Waste recycling-based preparation process for neodymium-iron-boron magnet

Abstract

The present invention belongs to the field of magnet preparation, and specifically relates to a waste recycling-based preparation process for a neodymium-iron-boron magnet. The preparation process is as follows: 1) pre-treating waste, then performing hydrogen decrepitation and jet milling of rare earth copper powder, ZrO2 and waste powder, to obtain a mixed powder; 2) placing the mixed powder of step (1) in a mold for orientation and pressing, then sintering, tempering and cooling, to obtain a neodymium-iron-boron magnet. The present invention efficiently recovers neodymium-iron-boron magnet raw materials from waste material, preventing waste of the waste material, and uses relatively cheap rare earths to form an Nd-rich phase in outer layers of magnet grains, reducing magnet costs. In addition, the neodymium-iron-boron magnet prepared by the present invention has good coercivity, remanence, magnetic energy product and high-temperature resistance.

Description

A preparation process of NdFeB magnets based on waste recycling Technical Field

[0001] The invention belongs to the field of magnet preparation, and in particular relates to a preparation process of a NdFeB magnet based on waste material recycling. Background Art

[0002] Neodymium iron boron magnets are the fastest-growing, most widely used, most cost-effective, and best-performing rare earth magnet material. my country is the largest producer of rare earth magnets, and the booming magnetic materials industry has led to rising neodymium prices. However, domestic NdFeB permanent magnets are experiencing overcapacity at the low end and insufficient capacity at the high end, and demand for high-performance NdFeB magnets continues to rise. With the upgrading of equipment, a large amount of NdFeB magnet waste is generated. NdFeB magnets are inherently brittle, making them prone to waste during processing. This not only increases production costs but also causes serious environmental pollution. Furthermore, rare earth resources are non-renewable. Considering economic benefits, environmental protection, and resource conservation, it is necessary to recover NdFeB magnets from waste. The current methods for recycling NdFeB magnets from waste materials include: first, melting the waste, adding NdFeB powder to the mixture, and remaking NdFeB magnets; second, crushing the waste, testing its composition, and then adding NdFeB powder to perform air flow grinding, pressing, and sintering to remake NdFeB magnets; however, these methods have poor recovery rates and waste non-renewable resources to a great extent.

[0003] NdFeB magnets are divided into bonded, hot-pressed and sintered types. Due to the large amount of adhesive added to the bonded NdFeB magnet, its density is generally only 80% of the theoretical density, so its magnetic properties are weaker than those of the sintered NdFeB magnets. In addition, the bonded NdFeB magnet is an isotropic magnet with the same magnetism in all directions, so it is convenient to make multi-pole integral magnets, but the magnetic properties, coercive force and operating temperature are relatively low; hot-pressed NdFeB magnets can achieve extremely high magnetic properties without basically using medium and heavy rare earths, and the processing loss is low, but they can only be made into ring shapes at present, which greatly limits the application scope of hot-pressed NdFeB. The technical barriers of hot-pressed NdFeB are high and its price is high; the mainstream product sintered NdFeB magnet has extremely high magnetic properties and is the magnetic material with the best magnetic properties at present, but it still has the defects of low material utilization, difficulty in processing, poor stability, poor corrosion resistance and easy deformation. Summary of the Invention

[0004] In order to solve the performance defects of existing NdFeB magnets, such as low material utilization, difficulty in processing, poor stability, and poor corrosion resistance, while taking into account economic benefits, environmental protection, and resource conservation, the present invention provides a preparation process for NdFeB magnets based on waste recycling.

[0005] The objects of the present invention are:

[0006] (1) It can efficiently recycle NdFeB magnets from waste materials, reduce the amount of neodymium elements, save resources and reduce costs;

[0007] (2) Ensure the chemical stability and corrosion resistance of NdFeB magnets;

[0008] (3) It can improve the performance of NdFeB magnets and increase the coercive force of the magnets.

