Preparation method of multifunctional protective coating of 2 / 17 type samarium-cobalt permanent magnet material

Abstract

The invention discloses a preparation method of a multifunctional protective coating of a 2: 17 type samarium-cobalt permanent magnet material, and belongs to the field of rare earth permanent magnet materials. The method comprises the following steps: step 1, preparing permeation source powder; step 2, carrying out embedding infiltration treatment; and step 3, aging heat treatment. The invention develops the magnet which is small in magnetic property loss and is provided with a protective layer with good hydrogen resistance, corrosion resistance and oxidation resistance on the surface; the microstructure of the protective layer sequentially comprises an exosmosis layer, a transition layer and a base body from outside to inside, the exosmosis layer is mainly a solid solution formed among Cr, Co and Fe, and the transition layer is mainly formed due to diffusion of elements in the base body. The magnetic performance of the magnet with the protective layer is basically not reduced after the magnet is oxidized for 200 hours in air at the temperature of 450 DEG C, the surface of the magnet is not broken after the magnet is kept for 20 hours in a hydrogen environment at the temperature of 150 DEG C and the pressure of 0.3 MPa, and the surface of the magnet is not obviously changed after the magnet is soaked in a 3.5 wt% NaCl solution at the temperature of 25 DEG C for one week.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials, specifically relating to a method for preparing a multifunctional protective coating for 2:17 type samarium cobalt permanent magnet materials. More specifically, by heating, active Cr atoms are attached to the magnet surface, and mutual diffusion occurs between them and Co and Fe atoms in the matrix to obtain a protective coating mainly composed of Cr-Co-Fe solid solution. This significantly improves the ability of samarium cobalt magnets to operate stably for extended periods in oxygen-containing atmospheres. Simultaneously, samarium cobalt permanent magnets with this protective layer exhibit significantly higher stability in hydrogen-containing atmospheres than uncoated magnets, showing no significant surface corrosion after immersion in a 3.5wt% NaCl solution for 168 hours. Background Technology

[0002] At present, high-performance samarium cobalt permanent magnet materials are required for long-term operation under high temperature conditions above 450°C, as well as for magnetic levitation bearings for multi-electric aircraft engines, special high-temperature motors, and electric propulsion systems for spacecraft.

[0003] However, samarium cobalt permanent magnets currently exhibit severe oxidation when used in environments above 400°C. Prolonged surface oxidation leads to significant loss of their magnetic properties, affecting normal operation.

[0004] Currently, the common anti-oxidation method for samarium cobalt permanent magnet materials is to electroplate nickel on the surface. The electroplating solution used in this technology causes serious environmental pollution, and it is difficult to achieve uniform electroplating on the surface of large permanent magnets. In addition, the electroplated coating is physically bonded to the substrate, and the bonding force is weak, so the coating is prone to peeling off during use. The embedding and infiltration method can prepare an infiltration layer with a relatively uniform thickness on the surface of the permanent magnet.

[0005] Samarium cobalt permanent magnets are prone to hydrogen absorption and breakage in environments with high hydrogen content. In humid environments, especially those related to marine environments, they may also undergo electrochemical reactions with various ions, affecting normal use. At room temperature, Cr2O3 has extremely low hydrogen permeability, and the Cr2O3 film has high density and a certain resistance to ions in the environment. Summary of the Invention

[0006] This invention proposes a method for preparing a multifunctional protective coating for 2:17 samarium cobalt permanent magnet materials. The method achieves a uniformly distributed multifunctional protective layer through interdiffusion between chromium and matrix elements, resulting in minimal loss of magnetic properties in the permanent magnet itself. The microstructure of the prepared protective layer, from the outside in, consists of an external diffusion layer (6–10 μm), a (3–5 μm) transition layer, and the matrix, with the external diffusion layer primarily being a Cr-Co-Fe solid solution. 2:17 samarium cobalt permanent magnets with this protective layer exhibit excellent oxidation resistance and hydrogen erosion resistance, and also demonstrate good corrosion resistance after prolonged immersion in a 3.5% wt NaCl solution.

