WO2022178958A1 - R-t-b-si-m-a-series rare earth permanent magnet - Google Patents

Abstract

Provided is an R-T-B-Si-M-A-series rare earth permanent magnet, mainly comprising the following components in percentages by mass: 29.0-32.8% of R, 0.9-0.98% of B, 0.01-0.1% of Si, 0.05-2% of M and 0.2-1% of A. In the R-T-B-series rare earth permanent magnet, the addition of a specified amount of Si and appropriate amounts of Cu and Ga result in the remanence and the coercive force being improved, and the consistency of the remanence and the coercive force of the magnet during mass production can be significantly improved.

Description

A kind of R-T-B-Si-M-A series rare earth permanent magnet technical field

The invention relates to an R-T-B-Si-M-A series rare earth permanent magnet, which belongs to the field of rare earth magnets.

Background technique

In recent years, rare earth permanent magnets containing R2T14B main phase have been widely used in servo motors, wind turbines, energy-saving air-conditioning compressors and new energy vehicles due to their high remanence and magnetic energy product. Based on the continuous pursuit of rare earth permanent magnets with low cost, high remanence and high coercivity, researchers and manufacturers have gradually discovered that in addition to using heavy rare earth elements, the purity of the main phase can be improved and the content of impurity elements can be reduced. To increase the remanence and reduce the ferromagnetism of the grain boundary phase to improve the coercivity is the main way to prepare high comprehensive performance rare earth permanent magnets.

Add a small amount of Cu or Ga to improve the wettability of grain boundaries, thereby increasing the coercivity, (such as reference 1 and 2), but the remanence will be significantly reduced. Since the rare earth grain boundary phase rich in Cu and Ga has a low melting point and is easy to be oxidized, the effective content in the whole preparation process will decrease. At the same time, the enrichment phase transition of the grain boundary phase caused by Cu and Ga occurs too fast, which increases the difficulty of control. It is not conducive to improving the consistency of product performance in mass production, and often requires special hydrogen breaking process or more severe sintering aging conditions.

In addition, C will reduce the melting point of the rare-earth-rich phase and increase the solubility of Fe, which will not only easily cause abnormal growth of the grains during sintering and poor squareness, but also enhance the ferromagnetism of the rare-earth-rich grain boundary phase, resulting in the deterioration of coercivity. . Therefore, controlling the carbon content is also a key method for the production of high-performance rare earth permanent magnets.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art and provide an R-T-B-Si-M-A series rare earth permanent magnet containing a trace amount of Si.

The technical scheme adopted in the present invention is:

An R-T-B-Si-M-A series rare earth permanent magnet mainly includes the following components in mass ratio:

The balance is T and inevitable impurities;

The R is selected from at least one of the following elements: Nd, Pr, Dy, Tb, Ho, La, Ce, Pm, Sm, Eu, Gd, Er, Tm, Yb, Lu or Y;

The M is selected from at least one of the following elements: Al, Sn, Ge, Ag, Au, Bi, Mn, Nb, Ti, Hf, Zr or Cr;

Described T is selected from at least one element in Fe and Co;

The A is selected from at least one element of Ga and Cu.

Si element has good bonding force with impurity elements such as O, S, P, etc., which can reduce the content of impurity elements in the main phase and improve the remanence. At the same time, the compound formed by Si has a higher melting point, and Si enters the grain boundary phase such as R6T13(Ga,Cu)1, which can delay the phase transformation rate, thereby avoiding the magnet consistency caused by the fact that different positions in the sintering or aging furnace cannot reach the set temperature at the same time. Reduce the problem, improve the adaptability of mass production, and have a certain effect of inhibiting grain growth. Combined with the low-carbon control process, the high coercivity and squareness of the magnet are effectively guaranteed.

In order to improve the detection accuracy, inductively coupled plasma mass spectrometer ICP-MS can be used to detect the Si content in the material, and the detection accuracy can reach 10ppb. The Si content in the Si-rich region can be detected by WDS in field emission electron probe microscope EPMA or scanning electron microscope EDS, and the detection limit is about 100 ppm.

