A method for optimizing the metallographic structure of NdFeB magnets

Abstract

The present invention belongs to the technical field of magnetic materials, and in particular, relates to a method for optimizing the metallographic structure of a neodymium iron boron magnet. The method comprises: 1) taking a thin sheet of neodymium iron boron magnet for pretreatment, placing it in a high-pressure hydrogen atmosphere for heat treatment, and obtaining a hydrogenated magnetic sheet; 2) subjecting the hydrogenated magnetic sheet to high-pressure argon gasification treatment, and then placing it in dilute sulfuric acid for reduced pressure immersion, to obtain an etched magnetic sheet; 3) placing the etched magnetic sheet in an alkaline solution of manganous hydroxide for immersion treatment, and then performing vacuum heat treatment to obtain a new magnetic sheet; 4) magnetizing the new magnetic sheet to complete the metallographic structure optimization of the neodymium iron boron magnet. The technical solution of the present invention can effectively post-process ultra-thin neodymium iron boron sheet magnets, improve some magnetic properties of existing magnetic sheets, and avoid damage to the magnets during the processing process, so that the magnets maintain the original basic magnetic properties and good structural strength, and have a universal effect on thin sheet magnets.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a method for optimizing the metallographic structure of a neodymium iron boron magnet. Background Art

[0002] Neodymium iron boron (NdFeB) is a rare earth permanent magnet material, known as the "king of magnets" for its excellent magnetic properties. It is mainly composed of neodymium (Nd), iron (Fe) and boron (B), has extremely high magnetic energy product and coercivity, and is widely used in computer, communication, medical, transportation and other fields.

[0003] Among them, the main component of NdFeB is the intermetallic compound RE 2 Fe 14 B, the content of rare earth metal neodymium is usually between 29% and 32.5%, the content of iron is between 63.95% and 68.65%, and the content of boron is relatively small, about 1.1% to 1.2%. These components constitute the main phase components of NdFeB magnets, and their metallographic structure is mainly composed of the main phase Nd 2 Fe 14 B and Nd-rich phase in the grain boundary phase. The composition, structure and distribution state of the grain boundary phase directly affect the magnetic properties, corrosion resistance and mechanical properties of the magnet. Among them, the α-Fe phase, as the largest harmful phase structure of NdFeB magnets, has also attracted much attention. Its melting point is as high as 1520 ℃, which is the phase with the highest melting point in the alloy and is the first to be folded out from the liquid alloy. α-Fe is a soft magnetic phase, and its existence leads to the reduction of the main phase and the increase of the Nd-rich phase, destroying the optimal ratio of the main phase and the Nd-rich phase, damaging the magnetic orientation of the main phase grains, and coarsening the grains in the local area during the sintering process, which not only deteriorates the magnetic properties, but also deteriorates the structure of the electroplating layer, affecting the protective effect.

[0004] Therefore, in recent years, there have been many studies on the metallographic structure optimization process of NdFeB magnets. Such as the double alloy method, grain boundary diffusion method and rapid solidification process. And the addition of alloy elements, such as Ti and other components, can effectively suppress α-Fe. However, it is difficult to use the above processes for ultra-thin magnetic sheets with a thickness of less than 1.0 mm, or even less than 0.5 mm, used in electronic appliances and smart devices. Among them, ultra-thin magnets have higher requirements for material uniformity and consistency, and the double alloy method is difficult to guarantee these characteristics of ultra-thin magnets. The same surface diffusion technology is not applicable because of the difficulty in controlling the thickness and uniformity of the coating. Especially for ultra-thin magnets with a thickness of less than 1 mm, the surface diffusion technology may be difficult to achieve effective diffusion layer control, and the rapid solidification process becomes inapplicable due to the difficulty in controlling the cooling rate and material thickness. This is because ultra-thin magnets have higher requirements for the uniformity and consistency of the cooling rate and cannot be effectively adapted for use.

[0005] At present, ultra-thin NdFeB magnets are usually made by amorphous rapid quenching, which is the most common and commonly used method for manufacturing ultra-thin NdFeB magnets. However, during the crystallization process of amorphous rapid quenching tape, the crystallization activation energy of α-Fe phase is low, so it is relatively 2 Fe 14 The B phase is more likely to precipitate. This means that in most cases, the α-Fe phase will take precedence over the Nd 2 Fe 14 Phase B precipitates. Compared with ultra-thin magnets, which are usually used in applications requiring high coercive force and magnetic energy product, the soft magnetism of the α-Fe phase may affect the local magnetic field distribution of the magnet, thereby affecting the overall performance. Due to its large size, the influence of the α-Fe phase on block magnets may not be as concentrated and significant as that on thin-sheet magnets, and it is suitable for the common processes such as the above-mentioned dual alloy method to inhibit the generation of the α-Fe phase.

