A method of processing sintered neodymium-iron-boron magnets

Abstract

The application discloses a processing method of sintered neodymium-iron-boron magnets. The processing method comprises the following steps: preparing sintered neodymium-iron-boron magnet blocks to be bonded; cleaning and roughening the bonding surface of the magnets; uniformly coating a composite powder on the bonding surface of the magnets. The composite powder comprises RE-M alloy powder and high-resistivity insulating powder. The magnets are subjected to segmented sintering while being subjected to pressure, and are cooled in the furnace after sintering is completed. The integrated combined sintered neodymium-iron-boron magnets are obtained after being discharged from the furnace. The method forms a firm metallurgical bond between the magnets by selecting a specific composite powder and optimizing the sintering process, so that the bending strength of the bonding interface is not less than 250 MPa, and the resistivity of the interface is improved by one order of magnitude. The method is particularly suitable for application fields such as high-speed motors and generators that have strict requirements on mechanical strength and eddy current loss.

Description

Technical Field

[0001] This invention belongs to the field of machining of sintered NdFeB magnets, and specifically relates to a method for bonding multiple magnets with high strength and high resistivity through composite powder bonding and high-temperature sintering. Background Technology

[0002] Sintered neodymium iron boron (NdFeB) permanent magnets are widely used in motors, generators, and acoustic devices due to their excellent magnetic properties. In practical applications, multiple magnets are often combined to achieve specific shapes or magnetic field distributions. Traditional bonding methods primarily use organic adhesives, but these methods have significant drawbacks: organic adhesives have poor heat resistance, easily aging and decomposing at high temperatures, leading to bonding failure; secondly, the bonding strength of organic adhesives is limited, making them unable to withstand high stress or impact loads. Furthermore, the adhesive layer may introduce additional air gaps, affecting the integrity of the magnetic circuit. In addition, in motor applications, especially high-frequency motors, the magnetic poles formed by splicing multiple magnets generate significant eddy current losses under alternating magnetic fields, leading to decreased efficiency and increased temperature rise. While traditional adhesives offer some insulation, their inherent temperature resistance and strength limitations restrict their application. Using only metal powder for bonding creates low-resistance paths, further exacerbating eddy current losses. Therefore, developing a magnet connection technology that can achieve both high-strength connection and effectively suppress interfacial eddy current loss has become an urgent technical problem to be solved in this field. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a processing method for composite sintered NdFeB magnets. This method achieves a strong and reliable metallurgical bond between magnets by selecting a specific composite powder bonding system and optimizing the sintering process, which significantly improves the bending strength of the magnet bonding interface.

[0004] This invention provides a method for processing sintered NdFeB magnets, comprising the following steps:

[0005] S1 Prepare at least two standard square-shaped sintered NdFeB magnets as the bonding substrate;

[0006] S2 performs surface cleaning and roughening treatment on the bonding surface of the magnet;

[0007] S3 uniformly coats the composite powder onto the bonding surface of the sintered NdFeB magnet. The composite powder comprises RE-M alloy powder and high resistivity insulating powder, wherein: RE is one or more of Pr, Nd, Dy, Tb, Gd, and Ho; M is one or more of Al, Cu, Fe, and Ga; and the high resistivity insulating powder is one or more of SiO2, Al2O3, and ZrO2. When the RE-M powder in the composite powder contains one or more of Dy and Tb elements, the sintered NdFeB magnet can achieve high-strength metallurgical bonding while also improving its coercivity.

[0008] S4 involves neatly stacking multiple magnets coated with composite powder along the bonding surface, then sintering them in sections while applying pressure. After sintering is completed, the magnets are cooled in the furnace to finally obtain a one-piece sintered NdFeB magnet.

[0009] Preferably, the surface cleaning in step S2 includes ultrasonic degreasing, chemical rust removal, ultrasonic water washing and drying, and the roughening treatment is to use sandpaper to polish the surface of the magnet to be bonded.

[0010] Preferably, the composite powder described in step S3 is coated on the magnet surface in a single-sided coating manner.

[0011] Preferably, the amount of composite powder used in step S3 is related to the width of the bonding gap, wherein the width of the bonding gap is 2% to 10% of the width of the bonded magnet. If the bonding gap is too thick, the combined magnet will be too large, reducing the remanent magnetic performance and causing material waste; if the bonding gap is too thin, the liquid phase formed during sintering cannot fully cover the bonding surface, resulting in insufficient bonding strength.

