Method for predicting room temperature magnetic properties of neodymium-iron-boron permanent magnets

Abstract

The application discloses a prediction method for room-temperature magnetic properties of a neodymium-iron-boron permanent magnet, and is a prediction method based on practice and theoretical analysis. The prediction method is obtained by deforming existing remanence and coercivity theoretical formulas, and is in a form containing phase composition parameters based on actual deformation from a theoretical phenomenological form. The prediction method calculates a proportion of a main phase (NdFeB) / non-magnetic phase (Non-magnetic Phase), establishes a calculation model of remanence and coercivity, realizes simple, efficient and accurate prediction of room-temperature magnetic properties of the neodymium-iron-boron permanent magnet, can bypass the non-magnetic phase composition and its components which cannot be quantitatively analyzed, clearly shows and calculates the influence of the components of the neodymium-iron-boron permanent magnet on the performance from a more macroscopic perspective, and can provide a universal and quantitative rapid solution for component design and process design of various neodymium-iron-boron permanent magnets.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of NdFeB permanent magnets, and particularly relates to a method for predicting the room-temperature magnetic performance of a NdFeB permanent magnet. BACKGROUND

[0002] The room-temperature magnetic performance, such as the residual magnetization (referred to as remanence) and the intrinsic coercivity (referred to as coercivity), of a NdFeB permanent magnet is highly dependent on its composition design. However, due to the complex processing system and the variety of composition components of a NdFeB permanent magnet, the mapping relationship from the composition design to the actual magnetic performance currently mainly relies on the accumulation of practical experience, and lacks a simple, systematic and highly accurate prediction method.

[0003] In theory, the phase composition of a NdFeB permanent magnet can be calculated based on the composition of the NdFeB permanent magnet. Specifically, the microstructure of a NdFeB permanent magnet is mainly determined by the following two types of phases:

[0004] 1) main phase: the main phase is a NdFeB phase, which is the main source of magnetism of the magnet and affects the remanence level, and the remanence represents the strength of magnetism;

[0005] 2) non-magnetic phase: the non-magnetic phase is a phase other than the main phase, which is composed of a variety of non-magnetic components and affects the coercivity level, and the coercivity represents the anti-demagnetization ability.

[0006] However, the composition of the non-magnetic phase is extremely complex, usually including a series of phases such as the metal Nd phase, various Nd oxide phases, Nd carbide phases, Nd amorphous phases, NdFeGa phases, and NdCu phases. Due to the multiple and complex actual composition of the non-magnetic phase, it is difficult to accurately analyze its composition quantitatively through equilibrium phase diagram analysis / theoretical calculation, which makes it extremely challenging to determine the composition of the non-magnetic phase and the overall magnetic performance of a NdFeB permanent magnet based on the composition of the NdFeB permanent magnet.

[0007] Currently, the composition optimization of a NdFeB permanent magnet still highly depends on experimental trial and error and experience accumulation, and lacks an efficient and reliable theoretical prediction method. Therefore, developing a prediction method that can systematically and accurately correlate the composition design and the magnetic performance is of great significance for improving the design and development efficiency of a NdFeB permanent magnet. SUMMARY

[0008] The technical problem to be solved by this invention is to provide a simple, efficient and accurate method for predicting the room temperature magnetic properties of NdFeB permanent magnets, which addresses the shortcomings of existing technologies. This method can bypass the non-magnetic phase composition and its components, which cannot be quantitatively analyzed, and concisely and clearly demonstrate and calculate the influence of the composition of NdFeB permanent magnets on their performance from a more macroscopic perspective. It can provide a general-purpose and quantitative rapid solution for the composition design and process design of various NdFeB permanent magnets.

[0009] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a method for predicting the room temperature magnetic properties of neodymium iron boron permanent magnets, comprising the following steps:

[0010] S1. Establish a residual magnetism calculation model:

[0011] Jr=A×J S [1-ω(Non-magnetic Phase)] (1)

[0012] Where Jr represents the remanence of the NdFeB permanent magnet, A represents the process constant in the production of the NdFeB permanent magnet, and J S J represents the saturation magnetic polarization intensity of the main phase in a NdFeB permanent magnet, determined based on composition calculations. S The unit is kGs, which is a commonly used unit in Gaussian system to express the magnetic polarization intensity or remanence of NdFeB permanent magnets. ω (Non-magnetic Phase) represents the mass fraction of the non-magnetic phase in NdFeB permanent magnets.