[0006] Therefore, developing a method for optimizing the metallographic structure of ultra-thin magnets to suppress or reduce the α-Fe phase is an effective means and an important research direction to improve the magnetic properties of ultra-thin magnets. Summary of the invention

[0007] In order to solve the problems that the ultra-thin NdFeB magnets with a thickness of ≤1.5 mm are affected by the harmful phase component α-Fe phase, resulting in poor performance, and there is currently no method that can effectively eliminate the α-Fe phase in the ultra-thin NdFeB magnets to achieve metallographic structure optimization, the present invention provides a metallographic structure optimization method for NdFeB magnets.

[0008] The main purpose of the present invention is:

[0009] 1. It can effectively remove the harmful phase component α-Fe in ultra-thin NdFeB magnetic sheets;

[0010] 2. The coercive force and magnetic energy product of the magnet can be effectively improved through treatment.

[0011] To achieve the above objectives, the present invention adopts the following technical solutions.

[0012] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0013] The method comprises:

[0014] 1) Pre-treat the thin NdFeB magnet and place it in a high-pressure hydrogen atmosphere for heat treatment to obtain a hydrogenated magnet sheet;

[0015] 2) After the hydrogenated magnetic sheet is treated with high-pressure argon gas inflation, it is placed in dilute sulfuric acid for reduced-pressure immersion to obtain an etched magnetic sheet;

[0016] 3) placing the etched magnetic sheet in an alkaline solution of manganous hydroxide for immersion treatment, and then performing vacuum heat treatment to obtain a new magnetic sheet;

[0017] 4) Magnetizing the new magnetic sheet completes the metallographic structure optimization of the NdFeB magnet.

[0018] As a preference,

[0019] Step 1) The thin-film NdFeB magnet is a thin-film magnet with a thickness of 0.2 to 1.5 mm;

[0020] Step 1) The pretreatment includes ultrasonic cleaning.

[0021] As a preference,

[0022] Step 1) The high-pressure hydrogen atmosphere is a hydrogen atmosphere with a gas pressure of 13 to 18 kPa;

[0023] Step 1) The heat treatment process is controlled at a temperature of 160-180°C and a heat treatment time of 45-75 min.

[0024] As a preference,

[0025] Step 2) The high-pressure argon gas filling treatment is to place the hydrogenated magnetic sheet in an argon atmosphere with a gas pressure of 3 to 7 kPa for at least 5 minutes, and then quickly transfer it to dilute sulfuric acid.

[0026] As a preference,

[0027] Step 2) the dilute sulfuric acid is a sulfuric acid aqueous solution with a concentration of 0.03 to 0.07 mol / L;

[0028] Step 2) The reduced pressure impregnation process controls the ambient gas pressure to ≤100 Pa, and the impregnation time is 30 to 120 s.

[0029] As a preference,

[0030] Step 3) the alkaline solution of manganous hydroxide is an aqueous solution of manganous hydroxide and sodium hydroxide;

[0031] In the aqueous solution of manganous hydroxide and sodium hydroxide:

[0032] The concentration of manganous hydroxide is 1 to 5 g / L;

[0033] The concentration of sodium hydroxide is 0.1-0.3 mol / L;

[0034] When preparing the aqueous solution of manganous hydroxide and sodium hydroxide, first prepare an aqueous solution of sodium hydroxide of corresponding concentration, then add manganous hydroxide and stir rapidly in a protective atmosphere to form a white sol for later use.

[0035] As a preference,

[0036] Step 3) the immersion treatment lasts for 30 to 60 seconds;

[0037] Step 3) After the immersion treatment is completed, the magnetic sheet is ultrasonically cleaned with deionized water under the condition of an ambient gas pressure of ≤100 Pa.

[0038] As a preference,

[0039] Step 3) The vacuum heat treatment is performed by heating the temperature to 260-290°C for 45-90 min under the condition of an ambient gas pressure of ≤50 Pa, and then cooling the temperature to 110-130°C for 45-90 min.

[0040] The key, difficulty and core of the technical solution of the present invention are to reduce the soft magnetic phase α-Fe phase in the NdFeB magnet, while effectively retaining the magnetic phase to ensure that the magnet has good basic magnetic properties. In addition, the technical solution of the present invention is to be effectively applicable to the processing of ultra-thin magnetic sheets.

[0041] In this regard, the present invention mainly adopts low-loss or even nearly lossless gas reaction as the core.

