Quenched alloy for rare earth magnet and a manufacturing method of rare earth magnet

Abstract

The present invention is provided with a quenched alloy for rare earth magnet and a manufacturing method of rare earth magnet. It comprises an R.sub.2T.sub.14B main phase, wherein R is selected from at least one rare earth element including Nd. The average grain diameter of the main phase in the brachyaxis direction is in a range of 1015 m and the average interval of the Nd rich phase is in a range of 1.03.5 m. In the fine powder of the above-mentioned quenched alloy, the number of magnet domains of a single grain decreases. Thus, it is easier for external magnetic field orientation to obtain high performance magnet, and the squareness, coercivity and the thermal resistance of the magnet are sufficiently improved.

Claims

1. A quenched alloy for rare earth magnet, comprising: an R.sub.2Fe.sub.14B main phase, wherein: R is selected from at least one rare earth element comprising Nd, an average grain diameter of a primary crystallization in a brachyaxis direction is in a range of 10.21-14.88 m, an average interval of a Nd rich phase is in a range of 1.15-2.77 m, the quenched alloy has an average thickness in a range of 0.2-0.4 mm, counted in weight percent, more than 95% of the quenched alloy has a thickness in a range of 0.1-0.7 mm, a raw material of the quenched alloy comprises: R: 13.5 at %-15.5 at %, B: 5.2 at %-5.8 at %, Cu: 0.1 at %-0.8 at %, Al: 0.1 at %-2.0 at %, an atomic percent of W is in a range of 0.0005 at %-0.03 at %, T: 0 at %-2.0 at %, T is selected from at least one of the elements Ti, Zr, V, Mo, Co, Zn, Ga, Nb, Sn, Sb, Hf, Bi, Ni, Si, Cr, Mn, S or P, and remaining components comprise Fe and unavoidable impurity, and the quenched alloy is obtained by strip casting a molten alloy fluid of the raw material and cooling at a cooling rate between 10.sup.2 C./s and 10.sup.4 C./s.

2. The quenched alloy for rare earth magnet according to claim 1, wherein an atomic percent of Cu is in a range of 0.3 at %-0.7 at %.

3. The quenched alloy for rare earth magnet according to claim 1, wherein the quenched alloy is kept in a material container for 0.5-5 hours in a preservation temperature of 500-700 C. after being cooled to 500-750 C.

4. A manufacturing method of rare earth magnet, comprising: coarsely crushing a quenched alloy for rare earth magnet to generate a powder, wherein: the quenched alloy comprises an R.sub.2T.sub.14B main phase, R is selected from at least one rare earth element comprising Nd, an average grain diameter of a primary crystallization in a brachyaxis direction is in a range of 10.21-14.88 m, an average interval of a Nd rich phase is in a range of 1.15-2.77 m, the quenched alloy has an average thickness in a range of 0.2-0.4 mm, counted in weight percent, more than 95% of the quenched alloy has a thickness in a range of 0.1-0.7 mm, a raw material of the quenched alloy comprises: R: 13.5 at %-15.5 at %, B: 5.2 at %-5.8 at %, Cu: 0.1 at %-0.8 at %, Al: 0.1 at %-2.0 at %, an atomic percent of W is in a range of 0.0005 at %-0.03 at %, T: 0 at %-2.0 at %, T is selected from at least one of the elements Ti, Zr, V, Mo, Co, Zn, Ga, Nb, Sn, Sb, Hf, Bi, Ni, Si, Cr, Mn, S or P, and remaining components comprise Fe and unavoidable impurity, and the quenched alloy is obtained by strip casting a molten alloy fluid of the raw material and cooling at a cooling rate between 10.sup.2 C./s and 10.sup.4 C./s; finely crushing the powder to fine powder; placing the fine powder under a magnetic field for pre-orientating and obtaining green compacts under a magnetic field; and sintering the green compacts in vacuum or in inert gas atmosphere in a temperature of 900 C.-1100 C.

5. The manufacturing method of rare earth magnet according to claim 4, wherein an atomic percent of Cu is in a range of 0.3 at %-0.7 at %.

6. The manufacturing method of rare earth magnet according to claim 4, wherein the quenched alloy is kept in a material container for 0.5-5 hours in a preservation temperature of 500-700 C. after being cooled to 500-750 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic diagram of the main phase crystal of Embodiment 2 of SC sheet magnified 1000 times under the Kerr metallographic microscopes in the first embodiment.

