A samarium-cobalt rare earth permanent magnet and a method for manufacturing the same

Abstract

The application discloses a samarium-cobalt rare earth permanent magnet, and a preparation method of the samarium-cobalt rare earth permanent magnet, and belongs to the technical field of permanent magnet materials.The permanent magnet is provided with a layer of original oxide film or nitride film on the surface.The preparation method comprises the following steps: casting an ingot, and then sequentially performing crushing, airflow grinding, magnetic field forming and sintering to prepare a dense precursor; grinding and polishing after cutting; solid solution treatment under vacuum and magnetic field conditions; cooling after aging treatment; and oxidation or nitriding treatment.The solid solution and aging treatment under the magnetic field conditions can effectively control the distribution of cell wall phases in the magnet, thereby controlling the magnetic properties of the samarium-cobalt rare earth permanent magnet, and being beneficial to the development of various grades of high-temperature-resistant samarium-cobalt rare earth permanent magnets.The cell wall phases of the magnet are controlled, so that the coercive force of the magnet is improved, the squareness of the magnet is also obviously improved, and the corrosion resistance of the magnet is also enhanced.

Description

Technical Field

[0001] This invention relates to a samarium cobalt rare earth permanent magnet and its preparation method, belonging to the field of samarium cobalt rare earth permanent magnets and their preparation methods. Background Technology

[0002] Rare earth permanent magnets are currently the most powerful permanent magnet materials, and they have permeated all aspects of production and daily life, including aerospace, new energy vehicles, intelligent manufacturing, and consumer appliances. Powder metallurgy is a well-known production process for rare earth permanent magnets, producing materials primarily composed of main phase grains and grain boundary phases. When rare earth permanent magnets operate in high-temperature and high-humidity environments, cathodes of varying sizes can form between the grains and grain boundaries, leading to chemical reactions that cause corrosion and grain shedding, thus affecting the normal use of the rare earth permanent magnets.

[0003] Currently, a corrosion-resistant metal layer is typically formed on the surface of rare-earth permanent magnet materials by coating them with a single-element metal layer. Chinese patents CN100456395C (authorization announcement number) and CN1933042 (publication number) disclose methods for improving the corrosion resistance of rare-earth permanent magnet materials by using metals or compounds such as Ni, Zn, Al, Cu, Cd, Cr, TiN, and ZrN as a metal coating, applied to the magnet surface using electroplating, electroless plating, or physical vapor deposition.

[0004] However, the above methods heavily rely on alkaline or acidic chemical solutions, which can easily lead to serious water pollution and affect human health. In addition, uniformly coating the magnet surface with polymer materials such as epoxy resin is also a common method to prevent magnet corrosion. However, polymer coating has the problem of difficulty in controlling the thickness, affecting the application of magnets in certain high-precision fields. Furthermore, polymer-coated magnets cannot be used at high temperatures, severely limiting the application areas of high-temperature rare-earth permanent magnet materials.

[0005] Currently, samarium-cobalt rare-earth permanent magnets are the most widely used rare-earth permanent magnets under high-temperature conditions. However, the control window for alloy composition is very narrow. Among these, the distribution and segregation of copper, especially in the cell wall phase, plays a crucial role in the temperature stability and squareness of the magnet. At present, the distribution of copper is usually controlled by adjusting the alloy composition and the solution aging process. However, there is usually a trade-off between achieving high coercivity and high squareness.

[0006] Therefore, in response to the above-mentioned technical problems, there is an urgent need to find a simple and economical magnet surface protection technology and cell wall phase control method to enable samarium cobalt rare earth permanent magnets to obtain good corrosion resistance while ensuring that the magnets themselves also have excellent magnetic properties. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a samarium cobalt rare earth permanent magnet and its preparation method. The method prepares a samarium cobalt rare earth permanent magnet with high corrosion resistance and high performance under high temperature conditions, which can maintain good magnetic properties while meeting the requirements of excellent magnet corrosion resistance.

