A preparation method of a samarium-cobalt-based permanent magnet based on rare earth-copper alloy grain boundary diffusion

Abstract

This invention provides a method for preparing samarium cobalt-based permanent magnets based on grain boundary diffusion of rare earth-copper alloys, relating to the field of permanent magnet materials technology. The invention first involves mixing Sm, Co, Fe, Cu, Zr, and optionally one or two of Ti and Hf, and then subjecting the mixture to melting, casting, powdering, magnetic field orientation pressing, cold isostatic pressing, sintering, solution treatment, and rapid cooling to obtain a solid-solution samarium cobalt-based sintered body A. Then, RE-Cu alloy powder B is coated onto at least one surface of the solid-solution samarium cobalt-based sintered body A, followed by composite aging treatment to obtain the samarium cobalt-based permanent magnet. This invention utilizes the low-melting-point or softened transient liquid phase formed by the RE-Cu alloy powder in the early stages of aging, which preferentially wets the grain boundaries and grain edge regions of the solid-solution SmCoFeCuZr-based sintered body, allowing Cu and a small amount of RE to rapidly diffuse along the grain boundaries, demonstrating promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet materials technology, and in particular to a method for preparing samarium cobalt-based permanent magnets based on rare earth-copper alloy grain boundary diffusion. Background Technology

[0002] Samarium cobalt-based permanent magnets of type 2:17 (SmCoFeCuZr) possess high Curie temperatures, good corrosion resistance, and excellent high-temperature magnetic stability, making them valuable for applications in aerospace, high-temperature motors, sensors, and high-reliability magnetic components. The magnetic properties of these materials primarily rely on the synergistic effect of the 2:17R cellular main phase, the 1:5H Cu-rich cell wall phase, and the grain boundary phase formed during aging. The Cu-rich cell wall phase and grain boundary phases significantly influence domain wall pinning, demagnetization curve squareness, and intrinsic coercivity. To improve remanence and energy product, increasing the Fe content in the alloy is typically necessary. However, increasing the Fe content complicates component diffusion and microstructure evolution during sintering, solution treatment, and aging, leading to problems such as insufficient Cu distribution in grain boundary or cell wall regions, localized rare earth element deficiencies, and abnormal Fe / Zr segregation. This results in decreased grain boundary phase continuity, uneven domain wall pinning strength, and insufficient magnetic stability.

[0003] Currently, to address the problem of Cu-poor grain boundaries or cell wall regions in samarium-cobalt-based permanent magnet materials, grain boundary control is typically achieved by adding Cu powder, Cu oxides, organocopper compounds, or Sm-Cu second-phase alloys. While these methods can improve Cu distribution to some extent, they still have limitations: adding Cu powder alone can lead to Cu enrichment in localized areas, forming non-magnetic Cu-rich regions that affect the continuity of the main phase and the retention of remanence; using Cu oxides or oxygen-containing additives can easily introduce oxygen impurities and form rare-earth oxide inclusions, weakening the grain boundary control effect; using organocopper compounds may result in residual carbon and oxygen; and using a single Sm-Cu alloy has limited synergistic compensation capabilities for Cu and rare-earth elements in grain boundary regions, and during conventional direct powder mixing and sintering, the added phase is prone to agglomeration or wetting lag, making it difficult to form a uniform pre-distribution state on the surface of the main alloy powder particles and at particle contact points.