[0042] During step 1), the pre-treated and cleaned NdFeB magnetic sheet is placed in a high-pressure hydrogen atmosphere. In fact, the present invention draws on part of the processing process in the existing HDDR process. In the conventional HDDR process, ultra-high pressure hydrogen and high temperature treatment are used to crush the basic NdFeB alloy, while the present invention uses high-pressure hydrogen with a much lower pressure than its gas pressure for heat treatment. During the heat treatment process of the present invention, the main phase in the original magnetic sheet will slowly hydrogenate and decompose. Unlike the HDDR process, the HDDR process uses excessive ultra-high pressure hydrogen heat treatment to completely decompose the main phase, but the technical solution of the present invention is a process method for post-optimization treatment of the finished magnetic sheet. The use of the same process will cause the magnetic sheet to be destroyed and crushed. Therefore, the present invention has determined an optimal environment through a large number of attempts, that is, heat treatment is carried out at a temperature of about 170°C for about 60 minutes in a hydrogen atmosphere of 13 to 18 kPa. The heat treatment process will cause the main phase to produce a certain degree of hydrogenation and decomposition, but will not cause the overall crushing and destruction of the magnetic sheet. For this process, the purpose is to make a small amount of the main phase Nd 2 Fe 14 B decomposes to form α-Fe, NdH 2 and Fe 2B. Similarly, the rare earth-containing magnetic phases such as the neodymium-rich phase will also undergo a certain degree of transformation. This transformation is carried out under high pressure atmosphere conditions, which can make it have a certain reaction depth, rather than just a surface reaction. The hydrogenated magnetic sheet treated with hydrogen actually protects the Nd element to a certain extent and forms a more dispersed Fe 2 Phase B. Achieve the effect of killing two birds with one stone. When the environment changes, the degree of hydrogenation may be low, which will lead to the loss of magnetic phase in the subsequent processing process, or the degree of hydrogenation may be too high, resulting in the destruction of the magnetic sheet. Therefore, for the hydrogenation process, the atmosphere and temperature need to be relatively strictly controlled.

[0043] Then, after the hydrogenation treatment is completed, the present invention uses the microenvironment constructed by the hydrogenation treatment to treat with ultra-low concentration of dilute sulfuric acid. In this treatment process, due to the previous hydrogenation treatment, the exposed Nd element and its compounds are effectively protected by hydrogenation, so that they are almost not lost in the process, and the stable open circuit potential of α-Fe in this solution condition is only about -0.57 V, showing an extremely low open circuit potential, which is much lower than the residual main phase and Fe 2 This results in its extremely high solubility in dilute sulfuric acid, while the other phases can remain relatively stable.

[0044] Therefore, in the process of step 2) of the present invention, directional elimination of α-Fe can be achieved. However, it should be noted that if it is only a simple immersion treatment, it will cause the formation of structures similar to "hole corrosion" and "pitting corrosion" on the surface of the magnetic sheet, which will cause the performance of the magnetic sheet to be damaged. In the subsequent treatment process, the magnetic sheet may collapse or even break, and the magnetic properties will decrease, and the corrosion resistance will also be weakened. Therefore, the present invention also adopts "inflation" and "vacuuming" treatment, which drives and changes the flow trend of dilute sulfuric acid through air pressure. This can increase the treatment depth, and secondly, it is conducive to achieving homogenization treatment, and avoids the situation where only the surface α-Fe soft magnetic phase is removed, resulting in a decrease in structural stability.

[0045] In addition to the "inflation" and "exhaustion" treatments, the dilute sulfuric acid immersion treatment also needs to avoid too long a treatment time to avoid excessive loss of α-Fe soft magnetic phase. In this regard, the present invention has obtained the following depth-treatment time rule in multiple experiments for the thickness of the currently available ultra-thin NdFeB magnetic sheets. When the magnetic sheet thickness is a standard sheet of 0.2 mm, the treatment time is 30 s, when the magnetic sheet thickness is a standard sheet of 0.35 mm, the treatment time is 50 s, when the magnetic sheet thickness is a standard sheet of 0.5 mm, the treatment time is 75 s, when the magnetic sheet thickness is a standard sheet of 1.0 mm, the treatment time is 105 s, and when the magnetic sheet thickness is a standard sheet of 1.5 mm, the treatment time is 120 s. This one-to-one corresponding treatment time can relatively effectively avoid excessive loss of α-Fe soft magnetic phase, effectively maintain the structural strength and density of the magnetic sheet, and can effectively remove the previously existing redundant α-Fe soft magnetic phase and optimize the magnetic properties of the magnetic sheet.