[0012] Preferably, the high resistivity insulating powder in step S3 constitutes 0.5% to 10% of the composite powder by mass. If the content of the high resistivity insulating powder exceeds 10%, although it is beneficial to improve the resistivity of the magnet interface, it will excessively crowd out the metal alloy phase, weaken the metallurgical bonding network, thereby reducing flexural strength and decreasing the density and porosity of the interface layer, making it impossible to achieve synergistic optimization of strength and resistivity. Therefore, the content of the insulating powder must be controlled within this equilibrium range.

[0013] Preferably, the mechanical pressure applied in step S4 is in the range of 0.5 MPa to 100 MPa.

[0014] Preferably, the segmented sintering process in step S4 involves first heating to 600–700°C at a rate of 8°C / min and holding for 3 hours. The low-temperature pretreatment temperature needs to be set according to the eutectic point or melting point of the low-melting-point phase of the RE-M alloy powder to ensure the smooth formation and pre-diffusion of the liquid phase. Then, the temperature is slowly heated to 900–960°C at a rate of 6°C / min and held for 5–7 hours. The temperature and time of the high-temperature stage are set based on the liquid-phase sintering characteristics of the RE-M alloy powder to achieve sufficient diffusion and metallurgical bonding at the interface.

[0015] Beneficial effects

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] 1. High-strength magnet bonding. Compared to the poor mechanical strength of magnets bonded with conventional adhesives, this invention uses a composite powder composed of RE-M alloy powder with specific components and high-resistivity insulating powder as the adhesive, combined with a segmented sintering process, to form a strong metallurgical bond at the magnet connection interface. The composite magnet prepared by this invention can achieve a bending strength of over 250 MPa at the bonding interface, far exceeding that of conventional adhesive bonding processes, and comparable to, or even surpassing, the bending strength of the magnet body itself.

[0018] 2. Excellent high-temperature resistance. Compared with conventional organic adhesives, which have poor heat resistance and are prone to aging and decomposition at high temperatures, leading to adhesive failure, the magnet adhesive layer in this invention is a metal powder alloy phase with a melting point much higher than the thermal decomposition temperature of organic adhesives. Therefore, the combined magnet prepared by this method can work stably for a long time at high temperatures and will not fail due to adhesive layer aging.

[0019] 3. Improving magnet resistivity and reducing eddy current losses. Simply using metal powder for bonding creates low-resistivity pathways, exacerbating eddy current losses. Therefore, by introducing high-resistivity insulating powder into the RE-M powder, the resistivity of the magnet bonding interface is increased by more than an order of magnitude compared to pure metal powder bonding, without significantly sacrificing bond strength. This effectively blocks low-resistivity pathways for eddy currents between the combined magnets, significantly reducing eddy current losses in applications such as high-speed motors, and improving motor efficiency and lifespan. This achieves synergistic optimization of mechanical strength and electromagnetic performance. Attached Figure Description

[0020] Figure 1 A schematic diagram illustrating the bonding process and mechanical pressure (F) applied to the sintered NdFeB magnets provided by this invention. Detailed Implementation

[0021] To provide a more specific and in-depth understanding of the technical solutions, beneficial effects, and implementation methods of the present invention, detailed descriptions will be provided below through specific embodiments and in conjunction with the accompanying drawings. It should be particularly noted that the embodiments described below are merely exemplary manifestations of the technical solutions of the present invention, and their scope is not limited to these embodiments. Based on the content disclosed in this invention, any other embodiments or equivalent substitutions obtained by those skilled in the art without departing from the concept of the present invention are all within the scope of protection claimed by the present invention.

[0022] Example 1:

[0023] This invention provides a method for processing sintered NdFeB magnets, with reference to... Figure 1 In the diagram, F represents the direction of mechanical pressure application, and the process includes the following steps:

[0024] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0025] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0026] S3 will Pr 69 Cu 31 The Al2O3 composite powder (95:5 by mass) is uniformly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0027] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0028] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0029] Next, continue heating to 940 ℃ at a rate of 6 ℃ / min and hold for 5 h;

[0030] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0031] Example 2:

[0032] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0033] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0034] S3. The composite powder of DyCu2:Al2O3 = 90:10 (mass ratio) is uniformly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0035] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0036] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0037] Next, continue heating to 940 ℃ at a rate of 6 ℃ / min and hold for 5 h;

