Mn-Al permanent magnet alloy and preparation method thereof

Abstract

The invention relates to the technical field of permanent magnet materials, in particular to a Mn-Al permanent magnet alloy and a preparation method thereof. Rare earth elements (Nd and / or Gd) are doped in a MnAl alloy matrix, and a trace of rare earth elements are distributed at a MnAl alloy tau phase crystal boundary as a dispersed phase and serve as a pinning center to effectively hinder magnetic domain motion, inhibit growth of tau phase crystal grains and refine the tau phase crystal grains, so that the magnetic domain motion is effectively inhibited, and the grain size of the tau phase is reduced. And the coercive force is greatly improved on the premise of keeping relatively high saturation magnetization intensity, tau phase stability and relatively high Curie temperature. According to the preparation method of the Mn-Al permanent magnet alloy, the traditional technology is simplified, repeatability and stability are good, and the preparation method is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of permanent magnetic materials, in particular to a Mn-Al permanent magnetic alloy and a preparation method thereof. BACKGROUND

[0002] Magnetic materials are various in types and widely applied in many fields. With the development of science and technology, the demand for permanent magnets is increasing in various industries. Magnetic materials can be classified into soft magnetic materials, hard (permanent) magnetic materials, giant magnetic materials, gyromagnetic materials, piezomagnetic materials, magnetic recording materials, semi-hard magnetic materials, magnetic electronic materials and other magnetic materials according to their properties and applications. The permanent magnetic materials widely used in modern industry and science and technology include four categories: cast permanent magnetic materials, ferrite permanent magnetic materials, rare earth permanent magnetic materials and other permanent magnetic materials. The mainstream permanent magnet materials on the market are divided into two types: the first type is Nd-Fe-B, Sm-Co-based and other rare earth permanent magnet materials, which are widely used due to their excellent magnetic properties (magnetic energy product is about 200-450kJ / m 3 ). However, these magnets contain a large amount of rare earth elements, resulting in high cost. The other type is ferrite permanent magnetic material, which has the advantages of low raw material cost and easy production, but the overall magnetic energy product is low (magnetic energy product is about 38kJ / m 3 ). Therefore, it is increasingly urgent and important to develop rare earth-free or low-rare earth permanent magnetic materials with excellent magnetic properties.

[0003] Mn-Al alloy (maximum theoretical magnetic energy product is about 112kJ / m 3 ) is a permanent magnet with L10 structure, and its overall magnetic properties are between RE-permanent magnet and ferrite permanent magnet. The raw material price is relatively low, and it has high temperature resistance, strong corrosion resistance, good mechanical processing performance and high mechanical strength, which is a strong candidate for developing new permanent magnet materials. However, the coercivity of the obtained Mn-Al permanent magnet alloy is still far from the maximum theoretical value, so it is the focus of researchers to obtain Mn-Al permanent magnet alloy with high coercivity. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a Mn-Al permanent magnet alloy and a preparation method thereof. The Mn-Al permanent magnet alloy provided by the present application has high coercivity and low cost.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions: This invention provides a Mn-Al permanent magnet alloy, comprising a MnAl matrix and RE doped in the MnAl matrix, wherein the RE is Nd and / or Gd; the main phase of the Mn-Al permanent magnet alloy is the τ phase, with some RE dissolved in the MnAl matrix and the remaining RE distributed at the τ phase grain boundaries; the chemical composition of the Mn-Al permanent magnet alloy is Mn49~59Al51~41REx, 0.00<x≤0.30; the coercivity of the Mn-Al permanent magnet alloy at room temperature is 563.2~2145.3 Oe, and the saturation magnetization is 3.1~93.6 emu / g.

[0006] The present invention provides a method for preparing the Mn-Al permanent magnet alloy described above, comprising the following steps: weighing metallic Mn, metallic Al and metallic RE according to the composition of each element in the target Mn-Al permanent magnet alloy, and smelting them to obtain a cast alloy; The as-cast alloy is subjected to a first annealing treatment to obtain an intermediate alloy; the holding temperature of the first annealing treatment is 870~1250℃. The intermediate alloy is subjected to a second annealing treatment to obtain the Mn-Al permanent magnet alloy; the holding temperature of the second annealing treatment is 400~600℃.

[0007] Preferably, the holding time for the first annealing treatment is 1 to 20 hours; the cooling method for the first annealing treatment is water cooling, air cooling, or wind cooling.

[0008] Preferably, the holding time for the second annealing treatment is 0.5 to 32 hours; the cooling method for the second annealing treatment is water cooling, air cooling, or wind cooling.

