Neodymium-iron-boron plated magnet and method for producing the same

Abstract

The application provides a neodymium-iron-boron electroplated magnet and a preparation method thereof. The method comprises the following steps: performing double-peak heat treatment on a sintered neodymium-iron-boron magnet; performing aging treatment on the magnet after the double-peak heat treatment to obtain a rough magnet; and performing electroplating treatment on the rough magnet after cutting to obtain the neodymium-iron-boron electroplated magnet. The application adopts the mode of double-peak heat treatment plus aging treatment to perform heat treatment on the neodymium-iron-boron magnet, and the double-peak heat treatment process makes the grain boundary phase of the magnet precipitate and remelt, which significantly improves the distribution uniformity of Fe elements and rare earth elements in the grain boundary phase of the magnet, thereby inhibiting the surface enrichment of the rare earth-rich phase of the rough magnet, improving the damage of the rare earth elements in the cutting process, and finally greatly improving the yield of the electroplated product and making the performance excellent.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a neodymium iron boron electroplated magnet and its preparation method. Background Technology

[0002] Sintered NdFeB magnets are widely used in power machinery, medical devices, the automotive industry, wind power generation, and electronics. With the miniaturization and micro-miniaturization of downstream products, the market demand for small, precision magnetic components is increasing. To reduce reliance on heavy rare earth elements, promote the balanced utilization of rare earth resources, and reduce production costs, it is necessary to prepare heavy rare earth-free sintered NdFeB magnets. However, heavy rare earth-free sintered NdFeB magnets are prone to high-temperature demagnetization after being processed into small products and subjected to electroplating, leading to a lower yield rate. Summary of the Invention

[0003] In view of this, in order to solve the aforementioned technical problems, this application provides a neodymium iron boron electroplated magnet and its preparation method.

[0004] The preparation method provided in this application includes:

[0005] The neodymium iron boron magnet undergoes a bimodal heat treatment, wherein the bimodal heat treatment includes:

[0006] The neodymium iron boron magnet is heated to a first temperature and held at that temperature for a first time, then cooled to a second temperature and held at that temperature for a second time, then heated to a third temperature and held at that temperature for a third time, and finally cooled to room temperature. The first temperature and the third temperature are both 900~950℃, the second temperature is 700~750℃, and the first time, the second time, and the third time are all 2~6h.

[0007] The magnet after the bimodal heat treatment is subjected to aging treatment to obtain a blank magnet, wherein the aging treatment temperature is 480~560℃ and the time is 2~8h; and

[0008] The blank magnet is cut and then electroplated to obtain the neodymium iron boron electroplated magnet;

[0009] The neodymium iron boron magnet comprises: rare earth element R, metallic element M, B element and Fe element. The rare earth element R includes Pr and Nd, the metallic element M includes at least one of Cu, Ga, Ti, Zr, Al, Co and Nb, the content of rare earth element R is 29.5wt%~33wt%, the content of metallic element M is 0.1~3wt%, the content of B element is 0.86wt%~0.92wt%, and the content of Fe element is 64~69.5wt%.

[0010] In some embodiments of this application, the neodymium iron boron magnet is a heavy rare earth-free magnet, which means that the sum of the contents of Dy and Tb in the neodymium iron boron magnet is less than 0.1 wt% based on the total mass fraction of the neodymium iron boron magnet.

[0011] In some embodiments of this application, the mass ratio of Fe to rare earth element R in the surface layer of the blank magnet is... The value is 2.0~2.4, and the surface layer is the area within 2mm deep along the pressing direction on the surface of the blank magnet.

[0012] In some embodiments of this application, the mass ratio of Fe to rare earth element R in the neodymium iron boron electroplated magnet is... and the mass ratio of Fe to rare earth element R in the surface layer of the blank magnet. Satisfy the following equation (1):

[0013] <2% formula (1).

[0014] In some embodiments of this application, the first temperature is equal to the third temperature.

[0015] In some embodiments of this application, the preparation method further includes:

[0016] The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets;

[0017] The rapidly solidifying sheets were subjected to hydrogen crushing and air jet milling to obtain alloy powder;

[0018] The alloy powder is pressed into a blank to obtain a billet; and

[0019] The blank is sintered to obtain the neodymium iron boron magnet.