Unlike the conventional addition of elements such as Cu, Ga, etc., which reduces the remanence Br and the magnetic energy product (BH) max, the present invention contains a trace amount of Si, that is, a content of 0.1 wt.% or less. Because it is a non-magnetic element, its content is small, and its content in the main phase is very small, and the magnetic dilution effect is very small; at the same time, Si can form high-melting rare earth compounds with impurities such as P and S, and disperse in the grain boundary phase, It can not only improve the purity and saturation magnetization of the main phase, but also play a certain role in pinning, inhibit the growth of grains, and facilitate obtaining higher density at a higher sintering temperature. Therefore, the trace addition of Si in the present invention is , but increase Br and (BH)max.

According to the existing literature reports, the addition of Cu and Ga improves the wettability of the rare earth-rich grain boundary phase, but also reduces its melting point, so the grain boundary phase transition rate increases. However, the temperature history of different areas in the sintering or aging furnace is different. The area close to the heating unit (molybdenum belt) has a fast heating rate, and the high temperature holding time is longer than that in the core area of the batch magnet. The area where the phase transition is too early is also prone to grain boundary phase. It grows up and distributes unevenly, which reduces the consistency of the magnetic properties of the magnet and increases the difficulty in engineering production. Si element and rare earth, Fe, Cu, Ga often form compounds with higher melting points, which delays the grain boundary phase transition. Before the grain boundary phase grows in the region near the heating unit, the grain boundary phase in the core also has enough phase Transformation, the consistency of grain boundary phase structure and magnetic properties of magnets in different regions of the furnace is improved. In the present invention, by setting a certain amount of Cu and Ga, the wettability of the rare-earth-rich grain boundary phase is improved, so that when Si forms a compound with impurity elements such as P, S, O, etc., the precipitation at the grain boundary and the direct contact with the grain are avoided. High mismatch energy, thereby reducing coercivity. At the same time, it is avoided that the excessive content of Cu and Ga leads to the increase and growth of the grain boundary phase, and even leads to excessive rotation of the main phase grains during the sintering process, resulting in insufficient remanence reduction.

It should be noted that the Si content of pure iron raw materials with a rare earth permanent magnet composition accounting for more than 50wt% is within 30ppm, while the Si content of rare earth metals such as PrNd about 30wt.% is also within 150ppm, and other metals such as Co and Cu are also within 150ppm. The Si content in the elemental substance is all less than 10ppm. Therefore, rare earth magnets with Si content less than 0.01 wt % can be easily obtained.

In the present invention, Si is added as an elemental raw material; of course, FeSi alloys or other alloys and compounds can also be selected to be added, or a raw material containing a certain amount of Si impurities can be selected to be added. In short, it is sufficient as long as the necessary amount of Si is contained in the final magnet.

Preferably, the main phase of the R-T-B-Si-M-A series rare earth permanent magnet is an R2T14B type compound, and the grain boundary phase between the main phases contains a Si-rich region with a Si content of 0.02wt.% to 2.0wt.%.

Preferably, the Si-rich region contains at least one of Ga and Cu elements, and the total mass fraction thereof is 0.05 wt. % to 10 wt. %.

Preferably, the Si-rich region contains at least one of P and S elements, and the total mass fraction thereof is 5 wt. % to 20 wt. %.

The C content in the R-T-B-Si-M-A series rare earth permanent magnet is controlled at 0.02wt.%-0.15wt.%. In the present invention, it is necessary to control the C content of the magnet to be 0.02wt.% to 0.15wt.% in order to obtain the corresponding effect. In general, C is mainly derived from the antioxidants and lubricants added during the preparation process to prevent oxidation of the powder and improve the fluidity of the powder to ensure stable magnetic properties, especially Br. The C content of the magnet can be easily reduced by controlling the amount of additives and the exhaust time before vacuum sintering.

Preferably, the R is selected from at least one of the following elements: Nd, Pr, Dy, Tb.

Preferably, the M is selected from at least one of the following elements: Al, Ti, Zr.

It should be noted that the magnets prepared under the condition that the raw material impurity content is very low and the process control is strictly controlled have less impurities such as P, S, O, etc., and under the limited microscopic detection ability, it is not necessarily 100% detected to contain P. , S, O and other impurity elements in the Si-rich region; at the same time, in the magnet with less Si content, the detection probability of the Si-rich region itself will also decrease, but the presence of Si element improves the local resistance of the magnet to P, S, The ability to contaminate or interfere with impurities such as O can be judged by the improvement of the consistency of the magnetic properties to determine the effect of the addition of trace Si elements.