[0046] After the above treatment, the present invention also requires effective cleaning and reconstruction of the magnetic sheet. In step 3), a low concentration of manganese hydroxide and sodium hydroxide aqueous solution (actually a white sol) can effectively neutralize and remove impurities for cleaning and deoxidation of the original magnetic sheet. In this process, some of the unnecessary oxides in the original magnetic sheet will be reduced and redistributed to achieve preliminary structural reconstruction. Finally, in step 4), it is actually a recombination process similar to the HDDR process. Through this process, the remaining α-Fe soft magnetic phase and Fe 2 B and NdH 2 The phases start to recombine and form a new matrix phase Nd 2 Fe 14 B. In addition, due to the existence of the crystal orientation relationship, namely the TME effect, the recombined matrix phase will inherit the crystal orientation of the original matrix phase. However, this process is actually also affected by step 2), because step 2 actually destroys the distribution of the original α-Fe soft magnetic phase. If the "inflation" and "exhaustion" treatments are not performed to change the elimination trend of the α-Fe soft magnetic phase, the crystal orientation of the matrix phase of the magnet will change, resulting in a decrease in magnetic properties. The present invention, through the coordination and treatment of step 2) and step 3), can more effectively and evenly eliminate the α-Fe soft magnetic phase and perform preliminary reconstruction, and construct a more effective matrix phase in the process of complete composite reconstruction. At the same time, because the distribution trend and distribution density of the α-Fe soft magnetic phase are changed, it can actually achieve more effective grain refinement.

[0047] Through the above treatment, the present invention can eliminate the excessive harmful phase α-Fe in the magnetic sheet as much as possible without damaging the magnetic sheet, and at the same time achieve a more effective grain refinement effect, which has a significant effect on improving the coercive force and magnetic energy product of the magnetic sheet.

[0048] The beneficial effects of the present invention are:

[0049] The technical solution of the present invention can effectively post-process ultra-thin NdFeB sheet magnets, improve some magnetic properties of existing magnetic sheets, and avoid damage to the magnets during the processing process, so that the magnets maintain their original basic magnetic properties and good structural strength, and has a universal effect on thin sheet magnets. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0051] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0052] Unless otherwise specified, in the aqueous solution of manganous hydroxide and sodium hydroxide used in the embodiment of the present invention: the concentration of manganous hydroxide is 3 g / L; the concentration of sodium hydroxide is 0.2 mol / L; when preparing the aqueous solution of manganous hydroxide and sodium hydroxide, first prepare an aqueous solution of sodium hydroxide of corresponding concentration, then add manganous hydroxide and stir rapidly in an argon atmosphere to form a white sol, and keep the argon atmosphere and stirring for storage for later use.

[0053] Example 1

[0054] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0055] The method comprises:

[0056] 1) A standard N35 magnetic sheet with a thickness of 0.35 mm was taken as the original magnetic sheet for pretreatment. The pretreatment process was to place the original magnetic sheet in a commercially available SL20 cleaning agent for ultrasonic cleaning for 20 s, then place it in deionized water and anhydrous ethanol for ultrasonic cleaning for 2 min respectively, and vacuum dry it to complete the pretreatment. After the pretreatment, the original magnetic sheet was placed in a 15 kPa high-pressure hydrogen atmosphere for heat treatment at 170 ℃ for 60 min to obtain a hydrogenated magnetic sheet;

[0057] 2) The hydrogenated magnetic sheet was placed in a 5 kPa high-pressure argon gas for 5 min, and the environment of the dilute sulfuric acid aqueous solution was pre-evacuated to ensure that the ambient pressure was ≤100 Pa. Then, the magnetic sheet was quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min, and the ambient pressure was maintained at ≤100 Pa for reduced pressure immersion for 50 s to obtain an etched magnetic sheet;

[0058] 3) The etched magnetic sheet was immersed in an aqueous solution of manganous hydroxide and sodium hydroxide for 40 seconds. After the immersion, the magnetic sheet was ultrasonically cleaned three times with deionized water under an atmosphere with an ambient gas pressure of ≤100 Pa, and then vacuum heat treated at 270 °C for 60 minutes under a vacuum condition with an ambient gas pressure of ≤50 Pa to obtain a new magnetic sheet;

[0059] 4) Placing the new magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0060] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0061]

[0062] From the above characterization results, the magnetic properties of NdFeB magnets (magnetic sheets) have been significantly optimized after the metallographic structure has been optimized by the present invention. The remanence has not changed much, and the present invention is not aimed at strengthening the remanence strength. Instead, it is to solve the problem of low coercive force and maximum magnetic energy product in existing ultra-thin magnetic sheets. Through effective optimization treatment, the proportion of α-Fe soft magnetic phase in the characterized sample magnetic sheet has dropped from 10.3% of the original magnetic sheet to 2.1%, which effectively and thoroughly removes the harmful phase α-Fe component, achieving a very effective optimization treatment effect. In addition, the density of the magnetic sheet before and after treatment decreased by ≤3%, indicating that the stable and dense structure of the magnet was effectively maintained during the treatment process, and its mechanical properties and structural stability were maintained.

