A magnetic flux guide enhancement repair process for low heavy rare earth magnet steels

Abstract

The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel, it is related to low heavy rare-earth magnetic steel repair field.The application discloses a kind of magnetism guide enhancement repair processes for low heavy rare-earth magnetic steel

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of low heavy rare earth magnetic steel repair, in particular to a magnetic guide enhancement repair process for low heavy rare earth magnetic steel. BACKGROUND

[0002] Low heavy rare earth magnetic steel, especially low dysprosium (Dy) and low terbium (Tb) neodymium-iron-boron permanent magnet material, is a core functional material supporting the development of modern high-efficiency energy-saving motors, new energy vehicle driving systems, wind power generation and precision servo control high-end equipment. Reducing the content of heavy rare earth is an inevitable choice to cope with the scarcity of strategic resources and cost pressure, but this inevitably sacrifices the intrinsic coercivity (Hcj) and temperature stability of the magnet, resulting in particularly prominent performance degradation problems in complex and severe service environments (such as high temperature, high humidity, high frequency vibration and alternating electromagnetic stress).

[0003] Performance degradation mainly manifests three interrelated failure modes: one is irreversible demagnetization caused by irreversible rotation of magnetic moment under high temperature conditions; two is intergranular corrosion preferentially occurring due to the low electrochemical potential of neodymium-rich grain boundary phase, and then causing damage to magnetic isolation phase; three is microcracks initiated and extending along the grain boundary under alternating stress, eventually leading to synchronous degradation of the structural integrity and magnetic properties of the magnet. The accumulation of these micro-damages not only causes irreversible loss of magnetic flux density (Br) and coercivity, but also directly leads to reduced motor efficiency, increased torque fluctuation and reduced operation reliability.

[0004] At present, the coping strategies for such performance degradation mainly include protection and repair. In terms of protection, traditional electroplating (such as nickel plating and zinc plating), physical vapor deposition (PVD) or spraying coating can delay surface corrosion to a certain extent, but cannot cope with internal damage that has already occurred, and is completely ineffective against demagnetization and cracks.

[0005] In terms of detection and repair, the existing technology has significant limitations: first, in the detection link, manual detection (such as magnetic measuring instrument, optical microscope) relying on offline sampling is inefficient and cannot realize real-time monitoring; conventional non-destructive testing techniques such as eddy current testing are only sensitive to surface defects, and ultrasonic testing is limited by material grain structure noise interference, making it difficult to accurately identify sub-surface invisible cracks and corrosion pores below 200 microns, and even more difficult to quickly quantify and locate demagnetization areas. Second, in the repair link, thermal processing methods such as laser cladding will produce a high-temperature heat-affected zone, which is easy to cause segregation of rare earth elements and growth of main phase grains, thus exacerbating performance degradation; local remagnetization technology can only temporarily restore apparent magnetic flux, and cannot repair damaged grain boundary microstructure, so it is only a temporary solution and the degradation will quickly occur again.

[0006] Therefore, there is an urgent need in the art to develop a new remanufacturing paradigm that must be able to achieve the leap from "accurate diagnosis" to "radical repair" to "performance gain". SUMMARY

[0007] The application aims to provide a magnetic guide enhancement repair process for low heavy rare earth magnetic steel, which can effectively repair the demagnetization, corrosion and micro-crack damage of the magnetic body, and also can actively improve the effective magnetic permeability of the magnetic body by constructing a high magnetic permeability channel at the grain boundary, so as to realize the performance surpassing of the repaired magnetic body and solve the technical problems of difficult repair and unable to improve the performance of the existing low heavy rare earth magnetic steel.

[0008] To solve the above technical problems, the application adopts the following technical solutions:

[0009] A magnetic guide enhancement repair process for low heavy rare earth magnetic steel, comprising the following steps:

[0010] S100, scanning the magnetic steel by using an online monitoring system, and performing registration and fusion on the collected data to generate a comprehensive damage map;

[0011] S200, according to the damage map, precisely coating a repair agent paste in the damage area, and synchronously heating, applying a gradient pulse magnetic field and ultrasonic vibration;

[0012] S300, after cooling, removing the excess repair agent, and then performing aging treatment;

[0013] In step S100, the online monitoring system comprises a pulse magnetic field unit, a Hall sensor array and a terahertz imaging unit; the repair agent composition comprises a nano Fe-Si-Al alloy and a low melting point alloy.