(2) FIG. 2 illustrates a schematic diagram of the internal of Nd rich phase of Embodiment 2 of SC sheet magnified 1000 times under 3D color scanning laser microscopes in the first embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) The present invention will be further described with the embodiments.

The First Embodiment

(4) Raw material preparation process: Nd with 99.5% purity, Dy with 99.8% purity, industrial FeB, industrial pure Fe, Cu and Al with 99.5% purity and W with 99.999% purity are prepared, counted in atomic percent.

(5) The contents of the elements are shown in TABLE 2.

(6) TABLE-US-00002 TABLE 2 proportioning of each element (at %) Number Nd Dy B Cu Al W Fe Comparing 13.8 1.0 5.2 0.05 0.4 0.01 rest sample 1 Embodiment 1 13.8 1.0 5.2 0.1 0.4 0.01 rest Embodiment 2 13.8 1.0 5.2 0.3 0.4 0.01 rest Embodiment 3 13.8 1.0 5.2 0.5 0.4 0.01 rest Embodiment 4 13.8 1.0 5.2 0.6 0.4 0.01 rest Embodiment 5 13.8 1.0 5.2 0.7 0.4 0.01 rest Embodiment 6 13.8 1.0 5.2 0.8 0.4 0.01 rest Comparing 13.8 1.0 5.2 0.9 0.4 0.01 rest sample 2

(7) Preparing 10 Kg of raw material respectively by weighing in accordance with each row of TABLE 2.

(8) In the melting process: each of the raw materials is put into an aluminum oxide made crucible and an intermediate frequency vacuum induction melting furnace is used to melt the raw material in 10.sup.2 Pa vacuum below 1500 C.

(9) In the casting process: Ar gas is supplied to the melting furnace so that the Ar pressure would reach 50000 Pa after the process of vacuum melting, then a single roller for quenching method is applied to quench. The quenched alloy is obtained in a cooling rate of 10.sup.2 C./s10.sup.4 C./s. The average thickness of the quenched alloy is 0.3 mm. Above 95% of the quenched alloy has a thickness in a range of 0.10.7 mm. The quenched alloy is kept in a temperature of 500 C. for 5 hours and then cooled to room temperature.

(10) In the hydrogen decrepitation process: at room temperature, the quenched alloy is put into a hydrogen decrepitation furnace. The furnace is then pumped to vacuum and then hydrogen of 99.5% purity is supplied into the container. The hydrogen pressure will reach 0.1 MPa. After two hours of standing, the container is heated and pumped for 2 hours at 500 C. and then the container gets cooled. The cooled coarse powder is then taken out.

(11) In the fine crushing process: jet milling process is used to finely crush the coarse powder in an atmosphere with the content of oxidizing gas below 100 ppm and under a pressure of 0.4 MPa to obtain a fine powder with an average particle size of 3.4 m. The oxidizing gas comprises oxygen or moisture.

(12) Part of the fine powder (30 wt % of the fine powder) after fine crushing is screened to remove the powder with grain diameter below 1.0 m. The screened fine powder is then mixed with the unscreened fine powder. In the mixture, the volume of powder with grain diameter below 1.0 m is decreased to below 10% of the total volume of the powder.

(13) Methyl caprylate is added to the fine powder after jet milling. The additive amount is 0.15% of the weight of the mixed powder. The mixture is comprehensively blended by a V-type mixer.

(14) In the compacting process under a magnetic field: a transverse type magnetic field molder is used and the powder with methyl caprylate is compacted to form a cube with sides of 25 mm in an orientation filed of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2. Then, the once-forming cube is demagnetized in a 0.2 T magnetic field.

(15) The once-forming compact (green compact) is sealed so as not to expose to air. The compact is secondary compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(16) In the sintering process: the green compact is moved to the sinter furnace for sintering, in a vacuum of 10.sup.3 Pa and respectively maintained for 1.5 hours in 200 C. and for 1.5 hours in 850 C., then sintering for 2 hours in 1080 C. After that, Ar gas is supplied into the sintering furnace so that the Ar pressure reaches 0.1 MPa and then it is cooled to room temperature.

(17) In the thermal treatment process: the sintered magnet is heated for 1 hour in 600 C. in the atmosphere of high purity Ar gas, then cooled to room temperature and taken out.