The beneficial effects of the present invention are mainly reflected in: the present invention in the R-T-B series rare earth permanent magnet, by adding a prescribed amount of Si, and an appropriate amount of Cu and Ga, the magnet remanence and coercivity are improved, and the mass production is significantly improved. Consistency of remanence and coercivity of magnets.

Description of drawings

Figure 1 is a schematic diagram of the method for testing the consistency of magnetic properties; samples were taken at different positions in the sintering furnace, and the average and standard deviation were calculated after the performance was measured.

FIG. 2 shows the cross-sectional microstructure of the magnet and the composition of the grain boundary phase observed by SEM [Japan Electronics Corporation (JEOL)] and EDS.

Figure 3 is the microstructure of experimental samples 4 and 5;

FIG. 4 is the microstructure of the experimental sample 21;

Fig. 5 is the microstructure of experimental sample 23;

Fig. 6 is that experimental sample 28 carries out ICP-MS test result;

FIG. 7 is the microstructure of the experimental sample 32 .

Detailed ways

The present invention is further described below in conjunction with specific embodiment, but the protection scope of the present invention is not limited to this:

The raw material alloys (strip strips) are cast according to the strip strip method. Various raw materials and intermediate alloys in the formula ratio are placed in a certain order in an intermediate frequency induction melting furnace for vacuum heating and melting. After refining for a few minutes, the melt is adjusted by power. The temperature is controlled within the set range, the crucible is tilted at a certain rate, poured into the tundish and continuously transported to the water-cooled copper roller to achieve rapid-setting cooling. By adjusting the temperature and flow of cooling water and the surface roughness of the copper roll, a quick-setting sheet (spinning sheet) with a thickness of about 0.3 mm and a microstructure mostly columnar crystals is obtained.

The strips are preferably crushed in two steps, hydrogen crushing and jet mill crushing, to achieve the desired particle size.

The hydrogen fragmentation is to use the strip-slinging sheet to absorb hydrogen and expand to generate cracks, thereby causing intergranular and transgranular fractures. Since the hydrogen absorption rate and hydrogen absorption amount of the main phase and the rare earth-rich grain boundary phase are different, the proportion of fractures along the grain boundary phase is greatly increased, which is beneficial to obtain single crystal powder. Hydrogen crushing is to expose the stripping sheet in a reaction kettle with a certain pressure of hydrogen, and the general hydrogen pressure is 0.01-0.09Mpa. Since hydrogen absorption is an exothermic reaction, the reaction kettle should be cooled during the hydrogen absorption process, preferably using cooling water spray. After the hydrogen absorption is completed, the excess hydrogen and the hydrogen adsorbed in the alloy are extracted by increasing the temperature in the reaction kettle and the vacuum pump group, so as to improve the stability of the powder.

Jet milling is to drive the coarse powder to collide with the target material or collide with each other through high-speed airflow to achieve further crushing. The gas can be selected from nitrogen, argon, helium and mixed gas mixed with a small amount of hydrogen or oxygen and other gases. The final particle size of the powder is controlled by the sorting wheel and the cyclone classifier in the jet mill, and D50<5.4 microns is preferably measured by an air-jet dispersion laser particle analyzer.

The fine powder is mixed with a certain amount of lubricant and antioxidant, and magnetic field orientation molding is carried out in an orientation press. In order to reduce the amount of additives to reduce the introduction of carbon impurities, one of the embodiments of the present invention is to use fine powder with D50>4.5 microns to ensure the fluidity of the powder and reduce the activity of the powder. At the same time, under the same orientation field, the powder The highest possible rotational driving force can be obtained to achieve a high degree of orientation. When using additives such as lubricants and antioxidants, additives with high volatility and low degreasing temperature are selected from known lubricants to achieve maximum removal of carbon atoms before sintering at high temperature and heat preservation.

The pressure during molding and the pressing process are not particularly limited, and the green density is preferably 3.6-4.5 g/cm ³ . Optionally, the molded compact is further subjected to cold isostatic pressing to eliminate cracks within the compact.

Sintering is generally carried out in a vacuum environment, preferably 10^-3 to -4Pa. Due to the discharge of additives and impurity gases in the low temperature section of the heating process, the instantaneous pressure may reach 10^-1Pa. In addition, in order to reduce the volatilization of rare earths on the surface of the compact in the high temperature holding section of sintering, a small amount of inert gas such as Ar gas can also be introduced at the rear end of the sintering. The general target sintering temperature is 950 to 1150 ° C, and the temperature is kept for 3 to 24 hours. In order to achieve low-temperature exhaust gas impurities and improve the temperature uniformity in the sintering furnace, the heating process is carried out in steps, and the temperature is maintained for a period of time at multiple temperatures.