[0014] The existing technology can only be protected (such as electroplating) or restored (such as remagnetization), and the target is to restore as before.

[0015] The application first proposes the concept of "functional repair" or "repair-enhancement" integration. By introducing nano soft magnetic material (Fe-Si-Al) into the repair agent and using a pulse magnetic field to guide its directional arrangement at the grain boundary, not only the damage is repaired in structure, but also the magnetic circuit is reconstructed in function, forming a high magnetic permeability channel.

[0016] After the precise application of the repair agent paste in the damaged area, only the thermal field is applied, and the low-melting-point alloy is melted by heating the repair agent to obtain fluidity. The repair agent can only rely on slow penetration by capillary action, which is low in efficiency and cannot be directional. The synchronous application of a gradient pulse magnetic field provides the main directional driving force (Lorentz force), which pushes the repair agent to penetrate and guide the directional arrangement of nano-soft magnetic particles. The synchronous application of ultrasonic vibration uses the "cavitation" and "acoustic streaming" effects to clean the interface, prevent agglomeration, enhance wetting, make the repair agent fully wet and penetrate into the finest cracks, and prevent internal defects such as pores. The three synchronous synergistic effects, through the coupling effect of multiple physical fields, together ensure that the repair agent can quickly, directionally, deeply, and densely penetrate into the microscopic defects of the magnet, and achieve the directional arrangement of nano-soft magnetic particles, ultimately achieving the dual goals of repair and enhancement.

[0017] Electromagnetic field generating unit: composed of a capacitor discharge pulse power supply and a magnetic pole head. The magnetic pole head needs to be designed as hollow or water-cooled to withstand the nearby thermal environment.

[0018] Precise temperature control unit: uses non-contact heating methods such as infrared laser or focused infrared lamp. The light path can be designed to irradiate from the gap of the magnetic pole head to the workpiece surface, thereby realizing the synchronization of heating and applying magnetic field in space.

[0019] Ultrasonic vibration unit: the ultrasonic transducer is integrated on the sample table or magnetic pole head, so that the vibration energy is directly transmitted to the workpiece.

[0020] Integrated control system: a total controller is used to coordinate the start, parameter output, and timing of the three systems, ensuring that the three systems start and end simultaneously and maintain stable parameters during the entire processing period.

[0021] Further, in step S100, a pulse magnetic field is applied to locally saturate the magnet; a Hall sensor array is used to collect the three-dimensional distribution of the surface magnetic field; and a terahertz imaging system is used to scan the surface and subsurface area at a frequency of 1-4 THz.

[0022] Under the existing technical conditions, the intensity of the pulse magnetic field can be 3.0T-5.0T, and the pulse width can be 2ms-20ms, which is used to locally saturate the magnet. The entire detection process can be completed in a short time (3 minutes), without the need to disassemble the magnet or motor, meeting the efficiency requirements of industrial online detection. At the same time, two types of most critical performance degradation information (demagnetization) and structure (cracks, corrosion) are obtained, and a complete damage image is drawn. Not only can defects be found, but also their three-dimensional coordinates can be precisely located, the demagnetization rate can be quantified, and the size and depth of the cracks can be measured, providing an absolute basis for subsequent precise repair.

[0023] Early invisible cracks and corrosion that have not caused significant magnetic flux loss cannot be found by using pulse magnetic field alone. And it is difficult to quantify the severity of demagnetization and distinguish whether a defect is a crack or a non-magnetic inclusion by using terahertz imaging alone.

[0024] The present scheme generates a comprehensive damage map through data registration and fusion, thereby being able to determine whether a magnetic field anomaly is caused by structural damage below; accurately assess the actual impact of structural damage on magnetic performance; and make dual qualitative, positioning and quantitative judgments on defects in terms of function and structure.

[0025] Further, in step S100, the comprehensive damage map content includes demagnetization area distribution and demagnetization intensity, the position, size and depth of invisible cracks and corrosion pores below the surface within 200 μm, and the coordinate positioning of the damage area.

[0026] Further, in step S200, the repair agent paste includes the following components by weight: 60-85 parts of composite repair agent powder, 10-30 parts of terpineol, 2-5 parts of ethyl cellulose, 0.5-1.5 parts of phosphate ester dispersant (such as BYK-110), and 0.1-0.5 parts of silicone leveling agent (such as BYK-320).