[0009] A preparation process of NdFeB magnets based on waste recycling,

[0010] The preparation process is as follows:

[0011] 1) Pre-treat the waste material, then take rare earth copper powder, ZrO2 and waste powder for hydrogen crushing and jet milling to obtain mixed powder;

[0012] 2) The mixed powder of step (1) is placed in a mold for orientation and pressing, sintered, tempered, and cooled to obtain a NdFeB magnet.

[0013] As a preference,

[0014] Step 1) The pretreatment step includes washing and drying, and after drying, crushing the waste to 60-200 mesh;

[0015] Step 1) The waste material is Nd2Fe that has failed at high temperature 14 B NdFeB magnet scrap, the residual magnetic intensity of NdFeB magnet before failure is ≥1.16 T, and the residual magnetic intensity after failure is ≤0.90 T.

[0016] As a preference,

[0017] Step 1) The rare earth copper powder has a mesh size of 100-200 meshes and is composed of La-Cu and / or Ce-Cu and / or Pr-Cu and / or Gd-Cu and / or Ho-Cu and / or Tb-Cu and / or Dy-Cu.

[0018] As a preference,

[0019] Step 1) The mesh size of the ZrO2 is 200-400 mesh.

[0020] As a preference,

[0021] Step 1) The mixed powder contains 5-10 wt% rare earth copper powder, 10-15 wt% ZrO2, and the remainder is waste powder.

[0022] As a preference,

[0023] Step 2) The orientation magnetic field strength is 1.2 to 1.35 T, and the orientation time is 25 to 30 minutes.

[0024] As a preference,

[0025] Step 2) The pressing is performed at a pressure of 200-240 MPa.

[0026] As a preference,

[0027] Step 2) The sintering is carried out in a non-nitrogen protective atmosphere or a vacuum atmosphere at a temperature of 900-1050° C. for 4-6 hours, and then kept at 700-900° C. for 1-3 hours.

[0028] As a preference,

[0029] Step 2) Before tempering, the steel is oil quenched for 0.5 to 1 hour and tempered at a temperature of 400 to 480° C. for 8 to 12 hours.

[0030] When existing NdFeB magnets are used in environments above 180°C, the magnetic Nd compound (R phase component) and Nd disorderly thermal diffusion occur, and the intrinsic coercivity of the magnet decreases rapidly with increasing temperature. The irreversible loss of magnetic flux in NdFeB magnets at higher temperatures increases significantly, resulting in a decrease in magnetic properties or even loss of magnetism. During hydrogen crushing, NdFeB expands along the grain boundaries and cracks are generated. During jet grinding, ZrO2 generates stress on the grain boundaries of the scrap. ZrO2 4+ Cu 2+ By introducing holes into the tetragonal crystal system of the magnet in the form of hole-type doping, the mechanical stability of the grain boundaries is destroyed, the particles undergo transgranular fracture, and the larger crystals are broken into more dispersed grains, thereby making the waste particles more evenly distributed and continuous, and able to be effectively re-oriented.

[0031] In addition, the selection of scrap will also have a certain impact on the process of the present invention. First of all, it depends on the original performance of the scrap, that is, the residual magnetism strength of the scrap before failure. The original residual magnetism of the scrap determines its original magnetocrystalline morphology and quality. If the original residual magnetism strength is low, there is often a poor coordination of the RMB three-phase in the original magnet, or due to the composition ratio or the processing technology, the R phase and the M phase are reduced and the B phase is more. The actual cause of its failure may be magnetocrystalline distortion caused by the diffusion or secondary growth of the B phase, or the residual magnetism deviation leads to the weakening of macro-magnetism. The B phase after diffusion or growth has a certain pinning effect, which will weaken the effect of re-orientation. Therefore, the selection of failed NdFeB magnet scrap with better original quality can ensure the process effect of the present invention more stably. Secondly, the remanence of the waste is also one of the factors that mainly affect the effect of the method of the present invention. As mentioned above, the weakening of magnetism caused by the diffusion or secondary growth of the B phase is usually difficult to cause the remanence of the high-quality magnet to drop below 1.02 T, because it does not destroy the magnetic phase (i.e., R phase and M phase) too much. The remanence intensity of the waste is significantly reduced to ≤0.9 T, which means that it can be basically determined that there are sufficient magnetic phases inside to produce disordered diffusion and disordered diffusion of Nd elements, which meets the requirements of the present invention for the state of the waste, and can easily realize the rearrangement of the R phase and the directional construction of Nd to form a new R phase component.