[0038] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0039] Comparative Example 1

[0040] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0041] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0042] S3 will Pr 69 Cu 31 Alloy powder is evenly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0043] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0044] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0045] Next, heat slowly to 940 ℃ at a rate of 6 ℃ / min and hold for 5 h;

[0046] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0047] Comparative Example 2

[0048] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0049] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0050] S3. DyCu2 alloy powder is evenly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0051] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0052] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0053] Next, heat slowly to 940 ℃ at a rate of 6 ℃ / min and hold for 6 h;

[0054] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0055] Comparative Example 3:

[0056] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0057] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0058] S3 will Tb2Fe 17 Alloy powder is evenly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0059] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0060] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0061] Next, the temperature was increased to 940 ℃ at a rate of 6 ℃ / min and held for 7 h.

[0062] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0063] Comparative Example 4:

[0064] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0065] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0066] S3 will Pr 84 Al 16 Alloy powder is evenly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0067] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0068] First, heat to 700℃ at a rate of 8℃ / min and hold for 3 hours;

[0069] Next, continue heating to 940 ℃ at a rate of 6 ℃ / min and hold for 6 h;

[0070] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0071] Comparative Example 5:

[0072] This comparative example uses conventional adhesive bonding techniques in the current field of magnet bonding. The specific steps are as follows:

[0073] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0074] S2 performs surface cleaning and roughening treatment on the bonding surfaces of each magnet;

[0075] S3. Apply 502 glue evenly to the upper and lower bonding surfaces of the middle magnet, with the coating thickness controlled at about 0.1mm.

[0076] S4. The three magnets are neatly stacked and placed in a special adhesive fixture. Pressure is applied to ensure that the adhesive layer is uniform.

[0077] S5 was left at room temperature for 12 hours to ensure complete curing of the adhesive, ultimately yielding the assembled sintered NdFeB magnet.

[0078] Comparative Example 6:

[0079] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0080] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0081] S3 will Pr 69 Cu 31 The Al2O3 composite powder (85:15 by mass) is uniformly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0082] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, which is carried out according to the following segmented sintering process:

[0083] First, heat to 650 ℃ at a rate of 8 ℃ / min and hold for 3 h;

[0084] Next, continue heating to 940 ℃ at a rate of 6 ℃ / min and hold for 5 h;

[0085] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0086] Comparative Example 7:

[0087] S1 Prepare three standard-sized square sintered iron boron magnets as the bonding substrate;

[0088] S2 cleans the surfaces of each magnet to be bonded, and then roughens them by sanding with sandpaper;

[0089] S3 will Pr 69 Cu 31 Alloy powder is evenly coated on the upper and lower bonding surfaces of the middle magnet, and the three magnets are neatly stacked.

[0090] S4 Then, a mechanical pressure of 0.8 MPa is applied to ensure close contact between the bonding surfaces and to simultaneously perform segmented sintering, followed by a single-segment sintering process:

[0091] The temperature was increased to 940℃ at a rate of 8℃ / min and held for 5 hours.

[0092] Finally, the furnace is cooled to room temperature, and the sintered NdFeB magnets are obtained by integral molding and assembly.

[0093] The sintered NdFeB magnets prepared in the various embodiments and comparative examples were subjected to bending strength tests, and the results are shown in Table 1 below:

[0094] Table 1

[0095]

[0096] As shown in Table 1, the composite powder bonding and segmented sintering process (as in Examples 1 and 2) achieves a higher metallurgical bond strength than the process using only RE-M powder (as in Comparative Examples 1, 2, 3, and 4), although the latter can achieve a lower interfacial resistivity. However, using composite powder to bond the combined magnets increases the resistivity of the bonding interface by an order of magnitude compared to metal powder without significantly sacrificing bond strength. Furthermore, the flexural strength of the combined magnets exceeds 250 MPa, reaching a level comparable to the magnet body itself. It is worth noting that the amount of high-resistivity insulating powder added must be strictly controlled. If the mass percentage of high-resistivity insulating powder in the composite powder exceeds 10% (as in Comparative Example 6), although it can further increase the interfacial resistivity, it will excessively sacrifice the continuous metallurgical network formed by the metal phase, leading to a decrease in the density of the interfacial layer and an increase in porosity, thus significantly reducing the flexural strength. Therefore, the content of high-resistivity insulating powder needs to be controlled within a suitable range of 0.5% to 10%. Furthermore, when the RE-M powder contains Dy and Tb heavy rare earth elements (as in Examples 2, 2, and 3), the combined sintered NdFeB magnets achieve both high bending strength and improved coercivity. Compared to using metal powder and a single-segment sintering process (as in Comparative Example 7), the combined magnets prepared using RE-M powder and a segmented sintering bonding process exhibit significantly improved bending strength, reaching a level comparable to the magnet body itself. Simultaneously, compared to Comparative Example 5, which uses a conventional 502 adhesive curing process, the metal powder bonding process in Comparative Examples 1, 2, 3, and 4 increases the bending strength of the combined magnets to approximately seven times that of the latter.