[0009] Preferably, the actual amount of metal Mn used is 2-5 wt% more than the theoretical amount calculated from the chemical composition formula, and the actual amount of metal RE used is 1-3 wt% more than the theoretical amount calculated from the chemical composition formula.

[0010] Preferably, the first and second annealing processes are performed under vacuum sealing conditions.

[0011] The present invention provides another method for preparing the above-mentioned Mn-Al permanent magnet alloy, comprising the following steps: weighing metal Mn, metal Al and metal RE according to the composition of each element in the Mn-Al permanent magnet alloy, and smelting them to obtain a master alloy ingot; The master alloy ingot is subjected to rapid melt quenching in a vacuum environment to obtain the Mn-Al permanent magnet alloy; the rapid melt quenching rate is 15~40m / s.

[0012] Preferably, the rapid quenching of the melt further includes a short-time heat treatment of the resulting alloy strip; the holding temperature of the short-time heat treatment is 400~600℃, and the holding time is 15~120min; the short-time heat treatment is carried out under vacuum conditions.

[0013] Preferably, the melt quenching rate is 20~25m / s.

[0014] Preferably, the cooling method for the short-time heat treatment is water cooling, air cooling, or wind cooling.

[0015] This invention provides a Mn-Al permanent magnet alloy, comprising a MnAl matrix and reticulum (RE) doped in the MnAl matrix, wherein the RE is Nd and / or Gd; the main phase of the Mn-Al permanent magnet alloy is the τ phase, with some RE dissolved in the MnAl matrix and the remaining RE distributed at the τ phase grain boundaries; the chemical composition of the Mn-Al permanent magnet alloy is Mn 49~59 Al 51~41 RE x , 0.00<x≤0.30; the coercivity of the Mn-Al permanent magnet alloy at room temperature is 563.2~2145.3Oe, and the saturation magnetization is 3.1~93.6emu / g.

[0016] This invention significantly improves coercivity by doping a MnAl alloy matrix with rare earth elements (Nd and / or Gd). Trace amounts of these rare earth elements are dispersed as a phase at the τ-phase grain boundaries of the MnAl alloy, acting as pinning centers to effectively hinder magnetic domain movement, suppress τ-phase grain growth, and refine the τ-phase grains. This results in a significantly improved coercivity while maintaining high saturation magnetization, τ-phase stability, and a high Curie temperature. The results of the embodiments show that when x=0.05, Mn... 54 Al 46 Nd 0.05 The alloy exhibits a coercivity of 2145.3 Oe. Furthermore, the addition of Nd increases the remanence ratio (the ratio between the remaining magnetization after demagnetization and the saturation magnetization, calculated as Mr / Ms) to 51.3%. This alloy significantly controls the amount of rare earth elements used, maintaining a low cost advantage while achieving high performance.

[0017] This invention provides a method for preparing the Mn-Al permanent magnet alloy described above. This invention simplifies the traditional process and has good repeatability and stability, making it suitable for industrial production. Attached Figure Description

[0018] Figure 1 XRD patterns of the as-cast Mn-Al permanent magnet alloys prepared in Examples 1-11 and Comparative Example 1; Figure 2 SEM images of some as-cast Mn-Al permanent magnet alloys; Figure 3 Hysteresis loop diagram of a portion of the cast Mn-Al permanent magnet alloy; Figure 4 XRD patterns of permanent magnet alloy strips prepared by melt quenching technology from the master alloys of Examples 12-17, Example 19 and Comparative Example 4; Figure 5 Hysteresis loop diagrams of some permanent magnet alloy strips obtained by melt rapid quenching technology from the master alloy; Figure 6 The XRD patterns are of alloy strips obtained from the master alloys of Examples 21-28 by melt rapid quenching and short-time heat treatment. Figure 7 Hysteresis loop diagram of a portion of permanent magnet alloy strips obtained by melting rapid quenching and short-time heat treatment of the master alloy. Detailed Implementation

[0019] This invention provides a Mn-Al permanent magnet alloy, comprising a MnAl matrix and reticulum (RE) doped in the MnAl matrix, wherein the RE is Nd and / or Gd; the main phase of the Mn-Al permanent magnet alloy is the τ phase, with some RE dissolved in the MnAl matrix and the remaining RE distributed at the τ phase grain boundaries; the chemical composition of the Mn-Al permanent magnet alloy is Mn 49~59 Al 51~41 RE x , 0.00<x≤0.30; the coercivity of the Mn-Al permanent magnet alloy at room temperature is 563.2~2145.3Oe, and the saturation magnetization is 3.1~93.6emu / g.