[0020] In some embodiments of this application, the sintering treatment is performed at a temperature of 1000~1100℃ for 2~10 hours.

[0021] In some embodiments of this application, the smelting temperature is 1300~1500℃, the hydrogen absorption pressure of the hydrogen crushing is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, the classifier wheel speed is 2000~3500r / min, and the average particle size of the alloy powder is... The thickness is 2.5~3.8μm.

[0022] In some embodiments of this application, the cooling rate from the third temperature to room temperature during the bimodal heat treatment is 3~10℃ / min, and the room temperature is 20~30℃.

[0023] In some embodiments of this application, the neodymium iron boron electroplated magnet is obtained by cutting the blank magnet and then electroplating it.

[0024] The blank magnet is cut into a base material with a predetermined size; and

[0025] The substrate is acid-washed and then electroplated to obtain the neodymium iron boron electroplated magnet.

[0026] In some embodiments of this application, the dimension of the substrate in any direction is less than 6 mm.

[0027] The neodymium iron boron electroplated magnet provided in this application is prepared by any of the preparation methods described above.

[0028] This application employs a dual-peak heat treatment combined with aging treatment to heat treat NdFeB magnets. The dual-peak heat treatment process remelts the grain boundary phase of the magnet, significantly improving the uniformity of the distribution of Fe and rare earth element R in the grain boundary phase of the magnet. This suppresses the enrichment of rare earth-rich phases on the surface of the blank magnet, improves the damage of rare earth elements during the cutting process, and ultimately greatly improves the yield of the electroplated finished product, resulting in excellent performance.

[0029] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0031] Figure 1 This is a process flow diagram for preparing a neodymium iron boron electroplated magnet according to an embodiment of this application.

[0032] Figure 2 A process flow diagram for preparing neodymium iron boron electroplated magnets is provided for another embodiment of this application. Detailed Implementation

[0033] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0034] The following disclosure provides numerous different embodiments or examples for implementing the invention. These are, of course, merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0035] Furthermore, unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that terms, such as those defined in common dictionaries, shall be interpreted as having the same meaning as they have in the context of the relevant technology and the invention, and shall not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0036] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings and examples, so as to better understand the solution of the present invention and its advantages in various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

[0037] For small-scale high-performance NdFeB magnets, especially high-performance heavy rare-earth-free magnets, the high-temperature demagnetization rate defect rate is relatively high during mass production. The inventors of this application have discovered that due to the influence of component adjustments in the formulation of high-performance heavy rare-earth-free magnets, the grain boundary phase is difficult to distribute uniformly during the rapid condensation process after the aging treatment of the raw magnet blank, leading to the easy local enrichment of triangular grain boundary phases on the surface. The machining of the raw magnet blank into smaller products has a significant impact on the surface damage of these smaller products. Furthermore, the surface of these smaller products contains a large amount of triangular grain boundary phases, which are easily removed during the electroplating and pickling processes. The combined effect of these two factors results in a higher high-temperature demagnetization rate for the smaller products obtained after machining and electroplating of the raw magnet surface. Therefore, this causes significant fluctuations in the high-temperature demagnetization rate of mass-produced heavy rare-earth-free NdFeB electroplated magnets.

[0038] The conventional approach is to control the microstructure of the triangular grain boundary region of the raw magnet to achieve a more rational elemental distribution. However, controlling the triangular grain boundary of NdFeB electroplated magnets without heavy rare earth elements is complex, influenced by numerous factors, and the implementation of microstructure control strategies in production management faces bottlenecks. Related technologies involve holding the raw magnet at a single temperature (900-950℃) after sintering, followed by cooling to room temperature, or holding it at two temperatures (900-950℃ and 500-600℃) after sintering, followed by cooling to room temperature. The inventors discovered that these methods cannot solve the problem of rare earth-rich phases accumulating on the surface of the raw magnet in the grain boundaries of the magnet under heavy rare earth-free formulation systems.