(18) In magnetic property evaluation process: the sintered magnet is tested by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(19) The minimum strength of the saturation magnetic field: when the magnetization voltage increases, the magnetic field strength increases 50% from a value. If the increment of (BH)max or Hcb of the samples is not exceed 1%, the magnetic field value is the minimum strength of the saturation magnetic field.

(20) In the testing process of the average grain diameter of the main phase: the SC sheet (the quenched alloy sheet) is put under the Kerr metallographic microscope magnified 200 times by photography and the roller surface is parallel to the lower edge of the view field. When testing, a straight line of 445 m at the center position of the view field is drawn and the number of main phase crystals going through the straight line is counted to determine the average grain diameter of the main phase crystal. The testing result is illustrated in FIG. 1.

(21) In the testing process of the Nd rich interval: the SC sheet is corroded by weak FeCl.sub.2 solution (FeCl.sub.2+HCl+alchol) and is then put under the 3D color scanning laser microscope magnified 1000 times by photography. The roller surface is parallel to the lower edge of the view field. When testing, a straight line of 283 m at the center position of the view field is drawn and the number of secondary crystals going through the straight line is counted to determine the Nd rich interval. The testing result is illustrated in FIG. 2.

(22) The evaluation of a magnetic property of the embodiments and the comparing samples are shown in TABLE 3.

(23) TABLE-US-00003 TABLE 3 the magnetic property evaluation of the embodiments and the comparing samples Average grain diameter of Average minimum main phase Nd rich voltage of crystal phase (BH) ma saturation (brachyaxis, interval Br Hcj SQ magnetization Number m) (m) (kGs) (kOe) (MGOe) (%) (volt) Comparing 25.22 3.80 13.4 13.5 41.7 87.5 2800 sample 1 Embodiment 1 14.88 2.42 13.8 15.2 45.7 96.8 2600 Embodiment 2 13.81 2.11 13.9 15.4 46.3 99.5 2600 Embodiment 3 13.26 1.82 14.1 15.4 48.2 99.7 2500 Embodiment 4 12.96 1.57 14.0 15.4 46.9 99.6 2500 Embodiment 5 11.99 1.26 14.0 15.9 46.8 99.6 2500 Embodiment 6 10.62 1.15 13.9 15.5 46.4 97.2 2500 Comparing 9.22 0.93 13.3 13.6 41.1 88.2 3000 sample 2

(24) In TABLE 3, the minimum voltage of saturation magnetization is the voltage value when the samples are saturated magnetized under the minimum strength of the magnetic field. In the present invention, magnetization is taken under the same magnetization device. Therefore, the magnetization voltage can represent the strength of the magnetic field.

(25) As can be seen from TABLE 3, when the amount of Cu in the magnet is less than 0.1 at %, the distribution of Cu in the grain boundary of the Nd rich phase is insufficient. Therefore, it is difficult to form a composite phase with Al in the grain boundary, which leads to the average grain diameter of the main phase crystal increasing, the average interval of Nd rich phase enlarging, the resistance to the nucleation and growth of the magnetic domain during orientation in the grain increasing, residual magnetization and BH(max) decreasing, and the magnetic performance decreasing.

(26) When the amount of Cu exceeds 0.8 at %, the amount of Cu in the grain is excessive, which leads to the average grain diameter of the main phase crystal decreasing, the average internal of Nd rich phase decreasing, the resistance to the nucleation and growth of the magnetic domain during orientation in the grain increasing, and the minimum strength of the saturation magnetic field increasing. It is not suited to use in a magnetic field in open-circuit state.

(27) When the amount of Cu is in a range of 0.1 at %0.8 at %, the squareness of the magnet exceeds 95% and it has good magnetization performance.

(28) When the amount of Cu is in a range of 0.3 at %0.7 at %, the squareness of the magnet exceeds 99%. The very good squareness can produce a magnet with good heat resistance performance.

(29) The 5% heating demagnetize (heat resistance) temperature of the comparing samples 1 and 2 are 60 C. and 80 C., while the 5% heating demagnetize (heat resistance) temperature of the embodiments 16 are 110 C., 125 C., 125 C., 125 C., 125 C. and 120 C.

The Second Embodiment

(30) In the raw material preparation process: Nd with 99.5% purity, Ho with 99.8% purity, industrial FeB, industrial pure Fe, Cu and Al with 99.5% purity and W with 99.999% purity are prepared, counted in atomic percent.

(31) The contents of the elements are shown in TABLE 4.