The sintered magnets generally undergo at least one stage of heat treatment at a temperature lower than the sintering temperature by 100°C or more. Preferably, the temperature is kept at 900°C for 3 hours, cooled to room temperature, and then kept at 500°C for 4 hours to further improve the coercivity of the magnet. In order to improve the processing performance of the product, the cooling rate can be slowed down after the heat treatment to reduce the internal stress.

Using wire EDM, double-end grinding and centerless grinding to take samples from the magnet, the sample size is a cylinder of Φ10*10mm, and the processing rate is moderately reduced to ensure the perpendicularity, concentricity and dimensional accuracy of the product.

The average value and standard deviation of Br and Hcj mentioned in each example are according to Fig. 1 in the front of the sintering furnace, in the middle and in the rear of the sintering furnace, respectively taking 9 samples, using NIM16000 to test 20 ℃, Φ10*10mm size 27 Br and Hcj are obtained from the demagnetization curve of the magnet, and then the average and arithmetic standard deviation are calculated;

ICP-OES and ICP-MS were comprehensively used to measure the mass fraction of Si elements with a mass fraction above and below 0.1 wt.%, respectively.

Example 1:

PrNd metal with a purity of more than 99.5wt%, Dy, Tb with a purity of more than 99.9wt%, electrolytic copper, electrical pure iron and low-carbon boron are mainly added, and other trace elements are added in the form of pure metal and Fe alloy. The Si content of all raw materials Below 30PPM. A strip-spin alloy with a thickness of 0.3 mm is obtained by melting the strip.

The alloy was crushed under 0.09Mpa hydrogen pressure and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The coarse alloy powder is further crushed by nitrogen jet mill to obtain fine powder with D50 of 4.6-4.8 microns.

Add 0.03wt% organic lubricant (organic lubricant is magnetic powder protective lubricant 3# produced by Tianjin Yuesheng New Materials Research Institute) to the fine powder, and press and form in a magnetic field. The orientation magnetic field is a static magnetic field of 1.9 T, and the pressing density is 3.9 to 4.1 g/cm. The atmosphere for all storage and transportation is argon atmosphere from the hydrogen breaking to entering the sintering furnace, so that a small amount of additives can also control the oxygen content of the magnet to a lower level.

The compact is sintered at 1050-1080℃ for 4.5h in a vacuum environment, and the sintering temperature is slightly adjusted according to the composition, with a density of >7.5g/ ^cm3 as the minimum requirement, and the grain size of the main phase cannot be larger than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is more than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely eliminated at the lowest possible temperature. After the vacuum degree is restored, the temperature continues to rise to the target sintering temperature. After sintering, the furnace is cooled to 870 ℃ first, then poured into argon and cooled to 700 ℃, and then the fan is forced to cool to room temperature. The magnets were kept at 900°C for 3h and cooled to room temperature, then kept at 500°C for 4h, then cooled to complete the heat treatment and cooled with argon.

Use ICP to test the content of each element, and use a carbon-sulfur analyzer to test the C content, which is expressed in mass percentage, as shown in the following table:

No.	Nd	Pr	Dy	Tb	Fe	Al	Co	Cu	Ga	Si	B	Ti	C
1	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.0003	0.95	0	0.03
2	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.005	0.95	0	0.04
3	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.01	0.95	0	0.03
4	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.05	0.95	0	0.04
5	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.1	0.95	0	0.04
6	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.11	0.95	0	0.03
7	23.25	7.75	0	0	bal	0	0.5	0.12	0.15	0.2	0.95	0	0.03
8	twenty four	8	0	0	bal	0	0.5	0.12	0.15	0.05	0.95	0	0.03
9	22.5	7.5	1	0	bal	0	0.5	0.12	0.15	0.05	0.95	0	0.04
10	22.875	7.625	0	0.5	bal	0	0.5	0.12	0.15	0.05	0.95	0	0.03
11	23.25	7.75	0	0	bal	0.2	0.5	0.12	0.15	0.05	0.95	0	0.03
12	23.25	7.75	0	0	bal	0.2	0	0.12	0.15	0.05	0.95	0	0.04
13	23.25	7.75	0	0	bal	0.2	0	0.25	0.3	0.05	0.95	0	0.03
14	23.25	7.75	0	0	bal	0.2	0	0.25	0.3	0.05	0.95	0.2	0.03

In addition, the oxygen content measured by the oxygen analyzer is 400-600 ppm, and sometimes a certain amount of impurity elements such as La, Ce, and Cr are detected. Due to their high solid solubility in the raw materials, it is difficult to ensure that they are completely zero.