[0004] Therefore, it is necessary to provide a grain boundary control technology suitable for SmCoFeCuZr samarium cobalt-based permanent magnet materials, which enables the synergistic introduction of Cu and rare earth elements into the grain boundary region under low oxygen content conditions, and improves the wetting and diffusion state of the diffusion source on the surface and near-surface grain boundaries of the solid solution sintered body before composite aging, thereby improving the continuity of the grain boundary phase, the uniformity of the cell wall phase composition distribution, and the stability of domain wall pinning during subsequent sintering, solid solution and aging processes, so as to take into account the remanence, coercivity, squareness of the demagnetization curve, magnetic energy product and mechanical reliability of the material. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing samarium cobalt-based permanent magnets based on grain boundary diffusion of rare earth-copper alloys. This invention utilizes the low-melting-point or softened transient liquid phase formed by RE-Cu alloy powder in the early stages of aging, which preferentially wets the grain boundaries and grain edge regions of the solid-solution SmCoFeCuZr-based sintered body, allowing Cu and a small amount of RE to rapidly diffuse in along the grain boundaries. Compared with pure Cu layers, RE-Cu alloys exhibit better grain boundary affinity and chemical potential matching; compared with Cu / CuO powder internal doping, this method does not change the overall composition of the main phase and can reduce the dilution of remanence by non-magnetic Cu, showing promising application prospects.

[0006] This invention relates to a method for preparing samarium-cobalt-based permanent magnets based on rare-earth-copper alloy grain boundary diffusion, comprising the following steps: S1. Using Sm, Co, Fe, Cu, and Zr as raw materials, and optionally adding Ti and / or Hf for batching, the solid solution samarium cobalt-based sintered body A is obtained through melting, casting, powdering, magnetic field orientation pressing, cold isostatic pressing, sintering, solution treatment, and rapid cooling. S2. Prepare RE-Cu alloy powder B, wherein RE contains at least Sm, and optionally contains one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Sc, and Y, and the atomic percentage of Cu in the RE-Cu alloy powder B is 22 at.%~48 at.%; S3. The RE-Cu alloy powder B is coated onto at least one surface of the solid solution samarium cobalt-based sintered body A, followed by composite aging treatment. The coating amount is 0.10 wt.% to 1.20 wt.% of the mass of the sintered body A. S4. The coated sintered body is subjected to a composite aging treatment, which includes the following steps: a grain boundary diffusion stage at 620℃~720℃ for 0.5~3 h, a first-level aging stage at 805℃~865℃ for 6~24 h, a second-level aging stage at 0.3℃ / min~0.9℃ / min cooling to 380℃~450℃ and holding for 2~10 h, and then cooling to room temperature to obtain a samarium cobalt-based permanent magnet.

[0007] RE-Cu alloy powder undergoes surface softening during the grain boundary diffusion stage or the initial stage of first-stage aging. After reaching its initial melting temperature, it forms a local transient liquid phase or a highly diffusive active phase, which then penetrates along the grain boundaries. During the slow cooling and second-stage aging stages, Cu further enriches itself in the cell wall phase at the grain edges, promoting the continuity of the Sm(Co,Cu)5 type cell wall phase, thereby improving the domain wall pinning strength.

[0008] Preferably, the atomic composition of the sintered body A satisfies R x Fe y Co 1-x-y-p-q Cup M q Wherein, R is Sm or one or more of Sm and Nd, Gd, Dy, Ho, Er, Pr; M is Zr, or one or two of Zr and Ti, Hf; 0.105≤x≤0.125, 0.25≤y≤0.40, 0.035≤p≤0.065, 0.015≤ q ≤0.030.

[0009] Preferably, the composition of the RE-Cu alloy powder B satisfies Sm α R ' β Cu 100-α-β ;where R ' It is one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Sc and Y; 35≤α≤75, 0<β≤35, 22≤100-α-β≤48, and the contents of α, β and Cu are all atomic percentages.

[0010] Preferably, the differential scanning calorimetry initial melting temperature of the RE-Cu alloy powder B is 500℃~790℃, and after reaching its initial melting temperature, it forms a local transient liquid phase or a highly diffusive active phase.

[0011] Preferably, the RE-Cu alloy powder B is a spinning powder, atomized powder, hydrogen-broken powder, or a combination thereof, and D 50 The particle size is 0.8~8.0 μm, and the oxygen content is ≤3000 ppm.

