R-FE-B-BASED SINTERED MAGNET WITH LOW B CONTENT AND PREPARATION METHOD THEREFOR

Abstract

Disclosed are an RFeB-based sintered magnet with a low B content and a preparation method therefor. The sintered magnet comprises the following components: 28.5 wt %-31.5 wt % of R, 0.86 wt %-0.94 wt % of B, 0.2 wt %-1 wt % of Co, 0.2 wt %-0.45 wt % of Cu, 0.3 wt %-0.5 wt % of Ga, 0.02 wt %-0.2 wt % of Ti, and 61 wt %-69.5 wt % of Fe. The sintered magnet has an R.sub.6-T.sub.13M.sub.1+ series phase accounting for 75% or more of the total volume of grain boundaries. The present invention selects optimal content ranges of R, B, Co, Cu, Ga, and Ti, and forms an R.sub.6-T.sub.13M.sub.1+ series phase of a special composition and increases its volume fraction in grain boundary phases, so as to acquire higher Hcj and SQ values.

Claims

1. An RFeB-based sintered magnet with a low B content, containing an R.sub.2Fe.sub.14B-type main phase, the R being at least one rare earth element comprising Nd, wherein: the RFeB-based sintered magnet comprises the following components: 28.5 wt %-31.5 wt % of R, 0.86 wt %-0.94 wt % of B, 0.2 wt %-1 wt % of Co, 0.2 wt %-0.45 wt % of Cu, 0.3 wt %-0.5 wt % of Ga, 0.02 wt %-0.2 wt % of Ti, and 61 wt %-69.5 wt % of Fe, and the RFeB-based sintered magnet has an R.sub.6-T.sub.13M.sub.1+ series phase accounting for 75% or more of a total volume of grain boundaries, wherein T is at least one selected from Fe or Co, M comprises 80 wt % or more of Ga and 20 wt % or below of Cu, and is 0.14-0.04.

2. The RFeB-based sintered magnet with the low B content according to claim 1, wherein: the components comprise 5.0 wt % or below of X and inevitable impurities, X is selected from at least one of a group of elements consisting of Zn, Al, In, Si, Ti, V, Cr, Mn, Ni, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, and W, and when X comprises at least one of Nb, Zr, or Cr, a total content of Nb, Zr, and Cr is 0.20 wt % or below.

3. The RFeB-based sintered magnet with the low B content according to claim 2, wherein a balance is Fe.

4. The RFeB-based sintered magnet with the low B content according to claim 2, wherein: the inevitable impurities comprise O, and an O content of the RFeB-based sintered magnet is 0.5 wt % or below.

5. The RFeB-based sintered magnet with the low B content according to claim 1, wherein the RFeB-based sintered magnet is an RFeB-based sintered magnet having been subjected to heat treatment.

6. The RFeB-based sintered magnet with the low B content according to claim 1, wherein: the RFeB-based sintered magnet is prepared according to a method comprising: preparing a molten raw material component liquid of the RFeB-based sintered magnet at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec into a quenched alloy; crushing the quenched alloy by alloy hydrogen absorption; micro-pulverizing the crushed quenched alloy into a fine powder; acquiring a formed body using a magnetic field forming method or by hot-pressing thermal deformation; sintering the formed body in a vacuum or inert gas at a temperature of 900 C.-1100 C.; and performing a heat treatment on the sintered formed body to acquire a product.

7. The RFeB-based sintered magnet with the low B content according to claim 1, wherein a content of Dy, Tb, Gd, or Ho in the R is 1% or below.

8. A method for preparing an RFeB-based sintered magnet with a low B content, containing an R.sub.2Fe.sub.14B-type main phase, the R being at least one rare earth element comprising Nd, wherein: the RFeB-based sintered magnet comprises the following components: 28.5 wt %-31.5 wt % of R, 0.86 wt %-0.94 wt % of B, 0.2 wt %-1 wt % of Co, 0.2 wt %-0.45 wt % of Cu, 0.3 wt %-0.5 wt % of Ga, 0.02 wt %-0.2 wt % of Ti, and 61 wt %-69.5 wt % of Fe, and the method comprises: preparing a molten raw material component liquid of the RFeB-based sintered magnet at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec into an alloy for the RFeB-based sintered magnet; crushing the alloy by alloy hydrogen absorption; micro-pulverizing the crushed alloy into a fine powder; acquiring a formed body using a magnetic field forming method; sintering the formed body in a vacuum or inert gas at a temperature of 900 C.-1100 C.; and performing a heat treatment on the sintered formed body to acquire a product.

9. The RFeB-based sintered magnet with the low B content according to claim 2, wherein: the RFeB-based sintered magnet is prepared according to a method comprising: preparing a molten raw material component liquid of the RFeB-based sintered magnet at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec into a quenched alloy; crushing the quenched alloy by alloy hydrogen absorption; micro-pulverizing the crushed quenched alloy into a fine powder; acquiring a formed body using a magnetic field forming method or by hot-pressing thermal deformation; sintering the formed body in a vacuum or inert gas at a temperature of 900 C.-1100 C.; and performing a heat treatment on the sintered formed body to acquire a product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a distribution diagram of Nd, Cu, Ga, and Co formed by EPMA mapping of a sintered magnet in Embodiment 1.7; and

[0026] FIG. 2 is a distribution diagram of Nd, Cu, Ga, and Co formed by EPMA mapping of a sintered magnet in Comparative Example 1.4.