[0039] Based on this, this application provides a method for preparing a neodymium iron boron electroplated magnet, such as... Figure 1 As shown, the process includes the following steps S50~S70.

[0040] S50: The neodymium iron boron magnet undergoes bimodal heat treatment.

[0041] Neodymium iron boron magnets include rare earth elements R, metallic elements M, B, and Fe. Rare earth elements R include Pr and Nd, and metallic elements M include at least one of Cu, Ga, Ti, Zr, Al, Co, and Nb.

[0042] The content of rare earth element R is 29.5wt%~33wt%, the content of metallic element M is 0.1~3wt%, the content of element B is 0.8wt%~1.0wt%, and the content of element Fe is 64~69.5wt%. By precisely controlling the content of magnet composition, it is beneficial to suppress the enrichment of rare earth phase on the surface of the blank magnet.

[0043] Preferably, the neodymium iron boron magnet used in this application is a heavy rare earth-free magnet. In this application, a heavy rare earth-free magnet means that, based on the total mass fraction of the neodymium iron boron magnet, the sum of the contents of Dy and Tb in the neodymium iron boron magnet is less than 0.1 wt%.

[0044] The bimodal heat treatment in this application includes: heating the sintered NdFeB magnet to a first temperature and holding it at that temperature for a first time, then cooling it to a second temperature and holding it at that temperature for a second time, then heating it to a third temperature and holding it at that temperature for a third time, and finally cooling it to room temperature.

[0045] Specifically, the bimodal heat treatment can be divided into three stages: First, the temperature is raised to a first temperature and held for a first time. Sufficient energy is provided during this stage to generate a liquid phase, where mass exchange and homogenization occur at the Fe-R binary eutectic temperature. Then, the temperature is lowered to a second temperature and held for a second time. By controlling the temperature difference between the first and second temperatures, ordered precipitation of the main phase and redistribution of the liquid phase are achieved. This stage realizes the liquid-to-solid transition, improving the distribution of Fe and R within the blank magnet. Next, the temperature is raised to a third temperature and held for a third time. Under the improved Fe and R distribution, a new round of mass exchange occurs, promoting grain boundary phase homogenization. Finally, the temperature is cooled to room temperature. This process significantly improves the uniformity of Fe and R distribution in heavy rare-earth-free magnets and inhibits the enrichment of rare-earth-rich phases on the surface of the blank magnet.

[0046] This application suppresses the rare earth phase enrichment on the surface of the blank magnet, thereby ultimately suppressing the performance abnormalities of the neodymium iron boron electroplated magnet.

[0047] The first and third temperatures are both 900~950℃, for example, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃. The second temperature is 700~750℃, for example, 700℃, 710℃, 720℃, 730℃, 740℃, or 750℃. The first, second, and third times are all 2~6 hours. If the second temperature is higher than 750℃, the temperature is too high, the difference in liquid phase state is small, and the precipitation and distribution adjustment process cannot be formed; if the second temperature is lower than 700℃, the temperature is too low, and low-melting-point metal elements in the magnet will participate in the precipitation process, affecting the cooling and redistribution process of rare earth elements R and Fe.

[0048] It is preferable that the first temperature and the third temperature are equal, which is beneficial to improving the uniformity of the distribution of Fe and rare earth element R in the magnet.

[0049] Optionally, the cooling rate from the first temperature to the second temperature in the bimodal heat treatment is 1~15℃ / min. This is beneficial for the cooling and redistribution of rare earth elements R and Fe.

[0050] Optionally, the cooling rate from the third temperature to room temperature in the bimodal heat treatment is 3~10℃ / min. If the cooling rate is too fast, the rare earth-rich phase is easily enriched on the surface of the blank magnet; if the rate is too low, the cooling time is too long, which can easily produce impurity phases that affect the magnetic properties. Optionally, the room temperature here is 20~30℃.

[0051] Alternatively, cooling to room temperature can be carried out in a protective atmosphere, such as an Ar atmosphere, to prevent other reactions of the magnet.

[0052] S60: The magnet after double-peak heat treatment is subjected to aging treatment to obtain a blank magnet.