[0008] The technical solution adopted in this invention is as follows:

[0009] A samarium cobalt rare earth permanent magnet, wherein a native oxide film or nitride film with a thickness of 0.01 μm-2 μm is formed on the surface of the permanent magnet;

[0010] According to the mass ratio, the alloy composition expression of the permanent magnet is (SmGdEr)m(FeCoCuZr)n, where 24.1≤m≤25.2 and 74.8≤n≤75.9;

[0011] The oxide film or nitrided film is a film formed by oxidizing or nitriding at least one metal selected from Sm, Gd, Er, Fe, Co, Zr, and Cu.

[0012] The preparation method of a samarium cobalt rare earth permanent magnet based on the above includes the following steps:

[0013] S1: The rare earth elements and metal elements in the permanent magnet are smelted into alloy ingots according to the proportions, and then successively processed by crushing, air jet milling, magnetic field forming and sintering to prepare a dense precursor.

[0014] S2: After cutting the precursor, grind and polish it to keep the surface clean and flat;

[0015] S3: After grinding and polishing, the precursor is placed in a magnetic field heat treatment device and then vacuumed. After heating to the solution temperature, a magnetic field is added to the device cavity to carry out solution treatment under magnetic field conditions.

[0016] S4: Maintain the temperature inside the equipment at 800-830℃ for aging treatment for 1-3 hours, then gradually reduce the temperature at a rate of 0.5-2℃ / min.

[0017] S5: When the temperature drops to 400-600℃, spray the mixed gas onto the magnet surface or briefly immerse the magnet in liquid nitrogen or liquid ammonia to rapidly cool the magnet, so that the surface metal elements of the magnet are oxidized or nitrided to form a passivation layer of oxide film or nitrided film.

[0018] As a preferred embodiment of the present invention, in step S3, the vacuum degree after the precursor is placed in the magnetic field heat treatment equipment is 4×10⁻⁶. -3 Pa.

[0019] As a preferred embodiment of the present invention, in step S3, the solution temperature range is 1140-1160℃.

[0020] As a preferred embodiment of the present invention, in step S3, the magnetic field strength is 2000 Gs-5000 Gs.

[0021] As a preferred embodiment of the present invention, in step S5, the mixed gas is a mixture of oxygen and argon with a content of 1% to 5%; or a mixture of ammonia and argon with a content of 5% to 50%; or a mixture of ammonia and argon with a content of 5% to 10%.

[0022] As a preferred embodiment of the present invention, in step S5, after spraying the mixed gas onto the surface of the magnet, the pressure inside the equipment chamber is maintained at 0.2 atmospheres.

[0023] As a preferred embodiment of the present invention, in step S5, before briefly immersing the magnet in liquid nitrogen or liquid ammonia, argon gas is introduced into the equipment chamber until the gas pressure inside the equipment is balanced.

[0024] The beneficial effects of this invention are as follows:

[0025] Solution treatment and aging under magnetic field conditions can effectively regulate the distribution of cell wall phases within the magnet, thereby controlling the magnetic properties of samarium cobalt rare earth permanent magnets and facilitating the development of various grades of high-temperature samarium cobalt rare earth permanent magnets. By regulating the cell wall phases of the magnet, the coercivity of the magnet can be improved, while the squareness of the magnet can also be significantly enhanced, and the corrosion resistance of the magnet can also be strengthened. Attached Figure Description

[0026] Figure 1 The image shows the Cu element distribution in the magnet prepared by the preparation method provided in Example 1.

[0027] Figure 2 This is a distribution diagram of Cu element in a magnet prepared by the preparation method provided in Example 2. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] A samarium cobalt rare earth permanent magnet, wherein a native oxide film or nitride film with a thickness of 0.01μm-2μm is formed on the surface of the permanent magnet;

[0030] According to the mass ratio, the alloy composition expression of the permanent magnet is (SmGdEr)m(FeCoCuZr)n, where 24.1≤m≤25.2 and 74.8≤n≤75.9;

[0031] The oxide film or nitrided film is a film formed by oxidizing or nitriding at least one metal selected from Sm, Gd, Er, Fe, Co, Zr, and Cu.