[0032] Furthermore, the mesh size of the rare earth copper powder used in the present invention must be controlled. A larger mesh size can damage the surface of the sintered magnet, reducing its magnetic properties. A smaller mesh size can affect the mixing effect and easily segregate the components, which in turn affects the performance of the sintered magnet. During orientation, the internal magnetic force of the magnet generates an attractive force. The rare earth copper powder interacts with the Nd and competes for position. When the magnet is heated, molecular motion intensifies, and the copper promotes the rare earth elements to enter the crystal lattice to form a solid solution. This also accelerates the movement of grain boundary dislocations. This means that the rare earth copper powder enhances the deformation capacity of the grain boundaries, thereby aligning the easy magnetization axes of the NdFeB magnets in an orderly manner along the orientation direction, achieving higher magnetic properties. The addition of rare earth copper powder facilitates grain boundary reconstruction, forming new grain boundaries that isolate adjacent grains. This weakens the magnetic coupling between tetragonal grains, inhibits the growth of anti-domained grains, and hinders the expansion of anti-domained grains. This results in the formation of highly anisotropic magnetocrystals on the magnet surface, enhancing the local magnetocrystalline anisotropy field. This attracts domains and acts as a dynamic pinning center, limiting the displacement of domain walls and thus improving the magnet's stability. Furthermore, the addition of rare earth copper powder adjusts the ratio of raw materials in the scrap powder, increasing the amount of inexpensive rare earths and reducing neodymium, thereby lowering the cost of the magnet. Cu, with its high chemical stability and an electrode potential 2.8 V higher than that of Nd, partially replaces the low-potential Nd, forming a new high-potential grain boundary phase in the system. This reduces the potential difference between the rare earth copper powder and the tetragonal magnet and enhances the corrosion resistance of the NdFeB magnet.

[0033] In the present invention, the rapid temperature increase during high-temperature sintering activates the rare earth elements, allowing the rare earth copper powder to partially fill the pores, slightly improving the magnet's refractoriness and ensuring extremely high thermal stability even above its original operating limit. After high-temperature sintering, a period of constant temperature treatment is performed to homogenize the magnet, ensuring that the tempered magnet has good magnetic properties and low high-temperature flux loss. This prevents large temperature gradients between different parts of the magnet, thereby preventing cracking during processing.

[0034] In the technical solution of the present invention, another core lies in the tempering process. First of all, the oil quenching reaction process is milder, the temperature can be accurately controlled, and the heat conduction rate is faster than that of water quenching, which makes the magnet more uniform, reduces the formation of cold quenching lines, reduces the possibility of magnet cracking, and can isolate the air to prevent surface oxidation. During the tempering process, the high-temperature liquid phase existing at the edge of the grain undergoes a phase change, and the eutectic product contains more Fe. Magnets with high Fe content tend to generate rare earth-Fe components with higher melting points. In this process, Nd atoms penetrate into the grain boundaries to form a continuous Nd-rich phase, filling the surface defects, thereby further improving the intrinsic coercive force of the magnet. Due to the volume effect generated by the phase change in the magnet, the magnet absorbs a large amount of fracture energy, so that the magnet obtains better toughness.