[0053] The aging treatment temperature is 480~560℃, for example, 480℃, 500℃, 520℃, 540℃ or 560℃. The aging treatment time is 2~8 hours.

[0054] Combining steps S50 and S60, this application is equivalent to performing four heat treatments on the sintered NdFeB magnet. First, the sintered NdFeB magnet is heated to 900-950℃ and held at that temperature. Then, it is cooled to 700-750℃ and held at that temperature. Next, it is heated to 900-950℃ and held at that temperature. Finally, it is cooled to room temperature and then heated to 480-560℃ and held at that temperature. Compared with the prior art, this effectively suppresses the enrichment of rare-earth phases on the surface of the blank magnet, ultimately suppressing the performance abnormalities of the NdFeB electroplated magnet.

[0055] S70: After cutting the blank magnet, electroplating is performed to obtain neodymium iron boron electroplated magnet.

[0056] Optionally, this step includes:

[0057] Cutting the blank magnet into a base material with a predetermined size; and

[0058] After pickling the substrate, an electroplating layer is applied to obtain a neodymium iron boron electroplated magnet.

[0059] Optionally, the dimension of the substrate obtained after cutting is less than 6 mm in any direction. For example, if cut into a polyhedron, the length of its longest side is less than 6 mm.

[0060] Optionally, the acid used for pickling includes at least one of nitric acid, sulfuric acid, or hydrochloric acid, wherein typical but non-limiting combinations are combinations of nitric acid and sulfuric acid, combinations of hydrochloric acid and sulfuric acid, or combinations of nitric acid and hydrochloric acid. Optionally, the concentration of the pickling acid solution is 0.5% to 5.0%, for example, it can be 0.5%, 1%, 1.2%, 1.3%, 1.5%, 2.0%, 2.2%, 2.5%, 3.0%, 3.2%, 3.5%, 4.0%, 4.2%, 4.5%, or 5.0%, etc. Optionally, the pickling temperature is 15% to 25°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, or 25°C, etc.

[0061] Optionally, the preparation method also includes degreasing after electroplating. There are no special restrictions on degreasing; any device and method known to those skilled in the art for degreasing can be used, and adjustments can be made according to the actual process.

[0062] This invention does not impose any special limitations on the apparatus and process parameters for the specific electroplating layers in the above-described process. Any apparatus and method known to those skilled in the art for electroplating can be used, and adjustments can be made according to the actual process. Optionally, the plating layer can be a nickel-copper-nickel plating layer, a zinc plating layer, a copper-nickel plating layer, a copper-nickel-phosphorus plating layer, a zinc-zinc-nickel plating layer, or a nickel plating layer.

[0063] Preferably, the electroplating solution for nickel plating mainly consists of nickel sulfate with a concentration of 200-350 g / L, nickel chloride with a concentration of 30 g / L-60 g / L, boric acid with a concentration of 30 g / L-60 g / L, sodium dodecyl sulfate with a concentration of 0.08 g / L-10 g / L, and water, with a pH value ranging from 3.8 to 4.8 and a temperature range from 45°C to 55°C.

[0064] Preferably, the electroplating solution for copper plating mainly consists of 250 g / L to 350 g / L potassium pyrophosphate, 30 g / L to 70 g / L copper pyrophosphate, and water, with a pH of 7.5 to 9.0 and a temperature range of 30°C to 50°C.

[0065] Preferably, the electroplating solution for zinc plating mainly consists of 100 g / L to 350 g / L of zinc sulfate, 100 g / L to 300 g / L of sodium sulfate, 5 g / L to 70 g / L of boric acid and water, with a pH of 3.0 to 5.0 and a temperature range of 20 to 45°C.

[0066] Preferably, the mass ratio of Fe to rare earth element R in the NdFeB electroplated magnet is... and the mass ratio of Fe to rare earth element R in the surface layer of the blank magnet The rate of change satisfies the following equation (1):

[0067] <2% formula (1).

