Polishing liquid for neodymium-iron-boron magnets, surface pretreatment method for neodymium-iron-boron magnets

Abstract

The application provides a polishing solution for a neodymium-iron-boron magnet and a surface pretreatment method for the neodymium-iron-boron magnet. The polishing solution comprises an etchant, an oxidant and a buffer; the etchant comprises one or more of sulfuric acid, hydrochloric acid and phosphoric acid; the oxidant comprises a nitrate and / or hydrogen peroxide; the buffer comprises citric acid and / or tartaric acid; and the nitrate is sodium nitrate and / or potassium nitrate. The polishing solution provided by the application can not only remove the oxide layer on the surface of the magnet and ensure the pickling effect, but also solve the problem of magnet surface dust after pickling.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of permanent magnets, and particularly relates to a polishing solution for a neodymium-iron-boron magnet and a surface pre-treatment method for a neodymium-iron-boron magnet. BACKGROUND

[0002] Neodymium-iron-boron magnets have been widely used in the fields of computers, network information, aerospace, communication, transportation, household appliances and other high-tech fields due to their excellent comprehensive magnetic properties. However, the surface of the neodymium-iron-boron magnet is loose and porous, and contains a highly active neodymium-rich phase, which makes the neodymium-iron-boron magnet prone to rust and corrosion, and thus needs to be surface corrosion-resistant treated. The current conventional surface corrosion-resistant treatment methods can be divided into electroplating, chemical plating, chemical conversion film, electrophoresis and vacuum plating, so as to obtain a metal or alloy film layer, a polymer coating, a chemical conversion film layer and a composite coating.

[0003] The key of the neodymium-iron-boron magnet surface corrosion-resistant treatment technology is the pre-treatment process, which aims to remove the oxide layer on the surface of the magnet to improve the corrosion resistance and film adhesion. At present, the commonly used pre-treatment process in industrial production is: grinding and chamfering-alkaline degreasing-acid pickling-activation. The acid pickling is a key step in the pre-treatment process, which mainly realizes the function of removing the oxide layer on the surface of the magnet. However, after the ordinary acid pickling process, the surface of the magnet will appear a phenomenon of hanging dust (hanging dust refers to the generation of some acid-insoluble substances on the surface of the magnet after acid pickling, such as iron and part of impurities to form insoluble substances, or due to the poor flatness of the magnet surface after ordinary acid pickling, forming a gray field of vision). In order to solve the problem of hanging dust on the surface of the magnet, ultrasonic water washing is generally required after acid pickling. Since the insoluble substances formed are combined with the surface of the magnet relatively firmly, it is usually necessary to prolong the ultrasonic time or increase the ultrasonic power. However, since the neodymium-iron-boron magnet is prone to corrosion, after long-time and high-power ultrasonic cleaning, the appearance is severely corroded and the flatness is low, which further affects the corrosion resistance and magnetic properties of the neodymium-iron-boron magnet.

[0004] To solve the above problems, CN101638782A discloses a sintered Nd-Fe-B magnet chemical polishing solution and a processing method. It uses a traditional "three-acid" process formula, i.e., a chemical polishing solution composed of nitric acid, phosphoric acid and sulfuric acid, to perform pickling polishing on the Nd-Fe-B magnet, which can achieve good flattening and uniform corrosion effect. However, to achieve a sustained good polishing effect, nitric acid needs to be continuously added to ensure the concentration of nitric acid in the polishing solution. However, nitric acid is a nitrogen-containing inorganic acid, which can easily produce a large amount of yellow smoke (i.e., nitrogen oxides) to pollute the environment during pickling polishing, and its large use can cause the nitrogen content in the discharged wastewater to be too high. In addition, although the polishing solution is configured by adding three strong acids, the content of nitric acid is much higher than that of phosphoric acid and sulfuric acid, and the polishing effect mainly depends on nitric acid. Therefore, additional addition of nitric acid cannot control the concentration of hydrogen ions and nitrate ions according to the needs, cannot balance the acidity and oxidizability of the solution in a controlled manner, the process is uncontrollable, and the polishing effect is affected, which is not suitable for batch use on the production line.