[0035] Within the scope of the present invention, samples tempered at temperatures above the magnet's lowest eutectic point (400°C) exhibit a significant improvement in intrinsic coercivity. As the tempering temperature increases, the magnitude of the intrinsic coercivity increase decreases. Studies have shown that a tempering temperature of 460°C produces magnets with minimal remanence change compared to pre-tempering. However, when the tempering temperature is below the magnet's eutectic transition temperature, the Nd-rich phase, which forms the thin grain boundary phase, tends to agglomerate. The presence of massive Nd-rich phases reduces their utilization. Only when the Nd-rich phase is continuously distributed along the main phase grain boundaries can it effectively isolate adjacent NdFeB grains, demagnetizing the NdFeB grains through exchange coupling. This reduces the formation of reversed magnetic domain nuclei between the NdFeB grains and effectively blocks the propagation of reversed magnetic domains, thereby improving the magnet's intrinsic coercivity. The absence of intergranular thin Nd-rich phases does not hinder the displacement of domain walls, and the reversal of magnetization in one grain drives the reversal of magnetization in other grains. In addition, if the tempering temperature is too high or the quenching speed is too fast, the stray field inside the magnet will increase as the gaps increase and lengthen, gaps that are not filled by the Nd-rich phase will appear at the grain boundaries, and magnetic poles perpendicular to the c-axis will appear in the microscopic area. In these areas, there will be reverse microscopic demagnetization fields, which will reduce the magnetic properties.

[0036] The present invention is beneficial in that:

[0037] (1) The present invention efficiently recovers NdFeB magnet raw materials from waste materials, thus avoiding waste of waste materials;

[0038] (2) The present invention uses relatively cheap rare earth to form an Nd-rich phase in the outer layer of the magnet grains, thereby reducing the cost of the magnet;

[0039] (3) The NdFeB magnets prepared by the present invention have good coercive force, remanence, magnetic energy product and high temperature resistance. Implementation Method

[0040] The present invention is further described in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0041] 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.

[0042] Unless otherwise specified, the waste materials used in the embodiments of the present invention are all purchased from high temperature failure Nd2Fe 14 B NdFeB magnets are mainly sourced from thermal engines and automotive engines, with an operating temperature of approximately 180-220 °C. Characterized by composition, they are basically Nd 12±2 at%, B 4.5±0.5 at%, with the remainder being Fe and unavoidable impurities. The original calibration remanence of the scrap is ≥1.17 T at 25 °C, and the remanence (Br) of the scrap after failure is ≤0.9 T, the intrinsic coercivity (Hcj) is ≥10 KOe, and the magnetic energy product (BH max ) ≥28 MGSOe.

[0043] Unless otherwise specified, the size of the NdFeB magnet obtained in the embodiment of the present invention is 40 mm×40 mm×30 mm. Example

[0044] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0045] 1) The waste was ultrasonically cleaned for 30 min, rinsed with clean water, dried, and crushed to 100 mesh. 100 mesh Ce-Cu alloy powder (purchased from KETAI, the same below) and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0046] The components of the mixed powder are 10 wt% Ce-Cu alloy, 13 wt% ZrO2, and the balance is waste powder;

[0047] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 °C for 5 h in a vacuum atmosphere, kept at 800 °C for 2 h, then rapidly oil quenched at 80 °C for 30 min, tempered at 460 °C for 10 h, and naturally cooled to obtain a NdFeB magnet.

[0048] The performance of the NdFeB magnet obtained in Example 1 was characterized and tested, and the results are shown in the following table:

[0049] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1614.2140.3475 ℃1.1613.0939.03125 ℃1.1511.7337.88180 ℃1.139.4036.33220 ℃1.114.4334.89

[0050] The above characterization results demonstrate that the NdFeB magnets obtained by the present invention possess excellent magnetic properties and exhibit relatively good high-temperature resistance. A magnet of the same standard as the scrap material before its failure was purchased. The residual magnetic properties of this magnet were characterized as 1.11 T at a test temperature of 180°C, and only 1.07 T at 220°C. While this exhibits inferior high-temperature resistance to the recycled magnets of the present invention, at room temperature (25°C), its residual magnetic properties were 1.19 T, exceeding those of the magnets of the present invention. This demonstrates that the present method can effectively regenerate scrap magnets. While it cannot completely restore the original magnetic properties of the scrap magnets, it comes very close. Furthermore, the regenerated magnets exhibit improved heat resistance and can be used in high-temperature operating environments. Example