[0063] Example 2

[0064] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0065] The method comprises:

[0066] 1) A standard N35 magnetic sheet with a thickness of 0.35 mm was taken as the original magnetic sheet for pretreatment. The pretreatment process was to place the original magnetic sheet in a commercially available SL20 cleaning agent for ultrasonic cleaning for 20 s, then place it in deionized water and anhydrous ethanol for ultrasonic cleaning for 2 min respectively, and vacuum dry it to complete the pretreatment. After the pretreatment, the original magnetic sheet was placed in a 13 kPa high-pressure hydrogen atmosphere for heat treatment at 170 ℃ for 60 min to obtain a hydrogenated magnetic sheet;

[0067] 2) The hydrogenated magnetic sheet was placed in a 5 kPa high-pressure argon gas for 5 min, and the environment of the dilute sulfuric acid aqueous solution was pre-evacuated to ensure that the ambient pressure was ≤100 Pa. Then, the magnetic sheet was quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min, and the ambient pressure was maintained at ≤100 Pa for reduced pressure immersion for 50 s to obtain an etched magnetic sheet;

[0068] 3) The etched magnetic sheet was immersed in an aqueous solution of manganous hydroxide and sodium hydroxide for 40 seconds. After the immersion, the magnetic sheet was ultrasonically cleaned three times with deionized water under an atmosphere with an ambient gas pressure of ≤100 Pa, and then vacuum heat treated at 270 °C for 60 minutes under a vacuum condition with an ambient gas pressure of ≤50 Pa to obtain a new magnetic sheet;

[0069] 4) Placing the new magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0070] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0071]

[0072] From the above characterization results, the present invention adopts a relatively low hydrogen atmosphere for hydrogenation treatment, and its treatment results are close to those of Example 1, but in terms of effect, the optimization and improvement effects of the coercive force and magnetic energy product in this example are reduced, and the proportion of α-Fe soft magnetic phase in the characterized sample magnetic sheet is reduced from 10.1% of the original magnetic sheet to 2.8%. This shows that the hydrogenation atmosphere has a direct impact on the elimination of the α-Fe soft magnetic phase of the present invention, and it significantly affects the treatment effect.

[0073] Example 3

[0074] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0075] The method comprises:

[0076] 1) A standard N35 magnetic sheet with a thickness of 0.35 mm was taken as the original magnetic sheet for pretreatment. The pretreatment process was to place the original magnetic sheet in a commercially available SL20 cleaning agent for ultrasonic cleaning for 20 s, then place it in deionized water and anhydrous ethanol for ultrasonic cleaning for 2 min respectively, and vacuum dry it to complete the pretreatment. After the pretreatment, the original magnetic sheet was placed in an 18 kPa high-pressure hydrogen atmosphere for heat treatment at 170 ℃ for 60 min to obtain a hydrogenated magnetic sheet;

[0077] 2) The hydrogenated magnetic sheet was placed in a 5 kPa high-pressure argon gas for 5 min, and the environment of the dilute sulfuric acid aqueous solution was pre-evacuated to ensure that the ambient pressure was ≤100 Pa. Then, the magnetic sheet was quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min, and the ambient pressure was maintained at ≤100 Pa for reduced pressure immersion for 50 s to obtain an etched magnetic sheet;

[0078] 3) The etched magnetic sheet was immersed in an aqueous solution of manganous hydroxide and sodium hydroxide for 40 seconds. After the immersion, the magnetic sheet was ultrasonically cleaned three times with deionized water under an atmosphere with an ambient gas pressure of ≤100 Pa, and then vacuum heat treated at 270 °C for 60 minutes under a vacuum condition with an ambient gas pressure of ≤50 Pa to obtain a new magnetic sheet;

[0079] 4) Placing the new magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0080] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0081]

[0082] From the above characterization results, this example uses a higher hydrogen pressure for hydrogenation treatment. After hydrogenation treatment, the coercive force and magnetic energy product are better than Example 1 and Example 2. Similarly, this example also characterizes the proportion of α-Fe soft magnetic phase, which also shows that the decrease in α-Fe soft magnetic phase is greater than that in Example 1 and Example 2. This shows that hydrogenation treatment with higher pressure hydrogen has a better effect on eliminating the α-Fe soft magnetic phase. However, from the characterization results, it can be seen that the residual magnetic strength of the sample magnetic sheet in this example has decreased. The R&D personnel believe that this involves excessive elimination of the α-Fe soft magnetic phase, which may affect the reconstruction of the matrix phase and the magnetic phase, resulting in a small amount of loss and loss.