(32) TABLE-US-00004 TABLE 4 proportioning of each element (at %) No. Nd Ho B Cu Al W Fe Comparing 14 1.0 5.8 0.5 0.05 0.005 rest sample 1 Embodiment 1 14 1.0 5.8 0.5 0.1 0.005 rest Embodiment 2 14 1.0 5.8 0.5 0.5 0.005 rest Embodiment 3 14 1.0 5.8 0.5 0.8 0.005 rest Embodiment 4 14 1.0 5.8 0.5 1.2 0.005 rest Embodiment 5 14 1.0 5.8 0.5 1.6 0.005 rest Embodiment 6 14 1.0 5.8 0.5 2.0 0.005 rest Comparing 14 1.0 5.8 0.5 2.2 0.005 rest sample 2

(33) Preparing 10 Kg of raw material respectively by weighing in accordance with each row of TABLE 4.

(34) In the melting process: each of the raw materials is put into an aluminum oxide made crucible and an intermediate frequency vacuum induction melting furnace is used to melt the raw material in 10.sup.2 Pa vacuum below 1500 C.

(35) In the casting process: Ar gas is supplied to the melting furnace so that the Ar pressure would reach 50000 Pa after the process of vacuum melting, then a single roller for quenching method is applied to quench. The quenched alloy is obtained in a cooling rate of 10.sup.2 C./s10.sup.4 C./s. The average thickness of the quenched alloy is 0.25 mm. Above 95% of the quenched alloy has a thickness in a range of 0.10.7 mm. The quenched alloy is kept in a temperature of 700 C. for 0.5 hours and then cooled to room temperature.

(36) In the hydrogen decrepitation process: at room temperature, the quenched alloy is put into a hydrogen decrepitation furnace. The furnace is then pumped to vacuum and then hydrogen of 99.5% purity is supplied into the container. The hydrogen pressure will reach 0.08 MPa. After two hours of standing, the container is heated and pumped for 1.5 hours at 480 C. and then the container gets cooled. The cooled coarse powder is then taken out.

(37) In the fine crushing process: jet milling process is used to finely crush the coarse powder in an atmosphere with the content of oxidizing gas below 100 ppm and under a pressure of 0.45 MPa to obtain a fine powder with an average particle size of 3.4 m. The oxidizing gas comprises oxygen or moisture.

(38) Methyl caprylate is added to the fine powder after jet milling. The additive amount is 0.2% of the weight of the mixed powder. The mixture is comprehensively blended by a V-type mixer.

(39) In the compacting process under a magnetic field: a transverse type magnetic field molder is used and the powder with methyl caprylate is compacted to form a cube with sides of 25 mm in an orientation filed of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2. Then, the once-forming cube is demagnetized in a 0.2 T magnetic field, the green compacts are taken out of the molder to another magnetic field, and the magnetic powder attached to the surface of the green compacts is secondary demagnetized.

(40) The once-forming compact (green compact) is sealed so as not to expose to air. The compact is secondary compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(41) In the sintering process: the green compact is moved to the sinter furnace for sintering, in a vacuum of 10.sup.3 Pa and respectively maintained for 2 hours in 200 C. and for 2 hours in 900 C., then sintering for 2 hours in 1020 C. After that, Ar gas is supplied into the sintering furnace so that the Ar pressure reaches 0.1 MPa and then it is cooled to room temperature.

(42) In the thermal treatment process: the sintered magnet is heated for 1 hour in 620 C. in the atmosphere of high purity Ar gas, then cooled to room temperature and taken out.

(43) In magnetic property evaluation process: the sintered magnet is tested by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(44) The minimum strength of the saturation magnetic field: when the magnetization voltage increases, the magnetic field strength increases 50% from a value. If the increment of (BH)max or Hcb of the samples is not exceed 1%, the magnetic field value is the minimum strength of the saturation magnetic field.

(45) In the testing process of the average grain diameter of the main phase: the SC sheet (the quenched alloy sheet) is put under the Kerr metallographic microscope magnified 200 times by photography and the roller surface is parallel to the lower edge of the view field. When testing, a straight line of 445 m at the center position of the view field is drawn and the number of main phase crystals going through the straight line is counted to determine the average grain diameter of the main phase crystal. The testing result is illustrated in FIG. 1.

