阅读说明：本技术 一种钕铁硼镀锌层无铬钝化液及钝化方法 (Chromium-free passivation solution and passivation method for neodymium iron boron zinc coating ) 是由 卢吉 陈小平 卢泽琴 王向东 黄涛 汪兵 刘清友 贾书君 于 2021-06-29 设计创作，主要内容包括：本发明涉及一种钕铁硼镀锌层无铬钝化液及钝化方法,属于电镀锌表面处理技术领域,本发明的钕铁硼镀锌层无铬钝化液,含有可溶性硅酸盐和可溶性铈(Ⅳ)盐,其中可溶性硅酸盐为成膜剂,可溶性铈(Ⅳ)盐为氧化成膜剂。解决了现有技术中硅酸盐镀锌层钝化膜易于脱落,在钕铁硼工件浸渍翻动过程中存在破损和脱落；钝化膜钝化速度快则钝化膜变薄,厚度不足；钝化过程中钝化膜不够致密,导致耐腐蚀性下降的问题。实现了对钕铁硼工件镀锌层的无铬化钝化耐腐蚀保护。(The invention relates to a chromium-free passivation solution for a neodymium iron boron zinc coating and a passivation method, belonging to the technical field of electrogalvanizing surface treatment. The problems that in the prior art, a silicate zinc coating passive film is easy to fall off, and the neodymium iron boron workpiece is damaged and falls off in the dipping and turning process are solved; when the passivation speed of the passivation film is high, the passivation film becomes thin and is insufficient in thickness; the passive film is not compact enough in the passivation process, which causes the problem of the reduction of the corrosion resistance. The chromium-free passivation corrosion-resistant protection of the zinc coating of the neodymium iron boron workpiece is realized.)

1. The chromium-free passivation solution for the neodymium iron boron zinc coating is characterized by comprising soluble silicate, soluble cerium (IV) salt and an auxiliary oxidant, wherein the soluble silicate is a film forming agent, and the soluble cerium (IV) salt is an oxidized film forming agent; the pH value of the passivation solution is 2.0-3.0;

the passivation solution is used for dipping neodymium iron boron products with surface zinc coatings.

2. The chromium-free passivation solution for the zinc-plated neodymium-iron-boron layer according to claim 1, wherein the concentration of soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

3. The chromium-free passivation solution for the NdFeB zinc coating as claimed in claim 2, wherein the soluble cerium (IV) salt is ceric sulfate.

4. The chromium-free passivation solution for the NdFeB zinc coating as claimed in claim 3, wherein the auxiliary oxidant is hydrogen peroxide, and the concentration of the hydrogen peroxide is 5 mL/L-20 mL/L.

5. The chromium-free passivation solution for the NdFeB zinc coating as claimed in claim 4, wherein the concentration of soluble silicate in the passivation solution is 5 g/L-35 g/L.

6. The chromium-free passivation solution for the NdFeB zinc coating as claimed in claim 1, wherein the passivation solution further comprises an acidifier, and the acidifier is sulfuric acid.

7. The chromium-free passivation solution for the NdFeB zinc coating as claimed in claim 6, wherein the passivation solution further comprises a film forming auxiliary agent, and the film forming auxiliary agent is soluble cobalt salt and soluble copper salt.

8. The chromium-free passivation solution for the NdFeB zinc coating of claim 7, wherein the concentration of the soluble cobalt salt in the passivation solution is 0.1-1.0 g/L, and the concentration of the soluble copper salt is 0.1-1.0 g/L.

9. A neodymium iron boron zinc coating chromium-free passivation method is characterized in that a neodymium iron boron product with a zinc coating on the surface is soaked by the neodymium iron boron zinc coating chromium-free passivation solution of claims 1 to 8, and the neodymium iron boron product is turned over during the soaking process.

10. The method for the chromium-free passivation of the zinc-plated neodymium-iron-boron layer according to claim 9, wherein the passivation treatment temperature is normal temperature, and the dipping time is 10 seconds to 120 seconds.