[0012] Preferably, the RE-Cu alloy powder B is coated onto the surface of the sintered body A with an organic slurry, wherein the organic slurry contains RE-Cu alloy powder B, anhydrous ethanol or ethyl acetate, ethyl cellulose or polyvinyl butyral binder, and the mass percentage of RE-Cu alloy powder B in the slurry is 20 wt.% to 75 wt.%.

[0013] Preferably, the sintered body after coating is vacuum dried at 80℃~180℃ for 0.5~3 h before composite aging, and the organic matter is removed at 300℃~420℃ for 0.5~2 h.

[0014] Preferably, the obtained samarium cobalt-based permanent magnet forms an RE-Cu gradient modification region from the coating surface into the magnet interior, the depth of the RE-Cu gradient modification region is 80~650 μm, and the Cu atom concentration at the grain boundary is 1.5~4.0 times that at the grain center.

[0015] Preferably, a discontinuous or semi-continuous RE-Cu enriched phase is formed at the grain boundaries of the obtained samarium cobalt-based permanent magnet, wherein the average continuous thickness of the RE-Cu enriched phase is ≤1.5 μm.

[0016] A second aspect of the present invention provides a samarium-cobalt-based permanent magnet prepared by the above method, wherein the samarium-cobalt-based permanent magnet comprises Sm2(Co,Fe). 17 The main phase, Sm(Co,Cu)5 cell wall phase and Zr-rich lamellar phase are present, and the continuity of the Sm(Co,Cu)5 cell wall phase within 500 nm of the grain edge is ≥75%.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention uses low-oxygen RE-Cu alloy powder as a grain boundary regulator, which can synergistically supplement Cu and rare earth elements into the grain boundary regions of SmCoFeCuZr samarium cobalt-based permanent magnet materials while reducing the introduction of impurities such as oxygen and carbon. Compared with adding Cu powder alone, this invention helps reduce the risk of forming local non-magnetic Cu-rich regions; compared with using Cu oxides or organocopper compounds, this invention helps reduce the adverse effects of oxide inclusions and residual impurities on grain boundary structure and magnetic properties.

[0018] This invention involves sintering, solution treatment, and rapid cooling of an SmCoFeCuZr sintered body, followed by coating the surface of the solution-treated sintered body with RE-Cu alloy powder. Through grain boundary diffusion during the early stage of composite aging and a first-stage aging process, the RE-Cu phase softens, wets, and diffuses at the coating surface and near-surface grain boundaries, thereby reducing the local agglomeration and component dilution problems caused by conventional direct doping. By incorporating a grain boundary diffusion stage during the early stage of composite aging, the RE-Cu alloy powder can form a wetting and diffusion-active RE-Cu phase during this early stage, preferentially spreading at the powder particle interface, thus reducing the problems of local agglomeration, segregation, or insufficient wetting of the added phase during conventional direct sintering.

[0019] This invention utilizes RE-Cu alloy powder containing Sm and at least one second rare earth element. The composite rare earth system can regulate local interfacial wetting and element diffusion behavior, making it easier for the Cu-rich / RE composite phase to distribute in grain boundaries, key regions, and subsequent cellular structure evolution-related regions. This composite rare earth system helps improve Cu-poor, rare earth-poor, and Fe / Zr-rich aberration problems in grain boundary regions, promoting the formation of continuous or semi-continuous, thin-layered, and relatively uniformly distributed RE-Cu composite grain boundary phases.