[0068] Based on the aforementioned control of the mass ratio of Fe to rare earth element R in the blank magnet, controlling the aforementioned rate of change can better suppress the performance abnormalities of heavy rare earth-free NdFeB electroplated magnets. There are no specific limitations on the method of controlling the mass ratio of Fe to rare earth element R in the NdFeB electroplated magnet; it can be achieved by adjusting the pickling or electroplating process. For example, the type of acid used in pickling, the acid concentration, the pickling temperature, the electroplating solution concentration, and the electroplating temperature can be adjusted. It is worth noting that the aforementioned rate of change indicates that by jointly controlling the mass ratio of Fe to rare earth element R in both the blank magnet and the NdFeB electroplated magnet, the performance abnormalities of heavy rare earth-free NdFeB electroplated magnets can be effectively overcome. If only conventional adjustments are made to the pickling or electroplating process without targeted control of the aforementioned rate of change, effective control of this rate of change cannot be achieved, and the prepared electroplated magnet will struggle to fundamentally overcome the performance abnormalities. The control of the above-mentioned rate of change is achieved through the organic combination and synergistic linkage of the blank magnet process and the electroplating process.

[0069] Figure 2 This application illustrates a method for preparing a neodymium iron boron electroplated magnet according to another embodiment of the present application. Figure 1 Based on the preparation method shown, the method further includes the following steps S10~S40.

[0070] S10: The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets.

[0071] Optionally, the melting temperature is 1300~1500℃.

[0072] S20: The quick-setting flakes are crushed by hydrogen and pulverized by air jet mill to obtain alloy powder.

[0073] Optionally, the hydrogen absorption pressure of the hydrogen crusher is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, and the classifier speed is 2000~3500r / min.

[0074] Optionally, the average particle size of the resulting alloy powder The thickness is 2.5~3.8μm.

[0075] S30: Press the alloy powder into shape to obtain a blank.

[0076] The specific process of compression molding will not be described in detail here.

[0077] S40: The blank is sintered to obtain sintered NdFeB magnets.

[0078] Optionally, the sintering temperature is 1000~1100℃, for example, 1020℃, 1040℃, 1060℃, 1080℃ or 1100℃; the sintering time is 2~10h.

[0079] The NdFeB electroplated magnets prepared by the method of this application undergo a bimodal heat treatment process, which effectively improves the damage caused by rare earth elements during cutting and electroplating, ultimately resulting in a significant increase in the yield and superior performance of the NdFeB electroplated magnets. Furthermore, by controlling the mass ratio of Fe to rare earth element R in the blank magnet and the rate of change of the mass ratio of Fe to rare earth element R in the magnet before and after electroplating, the performance abnormalities of NdFeB electroplated magnets can be effectively overcome. In some embodiments of this application, the magnetic properties of the NdFeB electroplated magnets provided by this application decrease very little, or even almost not at all, after high temperature, and the yield can reach 100%.

[0080] The present invention will now be described with reference to specific embodiments. The process conditions and values ​​used in the following embodiments and comparative examples are exemplary, and their possible ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be used. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can all be purchased from conventional channels or the market. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0081] Example 1

[0082] This embodiment prepares a heavy rare-earth neodymium iron boron electroplated magnet. The specific preparation process is as follows:

[0083] 1) Prepare the raw materials according to Table 1, melt the above raw materials at 1450℃, and cast the molten alloy obtained by melting onto the cooling roller to obtain the quick-setting sheet.

[0084] 2) The rapidly solidifying flakes were hydrogen-milled to obtain coarse alloy powder. The hydrogen absorption pressure for hydrogen milling was 0.2 MPa, and the dehydrogenation temperature was 560℃. The coarse alloy powder was then pulverized using an air jet mill to obtain alloy powder. During air jet milling, the grinding chamber pressure was 0.5 MPa, and the classifier speed was 3000 r / min. The average particle size D of the obtained alloy powder was... 50 It is 3.0 μm.

[0085] 3) The alloy powder is pressed into shape under the condition of orientation magnetic induction intensity of 2T to obtain a blank.

[0086] 4) The blank was sintered at 1050℃ for 8 hours to obtain neodymium iron boron magnets.