Technical Field

The invention relates to the technical field of electrogalvanizing surface treatment, in particular to a chromium-free passivation solution and a passivation method for a neodymium iron boron zinc coating.

Background

Neodymium-iron-boron, also known as neodymium-iron-boron magnet, is a tetragonal crystal formed by neodymium, iron and boron, and is a magnet prepared by powder metallurgy, spin-spray smelting and other methods, and is widely applied to electronic products, such as hard disks, mobile phones, earphones, tools powered by batteries and the like. Therefore, the neodymium iron boron products are all workpieces with small volumes. In order to prevent the oxidation corrosion of the neodymium iron boron workpiece, the surface is generally treated by a galvanizing process, and then passivation treatment is carried out on the surface of a galvanizing layer.

The passivation technology of zinc coating has been developed for three generations, the first being hexavalent chromate passivation. The second generation of trivalent chromium passivation has been developed over two decades and has been a substantial replacement for hexavalent chromium passivation, and the salt spray corrosion resistance of trivalent chromium passivation is comparable to that of hexavalent chromium passivation. The toxicity of the trivalent chromium is 1 percent of that of the hexavalent chromium, and the trivalent chromium framework film with excellent performance can be reserved, so that the corrosion resistance of the passivation film is ensured, and the passivation of the trivalent chromium is rapidly developed and basically replaces the passivation of the hexavalent chromium. However, a small amount of hexavalent chromium is often included in the trivalent chromium passivation film layer, and the possibility of converting trivalent chromium into hexavalent chromium also exists in the long-term use process.

Therefore, the search for an environmentally friendly chromium-free surface protection technology instead of chromate passivation and the ability to apply it to passivation of a neodymium iron boron zinc plating layer has become one of the hot technologies that are actively being studied and studied. The salt spray corrosion resistance of the third-generation inorganic salt chromium-free passivation of the current zinc coating can not reach the trivalent chromium passivation performance, and the requirement of the neodymium iron boron permanent magnet with higher corrosion resistance requirement can not be met. The current inorganic salt chromium-free passivation mainly comprises molybdate passivation, titanate passivation, silicate passivation and the like. Among them, molybdate is still a low-toxicity reagent and expensive in valence of chromium; the titanium salt passive film has no self-repairing capability and is easy to diffuse once corroded; the corrosion resistance of a passive film formed by the silicate used alone is poor, the pH value of the silicate passivation solution is unstable, and sol is easily formed.

The prior inorganic salt chromium-free passivation also comprises rare earth metal salt passivation, the rare earth salt film has low adhesive force, uneven film formation, easy loosening and easy falling off, needs a plurality of noble rare earth metals, has low price and extremely high cost. The popularization and application of the inorganic chromium-free zinc-plating passivation in the neodymium iron boron market are restricted.

Disclosure of Invention

In view of the above analysis, the invention aims to provide a chromium-free passivation solution for a neodymium iron boron zinc coating and a passivation method thereof, which solve the problems that in the prior art, a passivation film of the chromium-free zinc coating is easy to fall off, and the corrosion resistance is reduced due to damage and falling off in the dipping and turning process of a neodymium iron boron workpiece.

On one hand, the invention provides a chromium-free passivation solution for a neodymium iron boron zinc coating, which contains soluble silicate, soluble cerium (IV) salt and an auxiliary oxidant, wherein the soluble silicate is a film forming agent, and the soluble cerium (IV) salt is an oxidation film forming agent; the pH value of the passivation solution is 2.0-3.0;

the passivation solution is used for dipping neodymium iron boron products with surface zinc coatings.

Furthermore, the concentration of the soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

Further, the soluble cerium (IV) salt is ceric sulfate.

Further, the auxiliary oxidant is hydrogen peroxide.

Further, the concentration of the hydrogen peroxide is 5 mL/L-20 mL/L.

Furthermore, the concentration of the soluble silicate in the passivation solution is 5 g/L-35 g/L.

Further, the soluble silicate is one or the combination of sodium silicate and potassium silicate.

