HIGH-RESISTIVITY SINTERED SAMARIUM-COBALT MAGNET AND PREPARATION METHOD THEREOF

Abstract

The present invention discloses a high-resistivity sintered samarium-cobalt magnet and a preparation method thereof. According to the present invention, considering the specialty of sintered samarium-cobalt magnetic powder, fluoride or oxide is firstly prepared into nano-powder using high-energy ball milling, and the samarium-cobalt magnetic powder is prepared separately by rolling ball milling or high-speed jet milling, and then a certain electric field is applied in a fluoride suspension to drive the fluoride nano-powder to evenly cover a surface of the samarium-cobalt magnetic powder. The present invention breaks through the technical bottleneck that fluoride/oxide can improve the resistivity of a samarium-cobalt magnet but result in deterioration of the magnetic properties.

Claims

1. A method for preparing a high-resistivity sintered samarium-cobalt magnet, comprising the following steps: (1) weighing fluoride, mixing the fluoride with alcohol and a surfactant, and then performing high-energy ball milling to obtain fine fluoride powder, with an average particle size of 10-200 nm; (2) rinsing and drying the fine fluoride powder prepared in step (1) in an oxygen-free glove box to obtain fluoride powder; (3) weighing metal raw materials according to compositions of Sm.sub.2(CoFeCuZr).sub.17 alloy, and then smelting the raw materials uniformly to obtain alloy ingots; (4) crushing the alloy ingots, and obtaining magnetic powder by powder processing, with an average particle size of 2.5-5.2 μm; (5) mixing the fluoride powder prepared in step (2) with alcohol, and preparing a suspension by ultrasonic treatment; (6) spreading the magnetic powder prepared in step (4) evenly on a platinum sheet A at a bottom of a container, and pouring the suspension prepared in step (5) into the container; after pouring, placing a platinum sheet B on a surface of the liquid in a suspended manner, completely immersing the platinum sheet B in the suspension, then performing deposition treatment under an electric field, and applying a voltage to the platinum sheets A and B, with the platinum sheet B serving as a positive electrode and the platinum sheet A serving as a negative electrode, to obtain deposited magnetic powder; (7) performing magnetic field orientation molding and cold isostatic pressing on the deposited powder prepared in step (6) to obtain compacts; and (8) sintering, solution-treating and annealing the compacts prepared in step (7) to obtain a high-resistivity sintered samarium-cobalt magnet.

2. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein the fluoride in step (1) is one or more of calcium fluoride, magnesium fluoride, terbium fluoride, samarium fluoride, copper fluoride, zirconium fluoride, cobalt fluoride and iron fluoride, and the fluoride is 1-3% (by weight) of the magnetic powder in step (4).

3. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein the surfactant in step (1) is one or more of oleic acid, n-heptane, ethylene glycol, cyclohexane, acetic acid and aminocyclic acid.

4. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein in step (1), an addition amount of the surfactant is 2%-6% (by weight) of the fluoride.

5. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein in step (1), a ball-to-material ratio of the high-energy ball milling process is 10-25 based on a percentage by weight.

6. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein the Sm.sub.2(CoFeCuZr).sub.17 alloy in step (3) includes the following compositions based on a percentage by weight: 24≤Sm≤31, 5≤Fe≤30, 4≤Cu≤9, 2≤Zr≤4, and the remaining amount of Co.

7. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein the ultrasonic treatment time in step (5) is 0.5-4 h.

8. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein the voltage in step (6) is 3-10 V, and the time is 10-60 min.

9. The method for preparing a high-resistivity sintered samarium-cobalt magnet of claim 1, wherein in step (7), the magnetic field orientation forming process is performed at a magnetic field strength of 2 T and a pressure of 30-100 MPa.

10. A high-resistivity sintered samarium-cobalt magnet, comprising the following compositions based on a percentage by weight: 23.5≤Sm≤30.2, 4.8≤Fe≤29.7, 3.9>Cu≤8.9, 2≤Zr≤3.8, 0.02≤F≤0.08, 0.04≤TM≤0.2, and the remaining amount of Co, wherein TM is one or more of calcium, magnesium, terbium, copper, zirconium, cobalt and iron.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions and advantages of this application more clearly, this application will be described and explained below in combination with the embodiments. It should be understood that the specific embodiments described are used for explaining this application only, rather than limiting this application. On the basis of the embodiments in this application, all the other embodiments obtained by those of ordinary skill in the art without making creative efforts will fall within the protection scope of this application.