[0020] In this invention, the chemical composition of the Mn-Al permanent magnet alloy is Mn 49~59 Al 51~41 RE x 49~59 and 51~41 refer to a total mass of Mn and Al being 100%, with Mn accounting for 49~59% of the mass and Al accounting for 51~41% of the mass; 0.00 < x ≤ 0.30 means that the percentage of RE doping mass in the total mass of Mn and Al is >0 and ≤0.30. In the embodiments of the present invention, x can be 0.00, 0.10, 0.15, 0.20, 0.25 or 0.30, and the mass percentage of Mn can be 49, 50, 51, 52, 53, 54, 55, 56, 57, 58 or 59, and correspondingly, the mass percentage of Al can be 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41.

[0021] In this invention, the Mn-Al permanent magnet alloy is either a cast Mn-Al permanent magnet alloy or a thin strip of Mn-Al permanent magnet alloy. When it is a thin strip of Mn-Al permanent magnet alloy, the thin strip is a single τ phase, or the τ phase is the main phase, coexisting with the ε phase; when it is a cast Mn-Al permanent magnet alloy, the main phase is the τ phase, containing or not containing a small amount of the ε phase. In this invention, the τ phase content in the Mn-Al permanent magnet alloy is 80% or more.

[0022] In this invention, especially when the RE doping amount is 0.05~0.10% (i.e., x=0.05 or 0.10), the Mn-Al permanent magnet alloy not only possesses high coercivity but also high saturation magnetization. When the RE doping amount is 0.05~0.10%, the prepared as-cast Mn-Al permanent magnet alloy achieves a coercivity of 1202.5~2145.3 Oe and a saturation magnetization of 81.4~89.3 emu / g.

[0023] This invention significantly improves coercivity by doping a MnAl alloy matrix with rare earth elements (Nd and / or Gd). Trace amounts of these rare earth elements are dispersed as a phase at the τ-phase grain boundaries of the MnAl alloy, acting as pinning centers to effectively hinder magnetic domain movement, suppress τ-phase grain growth, and refine the τ-phase grains. This results in a substantial increase in coercivity while maintaining high saturation magnetization, τ-phase stability, and a high Curie temperature. The amount of rare earth elements added in this invention is extremely small, yet the coercivity improvement is significant, offering high cost-effectiveness.

[0024] In addition, adding trace amounts of rare earth elements to MnAl alloys can improve the alloy's magnetic properties and effectively prevent the alloy from cracking and uneven melting caused by excessive internal stress due to the addition of too many rare earth elements.

[0025] The present invention provides a method for preparing the Mn-Al permanent magnet alloy described above (referred to as Method 1), comprising the following steps: weighing metallic Mn, metallic Al and metallic RE according to the composition of each element in the target Mn-Al permanent magnet alloy, and smelting them to obtain a cast alloy; The as-cast alloy is subjected to a first annealing treatment to obtain an intermediate alloy; the holding temperature of the first annealing treatment is 870~1250℃. The intermediate alloy is subjected to a second annealing treatment to obtain the Mn-Al permanent magnet alloy; the holding temperature of the second annealing treatment is 400~600℃.

[0026] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0027] According to the composition of each element in the target Mn-Al permanent magnet alloy, the present invention weighs metallic Mn, metallic Al and metallic RE, and melts them to obtain a cast alloy.

[0028] In this invention, the actual amount of metal Mn is preferably 2-5 wt% more than the theoretical amount calculated from the chemical composition formula, and in specific embodiments, the excess can be 2, 3, 4, or 5 wt%; the actual amount of metal RE is preferably 1-3 wt% more than the theoretical amount calculated from the chemical composition formula, and in specific embodiments, the excess can be 1, 2, or 3 wt%; the actual amount of metal Al is preferably the theoretical amount calculated from the chemical composition formula.