[0027] The composite repair agent powder is obtained by compounding nano-sized Fe-Si-Al alloy powder and low-melting-point alloy powder at a mass ratio of 1:3-9.

[0028] The formulation adopts a very high functional phase content, much higher than that of conventional electronic pastes or thermal conductive paste, which ensures that there is sufficient material to fill defects and form a strengthening phase after repair, but this also brings great challenges of high viscosity, easy agglomeration and difficult construction. To solve this contradiction, the formulation introduces specific proportions of phosphate ester dispersant and silicone leveling agent: the dispersant can effectively adsorb on the surface of nano-powder, fundamentally preventing the agglomeration of high-activity nano-particles through steric hindrance or electrostatic repulsion, ensuring their uniform distribution in the system; the leveling agent significantly reduces the surface tension of the paste through a very low addition amount, so that it can better wet the substrate surface and level after coating, avoiding defects such as shrinkage holes, thereby realizing the unity of high solid content and good processability.

[0029] The composite repair agent powder is obtained by compounding nano-sized Fe-Si-Al soft magnetic powder and low-melting-point alloy powder at a mass ratio of 1:3-9, realizing the perfect fusion of function and process: the low-melting-point alloy acts as a "carrier" and "structural repair phase", which can flow and penetrate into micro defects after melting, realizing dense sealing; and the nano soft magnetic particles carried by it act as a "functional enhancement phase", which are arranged directionally under the action of subsequent pulse magnetic field, forming high magnetic permeability channels at grain boundaries, thereby upgrading the traditional passive repair to active performance gain.

[0030] The selection of the type and ratio of the organic carrier (terpineol and ethyl cellulose) not only provides suitable rheological properties during the process, but also completely volatilizes or pyrolyzes during the repair heating stage, leaving no residue and avoiding secondary damage to the magnet performance.

[0031] Further, the low melting point alloy is selected from Sn-Bi based alloy (CW-Sn42Bi58), Sn-In based alloy (In52Sn48) or In-Bi based alloy (In51.4Bi31.4Sn17.2) with a melting point of 60-200℃.

[0032] Further, the nanoscale Fe-Si-Al alloy powder is prepared by high-energy ball milling method: using micron-sized Fe-Si-Al alloy powder as raw material, high-speed ball milling for 20-80 hours under argon protection at a high ball-to-material ratio of 10-20:1, and adding 1-3wt% of anhydrous ethanol to obtain a nanometer powder with an average particle size in the range of 50-200nm.

[0033] Further, in step S200, the preparation method of the repair agent paste comprises the following steps:

[0034] Step 1: Add ethyl cellulose to terpineol, stir at 60-80℃ until completely dissolved to obtain a clear and transparent solution, and cool;

[0035] Step 2: Mix the composite repair agent powder with the dispersant uniformly and add it to the solution obtained in step 1, continue to stir until a uniform paste is formed;

[0036] Step 3: Grind the above paste into a fine and uniform paste, remove air bubbles under a vacuum degree of-0.095MPa or above for 3-5 minutes, filter through a 200-400 mesh screen to obtain the repair agent paste.

[0037] Firstly, a step-by-step preparation method is adopted, and a uniform organic carrier phase is formed by heating and dissolving, which provides a stable basic environment for the subsequent dispersion of the powder and avoids the problems of clumping and insolubility that may occur in direct mixing. Secondly, a pre-mixing step of dispersant is introduced, which makes the dispersant molecules preferentially coat the surface of the composite repair agent powder, thereby inhibiting the agglomeration tendency of nanoparticles due to high surface energy from the source. This is a key prerequisite for achieving high uniformity. Finally, a post-processing procedure combining high-shear grinding (such as three-roll milling) with vacuum degassing and precision filtration is adopted. High-shear grinding provides shear force far exceeding ordinary stirring, which can completely break up all soft and hard agglomerates, ensuring that each nanoparticle is fully wetted by the organic carrier, thereby forming a fine and uniform paste microstructure. The subsequent vacuum degassing effectively eliminates the gas involved in the process, preventing the formation of defects due to gas expansion during subsequent repair heating. The final filtration step ensures the purity and reliability of the paste, removing potential large particle impurities that may clog the dispensing equipment. The entire process chain is interconnected and synergistic, and the finally prepared paste has high solid content, excellent rheological properties (such as good thixotropy), long-term storage stability, and uniformity.