[0051] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0052] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0053] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0054] 2) The mixed powder of step (1) is placed in a mold and oriented at a magnetic field strength of 1.35T for 25 minutes, pressed at a pressure of 220 MPa for 20 minutes, sintered at 980℃ for 5 hours in a vacuum atmosphere, kept at 800℃ for 2 hours, then rapidly oil quenched at 80℃ for 30 minutes, tempered at 460℃ for 10 hours, and naturally cooled to obtain NdFeB magnets.

[0055] The performance of the NdFeB magnet obtained in Example 2 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0056] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1714.3742.5475 ℃1.1613.1241.33125 ℃1.1511.8140.04180 ℃1.129.5438.17220 ℃1.104.4836.39

[0057] From the above characterization results, it can be seen that the mesh size of the rare earth copper powder is increased in this embodiment, that is, the rare earth copper powder of Example 2 is finer, the surface of the obtained NdFeB magnet has no cracks or cracks, the volume has no obvious change, and its remanence and magnetic energy product are improved compared with Example 1, indicating that the mesh size of the rare earth copper powder is too small, which affects the mixing effect, the components are easily segregated, and the performance of the magnet after sintering is affected. Example

[0058] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0059] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 200 mesh Ce-Cu and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0060] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0061] 2) The mixed powder of step (1) is placed in a mold and oriented at a magnetic field strength of 1.35T for 25 minutes, pressed at a pressure of 220 MPa for 20 minutes, sintered at 980℃ for 5 hours in a vacuum atmosphere, kept at 800℃ for 2 hours, then rapidly oil quenched at 80℃ for 30 minutes, tempered at 460℃ for 10 hours, and naturally cooled to obtain NdFeB magnets.

[0062] The performance of the NdFeB magnet obtained in Example 3 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0063] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1614.3940.4575 ℃1.1613.1639.13125 ℃1.1411.8437.96180 ℃1.129.5536.41220 ℃1.104.4834.90

[0064] From the above characterization results, it can be seen that the mesh size of the rare earth copper powder is further increased in this embodiment compared with Example 2. The surface of the obtained NdFeB magnet is damaged and the magnetic energy product is reduced, but the remanence performance is still excellent.

[0065] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0066] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce and 220 mesh ZrO2 were then added to the waste powder for hydrogen crushing and jet milling to obtain a mixed powder.

[0067] The components of the mixed powder are Ce 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0068] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 °C for 5 h in a vacuum atmosphere, kept at 800 °C for 2 h, then rapidly oil quenched at 80 °C for 30 min, tempered at 460 °C for 10 h, and naturally cooled to obtain a NdFeB magnet.

[0069] The performance of the NdFeB magnet obtained in Comparative Example 1 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0070] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1513.5541.4375 ℃1.1513.0140.03125 ℃1.1311.8338.59180 ℃1.107.2935.02220 ℃1.063.4431.80

[0071] According to the above test results, the Br, Hcj and magnetic energy product of the NdFeB magnet obtained by using rare earth powder in this comparative example are reduced, indicating that Cu in the rare earth copper powder can promote the rare earth elements to enter the crystal lattice to form a solid solution, has high chemical stability, and its electrode potential is 2.8 V higher than that of Nd. It replaces part of the low-potential Nd, so that the system forms a new high-potential grain boundary phase, reduces the potential difference between the rare earth copper powder and the tetragonal magnet, and enhances the corrosion resistance of the NdFeB magnet. In the NdFeB magnet obtained by using rare earth powder, the inter-grain magnetic coupling and the anti-domain grains grow and expand, which causes the domain wall displacement on the magnet surface and poor magnet stability, thereby resulting in a decrease in magnetic properties and a weakening of heat resistance.