Further, the passivation solution also contains an acidifying agent, and the acidifying agent is sulfuric acid.

Furthermore, the passivation solution also contains a film forming auxiliary agent, wherein the film forming auxiliary agent is soluble cobalt salt and soluble copper salt.

Furthermore, in the passivation solution, the concentration of the soluble cobalt salt is 0.1 g/L-1.0 g/L, and the concentration of the soluble copper salt is 0.1 g/L-1.0 g/L.

On the other hand, the invention also provides a neodymium iron boron zinc coating chromium-free passivation method, the neodymium iron boron product with the surface zinc coating is dipped by using the neodymium iron boron zinc coating chromium-free passivation solution, and the neodymium iron boron product is turned over during dipping.

Further, the passivation treatment temperature is normal temperature, and the immersion time is 10 seconds to 120 seconds.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

1. in the passivation process, the neodymium iron boron workpiece needs to be continuously turned over, friction exists, and the requirement on the friction resistance of the passivation film is met, the passivation solution in the prior art cannot meet the requirement on the wear resistance, the passivation solution can rub with each other in the dipping process, and the passivation film is damaged to a certain extent and falls off, so that the corrosion resistance can be reduced; according to the invention, silicate and soluble cerium (IV) salt are used as film forming agents together, so that a passivation film formed by passivation has certain wear resistance, and the passivation film formed by the neodymium iron boron workpiece in the passivation process cannot be worn and fall off to reduce the corrosion resistance.

2. The silicate and the soluble cerium (IV) salt are jointly used as film forming agents, the soluble cerium (IV) salt is used as both the film forming agent and the oxidant, and zinc is oxidized by the cerium (IV) and converted into cerium (III) to participate in film forming. And the metal in the chromium-free metal passivation solution in the prior art only plays a role of film formation, and the soluble cerium (IV) salt provided by the invention is oxidized into the ion carrier capable of forming the film by adding an oxidant to form the film.

3. The pH value of the passivation solution is 2.0-3.0, so that the reduction of corrosion resistance caused by the over-coarse passivation film due to over-high pH can be effectively prevented, and meanwhile, the phenomenon that the passivation film becomes thin and has insufficient thickness due to over-low pH and over-high passivation dissolution speed can be prevented; the invention realizes the preparation of the passive film by accurately controlling the pH value.

4. The hydrogen peroxide is added as an auxiliary oxidant, and is different from the hydrogen peroxide as an oxidant in the prior art, and the hydrogen peroxide assists the action of the oxidant of the soluble cerium (IV) salt, so that the forming speed of the passivation film is improved, and the corrosion resistance of the passivation film is improved.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

FIG. 1 is a graph showing the macroscopic morphology of a galvanized product after chromium-free passivation;

FIG. 2 is a macroscopic view of a galvanized product of comparative example II after chromium-free passivation;

FIG. 3 is a diagram showing the macro morphology of a galvanized product after chromium-free passivation in comparison with example III;

FIG. 4 illustrates the macro morphology of a galvanized product after chromium-free passivation;

FIG. 5 shows the macroscopic morphology of the galvanized product of example two after chromium-free passivation.

Detailed Description

The most widely used electrogalvanizing is chromate passivation, which is compact and uniform and has excellent corrosion resistance. But is still not an ideal galvanizing passivating solution because of the existence of carcinogenic hexavalent chromium Cr (VI). At present, inorganic salt chromium-free passivation mainly comprises molybdate passivation, titanate passivation, silicate passivation, rare earth metal salt passivation and the like. Among them, molybdate is still a low-toxicity reagent and expensive in valence of chromium; the titanium salt passive film has no self-repairing capability and is easy to diffuse once corroded; but the rare earth salt has low film-forming adhesive force, uneven film-forming, easy loosening and easy falling off of the film, needs a plurality of precious rare earth metals, is not expensive and has extremely high cost; the corrosion resistance of a passive film formed by the silicate used alone is poor, the pH value of the silicate passivation solution is unstable, and sol is easily formed.