[0007] The present invention adopts the following technical solution:

[0008] A method for preparing a multifunctional protective coating for 2:17 type samarium cobalt permanent magnet materials includes the following steps:

[0009] Step 1: Prepare the infiltration source powder:

[0010] The components of the infiltration powder are made from the following raw materials by weight percentage: 25-45 wt% chromium powder as infiltration agent, 8-15 wt% ammonium chloride powder as catalyst, and the remainder as dispersant. Grind the infiltration powder in a mortar for 20-30 minutes to mix it evenly and set aside for use.

[0011] Step 2, Samarium-Cobalt Magnet Pretreatment:

[0012] The surface of the samarium cobalt magnet is polished step by step with sandpaper, then ultrasonically treated for 25-30 minutes to clean the surface, and then dried for later use.

[0013] Step 3, chromizing heat treatment:

[0014] Place the samarium cobalt magnet obtained in step two into the middle of the crucible, fill and compact the surrounding area with the embedding and infiltration reagent prepared in step one, then cover and seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace.

[0015] In an argon atmosphere, set the heating rate to 10–13 °C / min and begin heating. When the temperature reaches 780–850 °C, hold the temperature for 2–8 hours. Then cool the sample in air. Once the temperature drops to room temperature, remove the sample, ultrasonically clean it in alcohol for 25–30 minutes, and then dry it to obtain a chromium-impregnated magnet with a multifunctional protective layer on its surface.

[0016] Step 4, Aging Heat Treatment:

[0017] The chromium-impregnated magnet with a multifunctional protective layer on its surface, obtained in step three, is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10-12℃ / min, starting from room temperature. When the temperature rises to 800-830℃, it is held for 15-24 hours. Then, it is slowly cooled to 350-450℃ at a rate of 0.5-1.0℃ / min. After holding for 10-12 hours, it is quenched and cooled to room temperature before being removed, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface.

[0018] Preferably, in step one, the dispersant is one or more of the following: alumina, silicon dioxide, magnesium oxide, and calcium oxide powder.

[0019] Preferably, in step two, the samarium cobalt magnet is polished step by step with SiC sandpaper of 400#, 800#, 1000#, 1500# and 2000#, ultrasonically treated in alcohol for 25 to 30 minutes, and then dried.

[0020] Preferably, in step three, the chromium-impregnated magnet with a multifunctional protective layer on its surface has a total surface protective layer thickness of 6–15 μm.

[0021] Preferably, in step three, the chromium-diffused magnet with a multifunctional protective layer on its surface has a microstructure of the protective layer consisting of an external diffusion layer (6-10 μm), a (3-5 μm) transition layer, and a matrix, from the outside to the inside, wherein the external diffusion layer is mainly a Cr-Co-Fe solid solution.

[0022] Preferably, in step three, the chromium-impregnated magnet with a multifunctional protective layer on its surface has a critical load of 13-20 N when tested with a micron scratch tester.

[0023] Preferably, in step four, the rate control accuracy of the slow cooling is ±0.05℃ / min.

[0024] Preferably, in step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface, after being oxidized at 450°C for 200 hours, has a room temperature remanence loss of less than 0.03 kGs, a room temperature magnetic energy product loss of less than 0.1 MGOe, a high temperature (450°C) remanence loss of less than 0.03 kGs, and a high temperature (450°C) magnetic energy product loss of less than 0.08 MGOe.

[0025] Preferably, in step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface has a mass gain of 0.02–0.08 mg / cm³ per unit surface area after oxidation at 450°C for 200 hours. 2 .

[0026] Beneficial effects:

[0027] The advantages of this invention compared to the prior art are:

[0028] (1) Samarium cobalt magnets with this multifunctional protective layer have better stability in hydrogen environment than uncoated magnets.

[0029] (2) Samarium cobalt magnets with this multifunctional protective layer have better corrosion resistance in 3.5%wt NaCl solution compared to uncoated magnets.

[0030] (3) By heating, the transition element Cr is transformed into active atoms and deposited on the surface of the magnet. A protective layer containing Cr solid solution is generated through the diffusion and chemical reaction of Cr atoms with elements in the matrix. The protective layer has a high bonding force with the matrix.

