METHOD FOR PREPARING HIGH-PERFORMANCE ANISOTROPIC RARE-EARTH-FREE PERMANENT MAGNETS

Abstract

The present invention discloses a method for preparing high-performance anisotropic rare-earth-free permanent magnets, comprising the steps of: forming alloy ingots by melting according to a nominal composition of Mn.sub.xBi.sub.100-x, (45≤×≤55); then coarsely crushing the alloy ingots and passing the crushed material through a 100-mesh sieve to obtain coarse powder; putting an appropriate amount of Mn.sub.xBi.sub.100-x alloy coarse powder obtained into a ball-milling tank together with non-magnetic steel balls, with a ratio of ball to powder of 10:1; adding an appropriate amount of ethanol as solvent, and then adding a non-ionic surfactant polyvinylpyrrolidone (PVP) accounting for 5-15% of the power mass to assist in low-energy ball milling; washing the slurry obtained in anhydrous ethyl alcohol, and orientating and curing the washed magnetic powder in a magnetic field after adding binder to obtain high-performance anisotropic Mn—Bi alloy magnets finally.

Claims

1. A method for preparing high-performance anisotropic rare-earth-free permanent magnets comprises the steps of: 1. proportioning: Mn and Bi alloys with a purity of over 99.99% being weighed and proportioned according to a nominal composition of Mn.sub.xBi.sub.100-x, wherein 45≤×≤55; 2. melting: the proportioned raw materials being placed into an electric arc furnace under argon protection to obtain Mn.sub.xBi.sub.100-x, alloy ingots by using an arc-melting method; 3. coarse crushing, wherein the Mn.sub.xBi.sub.100-x alloy ingots obtained in step 2) being coarsely crushed and passed through a 100-mesh sieve to obtain coarse powder; 4. proportioning in a ball milling tank: an appropriate amount of the Mn.sub.xBi.sub.100-x, alloy coarse powder obtained in step 3) being put into a ball-milling tank together with non-magnetic steel balls, an appropriate amount of ethanol being added as solvent, and a certain mass of non-ionic surfactant being added; 5. low-energy ball milling: the ball-milling tank in step 4) being placed into a low-energy ball mill, a ball milling time and a ball milling speed being set, an alternating time for clockwise/counterclockwise rotation being set as 6 minutes, and the slurry obtained after ball milling being washed in anhydrous ethyl alcohol; 6. orientation and forming in a magnetic field: the washed magnetic powder being orientated, cured and formed in the magnetic field after a certain amount of binder is added to obtain high-performance anisotropic MnBi alloy magnets finally.

2. The method for preparing the high-performance anisotropic rare-earth-free permanent magnets according to claim 1, wherein: the non-ionic surfactant in step 4) is polyvinylpyrrolidone (PVP); the certain mass of the non-ionic surfactant is 5-15% of the powder mass; and a ratio of the ball to the powder is 10:1.

3. The method for preparing the high-performance anisotropic rare-earth-free permanent magnets according to claim 1, wherein: the ball milling time in step 5) is 1-6 hours, and the ball milling speed is 256 rpm.

4. The method for preparing the high-performance anisotropic rare-earth-free permanent magnets according to claim 1, wherein: the magnitude of the oriented magnetic field in step 6) is 3˜5 T.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a magnetic hysteresis loop of MnBi alloy magnets prepared by Embodiment 1.

[0020] FIG. 2 shows a magnetic hysteresis loop of MnBi alloy magnets prepared by Comparative Embodiment 1.

[0021] FIG. 3 shows a magnetic hysteresis loop of MnBi alloy magnets prepared by Embodiment 2.

[0022] FIG. 4 shows a magnetic hysteresis loop of MnBi alloy magnets prepared by Embodiment 3.

DESCRIPTION OF THE EMBODIMENTS

[0023] A further description is made to the present invention in combination with the drawings.

Embodiment 1

[0024] 1) Proportioning: Mn and Bi with a purity of over 99.99% were weighed and proportioned according to a nominal composition of Mn.sub.45Bi.sub.55;

[0025] 2) Melting: The proportioned raw materials were placed into an electric arc furnace under argon protection to obtain Mn.sub.45Bi.sub.55 alloy ingots by using an arc-melting method;

[0026] 3) Coarse crushing: The Mn.sub.45Bi.sub.55 alloy ingots obtained in step 2) were coarsely crushed and passed through a 100-mesh sieve to obtain coarse powder;

[0027] 4) Proportioning in a ball milling tank: An appropriate amount of Mn.sub.45Bi.sub.55 alloy coarse powder obtained in step 3) was put into a ball milling tank together with non-magnetic steel balls, an appropriate amount of ethanol was added as solvent, and polyvinylpyrrolidone (PVP) accounting for 5% of the power mass was then added to assist in ball milling;

[0028] 5) Low-energy ball milling: The ball milling tank in step 4) was placed into a low-energy ball mill, a ball milling time was set as 1 hour, a ball milling speed was set at 256 rpm, an alternating time for clockwise/counterclockwise rotation was set as 6 minutes, and the slurry obtained was washed in anhydrous ethyl alcohol;

[0029] 6) Orientation and forming of a magnetic field: The washed magnetic powder was orientated, cured and formed in a 3T magnetic field after a certain amount of binder was added to obtain high-performance anisotropic MnBi alloy magnets finally.

[0030] 7) The magnetic property was tested by using a vibrating sample magnetometer. The magnetic hysteresis loop is as shown in FIG. 1 and the test results are as shown in Table 1.