[0087] 5) The neodymium iron boron magnet is subjected to bimodal heat treatment. First, the neodymium iron boron magnet is heated to 900℃ and held for 2 hours, then cooled to 750℃ and held for 2 hours, then heated to 900℃ and held for 2 hours, and finally cooled to about 24℃ in Ar atmosphere.

[0088] 6) The magnet after double-peak heat treatment is subjected to aging treatment at a temperature of 500℃ for 8 hours to obtain a blank magnet.

[0089] 7) The blank magnet is cut using multi-wire cutting to obtain a size of 2mm (orientation direction). 1mm A 0.7mm thick substrate was used. The substrate was then electroplated with nickel, copper, and then nickel again. The nickel plating solution consisted of 250g / L nickel sulfate, 30g / L nickel chloride, 50g / L boric acid, 0.1g / L sodium dodecyl sulfate, and water, with a pH of 4 and a temperature of 45℃. Next, copper was electroplated using a solution of 350g / L potassium pyrophosphate, 40g / L copper pyrophosphate, and water, with a pH of 7.5 and a temperature of 35℃. Finally, nickel was electroplated using a solution of 300g / L nickel sulfate, 35g / L nickel chloride, 45g / L boric acid, 0.1g / L sodium dodecyl sulfate, and water, with a pH of 3.9 and a temperature of 45℃. The total coating thickness was 15μm, resulting in a heavy rare-earth neodymium iron boron electroplated magnet.

[0090] Example 2

[0091] Heavy rare earth-free NdFeB electroplated magnets were prepared using the same raw materials and preparation methods as in Example 1. The difference was that in step 7), the substrate was acid-washed and then electroplated with a zinc layer. The electroplating solution mainly consisted of 200 g / L zinc sulfate, 100 g / L sodium sulfate, 10 g / L boric acid and water, with a pH of 4.0, a temperature of 25°C, and a zinc layer thickness of 14 μm. Heavy rare earth-free NdFeB electroplated magnets were obtained. The remaining steps were the same as in Example 1.

[0092] Example 3

[0093] Heavy rare earth-free NdFeB electroplated magnets were prepared using raw materials different from those in Example 1 (see Table 1). The bimodal heat treatment in step 5) was as follows: the sintered NdFeB magnet was heated to 950°C and held for 2 hours, then cooled to 720°C and held for 6 hours, then heated to 950°C and held for 2 hours, and finally cooled to about 24°C in an Ar atmosphere. The remaining steps were the same as in Example 1.

[0094] Example 4

[0095] Heavy rare earth-free NdFeB electroplated magnets were prepared using raw materials different from those in Example 1 (see Table 1). The bimodal heat treatment in step 5) was as follows: the NdFeB magnet was heated to 920°C and held for 2 hours, then cooled to 720°C and held for 8 hours, followed by heating to 950°C and holding for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The aging treatment in step 6) was performed at 500°C for 8 hours. The remaining steps were the same as in Example 1.

[0096] Example 5

[0097] Heavy rare earth-free NdFeB electroplated magnets were prepared using raw materials different from those in Example 1 (see Table 1). The bimodal heat treatment in step 5) was as follows: the NdFeB magnet was heated to 900°C and held for 2 hours, then cooled to 750°C and held for 8 hours, followed by heating to 900°C and holding for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The aging treatment in step 6) was performed at 550°C for 8 hours. The remaining steps were the same as in Example 1.

[0098] Example 6

[0099] Heavy rare earth-free NdFeB electroplated magnets were prepared using raw materials different from those in Example 1 (see Table 1). The bimodal heat treatment in step 5) was as follows: the NdFeB magnet was heated to 900°C and held for 6 hours, then cooled to 700°C and held for 8 hours, then heated to 950°C and held for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The remaining steps were the same as in Example 1.

[0100] Example 7

[0101] Heavy rare earth-free NdFeB electroplated magnets were prepared using the same raw materials and preparation methods as in Example 1. The difference was that the bimodal heat treatment in step 5) was as follows: the NdFeB magnet was heated to 900°C and held for 2 hours, then cooled to 750°C and held for 2 hours, then heated to 930°C and held for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The remaining steps were the same as in Example 1.