[0031] (4) The protective layer obtained includes an external diffusion layer (6-10 μm) and a (3-5 μm) transition layer. There is no internal influence zone, resulting in less loss of magnetic properties of the magnet.

[0032] (5) The protective layer obtained is mainly a Cr-Co-Fe solid solution, rather than an intermetallic compound. This protective layer has good high-temperature oxidation resistance. Attached Figure Description

[0033] Figure 1 This is a cross-sectional SEM image of a 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 1;

[0034] Figure 2 Images of the surface of a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer and an uncoated magnet prepared in Example 1 before and after being kept in a hydrogen environment at 150°C and 0.3MPa for 20 hours;

[0035] Figure 3 These are surface photographs of a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer prepared in Example 1 and an uncoated magnet before and after corrosion in a 3.5wt% NaCl solution at 25°C for 168 hours.

[0036] Figure 4 The oxidation weight gain curve of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on the surface prepared in Example 1 after oxidation at 450°C for 200 hours;

[0037] Figure 5 The magnetic performance curves of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on the surface prepared in Example 1 before and after oxidation at 450°C for 200h at room temperature and high temperature are shown.

[0038] Figure 6 The 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 1, was subjected to bonding force testing using a micron scratch tester to obtain microscopic observation morphology, friction force changes, and acoustic emission signal maps. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0040] This invention proposes a method for preparing a multifunctional protective coating for 2:17 samarium cobalt permanent magnet materials, resulting in a protective layer with uniform thickness and minimal loss of magnetic properties in the magnet itself. The microstructure of the prepared protective layer, from the outside in, consists of a 6-10 μm infiltration layer, a 3-5 μm transition layer, and a substrate, wherein the infiltration layer is mainly a Cr-Co-Fe solid solution. The final product is a 2:17 samarium cobalt permanent magnet with excellent oxidation resistance and magnetic properties.

[0041] This invention relates to a method for preparing a multifunctional protective coating for 2:17 type samarium cobalt permanent magnet materials, comprising the following steps:

[0042] Step 1: Prepare the infiltration source powder:

[0043] The components of the infiltration powder are made from the following raw materials by weight percentage: 25-45 wt% chromium powder as infiltration agent, 8-15 wt% ammonium chloride powder as catalyst, and the remainder as dispersant. Grind the infiltration powder in a mortar for 20-30 minutes to mix it evenly and set aside for use.

[0044] Step 2, Samarium-Cobalt Magnet Pretreatment:

[0045] The surface of the samarium cobalt magnet is polished step by step with sandpaper, then ultrasonically treated for 25-30 minutes to clean the surface, and then dried for later use.

[0046] Step 3, chromizing heat treatment:

[0047] Place the samarium cobalt magnet obtained in step two into the middle of the crucible, fill and compact the surrounding area with the embedding and infiltration reagent prepared in step one, then cover and seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace.

[0048] In an argon atmosphere, set the heating rate to 10–13 °C / min and begin heating. When the temperature reaches 780–850 °C, hold the temperature for 2–8 hours. Then cool the sample in air. Once the temperature drops to room temperature, remove the sample, ultrasonically clean it in alcohol for 25–30 minutes, and then dry it. This yields a chromium-impregnated magnet with a multifunctional protective layer on its surface.

[0049] Step 4, Aging Heat Treatment:

[0050] The chromium-impregnated magnet with a multifunctional protective layer on its surface, obtained in step three, is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10-12℃ / min, starting from room temperature. When the temperature rises to 800-830℃, it is held for 15-24 hours. Then, it is slowly cooled to 350-450℃ at a rate of 0.5-1.0℃ / min. After holding for 10-12 hours, it is quenched and cooled to room temperature before being removed, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface.

[0051] In this invention, the chromizing heat treatment temperature is between 750-850℃, and the holding time is between 2-8 hours. The thickness of the final protective layer is controlled by changing the temperature and holding time.

[0052] Example 1:

[0053] The selected 2:17 type samarium cobalt permanent magnet has the composition Sm(Co) 0.73 Fe 0.16 Cu 0.08 Zr 0.03 ) 7.74 The chromizing heat treatment temperature is 800℃ and the holding time is 3h.