[0031] Comparative Embodiment 1

[0032] 1) Proportioning: Mn and Bi alloys with a purity of over 99.99% were weighed and proportioned according to a nominal composition of Mn.sub.45Bi.sub.55;

[0033] 2) Melting: The proportioned raw materials were placed into an electric arc furnace under argon protection to obtain Mn.sub.45Bi.sub.55 alloy ingots by using an arc-melting method;

[0034] 3) Coarse crushing: The Mn.sub.45Bi.sub.55 alloy ingots obtained in step 2) were coarsely crushed and passed through a 100-mesh sieve to obtain coarse powder;

[0035] 4) Proportioning in a ball milling tank: An appropriate amount of Mn.sub.45Bi.sub.55 alloy coarse powder obtained in step 3) was put into a ball milling tank together with non-magnetic steel balls, with a ratio of ball to powder of 10:1; an appropriate amount of ethanol was added as solvent, and no surfactant was added to assist in ball milling; and the ball milling tank was assembled and placed into a low-energy ball mill;

[0036] 5) Low-energy ball milling: The ball milling tank in step 4) was placed into a low-energy ball mill, a ball milling time was set as 1 hour, a ball milling speed was set at 256 rpm, an alternating time for clockwise/counterclockwise rotation was set as 6 minutes, and the slurry obtained was washed in anhydrous ethyl alcohol;

[0037] 6) Orientation and forming in a magnetic field: The washed magnetic powder was orientated, cured and formed in a 3 T magnetic field after a certain amount of binder was added to obtain MnBi alloy magnets finally.

[0038] 7) The magnetic property was tested by using a vibrating sample magnetometer. The magnetic hysteresis loop is as shown in FIG. 1 and the test results are as shown in Table 1.

Embodiment 2

[0039] 1) Proportioning: Mn and Bi with a purity of over 99.99% were weighed and proportioned according to a nominal composition of Mn.sub.50Bi.sub.50;

[0040] 2) Melting: The proportioned raw materials were placed into an electric arc furnace under argon protection to obtain Mn.sub.50Bi.sub.50 alloy ingots by using an arc-melting method;

[0041] 3) Coarse crushing: The Mn.sub.50Bi.sub.50 alloy ingots obtained in step 2) were coarsely crushed and passed through a 100-mesh sieve to obtain the coarse powder;

[0042] 4) Proportioning in a ball milling tank: An appropriate amount of Mn.sub.50Bi.sub.50 alloy coarse powder obtained in step 3) was put into a ball milling tank together with non-magnetic steel balls, an appropriate amount of ethanol was added as solvent, and polyvinylpyrrolidone (PVP) accounting for 10% of the power mass was then added to assist in ball milling;

[0043] 5) Low-energy ball milling: The ball milling tank in step 4) was placed into a low-energy ball mill, a ball milling time was set as 3 hours, a ball milling speed was set at 256 rpm, an alternating time for clockwise/counterclockwise rotation was set as 6 minutes, and the slurry obtained was washed in anhydrous ethyl alcohol;

[0044] 6) Orientation and forming in a magnetic field: The washed magnetic powder was orientated, cured and formed in a 4 T magnetic field after a certain amount of binder was added to obtain high-performance anisotropic MnBi alloy magnets finally.

[0045] 7) The magnetic property was tested by using a vibrating sample magnetometer. The magnetic hysteresis loop is as shown in FIG. 2 and the test results are as shown in Table 1.

Embodiment 3

[0046] 1) Proportioning: Mn and Bi with a purity of over 99.99% were weighed and proportioned according to a nominal composition of Mn.sub.55Bi.sub.45;

[0047] 2) Melting: The proportioned raw materials were placed into an electric arc furnace under argon protection to obtain Mn.sub.55Bi.sub.45 alloy ingots by using an arc-melting method;

[0048] 3) Coarse crushing: The Mn.sub.55Bi.sub.45 alloy ingots obtained in step 2) were coarsely crushed and passed through a 100-mesh sieve to obtain coarse powder;

[0049] 4) Proportioning in a ball milling tank: An appropriate amount of Mn.sub.55Bi.sub.45 alloy coarse powder obtained in step 3) was put into a ball milling tank together with a non-magnetic steel ball, with a ratio of ball to powder of 10:1; an appropriate amount of ethanol was added as solvent, and polyvinylpyrrolidone (PVP) accounting for 15% of the power mass was then added to assist in ball milling; and the ball milling tank was assembled and placed into a low-energy ball mill;

[0050] 5) Low-energy ball milling: The ball milling tank in step 4) was placed into a low-energy ball mill, a ball milling time was set as 6 hours, a ball milling speed was set at 256 rpm, an alternating time for clockwise/counterclockwise rotation was set as 6 minutes, and the slurry obtained was washed in anhydrous ethyl alcohol;

[0051] 6) Orientation and forming in a magnetic field: The washed magnetic powder was orientated, cured and formed in a 5 T magnetic field after a certain amount of binder was added to obtain high-performance anisotropic MnBi alloy magnets finally.

[0052] 7) The magnetic property was tested by using a vibrating sample magnetometer. The magnetic hysteresis loop is as shown in FIG. 3 and the test results are as shown in Table 1.

TABLE-US-00001 TABLE 1 Saturation Intrinsic Type of Magnetization M.sub.s Coercivity No. Surfactant (emu/g) H.sub.cj (kOe) Comparative No surfactant 27.85 12.6 Embodiment 1 added Embodiment 1 5% PVP added 37.90 13.7 Embodiment 2 10% PVP added 48.34 11.9 Embodiment 3 15% PVP added 57.50 14.1

[0053] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.