Preparation method of NdFeB magnet with high coercivity

[0027] Example 1:

[0028] 1) Preparation of sintered magnet: the weight ratio of neodymium, praseodymium, dysprosium, terbium, electrolytic iron, cobalt, copper, gallium, aluminum, zirconium, and boron: Nd-23.8%, Pr-5%, Dy-0.6%, Tb -0.4%, Co-0.5%, Cu-0.13%, Ga-0.1%, Al-0.1%, Zr-0.12%, B-1% ratio, the balance is iron and unavoidable impurities, in an inert gas environment The pouring is completed in the lower vacuum melting furnace, the pouring temperature is 1450℃, the quench roll speed is 60r/min, and the quench roll is filled with cooling water. The thickness of the obtained flakes is about 0.36mm; then, the flakes are made by HD powdering and jet milling. Magnetic powder with an average particle size of 3.4μm; Oriented compaction at room temperature and a magnetic field intensity of 2T orientation field to form a compact; Put the compact into a sintering furnace in an Ar atmosphere and sinter at 1100°C for 5 hours to obtain a green compact. The green body is aged for 5 hours at 500°C to obtain a sintered body. The sintered blank is processed into a magnet with a size of 40mm*20mm*4mm by machining, and after degreasing, pickling, activation, and deionized water washing, it is dried, and it is recorded as A0.

[0029] 2) The 2.4 μm terbium fluoride powder and ethanol are made into a uniformly mixed slurry in a weight ratio of 2:3. The spray method covers the surface of the treated sintered magnet A0, the thickness of the slurry is 100μm, and then it is dried in an argon atmosphere at 100°C, then sintered at 920°C for 16 hours, and aged at 580°C for 2 hours for grain boundary Diffusion treatment, denoted as A1.

[0030] 3) Prepare a uniform mixed slurry with 2.4 μm metal Tb powder, 1.3.5-trichlorotoluene, and organic solvent ethanol in a weight ratio of 4:1:5, where Tb powder is a mixture of metal Tb and terbium hydride The mass fraction of powder and metal Tb is 99%. The spray method covers the surface of the treated sintered magnet A0, the thickness of the slurry is 100μm, and then it is dried in an argon atmosphere at 100°C, then sintered at 920°C for 16 hours, and aged at 580°C for 2 hours for grain boundary Diffusion treatment, denoted as A2.

[0031] 4) The 2.4 μm metal Tb powder, the anti-oxidant m-trifluorotoluene, the binder butyral, and the organic solvent ethanol are prepared according to the weight ratio of 4:1:1:4 to prepare a uniform mixed slurry. The spray method covers the surface of the treated sintered magnet A0, the thickness of the slurry is 100μm, and then it is dried in an argon atmosphere at 100°C, then sintered at 920°C for 16 hours, and aged at 580°C for 2 hours for grain boundary Diffusion treatment, denoted as A3.

[0032] Take magnets A1, A2, and A3, respectively, mechanically grind off the surface of the magnet with a thickness of 50μm and 100μm, and use XRF (X-ray fluorescence spectroscopy) to test the fluorine content on the surface of the magnet. A1, the fluorine content on the surface of the magnet is 1.8%, and the A3 containing fluorine-containing antioxidant and binder is added, and the fluorine content on the surface of the magnet is 0.8%; the fluorine content of the magnets A2 and A3 with 100μm removed is almost undetectable, but adding The A1 of terbium fluoride has a fluorine content of 1.4% on the surface of the magnet. This is because the fluorine and Tb in the terbium fluoride in A1 diffuse into the magnet at the same time. After the surface of the product is 100μm away, the fluorine content on the surface of the magnet can still be detected by XRF; and the fluorine-containing antioxidant is added for bonding The fluorine element of A3 is derived from antioxidant. When dried at 100°C, the binder evaporates, while the antioxidant remains on the surface of the magnet, but it can volatilize completely during the sintering process. Therefore, after the magnet skin treatment, use XRF The F content can hardly be measured.