[0005] The content of the background section is only the technology known to the inventors, and does not necessarily represent the prior art in the field. SUMMARY

[0006] To solve the above technical problems, the present application provides a polishing solution for a Nd-Fe-B magnet, which comprises an etchant, an oxidizing agent and a buffer.

[0007] The etchant comprises one or more of sulfuric acid, hydrochloric acid and phosphoric acid.

[0008] The oxidizing agent comprises a nitrate and / or hydrogen peroxide.

[0009] The buffer comprises citric acid and / or tartaric acid.

[0010] The nitrate is sodium nitrate and / or potassium nitrate.

[0011] In some embodiments of the present application, the content of the etchant is 0.01wt% to 5wt%, the content of the oxidizing agent is 1.5wt% to 30wt%, and the content of the buffer is 1wt% to 5wt%.

[0012] In some embodiments of the present application, the oxidizing agent is the nitrate, and the use amount ratio of the etchant to the nitrate is 1:1 to 1:50, preferably 1:5 to 1:20.

[0013] In some embodiments of the present application, the oxidizing agent is hydrogen peroxide, and the use amount ratio of the etchant to the hydrogen peroxide is 1:1 to 1:100, preferably 1:10 to 1:50.

[0014] The present application further provides a surface pre-treatment method for a Nd-Fe-B magnet, comprising:

[0015] The neodymium-iron-boron magnet is subjected to degreasing treatment by using alkali liquor, and then is cleaned;

[0016] The magnet subjected to degreasing treatment is subjected to polishing treatment by using polishing liquor, and then is cleaned; and

[0017] The magnet subjected to polishing treatment is subjected to activation treatment by using activation liquor, and then is cleaned.

[0018] In some embodiments of the present application, the oxidizing agent in the polishing liquor is nitrate, and the treatment temperature during the polishing treatment is 30-50 DEG C.

[0019] In some embodiments of the present application, the oxidizing agent in the polishing liquor is hydrogen peroxide, and the treatment temperature during the polishing treatment is 10-30 DEG C.

[0020] In some embodiments of the present application, the polishing treatment time is 15-120 s.

[0021] In some embodiments of the present application, the pH value of the alkali liquor is 9-13, and the concentration is 15-45 g / L; the degreasing treatment temperature is 45-60 DEG C, and the time is 12-28 min.

[0022] In some embodiments of the present application, the activation liquor comprises one or more of sulfuric acid, hydrofluoric acid and ammonium hydrogen fluoride, preferably hydrofluoric acid; the activation treatment is carried out at room temperature, and the time is 10-30 s.

[0023] The polishing liquor provided by the present application can not only remove the oxide layer on the surface of the magnet, but also ensure the pickling effect, and solve the problem of magnet surface dust after pickling. The chemical polishing surface obtained by chemical polishing on the surface of the neodymium-iron-boron magnet has glossiness, surface flatness and approachable mirror polishing effect. Further, the polishing liquor does not use or directly use nitric acid, which can greatly reduce the total nitrogen content in the pickling wastewater, thereby reducing the cost of water treatment of pickling wastewater, and at the same time, will not produce yellow smoke to pollute the environment and reduce the harm to the health of the operators. In addition, the polishing liquor does not contain toxic and harmful substances, is stable and not easy to decompose, has a long use period, and can save cost.

[0024] The neodymium-iron-boron magnet treated by the surface pretreatment method provided by the present application has uniform corrosion on the surface, has glossiness, and is beneficial to the subsequent plating process.

[0025] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which constitute a part of this disclosure, are provided to further aid in understanding of the present disclosure and are incorporated in and constitute a part of this disclosure. Illustrative embodiments of the present disclosure and various features thereof are described or illustrated with reference to the accompanying drawings and / or the following description. The drawings described are in simplified form and are not to precise scale. Notably, for purposes of clarity and exemplification, certain specific embodiments of the application are shown in the drawings.