[0032] The preparation method of a samarium cobalt rare earth permanent magnet based on the above includes the following steps:

[0033] S1: The rare earth elements and metal elements in the permanent magnet are smelted into alloy ingots according to the proportions, and then successively processed by crushing, air jet milling, magnetic field forming and sintering to prepare a dense precursor.

[0034] S2: After cutting the precursor, grind and polish it to keep the surface clean and smooth;

[0035] S3: After grinding and polishing, the precursor is placed in a magnetic field heat treatment device and then vacuumed. After heating to the solution temperature, a magnetic field is added to the device cavity to carry out solution treatment under magnetic field conditions.

[0036] S4: Maintain the temperature inside the equipment at 800-830℃ for aging treatment for 1-3 hours, then gradually reduce the temperature at a rate of 0.5-2℃ / min.

[0037] S5: When the temperature drops to 400-600℃, spray the mixed gas onto the magnet surface or briefly immerse the magnet in liquid nitrogen or liquid ammonia to rapidly cool the magnet, so that the surface metal elements of the magnet are oxidized or nitrided to form a passivation layer of oxide film or nitrided film.

[0038] In step S3, the vacuum level after the precursor is placed in the magnetic field heat treatment equipment is 4×10⁻⁶. -3 Pa.

[0039] In step S3, the solution temperature range is 1140-1160℃.

[0040] In step S3, the magnetic field strength is 2000 Gs-5000 Gs.

[0041] In step S5, the mixed gas is a mixture of oxygen and argon with a content of 1% to 5%; or a mixture of ammonia and argon with a content of 5% to 50%; or a mixture of ammonia and argon with a content of 5% to 10%.

[0042] In step S5, after spraying the mixed gas onto the magnet surface, the pressure inside the equipment chamber is maintained at 0.2 atmospheres.

[0043] In step S5, before briefly immersing the magnet in liquid nitrogen or liquid ammonia, argon gas is introduced into the equipment chamber until the internal pressure is balanced.

[0044] The expression for the permanent magnet in Embodiments 1-2 of this invention is Sm 24.5 Co 50.7 Fe 17.6 Cu 4.3 Zr 2.9 .

[0045] Example 1

[0046] This embodiment describes a method for preparing a samarium-cobalt rare-earth permanent magnet, comprising the following steps:

[0047] S1: The rare earth elements and metal elements in the permanent magnet are smelted into alloy ingots according to the proportions, and then successively processed by crushing, air jet milling, magnetic field forming and sintering to prepare a dense precursor.

[0048] S2: The precursor is wire-cut and then polished to remove impurities and maintain a clean and smooth surface, resulting in a material with dimensions of 5×5×2mm. 3 A sheet magnet;

[0049] S3: Place the sheet magnet into the magnetic field heat treatment equipment and evacuate it to 4×10. -3 Pa, after heating to 1150℃, a magnetic field with a strength of 4000Gs is added to the equipment cavity, and then the temperature is maintained for 4 hours for solution treatment under magnetic field conditions.

[0050] S4: Maintain the magnetic field constant, lower the temperature inside the equipment cavity to 830℃ and keep it for 3 hours for aging treatment; then gradually lower the temperature at a rate of 0.7℃ / min.

[0051] S5: When the temperature drops to 400℃, a mixture of 1.5% oxygen and 98.5% argon is sprayed onto the magnet surface and the pressure inside the equipment cavity is maintained at 0.2 atmospheres until the magnet is rapidly cooled to room temperature, so that the metal elements on the magnet surface are oxidized to form an oxide film passivation layer.