[0083] Comparative Example 1

[0084] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0085] The method comprises:

[0086] 1) Take a standard N35 magnetic sheet with a thickness of 0.35 mm as the original magnetic sheet for pretreatment. The pretreatment process is to ultrasonically clean the original magnetic sheet in a commercially available SL20 cleaning agent for 20 s, and then ultrasonically clean it in deionized water and absolute ethanol for 2 min respectively, and then vacuum dry it to complete the pretreatment. After the pretreatment is completed, the original magnetic sheet is placed in a high-pressure hydrogen atmosphere of 10 kPa for heat treatment at 170 °C for 60 min to obtain a hydrogenated magnetic sheet;

[0087] 2) The hydrogenated magnetic sheet is subjected to a static inflation treatment in a high-pressure argon atmosphere of 5 kPa for 5 min. At the same time, the environment of the dilute sulfuric acid aqueous solution is pre-evacuated to ensure that the air pressure in its environment is ≤ 100 Pa. Then, it is quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min while maintaining the pressure, and the pressure is reduced to impregnate for 50 s while maintaining the environmental air pressure ≤ 100 Pa to obtain an etched magnetic sheet;

[0088] 3) The etched magnetic sheet is immersed in an aqueous solution of manganese hydroxide and sodium hydroxide for impregnation treatment for 40 s. After the impregnation is completed, the magnetic sheet is ultrasonically cleaned three times with deionized water under an atmosphere condition where the environmental gas pressure is ≤ 100 Pa, and then vacuum heat treatment is carried out at 270 °C for 60 min under a vacuum condition where the environmental air pressure is ≤ 50 Pa to obtain a new magnetic sheet;

[0089] 4) The new magnetic sheet is placed in a 2 T magnetization magnetic field for saturation magnetization to complete the optimization of the metallographic structure of the neodymium iron boron magnet, and an optimized sample magnetic sheet is obtained.

[0090] The performance of the N35 magnetic sheet before and after treatment is characterized and recorded as shown in the following table.

[0091]

[0092] Comparative Example 2

[0093] A method for optimizing the metallographic structure of a neodymium iron boron magnet,

[0094] The method includes:

[0095] 1) Take a standard N35 magnetic sheet with a thickness of 0.35 mm as the original magnetic sheet for pretreatment. The pretreatment process is to ultrasonically clean the original magnetic sheet in a commercially available SL20 cleaning agent for 20 s, and then ultrasonically clean it in deionized water and absolute ethanol for 2 min respectively, and then vacuum dry it to complete the pretreatment. After the pretreatment is completed, the original magnetic sheet is placed in a high-pressure hydrogen atmosphere of 20 kPa for heat treatment at 170 °C for 60 min to obtain a hydrogenated magnetic sheet;

[0096] 2) The hydrogenated magnetic sheet was placed in a 5 kPa high-pressure argon gas for 5 min, and the environment of the dilute sulfuric acid aqueous solution was pre-evacuated to ensure that the ambient pressure was ≤100 Pa. Then, the magnetic sheet was quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min, and the ambient pressure was maintained at ≤100 Pa for reduced pressure immersion for 50 s to obtain an etched magnetic sheet;

[0097] 3) The etched magnetic sheet was immersed in an aqueous solution of manganous hydroxide and sodium hydroxide for 40 seconds. After the immersion, the magnetic sheet was ultrasonically cleaned three times with deionized water under an atmosphere with an ambient gas pressure of ≤100 Pa, and then vacuum heat treated at 270 °C for 60 minutes under a vacuum condition with an ambient gas pressure of ≤50 Pa to obtain a new magnetic sheet;

[0098] 4) Placing the new magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0099] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0100]

[0101] Judging from the characterization results of Comparative Examples 1 and 2 above, excessive or insufficient hydrogen pressure will lead to different results of hydrogenation treatment. The most special one is the characterization result of Comparative Example 1. In the research and development process, the researchers believe that Comparative Example 1 should be able to retain a higher residual magnetic strength, but the optimization effect of coercive force and magnetic energy product is weak. However, after many tests, they are similar to the characterization results of Comparative Example 1. It was discovered in the subsequent research and development process that in the case of insufficient hydrogenation, the subsequent steps in the technical solution of the present invention may cause losses to rare earth components with low hydrogenation degree and unprotected conversion, which also significantly affects the subsequent reconstruction process, showing a more significant and direct decrease in residual magnetic strength. Comparative Example 2 shows that the performance of the magnetic sheet is reduced due to excessive hydrogenation. This is because the excessive elimination of the α-Fe soft magnetic phase causes the subsequent reconstruction process of the magnetic phase matrix to be affected.

[0102] Example 4

[0103] Based on Example 1, this example only uses N35 magnets of different thicknesses and performs the same metallographic structure optimization treatment as Example 1, and the only difference is that the reduced pressure immersion time in step 2) is changed. The magnetic sheets before and after the treatment are characterized and the data is recorded. Due to the limited length of the table, the data in the table below only shows the magnetic sheets after the treatment, and the display results only show the change trend compared with the change trend before the treatment.

[0104] The characterization record results are shown in the following table.