[0038] Further, in step S200, the heating temperature is 138-200℃; the gradient pulse magnetic field has a condition of 2.0-3.5T pulse magnetic field, a field strength gradient >50T / m, and a pulse frequency of 1-5Hz; and the ultrasonic vibration has a frequency of 20-40kHz and an amplitude of 1-5μm.

[0039] Further, in step S300, the cooling is performed in two steps: first, rapid cooling at a rate of 10-15℃ / s to 95-105℃, and then slow cooling to 20-30℃.

[0040] The purpose of the first rapid cooling (10-15℃ / s) is to make the molten low-melting-point alloy repair agent quickly cross the solidification point and achieve rapid solidification. This can effectively refine the solidification structure, prevent alloy component segregation, and ensure that the nano soft magnetic particles are quickly fixed at the preset grain boundary position, maintaining the directional arrangement structure imparted by the pulse magnetic field and laying the foundation for forming a continuous high magnetic permeability channel. The second slow cooling, from 95-105℃ to room temperature, can significantly reduce the thermal stress caused by the difference in thermal expansion coefficient between the repair area and the magnetic steel substrate, avoid the generation of micro-cracks in the brittle grain boundary region or the interior of the repair body, and thus ensure the structural integrity and long-term reliability of the repair area.

[0041] Further, in step S300, the aging treatment has a condition of 150-180℃ for 1-2 hours.

[0042] The role of aging treatment: promote interfacial diffusion and alloying, during the 1-2 hour holding process, further atomic interdiffusion will occur between the low melting point alloying elements (such as Sn, Bi, In) in the repair agent and the grain boundary phase (usually neodymium-rich phase) of the magnet steel matrix, which not only significantly enhances the metallurgical bonding strength of the repair agent / matrix interface and improves the bonding force, but also to a certain extent, modifies the original grain boundary phase and improves its stability. The temperature is lower than the sintering temperature of the main phase of the magnet, which will not damage its intrinsic magnetism, but it is sufficient to effectively eliminate the residual micro internal stress in the previous process steps (especially the quenching process), making the repaired magnet more stable in size. For the nanoscale soft magnetic Fe-Si-Al phase in the repair agent, this heat treatment process helps to stabilize its microstructure, optimize its magnetic properties, and ensure that the "high permeability channel" formed has persistent and stable performance.

[0043] Compared with the prior art, the beneficial effects of the present application are:

[0044] 1、The present application combines terahertz and magnetic field detection, which can not only quantitatively evaluate demagnetization, but also can detect invisible damage under the skin of 200μm, realize clear and accurate measurement. The multi-field coupling effect ensures that the repair agent can penetrate into the grain boundaries and the finest cracks, realize dense filling, and fundamentally block the damage propagation path. After repair, not only the magnetic flux density (Br) and coercive force (Hcj) of the magnet are restored, but also the magnetic flux recovery rate can reach 103%, and the effective permeability can be increased by 24%, and the crack repair depth is ≥175μm.

[0045] 2、The present application integrates online detection and repair, greatly shortens the maintenance time; local precise repair has small thermal influence on the magnet matrix, avoiding the performance degradation risk brought by overall heating; the repaired grain boundary phase has better mechanical strength and higher corrosion resistance, with a salt spray resistance time of ≥966h, improving the long-term reliability of the magnet in harsh working conditions; prolonging the service life of expensive low-heavy rare earth magnet steel, avoiding the high cost of replacing the whole machine, especially suitable for predictive maintenance of new energy vehicle drive motor, wind turbine and other large equipment. DETAILED DESCRIPTION

[0046] Example 1

[0047] The nanoscale Fe-Si-Al soft magnetic powder is prepared by high-energy ball milling method: using micron-sized Fe-Si-Al alloy powder (model: TITD-WFSA) as raw material, under argon protection, using a planetary ball mill with hard alloy balls as grinding medium, high-speed ball milling for 50 hours under high ball-to-material ratio (15:1), and adding 2wt% of process control agent anhydrous ethanol, finally obtaining nanometer powder with an average particle size in the range of 125nm.