[0029] In this invention, the melting is preferably vacuum argon arc melting; the vacuum argon arc melting preferably includes the following steps: first, the vacuum chamber is evacuated to a low vacuum level, so that the vacuum degree of the vacuum chamber reaches 5×10⁻⁶. -3 The pressure is below Pa, then argon gas is introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Under low vacuum evacuation conditions, the vacuum chamber is purged. After purging, the vacuum chamber is evacuated to a high vacuum to reduce the vacuum level to 1×10⁻⁶ Pa. -3 Below Pa, argon gas was then introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Arc melting is performed using Pa. During the melting process, the current is slowly adjusted to 100-150A (the adjustment rate is a conventional method in the art). After the raw material is completely melted and agglomerated into spherical liquids and exhibits good fluidity, it is suspended above the melt for 5-10 seconds. Then, the current is slowly reduced to 40-60A (the rate of reduction is not specifically limited and is a conventional method in the art), and suspended above the melt for 10-15 seconds. After the melt solidifies and the fluidity disappears, the current is slowly adjusted to the lowest value. In this invention, the gas washing treatment is preferably performed 3 times, and the duration of each gas washing is preferably 5 minutes. This invention preferably involves repeated melting 3 times. This invention, through vacuum argon arc melting and controlling the melting conditions, yields a cast master alloy with less loss, higher quality, and effectively prevents melting segregation, improving the uniformity of the alloy. In addition, the trace doping of rare earth elements Nd and / or Gd into the Mn-Al alloy can purify the Mn-Al alloy, enhance the fluidity of the sample during melting, and improve the melting effect.

[0030] After obtaining the as-cast alloy, the present invention performs a first annealing treatment on the as-cast alloy to obtain an intermediate alloy.

[0031] In this invention, the holding temperature of the first annealing treatment is 870~1250℃, and in specific embodiments it can be 900, 1000, 1050, 1100, 1150, 1200 or 1250℃; the holding time of the first annealing treatment is preferably 1~20h, and in specific embodiments it can be 5, 10, 14, 16, 18 or 20h; the cooling method of the first annealing treatment is preferably water cooling, air cooling or wind cooling, and in the embodiments of this invention it is water cooling, specifically rapid quenching with an ice-water mixture followed by soaking for half an hour. In this invention, the first annealing treatment is preferably carried out under vacuum sealing conditions. In this invention, the cast alloy is preferably wrapped in tantalum sheets and placed in a quartz tube before vacuum sealing. This invention utilizes the advantages of tantalum sheets, which have a high melting point and are refractory metals, to protect the cast alloy, prevent the volatilization of Mn, and ensure that the composition does not change during the annealing treatment; in addition, tantalum sheets can isolate the cast alloy from direct contact with the quartz tube, avoiding chemical reactions between the two. This invention achieves a uniform microstructure through a first annealing treatment, while simultaneously increasing the content of the τ phase. In this invention, the intermediate alloy is a cast alloy containing both ε and τ phase microstructures.

[0032] After obtaining the intermediate alloy, the present invention performs a second annealing treatment on the intermediate alloy to obtain the Mn-Al permanent magnet alloy.

[0033] In this invention, the holding temperature of the second annealing treatment is 400~600℃, specifically 400, 450, 500, 550 or 600℃ in the embodiments; the holding time of the second annealing treatment is preferably 0.5~32h, specifically 0.5, 1, 2, 5, 10, 15, 20, 25, 30 or 32h in the embodiments; the cooling method of the second annealing treatment is preferably water cooling, air cooling or wind cooling, and in the embodiments of this invention it is water cooling, specifically rapid quenching with an ice-water mixture followed by soaking for half an hour; the second annealing treatment is preferably carried out under vacuum sealing conditions. This invention uses the second annealing treatment to cause the ε phase structure in the intermediate alloy to undergo a martensitic transformation into the τ phase structure.

[0034] The Mn-Al permanent magnet alloy prepared by method one of this invention is a cast Mn-Al permanent magnet alloy, which can significantly improve the magnetic properties of Mn-Al permanent magnet alloys. The preparation method is simple, easy to operate, and has few processes, and has good prospects for industrial application.

[0035] MnAl alloys that have undergone two annealing treatments but have not been doped with rare earth elements have low coercivity at room temperature, approximately 441.5 Oe. However, the coercivity is significantly improved when trace amounts of rare earth elements (Nd and / or Gd) are added. The coercivity of the cast Mn-Al permanent magnet alloy with the highest coercivity is 2145.3 Oe, without sacrificing too much saturation magnetization.

[0036] In this invention, the coercivity of the as-cast Mn-Al permanent magnet alloy prepared by method one is 563.2~2145.3 Oe, and the saturation magnetization is 76.2~89.3 emu / g; when the RE doping amount is 0.05~0.10, the coercivity of the prepared as-cast Mn-Al permanent magnet alloy reaches 1202.5~2145.3 Oe, and the saturation magnetization reaches 81.4~89.3 emu / g.

