of the present invention.

FIG. 6 is a graph showing the polarization of Ni-Mo-P coatings prepared in a 3.5 wt.% NaCl solution according to a second test example of the present invention.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As mentioned above, the NaCl solution has strong penetration ability of chloride ions, and is easy to cause perforation corrosion to the amorphous Ni-Mo-P plating layer. Therefore, the invention provides a method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution; the invention will now be further described with reference to the drawings and detailed description.

First embodiment

A method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution comprises the following steps:

(1) cutting the Q235 serving as a base material into samples, sequentially polishing the samples by using 200-mesh, 400-mesh, 600-mesh, 800-mesh and 1000-mesh silicon carbide sand paper to enable the surfaces of the samples to be flat and bright, and washing the samples by using deionized water after finishing polishing.

(2) Carrying out oil removal treatment on the polished sample by alkali washing liquid: the alkaline washing liquid comprises the following specific components: NaOH 30g/L, Na₂CO₃25g/L，Na₄PO₄·12H₂O 10g/L，Na₂SiO₃·9H₂O10 g/L and OP-102 g/L. The alkali washing temperature is 85 ℃; the alkali washing time is 30min, and gas explosion stirring is adopted in the alkali washing process. And (5) washing with deionized water for 3 times after finishing the operation to remove residual alkali liquor.

(3) Carrying out rust removal treatment and flushing on the sample after oil removal by using a pickling solution: the pickling solution is HCl solution with the mass concentration of 30%; the pickling temperature is 28 ℃; the pickling time is 22 min. And after the acid liquor is washed for 3 times by deionized water to remove residual acid liquor.

(4) Sensitizing the sample after the rust removal treatment: the sensitizing solution is H with the mass concentration of 5%₂SO₄A solution; the sensitization temperature is 28 ℃; the sensitization time was 45 s. Followed by a rinse with deionized water.

(5) And (4) carrying out a chemical plating process on the sample obtained in the step (4): the temperature of a plating system is controlled by adopting a digital display constant-temperature water bath kettle, the plating temperature is 85 +/-2 ℃, the pH value of the plating solution is controlled to be 8.7, the pH value of the plating solution is adjusted by using ammonia water with the mass concentration of 5%, and the plating time is 4 hours. The chemical plating solution comprises the following components: 26g/L of nickel sulfate, 0.3g/L of sodium molybdate, 30g/L of sodium citrate, 12g/L of sodium acetate, 28g/L of sodium hypophosphite and 1.0mg/L of thiourea. Because the plating time is long, ammonia water with the mass concentration of 5% needs to be added into the plating solution every half hour to adjust the pH value, and the plating solution is ensured to realize long-time continuous plating.

(6) And (3) heat treatment: and (4) putting the base material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step (5) into a tubular furnace, performing the whole heat treatment process in an argon protective atmosphere, controlling the temperature of the tubular furnace at 200 ℃, preserving the heat for 16 hours, and cooling along with the furnace to obtain the heat-treated Ni-Mo-P alloy coating.

Second embodiment

A preparation method of a large-thickness high-phosphorus amorphous Ni-Mo-P electroless plating layer comprises the following steps:

(1) step (1) is the same as the first embodiment, and is not described again.

(2) Step (2) is the same as the first embodiment, and is not described again.

(3) Carrying out rust removal treatment and flushing on the sample after oil removal by using a pickling solution: the pickling solution is HCl solution with the mass concentration of 30%; the pickling temperature is 26 ℃; the pickling time is 24 min. And after the acid liquor is washed for 3 times by deionized water to remove residual acid liquor.

(4) Sensitizing the sample after the rust removal treatment: the sensitizing solution is H with the mass concentration of 8%₂SO₄A solution; the sensitization temperature is 26 ℃; the sensitization time was 50 s. Followed by a rinse with deionized water.

(5) And (4) carrying out a chemical plating process on the sample obtained in the step (4): the temperature of a plating system is controlled by adopting a digital display constant temperature water bath kettle, the plating temperature is 85 +/-2 ℃, the pH value of the plating solution is controlled to be 8.8, the pH value of the plating solution is adjusted by utilizing a sodium hydroxide solution with the mass concentration of 3%, and the plating time is 4 hours. The chemical plating solution comprises the following components: 27g/L of nickel sulfate, 0.5g/L of sodium molybdate, 30g/L of sodium citrate, 16g/L of sodium acetate, 20g/L of sodium hypophosphite and 1.1mg/L of thiourea serving as a stabilizer. Because the plating time is long, sodium hydroxide solution with the mass concentration of 3% needs to be added into the plating solution every half hour to adjust the pH value, and the plating solution is ensured to realize long-time continuous plating.