[0036] The “embodiment” mentioned in this application means that the specific features, structures or characteristics described in combination with an embodiment may be involved in at least one of the embodiments of this application. The phrase appearing in different places of this specification is neither necessarily the same embodiment, nor an independent or alternative embodiment that is mutually exclusive from other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments in case of no conflict.

[0037] Unless defined otherwise, the technical terms or scientific terms involved in this application should have the general meanings understood by those of ordinary skill in the technical field to which this application belongs. The words “a”, “an”, “one”, “the” and the like mentioned in this application may indicate the singular or the plural, rather than representing a quantitative limitation. The terms “including/comprising”, “containing”, “having” and any variant thereof mentioned in this application are intended to cover non-exclusive inclusion; the words “connection”, “interconnection”, “coupling” and the like are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The phrase “a plurality of” involved in this application means more than or equal to 2. “And/or” describes an association between associated objects, indicating that three relationships are available. For example, “A and/or B” can mean that A exists alone, A and B exist at the same time, and B exists alone. The terms “first”, “second”, “third” and the like involved in this application are only to distinguish similar objects, and do not represent a specific order of the objects.

EXAMPLE 1

[0038] A method for preparing a high-resistivity sintered samarium-cobalt magnet included the following steps:

[0039] (1) Calcium fluoride was weighed according to 1% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 2% (by weight) of the calcium fluoride, the calcium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 10:1 (that is, a mass ratio of steel balls to the calcium fluoride was 10:1) to obtain fine calcium fluoride powder with an average particle size of 10 nm. In the present invention, there is no limitation to the volume or mass of the alcohol, as long as a ball milling tank is fully filled.

[0040] (2) The fine calcium fluoride powder prepared in step (1) was rinsed and dried in an oxygen-free glove box (in the present invention, there is no limitation to the drying temperature; the drying was performed at a room temperature in this example) to obtain calcium fluoride powder.

[0041] (3) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=24%, Co=40%, Fe=30%, Cu=4% and Zr=2%, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots. The induction smelting or arc smelting in this example is a conventional smelting method in the art, and the present invention does not improve the steps and principles of the induction smelting or arc smelting.

[0042] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 3:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 2.5 μm. The coarse crushing was performed first using the jaw crusher, and then the fine crushing was performed using the disk crusher. There is no limitation to the particle size after fine crushing. The particle size of the magnetic powder after the fine crushing was 0-150 μm in this example.

[0043] (5) The calcium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 0.5 h. In the present invention, there is no specific limitation to a mass ratio of the calcium fluoride powder to the alcohol, as long as the fluoride can be immersed by the alcohol.

[0044] (6) The magnetic powder prepared in step (4) was spread evenly on a platinum sheet A at a bottom of a container, and the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending; after pouring, a platinum sheet B was placed on a surface of the liquid in a suspended manner, the platinum sheet B was completely immersed in the suspension, then deposition treatment was performed under an electric field, and a voltage of 3 V was applied to the platinum sheets A and B for 60 min, with the platinum sheet B serving as a positive electrode and the platinum sheet A serving as a negative electrode, to obtain deposited magnetic powder.

[0045] (7) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 30 MPa and cold isostatic pressing at a pressure of 200 MPa were performed on the deposited magnetic powder prepared in step (6) to obtain compacts.

[0046] (8) The compacts prepared in step (7) were sintered at a temperature of 1,240° C. for 0.5 h. The solution treatment was performed at a temperature of 1,185° C. for 2 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 870° C. for 5 h, then slowly cooling down at 0.5° C./min to 400° C. and keeping the temperature for 5 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=23.5%, Fe=29.7%, Cu=3.9%, Zr=2%, F=0.02%, Ca=0.04% and the remaining amount of Co (namely Co=40.84%).