[0020] This invention achieves the synergistic evolution of the RE-Cu composite grain boundary phase with the intragranular 2:17R cellular main phase and 1:5H Cu-rich cell wall phase through surface coating, pre-activation, first-stage aging, and second-stage aging. This is beneficial for improving the continuity of the grain boundary phase and the stability of domain wall pinning, thereby improving the intrinsic coercivity, squareness of the demagnetization curve, and uniformity of the microstructure of the material, while maintaining high remanence and magnetic energy product. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A method for preparing samarium-cobalt based permanent magnets based on rare-earth-copper alloy grain boundary diffusion, the steps of which are as follows: S1. Preparation of Alloy A: According to the atomic ratio Sm 0.114 Fe 0.32 Co 0.495 Cu 0.055 Zr 0.016 The raw materials Sm, Co, Fe, Cu, and Zr were placed in a vacuum induction melting furnace. After being evacuated to below 5 Pa, high-purity Ar was introduced to 60 kPa, and the furnace was melted at 1520℃. After refining, a rotating copper roller was used to spin the alloy to obtain alloy sheets with a thickness of 0.3 mm. The alloy sheets were then coarsely crushed to less than 40 mesh under a high-purity Ar atmosphere, and then ground into powder using a high-purity N2 air jet mill to obtain D. 50 SmCoFeCuZr alloy powder with a diameter of 5.8 μm was oriented and pressed in a magnetic field of 1.6 T, and then cold isostatically pressed at 200 MPa to obtain a compact. The compact was sintered at 1210 °C for 3 h in an Ar atmosphere, then cooled to 1185 °C for 6 h for solidification, and rapidly cooled to room temperature at a cooling rate of 120 °C / min to obtain a solid solution samarium cobalt-based sintered body A with a size of 10 mm × 10 mm × 3 mm. S2. Preparation of alloy B: According to the atomic ratio Sm 60 Nd5Cu 35 The raw materials were prepared by vacuum induction melting followed by strip spinning to produce RE-Cu alloy strips. The strips were then crushed and sieved under an Ar atmosphere to obtain D. 50 RE-Cu alloy powder B, with a diameter of 3.2 μm, was analyzed by DSC. The initial melting temperature of alloy B was 642℃, and the oxygen content of alloy B was 1850 ppm. S3. Surface Coating: Alloy B powder, anhydrous ethanol, and ethyl cellulose were mixed at a mass ratio of 60:38.5:1.5 and ball-milled for 2 hours to obtain a coating slurry. The slurry was uniformly coated onto two opposing surfaces of the solid solution sintered body A, perpendicular to the orientation direction. After coating, the surface was vacuum-dried at 120°C for 1 hour and then vacuum-degreased at 360°C for 1 hour. The coating amount of alloy B, based on the mass of sintered body A, was 0.45 wt.%. S4. Composite aging: The coated sintered body is placed in an Ar atmosphere heat treatment furnace, first held at 680℃ for 1 h, then heated to 840℃ and held for 14 h, then cooled to 420℃ at a rate of 0.6℃ / min and held for 6 h, and finally furnace cooled to room temperature to obtain samarium cobalt-based permanent magnets.

[0023] The obtained magnet was tested by EPMA, and the Cu atom concentration at the grain boundary was 2.7 times that at the grain center. According to TEM statistics, the continuity of the Sm(Co,Cu)5 cell wall phase within 500 nm at the grain edge was 86.4%.

[0024] Example 2 The difference from Example 1 is that alloy B has a composition of Sm. 55 Pr 10 Cu 35 The initial melting temperature of DSC is 628℃. 50 The thickness was 2.9 μm; the coating amount of alloy B was 0.45 wt.%, and the remaining process parameters were the same as in Example 1.

[0025] Example 3 The difference from Example 1 is that alloy B has a composition of Sm. 58 Gd7Cu 35 The initial melting temperature of DSC is 671℃. 50 The thickness is 3.5 μm; the coating amount of alloy B is 0.45 wt.%, and the other process parameters are the same as in Example 1.

[0026] Example 4 The difference from Example 1 is that alloy B has a composition of Sm. 52 Nd8Ho5Cu 35 The initial melting temperature of DSC is 664℃. 50 The thickness is 3.1 μm; the coating amount of alloy B is 0.50 wt.%, and the other process parameters are the same as in Example 1.

[0027] Example 5 The difference from Example 1 is that the coating amount of alloy B is 0.25 wt.%, the first-stage aging temperature is 835°C, the first-stage aging time is 16 h, and the other process parameters are the same as in Example 1.

