A method for preparing a surface coating of a neodymium-iron-boron sintered permanent magnet

Abstract

The application discloses a preparation method of a surface coating of a Nd-Fe-B sintered permanent magnet, and the process flow of the preparation method comprises the following steps: oil removal, water washing, acid pickling, water washing, ultrasonic dust removal, water washing, phosphating, water washing, sealing, water washing and blow-drying solidification; the phosphating solution is composed of a first phosphating solution, a second phosphating solution and a nano dispersant, and the mass ratio of the three is (0.5-1.5):(0.5-1.5):(1-3); the first phosphating solution comprises zinc dihydrogen phosphate, acid manganese phosphate, phosphoric acid, zinc nitrate, cobalt salt, a surfactant, nickel sulfate and a corrosion inhibitor; and the second phosphating solution comprises phosphoric acid, zinc oxide, cobalt salt, fluoride and a complexing agent. The method can realize high-efficiency and high-quality preparation of the surface coating of the permanent magnet, realizes significant improvement of the corrosion resistance of the permanent magnet without affecting the magnetic properties of the permanent magnet and without increasing the production cost, and effectively reduces the corner defect area and the corner defect proportion of the product.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of Nd-Fe-B sintered permanent magnets, and particularly relates to a preparation method of a surface coating of a Nd-Fe-B sintered permanent magnet. BACKGROUND

[0002] As a key functional material, Nd-Fe-B sintered permanent magnets have been widely used in the fields of electronic information, medical equipment, new energy vehicles, household appliances, robots and other high-tech fields. In most application fields, Nd-Fe-B sintered permanent magnets are packed in the rotors of compressors and motors, and these devices often need to work in harsh environments such as high temperature, high humidity, weak acidity or weak salinity. At the same time, due to the brittleness of Nd-Fe-B sintered permanent magnets, hydrogen embrittlement is prone to occur after pickling, resulting in serious product corner defects. Although slight corner defects do not significantly affect the overall performance of the rotors of compressors and motors, when the corner defect area is too large or the number of corner defects is too large, it will still adversely affect the operation reliability and service life of the equipment. Therefore, how to effectively improve the corrosion resistance of Nd-Fe-B sintered permanent magnets and reduce the corner defect area and the proportion of corner defects is particularly crucial.

[0003] Nd-Fe-B sintered permanent magnets are in a porous and loose state, and after high-temperature sintering, they are hard and brittle, which makes it difficult for the product to meet the requirements of high corrosion resistance and zero corner defects. At present, the industry mainly improves this problem through two technical approaches: one is to optimize the surface coating process to improve corrosion resistance, and the other is to increase the powder particle size to reduce corner defects. However, both methods have obvious limitations: the coating process is usually subject to customer-specified technical specifications and involves cost factors, and it is often difficult to implement major changes; while increasing the powder particle size can improve the corner defect problem, it will cause fluctuations in the magnetic properties of Nd-Fe-B sintered permanent magnets (mainly performance degradation), especially in Nd-Fe-B sintered permanent magnets that require GBD technology, such performance fluctuations may make the product unable to meet the design specifications. Therefore, under the premise of ensuring stable magnetic properties, how to effectively improve the corrosion resistance of Nd-Fe-B sintered permanent magnets and reduce the corner defect area and the proportion of corner defects has become a technical bottleneck that needs to be broken through in current process optimization.

[0004] To solve the problem of insufficient corrosion resistance of Nd-Fe-B sintered permanent magnets, a Chinese invention patent (application number: 201110411826.3) proposes a preparation method of a surface particle-enhanced organic corrosion-resistant coating of a Nd-Fe-B permanent magnet material. First, a phosphating film is prepared on the surface of the permanent magnet as a basic protective layer, and then a particle-enhanced organic composite coating is constructed on the surface of the phosphating film through a cathodic electrophoresis process to form a double protective system. The above technical solution requires two times of film plating, which leads to an extension of the production cycle, difficulty in material turnover, a substantial increase in management costs, and high requirements for the professionalism of employees. In addition, this technical solution does not solve the problem of hydrogen embrittlement of Nd-Fe-B sintered permanent magnets after pickling, nor does it improve the product corner defect problem. SUMMARY

[0005] To realize the feasibility of large-scale production, while taking into account cost-effectiveness and magnetic performance stability, the present application proposes a preparation method of a neodymium-iron-boron sintered permanent magnet surface coating, which uses a specific phosphating solution and combines a specific preparation process flow, and through a single phosphating operation, high-efficiency and high-quality preparation of the neodymium-iron-boron sintered permanent magnet surface coating can be realized, without affecting the magnetic performance of the neodymium-iron-boron sintered permanent magnet, without increasing the production cost, and under the premise of not affecting the magnetic performance of the neodymium-iron-boron sintered permanent magnet, the corrosion resistance of the neodymium-iron-boron sintered permanent magnet is significantly improved, while effectively reducing the corner missing area and corner missing ratio of the product.