Neodymium iron boron is a widely used permanent magnet material, has a great demand, and is galvanized on the surface of the neodymium iron boron in order to prevent the surface from changing, and then the galvanized layer is passivated. Because the galvanized neodymium iron boron is not a large metal plate or a metal sheet but small irregular parts with different shapes, a suspension coating mode is not adopted in the passivation process generally, but a dipping and rolling coating mode is adopted. The special passivation technology of the galvanized neodymium iron boron provides higher requirements for the chromium-free passivation solution, and the current chromium-free passivation solution for the zinc-coated neodymium iron boron can not meet the requirement of chromium-free treatment of the zinc-coated neodymium iron boron.

The invention provides a chromium-free passivation solution for a neodymium iron boron zinc coating, which can meet the special requirement of chromium-free neodymium iron boron zinc coating. The chromium-free passivation solution for the neodymium iron boron zinc coating contains soluble silicate and soluble cerium (IV) salt, wherein the soluble silicate is a film forming agent, and the soluble cerium (IV) salt is an oxidized film forming agent. The soluble silicate and soluble cerium (iv) salt may be dissolved in water to form an aqueous solution.

Compared with the prior passivation solution, the invention has the following remarkable characteristics:

(1) the chromium-free passivation solution for the neodymium iron boron zinc coating comprises two main components of film forming, namely a film forming agent and an oxidation film forming agent, wherein soluble silicate can form a silicon film, and soluble cerium (IV) salt can oxidize a zinc coating and form a cerium film, so that the two films are simultaneously formed in the process of passivating the zinc coating by the chromium-free passivation solution for the neodymium iron boron zinc coating, and the two films are not formed independently, are not two films in a covering relationship, but are mixed films which are simultaneously formed on the zinc coating surface and are uniformly dispersed into a whole.

(2) The soluble cerium (IV) salt adopted by the invention is an oxidant and a film-forming agent, and in the passivation solution, the oxidant mainly has the effect of oxidizing galvanized metal zinc to form a film. The soluble cerium (IV) salt is an oxidation film-forming agent, namely the soluble cerium (IV) salt has oxidation property and oxidizes zinc on the surface of the galvanized layer. The oxidation principle of the soluble cerium (iv) salt is that the soluble cerium (iv) salt oxidizes zinc, which is itself reduced to cerium (iii) by zinc. The cerium (III) is directly involved in the film-forming process and is converted to insoluble cerium (III) oxide and silicate compounds. Therefore, the soluble cerium (IV) salt can be used as an oxidant for oxidation, and cerium (III) after the oxidation reaction can be used as a film-forming agent for film formation.

(3) Through research, the passivation process of the neodymium iron boron zinc coating and the passivation solution is a solid-liquid heterogeneous reaction process, and the reaction only occurs at the interface of the solid and the liquid, namely, the passivation reaction process only occurs at the contact interface of the passivation solution and the zinc coating. Therefore, oxidant molecules in the passivation solution need to move to the interface of the passivation solution and the zinc coating through molecular motion to oxidize zinc, and meanwhile, film forming agent molecules need to move to the interface of the passivation solution and the zinc coating through molecular motion to form a film. In the traditional mode of combining the oxidant and the film forming agent, after the oxidant molecules are oxidized, the oxidant molecules need to move away from an interface where the passivation solution is contacted with the zinc coating layer, and the film forming agent molecules need to move to reach the interface where the passivation solution is contacted with the zinc coating layer. The soluble cerium (IV) salt of the oxidation film-forming agent reduces zinc into cerium (III) after zinc is oxidized when molecules move to an interface where passivation solution and a zinc coating are contacted, and the cerium (III) is formed into a film in situ after being generated in situ at the interface where the passivation solution and the zinc coating are contacted, so that the speed of passivation film formation is accelerated, the influence caused by the molecular motion of other components of the passivation solution in the process of bonding oxidation and film formation is effectively prevented, and the uniformity and compactness of passivation film formation are improved.

Specifically, the concentration of the soluble silicate in the passivation solution is 5 g/L-35 g/L.