[0037] The present invention provides another preparation method of the Mn-Al permanent magnet alloy described in the above scheme, comprising the following steps: weighing metal Mn, metal Al and metal RE according to the composition of each element in the Mn-Al permanent magnet alloy, and smelting them to obtain a master alloy ingot; The master alloy ingot is subjected to rapid melt quenching in a vacuum environment to obtain the Mn-Al permanent magnet alloy; the rapid melt quenching rate is 15~40m / s.

[0038] In this invention, the smelting process is the same as in Method 1, and will not be repeated here.

[0039] After obtaining the master alloy ingot, the present invention performs melt rapid quenching on the master alloy ingot in a vacuum environment to obtain the Mn-Al permanent magnet alloy.

[0040] In this invention, the melt quenching rate is 15~40 m / s, and in specific embodiments it can be 15, 20, 25, 30, 35 or 40 m / s. In this invention, when the melt quenching rate is 20~25 m / s, the prepared Mn-Al permanent magnet alloy not only has high coercivity but also high saturation magnetization. Specifically, when the RE doping amount is 0.10, the melt quenching rate is 20~25 m / s and no short-time heat treatment is performed, the prepared Mn-Al permanent magnet alloy (alloy strip) achieves a coercivity of 1622.5~1790.5 Oe and a saturation magnetization of 72.7~74.6 emu / g.

[0041] In this invention, the method of rapid melt quenching without short-time heat treatment is referred to as Method Two. The Mn-Al permanent magnet alloy prepared by Method Two is an alloy strip with ε-phase and τ-phase microstructures, with the τ-phase microstructure being dominant.

[0042] In this invention, under the same rare earth doping amount, the Mn-Al permanent magnet alloy prepared by method two has finer grains and significantly increased coercivity compared to the Mn-Al permanent magnet alloy prepared by method one.

[0043] After completing the rapid quenching of the melt, the present invention preferably further includes short-time heat treatment of the obtained alloy strip to obtain the Mn-Al permanent magnet alloy (referred to as Method 3).

[0044] In this invention, the holding temperature for the short-time heat treatment is preferably 400~600℃, and the holding time is preferably 15~120min; the short-time heat treatment is preferably carried out under vacuum conditions. In specific embodiments, the holding temperature for the short-time heat treatment can be 400, 450, 500, 550 or 600℃, and the holding time can be 15, 30, 60, 90 or 120min.

[0045] The coercivity of the Mn-Al permanent magnet alloy prepared by the present invention through short-time heat treatment (method 3) is slightly reduced, but the saturation magnetization is significantly improved, and both the remanence and remanence ratio are improved.

[0046] The following detailed description of the Mn-Al permanent magnet alloy and its preparation method provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0047] Examples 1-11 and Comparative Examples 1-3 The preparation method of as-cast Mn-Al permanent magnet alloy adopts the following steps: Step (1): According to the nominal molecular formula Mn 54 Al 46 RE x (RE represents Nd or Gd), where the ratio is 0.00≤x≤0.30 (see Table 1 for specific values). Weigh the raw materials Mn, Al, and rare earth Nd / Gd, and melt the raw materials using a vacuum argon arc melting method. During melting, first evacuate the vacuum chamber to a low vacuum level of 5×10⁻⁶. -3 The pressure is below Pa, then argon gas is introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Under low vacuum evacuation conditions, the vacuum chamber was purged three times, with each purging lasting 5 minutes. After purging, the vacuum chamber was evacuated to a high vacuum to reduce the vacuum level to 1 × 10⁻⁶ Pa. -3 Below Pa, argon gas was then introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Pa is used for arc ignition melting. During the melting process, the current is slowly adjusted to the range of 100~150A. After the raw material is completely melted and agglomerated into a spherical liquid and exhibits good fluidity, it is suspended above the sample for 5~10s. Then the current is slowly reduced to 40~60A and suspended above the sample for 10~15s. After the sample solidifies and the fluidity disappears, the current is slowly adjusted to the lowest value (10A). The melting is repeated 3 times to obtain the cast alloy. Step (2): The as-cast alloy prepared in step (1) is wrapped in tantalum sheet, placed in a quartz tube and vacuum sealed. After sealing, it is sealed with alcohol and left to stand overnight. Then, it is annealed twice. The first annealing is carried out at 1100℃ for 16 hours and then rapidly quenched with an ice-water mixture. The second annealing is carried out at 500℃ for 2 hours and then rapidly quenched with an ice-water mixture to obtain the as-cast Mn-Al permanent magnet alloy.