[0027] Figure 1 A process flow diagram of surface pre-treatment of a neodymium-iron-boron magnet is shown. DETAILED DESCRIPTION

[0028] In the following description, certain specific embodiments of the application will be described only by way of example with reference to the attached drawings. As would be obvious to those skilled in the art, the described embodiments can be modified in various different manners, without departing from the spirit or scope of the application. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0029] The following disclosure provides many different embodiments, or examples, for implementing the present application. For purposes of explanation and as required by the

[0030] Furthermore, unless otherwise indicated herein, use of the singular includes the plural and vice versa, as well as the use of "only" or "exactly" or the like indicates the inclusion of both that term or those terms and the plural. Thus, reference to "a" or "only a" or "the" is a reference to one or more, and is not to be limited to the singular. Also, the use of the term "if" has the same meaning as "when" and "when" has the same meaning as "if," unless otherwise indicated herein. In addition, the use of "including" and "comprising" has the same meaning as "including and / or comprising." Furthermore, the use of "or" as a conjunction is used similarly as "and / or", unless otherwise indicated herein. Moreover, the use of "about" or "approximately" in connection with a value means that the value is within a reasonable but explicit range of the stated value, as would be recognized by one skilled in the art.

[0031] "about" or "approximately," as used herein, includes the stated value and means within a reasonable but explicit range of deviation from the stated value, as determined by one of ordinary skill in the art. For example, "about" can mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0032] The specific embodiments of the present application will be described in greater detail below with reference to the drawings and examples. However, the following description of the specific embodiments and examples is merely illustrative in nature and is in no way intended to limit the application, its application or uses.

[0033] In the following description, the "neodymium-iron-boron magnet" is simply referred to as "magnet".

[0034] The polishing solution provided by the present application comprises an etchant, an oxidant and a buffer. The etchant comprises one or more of sulfuric acid, hydrochloric acid and phosphoric acid; the oxidant comprises nitrate and / or hydrogen peroxide; and the buffer comprises citric acid and / or tartaric acid. The polishing solution provided by the present application uses water as solvent. In the present application, the nitrate is optionally sodium nitrate and / or potassium nitrate.

[0035] The etchant in the present application is mainly used to provide hydrogen ions, maintain the acidic environment of the polishing solution, remove the oxide layer and part of the insoluble substances on the surface of the magnet. The oxidant is mainly used to provide nitrate ions or the oxidant can be hydrogen peroxide, so as to ensure that the polishing solution has oxidizing property. While the etchant continuously removes the oxide layer on the surface of the magnet to expose the metal, the nitrate ions can exert their oxidizing property in the acidic environment, or the hydrogen peroxide itself continuously oxidizes the exposed metal to form an oxide layer. The polishing solution has both acidity and oxidizing property, and through balancing the two reaction processes, the surface of the magnet is continuously repaired and flattened, so that the oxide layer and insoluble substances on the surface of the magnet are removed while the flatness of the surface of the magnet is ensured, and the surface of the magnet has mirror gloss. The buffer is an organic weak acid, and the hydrogen ion dissociation process is relatively slow. While providing hydrogen ions, the buffer can reduce the reaction intensity of the polishing process, so that the entire polishing process is safe and controllable. The polishing solution provided by the present application not only can remove the oxide layer on the surface of the magnet to ensure the pickling effect, but also can solve the problem of dust hanging on the surface of the magnet after pickling. Moreover, since nitric acid is not directly added in the polishing process and the polishing solution further comprises a buffer, when the neodymium-iron-boron magnet is chemically polished, the entire polishing process is safe and controllable, and the surface of the magnet after polishing is uniformly corroded and has gloss, which is beneficial to the subsequent plating process.

[0036] Further, the polishing solution provided by the present application does not use or directly use nitric acid, so that the total nitrogen content in the pickling wastewater can be greatly reduced, thereby reducing the cost of treating the pickling wastewater, and at the same time, yellow smoke pollution to the environment is avoided and the harm to the health of the operators is reduced. Moreover, the polishing solution does not contain toxic and harmful substances, is stable and not easy to decompose, has a long use period, and can save cost.

[0037] In the present application, the etchant is preferably sulfuric acid. Sulfuric acid does not cause corrosion to the magnet itself and has strong acidity.

[0038] The acids used in the present application are all preferably diluted acid solutions, and the concentration of the acid solution after dilution before being added to the polishing solution is less than 15wt%.

[0039] The hydrogen peroxide, citric acid and tartaric acid used in the present application are all preferably saturated solutions.