(46) In the testing process of the Nd rich interval: the SC sheet is corroded by weak FeCl.sub.2 solution (FeCl.sub.2+HCl+alchol) and is then put under the 3D color scanning laser microscope magnified 1000 times by photography. The roller surface is parallel to the lower edge of the view field. When testing, a straight line of 283 m at the center position of the view field is drawn and the number of secondary crystals going through the straight line is counted to determine the Nd rich interval. The testing result is illustrated in FIG. 2.

(47) The evaluation of a magnetic property of the embodiments and the comparing samples are shown in TABLE 5.

(48) TABLE-US-00005 TABLE 5 the magnetic property evaluation of the embodiments and the comparing samples Average grain diameter of minimum main phase Average Nd voltage of crystal rich phase (BH) saturation (brachyaxis, interval Br Hcj max magnetization Number m) (m) (kGs) (kOe) (MGOe) (volt) Comparing 19.34 3.80 13.4 13.8 42.8 2800 sample 1 Embodiment 1 14.90 3.47 14.2 15.0 48.6 2600 Embodiment 2 13.62 3.03 14.1 15.3 48.2 2600 Embodiment 3 12.25 2.77 14.0 16.0 47.1 2500 Embodiment 4 11.90 2.40 13.9 16.4 46.6 2500 Embodiment 5 11.44 1.52 13.7 16.8 45.3 2500 Embodiment 6 10.22 1.21 13.5 17.2 44.0 2600 Comparing 9.29 0.92 13.4 13.8 42.2 2900 sample 2

(49) In TABLE 5, the minimum voltage of saturation magnetization is the voltage value when the samples are saturated magnetized under the minimum strength of the saturation magnetic field. In the present invention, magnetization is taken under the same magnetization device. Therefore, the magnetization voltage can represent the strength of the magnetic field.

(50) SQ of Embodiments 16 reach to more than 99%, while SQ of the comparing samples 12 are less than 85%.

(51) As can be seen from TABLE 5, when the amount of Al of the magnet is less than 0.1 at %, the distribution of Al in the grain boundary of the Nd rich phase and the main phase is insufficient. Therefore, it is difficult to form a composite phase with Cu in the grain boundary, which leads to that the average grain diameter of the main phase crystal increasing and the average interval of Nd rich phase enlarging, the resistance to the nucleation and growth of the magnetic domain during orientation in the grain increasing, residual magnetization and BH(max) decreasing, and the magnetic performance decreasing.

(52) When the amount of Al exceeds 2.0 at %, the amount of Al in the grain is excessive, which leads to the average grain diameter of the main phase crystal decreasing, the average internal of Nd rich phase decreasing, the resistance to the nucleation and growth of the magnetic domain during orientation in the grain increasing, and the minimum strength of the saturation magnetic field to increasing. It is not suited to use in a magnetic field in open-circuit state.

The Third Embodiment

(53) In the raw material preparation process: Nd with 99.5% purity, Ho with 99.5% purity, industrial FeB, industrial pure Fe, Al, Cu, Zr and Co with 99.5% purity and W with 99.999% purity are prepared, counted in atomic percent.

(54) The contents of the elements are shown in TABLE 6.

(55) TABLE-US-00006 TABLE 6 proportioning of each element (at %) Number Nd Ho B Cu Al Co Zr W Fe Comparing 14 1.2 5.0 0.5 0.6 0.3 0.5 0.002 rest sample 1 Comparing 14 1.2 5.1 0.5 0.6 0.3 0.5 0.002 rest sample 2 Embodiment 1 14 1.2 5.2 0.5 0.6 0.3 0.5 0.002 rest Embodiment 2 14 1.2 5.3 0.5 0.6 0.3 0.5 0.002 rest Embodiment 3 14 1.2 5.4 0.5 0.6 0.3 0.5 0.002 rest Embodiment 4 14 1.2 5.5 0.5 0.6 0.3 0.5 0.002 rest Embodiment 5 14 1.2 5.6 0.5 0.6 0.3 0.5 0.002 rest Embodiment 6 14 1.2 5.7 0.5 0.6 0.3 0.5 0.002 rest Embodiment 7 14 1.2 5.8 0.5 0.6 0.3 0.5 0.002 rest Comparing 14 1.2 5.9 0.5 0.6 0.3 0.5 0.002 rest sample 3

(56) Preparing 10 Kg of raw material respectively by weighing in accordance with each row of TABLE 6.