[0048] Example 2

[0049] The nanoscale Fe-Si-Al soft magnetic powder is prepared by high-energy ball milling: micron-sized Fe-Si-Al alloy powder (model: TITD-WFSA) is used as raw material, a planetary ball mill is used under argon protection, hard alloy balls are used as grinding medium, high ball-to-material ratio (10:1) is used for high-speed ball milling for 20 hours, and 1wt% of process control agent anhydrous ethanol is added, and finally nanometer powder with an average particle size in the range of 50nm is obtained.

[0050] Example 3

[0051] The nanoscale Fe-Si-Al soft magnetic powder is prepared by high-energy ball milling: micron-sized Fe-Si-Al alloy powder (model: TITD-WFSA) is used as raw material, a planetary ball mill is used under argon protection, hard alloy balls are used as grinding medium, high ball-to-material ratio (20:1) is used for high-speed ball milling for 80 hours, and wt% of process control agent anhydrous ethanol is added, and finally nanometer powder with an average particle size in the range of 200nm is obtained.

[0052] Example 4

[0053] The repair agent paste comprises the following components: composite repair agent powder 680g, terpineol 200g, ethyl cellulose 35g, phosphate ester dispersant 10g, and silicone leveling agent 3g.

[0054] The composite repair agent powder is obtained by compounding nanoscale Fe-Si-Al alloy powder (prepared by the method of Example 1) and low-melting-point alloy powder in a mass ratio of 1:6.

[0055] The low-melting-point alloy is Sn-Bi-based alloy (CW-Sn42Bi58) with a melting point of 138℃.

[0056] The preparation method of the repair agent paste comprises the following steps:

[0057] Step 1: Add ethyl cellulose to terpineol, stir at 70℃ until completely dissolved to obtain a clear transparent solution, and cool;

[0058] Step 2: Mix the composite repair agent powder and the dispersant uniformly, and then add them to the solution obtained in Step 1, and continuously stir until a uniform paste is formed;

[0059] Step 3: Grind the above paste into a fine and uniform paste, remove air bubbles under a vacuum degree of -0.1MPa for 4 minutes, filter through a 300-mesh sieve, and obtain the repair agent paste.

[0060] Example 5

[0061] The repair agent paste comprises the following components: composite repair agent powder 600 g, terpineol 100 g, ethyl cellulose 20 g, phosphate ester dispersant 5 g, and silicone leveling agent 1 g.

[0062] The composite repair agent powder is obtained by compounding nano Fe-Si-Al alloy powder (prepared by the method of Example 1) and low-melting-point alloy powder at a mass ratio of 1:3.

[0063] The low-melting-point alloy is an In-Bi-based alloy (In51.4Bi31.4Sn17.2) with a melting point of 200℃.

[0064] The preparation method of the repair agent paste comprises the following steps:

[0065] Step 1: Add ethyl cellulose to terpineol, stir at 60℃ until completely dissolved to obtain a clear transparent solution, and cool;

[0066] Step 2: Mix the composite repair agent powder and the dispersant uniformly, and then add them to the solution obtained in Step 1, and continuously stir until a uniform paste is formed;

[0067] Step 3: Grind the paste to a fine and uniform paste, remove air bubbles under a vacuum degree of -0.098 MPa for 3 minutes, filter through a 200-mesh sieve, and obtain the repair agent paste.

[0068] Example 6

[0069] The repair agent paste comprises the following components: composite repair agent powder 600 g, terpineol 100 g, ethyl cellulose 20 g, phosphate ester dispersant 5 g, and silicone leveling agent 1 g.

[0070] The composite repair agent powder is obtained by compounding nano Fe-Si-Al alloy powder (prepared by the method of Example 1) and low-melting-point alloy powder at a mass ratio of 1:9.

[0071] The low-melting-point alloy is an In-Bi-based alloy (In51.4Bi31.4Sn17.2) with a melting point of 200℃.

[0072] The preparation method of the repair agent paste comprises the following steps:

[0073] Step 1: Add ethyl cellulose to terpineol, stir at 60℃ until completely dissolved to obtain a clear transparent solution, and cool;

[0074] Step 2: Mix the composite repair agent powder and the dispersant uniformly, and then add them to the solution obtained in Step 1, and continuously stir until a uniform paste is formed;

[0075] Step 3, grinding the paste to a fine and uniform paste, removing bubbles under a vacuum degree of -0.12 MPa for 5 minutes, filtering through a 400-mesh screen, to obtain the repair agent paste.