[0054] Step 1: Prepare the infiltration source powder:

[0055] The components of the infiltration powder are made from the following raw materials by weight percentage: 30 wt% chromium powder as infiltration agent, 8 wt% ammonium chloride powder as catalyst, and the remainder being 10 wt% silica powder and 52 wt% alumina powder. The infiltration powder is ground in a mortar for 25 minutes and mixed evenly for later use.

[0056] Step 2, Samarium-Cobalt Magnet Pretreatment:

[0057] The samarium cobalt magnet was polished with SiC sandpaper of grades 400#, 800#, 1000#, 1500#, and 2000# in turn. It was then ultrasonically treated in alcohol for 25 minutes, dried, and ready for use.

[0058] Step 3, chromizing heat treatment:

[0059] Place the samarium cobalt magnet obtained in step two into the middle of the crucible, fill and compact the surrounding area with the embedding and infiltration reagent prepared in step one, then cover and seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace.

[0060] In an argon atmosphere, the heating rate was set to 12℃ / min, and heating was started. When the temperature reached 800℃, it was held for 3 hours. Then it was cooled in air. After the temperature dropped to room temperature, the sample was taken out, ultrasonically cleaned in alcohol for 25 minutes, and dried to obtain a chromium-impregnated magnet with a multifunctional protective layer on the surface.

[0061] Step 4, Aging Heat Treatment:

[0062] The chromium-impregnated magnet with a multifunctional protective layer on its surface, obtained in step three, is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10℃ / min, and heating begins from room temperature. When the temperature rises to 815℃, it is held for 24 hours. Then, it is slowly cooled to 400℃ at a rate of 0.5℃ / min. After holding at this temperature for 12 hours, it is quenched and cooled to room temperature before being removed, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface.

[0063] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer prepared in Example 1 was characterized by SEM analysis, such as... Figure 1 As shown, the surface microstructure of the permanent magnet consists of three layers from the outside in: an external diffusion layer, a transition layer, and a substrate. The total thickness of the protective layer is approximately 9 μm, with the external diffusion layer being approximately 6 μm thick and the transition layer approximately 3 μm thick. The external diffusion layer is mainly composed of a Cr-Co-Fe solid solution.

[0064] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 1, showed a mass gain of 0.027 mg / cm³ per unit surface area after oxidation at 450°C for 200 h. 2 .

[0065] The magnetic properties of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on the surface prepared in Example 1, and the uncoated magnet were tested at room temperature and at a high temperature of 450°C, as shown in the curves. Figure 5 As shown, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective coating has a remanence of 9.68 kGs at room temperature and a maximum energy product of 21.18 MGOe. At high temperature (450℃), the remanence is 7.87 kGs and the maximum energy product is 12.80 MGOe. The uncoated magnet has a remanence of 9.85 kGs at room temperature and a maximum energy product of 22.75 MGOe. At high temperature (450℃), the remanence is 7.99 kGs and the maximum energy product is 13.79 MGOe.

[0066] The 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 1, and the uncoated magnet were placed in a hydrogen environment at 150°C and 0.3 MPa for 20 hours. Figure 2 As shown, the uncoated magnets were severely broken, while the 2:17 type samarium cobalt permanent magnets with a protective coating on their surface did not break.

[0067] The 2:17 type samarium cobalt permanent magnet with a protective surface layer prepared in Example 1 and the uncoated magnet were immersed in a 3.5wt% NaCl solution at 25°C for one week. Figure 3 As shown, the surface of the uncoated magnet, especially at the corners, is severely corroded, while the surface of the 2:17 type samarium cobalt permanent magnet with a protective layer is basically uncorroded.