DETAILED DESCRIPTION

[0027] The present disclosure is further described in detail in conjunction with embodiments hereinafter.

[0028] The magnetic property evaluation process, component determination, and FE-EPMA testing methods mentioned in the embodiments are as follows:

[0029] Magnetic Property Evaluation Process: the magnetic performance of a sintered magnet is determined by using the NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology of China.

[0030] Component Determination: Each component is determined using a high-frequency inductively coupled plasma emission spectrometer (ICP-OES). In addition, O (oxygen amount) is determined using a gas analysis device based on a gas fusion-infrared absorption method; N (nitrogen amount) is determined using a gas analysis device based on a gas fusion-thermal conductivity method; and C (carbon amount) is determined using a gas analysis device based on a combustion-infrared absorption method.

[0031] FE-EPMA Testing: The surface which is perpendicular to the orientation direction of a sintered magnet is polished, and is detected using a field emission electron probe microanalyzer (FE-EPMA) [Japan Electron Optics Laboratory Co., Ltd. (JEOL), 8530F]. First, an R.sub.6-T.sub.13-M phase in a magnet and the contents of Ga and Cu in M are determined by quantitative analysis and mapping under test conditions of an acceleration voltage of 15 kV and a probe beam current of 50 nA. Then statistics on the volume fraction of the R.sub.6-T.sub.13-M phase are collected by backscatter electron imaging (BSE). The specific method is as follows: randomly capturing 10 BSE images with a magnification of 2000, and using image analysis software to calculate the proportion.

[0032] In the present invention, the selected heat treatment temperature range and heat treatment method are conventional choices in the industry and is usually a two-stage heat treatment, in which the first-stage heat treatment temperature is 800 C.-950 C., and the second-stage heat treatment temperature is 400 C.-650 C.

[0033] In a recommended embodiment, the components comprise X of 5.0 wt % or below and inevitable impurities, wherein X is selected from at least one of the group of elements consisting of Zn, Al, In, Si, Ti, V, Cr, Mn, Ni, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, and W. When X comprises at least one of Nb, Zr, or Cr, the total content of Nb, Zr, and Cr is 0.20 wt % or below.

[0034] In a recommended embodiment, the balance is Fe.

[0035] In a recommended embodiment, the inevitable impurities comprise O, and the O content of the sintered magnet is 0.5 wt % or below. Although magnets with low oxygen contents (5000 ppm or below) have good magnetic properties, grains thereof tend to aggregate and grow during sintering at higher temperatures. Therefore, the magnets are more sensitive to respond to effects produced by extremely small microstructural improvements of quenched alloys, powders, and sintered magnets. At the same time, due to the low oxygen content, less RO compounds are present, R can be more fully utilized to form the R.sub.6-T.sub.13-M phase to increase the Hcj, and RO compound impurity phases are less and the squareness increases.

[0036] In addition, the inevitable impurities mentioned in the present invention further comprise small amounts of C, N, S, P, and other impurities inevitably mixed in the raw materials or in the manufacturing process. Therefore, in the manufacturing process of the sintered magnet mentioned in the present invention, it is better to control the C content to be 0.25 wt % or below, more preferably 0.1 wt % or below, the N content to be 0.15 wt % or below, the S content to be 0.05 wt % or below, and the P content to be 0.05 wt % or below.

[0037] It should be noted that the steps of manufacturing the magnet in the low oxygen environment belong to the prior art, and all embodiments of the present disclosure are implemented with the steps of manufacturing the magnet in the low oxygen environment, which are not described in detail herein again.

[0038] In a recommended embodiment, the micro-pulverization is a jet pulverization process. In the above manner, the degree of dispersion of the R.sub.6-T.sub.13-M phase in the sintered magnet is further increased.

[0039] In a recommended embodiment, the content of Dy, Tb, Gd, or Ho in R is 1% or below. For sintered magnets with a Dy, Tb, Gd, or Ho content of 1% or below, the presence of the R.sub.6-T.sub.13M.sub.1+ series phase improves the effect of increasing the Hcj of the magnets more significantly.

Embodiment 1

[0040] Raw material Preparation Process: Nd and Dy with a purity of 99.5%, industrial FeB, industrial pure Fe, and Co, Cu, Ti, Ga, and Al with a purity of 99.9% were prepared.

[0041] Smelting Process: The prepared raw materials were put into a crucible made of alumina, and vacuum smelting was carried out in a high-frequency vacuum induction smelting furnace in a vacuum at 10.sup.2 Pa at a temperature of 1500 C. or below.