(57) In the melting process: each of the raw materials is put into an aluminum oxide made crucible and an intermediate frequency vacuum induction melting furnace is used to melt the raw material in 10.sup.2 Pa vacuum below 1500 C.

(58) In the casting process: Ar gas is supplied to the melting furnace so that the Ar pressure would reach 60000 Pa after the process of vacuum melting, then a single roller for quenching method is applied to quench. The quenched alloy is obtained in a cooling rate of 10.sup.2 C./s10.sup.4 C./s. The average thickness of the quenched alloy is 0.38 mm. Above 95% of the quenched alloy has a thickness in a range of 0.10.7 mm. The quenched alloy is kept in a temperature of 600 C. for 3 hours and then cooled to room temperature.

(59) In the hydrogen decrepitation process: at room temperature, the quenched alloy is put into a hydrogen decrepitation furnace. The furnace is then pumped to be vacuum and then hydrogen of 99.5% purity is supplied into the container. The hydrogen pressure will reach 0.09 MPa. After two hours of standing, the container is heated and pumped for 2 hours at 520 C. and then the container gets cooled. The cooled coarse powder is then taken out.

(60) In the fine crushing process: jet milling process is used to finely crush the coarse powder in an atmosphere with the content of oxidizing gas below 100 ppm and under a pressure of 0.5 MPa to obtain a fine powder with an average particle size of 3.6 m. The oxidizing gas comprises oxygen or moisture.

(61) Methyl caprylate is added to the fine powder after jet milling. The additive amount is 0.2% of the weight of the mixed powder. The mixture is comprehensively blended by a V-type mixer.

(62) In the compacting process under a magnetic field: a transverse type magnetic field molder is used, the powder with methyl caprylate is compacted to form a cube with sides of 25 mm in an orientation filed of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2. Then, the once-forming cube is demagnetized in a 0.2 T magnetic field, the green compacts are taken out of the molder to another magnetic field, and the magnetic powder attached to the surface of the green compacts is secondary demagnetized.

(63) The once-forming compact (green compact) is sealed so as not to expose to air. The compact is secondary compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(64) In the sintering process: the green compact is moved to the sinter furnace for sintering, in a vacuum of 10.sup.3 Pa and respectively maintained for 2 hours in 200 C. and for 2 hours in 800 C., then sintering for 2 hours in 1030 C. After that, Ar gas is supplied into the sintering furnace so that the Ar pressure reaches 0.1 MPa and then it is cooled to room temperature.

(65) In the thermal treatment process: the sintered magnet is heated for 1 hour in 580 C. in the atmosphere of high purity Ar gas, then cooled to room temperature and taken out.

(66) In magnetic property evaluation process: the sintered magnet is tested by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(67) The minimum strength of the saturation magnetic field: when the magnetization voltage increases, the magnetic field strength increases 50% from a value. If the increment of (BH)max or Hcb of the samples is not exceed 1%, the magnetic field value is the minimum strength of the saturation magnetic field.

(68) In the testing process of the average grain diameter of the main phase: the SC sheet (the quenched alloy sheet) is put under the Kerr metallographic microscope magnified 200 times by photography and the roller surface is parallel to the lower edge of the view field. When testing, a straight line of 445 m at the center position of the view field is drawn and the number of main phase crystals going through the straight line is counted to determine the average grain diameter of the main phase crystal. The testing result is illustrated in FIG. 1.

(69) In the testing process of the Nd rich interval: the SC sheet is corroded by weak FeCl.sub.2 solution (FeCl.sub.2+HCl+alchol) and is then put under the 3D color scanning laser microscope magnified 1000 times by photography. The roller surface is parallel to the lower edge of the view field. When testing, a straight line of 283 m at the center position of the view field is drawn and the number of secondary crystals going through the straight line is counted to determine the Nd rich interval. The testing result is illustrated in FIG. 2.

(70) The evaluation of a magnetic property of the embodiments and the comparing samples are shown in TABLE 7.