(6) And (3) heat treatment: and (4) putting the base material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step (5) into a tubular furnace, carrying out the whole heat treatment process in an argon protective atmosphere, controlling the temperature of the tubular furnace at 250 ℃, preserving the heat for 4 hours, and cooling along with the furnace to obtain the heat-treated Ni-Mo-P alloy coating.

Third embodiment

(1) step (1) is the same as the first embodiment, and is not described again.

(2) Carrying out oil removal treatment on the polished sample by alkali washing liquid: the alkaline washing liquid comprises the following specific components: NaOH25g/L, Na₂CO₃20g/L，Na₄PO₄·12H₂O 8g/L，Na₂SiO₃·9H₂O13 g/L and OP-103 g/L. The alkali washing temperature is 75 ℃; the alkali washing time is 40min, and gas explosion stirring is adopted in the alkali washing process. And (4) washing with deionized water after the completion to remove residual alkali liquor.

(3) Carrying out rust removal treatment and flushing on the sample after oil removal by using a pickling solution: the pickling solution is HCl solution with the mass concentration of 25%; the pickling temperature is 28 ℃; the pickling time is 25 min. And after the acid liquor is washed for 3 times by deionized water to remove residual acid liquor.

(4) Sensitizing the sample after the rust removal treatment: the sensitizing solution is H with the mass concentration of 5%₂SO₄A solution; the sensitization temperature is 25 ℃; the sensitization time was 60 s. Followed by a rinse with deionized water.

(5) And (4) carrying out a chemical plating process on the sample obtained in the step (4): the temperature of a plating system is controlled by adopting a digital display constant-temperature water bath kettle, the plating temperature is 82 +/-2 ℃, the pH value of the plating solution is controlled to be 8.5, the pH value of the plating solution is adjusted by using ammonia water with the mass concentration of 5%, and the plating time is 3.8 h. The chemical plating solution comprises the following components: 25g/L of nickel sulfate, 0.4g/L of sodium molybdate, 33g/L of sodium citrate, 15g/L of sodium acetate, 27g/L of sodium hypophosphite and 1.2mg/L of thiourea. Because the plating time is long, ammonia water with the mass concentration of 5% needs to be added into the plating solution every half hour to adjust the pH value, and the plating solution is ensured to realize long-time continuous plating.

(6) And (3) heat treatment: and (4) putting the base material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step (5) into a tubular furnace, performing the whole heat treatment process in an argon protective atmosphere, controlling the temperature of the tubular furnace at 100 ℃, preserving the heat for 36 hours, and cooling along with the furnace to obtain the heat-treated Ni-Mo-P alloy coating.

Fourth embodiment

(1) step (1) is the same as the first embodiment, and is not described again.

(2) Carrying out oil removal treatment on the polished sample by alkali washing liquid: the alkaline washing liquid comprises the following specific components: NaOH 28g/L, Na₂CO₃28g/L，Na₄PO₄·12H₂O 7g/L，Na₂SiO₃·9H₂O12 g/L and OP-104 g/L. The alkali washing temperature is 80 ℃; the alkali washing time is 35min, and gas explosion stirring is adopted in the alkali washing process. And (4) washing with deionized water after the completion to remove residual alkali liquor.

(3) Carrying out rust removal treatment and flushing on the sample after oil removal by using a pickling solution: the pickling solution is HCl solution with the mass concentration of 25%; the pickling temperature is 30 ℃; the pickling time is 15 min. And after the acid liquor is washed for 3 times by deionized water to remove residual acid liquor.

(4) And (3) activating the sample after the rust removal treatment: the sensitizing solution is H with the mass concentration of 8%₂SO₄A solution; the sensitization temperature is 30 ℃; the sensitization time was 30 s. Followed by a rinse with deionized water.