COMPARATIVE EXAMPLE 1-1

[0047] A method for preparing a high-resistivity sintered samarium-cobalt magnet included the following steps:

[0048] (1) Calcium fluoride was weighed according to 1% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 2% (by weight) of the calcium fluoride, the calcium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 10:1 (that is, a mass ratio of steel balls to the calcium fluoride was 10:1) to obtain fine calcium fluoride powder with an average particle size of 10 nm.

[0049] (2) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=24%, Co=40%, Fe=30%, Cu=4% and Zr=2%, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0050] (3) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (2) using a jaw crusher and a disk crusher, respectively, then the fine calcium fluoride powder prepared in step (1) was added, and powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 3:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 2.5 μm.

[0051] (4) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 30 MPa and cold isostatic pressing at a pressure of 200 MPa were performed on the magnetic powder prepared in step (3) to obtain compacts.

[0052] (5) The compacts prepared in step (4) were sintered at a temperature of 1,240° C. for 0.5 h. The solution treatment was performed at a temperature of 1,185° C. for 2 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 870° C. for 5 h, then slowly cooling down at 0.5° C./min to 400° C. and keeping the temperature for 5 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=23.5%, Fe=29.7%, Cu=3.9%, Zr=2%, F=0.02%, Ca=0.04% and the remaining amount of Co.

[0053] All the other conditions in this comparative example were the same as those in example 1.

COMPARATIVE EXAMPLE 1-2

[0054] (1) Calcium fluoride was weighed according to 1% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 2% (by weight) of the calcium fluoride, the calcium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 10:1 to obtain fine calcium fluoride powder with an average particle size of 10 nm.

[0055] (2) The fine calcium fluoride powder prepared in step (1) was rinsed and dried in an oxygen-free glove box to obtain calcium fluoride powder.

[0056] (3) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=24%, Co=40%, Fe=30%, Cu=4% and Zr=2%, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0057] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 3:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 2.5 μm.

[0058] (5) The calcium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 0.5 h.

[0059] (6) The magnetic powder prepared in step (4) was spread evenly at a bottom of a container, the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending, and the immersion lasted for 60 min without applying any voltage to obtain immersed magnetic powder.

[0060] (7) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 30 MPa and cold isostatic pressing at a pressure of 200 MPa were performed on the immersed magnetic powder prepared in step (6) to obtain compacts.

[0061] (8) The compacts prepared in step (7) were sintered at a temperature of 1,240° C. for 0.5 h. The solution treatment was performed at a temperature of 1,185° C. for 2 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 870° C. for 5 h, then slowly cooling down at 0.5° C./min to 400° C. and keeping the temperature for 5 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=23.5%, Fe=29.7%, Cu=3.9%, Zr=2%, F=0.02%, Ca=0.04% and the remaining amount of Co (namely Co=40.84%).

[0062] All the other conditions in this comparative example were the same as those in example 1.

EXAMPLE 2

[0063] (1) Magnesium fluoride was weighed according to 2% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 4% (by weight) of the magnesium fluoride, the magnesium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 18:1 (that is, a mass ratio of steel balls to the magnesium fluoride was 18:1) to obtain fine magnesium fluoride powder with an average particle size of 100 nm. The alcohol was used as a medium for filling a ball milling tank. In the present invention, there is no limitation to the volume or mass of the alcohol, as long as the ball milling tank is fully filled.

[0064] (2) The fine powder prepared in step (1) was placed in an oxygen-free glove box, and the fine magnesium fluoride powder was rinsed and dried to obtain magnesium fluoride powder.

[0065] (3) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=27%, Co=46%, Fe=18%, Cu=6% and Zr=3%, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0066] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 6:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 4 μm.

[0067] (5) The magnesium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 2.5 h. In the present invention, there is no specific limitation to a mass ratio of the magnesium fluoride powder to the alcohol, as long as the fluoride can be immersed by the alcohol.

[0068] (6) The magnetic powder prepared in step (4) was spread evenly on a platinum sheet A at a bottom of a container, and the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending; after pouring, a platinum sheet B was placed on a surface of the liquid in a suspended manner, the platinum sheet B was completely immersed in the suspension, then deposition treatment was performed under an electric field, and a voltage of 7 V was applied to the platinum sheets A and B for 35 min, with the platinum sheet B serving as a positive electrode and the platinum sheet A serving as a negative electrode, to obtain deposited magnetic powder.