[0042] Casting Process: An Ar gas was introduced into the smelting furnace after the vacuum smelting until the gas pressure reached 50,000 Pa, and then casting was performed using a single-roller quenching process at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec to acquire a quenched alloy. The quenched alloy was subjected to thermal insulation heat treatment at 600 C. for 60 minutes, and then cooled to room temperature.

[0043] Hydrogen Decrepitation Process: A hydrogen decrepitation furnace in which the quenched alloy was placed was vacuumized at room temperature, and then a hydrogen gas with a purity of 99.5% was introduced into the hydrogen decrepitation furnace. The hydrogen pressure was maintained at 0.1 MPa. After full hydrogen absorption, the hydrogen decrepitation furnace was vacuumized while the temperature was raised to a temperature of 500 C., then cooling was performed, and the hydrogen decrepitated powder was extracted.

[0044] Micro-Pulverization Step: Under a nitrogen atmosphere with an oxidizing gas content of 100 ppm or below, the hydrogen decrepitated powder was subjected to jet mill pulverization under a pressure of 0.4 MPa for 2 hours in a pulverization chamber to acquire a fine powder. The oxidizing gas refers to oxygen or moisture.

[0045] Methyl octoate was added to the jet mill pulverized powder. The amount of the methyl octoate added was 0.15% of the weight of the mixed powder, and the mixture was then fully mixed using a V-type mixer.

[0046] Magnetic Field Forming Process: Using a right-angle oriented magnetic field forming machine, in a 1.8 T oriented magnetic field and under a forming pressure of 0.4 ton/cm.sup.2, the above powder with the methyl octoate added was formed into a cube with a side length of 25 mm by primary forming, and the cube was demagnetized in a 0.2 T magnetic field after the primary forming.

[0047] In order to prevent the formed body from being exposed to air after the primary forming, the formed body was sealed, and was then subjected to secondary forming using a secondary forming machine (isostatic pressing forming machine) under a pressure of 1.4 ton/cm.sup.2.

[0048] Sintering Process: Each formed body was transferred to a sintering furnace for sintering in a vacuum at 10.sup.3 Pa, each maintained at 200 C. and 800 C. for 2 hours, followed by sintering at 1060 C. for 2 hours. Afterwards, an Ar gas was introduced until the gas pressure reached 0.1 MPa, and then the sintered body was cooled to room temperature.

[0049] Heat Treatment Process: The sintered body was subjected to primary heat treatment at 900 C. for 2 hours in a high-purity Ar gas, followed by secondary heat treatment at 520 C. for 2 hours, and was then cooled to room temperature and extracted.

[0050] Processing Process: The sintered body was processed into a magnet with a diameter of 10 mm and a thickness of 5 mm, with the direction of the thickness being the orientation direction of the magnetic field, to acquire a sintered magnet.

[0051] The magnets prepared from the sintered bodies in the embodiments and comparative examples were directly subjected to ICP-OES testing and magnetic property testing to evaluate their magnetic properties. The components and evaluation results of the magnets in the embodiments and comparative examples are shown in Table 1 and Table 2:

TABLE-US-00001 TABLE 1 Compositional Proportions of Elements (wt %) No. Nd Dy B Co Cu Ga Ti Al O Fe Comparative Example 1.1 28.5 0.5 0.83 0.42 0.40 0.42 0.05 0.2 0.1 Balance Embodiment 1.1 28.5 0.5 0.86 0.42 0.40 0.42 0.05 0.2 0.1 Balance Embodiment 1.2 28.5 0.5 0.89 0.42 0.40 0.42 0.05 0.2 0.1 Balance Embodiment 1.3 28.5 0.5 0.92 0.42 0.40 0.42 0.05 0.2 0.1 Balance Embodiment 1.4 28.5 0.5 0.94 0.42 0.40 0.42 0.05 0.2 0.1 Balance Comparative Example 1.2 28.5 0.5 0.96 0.42 0.40 0.42 0.05 0.2 0.1 Balance Comparative Example 1.3 28.0 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance Embodiment 1.5 28.5 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance Embodiment 1.6 29.5 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance Embodiment 1.7 30.5 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance Embodiment 1.8 31.5 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance Comparative Example 1.4 32.0 0 0.88 0.45 0.30 0.35 0.1 0.1 0.1 Balance

TABLE-US-00002 TABLE 2 Evaluation of Magnetic Properties of Embodiments Br Hcj SQ (BH)max No. (kGs) (kOe) (%) (MGOe) Comparative Example 1.1 14.15 10.0 82.3 47.5 Embodiment 1.1 13.97 18.1 98.4 47.1 Embodiment 1.2 13.9 19.3 99.4 46.4 Embodiment 1.3 13.95 19.7 99.6 46.9 Embodiment 1.4 13.8 18.6 99.3 45.9 Comparative Example 1.2 13.35 16.0 99.2 43.0 Comparative Example 1.3 14.18 8.0 85.6 48.5 Embodiment 1.5 14.22 17.8 98.4 48.8 Embodiment 1.6 14.14 18.2 99.4 48.2 Embodiment 1.7 14.05 18.7 99.5 47.6 Embodiment 1.8 13.89 18.5 99.4 46.6 Comparative Example 1.4 13.52 15.0 99.4 44.0