[0076] Comparative Example 1

[0077] In the formula, the composite repair agent powder is obtained by compounding the nanoscale Fe-Si-Al alloy powder (prepared by the method of Example 1) and the Sn-Bi-based alloy powder (CW-Sn42Bi58) at a mass ratio of 1:1. The remaining formula components, parameters, and preparation methods are the same as those of Example 4.

[0078] Comparative Example 2

[0079] In the formula, the composite repair agent powder is obtained by compounding the nanoscale Fe-Si-Al alloy powder (prepared by the method of Example 1) and the Sn-Bi-based alloy powder (CW-Sn42Bi58) at a mass ratio of 1:15. The remaining formula components, parameters, and preparation methods are the same as those of Example 4.

[0080] The performance parameters of the repair agent pastes prepared in Examples 4-6 and Comparative Examples 1-2 are shown in Table 1.

[0081] Table 1 Performance parameters of repair agent pastes prepared in Examples 4-6 and Comparative Examples 1-2

[0082]

[0083] As can be seen from Table 1, the repair agent pastes prepared in Examples 4-6 have a magnetic permeability improvement of up to 29%, a crack repair depth of up to 200 μm, a corrosion protection of up to 1030 h, and an interfacial bonding strength of ≥ 78%.

[0084] In Comparative Example 1, the excess nanometer powder is completely coated by the low-melting-point alloy, which is easily oxidized and agglomerated during the process, thereby blocking the penetration channels and resulting in a weak magnetic permeability improvement (10%) and a bonding strength (55 MPa).

[0085] In Comparative Example 2, the functional phase is insufficient to form a continuous magnetic permeability enhancement network, so the magnetic permeability improvement is weak (5%), and the performance enhancement effect is lost.

[0086] It is shown that the nanometer powder and the low-melting-point alloy are in a mass ratio range of 1:3-9, which ensures that there are sufficient nanometer particles to construct high-magnetic-permeability channels and ensures that there is sufficient low-melting-point alloy as a carrier to achieve good penetration and bonding.

[0087] Example 7

[0088] A magnetic permeability enhancement repair process for low-heavy-rare-earth magnetic steel, comprising the following steps:

[0089] S100, scanning the magnetic steel by using an online monitoring system, registering and fusing the collected data to generate a comprehensive damage map; the online monitoring system comprises a pulsed magnetic field unit, a Hall sensor array (model GDB-H-S64) and a terahertz imaging unit (model MICROXCAM-384I-THZ); local saturation magnetization of the magnet is performed by applying a pulsed magnetic field, the surface magnetic field distribution is collected by using the Hall sensor array to form distribution data; the surface and subsurface regions are scanned by using the terahertz imaging system at a frequency of 0.5 THz; the comprehensive damage map includes the demagnetization region distribution and demagnetization strength, the position, size and depth of the invisible cracks and corrosion pores below the surface to a depth of ≤200 μm, and the coordinate positioning of the damage region.

[0090] S200, after precisely coating the repair agent paste (prepared by the method of Example 4) on the damage region according to the damage map, simultaneously heating, applying a gradient pulsed magnetic field and ultrasonic vibration; the heating temperature is 170°C; the gradient pulsed magnetic field has a condition of a 2.8T pulsed magnetic field, a field strength gradient of 55T / m and a pulse frequency of 3Hz; the ultrasonic vibration has a frequency of 30kHz and an amplitude of 3μm.

[0091] S300, first rapidly cooling to 100°C at a rate of 12°C / s, and then slowly cooling to 25°C. After cooling, the excess repair agent is removed, and then aging treatment is performed: 165°C for 1.5 hours.