The soluble silicate is a film forming agent in the passivation solution, and forms a film together with the soluble cerium (IV) salt of the oxidized film forming agent. Two films are formed simultaneously in the process of passivating the zinc coating by the chromium-free passivation solution for the neodymium iron boron zinc coating, and the two films are not formed independently, are not two films in a covering relationship, and are mixed films which are formed simultaneously on the zinc coating surface and are mutually uniformly dispersed into a whole. According to research, the silicate concentration can influence the component proportion of the formed mixed film, if the silicate concentration is too low, the proportion of silicon in the passive film formed by the passivation solution is low, the corrosion resistance of the film is reduced, and if the silicate concentration is too high, the proportion of cerium in the passive film formed by the passivation solution is reduced, and the compactness of the passive film is also influenced. Tests show that when the concentration of the soluble silicate is lower than 5g/L, the formed passivation film has poor compactness and poor corrosion resistance, and when the concentration of the soluble silicate is higher than 35g/L, the proportion of silicon and the proportion of cerium in the formed passivation film are too high and too low due to too high concentration of the silicate, so that when passivation is carried out, the adhesion of the film is reduced due to too high proportion of silicon in the components of the film in the process of dip-coating of the neodymium iron boron workpiece, and a little damage and falling of the passivation film can occur due to slight friction and collision of the neodymium iron boron workpiece in the process of coating, and the requirement on corrosion resistance cannot be met.

In particular, the soluble cerium (iv) salt may be ceric sulfate.

The soluble cerium (iv) salt of the present invention is an oxidation film-forming agent, and oxidizes the zinc coating layer by using the oxidation ability of cerium (iv), which is completely different from the principle of adding cerium (iii) as an auxiliary agent in the prior art.

Specifically, the concentration of the soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

Because the soluble cerium (IV) salt is an oxidation film-forming agent, the zinc coating is oxidized by utilizing the oxidation capability of the cerium (IV) and also participates in film formation as the film-forming agent, the addition amount of the soluble cerium (IV) salt is used as a main component and is far higher than that of the cerium (III) added as an auxiliary agent in the prior art. Through research, the concentration of the soluble cerium (IV) salt is lower than 5g/L, and the content of cerium in the formed passivation film is insufficient, so that the requirement on corrosion resistance cannot be met. A concentration of the soluble cerium (IV) salt higher than 20g/L causes waste and increases the cost. Therefore, the concentration of the soluble cerium (IV) salt in the passivation solution is 5g/L to 20 g/L.

Specifically, the pH value of the passivation solution can be 2.0-3.0.

Through research, the passivation solution utilizes an oxidation film-forming agent to carry out oxidation passivation on the neodymium iron boron zinc coating and needs to react in an acidic environment. However, tests show that the effect is best when the pH value of the passivation solution is within the range of 2.0-3.0, if the pH value of the passivation solution is too high, namely the pH value is more than 3.0, the passivation film is rough, the corrosion resistance of the passivation film is reduced, if the pH value of the passivation solution is too low, namely the pH value is less than 2.0, the composite film of cerium and silicate generated after passivation is easily and partially dissolved by acid again, the generated passivation film is thinned, and the high-quality passivation film is difficult to form. Therefore, in order to obtain a compact passivation film, the pH value of the passivation solution is controlled within the range of 2.0-3.0, so that a compact passivation film with proper thickness is obtained in the passivation process, and the requirement on corrosion resistance is met.

Specifically, the passivation solution also comprises a film-forming auxiliary agent, wherein the film-forming auxiliary agent is soluble cobalt salt and soluble copper salt.

In one possible embodiment, the soluble cobalt salt is cobalt sulfate and the soluble copper salt is copper sulfate.

The soluble cobalt salt has obvious effect on improving the corrosion resistance of the passive film and inhibiting the generation and the expansion of the pitting corrosion of the passive film.

The corrosion resistance of the passive film can be further improved by the soluble copper salt, and the color of the passive film can be adjusted due to the obvious color of copper ions.