[0033] The magnetic properties of the A0, A1, A2, and A3 magnets and the XRF test results of the fluorine content of the A1, A2, and A3 magnets after the surface layer is ground off are shown in Table 1:

[0034] Table 1 Comparison of magnetic properties of A1, A2, A3 and A0

[0035] project

[0036] From the data in Table 1, we can see that A1 magnet: using a mixed slurry of terbium fluoride and organic solvent ethanol, its coercivity rises from 15.02kOe of A0 to 24.37kOe, and after XRF detection, the surface of A1 magnet The content of F is much higher because the diffusion of terbium fluoride is relatively pure metal Tb. Not only can the heavy rare earth element terbium diffuse to the grain boundary of the magnet, but also the fluorine element will diffuse into the magnet at the same time as the terbium, thus affecting the weight The diffusion effect of the rare earth element terbium has an impact on the increase of the coercive force of the magnet. The coercive force of the A1 magnet is increased by about 9.3kOe; A2: using metal Tb powder, 1,3,5-trichlorotoluene, and organic solvent ethanol The coercivity of the mixed slurry increased from 15.02kOe of A0 to 25.49kOe, and the coercive force increased significantly, exceeding 10kOe, while the remanence of A0 to A2 was from 14.36kGs to 14.14kGs, and there was no significant decrease ; A3: Using a mixed slurry of metal Tb powder, m-difluorotoluene, butyral, and organic solvent ethanol, the coercive force increased from 15.02kOe of A0 to 26.58kOe, the coercive force increased the most, exceeding 11.5kOe, In terms of remanence, A0 to A3 range from 14.36kGs to 14.13kGs, and there is no significant reduction; as we all know, the use of pure metal diffusion process, the metal is easy to oxidize, so it is usually replaced by metal fluoride that is not easily oxidized and has low cost. The above-mentioned experimental results prove that the fluorine in the fluoride will diffuse into the magnet at the same time as the heavy rare earth metals, which will also affect the performance of the magnet.

[0037] The above A1, A2, and A3 magnets were subjected to a corrosion resistance test for 4 days PCT. The test results are shown in Table 2.

[0038] Table 2 Comparison of A1, A2, A3 magnets with 4 days PCT

[0039]

[0040] It can be seen from the test results in Table 2 that the corrosion resistance of A3 products is the best. This is because A3 products use fluorine-containing antioxidants as antioxidants to prevent oxidation of Tb powder, while A2 products use chlorine-containing antioxidants. Antioxidant, chlorine ion easily reacts electrochemically with neodymium in the magnet, causing the magnet to corrode and pulverize. The fluorine-containing antioxidant has high chemical stability and does not react electrochemically with neodymium and will not cause corrosion of the magnet. It is lighter in weight, easy to volatilize, and does not stay on the surface of the magnet, thereby affecting the surface characteristics of the magnet.

[0041] Example 2:

[0042] 1) The weight ratio of neodymium, dysprosium, terbium, cobalt, copper, aluminum and boron: Nd-30.1%, Dy-0.5%, Co-0.8%, Cu-0.13%, Al-0.2%, B-1% Proportion, the balance is Fe and unavoidable impurities. The pouring is completed in a vacuum melting furnace under an inert gas environment, the pouring temperature is 1450℃, the quenching roller speed is 65r/min, and cooling water is passed through the quenching roller. The thickness of the obtained scale is about 0.32mm; Then, the scales are powdered by HD and jet milled to produce magnetic powder with an average particle size of 3.2μm; Orientation is pressed under an environment with a 2T orientation field at room temperature and a magnetic field strength to form a compact; In a sintering furnace under Ar atmosphere, sintered at 1060°C for 6 hours to obtain a green compact, and the green compact was aged at 510°C for 4 hours to obtain a sintered compact. Machining the sintered blank into a magnet with a size of 40mm*20mm*4mm by machining, and after degreasing, pickling, activation and deionized water washing, and drying, it is recorded as B0;

[0043] 2) Prepare a uniform mixed slurry with 2.0 μm DyF powder and organic solvent acetone in a weight ratio of 3:2. The coating method covers the surface of the treated sintered magnet B0, the thickness of the slurry is 50μm, and then it is dried at 80°C in an argon atmosphere, then sintered at 800°C for 8 hours, and aged at 520°C for 4 hours to crystallize The boundary diffusion treatment is denoted as B1.