[0102] Example 8

[0103] Heavy rare earth-free NdFeB electroplated magnets were prepared using raw materials different from those in Example 1 (see Table 1). The bimodal heat treatment in step 5) was as follows: the NdFeB magnet was heated to 950°C and held for 2 hours, then cooled to 700°C and held for 2 hours, then heated to 900°C and held for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The remaining steps were the same as in Example 1.

[0104] Comparative Example 1

[0105] Heavy rare earth-free NdFeB electroplated magnets were prepared using the same raw materials and preparation methods as in Example 1. The difference was that the bimodal heat treatment in step 5) was omitted, and the aging treatment in step 6) was performed at a temperature of 900°C for 8 hours. After cooling to room temperature, the temperature was raised to 500°C for another 8 hours, followed by cooling to room temperature to obtain the blank magnet. The remaining steps were the same as in Example 1.

[0106] Comparative Example 2

[0107] Heavy rare earth-free NdFeB electroplated magnets were prepared using the same raw materials and preparation methods as in Example 1. The difference was that the bimodal heat treatment in step 5) was changed to a two-stage heat treatment: the NdFeB magnet was heated to 900°C and held for 2 hours, then cooled to approximately 24°C under an Ar atmosphere, then heated to 700°C and held for 2 hours, and finally cooled again to approximately 24°C under an Ar atmosphere. The remaining steps were the same as in Example 1.

[0108] Comparative Example 3

[0109] Heavy rare earth-free NdFeB electroplated magnets were prepared using the same raw materials and preparation methods as in Example 1, but the temperature of the bimodal heat treatment in step 5) was different. First, the NdFeB magnet was heated to 800°C and held for 2 hours, then cooled to 750°C and held for 2 hours, then heated to 800°C and held for 2 hours, and finally cooled to approximately 24°C under an Ar atmosphere. The remaining steps were the same as in Example 1.

[0110] Test method:

[0111] (1) The mass ratio of Fe to rare earth element R in the surface layer of the blank magnet Samples were taken from any position 2 mm deep along the pressing direction on the surface of the blank magnet, and calculated after ICP testing. The ratio was determined after testing 10 unfinished magnet blanks. The arithmetic mean of the ratios is used as the test result.

[0112] (2) The mass ratio of Fe to rare earth element R in neodymium iron boron electroplated magnets After removing the plating, samples were taken at arbitrary locations on the NdFeB electroplated magnet, and the results were calculated after ICP testing. The ratio was tested using six neodymium iron boron electroplated magnets, and the arithmetic mean of the six results was used as the test result.

[0113] (3) High-temperature demagnetization rate: After saturating the neodymium iron boron electroplated magnet, the magnetic flux value 1 of the magnet is measured. Then, the magnet is placed on an aluminum plate and put into an oven. The temperature is raised to 150℃ and kept at that temperature for 2 hours. After cooling to room temperature, the magnetic flux value 2 of the magnet is measured. The high-temperature demagnetization rate of the magnet is calculated as (magnetic flux value 1 - magnetic flux value 2) / magnetic flux value 1. 100% of the magnets were selected, and the high-temperature demagnetization rate was measured. A single magnet with a high-temperature demagnetization rate >3% was considered abnormal. The number of magnets with abnormal high-temperature demagnetization rates among the 1000 magnets was counted, and the proportion of abnormal high-temperature demagnetization rates was calculated.

[0114] The test results of the electroplated magnets prepared in the examples and comparative examples are shown in Table 2.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119] In Comparative Example 1, there was no bimodal heat treatment, and the aging treatment was a two-stage heat treatment. The change rate of the mass ratio of Fe to rare earth element R before and after electroplating of the obtained electroplated magnet was close to 6%, and the abnormal proportion of high-temperature demagnetization rate exceeded 10%, resulting in a low pass rate.

[0120] In Comparative Example 2, the bi-peak heat treatment was changed to a two-stage heat treatment. The change rate of the mass ratio of Fe to rare earth element R before and after electroplating of the resulting electroplated magnet exceeded 4%, the abnormal proportion of high-temperature demagnetization rate exceeded 8%, and the pass rate was also low.