[0069] (7) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 60 MPa and cold isostatic pressing at a pressure of 270 MPa were performed on the deposited magnetic powder prepared in step (6) to obtain compacts.

[0070] (8) The compacts prepared in step (7) were sintered at a temperature of 1,210° C. for 2.5 h. The solution treatment was performed at a temperature of 1,160° C. for 5 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 800° C. for 13 h, then slowly cooling down at 1° C./min to 400° C. and keeping the temperature for 13 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=26.8%, Fe=17.3%, Cu=5.9%, Zr=2.9%, F=0.05%, Mg=0.1%, and the remaining amount of Co (namely Co=46.95%).

COMPARATIVE EXAMPLE 2-1

[0071] (1) Magnesium fluoride was weighed according to 2% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 4% (by weight) of the magnesium fluoride, the magnesium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 18:1 to obtain fine magnesium fluoride powder with an average particle size of 100 nm.

[0072] (2) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=27%, Co=46%, Fe=18%, Cu=6% and Zr=3%, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0073] (3) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (2) using a jaw crusher and a disk crusher, respectively, then the fine magnesium fluoride powder prepared in step (1) was added, and powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 6:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 4 μm.

[0074] (4) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 60 MPa and cold isostatic pressing at a pressure of 270 MPa were performed on the magnetic powder prepared in step (3) to obtain compacts.

[0075] (5) The compacts prepared in step (4) were sintered at a temperature of 1,210° C. for 2.5 h. The solution treatment was performed at a temperature of 1,160° C. for 5 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 800° C. for 13 h, then slowly cooling down at 1° C./min to 400° C. and keeping the temperature for 13 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=26.8%, Fe=17.3%, Cu=5.9%, Zr=2.9%, F=0.05%, Mg=0.1%, and the remaining amount of Co (namely Co=46.95%).

[0076] All the other conditions in this comparative example were the same as those in example 2.

COMPARATIVE EXAMPLE 2-2

[0077] (1) Magnesium fluoride was weighed according to 2% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 4% (by weight) of the magnesium fluoride, the magnesium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 18:1 to obtain fine magnesium fluoride powder with an average particle size of 100 nm.

[0078] (2) The fine powder prepared in step (1) was placed in an oxygen-free glove box, and the fine magnesium fluoride powder was rinsed and dried to obtain magnesium fluoride powder.

[0079] (3) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm=27%, Co=46%, Fe=18%, Cu=6% and Zr=3%, and then the raw materials were smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0080] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 6:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 4 μm.

[0081] (5) The magnesium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 2.5 h.

[0082] (6) The magnetic powder prepared in step (4) was spread evenly at a bottom of a container, and the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending, and the immersion lasted for 35 min without applying any voltage to obtain immersed magnetic powder.

[0083] (7) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 60 MPa and cold isostatic pressing at a pressure of 270 MPa were performed on the immersed magnetic powder prepared in step (6) to obtain compacts.

[0084] (8) The compacts prepared in step (7) were sintered at a temperature of 1,210° C. for 2.5 h. The solution treatment was performed at a temperature of 1,160° C. for 5 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 800° C. for 13 h, then slowly cooling down at 1° C./min to 400° C. and keeping the temperature for 13 h. A final-state magnet obtained included the following compositions based on a percentage by weight: Sm=26.8%, Fe=17.3%, Cu=5.9%, Zr=2.9%, F=0.05%, Mg=0.1%, and the remaining amount of Co.

[0085] All the other conditions in this comparative example were the same as those in example 2.

EXAMPLE 3

[0086] (1) Terbium fluoride was weighed according to 3% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 6% (by weight) of the terbium fluoride, the terbium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 25:1 (that is, a mass ratio of steel balls to the terbium fluoride was 25:1) to obtain fine terbium fluoride powder with an average particle size of 200 nm. The alcohol was used as a medium for filling a ball milling tank. In the present invention, there is no limitation to the volume or mass of the alcohol, as long as the ball milling tank is fully filled.

[0087] (2) The fine powder prepared in step (1) was placed in an oxygen-free glove box, and the fine terbium fluoride powder was rinsed and dried to obtain terbium fluoride powder.