[0028] Example 6 The difference from Example 1 is that the coating amount of alloy B is 0.80 wt.%, the first-stage aging temperature is 845°C, the first-stage aging time is 12 h, and the other process parameters are the same as those in Example 1.

[0029] Example 7 The difference from Example 1 is that the composition of alloy A is Sm 0.109 Nd0.005 Fe 0.33 Co 0.485 Cu 0.055 Zr 0.016 Alloy B has the composition Sm 55 Nd 10 Cu 35 The remaining process parameters are the same as in Example 1.

[0030] Example 8 The difference from Example 1 is that the composite aging process is to hold at 650°C for 2 hours, then at 850°C for 10 hours, and then cool to 400°C at a rate of 0.5°C / min and hold for 8 hours. The remaining process parameters are the same as in Example 1.

[0031] Comparative Example 1 The difference from Example 1 is that alloy B is not coated, and only the solid solution sintered body A is subjected to the same composite aging treatment as in Example 1.

[0032] Comparative Example 2 The difference from Example 1 is that pure Cu powder is used instead of alloy B and Cu powder D. 50 The thickness is 3.0 μm, the coating amount is 0.45 wt.% based on Cu mass, and the other process parameters are the same as in Example 1.

[0033] Comparative Example 3 The difference from Example 1 is that alloy B powder is mixed with alloy A powder at 0.45 wt.% before orientation pressing, and then the magnet is prepared according to the sintering, solution treatment and composite aging process of Example 1, without performing solution surface coating.

[0034] Comparative Example 4 The difference from Example 1 is that the coating amount of alloy B is 1.80 wt.%, and the other process parameters are the same as in Example 1.

[0035] Comparative Example 5 The difference from Example 1 is that alloy B has a composition of Sm. 40 Cu 60 The initial melting temperature of DSC was 481℃, and the other process parameters were the same as in Example 1.

[0036] Detection method: Magnetic properties were tested using a pulsed magnetic field magnetometer or a permanent magnet material magnetic property testing system. Test samples were uniformly 10 mm × 10 mm × 3 mm squares, and demagnetization factor correction was performed according to the test direction. The test temperature was 20℃. Five samples were taken from each group, and the results are expressed as mean ± standard deviation.

[0037] Diffusion depth was determined using EPMA; grain boundary Cu enrichment factor, RE-Cu enriched phase thickness, and cell wall phase continuity were determined using STEM-EDS / TEM. At least 20 grain boundary points and 20 grain center points were collected at 100 μm, 200 μm from the coated surface, and near the diffusion front, respectively, and the ratio of grain boundary Cu atom concentration to grain center Cu atom concentration was calculated. The depth of the region where the RE or Cu content was continuously 10% higher than the corresponding depth benchmark value of the uncoated control sample was defined as the RE-Cu modification depth.

[0038] Cell wall phase continuity was statistically determined using TEM images, specifically the ratio of the continuous length of the Sm(Co,Cu)5 cell wall phase within a 500 nm range at the grain edge to the theoretical total cell wall length.

[0039] Table 1. Test results (n=5, mean ± standard deviation)

[0040] Note: Hk is the absolute value of the magnetic field when the magnetic induction intensity drops to 0.9 Br on the demagnetization curve.

[0041] As can be seen from the table, compared with Comparative Example 1, Examples 1-8 significantly increased Hcj, Hk, Hk / Hcj, and (BH) while maintaining Br within the range of 11.78-12.02 kG. max Comparative Example 2 used pure Cu powder coating. Due to the lack of low-melting-point wetting and grain boundary chemical potential regulation effects of RE-Cu, the diffusion depth and cell wall phase continuity were lower than those of the examples. Comparative Example 3 internally incorporated RE-Cu alloy. Although Hcj was improved, Br and (BH)... max The significant decrease indicates that exogenous grain boundary diffusion is superior to overall internal doping. Comparative Examples 4 and 5 show that excessive diffusion source or excessive Cu content will form a thicker nonmagnetic RE-Cu-rich layer, reducing Br, squareness, and magnetic energy product.