Samples were taken from the magnet by wire EDM, double-end grinding and centerless grinding, and the sample size was a cylinder of Φ10*10mm. Using NIM16000 to test the demagnetization curve of the sample and obtain Br, Hcj and SQ, the properties are shown in the following table:

The effect of performance and consistency of typical Si content is shown in Figure 2.

The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed by SEM [Japan Electronics Co., Ltd. (JEOL)] and EDS. The special microstructure of experiments 4 and 5 is shown in Figure 3, and the composition of the grain boundary phase is shown in the following table:

It can be seen that the grain boundary phase between the main phases contains Si-rich regions with Si content ranging from 0.35 wt.% to 1.99 wt.%.

Combined with the energy spectrum of the Si-rich grain boundary phase and the magnetic properties of No. 1-5 samples, it can be seen that Si can adsorb the P and S impurity elements in the main phase and improve the remanence of the magnet. At the same time, the high-melting rare earth compounds generated by impurities such as Si and P and S are dispersed in the grain boundary phase, which can inhibit the growth of grains and improve the coercive force of the magnet.

In conclusion, with a moderate amount of Si addition (more than 0.01wt.%, less than 0.10wt.%), the Br and Hcj of the magnet increased slightly, and the SQ increased significantly. At the same time, the consistency of magnetic properties of magnets at different positions in the same batch of sintering furnaces is significantly improved. When the Si content exceeds a certain amount, the magnetic properties of the magnet are significantly degraded. At the same time, the addition of a small amount of Si does not affect the addition effect of other elements. For example, adding a certain amount of Dy and Tb will increase the coercive force and decrease the remanence correspondingly, but the consistency of squareness and magnetic properties is in Si A high level was maintained at 0.05 wt. % addition.

Example 2:

It is mainly composed of PrNd metal with a purity of more than 99.5wt%, electrolytic copper with a purity of more than 99.9wt%, electrical pure iron and low carbon boron, and other trace elements are added in the form of pure metal and Fe alloy. The Si content of all raw materials is less than 30PPM. A strip-spin alloy with a thickness of 0.3 mm is obtained by melting the strip.

The alloy was crushed under 0.09Mpa hydrogen pressure and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The coarse alloy powder is further crushed by a nitrogen jet mill to obtain a fine powder with a D50 of 4.6-4.8 microns.

0.03wt% organic lubricant was added to the fine powder, and it was pressed and formed in a magnetic field. The orientation magnetic field was a static magnetic field of 1.9 T, and the pressing density was 3.9 to 4.1 g/cm ³ . From the hydrogen breaking to entering the sintering furnace, the atmosphere for all storage and transportation is an argon atmosphere, so that a small amount of additives can also control the oxygen content of the magnet to a lower level.

The compact is sintered at 1030-1050 ℃ for 4.5 hours in a vacuum environment, and the sintering temperature is slightly adjusted according to the composition, with a density of >7.5g/cm ³ as the minimum requirement, and the grain size of the main phase cannot be larger than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is more than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely eliminated at the lowest possible temperature. After the vacuum degree is restored, the temperature continues to rise to the target sintering temperature. After sintering, the furnace is cooled to 870 ℃ first, then poured into argon and cooled to 700 ℃, and then the fan is forced to cool to room temperature. The magnets were kept at 900°C for 3h and cooled to room temperature, then kept at 500°C for 4h, then cooled to complete the heat treatment and cooled with argon.