[0044] 3) Prepare a homogeneous mixed slurry with 2.0 μm metal Dy powder, 1.3.5-trichlorotoluene, and organic solvent acetone in a weight ratio of 3:1:1. The coating method covers the surface of the treated sintered magnet B0, the thickness of the slurry is 50μm, and then it is dried at 80°C in an argon atmosphere, then sintered at 800°C for 8 hours, and aged at 520°C for 4 hours to crystallize The boundary diffusion treatment is denoted as B2.

[0045] 4) Prepare a homogeneous mixed slurry with 2.0 μm metal Dy powder, o-fluorotoluene, polyethylene, and organic solvent acetone in a weight ratio of 30:10:1:9. The coating method covers the surface of the treated sintered magnet B0, the thickness of the slurry is 50μm, and then it is dried at 80°C in an argon atmosphere, then sintered at 800°C for 8 hours, and aged at 520°C for 4 hours to crystallize The boundary diffusion treatment is denoted as B3.

[0046] Take magnets B1, B2, and B3, respectively, mechanically grind off the surface of the magnet with thickness of 50μm and 100μm, and use XRF (X-ray fluorescence spectroscopy) to test the fluorine content on the surface of the magnet. The magnet B2 with 50μm removed is almost undetectable Fluorine content, B1 with dysprosium fluoride added, the fluorine content on the magnet surface is 1.4%, and the fluorine-containing antioxidant B3 is added, and the fluorine content on the magnet surface is 0.2%; fluorine is almost undetectable on the magnets B2 and B3 with 100μm removed The fluorine content on the surface of the magnet is 1.1% with B1 added with dysprosium fluoride. This is because the fluorine and dysprosium of dysprosium fluoride in the B1 magnet diffuse into the inside of the magnet at the same time. After the surface of the product is polished to 100μm, the fluorine content of the magnet surface can still be detected by XRF; and fluorine-containing antioxidant and binder are added B3, the fluorine element comes from the antioxidant. When dried at 80℃, the binder evaporates, but the antioxidant remains on the surface of the magnet, and can be completely volatilized during the sintering process, because after the magnet skin treatment, it is almost measured by XRF The F content is not shown.

[0047] The magnetic properties of the B0, B1, B2, and B3 magnets and the XRF test results of the fluorine content of the B1, B2, and B3 magnets after the surface layer is ground off are shown in Table 3:

[0048] Table 3 Comparison of magnetic properties of B1, B2, B3 and B0

[0049] project

[0050] From the data in Table 3, it can be seen that B1: Using a mixed slurry of terbium fluoride and organic solvent acetone, the coercivity increased from 14.31kOe to 20.28kOe. After XRF detection, the F content on the surface of the B1 magnet is higher. Because fluoride diffusion is better than pure metal diffusion, not only the heavy rare earth element terbium can diffuse into the grain boundary of the magnet, but also the fluorine element will diffuse into the magnet together with terbium, thus affecting the diffusion effect of the heavy rare earth terbium, and then the magnet The increase in coercivity has an impact, so the coercivity increase of B1 magnet is about 6kOe; B2: using pure metal Dy, 1,3,5-trichlorotoluene, organic solvent acetone mixed slurry, coercivity from 14.31 When kOe rises to 20.94kOe, the coercive force increases greatly, while the remanence B0 to B2 is from 13.8kGs to 13.66kGs, and there is no obvious decrease. B3: Using a mixed slurry of metal Dy powder, o-fluorotoluene, polyethylene, and organic solvents, the coercivity rises from 14.31kOe to 21.75kOe, with the largest increase in coercivity, about 7.5kOe, and the remanence B0 to B3 are There is no significant decrease from 13.8kGs to 13.64kGs.

[0051] The above-mentioned B1, B2, and B3 magnets were subjected to the corrosion resistance test for 4 days PCT. The test results are shown in Table 4:

[0052] Table 4 4-day PCT comparison of magnets B1, B2, and B3

[0053]

[0054] It can be seen from the test results in Table 4 that the B3 product has the best corrosion resistance. This is because the B3 product uses a fluorine-containing antioxidant as an antioxidant to prevent the oxidation of metal Dy powder, while the B2 product’s antioxidant uses chlorine The anti-oxidant, the chlorine ion easily reacts with the neodymium in the magnet, causing the magnet to corrode and pulverize. The fluorine-containing anti-oxidant has high chemical stability, does not electrochemically react with neodymium, and does not cause the magnet to corrode.