[0048] Table 1. Rare earth doping types and amounts in Examples 1-11 and Comparative Examples 1-3

[0049] Structural testing and characterization: X-ray diffraction (XRD) tests were performed on the as-cast Mn-Al permanent magnet alloys prepared in Examples 1-11 and Comparative Examples 1-3. The test results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the main phase of the obtained as-cast Mn-Al permanent magnet alloy is the τ phase.

[0050] To determine the phase distribution of rare earth elements in Mn-Al alloys and whether the heat-treated alloy samples are single-phase, metallographic analysis was performed. Specifically, the metallographic structure was extracted by mounting the as-cast Mn-Al permanent magnet alloy sample and then observing it using a scanning electron microscope (SEM). The analysis focused on the presence of rare earth elements in the Mn-Al permanent magnet alloy. 54 Al 46 Nd 0.00 (Comparative Example 1) Mn 54 Al 46 Nd 0.10 (Example 2) Mn 54 Al 46 Nd 0.20 (Example 4) Mn 54 Al 46 Nd 0.30 (Example 5), Mn 54 Al 46 Gd 0.10 (Example 7), Mn 54 Al 46 Gd 0.20 (Example 9) Mn 54 Al 46 Gd 0.30 The test results of (Example 11) are as follows: Figure 2 As shown, Figure 2 The results showed that most of the rare earth atoms in the sample were distributed at the grain boundaries of the alloy, while the alloy without rare earth elements (Mn) 54 Al 46 Nd 0.00 It exists in the form of a single phase.

[0051] To test the hysteresis loop of the sample at room temperature, the magnetic properties of the sample were measured using a vibrating sample magnetometer (VSM). The specific method is as follows: As-cast Mn-Al permanent magnet alloy samples ranging from 1 to 20 mg were selected. An external magnetic field of up to 2 T was applied. The as-cast Mn-Al permanent magnet alloy did not reach saturation under the 2 T external magnetic field. The saturation magnetization of the as-cast Mn-Al permanent magnet alloy was then estimated based on the law of approaching saturation. Some test results are shown below. Figure 3 As shown in the figure. Detailed data is shown in Table 2.

[0052] Table 2. Magnetic property data of the as-cast Mn-Al permanent magnet alloys prepared in Examples 1-11 and Comparative Example 1

[0053] like Figure 3 As shown, the as-cast permanent magnet alloy material obtained after two annealing processes contains undoped Mn. 54 Al 46 The coercivity of the alloy is approximately 441.5 Oe, and the saturation magnetization is approximately 93.6 emu / g. The coercivity of the cast permanent magnet alloy with rare earth Nd doping amount x=0.05 is larger than that of other cast permanent magnet alloys with different composition ratios, with a coercivity of approximately 2145.3 Oe and a saturation magnetization of approximately 89.3 emu / g. With trace doping of rare earth elements, the coercivity is improved in the range of x≤0.30, and the saturation magnetization does not decrease significantly.

[0054] Examples 12-17 and Comparative Example 4 Step (1): According to the nominal molecular formula Mn 54 Al 46 RE x (RE represents Nd or Gd), where the ratio is 0.00≤x≤0.30 (see Table 3 for specific values). Weigh the raw materials Mn, Al, and rare earth Nd / Gd, and melt the raw materials using a vacuum argon arc melting method. During melting, first evacuate the vacuum chamber to a low vacuum level of 5×10⁻⁶. -3 The pressure is below Pa, then argon gas is introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Under low vacuum evacuation conditions, the vacuum chamber was purged three times, with each purging lasting 5 minutes. After purging, the vacuum chamber was evacuated to a high vacuum to reduce the vacuum level to 1 × 10⁻⁶ Pa. -3 Below Pa, argon gas was then introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4Pa is used for arc ignition melting. During the melting process, the current is slowly adjusted to the range of 100~150A. After the raw material is completely melted and agglomerated into a spherical liquid and exhibits good fluidity, it is suspended above the sample for 5~10s. Then the current is slowly reduced to 40~60A and suspended above the sample for 10~15s. After the sample solidifies and the fluidity disappears, the current is slowly adjusted to the lowest value (10A). The melting is repeated 3 times to obtain the master alloy ingot. Step (2): The master alloy ingot prepared in step (1) is rapidly cooled in an induction melting and spinning device in an argon atmosphere using a melt rapid quenching technique at a specific roller speed (the rapid quenching rate for each embodiment is shown in Table 3) to obtain a permanent magnet alloy strip.