(5) And (4) carrying out a chemical plating process on the sample obtained in the step (4): the temperature of a plating system is controlled by adopting a digital display constant-temperature water bath kettle, the plating temperature is 88 +/-2 ℃, the pH value of the plating solution is controlled at 8.6, the pH value of the plating solution is adjusted by utilizing a sodium hydroxide solution with the mass concentration of 4%, and the plating time is 4.2 h. The chemical plating solution comprises the following components: 26g/L of nickel sulfate, 0.5g/L of sodium molybdate, 32g/L of sodium citrate, 15g/L of sodium acetate, 20g/L of sodium hypophosphite and 1.0mg/L of thiourea serving as a stabilizer. Because the plating time is long, sodium hydroxide solution with the mass concentration of 4% needs to be added into the plating solution every half hour to adjust the pH value, and the plating solution is ensured to realize long-time continuous plating.

(6) And (3) heat treatment: and (4) putting the base material with the amorphous Ni-Mo-P coating plated on the surface obtained in the step (5) into a tubular furnace, carrying out the whole heat treatment process in an argon protective atmosphere, controlling the temperature of the tubular furnace at 300 ℃, preserving the heat for 1h, and cooling along with the furnace to obtain the heat-treated Ni-Mo-P alloy coating.

First test example

A method for obtaining a passivation region of an amorphous Ni-Mo-P coating in a salt solution is the same as that in example 1, except that the sample after chemical plating in the step (5) is not subjected to further heat treatment.

Second test example

A method for obtaining a passivation region of an amorphous Ni-Mo-P coating in a salt solution is the same as that in example 2, except that the sample after chemical plating in the step (5) is not subjected to further heat treatment.

Performance testing

The tests of the Ni-Mo-P-containing coating prepared in the first embodiment, the second embodiment, the first test example and the second test example are taken as examples, and the performances are tested as follows:

(1) XRD test

Fig. 1 and 2 are XRD test charts of the Ni-Mo-P plating layers prepared in the first and second examples, and it can be seen from the charts that neither XRD curve has a distinct and sharp diffraction peak, but there is a diffuse scattering "steamed bread peak" approximately symmetrically distributed near 45 °, which indicates that the arrangement of plating atoms in space is disordered, and has an amorphous structure characteristic, indicating that both plating layers are amorphous plating layers.

(2) Corrosion resistance test

Polarization curves of the Ni-Mo-P plating layers of the first, second, first and second examples in a 3.5 wt.% NaCl solution were measured at room temperature using an electrochemical workstation, as shown in fig. 3 to 6, respectively.

The apparent passivation interval, which ranges from-0.17V to 0V, can be seen from the polarization curve of fig. 3. The apparent passivation interval, which ranges from-0.19V to 0.1V, can also be seen from the polarization curve of fig. 4. The passivation interval appearing in the polarization curve is long or short, which shows that the coating can effectively prevent the perforation corrosion of chloride ions, and the method of the invention can enable the amorphous Ni-Mo-P coating to have the passivation interval in the salt solution.

As can be seen from the polarization curves of FIGS. 5 and 6, the amorphous Ni-Mo-P coating without subsequent heat treatment has no obvious passivation region on the polarization curve in the salt solution, indicating that the amorphous Ni-Mo-P coating without subsequent heat treatment is not very resistant to the pitting corrosion by chlorine ions.

(3) Coating composition and thickness measurement

In the first example, the content of P element in the amorphous Ni-Mo-P plating layer was 12.80 wt.%, the content of Mo element was 2.66 wt.%, and the balance was Ni. The surface of the plating layer is smooth and has no holes. The cross section showed good bonding of the coating to the substrate and uniform thickness with an average thickness of 38.0 μm.

In the second example, the content of P element in the amorphous Ni-Mo-P plating layer was 12.84 wt.%, the content of Mo element was 4.28 wt.%, and the balance was Ni. The surface of the plating layer is smooth and has no holes. The cross section shows that the coating is well combined with the substrate and has uniform thickness, and the average thickness is 37.6 mu m.

It can be seen that in the plating solution containing Mo and P elements, the method of the invention realizes reasonable control of the addition amount of the Mo element in the plating layer and ensures the P content in the plating layer, thereby obviously improving the non-crystallization degree of the plating layer and leading the plating layer to have good thermal stability and corrosion resistance.