TABLE-US-00003 TABLE 3 FE-EPMA Single Point Quantitative Analysis Result of Sintered Magnet in Embodiment 1.7 (at %) Nd Fe Co Ga Cu B Phase component Point 1 29.99 65.03 0.31 4.23 0.44 0 R.sub.6-T.sub.13-M Point 2 11.96 80.4 1.55 0.21 0.07 5.81 R.sub.2-T.sub.14-B

[0052] Our conclusion is as follows:

[0053] For a sintered magnet with low TRE (total rare earths), when the B content is less than 0.86 wt %, due to the overly low B content, excessive 2-17 phases are generated, and synergistic addition of Co, Cu, Ga, and Ti forms only a small amount of R.sub.6-T.sub.13-M phase in grain boundaries, which has no obvious improvement to the Hcj of the sintered magnet and decreases the squareness. By contrast, when the B content exceeds 0.94 wt %, because the B content increases, a B-rich phase is generated, such as R.sub.1.1Fe.sub.4B.sub.4, resulting in a decrease in the volume fraction of a main phase and a decrease in the Br of the sintered magnet, the synergistic addition of Co, Cu, Ga, and Ti forms little or no R.sub.6-T.sub.13-M phase, and there is no obvious improvement to the Hcj of the sintered magnet. However, for a B content of 0.86 wt %-0.94 wt %, the synergistic addition of Co, Cu, Ga, and Ti ensures that a sufficient volume fraction of R.sub.6-T.sub.13-M phase is generated in the grain boundaries, and there is more obvious improvement to the properties of the sintered magnet.

[0054] In addition, for a sintered magnet with a low B content, when the TRE (total rare earths) content is less than 28.5 wt %, the TRE content is overly low and -Fe precipitates, resulting in a decrease in the properties of the sintered magnet. By contrast, when the TRE content exceeds 31.5 wt %, since the TRE content increases, the volume fraction of a main phase decreases; therefore, the Br of the sintered magnet decreases. Furthermore, synergistic addition of Co, Cu, Ga, and Ti has no obvious improvement to the Hcj of the sintered magnet because R generates more other RGaCu phases in grain boundaries, which leads to a decrease in the proportion of an R.sub.6-T.sub.13-M phase. However, for TRE of 28.5 wt %-31.5 wt %, the synergistic addition of Co, Cu, Ga, and Ti ensures that a sufficient volume fraction of R.sub.6-T.sub.13-M phase is generated in the grain boundaries of the low-B magnet, and there is more obvious improvement to the properties of the sintered magnet.

[0055] The sintered magnet in Embodiment 1.7 was subjected to an FE-EPMA test, and the results are shown in FIG. 1 and Table 3, where FIG. 1 is the concentration distribution of Nd, Cu, Ga, and Co and an BSE image of corresponding positions, and Table 3 is single-point quantitative analysis results showing that at least three phases are present in the BSE image. The gray-white region 1 is an R.sub.6-T.sub.13-M phase, where R is Nd, T is mainly Fe and Co, M comprises 80 wt % or more of Ga and 20 wt % or below of Cu. The black region 2 is an R.sub.2Fe.sub.14B main phase, and the bright white region 3 is other R-rich phases. Ten BSE images with a magnification of 2000 were captured randomly, and the volume fraction of the R.sub.6-T.sub.13-M phase was calculated using image analysis software, which can show that the R.sub.6-T.sub.13-M phase accounted for 80% or more of the total volume of grain boundaries in the sample of this embodiment. Similarly, the sintered magnets in Embodiments 1.1-1.6 and Embodiment 1.8 were subjected to FE-EPMA tests, in all of which it can be observed that the volume of the R.sub.6-T.sub.13-M phase accounted for 75% or more of the total volume of grain boundaries. In the R.sub.6-T.sub.13-M phase, R is Nd, or Nd and Dy, T is mainly Fe and Co, and M comprises 80 wt % or more of Ga and 20 wt % or below of Cu.

[0056] An FE-EPMA test was performed on Comparative Example 1.4. The results are shown in FIG. 2, which represents the concentration distribution of Nd, Cu, Ga, and Co and an BSE image of corresponding positions. The gray-white region 1a in the BSE image is an R.sub.6-T.sub.13-M phase, the black region 2a is an R.sub.2Fe.sub.14B main phase, and the bright white region 3a is other R-rich phases. It can be seen that the gray-white R.sub.6-T.sub.13M phase in the grain boundary phases of the comparative example has a small proportion, and most are bright white Nd-rich phases of other compositions.

[0057] Comparative Examples 1.1-1.3 were tested, in which almost no R.sub.6-T.sub.13M phase was observed in the grain boundaries of the sintered magnets, or the volume of the R.sub.6-T.sub.13M phase was less than 75% of the total volume of the grain boundaries.