[0097] It should be noted that in other embodiments, the objective of this invention can be achieved when the experimental process meets the following conditions:

[0098] The mass percentage of insulating powder in the composite powder in step S3 is preferably 0.5% to 10%, specifically 0.5%, 3%, 5%, 8%, 10%, etc.; as for the type of insulating powder, one or more of SiO2, Al2O3, and ZrO2 can be selected, all of which can achieve similar effects.

[0099] For step S4, the range of applied mechanical pressure is 0.5 MPa to 100 MPa, specifically 0.5 MPa, 20 MPa, 70 MPa, or 100 MPa, etc.; for the temperature and holding time of the segmented sintering, the temperature of the first sintering is preferably 600 to 700 ℃, specifically 600 ℃, 650 ℃, or 700 ℃, and the time is preferably 2 to 4 h, specifically 2 h, 3 h, or 4 h; the temperature of the second sintering is preferably 900 ℃ to 960 ℃, specifically 900 ℃, 930 ℃, or 960 ℃, etc., and the time is preferably 5 to 7 h, specifically 5 h, 6 h, or 7 h.

[0100] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are protected by the present invention.

Claims

1. A method of processing sintered neodymium-iron-boron magnets, characterized in that, The method comprises the following steps: S1 providing at least two sintered Nd-Fe-B magnets to be bonded; S2 performing surface cleaning and roughening treatment on the bonding surface of the sintered Nd-Fe-B magnets; S3 uniformly coating a composite powder on the bonding surface of at least one of the sintered Nd-Fe-B magnets, the composite powder comprising RE-M alloy powder and insulating powder, wherein RE is one or more of Pr, Nd, Dy, Tb, Gd and Ho, M is one or more of Al, Cu, Fe and Ga, and the insulating powder is one or more of SiO2, Al2O3 and ZrO2; the mass percentage of the insulating powder in the composite powder is 0.5%-10%; S4 stacking the sintered Nd-Fe-B magnets coated with the composite powder along the bonding surface, then performing sectional sintering while applying pressure, and finally cooling in the furnace after sintering to obtain an integrally formed combined sintered Nd-Fe-B magnet.

2. The method of processing sintered neodymium-iron-boron magnets according to claim 1, characterized in that The surface cleaning in step S2 comprises sequentially performing ultrasonic oil removal, chemical rust removal, ultrasonic water washing and drying.

3. The method of processing sintered neodymium-iron-boron magnets according to claim 1, characterized in that The roughening treatment in step S2 is to polish the bonding surface of the sintered Nd-Fe-B magnet using sandpaper, and the roughness Ra is 0.8-3.2 μm.

4. The method of processing a sintered neodymium-iron-boron magnet according to claim 1, characterized in that The amount of the composite powder in step S3 is related to the bonding gap width, wherein the bonding gap width is 2%-10% of the width of the sintered Nd-Fe-B magnet to be bonded.

5. The method of processing sintered neodymium-iron-boron magnets according to claim 1, characterized in that The coating method of the composite powder on the surface of the sintered Nd-Fe-B magnet in step S3 is single-sided coating.

6. The method of processing sintered neodymium-iron-boron magnets according to claim 1, characterized in that The range of the applied pressure in step S4 is 0.5 MPa-100 MPa.

7. The method of processing sintered neodymium-iron-boron magnets according to claim 1, characterized in that The sectional sintering treatment in step S4 is to first sinter at 600-700 ℃, and then sinter at 900 ℃-960 ℃.

8. The method of processing sintered neodymium-iron-boron magnets according to claim 7, characterized in that The holding time at 600-700 ℃ is 2-4 h.

9. The method of processing sintered neodymium-iron-boron magnets according to claim 7, characterized in that The holding time at 900-960 ℃ is 5-7 h.

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