[0072] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0073] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and waste powder were then hydrogen crushed and jet milled to obtain a mixed powder.

[0074] The composition of the mixed powder is Ce-Cu 10 wt%, and the balance is waste powder;

[0075] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 °C for 5 h in a vacuum atmosphere, kept at 800 °C for 2 h, then rapidly oil quenched at 80 °C for 30 min, tempered at 460 °C for 10 h, and naturally cooled to obtain a NdFeB magnet.

[0076] The performance of the NdFeB magnet obtained in Comparative Example 2 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0077] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1314.3540.8875 ℃1.1313.1038.73125 ℃1.1211.7837.55180 ℃1.119.5135.69220 ℃1.094.4231.95

[0078] According to the above test results, in this comparative example, without adding ZrO2, the magnetic properties of the obtained NdFeB magnets are reduced, which shows that ZrO2 can destroy the mechanical stability of the grain boundaries, so that larger crystals are broken into more dispersed grains, thereby making the waste particles more evenly distributed and continuous, so that the powder can be effectively oriented. Without adding ZrO2, the internal components of the NdFeB magnets obtained by jet milling are segregated, which ultimately leads to a significant reduction in the magnetic energy product.

[0079] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0080] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0081] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0082] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 ° C for 5 h in a vacuum atmosphere, kept at 800 ° C for 2 h, then rapidly oil quenched at 80 ° C for 30 min, tempered at 390 ° C for 10 h, and naturally cooled to obtain NdFeB magnets.

[0083] The performance of the NdFeB magnet obtained in Comparative Example 3 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0084] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1613.0839.1575 ℃1.1512.0238.23125 ℃1.1310.8736.19180 ℃1.118.6535.04220 ℃1.084.3033.66

[0085] According to the above test results, the tempering temperature was lowered in this comparative example, and the magnetic properties of the obtained NdFeB magnet were reduced. This temperature is lower than the lowest eutectic temperature of the magnet. After tempering at 390 ° C, the NdFeB magnet had fewer internal grains and significantly more blocky Nd-rich phase than the NdFeB magnet obtained in Example 2. This indicates that the Nd-rich phase, which is the source of the thin-layer grain boundary phase, tends to agglomerate. The presence of blocky Nd-rich phase affects the utilization rate of the Nd-rich phase. Reverse magnetization domain cores are formed between the NdFeB grains, and reverse magnetic domain propagation reduces the stability of the magnet, thereby reducing the intrinsic coercivity of the magnet. In addition, the agglomerated Nd has a stronger diffusion tendency in a high-temperature working environment, which also shows that its heat resistance is weakened.

[0086] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0087] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0088] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0089] 2) The mixed powder of step (1) is placed in a mold and oriented at a magnetic field strength of 1.35T for 25 minutes, pressed at a pressure of 220 MPa for 20 minutes, sintered at 980℃ for 5 hours in a vacuum atmosphere, kept at 800℃ for 2 hours, then water quenched at 80℃ for 0.5 hours, and tempered at 500℃ for 10 hours to obtain a NdFeB magnet.

[0090] The performance of the NdFeB magnet obtained in Comparative Example 4 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0091] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1211.2536.5175 ℃1.1210.1335.37125 ℃1.109.4433.90180 ℃1.086.6332.40220 ℃1.053.3230.11

[0092] According to the above test results, the NdFeB magnets obtained by changing the quenching method not only have reduced magnetic properties, but also have surface cracks. As the gaps increase and extend, the stray field inside the magnet increases, gaps that are not filled by the Nd-rich phase appear at the grain boundaries, and magnetic poles perpendicular to the c-axis appear in the microscopic area. In these areas, there are reverse microscopic demagnetization fields, which will reduce the magnetic properties.

[0093] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0094] 1) The waste was ultrasonically cleaned for 30 minutes, then rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and 220 mesh ZrO2 were then hydrogen crushed and jet milled with the waste powder to obtain a mixed powder.