(71) TABLE-US-00007 TABLE 7 the magnetic property evaluation of the embodiments and the comparing samples Average grain diameter of minimum main phase Average Nd voltage of crystal rich phase (BH) ma saturation (brachyaxis, interval Br Hcj magnetization Number m) (m) (kGs) (kOe) (MGOe) (volt) Comparing 20.56 3.96 12.8 14.5 38.1 3200 sample 1 Comparing 18.27 3.65 13.0 14.9 39.3 3100 sample 2 Embodiment 1 14.86 3.34 13.7 16.0 44.6 2500 Embodiment 2 14.49 3.04 13.8 16.1 45.7 2500 Embodiment 3 14.25 2.50 14.1 16.2 48.2 2500 Embodiment 4 13.76 2.04 14.1 16.3 48.0 2500 Embodiment 5 12.53 1.65 13.9 16.3 46.6 2500 Embodiment 6 11.23 1.46 13.8 16.3 45.8 2500 Embodiment 7 10.21 1.42 13.8 16.2 45.8 2500 Comparing 9.20 1.36 13.2 14.8 40.1 2800 sample 3

(72) In TABLE 7, the minimum voltage of saturation magnetization is the voltage value when the samples are saturated magnetized under the minimum strength of the saturation magnetic field. In the present invention, magnetization is taken under the same magnetization device. Therefore, the magnetization voltage can represent the strength of the magnetic field.

(73) SQ of Embodiments 17 reach to more than 99%, while SQ of the comparing samples 13 are less than 85%.

(74) As can be seen from TABLE 7, when the amount of B of the magnet is less than 5.2 at %, the distribution of B in the grain boundary of the Nd rich phase and the main phase is insufficient. Therefore, the average grain diameter of the main phase crystal increases and the average interval of Nd rich phase enlarges, the resistance to the nucleation and growth of the magnetic domain during orientation in the grain increases, residual magnetization and BH(max) decrease, and the magnetic performance decreases.

(75) When the amount of B of the magnet is less than 5.8 at %, residual magnetization and BH(max) decrease, it is difficult to obtain high performance magnet.

The Fourth Embodiment

(76) In the raw material preparation process: Nd with 99.5% purity, industrial FeB, industrial pure Fe, Al, Cu, Zr and Co with 99.5% purity and W with 99.999% purity are prepared, counted in atomic percent.

(77) To accurately control the proportion of W, in this embodiment, no W exists in Fd, Fe, B, Al, Cu, Zn and Co. All W comes from the W metal.

(78) The contents of the elements are shown in TABLE 8.

(79) TABLE-US-00008 TABLE 8 proportioning of each element (at %) Number Nd B Cu Al Co Zr W Fe Comparing 14.5 5.5 0.4 0.5 0.3 0.3 0.0001 rest sample 1 Embodiment 1 14.5 5.5 0.4 0.5 0.3 0.3 0.0005 rest Embodiment 2 14.5 5.5 0.4 0.5 0.3 0.3 0.002 rest Embodiment 3 14.5 5.5 0.4 0.5 0.3 0.3 0.01 rest Embodiment 4 14.5 5.5 0.4 0.5 0.3 0.3 0.03 rest Comparing 14.5 5.5 0.4 0.5 0.3 0.3 0.04 rest sample 2

(80) Preparing 100 Kg of raw material respectively by weighing in accordance with each row of TABLE 8.

(81) In the melting process: each of the raw materials is put into an aluminum oxide made crucible and an intermediate frequency vacuum induction melting furnace is used to melt the raw material in 10.sup.2 Pa vacuum below 1500 C.

(82) In the casting process: Ar gas is supplied to the melting furnace so that the Ar pressure would reach 45000 Pa after the process of vacuum melting, then a single roller for quenching method is applied to quench. The quenched alloy is obtained in a cooling rate of 10.sup.2 C./s10.sup.4 C./s. The average thickness of the quenched alloy is 0.25 mm. Above 95% of the quenched alloy has a thickness in a range of 0.10.7 mm. The quenched alloy is kept in a temperature of 560 C. for 0.5 hours and then cooled to room temperature.

(83) In the hydrogen decrepitation process: at room temperature, the quenched alloy is put into a hydrogen decrepitation furnace. The furnace is then pumped to vacuum and then hydrogen of 99.5% purity is supplied into the container. The hydrogen pressure will reach 0.085 MPa. After two hours of standing, the container is heated and pumped for 2 hours at 540 C., and then the container gets cooled. The cooled coarse powder is then taken out.

(84) In the fine crushing process: jet milling process is used to finely crush the coarse powder in an atmosphere with the content of oxidizing gas below 100 ppm and under a pressure of 0.55 MPa to obtain a fine powder with an average particle size of 3.6 m. The oxidizing gas comprises oxygen or moisture.