[0040] In some embodiments of the present application, the content of the corrosion agent in the polishing solution is about 0.01wt% to about 5wt%, preferably about 0.5wt% to about 5wt%. If the content of the corrosion agent is less than 0.5wt%, the concentration of hydrogen ions in the polishing solution cannot be guaranteed, which in turn affects the removal effect of the surface oxide layer and part of the insoluble matter in the polishing process. If the content of the corrosion agent is more than 5wt%, the polishing solution is relatively strong in acidity, which cannot effectively balance the acidity and oxidizability of the polishing solution, causing the reaction rate of removing the surface oxide layer and part of the insoluble matter in the polishing process to be accelerated, which is not conducive to the flattening and repairing process of the surface of the magnet, and in turn affects the flatness of the surface of the magnet after polishing and the performance of the magnet.

[0041] In some embodiments of the present application, the content of the oxidizing agent in the polishing solution is about 1.5wt% to about 30wt%. If the content of the oxidizing agent is less than 1.5wt%, the concentration of hydrogen ions in the polishing solution cannot be matched, which cannot guarantee that the oxidizing effect of the polishing solution can match the pickling effect, and in turn affects the flatness of the surface of the magnet after polishing. If the content of the oxidizing agent is more than 30wt%, the pickling rate is unchanged, that is, the rate of exposing the metal by removing the surface oxide layer of the magnet is unchanged, and the content of the oxidizing agent in the polishing solution is too high, which cannot fully play the oxidizing effect of the oxidizing agent, causing a lot of idle oxidizing agent in the polishing solution. If the used oxidizing agent is nitrate, the content of the oxidizing agent higher than 30wt% will increase the ineffective nitrogen content in the polishing solution, which is not conducive to the subsequent treatment of the polishing waste liquid. If the used oxidizing agent is hydrogen peroxide, when the content of the oxidizing agent is higher than 30wt%, too much idle hydrogen peroxide will decompose due to its instability, which increases the production cost. Alternatively, when the used oxidizing agent is nitrate, the content of the nitrate is about 1.5wt% to about 10wt%, and when the used oxidizing agent is hydrogen peroxide, the content of the hydrogen peroxide is about 5wt% to 30wt%. 。

[0042] In some embodiments of the present application, the content of the buffering agent in the polishing solution is about 1wt% to about 5wt%, and the rest is water. The polishing solution with this ratio has the best performance.

[0043] In some embodiments of the present application, when the used oxidizing agent is nitrate, the usage ratio of the corrosion agent to the nitrate is about 1:1 to about 1:50, preferably about 1:5 to about 1:20. Under this ratio, the acidity and oxidizability in the polishing solution can be balanced, thereby obtaining a better polishing effect.

[0044] In some embodiments of the present application, when the oxidizing agent used is hydrogen peroxide, the ratio of the amount of the etchant to the amount of hydrogen peroxide is about 1:1 to about 1:100, preferably about 1:10 to about 1:50. Similarly, at this ratio, the acidity and oxidizing property of the polishing solution are balanced, thus achieving a better polishing effect.

[0045] Figure 1 A surface pretreatment method of a Nd-Fe-B magnet is shown, which comprises the following steps S1-S3.

[0046] S1: degreasing the Nd-Fe-B magnet with an alkaline solution, and then washing.

[0047] Optionally, the pH value of the alkaline solution used in this step is about 9 to about 13, and the concentration is about 15 g / L to about 45 g / L.

[0048] Optionally, in this step, the degreasing temperature is about 45°C to about 60°C, and the time is about 12 min to about 28 min.

[0049] Optionally, in this step, the washing is performed with clean water, and can be performed for 1-3 times, each time for about 30 s to about 60 s.

[0050] After this step, the oil on the surface of the magnet can be removed.

[0051] S2: polishing the degreased magnet with a polishing solution, and then washing.

[0052] The polishing solution used in this step is any of the aforementioned polishing solutions, and the specific components and corresponding technical effects thereof will not be described here.