[0105]

[0106] In the table:

[0107] Data column A records the original magnetic sheet thickness in mm;

[0108] Data column B1 records the residual magnetic intensity Br in mT;

[0109] Data column B2 records the intrinsic coercivity Hcj in kA / m;

[0110] Data column B3 records the maximum energy product (BH) max , unit is kJ / m 3 ;

[0111] The data “≈” in the table means that the difference before and after treatment is less than 3% of the characteristic value before treatment, and the data “↑” means that the corresponding data after treatment increases compared with that before treatment and the increase is greater than 3%. + "" indicates that the corresponding data after treatment increased compared with that before treatment and the increase was greater than 5%. "↓" indicates that the corresponding data after treatment decreased compared with that before treatment and the decrease was greater than 3%. + " indicates that the corresponding data after treatment decreased compared with that before treatment and the decrease rate was greater than 5%.

[0112] From the results in the above table, it can be clearly seen that for magnetic sheets of different thicknesses, the duration of the reduced pressure immersion treatment has a greater impact on its treatment effect. Unlike hydrogen, the diffusion of hydrogen is more efficient under high pressure and high temperature, and the thickness of the magnetic sheet has a relatively limited impact on it, and the magnets optimized by the present invention are all ultra-thin magnetic sheets, so the impact is not significant, and no further description is given. However, for the reduced pressure immersion process, although the wetting and diffusion of dilute sulfuric acid has been improved, there are still difficulties, so the duration affects its effect. However, due to the excessive duration, the actual total content of the α-Fe soft magnetic phase in different thicknesses is also different. When the α-Fe soft magnetic phase is eliminated, the remaining phase components will be lost as small anodes, so it can be seen that the comprehensive performance of the magnetic sheet with an ultra-small thickness of 0.20 mm has greatly decreased during the long immersion treatment process. It can be seen that in the technical solution of the present invention, if the treatment process is not relatively finely controlled, there is a possibility of damage to the magnetic sheet. Therefore, for the technical solution of the present invention, especially for the treatment process of reduced pressure immersion, it is necessary to control it very strictly.

[0113] Comparative Example 3

[0114] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0115] The method comprises:

[0116] 1) A standard N35 magnetic sheet with a thickness of 0.35 mm was taken as the original magnetic sheet for pretreatment. The pretreatment process was to place the original magnetic sheet in a commercially available SL20 cleaning agent for ultrasonic cleaning for 20 s, then place it in deionized water and anhydrous ethanol for ultrasonic cleaning for 2 min respectively, and vacuum dry it to complete the pretreatment. After the pretreatment, the original magnetic sheet was placed in a 15 kPa high-pressure hydrogen atmosphere for heat treatment at 170 ℃ for 60 min to obtain a hydrogenated magnetic sheet;

[0117] 2) Immerse the hydrogenated magnetic sheet in a 0.05 mol / L dilute sulfuric acid aqueous solution, maintain the ambient pressure ≤100 Pa, and immerse under reduced pressure for 50 s to obtain an etched magnetic sheet;

[0118] 3) The etched magnetic sheet was immersed in an aqueous solution of manganous hydroxide and sodium hydroxide for 40 seconds. After the immersion, the magnetic sheet was ultrasonically cleaned three times with deionized water under an atmosphere with an ambient gas pressure of ≤100 Pa, and then vacuum heat treated at 270 °C for 60 minutes under a vacuum condition with an ambient gas pressure of ≤50 Pa to obtain a new magnetic sheet;

[0119] 4) Placing the new magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0120] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0121]

[0122] From the above characterization results, the reduced pressure impregnation process in step 2) was adjusted in this treatment process, and the "inflation" process was not performed, which led to a significant decrease in the treatment effect. Although the coercive force and magnetic energy product have been improved, the residual magnetic strength has decreased significantly, indicating that the "inflation" and "evacuation" processes without high and low pressure will actually cause the loss of effective components of the effective magnetic phase and matrix phase, and may produce an effect similar to "corrosion", and the comprehensive treatment effect will be significantly reduced.

[0123] Comparative Example 4

[0124] A method for optimizing the metallographic structure of a neodymium iron boron magnet.

[0125] The method comprises:

[0126] 1) A standard N35 magnetic sheet with a thickness of 0.35 mm was taken as the original magnetic sheet for pretreatment. The pretreatment process was to place the original magnetic sheet in a commercially available SL20 cleaning agent for ultrasonic cleaning for 20 s, then place it in deionized water and anhydrous ethanol for ultrasonic cleaning for 2 min respectively, and vacuum dry it to complete the pretreatment. After the pretreatment, the original magnetic sheet was placed in a 15 kPa high-pressure hydrogen atmosphere for heat treatment at 170 ℃ for 60 min to obtain a hydrogenated magnetic sheet;

[0127] 2) The hydrogenated magnetic sheet was placed in a 5 kPa high-pressure argon gas for 5 min, and the environment of the dilute sulfuric acid aqueous solution was pre-evacuated to ensure that the ambient pressure was ≤100 Pa. Then, the magnetic sheet was quickly transferred and immersed in a 0.05 mol / L dilute sulfuric acid aqueous solution within 1 min, and the ambient pressure was maintained at ≤100 Pa for reduced pressure immersion for 50 s to obtain an etched magnetic sheet;

[0128] 3) Placing the etched magnetic sheet in a 2 T magnetizing magnetic field for saturation magnetization completes the metallographic structure optimization of the NdFeB magnet and obtains the optimized sample magnetic sheet.