[0006] The technical solution adopted by the present application to solve the above technical problems is: a preparation method of a neodymium-iron-boron sintered permanent magnet surface coating, the process flow of the preparation method includes: oil removal → water washing → acid pickling → water washing → ultrasonic desmutting → water washing → phosphating → water washing → sealing → water washing → blow-drying and curing, the phosphating solution used in the phosphating is compounded by a first phosphating solution, a second phosphating solution and a nano dispersant, the mass ratio of the first phosphating solution, the second phosphating solution and the nano dispersant is (0.5~1.5):(0.5~1.5):(1~3), the composition of the first phosphating solution includes zinc dihydrogen phosphate, acid manganese phosphate, phosphoric acid, zinc nitrate, cobalt salt, surfactant, nickel sulfate and corrosion inhibitor, and the composition of the second phosphating solution includes phosphoric acid, zinc oxide, cobalt salt, fluoride and complexing agent.

[0007] The present application uses a specific phosphating solution and combines a specific preparation process flow, and through a single phosphating operation, high-efficiency and high-quality preparation of the neodymium-iron-boron sintered permanent magnet surface coating can be realized. Through detection, the method of the present application can effectively reduce the defects in the production process of the neodymium-iron-boron sintered permanent magnet, reduce the product watermark yellowing ratio and corner missing ratio to below 2%, and under the premise of not affecting the magnetic performance of the neodymium-iron-boron sintered permanent magnet and not increasing the production cost, the corrosion resistance of the neodymium-iron-boron sintered permanent magnet is significantly improved, while effectively reducing the corner missing area and corner missing ratio of the product.

[0008] The method of the present application not only reduces the production links of coating preparation and reduces the risk of personnel operation errors, but also maintains the stability of product performance, and provides a more competitive technical solution for the industrial production of neodymium-iron-boron sintered permanent magnets. The method of the present application has simple process, low cost, does not produce waste gas and waste residue, has high quality of the prepared surface coating, does not need post-treatment, and has good environmental protection.

[0009] As a preferred, the concentration of the phosphating solution is 15%±1%, the phosphating temperature is 40~60℃, and the phosphating time is 1000~1200 s.

[0010] As preferred, the first phosphating liquid is a product of a commercially available type FX-022, the second phosphating liquid is a product of a commercially available type NPS-05C, and the nano-dispersant is a product of a commercially available type SFT-1388.

[0011] As preferred, the mass ratio of the first phosphating liquid, the second phosphating liquid and the nano-dispersant is 1:1:2.

[0012] As preferred, the washing between the phosphating and the sealing is performed by using deionized water, and the conductivity of the deionized water used is ≤2 μS / cm. The deionized water washing after the phosphating can remove the residual phosphating liquid on the surface of the permanent magnet, ensure the quality of the coating on the surface of the permanent magnet, and improve the corrosion resistance and the compatibility with subsequent processes.

[0013] As preferred, the deionized water washing is performed twice to further strengthen the phosphating effect and ensure the quality of the coating.

[0014] As preferred, the oil removal is performed by adding an oil removal powder into the oil removal liquid, and the addition ratio of the oil removal powder in the oil removal liquid is 1.00%±0.05%.

[0015] As preferred, the acid pickling is performed by using nitric acid with a concentration of 3%±0.1% as the acid pickling liquid.

[0016] As preferred, a desmutting agent is added into the desmutting liquid used in the ultrasonic desmutting, and the addition ratio of the desmutting agent in the ultrasonic desmutting liquid is 3%±0.1%, and the ultrasonic frequency used in the ultrasonic desmutting is 28 kHz ~32 kHz.

[0017] As preferred, a sealing agent is added into the sealing liquid used in the sealing, and the addition ratio of the sealing agent in the sealing liquid is 10%±1%. The sealing process can fill the micropores of the phosphating film, form a dense protective layer, significantly improve the consistency of the coating, and thus improve the corrosion resistance and wear resistance of the permanent magnet, and reduce the proportion of the product with yellowish watermarks and missing corners.