[0068] The magnetic property changes of the 2:17 type samarium cobalt permanent magnet with a protective surface layer prepared in Example 1 and the uncoated magnet after oxidation at 450°C for 200 hours are shown in the figure. Figure 5 As shown, the 2:17 type samarium cobalt permanent magnet with a protective coating has a remanence of 9.69 kGs at room temperature and a maximum energy product of 21.22 MGOe. At high temperature (450℃), the remanence is 7.87 kGs and the maximum energy product is 12.76 MGOe (the remanence and energy product at room temperature decrease by 0%, 0%, and at 450℃, they decrease by 0%, 0.31%, respectively). The uncoated magnet has a remanence of 9.62 kGs at room temperature. The maximum magnetic energy product is 20.39 MGOe, the remanence at high temperature (450℃) is 7.78 kGs, and the maximum magnetic energy product is 12.14 MGOe (the remanence and magnetic energy product at room temperature decrease by 2.3% and 10.3%, respectively, and the remanence and magnetic energy product at 450℃ decrease by 2.6% and 12.0%, respectively). The magnetic properties of this 2:17 type samarium cobalt permanent magnet with a protective layer on its surface remain basically unchanged after long-term oxidation in a high-temperature atmospheric environment.

[0069] The 2:17 samarium cobalt permanent magnet with a protective layer on its surface, prepared in Example 1, was subjected to adhesion testing using a micron scratch analyzer. Microscopic observations were conducted to obtain its morphology, frictional force changes, and acoustic emission signal patterns. Figure 6 As shown, its critical load is approximately 13.3-14.5 N.

[0070] Example 2:

[0071] The selected 2:17 type samarium cobalt permanent magnet has the composition Sm(Co) 0.73 Fe 0.16 Cu 0.08 Zr 0.03 ) 7.74 The chromizing heat treatment temperature is 810℃ and the holding time is 5h.

[0072] Step 1: Prepare the infiltration source powder:

[0073] The components of the infiltration powder are made from the following raw materials by weight percentage: 35wt% chromium powder as infiltration agent, 9wt% ammonium chloride powder as catalyst, and the remainder being 10wt% silica powder and 46wt% alumina powder. The infiltration powder is ground in a mortar for 25 minutes and mixed evenly for later use.

[0074] Step 2, Samarium-Cobalt Magnet Pretreatment:

[0075] The samarium cobalt magnet was polished with SiC sandpaper of grades 400#, 800#, 1000#, 1500#, and 2000# in turn. It was then ultrasonically treated in alcohol for 25 minutes, dried, and ready for use.

[0076] Step 3, chromizing heat treatment:

[0077] Place the samarium cobalt magnet obtained in step two into the middle of the crucible, fill and compact the surrounding area with the embedding and infiltration reagent prepared in step one, then cover and seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace.

[0078] In an argon atmosphere, the heating rate was set to 12℃ / min, and heating was started. When the temperature reached 810℃, it was held for 5 hours. Then it was cooled in air. After the temperature dropped to room temperature, the sample was taken out, ultrasonically cleaned in alcohol for 25 minutes, and then dried to obtain a chromium-impregnated magnet with a multifunctional protective layer on the surface.

[0079] Step 4, Aging Heat Treatment:

[0080] The chromium-impregnated magnet obtained in step three is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10℃ / min, and the heating starts from room temperature. When the temperature rises to 815℃, it is held for 24 hours. Then, it is slowly cooled to 400℃ at a rate of 0.5℃ / min. After holding for 12 hours, it is quenched and cooled to room temperature before being taken out, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on the surface.

[0081] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 2, was characterized by SEM analysis. The surface microstructure of the permanent magnet consists of three layers from the outside in: an external diffusion layer, a transition layer, and a substrate. The total thickness of the protective layer is approximately 10 μm, of which the thickness of the external diffusion layer is approximately 7 μm and the thickness of the transition layer is approximately 3 μm. The external diffusion layer is mainly composed of a Cr-Co-Fe solid solution.

[0082] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 2, was subjected to an oxidation experiment at 450°C for 200 hours. The mass gain per unit surface area after oxidation at 450°C for 200 hours was 0.021 mg / cm³. 2 .

[0083] The magnetic properties of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 2, were tested before and after oxidation at 450°C for 200 hours. Before oxidation, the remanence of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface was 9.65 kGs at room temperature and the maximum energy product was 21.09 MGOe. At high temperature (450°C), the remanence was 7.82 kGs and the maximum energy product was 12.66 MGOe. After oxidation, the magnetic properties of the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface were tested. The cobalt permanent magnet has a remanence of 9.65 kGs and a maximum energy product of 21.02 MGOe at room temperature, and a remanence of 7.81 kGs and a maximum energy product of 12.64 MGOe at high temperature (450℃). (The remanence and energy product at room temperature decrease by 0% and 0.33%, respectively, and the remanence and energy product at 450℃ decrease by 0.13% and 0.16%, respectively). The 2:17 type samarium cobalt permanent magnet with a protective layer on its surface has essentially unchanged magnetic properties after long-term oxidation in a high-temperature atmospheric environment.