[0055] Example 3:

[0056] 1) The weight ratio of neodymium, dysprosium, terbium, cobalt, copper, aluminum and boron: Nd-30.5%, Tb-0.5%, Co-1.1%, Cu-0.16%, Al-0.4%, B-1.02% Proportion, the balance is Fe and unavoidable impurities. The pouring is completed in a vacuum melting furnace under an inert gas environment, the pouring temperature is 1460℃, the quenching roll speed is 70r/min, and cooling water is passed through the quenching roll. The thickness of the obtained scale is about 0.3mm; then the scales are made into magnetic powder with an average particle size of 3.0μm through HD powdering and jet milling; they are oriented and pressed in an environment with a 2T orientation field at room temperature and a magnetic field strength to form compacts; and then aging at 530℃ , The aging time is 4.0h, and the sintered blank is obtained. The sintered blank is processed into a magnet with a size of 40mm*20mm*4mm by machining, and after degreasing, pickling, activation, and deionized water washing, the magnet is dried, and it is recorded as C0.

[0057] 2) Mixing powder of 3.2 μm dysprosium fluoride and terbium fluoride (wherein the weight ratio of dysprosium fluoride is 40%) and organic solvent benzaldehyde in a weight ratio of 4:1 to prepare a uniform mixed slurry. The dipping method covers the surface of the treated sintered magnet C0, the thickness of the slurry is 20μm, and then it is dried in an argon atmosphere at 60°C, sintered at 960°C for 6 hours, and then aged at 460°C for 6 hours for grain boundary Diffusion treatment, denoted as C1.

[0058] 3) Mixing powder composed of 3.2μm metal Dy powder and metal Tb powder (the weight ratio of metal Dy powder is 40%), p-fluorotoluene, polyethylene, organic solvent benzaldehyde, according to the weight ratio of 16:1:1 : The ratio of 2 makes a uniform mixed slurry. The dipping method covers the surface of the treated sintered magnet C0, the thickness of the slurry is 20μm, and then it is dried in an argon atmosphere at 60°C, sintered at 960°C for 6 hours, and then aged at 460°C for 6 hours for grain boundary Diffusion treatment, denoted as C2.

[0059] Take the C1 and C2 magnets respectively, mechanically grind the surface of the magnet with thickness of 50μm and 100μm, and use XRF (X-ray fluorescence spectroscopy) to test the fluorine content on the surface of the magnet. The 50μm C1 magnet is ground away. The fluorine content on the surface of the magnet is 2.11%, a 100μm C1 magnet is ground away, and the fluorine content on the surface of the magnet is 0.9%. This is because the fluorine in the terbium fluoride in C1 and Dy/Tb diffuse into the inside of the magnet at the same time. After the surface of the product is polished to 100μm, the fluorine content on the surface of the magnet can still be detected by XRF; and the addition of fluorine-containing antioxidant and adhesion The C2 and fluorine elements of the binder come from antioxidants, which can be almost completely volatilized during the sintering process. After the magnet skin is treated, the F content can hardly be measured by XRF.

[0060] The magnetic properties of the C0, C1, and C2 magnets and the XRF test results of the fluorine content of the C1, C2 magnets after the surface layer is ground off are shown in Table 5:

[0061] Table 5 Comparison of magnetic properties of C1, C2 and C0

[0062] project

[0063] From the data in Table 5, it can be seen that the product C2 using the mixed slurry containing metal powder, antioxidant, binder, and organic solvent is better than the product C1 made directly using the fluoride and organic solvent mixed slurry. The coercivity increases more rapidly, but the remanence is not significantly reduced, and the product performance is better.

[0064] The above C1 and C2 magnets were subjected to the corrosion resistance test for 4 days PCT, and the test results are shown in Table 6.

[0065] Table 6 Comparison of C1 and C2 magnets with 4 days PCT

[0066]

[0067] It can be seen from the test results in Table 6 that the C2 product has the best corrosion resistance.