[0053] When the oxidizing agent in the polishing solution used is nitrate, the polishing temperature in this step can be about 30°C to about 50°C. At this temperature, a better polishing effect can be achieved. If the temperature exceeds 50°C, on the one hand, the energy consumption and production cost will increase, and on the other hand, the nitrate ions will accelerate the oxidation of the divalent iron ions in the solution to trivalent iron ions, accelerate the consumption of nitrate ions, and reduce the service life of the polishing solution.

[0054] When the oxidizing agent in the polishing solution used is hydrogen peroxide, the polishing temperature in this step can be about 10°C to about 30°C. The chemical polishing process generates heat, and at the same time, the polishing of the Nd-Fe-B magnet produces trivalent iron ions, which itself catalyzes and promotes the decomposition of hydrogen peroxide. If the temperature exceeds 30°C, the above catalytic decomposition process will be accelerated, thus reducing the service life of the polishing solution, further reducing the polishing efficiency, and increasing the production cost.

[0055] Optionally, the magnet is cleaned with water in this step, and the cleaning can be performed for 1-3 times, each time for about 30-60 seconds.

[0056] Through this step, the oxide layer and the ash layer on the surface of the magnet can be removed.

[0057] S3: The magnet after the polishing treatment is activated by using an activation solution, and then cleaned.

[0058] Optionally, the activation solution used in this step comprises one or more of sulfuric acid, hydrofluoric acid and ammonium hydrogen fluoride, and preferably hydrofluoric acid. In this step, the concentration of the sulfuric acid can be about 0.5wt%-about 5wt%, the concentration of the hydrofluoric acid can be about 0.5wt%-about 5wt%, and the concentration of the ammonium hydrogen fluoride can be about 0.5wt%-about 10wt%. Preferably, the hydrofluoric acid used in this step has a concentration of about 0.5wt%.

[0059] Optionally, the activation treatment in this step is performed at room temperature, and the time is about 10 seconds to about 30 seconds.

[0060] Optionally, the magnet is cleaned with water in this step, and the cleaning can be performed for 1-3 times, each time for about 30-60 seconds.

[0061] Through this step, the surface of the magnet is in an activated state, which is beneficial to the subsequent plating process.

[0062] The surface of the Nd-Fe-B magnet treated by the surface pretreatment method provided by the present application is uniformly corroded, has glossiness, and can be close to a mirror surface. The roughness of the polished magnet surface is 0.35μm-0.65μm, and the flatness is high, which is beneficial to the subsequent plating process.

[0063] The present application will be described below with reference to specific examples. The process condition values in the following examples and comparative examples are exemplary, and the value range can be as shown in the foregoing summary of the application. For the process parameters not specifically mentioned, the conventional techniques can be referred to. Unless specifically indicated, the reagents and instruments used in the technical solutions provided by the present application can be purchased from conventional channels or markets.

[0064] The interfacial adhesion between the coating and the magnet in the following examples and comparative examples is measured after the magnet is pre-treated and then coated. The interfacial adhesion between the coating and the magnet is measured by a tensile test, and the interfacial adhesion is the average of the interfacial adhesion of a plurality of tensile tests (e.g., ten tensile tests). The PCT high temperature and high pressure test is conducted at a temperature of 150°C, 2 atmospheres, and a relative humidity of 100%. The high temperature demagnetization rate is [(magnetic flux at room temperature) - (magnetic flux of the magnet after the magnet is heated at a high temperature for a period of time and then returned to room temperature)] / (magnetic flux of the magnet at room temperature) x 100%. The high temperature demagnetization rate is the average of the high temperature demagnetization rates of a plurality of magnets (e.g., ten magnets). The other measurement methods are known in the art.

[0065] The Nd-Fe-B magnets used in the following examples and comparative examples are not pre-treated and not coated (for better distinction, the magnets are referred to as "black pieces" in the following examples and comparative examples). The composition of the magnets is 30 wt% PrNd, 0.96 wt% B, 0.12 wt% Cu, 0.08 wt% Ti, 0.9 wt% Co, 0.4 wt% Al, and the balance of Fe. The properties of the magnets are shown in Table 1.

[0066] Example 1

[0067] In this example, the Nd-Fe-B magnets are pre-treated on the surface. The pre-treatment process is as follows:

[0068] S1. The Nd-Fe-B magnets (i.e., the black pieces) are degreased in an alkaline solution. After the degreasing, the magnets are washed with water twice. The alkaline solution used is a sodium carbonate solution with a concentration of about 20 g / L and a pH of about 10. The degreasing is conducted at a temperature of about 60°C for about 15 min. Each water washing is conducted for about 60 s.