[0055] Table 3. Doping amount and preparation conditions of permanent magnet alloy strips in Examples 12-17 and Comparative Example 2

[0056] Examples 21-28 Step (1): According to the nominal molecular formula Mn 54 Al 46 RE x (RE represents Nd or Gd), where the ratio is 0.00≤x≤0.30 (see Table 3 for specific values). Weigh the raw materials Mn, Al, and rare earth Nd / Gd, and melt the raw materials using a vacuum argon arc melting method. During melting, first evacuate the vacuum chamber to a low vacuum level of 5×10⁻⁶. -3 The pressure is below Pa, then argon gas is introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Under low vacuum evacuation conditions, the vacuum chamber was purged three times, with each purging lasting 5 minutes. After purging, the vacuum chamber was evacuated to a high vacuum to reduce the vacuum level to 1 × 10⁻⁶ Pa. -3 Below Pa, argon gas was then introduced to bring the vacuum chamber pressure to 1×10⁻⁶. 4 Pa is used for arc ignition melting. During the melting process, the current is slowly adjusted to the range of 100~150A. After the raw material is completely melted and agglomerated into a spherical liquid and exhibits good fluidity, it is suspended above the sample for 5~10s. Then the current is slowly reduced to 40~60A and suspended above the sample for 10~15s. After the sample solidifies and the fluidity disappears, the current is slowly adjusted to the lowest value (10A). The melting is repeated 3 times to obtain the master alloy ingot. Step (2): The master alloy ingot prepared in step (1) is rapidly cooled into alloy strips in an induction melting and spinning device in an argon atmosphere, using a specific roller speed (the rapid quenching rate of each embodiment is shown in Table 4) in combination with melt rapid quenching technology.

[0057] Step (3): Place the alloy strip prepared in step (2) into a quartz tube and vacuum seal it. Then treat it at 500℃ for a period of time (the treatment time is shown in Table 4). Then put it into an ice-water mixture to cool it rapidly to room temperature and soak it for half an hour to obtain a high-performance permanent magnet alloy strip.

[0058] Table 4. Doping amount and preparation conditions of permanent magnet alloy strips in Examples 14, 21-28

[0059] Structural testing and characterization: XRD tests were performed on the alloy strips obtained from the master alloys of Examples 12-17, Example 19, and Comparative Example 4 using melt rapid quenching technology. The results are shown in the figure. Figure 4 ,Depend on Figure 4 It can be seen that the alloy ribbon obtained by melt rapid quenching of the master alloy has two phases, τ and ε, coexisting. XRD tests were performed on the permanent magnet alloy ribbons prepared by melt rapid quenching followed by short-time heat treatment in Examples 14 and 21-24. The results are shown in [Figure 1]. Figure 6 .Depend on Figure 6 It can be seen that the permanent magnet alloy strip obtained by rapid quenching after short-time heat treatment of the alloy strip is completely transformed into the τ phase through martensitic phase transformation.

[0060] The hysteresis loops of the permanent magnet alloy strips prepared in Examples 12-20 and Comparative Example 4 were tested to obtain magnetic property data. Some test results are shown in […]. Figure 5 Detailed magnetic properties data are shown in Table 5.

[0061] Table 5. Coercivity and saturation magnetization of permanent magnet alloy strips obtained from the master alloy by melt rapid quenching technology

[0062] like Figure 5 As shown, permanent magnet alloy strips were prepared by melt rapid quenching technology (hub speed of 15~40 m / s) on the master alloy obtained by smelting. The permanent magnet alloy strip prepared at a hub speed of 25 m / s had the best comprehensive magnetic properties. The permanent magnet alloy strip with trace rare earth Nd doping (x=0.10) had a coercivity of about 1790.5 Oe and a saturation magnetization of about 72.4 emu / g. The permanent magnet alloy strip without rare earth doping Mn had a coercivity of about 1790.5 Oe and a saturation magnetization of about 72.4 emu / g. 54 Al 46 The permanent magnet alloy strip made from the master alloy at a hub speed of 25 m / s has a coercivity of approximately 1044.2 Oe and a saturation magnetization of approximately 89.3 emu / g. The saturation magnetization of the strip made by trace doping with rare earth elements is lower than that of the undoped permanent magnet alloy strip, but the coercivity is significantly improved.

[0063] The hysteresis loops of the permanent magnet alloy strips prepared in Examples 21-28 were tested to obtain magnetic property data. Some test results are shown in […]. Figure 7 Detailed magnetic property data are shown in Table 6.