[0018] Compared with the prior art, the present application has the following advantages: the preparation method of the surface coating of the Nd-Fe-B sintered permanent magnet adopts a specific phosphating solution and a specific preparation process flow, and high efficiency and high quality of the surface coating of the Nd-Fe-B sintered permanent magnet can be realized through a single phosphating operation, the corrosion resistance of the Nd-Fe-B sintered permanent magnet is significantly improved without affecting the magnetic properties of the Nd-Fe-B sintered permanent magnet and increasing the production cost, and the corner missing area and the corner missing ratio of the product are effectively reduced. Through detection, the method can effectively reduce the defects in the production process of the Nd-Fe-B sintered permanent magnet, and the product watermark yellow ratio and the corner missing ratio are reduced to less than 2%. The method not only reduces the production links of the coating preparation and reduces the risk of personnel operation errors, but also maintains the stability of the product performance, and provides a more competitive technical solution for the industrial production of the Nd-Fe-B sintered permanent magnet. The method has simple process, low cost, no waste gas and waste residue, high quality of the prepared surface coating, no need for post-treatment, and good environmental protection. DETAILED DESCRIPTION

[0019] The present application will be further described in detail below in combination with examples.

[0020] Six examples and twelve comparative examples of Nd-Fe-B sintered permanent magnets were selected, phosphating was performed on the Nd-Fe-B sintered permanent magnets by using different phosphating solutions to prepare surface coatings. In order to facilitate comparison, the preparation methods of the coatings of the examples and the comparative examples were only different in the formula of the phosphating solution. There were four kinds of phosphating solutions, and the same concentration of A or B or C or D was added. A is a phosphating solution product with a model number of FX-022 provided by Ningbo Haishu Gaqiao Yongrun Surface Treatment Agent Business Department, which is a purple red transparent liquid with a pH value of 1.0-2.0 and a specific gravity of 1.35 g / cm 3 , and its composition includes zinc dihydrogen phosphate, acid manganese phosphate, phosphoric acid, zinc nitrate, cobalt salt, surfactant, nickel sulfate and corrosion inhibitor; B is a phosphating solution product with a model number of NPS-05C provided by Ningbo Haishu District Yongfu Chemical Co., Ltd., which is a light brown liquid with a pH value of 1.5 or more and a relative density of 1.20 with respect to water, a boiling point of > 115℃, and its composition includes phosphoric acid, zinc oxide, cobalt salt, fluoride and complexing agent; C is a nano dispersant product with a model number of SFT-1388 provided by Dongguan Fite Cleaning Technology Co., Ltd., which is a liquid with a pH value of 6.5-8.5, a boiling point of 150-200℃, a volatile point of > 55℃, a slight odor, a melting point of < -10℃, a combustion point of > 200℃, and a water solubility of < 2wt% at 20℃; D is compounded by A, B and C in a mass ratio of 1:1:2.

[0021] 6 examples are examples 1-1, 1-2, 1-3, 1-4, 1-5 and 1-6 respectively using phosphating solution with additive D; 12 comparative examples are comparative examples 1-1, 1-2, 1-3 and 1-4 respectively using phosphating solution with additive A, comparative examples 2-1, 2-2, 2-3 and 2-4 respectively using phosphating solution with additive B, and comparative examples 3-1, 3-2, 3-3 and 3-4 respectively using phosphating solution with additive C.

[0022] The process flow of the preparation method of the coating of each example and comparative example includes: oil removal → water washing (1 time) → pickling → water washing (2 times) → ultrasonic desmutting → water washing (1 time) → phosphating → water washing (2 times) → sealing → water washing (2 times) → blow drying and curing, and the specific process flow and process parameters are shown in Table 1.

[0023] Table 1: Process flow and process parameters of coating preparation of each example and comparative example

[0024]

[0025] The oil removal powder used in each comparative example and example is a product provided by Ganzhou Yingteng Environmental Protection Technology Co., Ltd., which is in the form of powder and consists of soda ash, phosphoric acid complexing agent, ammonium salt antirust agent and surfactant, etc.; the desmutting agent is a product with model number DS-550 provided by Yantai Deshan Chemical Co., Ltd., which consists of sodium hydroxide (<7.0%), soda ash (<20.0%), triethanolamine (<40.0%) and acrylic acid salt polymer (<2.0%); the sealing agent is a product with model number BW-608 provided by Beijing Eirsm Technology Co., Ltd., which is a yellowish translucent liquid with a specific gravity of 1.150±0.05 g / cm 3 , a pH value of 12.0-13.0, no flash point and non-combustible, and consists of 40% silica gel, 1% nano silicon dioxide, 5% sodium benzoate, 6% soda ash and 8% triethanolamine.