Embodiment 2

[0058] Raw Material Preparation Process: Nd and Dy with a purity of 99.8%, industrial FeB, industrial pure Fe, and Co, Cu, Ti, Ga, Zr, and Si with a purity of 99.9% were prepared.

[0059] Smelting Process: The prepared raw materials were put into a crucible made of alumina, and vacuum smelting was carried out in a high-frequency vacuum induction smelting furnace in a vacuum at 510.sup.2 Pa at a temperature of 1500 C. or below.

[0060] Casting Process: An Ar gas was introduced into the smelting furnace after the vacuum smelting until the gas pressure reached 55,000 Pa, under which casting was performed, followed by quenching at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec to acquire a quenched alloy.

[0061] Hydrogen Decrepitation Process: A hydrogen decrepitation furnace in which the quenched alloy was placed was vacuumized at room temperature, and then a hydrogen gas with a purity of 99.9% was introduced into the hydrogen decrepitation furnace. The hydrogen pressure was maintained at 0.15 MPa. After full hydrogen absorption, the hydrogen decrepitation furnace was vacuumized while the temperature was raised for full dehydrogenation, then cooling was performed, and the hydrogen decrepitated powder was extracted.

[0062] Micro-Pulverization Step: Under a nitrogen atmosphere with an oxidizing gas content of 150 ppm or below, the hydrogen decrepitated powder was subjected to jet mill pulverization under a pressure of 0.38 MPa for 3 hours in a pulverization chamber to acquire a fine powder. The oxidizing gas refers to oxygen or moisture.

[0063] Zinc stearate was added to the jet mill pulverized powder. The amount of the zinc stearate added was 0.12% of the weight of the mixed powder, and the mixture was then fully mixed using a V-type mixer.

[0064] Magnetic Field Forming Process: Using a right-angle oriented magnetic field forming machine, in a 1.6 T oriented magnetic field, and under a forming pressure of 0.35 ton/cm.sup.2, the above powder with the zinc stearate added was formed into a cube with a side length of 25 mm by primary forming, and the cube was demagnetized in a 0.2 T magnetic field after the primary forming.

[0065] In order to prevent the formed body from being exposed to air after the primary forming, the formed body was sealed and was then subjected to secondary forming using a secondary forming machine (isostatic pressing forming machine) under a pressure of 1.3 tons/cm.sup.2.

[0066] Sintering Process: Each formed body was transferred to a sintering furnace for sintering in a vacuum at 510.sup.3 Pa, each maintained at 300 C. and 600 C. for 1 hour, followed by sintering at 1040 C. for 2 hours. Afterwards, an Ar gas was introduced until the gas pressure reached 0.1 MPa, and then the sintered body was cooled to room temperature.

[0067] Heat Treatment Process: The sintered body was subjected to primary heat treatment at 880 C. for 3 hours in a high-purity Ar gas, followed by secondary heat treatment at 500 C. for 3 hours, and was then cooled to room temperature and extracted.

[0068] Processing Process: The sintered body was processed into a magnet with a diameter of 20 mm and a thickness of 5 mm, with the direction of the thickness being the orientation direction of the magnetic field, to acquire a sintered magnet.

[0069] The magnets prepared from the sintered bodies in the embodiments and comparative examples were directly subjected to ICP-OES testing and magnetic property testing to evaluate their magnetic properties. The components and evaluation results of the magnets in the embodiments and comparative examples are shown in Table 4 and Table 5:

TABLE-US-00004 TABLE 4 Compositional Proportions of Elements (wt %) No. Nd Dy B Co Cu Ga Ti Zr Si O Fe Comparative 30.0 0.1 0.92 0.4 0.1 0.45 0.12 0.1 0.2 0.12 Balance Example 2.1 Embodiment 2.1 30.0 0.1 0.92 0.4 0.2 0.45 0.12 0.1 0.2 0.12 Balance Embodiment 2.2 30.0 0.1 0.92 0.4 0.30 0.45 0.12 0.1 0.2 0.12 Balance Embodiment 2.3 30.0 0.1 0.92 0.4 0.45 0.45 0.12 0.1 0.2 0.12 Balance Comparative 30.0 0.1 0.92 0.4 0.55 0.45 0.12 0.1 0.2 0.12 Balance Example 2.2 Comparative 29.9 0.1 0.89 0.1 0.40 0.4 0.08 0.2 0.15 0.12 Balance Example 2.3 Embodiment 2.4 29.9 0.1 0.89 0.2 0.40 0.4 0.08 0.2 0.15 0.12 Balance Embodiment 2.5 29.9 0.1 0.89 0.5 0.40 0.4 0.08 0.2 0.15 0.12 Balance Embodiment 2.6 29.9 0.1 0.89 0.8 0.40 0.4 0.08 0.2 0.15 0.12 Balance Embodiment 2.7 29.9 0.1 0.89 1.0 0.40 0.4 0.08 0.2 0.12 0.12 Balance Comparative 29.9 0.1 0.89 1.1 0.40 0.4 0.08 0.2 0.15 0.12 Balance Example 2.4