Use ICP to test the content of each element, and use a carbon-sulfur analyzer to test the C content, which is expressed in mass percentage, as shown in the following table:

No.	Nd	Pr	Dy	Tb	Fe	Al	Co	Cu	Ga	Si	B	Ti		C
15	twenty four	8	0	0	bal	0	0.5	0	0.15	0.1	0.98	0.15	0.03
16	twenty four	8	0	0	bal	0	0.5	0	0.2	0.1	0.98	0.15	0.04
17	twenty four	8	0	0	bal	0	0.5	0	1	0.1	0.98	0.15	0.03
18	twenty four	8	0	0	bal	0	0.5	0.1	0	0.1	0.98	0.15	0.04
19	twenty four	8	0	0	bal	0	0.5	0.2	0	0.1	0.98	0.15	0.03
20	twenty four	8	0	0	bal	0	0.5	1	0	0.1	0.98	0.15	0.04
twenty one	twenty four	8	0	0	bal	0	0.5	0.1	0.12	0.1	0.98	0.15	0.03
twenty two	twenty four	8	0	0	bal	0	0.5	0.2	0.3	0.1	0.98	0.15	0.03
twenty three	twenty four	8	0	0	bal	0	0.5	0.4	0.5	0.1	0.98	0.15	0.04
twenty four	twenty four	8	0	0	bal	0	0.5	0.6	0.5	0.1	0.98	0.15	0.03
25	twenty four	8	0	0	bal	0	0.5	0.5	0.6	0.1	0.98	0.15	0.04
26	twenty four	8	0	0	bal	0	0.5	0.8	0.2	0.1	0.98	0.15	0.04
27	twenty four	8	0	0	bal	0	0.5	0.7	0.5	0.11	0.98	0.15	0.04

Samples were taken from the magnet by wire EDM, double-end grinding and centerless grinding, and the sample size was a cylinder of Φ10*10mm. The demagnetization curve of the sample was tested with NIM16000 and Br, Hcj and SQ were obtained.

The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed by SEM [Japan Electronics Co., Ltd. (JEOL)] and EDS. The special microstructure of Experiment 21 is shown in Fig. 4, and the composition of the grain boundary phase is shown in the following table:

It can be seen that the grain boundary phase between the main phases contains Si-rich regions with a Si content of 0.58 wt.% to 0.9 wt.%.

The special microstructure of Experiment 23 is shown in Fig. 5, and the composition of the grain boundary phase is shown in the following table:

It can be seen that the grain boundary phase between the main phases contains Si-rich regions with a Si content of 0.47 wt. % to 1.2 wt. %.

Cu and Ga elements can improve the wettability between the grain boundary phase and the main phase, so that the grain boundary phase distribution is more uniform, and at the same time, it wraps the Si compound at the grain boundary and avoids direct contact with the main phase, thereby improving the coercivity of the magnet. The magnetic properties of samples No. 15-23 show that adding appropriate amount of Cu and Ga under the condition of forming Si compound can improve the remanence and coercivity of the magnet at the same time.

In conclusion, although 0.05 wt.% Si content was added, when the sum of Ga and Cu content was less than 0.2 wt.%, the performance consistency and squareness optimization did not achieve good results. When the content of Ga and Cu is greater than 1 wt.%, the remanence and coercivity decrease significantly, and the performance fluctuation increases. According to the analysis of SEM results, it can be found that excessive Ga and Cu easily lead to large Ga and Cu-rich phases, which improve the local Stray fields and demagnetization fields, causing performance degradation.

Example 3:

PrNd metal with a purity of more than 99.5wt%, Tb with a purity of more than 99.9wt%, electrolytic copper, electrical pure iron and low-carbon boron are mainly used, and other trace elements are added in the form of pure metal and Fe alloy. C raw materials are added, and the Si content of all raw materials is less than 30PPM. A strip-spin alloy with a thickness of 0.3 mm is obtained by melting the strip.

The alloy was crushed under 0.09Mpa hydrogen pressure and heated to 580°C for dehydrogenation. After cooling, 0.08 wt% zinc stearate was added to the crude alloy powder and mixed for 3 hours. The coarse alloy powder is further crushed by a nitrogen jet mill to obtain a fine powder with a D50 of 4.6-4.8 microns.

0.03wt% organic lubricant was added to the fine powder, and the addition amount of organic lubricant in experiments 32-33 was 0.08wt% and 0.2wt%, respectively, to change the final carbon content of the magnet, which was pressed and formed in a magnetic field. The orientation magnetic field was a static magnetic field of 1.9 T, and the pressing density was 3.9 to 4.1 g/cm ³ . From the hydrogen breaking to entering the sintering furnace, the atmosphere for all storage and transportation is an argon atmosphere, so that a small amount of additives can also control the oxygen content of the magnet to a lower level.