[0129] The performance of N35 magnetic sheets before and after treatment was characterized and recorded, as shown in the following table.

[0130]

[0131] From the above characterization results, this example did not use an aqueous solution of manganous hydroxide and sodium hydroxide for neutralization, impurity removal and pre-reconstruction treatment, resulting in a more obvious decrease in its residual magnetic strength relative to the embodiment, and the coercive force and magnetic energy product improvement effect is poor, especially the improvement effect of intrinsic coercive force and maximum magnetic energy product is far lower than expected. At the same time, the density characterization results also show that the density of the treated sample magnetic sheet is reduced by more than 3% compared with the original magnetic sheet, resulting in a more obvious decrease. It shows that deoxidation, pre-reconstruction and neutralization of impurities generated in the previous treatment steps with manganous hydroxide under alkaline conditions have a significant effect. Therefore, if conditions permit, corresponding treatment should still be carried out. Otherwise, although the decrease in residual magnetic strength is barely acceptable, the optimization and improvement effect is relatively poor, and it is difficult to achieve the best effect.

Claims

1. A method for optimizing the metallographic structure of a neodymium iron boron magnet, characterized in that: The method comprises: 1) Pre-treat the thin NdFeB magnet and place it in a high-pressure hydrogen atmosphere for heat treatment to obtain a hydrogenated magnet sheet; 2) After the hydrogenated magnetic sheet is treated with high-pressure argon gas inflation, it is placed in dilute sulfuric acid for reduced-pressure immersion to obtain an etched magnetic sheet; 3) placing the etched magnetic sheet in an alkaline solution of manganous hydroxide for immersion treatment, and then performing vacuum heat treatment to obtain a new magnetic sheet; 4) Magnetizing the new magnetic sheet completes the metallographic structure optimization of the NdFeB magnet; Step 1) The high-pressure hydrogen atmosphere is a hydrogen atmosphere with a gas pressure of 13 to 18 kPa; Step 1) The heat treatment process is controlled at a temperature of 160-180°C and a heat treatment time of 45-75 min; Step 2) The high-pressure argon gas filling treatment is to place the hydrogenated magnetic sheet in an argon atmosphere with a gas pressure of 3 to 7 kPa for at least 5 minutes, and then quickly transfer it to dilute sulfuric acid; Step 2) the dilute sulfuric acid is a sulfuric acid aqueous solution with a concentration of 0.03 to 0.07 mol / L; Step 2) The reduced pressure impregnation process controls the ambient gas pressure to ≤100 Pa, and the impregnation time is 30 to 120 s.

2. The method for optimizing the metallographic structure of a NdFeB magnet according to claim 1, characterized in that: Step 1) The thin-film NdFeB magnet is a thin-film magnet with a thickness of 0.2 to 1.5 mm; Step 1) The pretreatment includes ultrasonic cleaning.

3. The method for optimizing the metallographic structure of a NdFeB magnet according to claim 1, characterized in that: Step 3) the alkaline solution of manganous hydroxide is an aqueous solution of manganous hydroxide and sodium hydroxide; In the aqueous solution of manganous hydroxide and sodium hydroxide: The concentration of manganous hydroxide is 1 to 5 g / L; The concentration of sodium hydroxide is 0.1-0.3 mol / L; When preparing the aqueous solution of manganous hydroxide and sodium hydroxide, first prepare an aqueous solution of sodium hydroxide of corresponding concentration, then add manganous hydroxide and stir rapidly in a protective atmosphere to form a white sol for later use.

4. The method for optimizing the metallographic structure of a NdFeB magnet according to claim 3, characterized in that: Step 3) the immersion treatment lasts for 30 to 60 seconds; Step 3) After the immersion treatment is completed, the magnetic sheet is ultrasonically cleaned with deionized water under the condition of an ambient gas pressure of ≤100 Pa.

5. A method for optimizing the metallographic structure of a NdFeB magnet according to claim 1, 3 or 4, characterized in that: Step 3) The vacuum heat treatment is performed by heating the temperature to 260-290°C for 45-90 min under the condition of an ambient gas pressure of ≤50 Pa, and then cooling the temperature to 110-130°C for 45-90 min.

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