[0095] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0096] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 ° C for 5 h in a vacuum atmosphere, rapidly oil quenched at 80 ° C for 30 min, tempered at 460 ° C for 10 h, and naturally cooled to obtain a NdFeB magnet.

[0097] The performance of the NdFeB magnet obtained in Comparative Example 5 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0098] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1211.5235.1675 ℃1.1210.3133.25125 ℃1.109.2431.40180 ℃1.086.0630.01220 ℃1.053.0328.67

[0099] Judging from the above characterization results, the NdFeB magnets obtained without heat preservation after sintering also showed reduced magnetic properties and surface cracking, which proved that the magnets were not homogenized at this time, had poor magnetic properties and high high-temperature flux loss. Due to the large temperature gradient of various parts of the magnets, the intrinsic coercive force was greatly reduced and the magnets cracked.

[0100] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0101] 1) Using NdFeB magnets of the same standard as in Example 1 but not completely obsolete as "scrap", but having aged significantly and with a residual magnetic property (at 25°C) reduced to 1.02 T, the scrap was ultrasonically cleaned for 30 minutes, rinsed with clean water, dried, and crushed to 100 mesh. 150 mesh Ce-Cu and 220 mesh ZrO2 were then mixed with the scrap powder and hydrogen crushed and jet milled to obtain a mixed powder.

[0102] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0103] 2) The mixed powder of step (1) is placed in a mold and oriented at a magnetic field strength of 1.35T for 25 minutes, pressed at a pressure of 220 MPa for 20 minutes, sintered at 980℃ for 5 hours in a vacuum atmosphere, kept at 800℃ for 2 hours, then rapidly oil quenched at 80℃ for 30 minutes, tempered at 460℃ for 10 hours, and naturally cooled to obtain NdFeB magnets.

[0104] The performance of the NdFeB magnet obtained in Comparative Example 6 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0105] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1413.1741.0675 ℃1.1312.1940.11125 ℃1.1210.3239.26180 ℃1.109.0736.91220 ℃1.074.5235.30

[0106] The above characterization results show that the choice of "scrap" will also significantly affect the magnetic properties of the NdFeB magnets produced by the process of the present invention. This is mainly because although the scrap used in this example has been significantly aged and the residual magnetic properties have been significantly reduced, the scrap required by the present invention is that the R phase has been fully transferred or even decomposed, resulting in a large amount of disordered diffusion of Nd and the formation of locally enriched magnets in the form of agglomerates. This is then "attacked" by the rare earth alloy and zirconia, allowing the internal structure to be effectively rearranged to facilitate secondary orientation. However, the aging process of the magnet is still ongoing, and no very significant Nd enrichment has occurred, resulting in poor effect of the rare earth alloy and zirconia, and even possible negative effects.

[0107] A preparation process for NdFeB magnets based on waste recycling, the preparation process is as follows:

[0108] 1) A relatively low-quality NdFeB magnet from a certain brand (Br=1.13 T at 25°C, brand R2Fe 14 B 1.5 ), laboratory aging, heat treatment at 180 ℃ to reduce its magnetic properties to ≤0.9 T (Br=0.88 T at 25 ℃) and then used as waste material, ultrasonic cleaning the waste material for 30 min, then rinse with clean water, dry and crush the waste material to 100 mesh, then take 150 mesh Ce-Cu and 220 mesh ZrO2 and waste powder, hydrogen crushing and jet milling to obtain mixed powder;

[0109] The components of the mixed powder are Ce-Cu 10 wt%, ZrO2 13 wt%, and the balance is waste powder;

[0110] 2) The mixed powder of step (1) was placed in a mold and oriented at a magnetic field strength of 1.35 T for 25 min, pressed at a pressure of 220 MPa for 20 min, sintered at 980 °C for 5 h in a vacuum atmosphere, kept at 800 °C for 2 h, then rapidly oil quenched at 80 °C for 30 min, tempered at 460 °C for 10 h, and naturally cooled to obtain a NdFeB magnet.