TABLE-US-00005 TABLE 5 Evaluation of Magnetic Properties of Embodiments Br Hcj SQ (BH)max No. (kGs) (kOe) (%) (MGOe) Comparative Example 2.1 14.01 15 88.5 47.4 Embodiment 2.1 14.08 17.5 99.2 47.9 Embodiment 2.2 14.03 18.1 99.2 47.5 Embodiment 2.3 14.05 17.9 99.3 47.7 Comparative Example 2.2 13.91 14.5 97.6 46.7 Comparative Example 2.3 13.81 15.6 98.2 46.0 Embodiment 2.4 13.98 17.2 99.5 47.2 Embodiment 2.5 14.08 18.2 99.6 47.9 Embodiment 2.6 14.02 17.6 99.4 47.5 Embodiment 2.7 14.02 17.3 99.6 47.5 Comparative Example 2.4 13.85 15.2 99.1 46.3

[0070] Our conclusion is as follows:

[0071] For a low TRE (total rare earths) and low B series sintered magnet, when the Cu content is less than 0.2 wt %, due to the overly low Cu content, no sufficient amount of Cu entering grain boundaries exists, synergistic addition of Co, Ga, and Ti does not form an insufficient R.sub.6-T.sub.13-M phase in the grain boundaries, and there is no obvious improvement to the Hcj of the sintered magnet. Similarly, when the Cu content exceeds 0.45 wt %, because the Cu content is excessive, the content of Cu in M in the formed R.sub.6-T.sub.13-M phase is higher than 20%, and the synergistic addition of Co, Ga, and Ti also has no obvious improvement to the properties of the sintered magnet. However, for a Cu content of 0.2 wt %-0.45 wt %, the synergistic addition of Co, Ga, and Ti ensures that 75% or more of the R.sub.6-T.sub.13-M phase is generated in the grain boundaries, the Ga content in M is greater than 80% and the Cu content is less than 20%, and there is more obvious improvement to the properties of the sintered magnet.

[0072] For the low TRE (total rare earths) and low B series sintered magnet, when the Co content is less than 0.2 wt %, due to the overly low Co content, other RCo phases are preferentially formed, synergistic addition of Cu, Ga, and Ti does not form a sufficient R.sub.6-T.sub.13-M phase in the grain boundaries, and there is no obvious improvement to the properties of the sintered magnet. Similarly, when the Co content exceeds 1.0 wt %, due to the excessive Co content, a part of Co enters the grain boundaries, the synergistic addition of Cu, Ga, and Ti forms an R.sub.6-T.sub.13-M phase with a Ga content lower than 80% in M, and there is no obvious improvement to the properties of the sintered magnet. However, for a Co content of 0.2 wt %-1.0 wt %, the synergistic addition of Cu, Ga, and Ti ensures that 75% or more of the R.sub.6-T.sub.13-M phase is generated in the grain boundaries, the Ga content in M is greater than 80% and the Cu content is lower than 20%, and there is more obvious improvement to the properties of the sintered magnet.

[0073] Similarly, the sintered magnets in Embodiments 2.1-2.7 were subjected to FE-EPMA tests, in which the R.sub.6-T.sub.13-M phase accounting for 75% or more of the total volume of the grain boundaries can be observed, where R is Nd and Dy, T is mainly Fe and Co, and M comprise 80 wt % or more of Ga and 20 wt % or below of Cu.

[0074] Furthermore, the sintered magnets in Comparative Example 2.2 and Comparative Example 2.4 were subjected to FE-EPMA tests, in which an R.sub.6-T.sub.13-M phase was observed in the grain boundaries of the sintered magnets. The R.sub.6-T.sub.13-M phase accounted for 75% or more of the total volume of the grain boundaries, but the content of Ga in M was less than 80 wt %.

[0075] The sintered magnets of Comparative Example 2.1 and Comparative Example 2.3 were subjected to FE-EPMA tests, in which an R.sub.6-T.sub.13-M phase was observed in the grain boundaries of the sintered magnets. The R.sub.6-T.sub.13-M phase was less than 75% of the total volume of the grain boundaries.

Embodiment 3

[0076] Raw Material Preparation Process: Nd and Dy with a purity of 99.8%, industrial FeB, industrial pure Fe, and Co, Cu, Ti, Ga, Ni, Nb, and Mn with a purity of 99.9% were prepared.

[0077] Smelting Process: The prepared raw materials were put into a crucible made of alumina, and vacuum smelting was carried out in a high-frequency vacuum induction smelting furnace in a vacuum at 510.sup.2 Pa.

[0078] Casting Process: An Ar gas was introduced into the smelting furnace after the vacuum smelting until the gas pressure reached 45,000 Pa, under which casting was performed, followed by quenching at a cooling rate of 10.sup.2 C./sec-10.sup.4 C./sec to acquire a quenched alloy.