[0026] For the neodymium-iron-boron sintered permanent magnets with the above-mentioned surface coating prepared in the 6 examples and 12 comparative examples, a workpiece appearance and size automatic detector (CCD) is used to detect the surface watermark yellowing and corner missing of each example and comparative example, and the watermark yellowing proportion and corner missing proportion are calculated respectively. The detection standard is as follows:

[0027] Watermark yellowing: determined as watermark yellowing through CCD image analysis with a color difference ΔE≥5 (based on standard white plate) and an area ≥1 mm 2 ;

[0028] Corner missing: a single corner missing area ≥0.2 mm 2 (according to CCD profile analysis) and the number of corner missing is counted per product.

[0029] The kind, concentration of phosphating solution and the proportion of watermark yellowing and the proportion of missing corner of the coating of each embodiment and the comparative example are shown in Table 2.

[0030] Table 2: The kind, concentration of phosphating solution and the proportion of watermark yellowing and the proportion of missing corner of the coating of each embodiment and the comparative example

[0031]

[0032] As shown in Table 2, the method of the application can effectively reduce the defects in the production process of Nd-Fe-B sintered permanent magnet, reduce the proportion of watermark yellowing from 2.25% to 5.12% to 0.94% to 1.66%, and reduce the proportion of missing corner from 3.03% to 11.24% to 1.05% to 1.86%.

[0033] For the comparative examples 1-2, 2-2, 3-2 and the embodiment 1-3, which add phosphating solution with the same concentration but different formula, the whole sequence flow conversion working hours, the number of workers required for whole sequence and the product production efficiency of the coating preparation are shown in Table 3.

[0034] Table 3: The whole sequence flow conversion working hours, the number of workers required for whole sequence and the product production efficiency of the coating preparation of different comparative examples and embodiments

[0035]

[0036] As shown in Table 2 and Table 3, the method of the application can realize the efficient and high-quality preparation of the surface coating of Nd-Fe-B sintered permanent magnet, effectively improve the product production efficiency and the labor efficiency, and reduce the product production cost. After the surface coating is prepared by the method of the application, the magnetic properties of the Nd-Fe-B sintered permanent magnet are not affected, the corrosion resistance is significantly improved, and the missing corner area and the proportion of missing corner are effectively reduced.

Claims

1. A method for producing a surface coating of a NdFeB sintered permanent magnet, characterized by, The process flow of the preparation method comprises: oil removal, water washing, acid pickling, water washing, ultrasonic desmutting, water washing, phosphating, water washing, sealing, water washing, and blow drying and curing, the phosphating liquid used in the phosphating is compounded from a first phosphating liquid, a second phosphating liquid, and a nano dispersant, the mass ratio of the first phosphating liquid, the second phosphating liquid, and the nano dispersant is (0.5-1.5) : (0.5-1.5) : (1-3), the composition of the first phosphating liquid comprises zinc dihydrogen phosphate, acid manganese phosphate, phosphoric acid, zinc nitrate, cobalt salt, surfactant, nickel sulfate, and corrosion inhibitor, the composition of the second phosphating liquid comprises phosphoric acid, zinc oxide, cobalt salt, fluoride, and complexing agent, the first phosphating liquid is a product of a commercially available type FX-022, the second phosphating liquid is a product of a commercially available type NPS-05C, and the nano dispersant is a product of a commercially available type SFT-1388.

2. The method for preparing a surface coating of a Nd-Fe-B sintered permanent magnet according to claim 1, characterized in that, The concentration of the phosphating liquid is 15%±1%, the phosphating temperature is 40-60℃, and the phosphating time is 1000-1200s.

3. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The mass ratio of the first phosphating liquid, the second phosphating liquid, and the nano dispersant is 1:1:

2. ​ 4. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The water washing between the phosphating and the sealing uses deionized water, and the conductivity of the deionized water used is ≤2 μS / cm. ​ 5. The method of claim 4, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The deionized water washing is performed twice. ​ 6. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The oil removal liquid used in the oil removal is added with an oil removal powder, and the addition ratio of the oil removal powder in the oil removal liquid is 1.00%±0.05%. ​ 7. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The acid pickling uses nitric acid with a concentration of 3%±0.1% as the acid pickling liquid. ​ 8. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The desmutting liquid used in the ultrasonic desmutting is added with a desmutting agent, the addition ratio of the desmutting agent in the ultrasonic desmutting liquid is 3%±0.1%, and the ultrasonic frequency used in the ultrasonic desmutting is 28 kHz-32 kHz. ​ 9. The method of claim 1, wherein the surface coating of the Nd-Fe-B sintered permanent magnet is prepared by the steps of: The sealing liquid used in the sealing is added with a sealing agent, and the addition ratio of the sealing agent in the sealing liquid is 10%±1%. ​

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