[0069] S2. The degreased Nd-Fe-B magnets are polished in a chemical polishing solution. After the polishing, the magnets are washed with water twice. The polishing solution comprises about 1 wt% sulfuric acid, about 17.5 wt% hydrogen peroxide, about 2 wt% citric acid, and the balance of water. The sulfuric acid used has a concentration of about 10 wt% before being added to the polishing solution. The hydrogen peroxide used is a saturated hydrogen peroxide solution. The citric acid used is a saturated citric acid solution. The polishing is conducted at a temperature of about 10°C for about 30 s. Each water washing is conducted for about 60 s.

[0070] S3. The polished Nd-Fe-B magnets are activated. After the activation, the magnets are washed with water twice.

[0071] The activation solution comprises about 0.5 wt% hydrofluoric acid. The activation is conducted for about 20 s. Each water washing is conducted for about 60 s.

[0072] The properties of the obtained magnet are shown in Table 1.

[0073] The obtained magnet was electroplated: electroplated nickel-copper-nickel, set the current to 20 A, electroplated in a nickel sulfamate solution for 60 min, then set the current to 35 A, electroplated in a copper citrate solution for 60 min, and finally set the current to 2 A, electroplated in a nickel sulfate solution for 60 min.

[0074] Example 2

[0075] The difference between this example and Example 1 is that the content of sulfuric acid in the polishing solution used is about 0.5 wt%, the content of hydrogen peroxide is about 10 wt%, and the polishing time is about 50 s.

[0076] The properties of the obtained magnet are shown in Table 1.

[0077] Example 3

[0078] The difference between this example and Example 1 is that the content of sulfuric acid used in the polishing solution is about 3 wt%, and the content of hydrogen peroxide is about 30 wt%.

[0079] The properties of the obtained magnet are shown in Table 1.

[0080] Example 4

[0081] The difference between this example and Example 1 is that the etchant in the polishing solution is phosphoric acid. The content of phosphoric acid is about 2.5 wt%, and the content of hydrogen peroxide is about 30 wt%.

[0082] The properties of the obtained magnet are shown in Table 1.

[0083] Example 5

[0084] The difference between this example and Example 1 is that the oxidizing agent in the polishing solution is potassium nitrate. The content of potassium nitrate is about 5 wt%. The content of sulfuric acid in the polishing solution is about 0.5 wt%, and the use temperature of the polishing solution is 40°C.

[0085] The properties of the obtained magnet are shown in Table 1.

[0086] Example 6

[0087] The difference between this example and Example 1 is that the content of sulfuric acid in the polishing solution is about 0.35 wt%, and the polishing time is about 50 s.

[0088] The properties of the obtained magnet are shown in Table 1.

[0089] Example 7

[0090] The difference between this example and Example 1 is that the temperature of the polishing treatment is 35°C.

[0091] The properties of the obtained magnets are shown in Table 1.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the polishing liquid used in the polishing process comprises 1 wt % of sulfuric acid and the balance of water.

[0094] The properties of the obtained magnets are shown in Table 1.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 5 is that the polishing liquid used in the polishing process is composed of 5 wt% nitric acid and the balance water. The properties of the obtained magnet are shown in Table 1.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 3 is that the polishing liquid used in the polishing process contains 5 wt % sulfuric acid and the balance water.

[0099] The properties of the obtained magnets are shown in Table 1.

[0100] Table 1 Magnet properties

[0101] High temperature magnetic reduction rate / % Surface roughness Ra / pm Magnet plating adhesion / N Black patch 2.46 0.742 - Example 1 2.52 0.393 1094.0 Example 2 2.79 0.498 954.7 Example 3 3.37 0.614 891.7 Example 4 2.88 0.645 807.2 Example 5 2.75 0.621 977.8 Example 6 2.49 0.736 822.1 Example 7 3.01 0.859 699.8 Comparative Example 1 3.19 1.266 689.1 Comparative Example 2 2.92 0.683 716.0 Comparative Example 3 3.78 1.415 552.8

[0102] As can be seen from Table 1 above, in Examples 1-5, after pre-treatment with the polishing liquid of the present invention, it was found that the surface roughness of the magnet was lower than that of the black sheet, and the surface flatness was good. It had a low effect on the high-temperature demagnetization rate of the magnet, which was beneficial to the bonding strength between the coating and the substrate.