Specifically, in the passivation solution, the concentration of soluble cobalt salt is 0.1 g/L-1.0 g/L, preferably, the concentration of soluble cobalt salt is 0.5g/L, the concentration of soluble copper salt is 0.1 g/L-1.0 g/L, preferably, the concentration of soluble copper salt is 0.5 g/L.

The cobalt salt and the copper salt play an auxiliary role, and are the same as the soluble cerium (IV) salt which reduces zinc into cerium (III) after oxidation, insoluble copper and insoluble cobalt are formed by copper ions and cobalt ions, and the insoluble copper and the insoluble cobalt are simultaneously formed into a film by film forming agents, namely silicate and cerium (III) to form a silicon-cerium-cobalt-copper mixed film, so that a passivation film formed by the passivation solution has better corrosion resistance. However, tests show that when the concentration of the copper salt and the cobalt salt is too high to be more than 1.0g/L, the film-forming agent and the oxidized film agent can be assisted to form a film, but due to the too high content of the copper ions and the cobalt ions, the film-forming compactness is poor because the film-forming agent is interfered by the silicate of the film-forming agent and the oxidized cerium (III) of the oxidized film agent. And when the concentration of the copper salt and the cobalt salt is lower than 0.1g/L, the auxiliary film forming effect cannot be realized.

Specifically, the passivation solution further comprises an auxiliary oxidant, and the auxiliary oxidant is hydrogen peroxide.

The hydrogen peroxide belongs to an auxiliary oxidant, namely the hydrogen peroxide also participates in oxidation as an oxidant, but the auxiliary soluble cerium (IV) salt is mainly embodied in two aspects: firstly, the soluble cerium salt is consumed greatly as an oxidant, but the soluble silicate and cerium form a film together as the film forming agent, so the consumption of cerium as the film forming agent is less than that of cerium as the oxidant, and if the soluble cerium (IV) salt is added in excess, the cost is seriously increased, so hydrogen peroxide is added for assisting oxidation, and the content part of the soluble cerium (IV) salt which is used as the oxidant is supplemented; secondly, the hydrogen peroxide can improve the oxidation potential of the whole passivation solution, even if the whole passivation solution is in an oxidation environment, other reductive impurities or other reductive substances in the air are prevented from consuming cerium (IV), the oxidation efficiency is improved, and the density reduction of a passivation film caused by the uneven oxidation rate of the interface of the passivation solution and a zinc coating is prevented.

In one possible embodiment, the hydrogen peroxide concentration is from 5mL/L to 20mL/L, such as 8mL/L, 10mL/L, 12mL/L, 14mL/L, 16mL/L, 18 mL/L. Preferably, the hydrogen peroxide concentration is 10 mL/L.

Through tests, the concentration of hydrogen peroxide is lower than 5mL/L, the content of hydrogen peroxide is insufficient, and zinc on the surface of a galvanized layer cannot be completely oxidized by matching with soluble cerium (IV) salt, so that the oxidation rate is slow and the formed film is not compact enough. When the content of the hydrogen peroxide is too high, waste is caused, so that the concentration of the hydrogen peroxide is below 20 mL/L.

Specifically, the passivating solution also comprises an acidifying agent, and the acidifying agent can be sulfuric acid.

The acidifying agent provides an acidic environment during passivation, and the concentration of the sulfuric acid is 5 mL/L-20 mL/L.

In one possible embodiment, in order to achieve the desired pH of the passivation solution, the pH needs to be adjusted by adding a suitable amount of sodium hydroxide.

The invention also provides a neodymium iron boron zinc coating chromium-free passivation method, the neodymium iron boron product with the surface zinc coating is dipped by the neodymium iron boron zinc coating chromium-free passivation solution, and the neodymium iron boron workpiece is rolled simultaneously in the dipping process.