[0111] The performance of the NdFeB magnet obtained in Comparative Example 7 was subjected to the same characterization test as in Example 1, and the results are shown in the following table:

[0112] Test temperatureBr(T)Hcj(KOe)BH max (MGSOe) 25 ℃1.1012.3639.9875 ℃1.0811.0239.02125 ℃1.069.8538.13180 ℃1.038.3136.15220 ℃0.984.0634.87

[0113] From the above characterization results, it can be seen that for magnets with more B phase and weaker original magnetic properties, although the method of the present invention can also achieve their regeneration and recovery, so that they regain magnetic properties, their high temperature resistance is significantly weakened, and the magnetic properties of the obtained permanent magnets cannot be effectively improved. Therefore, from the comparison of Comparative Examples 6 and 7 with the embodiment, it can be found that the technical solution of the present invention is actually generally applicable to conventional Nd2Fe 14 Magnet B is regenerated and repaired, and used as waste to prepare new high-temperature resistant magnets. Although the magnetic properties of the magnets are weakened, the heat resistance can be significantly improved. However, it should be noted that the waste materials applicable to the method of the present invention should be waste materials that have undergone high-temperature thermal failure and meet certain standards, because the diffusion and enrichment of components generated during the thermal failure process are beneficial to the implementation of the method of the present invention.

Claims

1. A process for preparing NdFeB magnets based on waste recycling, characterized in that: The preparation process is as follows: 1) Pre-treat the waste material, and then take the rare earth copper powder, ZrO2 and the waste powder for hydrogen crushing and jet milling to obtain a mixed powder; 2) The mixed powder of step (1) is placed in a mold for orientation and pressing, sintered, tempered, and cooled to obtain a NdFeB magnet.

2. The process for preparing NdFeB magnets based on waste recycling according to claim 1, characterized in that: Step 1) The pretreatment step includes washing and drying, and after drying, the waste is crushed to 60-200 mesh; Step 1) The waste material is high-temperature failed NdFeB magnet waste material, the residual magnetic strength of the NdFeB magnet before failure is ≥1.16 T, and the residual magnetic strength after failure is ≤0.90 T.

3. A process for preparing NdFeB magnets based on waste recycling according to claim 1 or 2, characterized in that: Step 1) The rare earth copper powder has a mesh size of 100-200 meshes, and its components are La-Cu and / or Ce-Cu and / or Pr-Cu and / or Gd-Cu and / or Ho-Cu and / or Tb-Cu and / or Dy-Cu.

4. A process for preparing NdFeB magnets based on waste recycling according to claim 1 or 2, characterized in that: Step 1) The mesh size of ZrO2 is 200-400 meshes.

5. The process for preparing NdFeB magnets based on waste recycling according to claim 1, characterized in that: Step 1) The mixed powder contains 5-10 wt% rare earth copper powder, 10-15 wt% ZrO2, and the remainder is waste powder.

6. The process for preparing NdFeB magnets based on waste recycling according to claim 1, characterized in that: Step 2) The orientation magnetic field strength is 1.2-1.35 T, and the orientation time is 25-30 min.

7. The process for preparing NdFeB magnets based on waste recycling according to claim 1, characterized in that: Step 2) The pressing is performed at a pressure of 200-240 MPa.

8. The process for preparing NdFeB magnets based on waste recycling according to claim 1, characterized in that: Step 2) The sintering is carried out in a non-nitrogen protective atmosphere or a vacuum atmosphere at a temperature of 900-1050° C. for 4-6 h, and then kept at 700-900° C. for 1-3 h.

9. A process for preparing NdFeB magnets based on waste recycling according to claim 1 or 8, characterized in that: Step 2) Before tempering, the steel is oil quenched for 0.5 to 1 h and tempered at a temperature of 400 to 480 °C for 8 to 12 h.