[0088] (3) Metal raw materials were weighed according to compositions based on a percentage by weight: Sm:Co:Fe:Cu:Zr=31:51:5:9:4, and then the raw materials were smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0089] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 8:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 5.2 μm.

[0090] (5) The terbium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 4 h. In the present invention, there is no specific limitation to a mass ratio of the magnesium fluoride powder to the alcohol, as long as the fluoride can be immersed by the alcohol.

[0091] (6) The magnetic powder prepared in step (4) was spread evenly on a platinum sheet A at a bottom of a container, and the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending; after pouring, a platinum sheet B was placed on a surface of the liquid in a suspended manner, the platinum sheet B was completely immersed in the suspension, then deposition treatment was performed under an electric field, and a voltage of 10 V was applied to the platinum sheets A and B for 10 min, with the platinum sheet B serving as a positive electrode and the platinum sheet A serving as a negative electrode, to obtain deposited magnetic powder.

[0092] (7) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 100 MPa and cold isostatic pressing at a pressure of 350 MPa were performed on the deposited magnetic powder prepared in step (6) to obtain compacts.

[0093] (8) The compacts prepared in step (7) were sintered at a temperature of 1,190° C. for 4 h. The solution treatment was performed at a temperature of 1,130° C. for 8 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 750° C. for 20 h, then slowly cooling down at 1.5° C./min to 400° C. and keeping the temperature for 20 h. A final-state magnet obtained was a high-resistivity sintered samarium-cobalt magnet, including the following compositions based on a percentage by weight: Sm=30.2%, Fe=4.8%, Cu=8.9%, Zr=3.8%, F=0.08%, TM=0.2%, and the remaining amount of Co, wherein TM was terbium.

COMPARATIVE EXAMPLE 3-1

[0094] (1) Terbium fluoride was weighed according to 3% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 6% (by weight) of the terbium fluoride, the terbium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 25:1 to obtain fine terbium fluoride powder with an average particle size of 200 nm.

[0095] (2) Metal raw materials were weighed based on a percentage by weight according to a chemical formula of Sm.sub.31Co.sub.51Fe.sub.5Cu.sub.9Zr.sub.4 and the remaining amount of Co, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0096] (3) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (2) using a jaw crusher and a disk crusher, respectively, then the fine terbium fluoride powder prepared in step (1) was added, and powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 8:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 5.2 μm.

[0097] (4) Magnetic field orientation molding at a magnetic filed strength of 2 T and a pressure of 100 MPa and cold isostatic pressing at a pressure of 350 MPa were performed on the magnetic powder prepared in step (3) to obtain compacts.

[0098] (5) The compacts prepared in step (4) were sintered at a temperature of 1,190° C. for 4 h. The solution treatment was performed at a temperature of 1,130° C. for 8 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 750° C. for 20 h, then slowly cooling down at 1.5° C./min to 400° C. and keeping the temperature for 20 h. A final-state magnet obtained was a sintered samarium-cobalt magnet, including the following compositions based on a percentage by weight: Sm=30.2, Fe=4.8, Cu=8.9, Zr=3.8, F=0.08, TM=0.2, and the remaining amount of Co, wherein TM was terbium.

[0099] All the other conditions in this comparative example were the same as those in example 3.

COMPARATIVE EXAMPLE 3-2

[0100] (1) Terbium fluoride was weighed according to 3% (by weight) of magnetic powder, oleic acid was weighed with an addition amount of 6% (by weight) of the terbium fluoride, the terbium fluoride and the oleic acid were mixed with alcohol, and then high-energy ball milling was performed at a ball-to-material ratio of 25:1 to obtain fine terbium fluoride powder with an average particle size of 200 nm.

[0101] (2) The fine powder prepared in step (1) was placed in an oxygen-free glove box, and the fine terbium fluoride powder was rinsed and dried to obtain terbium fluoride powder.

[0102] (3) Metal raw materials were weighed based on a percentage by weight according to a chemical formula of Sm.sub.31Co.sub.51Fe.sub.5Cu.sub.9Zr.sub.4 and the remaining amount of Co, and then smelted uniformly by induction melting or arc melting to obtain alloy ingots.