[0092] Example 8

[0093] A magnetic flux enhancement repair process for low heavy rare earth magnetic steel, comprising the following steps:

[0094] S100, scanning the magnetic steel by using an online monitoring system, registering and fusing the collected data to generate a comprehensive damage map; the online monitoring system comprises a pulsed magnetic field unit, a Hall sensor array (model GDB-H-S64) and a terahertz imaging unit (model MICROXCAM-384I-THZ); local saturation magnetization of the magnet is performed by applying a pulsed magnetic field, the surface magnetic field distribution is collected by using the Hall sensor array to form distribution data; the surface and subsurface regions are scanned by using the terahertz imaging system at a frequency of 0.1 THz; the comprehensive damage map includes the demagnetization region distribution and demagnetization strength, the position, size and depth of the invisible cracks and corrosion pores below the surface to a depth of ≤200 μm, and the coordinate positioning of the damage region.

[0095] S200, after precisely coating the repair agent paste (prepared by the method of Example 4) on the damage region according to the damage map, simultaneously heating, applying a gradient pulsed magnetic field and ultrasonic vibration; the heating temperature is 138°C; the gradient pulsed magnetic field has a condition of a 2.0T pulsed magnetic field, a field strength gradient of 50.1T / m and a pulse frequency of 1Hz; the ultrasonic vibration has a frequency of 20kHz and an amplitude of 1μm.

[0096] S300, first quench to 95℃ at a rate of 10℃ / s, then slow cooling to 30℃. After cooling, remove excess repair agent, and then perform aging treatment: 150℃ for 1 hour.

[0097] Example 9

[0098] A magnetic flux guide enhancement repair process for low heavy rare earth magnetic steel, comprising the following steps:

[0099] S100, using an online monitoring system to scan the magnetic steel, registering and fusing the collected data to generate a comprehensive damage map; the online monitoring system includes a pulsed magnetic field unit, a Hall sensor array (model GDB-H-S64), and a terahertz imaging unit (model MICROXCAM-384I-THZ); the pulsed magnetic field is applied to locally saturate the magnetization, and the Hall sensor array is used to collect the surface magnetic field distribution to form the distribution data; the surface and subsurface regions are scanned by the terahertz imaging system, with a frequency of 1.0 THz; the comprehensive damage map includes the demagnetization region distribution and demagnetization strength, the location, size, and depth of the hidden cracks and corrosion pores below the surface ≤200μm, and the coordinate positioning of the damage region.

[0100] S200, according to the damage map, precisely apply the repair agent paste (prepared by the method of Example 4) to the damage area, and simultaneously heat, apply a gradient pulsed magnetic field, and apply ultrasonic vibration; the heating temperature is 200℃; the gradient pulsed magnetic field conditions are: a 3.5T pulsed magnetic field, a field strength gradient of 60T / m, and a pulse frequency of 5Hz; the ultrasonic vibration frequency is 40kHz, and the amplitude is 5μm.

[0101] S300, first quench to 105℃ at a rate of 15℃ / s, then slow cooling to 30℃. After cooling, remove excess repair agent, and then perform aging treatment: 180℃ for 2 hours.

[0102] Comparative Example 3

[0103] In process step S200, no ultrasonic vibration is applied. The remaining process parameters are exactly the same as in Example 7.

[0104] Comparative Example 4

[0105] In process step S200, no gradient pulsed magnetic field is applied. The remaining process parameters are exactly the same as in Example 7.

[0106] Comparative Example 5

[0107] Step S200 is modified as follows: first heat and coat the repair agent and hold for 3 minutes; stop heating, and then apply the same pulsed magnetic field and ultrasonic vibration for 3 minutes. The remaining process parameters are exactly the same as in Example 7.

[0108] The performance parameters of the low heavy rare earth magnetic steel repaired by the repair process of application examples 7-9 and comparative examples 3-5 are shown in table 2.

[0109] Table 2 Performance parameters of the low heavy rare earth magnetic steel repaired by the repair process of application examples 7-9 and comparative examples 3-5

[0110]

[0111] Note: The test method of magnetic flux recovery rate is the ratio of the magnetic flux after repair to the original new product magnetic flux.

[0112] The test method of irreversible loss of magnetic flux after high temperature aging is the loss rate of magnetic flux after 1000 hours of 180℃ heat preservation.

[0113] From table 2, in examples 7-9, the magnetic flux recovery rate can reach 103%, the permeability is increased by ≥24%, the crack repair depth is ≥175μm, the interface bonding strength is ≥83MPa, the salt spray resistance time is ≥966h, and the irreversible loss of magnetic flux after high temperature aging is ≤3.7%.