(85) In the compacting process under a magnetic field: a transverse type magnetic field molder is used, the powder with methyl caprylate is compacted to form a cube with sides of 25 mm in an orientation filed of 1.8 T and under a compacting pressure of 0.2 ton/cm.sup.2. Then, the once-forming cube is demagnetized in a 0.2 T magnetic field, the green compacts are taken out of the molder to another magnetic field, and the magnetic powder attached to the surface of the green compacts is secondary demagnetized.

(86) The once-forming compact (green compact) is sealed so as not to expose to air. The compact is secondary compacted by a secondary compact machine (isostatic pressing compacting machine) under a pressure of 1.4 ton/cm.sup.2.

(87) In the sintering process: the green compact is moved to the sintering furnace to sinter, in a vacuum of 10.sup.3 Pa and respectively maintained for 2 hours in 200 C. and for 2 hours in 700 C., then sintering for 2 hours in 1050 C. After that, Ar gas is supplied into the sintering furnace so that the Ar pressure reaches 0.1 MPa and then it is cooled to room temperature.

(88) In the thermal treatment process: the sintered magnet is heated for 1 hour in 620 C. in the atmosphere of high purity Ar gas, then cooled to room temperature and taken out.

(89) In magnetic property evaluation process: the sintered magnet is tested by NIM-10000H type nondestructive testing system for BH large rare earth permanent magnet from National Institute of Metrology.

(90) The minimum strength of the saturation magnetic field: when the magnetization voltage increases, the magnetic field strength increases 50% from a value. If the increment of (BH)max or Hcb of the samples is not exceed 1%, the magnetic field value is the minimum strength of the saturation magnetic field.

(91) In the testing process of the average grain diameter of the main phase: the SC sheet (the quenched alloy sheet) is put under the Kerr metallographic microscope magnified 200 times by photography and the roller surface is parallel to the lower edge of the view field. When testing, a straight line of 445 m at the center position of the view field is drawn and the number of main phase crystals going through the straight line is counted to determine the average grain diameter of the main phase crystal. The testing result is illustrated in FIG. 1.

(92) In the testing process of the Nd rich interval: the SC sheet is corroded by weak FeCl.sub.2 solution (FeCl.sub.2+HCl+alchol) and is then put under the 3D color scanning laser microscope magnified 1000 times by photography. The roller surface is parallel to the lower edge of the view field. When testing, a straight line of 283 m at the center position of the view field is drawn and the number of secondary crystals going through the straight line is counted to determine the Nd rich interval. The testing result is illustrated in FIG. 2.

(93) The evaluation of a magnetic property of the embodiments and the comparing samples are shown in TABLE 9.

(94) TABLE-US-00009 TABLE 9 the magnetic property evaluation of the embodiments and the comparing samples Average grain diameter of minimum main phase Average Nd voltage of crystal rich phase saturation (brachyaxis, interval Br Hcj (BH) max magnetization Number m) (m) (kGs) (kOe) (MGOe) (volt) Comparing 16.23 2.25 12.8 13.2 38.1 2800 sample 1 Embodiment 1 13.01 2.10 13.9 16.1 46.4 2500 Embodiment 2 12.48 1.98 14.2 16.2 48.4 2500 Embodiment 3 11.94 1.90 14.2 16.3 48.3 2500 Embodiment 4 11.45 1.86 14.0 16.3 47.0 2500 Comparing 9.90 1.82 12.9 14.3 38.3 2800 sample 2

(95) In TABLE 9, the minimum voltage of saturation magnetization is the voltage value when the samples are saturated magnetized under the minimum strength of the saturation magnetic field. In the present invention, magnetization is taken under the same magnetization device. Therefore, the magnetization voltage can represent the strength of the magnetic field.

(96) SQ of Embodiments 14 reach to more than 99%, while SQ of the comparing samples 12 are less than 90%.

(97) As can be seen from TABLE 9, the ionic radius and the electronic structure of W are different from that of the rare earth elements. Fe, B, and almost no W exists in the R.sub.2Fe.sub.14B main phase. A small amount of W separates out of the R.sub.2Fe.sub.14B main phase during the cooling process of the molten fluids and concentrates to the grain boundary and then separates out in tiny and uniform way. Therefore, appropriate addition of W can be used to control the grain diameter of the main phase crystal of the alloy and thus improve the orientation of the magnet.

(98) Although the present invention has been described with reference to the preferred embodiments thereof for carrying out the patent for invention, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the patent for invention, which is intended to be defined by the appended claims.