[0042] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing samarium-cobalt-based permanent magnets based on rare-earth-copper alloy grain boundary diffusion, characterized in that, Includes the following steps: S1. Using Sm, Co, Fe, Cu, and Zr as raw materials, and optionally adding Ti and / or Hf for batching, the solid solution samarium cobalt-based sintered body A is obtained through melting, casting, powdering, magnetic field orientation pressing, cold isostatic pressing, sintering, solution treatment, and rapid cooling. S2. Prepare RE-Cu alloy powder B, wherein RE contains at least Sm, and optionally contains one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Sc, and Y, and the atomic percentage of Cu in the RE-Cu alloy powder B is 22 at.%~48 at.%; S3. The RE-Cu alloy powder B is applied to at least one surface of the solid solution samarium cobalt-based sintered body A, and the coating amount is 0.10 wt.% to 1.20 wt.% of the mass of the sintered body A. S4. The coated sintered body is subjected to a composite aging treatment, which includes the following steps: a grain boundary diffusion stage at 620℃~720℃ for 0.5~3 h, a first-level aging stage at 805℃~865℃ for 6~24 h, a second-level aging stage at 0.3℃ / min~0.9℃ / min cooling to 380℃~450℃ and holding for 2~10 h, and then cooling to room temperature to obtain a samarium cobalt-based permanent magnet.

2. The preparation method according to claim 1, characterized in that, The atomic composition of the sintered body A satisfies R x Fe y Co 1-x-y-p-q Cu p M q Wherein, R is Sm or one or more of Sm and Nd, Gd, Dy, Ho, Er, Pr; M is Zr, or one or two of Zr and Ti, Hf; 0.105≤x≤0.125, 0.25≤y≤0.40, 0.035≤p≤0.065, 0.015≤ q ≤0.

030.

3. The preparation method according to claim 1, characterized in that, The composition of the RE-Cu alloy powder B satisfies Sm α R ' β Cu 100-α-β ;where R ' It is one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Sc and Y; 35≤α≤75, 0<β≤35, 22≤100-α-β≤48, and the contents of α, β and Cu are all atomic percentages.

4. The preparation method according to claim 1, characterized in that, The differential scanning calorimetry initial melting temperature of the RE-Cu alloy powder B is 500℃~790℃.

5. The preparation method according to claim 1, characterized in that, The RE-Cu alloy powder B is a type of powder for spinning, gas atomization, hydrogen fragmentation, or a combination thereof. 50 The particle size is 0.8~8.0 μm, and the oxygen content is ≤3000 ppm.

6. The preparation method according to claim 1, characterized in that, The RE-Cu alloy powder B is coated onto the surface of the sintered body A with an organic slurry. The organic slurry contains RE-Cu alloy powder B, anhydrous ethanol or ethyl acetate, ethyl cellulose or polyvinyl butyral binder, and the mass percentage of RE-Cu alloy powder B in the slurry is 20 wt.% to 75 wt.%.

7. The preparation method according to claim 1, characterized in that, The coated sintered body was vacuum dried at 80℃~180℃ for 0.5~3 h before composite aging, and the organic matter was removed at 300℃~420℃ for 0.5~2 h.

8. The preparation method according to claim 1, characterized in that, The resulting samarium cobalt-based permanent magnet forms an RE-Cu gradient modification region from the coating surface into the magnet interior. The depth of the RE-Cu gradient modification region is 80~650 μm, and the Cu atom concentration at the grain boundary is 1.5~4.0 times that at the grain center.

9. The preparation method according to claim 1, characterized in that, The resulting samarium cobalt-based permanent magnets include Sm2(Co,Fe). 17 The main phase, Sm(Co,Cu)5 cell wall phase and Zr-rich lamellar phase are present, and the continuity of the Sm(Co,Cu)5 cell wall phase within 500 nm of the grain edge is ≥75%.

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