[0103] The concentration of sulfuric acid used in Example 6 is 0.35wt%. Due to insufficient acid strength, the removal effect of insoluble substances on the surface of the magnet is poor. Therefore, the surface roughness of the obtained magnet is less improved than that of the black sheet. However, it can still effectively remove the oxide layer on the surface of the magnet, so the bonding force between the coating and the substrate is still relatively good.

[0104] In Example 7, when hydrogen peroxide is used as the oxidant in the polishing liquid, when the operating temperature is higher than 30°C, the decomposition rate of hydrogen peroxide is accelerated, which is not conducive to polishing. Not only is the oxide layer on the surface of the substrate not completely removed, but insoluble substances are generated on the surface of the magnet, making the surface roughness of the magnet higher than that of the black sheet, and the bonding force between the coating and the substrate is also relatively low.

[0105] In Comparative Examples 1 and 3, only sulfuric acid was used to pre-treat the magnets, and it was found that the roughness of the magnet surface and the high-temperature demagnetization rate were significantly deteriorated.

[0106] Obviously, the above embodiments are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes. Based on the above description, other different forms of changes or variations can also be made by those skilled in the art. Here, all the implementation modes do not need to be exhausted, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A polishing liquid for neodymium iron boron magnets, characterized in that: including corrosive agents, oxidizing agents, and buffers; Wherein, the corrosive agent includes one or more of sulfuric acid, hydrochloric acid and phosphoric acid; The oxidizing agent includes nitrate and / or hydrogen peroxide; The buffer comprises citric acid and / or tartaric acid; The nitrate is sodium nitrate and / or potassium nitrate; wherein the content of the corrosive agent is 0.5wt%~5wt%, the content of the oxidant is 1.5wt%~30wt%, the content of the buffer is 1wt%~5wt%, and the balance is water.

2. The polishing liquid according to claim 1, characterized in that The oxidant is the nitrate, and the usage ratio of the corrosive agent to the nitrate is 1:1 to 1:

50.

3. The polishing liquid according to claim 2, characterized in that The usage ratio of the corrosive agent to the nitrate is 1:5 to 1:

20.

4. The polishing liquid according to claim 1, characterized in that The oxidant is hydrogen peroxide, and the usage ratio of the corrosive agent to the hydrogen peroxide is 1:1 to 1:

100.

5. The polishing liquid according to claim 1, characterized in that The usage ratio of the corrosive agent to the hydrogen peroxide is 1:10 to 1:

50.

6. A surface pretreatment method for NdFeB magnets, characterized in that: include: Use alkaline solution to degrease the NdFeB magnets and then clean them; Polishing the degreased magnet using the polishing liquid described in any one of claims 1 to 5, and then cleaning it; as well as The polished magnet is activated with an activation liquid and then cleaned.

7. The surface pretreatment method according to claim 6, characterized in that: The oxidant in the polishing liquid is nitrate, and the processing temperature during the polishing process is 30° C. to 50° C.

8. The surface pretreatment method according to claim 6, characterized in that: The oxidant in the polishing liquid is hydrogen peroxide, and the processing temperature during the polishing process is 10° C. to 30° C.

9. The surface pretreatment method according to claim 7 or 8, characterized in that: The polishing time is 15s to 120s.

10. The surface pretreatment method according to claim 6, characterized in that: The pH value of the alkali solution is 9-13, and the concentration is 15g / L-45g / L; the temperature of the degreasing treatment is 45°C-60°C, and the time is 12min-28min.

11. The surface pretreatment method according to claim 6, characterized in that: The activation solution includes one or more of sulfuric acid, hydrofluoric acid and ammonium bifluoride; the activation treatment is carried out at room temperature for 10s to 30s.

12. The surface pretreatment method according to claim 6, characterized in that: The activation solution is hydrofluoric acid.

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