[0114] In comparative example 3, lacking ultrasonic cleaning and assisted permeation, the repair agent penetration ability is greatly reduced, the crack repair depth (80μm) and bonding strength (55MPa) are significantly decreased, resulting in poor durability (400h of salt spray resistance) and aging resistance (loss of 8.2%).

[0115] In comparative example 4, lacking the directional driving of magnetic field, the nanoparticles cannot form a high magnetic permeability path, and the permeability is only increased by 3%, which is almost ineffective; the repair agent only penetrates by capillary action, and the repair depth is the shallowest (40μm).

[0116] In comparative example 5, the step-by-step process destroys the synchronization effect, and all indicators are far inferior to example 7 which is synchronously processed.

[0117] It is illustrated that the "thermal-magnetic-acoustic" three-field synchronous application of the present application is an indivisible technical whole.

Claims

1. A flux guide enhancement repair process for low heavy rare earth magnetic steels, characterized by, The method comprises the following steps: S100, scanning the magnetic steel by using an online monitoring system, registering and fusing the collected data, and generating a comprehensive damage map; S200, according to the damage map, accurately coating the repair agent paste in the damage area, and synchronously heating, applying a gradient pulse magnetic field and ultrasonic vibration; S300, after cooling, removing the excess repair agent, and then performing aging treatment; In step S100, the online monitoring system comprises a pulse magnetic field unit, a Hall sensor array and a terahertz imaging unit; In step S200, by weight, the repair agent paste comprises the following components: 60-85 parts of a composite repair agent powder, 10-30 parts of terpineol, 2-5 parts of ethyl cellulose, 0.5-1.5 parts of a phosphate ester dispersant and 0.1-0.5 parts of a silicone leveling agent; The composite repair agent powder is obtained by compounding a nano Fe-Si-Al alloy powder and a low-melting-point alloy powder at a mass ratio of 1:3-9; The low-melting-point alloy is selected from Sn-Bi-based alloy, Sn-In-based alloy or In-Bi-based alloy, and has a melting point of 60-200℃.

2. The repair process of claim 1, wherein, In step S100, a pulse magnetic field is applied to locally saturate the magnetization of the magnet, a Hall sensor array is used to collect the surface magnetic field distribution, and distribution data are formed; a terahertz imaging system is used to scan the surface and subsurface area, and the frequency is 0.1-1.0 THz.

3. The repair process of claim 1, wherein, In step S100, the comprehensive damage map includes the distribution and intensity of demagnetization, the location, size and depth of hidden cracks and corrosion pores below the surface to a depth of ≤200 μm, and the coordinate positioning of the damage area.

4. The repair process of claim 1, wherein, The nano Fe-Si-Al alloy powder is prepared by a high-energy ball milling method: using a micron Fe-Si-Al alloy powder as a raw material, high-speed ball milling for 20-80 hours under argon protection at a high ball-to-material ratio of 10-20:1, and adding 1-3 wt% of anhydrous ethanol to obtain a nano powder with an average particle size in the range of 50-200 nm.

5. The repair process of claim 1, wherein, In step S200, the preparation method of the repair agent paste comprises the following steps: Step 1, adding ethyl cellulose to terpineol, stirring at 60-80℃ until complete dissolution to obtain a clear and transparent solution, and cooling; Step 2, uniformly mixing the composite repair agent powder and the dispersant, and then adding them to the solution obtained in step 1, and continuously stirring until a uniform paste is formed; Step 3, grinding the paste to a fine and uniform paste, removing air bubbles under a vacuum degree of-0.095 MPa or above for 3-5 minutes, and filtering through a 200-400 mesh screen to obtain the repair agent paste.

6. The repair process of claim 1, wherein, In step S200, the heating temperature is 138-200℃; the gradient pulse magnetic field has a condition of a 2.0-3.5 T pulse magnetic field, a field strength gradient of >50 T / m and a pulse frequency of 1-5 Hz; the ultrasonic vibration has a frequency of 20-40 kHz and an amplitude of 1-5 μm.

7. The repair process of claim 1, wherein, In step S300, the cooling is performed by a two-step method: first, rapidly cooling at a rate of 10-15℃ / s to 95-105℃, and then slowly cooling to 20-30℃.

8. The repair process of claim 1, wherein, In step S300, the aging treatment has a condition of being heated at 150-180℃ for 1-2 hours.

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