Neodymium iron boron is an artificially synthesized magnet widely used in electronic products, such as hard disks, mobile phones, earphones, and battery-powered tools. Therefore, the neodymium iron boron products are all workpieces with small volumes. In the process of passivating the neodymium iron boron, a hanging coating method used by large-scale iron plates, iron sheets and the like cannot be adopted, and in order to enable the surface of each workpiece of the neodymium iron boron to be contacted with the passivation solution, the workpiece needs to be turned over, so that the condition that the surfaces of the neodymium iron boron workpieces are shielded from each other and cannot be contacted with the passivation solution, and the coating in the dipping process is not uniform is prevented.

Specifically, the passivation treatment temperature of the neodymium iron boron zinc coating chromium-free passivation method is normal temperature, and the dipping time is 10-120 seconds.

The passivation method can be processed at normal temperature, does not need heating, and is convenient for industrial popularization. Meanwhile, the dipping time is 10-120 seconds, and experiments show that the passivating solution provided by the invention has two film forming agents, the dipping time is less than 10 seconds, so that the film forming effect is poor, and the corrosion resistance does not meet the requirements, but the dipping time is not too long, when the dipping time exceeds 120 seconds, the passivating film is completely formed, and the too long dipping can generate acid to dissolve the passivating film again, so that the passivating film is roughened, and the corrosion resistance is reduced.

The following detailed description of the preferred embodiments of the invention is provided to illustrate the principles of the invention and not to limit the scope of the invention.

Example one

The invention discloses a chromium-free passivation solution for a neodymium iron boron zinc coating and a passivation method.

At normal temperature, 25g of sodium silicate, 10g of ceric sulfate, 10mL of sulfuric acid (98 wt%) and 10mL of hydrogen peroxide (30 wt%) are added into deionized water, the mixture is stirred uniformly to be completely dissolved, the volume is constant to prepare 2L solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The obtained passivation solution comprises the following main components in percentage by weight:

25g/L of sodium silicate;

ceric sulfate 10 g/L;

10mL/L of sulfuric acid;

10mL/L of hydrogen peroxide.

At normal temperature, immersing the neodymium iron boron galvanized product in a 3% nitric acid solution, washing with water, then immersing the product in a passivation solution for passivation for 20 seconds, continuously turning over in the passivation process to ensure that each product is uniformly passivated, and washing and drying with water after the product is passivated to obtain a uniform and compact colored passivation film, as shown in fig. 4.

Comparative example 1

At normal temperature, 25g of sodium silicate, 10g of ceric sulfate and 10mL of sulfuric acid (98 wt%) are stirred uniformly to be completely dissolved, a solution with a constant volume is prepared into 1L, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use.

And soaking the obtained neodymium iron boron galvanized product in a 3% nitric acid solution, washing with water, then soaking the product in a passivation solution for passivation for 20 seconds, continuously turning over the product in the passivation process to ensure that each product is uniformly passivated, and washing and drying the passivated product with water.

Comparative example No. two

At normal temperature, 10g of ceric sulfate, 10mL of sulfuric acid (98 wt%) and 10mL of hydrogen peroxide (30 wt%) are added into deionized water, stirred uniformly to be completely dissolved, the volume is constant to prepare 1L of solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. Immersing the neodymium iron boron galvanized product in a 3% nitric acid solution, washing with water, then immersing the product in a passivation solution for passivation for 20 seconds, continuously turning over the product in the passivation process to ensure that each product is uniformly passivated, and washing and drying the passivated product with water.

Comparative example No. three

At normal temperature, 25g of sodium silicate, 10mL of sulfuric acid (98 wt%) and 10mL of hydrogen peroxide (30 wt%) are added into deionized water, the mixture is stirred uniformly to be completely dissolved, a volume is determined to prepare 1L of solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. Immersing the neodymium iron boron galvanized product in a 3% nitric acid solution, washing with water, then immersing the product in a passivation solution for passivation for 20 seconds, continuously turning over the product in the passivation process to ensure that each product is uniformly passivated, and washing and drying the passivated product with water.

Comparative example and example the salt spray test results of the neodymium iron boron zinc plating chromium-free passivation product are shown in table 1.