The compact is sintered at 1030-1050 ℃ for 4.5 hours in a vacuum environment, and the sintering temperature is slightly adjusted according to the composition, with a density of >7.5g/ ^cm3 as the minimum requirement, and the grain size of the main phase cannot be larger than 15 microns. The sintering temperature is controlled by vacuum degree. When the vacuum degree is more than 7*10^-3Pa, the heat preservation is started to ensure that the additives are completely eliminated at the lowest possible temperature. After the vacuum degree is restored, the temperature continues to rise to the target sintering temperature. After sintering, the furnace is cooled to 870 ℃ first, then poured into argon and cooled to 700 ℃, and then the fan is forced to cool to room temperature. The magnet was kept at 900°C for 3h, cooled to room temperature, then kept at 500°C for 4h, then cooled to complete the heat treatment and cooled with argon.

Use ICP to test the content of each element, and use a carbon-sulfur analyzer to test the C content, which is expressed in mass percentage, as shown in the following table:

No.	Nd	Pr	Dy	Tb	Fe	Al	Co	Cu	Ga	Si	B	Zr	C
28	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.02
29	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.05
30	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.15
31	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.2
32	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.08
33	23.1	7.7	0	5.3	bal	0	3	0.15	0.2	0.06	0.97	0.12	0.18

The ICP-MS test results of the No. 28 experimental sample are shown in Figure 6. Comparing the ICP and ICP-MS results, it can be seen that the Si content of the NO28-33 sample is about 600 ppm, and the addition of lubricant did not cause the abnormality of Si element in the magnet manufacturing process. loss.

Samples were taken from the magnet by wire EDM, double-end grinding and centerless grinding, and the sample size was a cylinder of Φ10*10mm. Using NIM16000 to test the demagnetization curve of the sample and obtain Br, Hcj and SQ, as shown in the following table:

The cross-sectional microstructure of the magnet and the composition of the grain boundary phase were observed by SEM [Japan Electronics Co., Ltd. (JEOL)] and EDS. The special microstructure of Experiment 32 is shown in Figure 7, and the composition of the grain boundary phase is shown in the following table:

It can be seen that the grain boundary phase between the main phases contains Si-rich regions with Si content ranging from 0.02 wt.% to 0.96 wt.%.

Carbon reacts with rare earth elements at grain boundaries to form carbides, reducing the content of rare earth rich phases at grain boundaries and reducing the coercivity of the magnet. Combining the energy spectrum with the magnetic properties of NO.28-33 magnets, it can be seen that the Si compounds formed at the grain boundaries cannot improve the coercivity of the magnets when the carbon content is high.

In conclusion, the coercivity and squareness of the magnets decreased significantly after the carbon content was higher than 0.15wt.%.

Claims (7)

1. An R-T-B-Si-M-A series rare earth permanent magnet mainly includes the following components in mass ratio:

   

   The balance is T and inevitable impurities;

   The R is selected from at least one of the following elements: Nd, Pr, Dy, Tb, Ho, La, Ce, Pm, Sm, Eu, Gd, Er, Tm, Yb, Lu or Y;

   The M is selected from at least one of the following elements: Al, Sn, Ge, Ag, Au, Bi, Mn, Nb, Ti, Hf, Zr or Cr;

   Described T is selected from at least one element in Fe and Co;

   The A is selected from at least one element of Ga and Cu.
2. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 1, wherein the main phase of the R-T-B-Si-M-A series rare earth permanent magnet is R2T14B type compound, and the grain boundary phase between the main phases contains Si Si-rich regions with a content of 0.02 wt. % to 2.0 wt. %.
3. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 2, characterized in that the Si-rich region contains at least one of Ga and Cu elements, and the total mass fraction thereof is 0.05wt.%～10wt.% .
4. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 2, wherein the Si-rich region contains at least one of P and S elements, and the total mass fraction thereof is 5wt.%-20wt.%.
5. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 1 is characterized in that the C content in the R-T-B-Si-M-A series rare earth permanent magnet is controlled at 0.02wt.%～0.15wt.%.
6. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 1, wherein the R is selected from at least one of the following elements: Nd, Pr, Dy, Tb.
7. The R-T-B-Si-M-A series rare earth permanent magnet according to claim 1, characterized in that the M is selected from at least one of the following elements: Al, Ti, Zr.

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