In addition, the thickness of the current amorphous Ni-Mo-P coating is generally between several micrometers and 20 micrometers, which is one of the important reasons for restricting the application of the coating of the type, and researches show that the porosity of the coating does not have obvious influence on the coating performance only when the coating thickness reaches more than 30 micrometers. The invention ensures the stability of the plating solution by using ammonia water/diluted sodium hydroxide solution to adjust the pH value of the plating solution within a set range all the time in the plating process, thereby meeting the requirement of long-time plating, ensuring the obtaining of a high-phosphorus amorphous Ni-Mo-P plating layer with large thickness by keeping the stability of the plating solution for a long time, and reducing the influence of gaps/holes on the plating layer.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for obtaining a passivation interval of an amorphous Ni-Mo-P coating in a salt solution is characterized by comprising the following steps:

(1) polishing, deoiling and derusting the base material, and then carrying out sensitization treatment for later use;

(2) putting the base material sensitized in the step (1) into a plating solution for chemical plating, wherein the plating solution comprises the following components: 25-27 g/L of nickel sulfate, 0.3-0.5 g/L of sodium molybdate, 30-33 g/L of sodium citrate, 12-16 g/L of sodium acetate, 20-28 g/L of sodium hypophosphite and 1.0-1.2 mg/L of thiourea;

2. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in claim 1, wherein in the step (2), the plating temperature is 80-90 ℃, and the plating time is not less than 3.8 h.

3. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution according to claim 1, wherein in the step (2), the pH value of the plating solution is controlled between 8.5 and 8.8 during the plating process, and the pH value of the plating solution is adjusted to be always within the range by using an alkaline solution during the plating process;

preferably, the pH is controlled within the above range by adding an alkaline solution to the plating solution every half hour;

preferably, the alkaline solution comprises ammonia or sodium hydroxide; more preferably, the mass concentration of the alkaline solution is 3-5%.

4. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in claim 1, wherein in the step (4), the protective atmosphere is argon or nitrogen.

5. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in any one of claims 1-4, wherein in the step (1), the polishing method comprises: and sequentially selecting 200-mesh, 400-mesh, 600-mesh, 800-mesh and 1000-mesh silicon carbide sand paper to polish the base material to enable the surface of the base material to be flat and bright, and then washing the base material by using deionized water.

6. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in any one of claims 1-4, wherein in the step (1), the oil removing method is alkali cleaning oil; preferably, the alkaline wash solution comprises the following components: NaOH 25-30g/L, Na₂CO₃20-25g/L，Na₄PO₄·12H₂O 7-10g/L，Na₂SiO₃·9H₂O10-13 g/L, OP-102-4 g/L; preferably, the alkali washing temperature is 75-85 ℃; the alkali washing time is 30-40 min; gas explosion stirring; and (4) washing with deionized water after alkali washing is finished.

7. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in any one of claims 1 to 4, wherein in the step (1), the rust removal method is acid pickling rust removal; preferably, the pickling solution is HCl solution with the mass concentration of 25-30%, and the pickling temperature is 25-30 ℃; the pickling time is 15-25 min; and (4) washing with deionized water after pickling is finished.

8. The method for obtaining the passivation interval of the amorphous Ni-Mo-P coating in the salt solution as claimed in any one of claims 1 to 4, wherein in the step (1), the sensitization treatment method comprises: the sensitizing solution is H with the mass concentration of 5-8%₂SO₄The solution has a sensitization temperature of 25-30 ℃ and is used for sensitizationThe time is 30-60 s; and (5) washing with deionized water after finishing the process.

9. The method for obtaining the passivation zone of the amorphous Ni-Mo-P coating in the salt solution as claimed in any one of claims 1 to 4, wherein in the step (4), the maximum heat treatment time is 36h when the heat treatment temperature is 100 ℃;

preferably, the maximum heat treatment time is 24h when the heat treatment temperature is 200 ℃;

preferably, the maximum heat treatment time is 16h when the heat treatment temperature is 250 ℃;

preferably, the maximum heat treatment time is 1h at a heat treatment temperature of 300 ℃.

10. Use of the method for obtaining the occurrence of passivated regions of an amorphous Ni-Mo-P coating in a salt solution according to any of claims 1 to 9 in the surface treatment of materials.