[0103] (4) Coarse crushing and fine crushing were performed on the alloy ingots prepared in step (3) using a jaw crusher and a disk crusher, respectively, and then powder processing was performed on the finely crushed powder using a stirring mill or rolling ball mill at a ball-to-material mass ratio of 8:1, with 120# high-purity gasoline or high-purity methylbenzene serving as a medium for the ball milling, to obtain magnetic powder with an average particle size of 5.2 μm.

[0104] (5) The terbium fluoride powder prepared in step (2) was mixed with alcohol, and a suspension was obtained by ultrasonic treatment for 4 h.

[0105] (6) The magnetic powder prepared in step (4) was spread evenly at a bottom of a container, and the suspension prepared in step (5) was slowly poured into the container to avoid the magnetic powder from suspending, and the immersion lasted for 10 min without applying any voltage to obtain immersed magnetic powder.

[0106] (7) Magnetic field orientation molding at a magnetic field strength of 2 T and a pressure of 100 MPa and cold isostatic pressing at a pressure of 350 MPa were performed on the immersed magnetic powder prepared in step (6) to obtain compacts.

[0107] (8) The compacts prepared in step (7) were sintered at a temperature of 1,190° C. for 4 h. The solution treatment was performed at a temperature of 1,130° C. for 8 h, and the compacts were cooled down to a room temperature. Afterwards, annealing was performed by keeping a temperature of 750° C. for 20 h, then slowly cooling down at 1.5° C./min to 400° C. and keeping the temperature for 20 h. A final-state magnet obtained was a sintered samarium-cobalt magnet, including the following compositions based on a percentage by weight: Sm=30.2, Fe=4.8, Cu=8.9, Zr=3.8, F=0.08, TM=0.2, and the remaining amount of Co, wherein TM was terbium.

[0108] All the other conditions in this comparative example were the same as those in example 3.

[0109] The magnets prepared in the above-mentioned examples and comparative examples were tested. The magnetic properties of the magnets were tested using a pulsed magnetometer at a maximum magnetic field of 11 T, and the magnetic properties were determined at a room temperature. The resistivity was detected using a four-point method. The detection results are as shown in Table 1.

TABLE-US-00001 TABLE 1 Magnetic Properties and Resistivity Data of the Magnets Prepared in the Examples and the Comparative Examples (BH)max Resistivity Item Br (kG) Hcj (kOe) (MGOe) (μΩ .Math. mm) Example 1 11.72 19.83 31.60 143.50 Comparative 10.56 11.34 22.92 139.60 Example 1-1 Comparative 10.91 13.70 26.38 126.70 Example 1-2 Example 2 11.28 27.63 29.57 156.80 Comparative 9.80 8.73 18.50 154.90 Example 2-1 Comparative 10.76 19.37 24.74 136.50 Example 2-2 Example 3 9.61 22.46 22.10 187.30 Comparative 7.30 8.91 10.87 178.80 Example 3-1 Comparative 8.91 17.65 17.88 156.40 Example 3-2

[0110] It can be seen from Table 1 that the magnetic properties of the magnets in examples 1-3 are all better than those in the comparative examples, indicating that adding fluoride in the preparation method of the present invention can effectively improve the resistivity of the magnets and maintain the high magnetic properties of the magnets at the same time. In comparative examples 1-2, 2-2 and 3-2, the fluoride is simply mixed with the magnetic powder, the resistivity of the magnet can be improved, but the magnetic properties deteriorate rapidly. The properties of the magnets in comparative examples 1-3, 2-3 and 3-3 show that when no voltage is applied, the effect on improving the resistivity of the magnets is poor, and the magnetic properties are also affected to a certain extent.

[0111] Those skilled in the art should understand that the technical features of those embodiments can be combined freely, and not all the technical features of all possible combinations in those embodiments are described to make the description concise. However, all the combinations of these technical features should be deemed as the scope recorded in the specification as long as there is no contradiction therein.

[0112] The above-mentioned embodiments only express several implementation modes of this application, and are specifically described in details, but it cannot be understood as a limitation to the scope of the present invention. It should be noted that for those of ordinary skill in the art, a number of improvements and modifications can be made without departing from the principle of the present invention. Such improvements and modifications should also fall within the protection scope of the present invention.