[0121] In Comparative Example 3, although there was a double-peak heat treatment, the temperature was only 800℃, and the Fe element and rare earth element R could not be effectively homogenized. Therefore, the change rate of the mass ratio of Fe element to rare earth element R before and after electroplating of the electroplated magnet exceeded 3%, the abnormal proportion of high-temperature demagnetization rate was close to 8%, and the pass rate was also low.

[0122] As can be seen from the above embodiments and comparative examples, this application uses a dual-peak heat treatment plus aging treatment to heat treat NdFeB magnets. The dual-peak heat treatment process causes the grain boundary phase of the magnet to precipitate and remelt, which significantly improves the uniformity of the distribution of Fe and rare earth elements in the grain boundary phase of the magnet. This suppresses the enrichment of rare earth-rich phases on the surface of the blank magnet, improves the damage of rare earth elements in the cutting process, and ultimately greatly improves the yield of electroplated products, resulting in excellent performance.

[0123] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a neodymium iron boron electroplated magnet, characterized in that, include: The neodymium iron boron magnet undergoes a bimodal heat treatment, wherein the bimodal heat treatment includes: The neodymium iron boron magnet is heated to a first temperature and held at that temperature for a first time, then cooled to a second temperature and held at that temperature for a second time, then heated to a third temperature and held at that temperature for a third time, and finally cooled to room temperature. The first temperature and the third temperature are both 900~950℃, the second temperature is 700~750℃, and the first time, the second time, and the third time are all 2~6h. The magnet after the bimodal heat treatment is subjected to aging treatment to obtain a blank magnet, wherein the aging treatment temperature is 480~560℃ and the time is 2~8h; and The blank magnet is cut and then electroplated to obtain the neodymium iron boron electroplated magnet; The neodymium iron boron magnet comprises: rare earth element R, metallic element M, B element and Fe element. The rare earth element R includes Pr and Nd, the metallic element M includes at least one of Cu, Ga, Ti, Zr, Al, Co and Nb, the content of rare earth element R is 29.5wt%~33wt%, the content of metallic element M is 0.1~3wt%, the content of B element is 0.86wt%~0.92wt%, and the content of Fe element is 64~69.5wt%.

2. The preparation method according to claim 1, wherein the neodymium iron boron magnet is a heavy rare earth-free magnet.

3. The preparation method according to claim 1, characterized in that, The mass ratio of Fe to rare earth element R in the surface layer of the blank magnet The value is 2.0~2.4, and the surface layer is the area within 2mm deep along the pressing direction on the surface of the blank magnet.

4. The preparation method according to claim 1, characterized in that, The mass ratio of Fe to rare earth element R in the neodymium iron boron electroplated magnet and the mass ratio of Fe to rare earth element R in the surface layer of the blank magnet. The following conditions must be met: 。 5. The preparation method according to claim 1, characterized in that, The first temperature is equal to the third temperature.

6. The preparation method according to claim 1, characterized in that, Also includes: The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets; The rapidly solidifying sheets were subjected to hydrogen crushing and air jet milling to obtain alloy powder; The alloy powder is pressed into a blank to obtain a billet; and The blank is sintered to obtain the neodymium iron boron magnet.

7. The preparation method according to claim 6, characterized in that, The smelting temperature is 1300~1500℃, the hydrogen absorption pressure of the hydrogen crushing is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, the classifier wheel speed is 2000~3500r / min, and the average particle size of the alloy powder is... The thickness is 2.5~3.8μm.

8. The preparation method according to claim 1, characterized in that, In the bimodal heat treatment, the cooling rate from the third temperature to room temperature is 3~10℃ / min, and the room temperature is 20~30℃.

9. The preparation method according to claim 1, characterized in that, The blank magnet is cut and then electroplated to obtain the neodymium iron boron electroplated magnet, comprising: The blank magnet is cut into a base material with a predetermined size; and The substrate is acid-washed and then electroplated to obtain the neodymium iron boron electroplated magnet.

10. The preparation method according to claim 9, characterized in that, The dimension of the substrate in any direction is less than 6 mm.

11. A neodymium iron boron electroplated magnet, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 10.

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