Table 1 results of comparative examples one to three and example one salt spray experiment

Passivation solution	Macroscopic appearance	Salt spray rusting time (h)
			Comparative example passivation solution	See FIG. 1	12
Comparative example II passivation solution	See FIG. 2	4
			Comparative example III passivation solution	See FIG. 3	8
Example A passivation solution	See FIG. 4	20

By way of comparison:

comparative example one passivation solution was added with no hydrogen peroxide, and the soluble cerium (iv) salt in the passivation solution was both a film-forming agent and an oxidizing agent, but was still able to form a film, but due to lack of hydrogen peroxide for assisted oxidation, the oxidation ability was insufficient, resulting in a too thin passivation film, which was close to white passivation from appearance observation, as shown in fig. 1. White rust appears in 12 hours of salt spray experiments due to poor corrosion resistance of the passivation film caused by the thin passivation film.

The passivation solution of comparative example two is not added with sodium silicate, which is one of the main film forming agents in the passivation solution, because the passivation film lacks the main film forming agent, although the soluble cerium (IV) salt can also be reduced to form a film, the film component is single, the formed passivation film is obviously not dense and rough, and the passivation film is a rough gray blue passivation film as shown in figure 2. Due to the fact that the corrosion resistance of the passivation film is poor due to the fact that the passivation film is rough, white rust appears in 4 hours of a salt spray experiment.

And in the third passivation solution of the comparative example, no ceric sulfate is added, the ceric sulfate is not only an oxidant but also a main film forming agent in the passivation solution, and because the main film forming agent is lacked in the passivation film, the passivation film is formed only by sodium silicate, so that the formed passivation film is dark and rough and has obvious scratches, and the passivation film is a rough blue-yellow passivation film as shown in fig. 3. The corrosion resistance of the passive film is poor due to the fact that the passive film is dark, rough and scratched, and white rust appears in 8 hours of a salt spray experiment.

The components in the passivation solution of the embodiment one are complete, the passivation film of the neodymium iron boron galvanized product passivated by the passivation solution is bright, compact and scratch-free, and the passivation film is a bright and compact color passivation film as shown in fig. 4. The passive film does not corrode in a neutral salt spray test for 20 hours.

Therefore, the silicate and the soluble cerium (IV) salt are jointly used as the film forming agent, the soluble cerium (IV) salt is used as the film forming agent and the oxidant, and the hydrogen peroxide is used as the auxiliary oxidant.

Example two

The invention discloses a chromium-free passivation solution for a neodymium iron boron zinc coating and a passivation method.

At normal temperature, 25g of sodium silicate, 10g of ceric sulfate, 0.5g of cobalt sulfate, 0.5g of copper sulfate, 10mL of sulfuric acid (98 wt%) and 10mL of hydrogen peroxide (30 wt%) are added into deionized water, stirred uniformly to be completely dissolved, the volume is constant to prepare 2L solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The obtained passivation solution comprises the following main components in percentage by weight:

25g/L of sodium silicate;

ceric sulfate 10 g/L;

0.5g/L of cobalt sulfate;

copper sulfate 0.5 g/L;

10mL/L of sulfuric acid;

10mL/L of hydrogen peroxide.

At normal temperature, immersing the neodymium iron boron galvanized product in a 3% nitric acid solution, washing with water, then immersing the product in a passivation solution for passivation for 20 seconds, continuously turning over in the passivation process to ensure that each product is uniformly passivated, and washing and drying with water after the product is passivated to obtain a uniform and compact colored passivation film, as shown in fig. 5.

Table 2 results of the second salt spray experiments in examples one and two

Passivation solution	Macroscopic appearance	Salt spray rusting time (h)
			Example A passivation solution	See FIG. 4	20
EXAMPLE two passivation solution	See FIG. 5	24

As shown in table 2, as can be seen from the comparison between the first example and the second example, the first example does not add the auxiliary film-forming agents of cobalt sulfate and copper sulfate, but does not affect the obtainment of the high-quality passivation film, but the addition of the cobalt disulfide and the copper sulfate can further improve the corrosion resistance of the formed passivation film.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.