[0084] The 2:17 samarium cobalt permanent magnet with a protective layer on its surface prepared in Example 2 was tested for bonding force using a micron scratch tester, and its critical load was approximately 13.7-15.1 N.

[0085] Example 3:

[0086] The selected 2:17 type samarium cobalt permanent magnet has the composition Sm(Co) 0.73 Fe 0.16 Cu 0.08 Zr 0.03 ) 7.74 The chromizing heat treatment temperature is 820℃ and the holding time is 7h.

[0087] Step 1: Prepare the infiltration source powder:

[0088] The components of the infiltration powder are made from the following raw materials by weight percentage: 35wt% chromium powder as infiltration agent, 9wt% ammonium chloride powder as catalyst, and the remainder being 10wt% silica powder and 46wt% alumina powder. The infiltration powder is ground in a mortar for 25 minutes and mixed evenly for later use.

[0089] Step 2, Samarium-Cobalt Magnet Pretreatment:

[0090] The samarium cobalt magnet was polished with SiC sandpaper of grades 400#, 800#, 1000#, 1500#, and 2000# in turn. It was then ultrasonically treated in alcohol for 25 minutes, dried, and ready for use.

[0091] Step 3, chromizing heat treatment:

[0092] Place the samarium cobalt magnet obtained in step two into the middle of the crucible, fill and compact the surrounding area with the embedding and infiltration reagent prepared in step one, then cover and seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace.

[0093] In an argon atmosphere, the heating rate was set to 12℃ / min, and heating was started. When the temperature reached 820℃, it was held for 7 hours. Then, it was cooled in air. After the temperature dropped to room temperature, the sample was taken out, ultrasonically cleaned in alcohol for 25 minutes, and then dried to obtain a chromium-impregnated magnet with a multifunctional protective layer on the surface.

[0094] Step 4, Aging Heat Treatment:

[0095] The chromium-impregnated magnet with a multifunctional protective layer on its surface, obtained in step three, is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10℃ / min, and the magnet is heated from room temperature. When the temperature reaches 815℃, it is held for 24 hours. Then, it is slowly cooled to 400℃ at a rate of 0.5℃ / min. After holding for 10 hours, it is quenched and cooled to room temperature before being removed, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface.

[0096] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 3, was characterized by SEM analysis. The surface microstructure of the permanent magnet consists of three layers from the outside in: an external diffusion layer, a transition layer, and a substrate. The total thickness of the protective layer is approximately 12 μm, of which the thickness of the external diffusion layer is approximately 9 μm and the thickness of the transition layer is approximately 3 μm. The external diffusion layer is mainly a Cr-Co-Fe solid solution.

[0097] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 3, was subjected to an oxidation experiment at 450°C for 200 hours. The mass gain per unit surface area after oxidation at 450°C for 200 hours was 0.020 mg / cm³. 2 .

[0098] The magnetic properties of the 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 3, were tested before and after oxidation at 450°C for 200 hours. Before oxidation, the remanence of the 2:17 samarium cobalt permanent magnet with a multifunctional protective layer at room temperature was 9.61 kGs, and the maximum energy product was 21.01 MGOe. At high temperature (450°C), the remanence was 7.79 kGs, and the maximum energy product was 12.58 MGOe. After oxidation, the magnetic properties of the 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface were tested. The permanent magnet has a remanence of 9.61 kGs and a maximum energy product of 20.98 MGOe at room temperature, and a remanence of 7.78 kGs and a maximum energy product of 12.55 MGOe at high temperature (450℃). (The remanence and energy product at room temperature decreased by 0% and 0.14%, respectively, and the remanence and energy product at 450℃ decreased by 0.13% and 0.24%, respectively). The 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface has essentially unchanged magnetic properties after long-term oxidation in a high-temperature atmospheric environment.