[0052] The magnetic properties of the magnet were tested using PFM, and the weight loss of the magnet was tested using a salt spray chamber. The corrosion resistance of the magnet was evaluated by the weight loss of the magnet. The test results are shown in Tables 1 and 2 below, where 1, 2, and 3 correspond to the three samples prepared by the preparation method provided in Example 1.

[0053] Table 1: Magnetic properties of magnets.

[0054]

[0055]

[0056] As can be seen from Table 1, the method provided in this embodiment can regulate the cell wall phase of the magnet, thereby improving the coercivity of the magnet and significantly enhancing its squareness.

[0057] Table 2: Weight loss test on magnet surface.

[0058]

[0059] The lower the weight loss rate, the stronger the corrosion resistance of the magnet. As shown in Table 2, the weight loss rate of the magnet prepared by this invention is ≤0.11 mg / cm³. 2 It is far superior to the reference sample of 1.88 mg / cm³. 2 The weight loss rate indicates that the corrosion resistance of the magnet has been enhanced.

[0060] Figure 1 A Cu elemental distribution map is provided in the magnet prepared in Example 1, from... Figure 1 As can be seen, after aging treatment under magnetic field conditions, most of the copper elements are still distributed in the cell wall phase, and a large amount of copper elements can also be observed inside the cells. Therefore, it can be shown that by solid solution and aging treatment under magnetic field conditions, the distribution of the cell wall phase in the magnet can be effectively controlled, thereby controlling the magnetic properties of samarium cobalt rare earth permanent magnets, which is conducive to the development of various grades of high-temperature samarium cobalt magnets.

[0061] Example 2

[0062] This embodiment describes a method for preparing a samarium-cobalt rare-earth permanent magnet, comprising the following steps:

[0063] S1: The rare earth elements and metal elements in the permanent magnet are smelted into alloy ingots according to the proportions, and then successively processed by crushing, air jet milling, magnetic field forming and sintering to prepare a dense precursor.

[0064] S2: The precursor is wire-cut and then polished to remove impurities and maintain a clean and smooth surface, resulting in a material with dimensions of 5×5×2mm. 3 A sheet magnet;

[0065] S3: Place the sheet magnet into the magnetic field heat treatment equipment and evacuate it to 4×10. -3 Pa, after heating to 1150℃, a magnetic field with a strength of 4000Gs is added to the equipment cavity, and then the temperature is maintained for 4 hours for solution treatment under magnetic field conditions.

[0066] S4: Maintain the magnetic field constant, lower the temperature inside the equipment cavity to 830℃ and keep it for 3 hours for aging treatment; then gradually lower the temperature at a rate of 0.7℃ / min.

[0067] S5: When the temperature drops to 400℃, fill the equipment with argon gas until the gas pressure inside the equipment cavity is balanced. Open the airtight valve connecting the equipment to the liquid nitrogen tank, quickly immerse the magnet in liquid nitrogen and then quickly remove the magnet. The magnet is rapidly cooled under the action of liquid nitrogen, which causes the metal elements on the surface of the magnet to be nitrided, forming a nitrided passivation layer.

[0068] The magnetic properties of the magnet were tested using PFM, and the weight loss of the magnet was tested using a salt spray chamber. The corrosion resistance of the magnet was evaluated by the weight loss of the magnet. The test results are shown in Tables 3 and 4 below, where 1, 2, and 3 correspond to the three samples prepared by the preparation method provided in Example 2.

[0069] Table 3: Magnetic properties of magnets.

[0070] serial number Remanence (Br) Coercivity (Hcj) Magnetic energy product (BH) Squareness Reference sample 11.92 20.55 33.07 0.503 1 10.56 24.8 26.5 0.591 2 10.72 25.6 27.8 0.672 3 10.81 22.5 28.2 0.568

[0071] As can be seen from Table 3, the remanence of the magnet prepared by the method provided in this embodiment is reduced, which is related to the difference in the distribution of Cu element in the cell wall phase of the magnet. The method provided in this embodiment can also regulate the cell wall phase of the magnet, which can significantly improve the squareness of the magnet while increasing the coercivity of the magnet.