[0064] Table 6. Coercivity and saturation magnetization of alloy strips prepared by melt rapid quenching followed by short-time heat treatment

[0065] like Figure 7 As shown, Mn 54 Al 46 Nd 0.10 Permanent magnet alloy strips made from alloys of the specified composition at a hub speed of 25 m / s were annealed at 500℃ for 15 min. The saturation magnetization of the permanent magnet alloy strips significantly improved, while the coercivity did not decrease substantially. After heat treatment, the coercivity of the permanent magnet alloy strips was approximately 1662.4 Oe, and the saturation magnetization was approximately 90.5 emu / g. Mn 54 Al 46 Gd 0.20 The coercivity of the permanent magnet alloy strip obtained under the same conditions is approximately 1976.8 Oe, and the saturation magnetization is approximately 84.6 emu / g.

[0066] A comparison of the hysteresis loops of three types of permanent magnet alloy materials prepared by different methods revealed the following: like Figure 3 As shown, in Mn 54 Al 46 Trace doping of rare earth elements Nd and / or Gd significantly improves the coercivity of the as-cast alloy, and the as-cast alloy does not exhibit a significant decrease in saturation magnetization; for example Figure 5 As shown, after rapid melt quenching of the master alloy ingot, the coercivity of the alloy strip prepared from the master alloy with trace Nd doping is significantly improved compared to that of the alloy strip obtained from the undoped master alloy. Furthermore, the coercivity of the alloy strip obtained from rapid melt quenching is significantly improved compared to that of the as-cast permanent magnet alloy prepared through two annealing treatments. Figure 7 As shown, after further short-time heat treatment of the alloy strip obtained by rapid melt quenching, the coercivity decreased slightly but the saturation magnetization was significantly improved, and both the remanence and remanence ratio were improved.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Mn-Al permanent magnet alloy, characterized in that, The Mn-Al permanent magnet alloy comprises a MnAl matrix and reticulum (RE) doped in the MnAl matrix, wherein the RE is Nd and / or Gd; the main phase of the Mn-Al permanent magnet alloy is the τ phase, with some RE dissolved in the MnAl matrix and the remaining RE distributed at the τ phase grain boundaries; the chemical composition of the Mn-Al permanent magnet alloy is Mn 49~59 Al 51~41 RE x , 0.00<x≤0.30; the coercivity of the Mn-Al permanent magnet alloy at room temperature is 563.2~2145.3Oe, and the saturation magnetization is 3.1~93.6emu / g.

2. A method for preparing the Mn-Al permanent magnet alloy according to claim 1, characterized in that, Includes the following steps: Based on the composition of each element in the target Mn-Al permanent magnet alloy, weigh metallic Mn, metallic Al and metallic RE, and smelt them to obtain the cast alloy. The as-cast alloy is subjected to a first annealing treatment to obtain an intermediate alloy; the holding temperature of the first annealing treatment is 870~1250℃. The intermediate alloy is subjected to a second annealing treatment to obtain the Mn-Al permanent magnet alloy; the holding temperature of the second annealing treatment is 400~600℃.

3. The preparation method according to claim 2, characterized in that, The holding time for the first annealing treatment is 1 to 20 hours; the cooling method for the first annealing treatment is water cooling, air cooling, or wind cooling.

4. The preparation method according to claim 2, characterized in that, The holding time for the second annealing treatment is 0.5 to 32 hours; the cooling method for the second annealing treatment is water cooling, air cooling, or wind cooling.

5. The preparation method according to claim 2, characterized in that, The actual amount of metal Mn used is 2-5 wt% more than the theoretical amount calculated from the chemical composition, and the actual amount of metal RE used is 1-3 wt% more than the theoretical amount calculated from the chemical composition.

6. The preparation method according to claim 2, characterized in that, The first and second annealing processes are performed under vacuum sealing conditions.

7. A method for preparing the Mn-Al permanent magnet alloy according to claim 1, characterized in that, Includes the following steps: Based on the composition of each element in the Mn-Al permanent magnet alloy, weigh the metallic Mn, metallic Al and metallic RE, and smelt them to obtain the master alloy ingot; The master alloy ingot is subjected to rapid melt quenching in a vacuum environment to obtain the Mn-Al permanent magnet alloy; the rapid melt quenching rate is 15~40m / s.

8. The preparation method according to claim 7, characterized in that, The process of rapidly quenching the melt further includes short-time heat treatment of the resulting alloy strip; the holding temperature of the short-time heat treatment is 400~600℃, and the holding time is 15~120min; the short-time heat treatment is carried out under vacuum conditions.

9. The preparation method according to claim 7 or 8, characterized in that, The melt quenching rate is 20~25m / s.

10. The preparation method according to claim 8, characterized in that, The cooling method for the short-time heat treatment is water cooling, air cooling, or wind cooling.

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