[0079] Hydrogen Decrepitation Process: A hydrogen decrepitation furnace in which the quenched alloy was placed was vacuumized at room temperature, and then a hydrogen gas with a purity of 99.9% was introduced into the hydrogen decrepitation furnace. The hydrogen pressure was maintained at 0.12 MPa. After full hydrogen absorption, the hydrogen decrepitation furnace was vacuumized while the temperature was raised for full dehydrogenation, then cooling was performed, and the hydrogen decrepitated powder was extracted.

[0080] Micro-Pulverization Step: Under a nitrogen atmosphere with an oxidizing gas content of 200 ppm or below, the hydrogen decrepitated powder was subjected to jet mill pulverization under a pressure of 0.42 MPa for 2 hours in a pulverization chamber to acquire a fine powder. The oxidizing gas refers to oxygen or moisture.

[0081] Zinc stearate was added to the jet mill pulverized powder. The amount of the zinc stearate added was 0.1% of the weight of the mixed powder, and the mixture was then fully mixed using a V-type mixer.

[0082] Magnetic Field Forming Process: Using a right-angle oriented magnetic field forming machine, in a 1.5 T oriented magnetic field, and under a forming pressure of 0.45 ton/cm.sup.2, the above powder with the zinc stearate added was formed into a cube with a side length of 25 mm by primary forming, and the cube was demagnetized after the primary forming.

[0083] In order to prevent the formed body from being exposed to air after the primary forming, the formed body was sealed, and was then subjected to secondary forming using a secondary forming machine (isostatic pressing forming machine) under a pressure of 1.2 ton/cm.sup.2.

[0084] Sintering Process: Each formed body was transferred to a sintering furnace for sintering in a vacuum at 510.sup.4 Pa, each maintained at 300 C. and 700 C. for 1.5 hours, followed by sintering at 1050 C. Afterwards, an Ar gas was introduced until the gas pressure reached the atmospheric pressure, and then the sintered body was cooled to room temperature by circulation.

[0085] Heat Treatment Process: The sintered body was subjected to primary heat treatment at 890 C. for 3.5 hours in a high-purity Ar gas, followed by secondary heat treatment at 550 C. for 3.5 hours, and was then cooled to room temperature and extracted.

[0086] Processing Process: The sintered body was processed into a magnet with a diameter of 20 mm and a thickness of 5 mm, with the direction of the thickness being the orientation direction of the magnetic field, to acquire a sintered magnet.

[0087] The magnets prepared from the sintered bodies in the embodiments and comparative examples were directly subjected to ICP-OES testing and magnetic property testing to evaluate their magnetic properties. The components and evaluation results of the magnets in the embodiments and comparative examples are shown in Table 6 and Table 7:

TABLE-US-00006 TABLE 6 Compositional Proportions of Elements (wt %) No. Nd Dy B Co Cu Ga Ti Ni Nb Mn O Fe Comparative Example 3.1 29.4 1.0 0.90 0.5 0.25 0.2 0.16 0.2 0.1 0.02 0.15 Balance Embodiment 3.1 29.4 1.0 0.90 0.5 0.25 0.3 0.16 0.2 0.1 0.02 0.15 Balance Embodiment 3.2 29.4 1.0 0.90 0.5 0.25 0.4 0.16 0.2 0.1 0.02 0.15 Balance Embodiment 3.3 29.4 1.0 0.90 0.5 0.25 0.5 0.16 0.2 0.1 0.02 0.15 Balance Embodiment 3.4 29.4 1.5 0.90 0.5 0.25 0.5 0.16 0.2 0.1 0.02 0.15 Balance Comparative Example 3.2 29.4 1.0 0.90 0.5 0.25 0.6 0.16 0.2 0.1 0.02 0.15 Balance Comparative Example 3.3 29.4 1.5 0.90 0.5 0.25 0.6 0.16 0.2 0.1 0.02 0.15 Balance Comparative Example 3.4 29.5 1.0 0.94 0.6 0.3 0.38 0.01 0.1 0.05 0.05 0.15 Balance Embodiment 3.5 29.5 1.0 0.94 0.6 0.3 0.38 0.02 0.1 0.05 0.05 0.15 Balance Embodiment 3.6 29.5 1.0 0.94 0.6 0.3 0.38 0.08 0.1 0.05 0.05 0.15 Balance Embodiment 3.7 29.5 1.0 0.94 0.6 0.3 0.38 0.14 0.1 0.05 0.05 0.15 Balance Embodiment 3.8 29.5 1.0 0.94 0.6 0.3 0.38 0.2 0.1 0.05 0.05 0.15 Balance Comparative Example 3.5 29.5 1.0 0.94 0.6 0.3 0.38 0.24 0.1 0.05 0.05 0.15 Balance