[0072] Table 4: Weight loss test on magnet surface.

[0073]

[0074] The lower the weight loss rate, the stronger the corrosion resistance of the magnet. As shown in Table 4, the weight loss rate of the magnet prepared by this invention is ≤0.1 mg / cm³. 2 It is far superior to the reference sample of 1.33 mg / cm³. 2 The weight loss rate indicates that the corrosion resistance of the magnet has been significantly improved.

[0075] Figure 2 A Cu elemental distribution map is provided in the magnet prepared in Example 2, from... Figure 2 It can also be seen that after aging treatment under magnetic field conditions, most of the copper elements are still distributed in the cell wall phase, and a large amount of copper elements can also be observed inside the cells. Therefore, it can be shown that by solid solution and aging treatment under magnetic field conditions, the distribution of the cell wall phase in the magnet can be effectively controlled, thereby controlling the magnetic properties of samarium cobalt rare earth permanent magnets, which is conducive to the development of various grades of high-temperature samarium cobalt magnets.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A samarium-cobalt rare-earth permanent magnet, characterized in that, The permanent magnet has a native oxide or nitride film with a thickness of 0.01 μm to 2 μm formed on its surface; According to the mass ratio, the alloy composition expression of the permanent magnet is (SmGdEr)m(FeCoCuZr)n, where 24.1≤m≤25.2 and 74.8≤n≤75.9; The oxide film or nitride film is a film formed by oxidizing or nitriding at least one metal selected from Sm, Gd, Er, Fe, Co, Zr, and Cu; The preparation method of samarium cobalt rare earth permanent magnets includes the following steps: S1: The rare earth elements and metal elements in the permanent magnet are smelted into alloy ingots according to the proportions, and then successively processed by crushing, air jet milling, magnetic field forming and sintering to prepare a dense precursor. S2: After cutting the precursor, grind and polish it to keep the surface clean and flat; S3: After grinding and polishing, the precursor is placed in a magnetic field heat treatment device and then vacuumed. After heating to the solution temperature, a magnetic field is added to the device cavity to carry out solution treatment under magnetic field conditions. S4: Maintain the temperature inside the equipment at 800-830℃ for aging treatment for 1-3 hours, then gradually reduce the temperature at a rate of 0.5-2℃ / min. S5: When the temperature drops to 400~600℃, spray the mixed gas onto the magnet surface or briefly immerse the magnet in liquid nitrogen or liquid ammonia to cool the magnet rapidly, so that the metal elements on the magnet surface are oxidized or nitrided to form a passivation layer of oxide film or nitrided film.

2. The samarium cobalt rare earth permanent magnet according to claim 1, characterized in that, In step S3, the vacuum level after the precursor is placed in the magnetic field heat treatment equipment is 4×10⁻⁶. -3 Pa.

3. A samarium-cobalt rare-earth permanent magnet according to claim 1, characterized in that, In step S3, the solution temperature range is 1140-1160℃.

4. A samarium-cobalt rare-earth permanent magnet according to claim 1, characterized in that, In step S3, the magnetic field strength is 2000 Gs-5000 Gs.

5. A samarium-cobalt rare-earth permanent magnet according to claim 1, characterized in that, In step S5, the mixed gas is a mixture of oxygen and argon with a content of 1% to 5%; or a mixture of ammonia and argon with a content of 5% to 50%; or a mixture of ammonia and argon with a content of 5% to 10%.

6. A samarium-cobalt rare-earth permanent magnet according to claim 1, characterized in that, In step S5, after spraying the mixed gas onto the magnet surface, the pressure inside the equipment chamber is maintained at 0.2 atmospheres.

7. A samarium-cobalt rare-earth permanent magnet according to claim 1, characterized in that, In step S5, before briefly immersing the magnet in liquid nitrogen or liquid ammonia, argon gas is introduced into the equipment chamber until the internal pressure is balanced.

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