[0099] The 2:17 samarium cobalt permanent magnet with a multifunctional protective layer on its surface, prepared in Example 3, was tested for adhesion using a micron scratch tester, and its critical load was approximately 15.0-16.3 N.

[0100] The embodiments described above are merely preferred embodiments of the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. It should be noted that various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a multifunctional protective coating for a 2:17 type samarium cobalt permanent magnet material, characterized in that, Includes the following steps: Step 1: Prepare the infiltration source powder: The infiltration powder is made from the following raw materials by weight percentage: 25-45 wt% chromium powder as infiltration agent, 8-15 wt% ammonium chloride powder as catalyst, and the remainder as dispersant. The dispersant is composed of one or more of alumina, silica, magnesium oxide and calcium oxide powder. The infiltration powder is ground in a mortar for 20-30 minutes and mixed evenly for later use. Step 2, Samarium-Cobalt Magnet Pretreatment: The surface of the samarium cobalt magnet is polished step by step with sandpaper, then ultrasonically treated for 25-30 minutes to clean the surface, and then dried for later use. Step 3, chromizing heat treatment: Place the samarium cobalt magnet obtained in step two into the center of the crucible, fill and compact the surrounding area with the infiltration powder prepared in step one, then seal the crucible with a lid and wrap it tightly with nickel-chromium alloy wire; then place the crucible in the center of a slightly larger crucible, fill and compact the surrounding area with SiC powder, cover the larger crucible with a lid, wrap it tightly with nickel-chromium alloy wire, and place it in a vacuum heat treatment furnace. In an argon atmosphere, the heating rate is set to 10-13℃ / min. Heating begins, and when the temperature reaches 780-850℃, it is held for 2-8 hours. Then, it is cooled in air. Once the temperature drops to room temperature, the sample is removed, sonicated for 25-30 minutes, and then dried to obtain a chromium-impregnated magnet with a multifunctional protective layer on the surface. Step 4, Aging Heat Treatment: The chromium-doped magnet obtained in step three is placed in a vacuum heat treatment furnace. Under vacuum conditions, the heating rate is set to 10-12℃ / min, starting from room temperature. When the temperature rises to 800-830℃, it is held for 15-24 hours. Then, it is slowly cooled to 350-450℃ at a rate of 0.5-1.0℃ / min. After holding for 10-12 hours, it is quenched and cooled to room temperature before being removed, thus obtaining a 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on the surface.

2. The method according to claim 1, characterized in that: In step two, the progressive polishing is carried out using 400#, 800#, 1000#, 1500#, and 2000# sandpaper in sequence.

3. The method according to claim 1, characterized in that: In step three, the magnet with a multifunctional protective layer on its surface has a total protective layer thickness of 6-15 μm.

4. The method according to claim 1, characterized in that: In step three, the magnet with a multifunctional protective layer on its surface has a microstructure of infiltration layer consisting of an outer infiltration layer (6-10 μm), a (3-5 μm) transition layer, and a substrate, from the outside to the inside.

5. The method according to claim 1, characterized in that: In step four, the rate control accuracy of the slow cooling is ±0.05℃ / min.

6. The method according to claim 1, characterized in that: In step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface did not break after being kept in a hydrogen environment at 150°C for 20 hours.

7. The method according to claim 1, characterized in that: In step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface showed no obvious corrosion after being immersed in a 3.5%wt NaCl solution at 25°C for 168 hours.

8. The method according to claim 1, characterized in that: In step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface has a critical load of 13-20 N when tested with a micron scratch tester.

9. The method according to claim 1, characterized in that: In step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface, after being oxidized at 450°C for 200 hours, has a room temperature remanence loss of less than 0.03 kGs, a room temperature magnetic energy product loss of less than 0.1 MGOe, a high temperature (450°C) remanence loss of less than 0.03 kGs, and a high temperature (450°C) magnetic energy product loss of less than 0.08 MGOe.

10. The method according to claim 1, characterized in that: In step four, the 2:17 type samarium cobalt permanent magnet with a multifunctional protective layer on its surface exhibits a mass gain of 0.02–0.08 mg / cm³ per unit surface area after oxidation at 450°C for 200 hours. 2 .

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