TABLE-US-00007 TABLE 7 Evaluation of Magnetic Properties of Embodiments Br Hcj SQ (BH)max No. (kGs) (kOe) (%) (MGOe) Comparative Example 3.1 13.72 15.8 99 45.5 Embodiment 3.1 13.88 18.9 99.6 46.5 Embodiment 3.2 13.85 19.7 99.7 46.3 Embodiment 3.3 13.80 20.2 99.6 46.0 Embodiment 3.4 13.78 20.3 99.7 45.6 Comparative Example 3.2 13.61 16.5 98.9 44.7 Comparative Example 3.3 13.51 17.5 99.0 44.1 Comparative Example 3.4 13.52 16.2 88.7 44.1 Embodiment 3.5 13.88 18.1 99.5 46.5 Embodiment 3.6 13.85 18.7 99.8 46.3 Embodiment 3.7 13.82 19.4 99.5 46.1 Embodiment 3.8 13.82 19.8 99.6 46.1 Comparative Example 3.5 13.72 16.2 89.4 45.5

[0088] Our conclusion is as follows:

[0089] For a low TRE (total rare earths) and low B series sintered magnet, when the Ga content is less than 0.3 wt %, due to the overly low Ga content, synergistic addition of Co, Cu, and Ti forms an R.sub.6-T.sub.13-M phase with a Ga content lower than 80% in M, and there is no obvious improvement to the properties of the sintered magnet. Similarly, when the Ga content exceeds 0.5 wt %, due to the excessive Ga content, other RGaCu phases (such as an R.sub.6-T.sub.2-M.sub.2 phase) are generated, the volume fraction of these phases in grain boundaries is higher than 25%, the synergistic addition of Co, Cu, and Ti does not form an sufficient R.sub.6-T.sub.13-M phase in the grain boundaries, and there is no obvious improvement to the properties of the sintered magnet. However, for a Ga content of 0.3 wt %-0.5 wt %, the synergistic addition of Co, Cu, and Ti ensures that 75% or more of the R.sub.6-T.sub.13-M phase is generated in the grain boundaries, the Ga content in M is greater than 80% and the Cu content is lower than 20%, and there is more obvious improvement to the properties of the sintered magnet.

[0090] At the same time, for the low TRE (total rare earths) and low B series sintered magnet, Ga, Cu, Co, and Ti are kept within the scope of the claims. When the Dy content is lower than 1%, the increase in Hcj is more obvious. For example, compared with Comparative Example 3.2, the Hcj of the sintered magnet in Embodiment 3.3 is increased by 3.7 kOe. Further, in Embodiment 3.4, when the Dy content is greater than 1%, the synergistic addition of Ga, Cu, Co, and Ti increases the Hcj of the sintered magnet by only 2.8 kOe compared with the Hcj of the sintered magnet in Comparative Example 3.3.

[0091] For the low TRE (total rare earths) and low B series sintered magnet, when the Ti content is less than 0.02 wt %, due to the overly low Ti content, it is difficult to perform high-temperature sintering, resulting in insufficiently dense sintering, and therefore the Br of the sintered magnet decreases. When sintering is insufficient, synergistic addition of Cu, Ga, and Co cannot form sufficient R.sub.6-T.sub.13-M in the grain boundaries in subsequent heat treatment, and there is no obvious improvement to the properties of the sintered magnet. Similarly, when the Ti content exceeds 0.2 wt %, due to the excessive Ti content, a TiBx phase is easily formed, consequently consuming a part of the B content. The insufficient B content leads to an increase in an R.sub.2-T.sub.17 phase, the synergistic addition of Cu, Ga, and Co does not form a sufficient R.sub.6-T.sub.13M phase in the grain boundaries, and there is no obvious improvement to the properties of the sintered magnet. However, for a Ti content of 0.02 wt %-0.2 wt %, the synergistic addition of Cu, Ga, and Co allows full sintering of the magnet, and it can be ensured that 75% or more of the R.sub.6-T.sub.13-M phase is generated in the grain boundaries in the subsequent heat treatment, the Ga content in M is greater than 80% and the Cu content is lower than 20%, and there is more obvious improvement to the properties of the sintered magnet.

[0092] Similarly, the sintered magnets in Embodiments 3.1-3.8 were subjected to FE-EPMA tests, in which the R.sub.6-T.sub.13-M phase accounting for 75% or more of the total volume of the grain boundaries can be observed, where R is Nd and Dy, T is mainly Fe and Co, and M comprises 80 wt % or more of Ga and 20 wt % or below of Cu.

[0093] In addition, Comparative Example 3.1 was subjected to an FE-EPMA test, in which an R.sub.6-T.sub.13-M phase was observed in the grain boundaries of the sintered magnet, and the R.sub.6-T.sub.13-M phase accounted for 75% or more of the total volume of the grain boundaries, but the content of Ga in M is less than 80 wt %.

[0094] Comparative Examples 3.2, 3.3, 3.4, and 3.5 were subjected to FE-EPMA tests, in which an R.sub.6-T.sub.13-M phase was observed in the grain boundaries of the sintered magnets, and the R.sub.6-T.sub.13-M phase was less than 75% of the total volume of the grain boundaries.

[0095] The embodiments described above only serve to further illustrate some particular embodiments of the present disclosure; however, the present invention is not limited to these embodiments. Any simple alterations, equivalent changes, and modifications made to the embodiments above according to the technical essence of the present invention shall fall within the protection scope of the technical solutions of the present invention.