[0013] J S The formula for calculation is:

[0014]

[0015] Wherein, ω(Nd), ω(Pr), ω(Ce), ω(Gd), ω(Tb), ω(Dy), ω(Ho), ω(Fe), ω(Co), and ω(Al) represent the mass fractions of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho, Fe, Co, and Al in the formulation design of NdFeB permanent magnets, respectively.

[0016] S2. Establish a coercivity calculation model:

[0017] Hcj=B×H A -J S ×[C0+C1ω(Non-magnetic Phase)] (2)

[0018] Wherein, Hcj represents the coercivity of the NdFeB permanent magnet; B represents the magnetocrystalline anisotropy field coefficient determined by the microstructure of the NdFeB permanent magnet. In the NdFeB permanent magnet, the coercivity originates from the resistance of the magnetocrystalline anisotropy field in the NdFeB lattice to the rotation of the magnetic moment of the atom from the original magnetization direction. The magnetocrystalline anisotropy field in the lattice depends on the rare earth composition design. The actual demagnetization process usually originates from the surface of the micro-grains. Due to the presence of many defects on the surface, the actual magnetocrystalline anisotropy field capability is less than 100%. In model (2), this process is described by the coefficient B, which is derived from J. S The microscopic dispersion magnetic field is the main reason why the coercivity of NdFeB permanent magnets is lower than that of magnetocrystalline anisotropic field designs; H A H represents the magnetocrystalline anisotropy field determined by rare earth elements in neodymium iron boron permanent magnets. A The unit is kOe, which is a commonly used unit in the Gaussian system to express the magnetic field strength or coercivity of NdFeB permanent magnets; C0 represents the micro-dispersive magnetic field coefficient that is independent of the phase composition of NdFeB permanent magnets and only related to the manufacturing process of NdFeB permanent magnets; C1 represents the micro-dispersive magnetic field coefficient that is related to the mass fraction of non-magnetic phase in NdFeB permanent magnets; C0 + C1ω (Non-magnetic Phase) constitutes the complete micro-dispersive magnetic field coefficient.

[0019] H A The formula for calculation is:

[0020]

[0021] S3. Based on statistical analysis of literature and production practice data, the following values ​​were determined: A = 0.985, B = 0.65, C0 = 2.4233, C1 = -4.2798;

[0022] Define parameter T to satisfy:

[0023] T = ω(Fe) + ω(Co) - 1.9ω(Ga)

[0024] Wherein, ω(Ga) represents the mass fraction of element Ga in the formulation design of neodymium iron boron permanent magnets;

[0025] The mass fraction of the non-magnetic phase in a neodymium iron boron permanent magnet is defined to satisfy:

[0026] ω(Non-magnetic Phase)=1-(0.0160×T-0.1650)

[0027] Place A and J S Substituting the values ​​of ω (Non-magnetic Phase) into model (1), the predicted value of the remanence Jr of the NdFeB permanent magnet is obtained; B and H are then used to... A J SSubstituting the values ​​of C0, C1, and ω (Non-magnetic Phase) into model (2), the predicted value of the coercivity Hcj of the neodymium iron boron permanent magnet is obtained.

[0028] Preferably, the process of establishing model (1) is as follows:

[0029] The theoretical formula for the remanence of neodymium iron boron permanent magnets is:

[0030]

[0031] Where A0 represents the volume fraction of positive domains in the NdFeB permanent magnet, the actual NdFeB permanent magnet can be regarded as being composed of small magnetic domains, among which the magnetic domains with the same direction of magnetization are called positive domains, and the magnetic domains with the opposite direction of magnetization are called negative domains. Only positive domains contribute to the magnetic strength; β is ω (Non-magnetic Phase) in the models (1) and (2), d 磁体 d represents the actual density of the neodymium iron boron permanent magnet. 理论 This represents the theoretical density of neodymium iron boron permanent magnets; This indicates the effect of the density of the sintered NdFeB permanent magnet on its remanence. A value of 100% indicates that the interior of the NdFeB permanent magnet is completely dense; in reality... The value is slightly less than 100%; θ represents the grain orientation degree. The value of θ reflects the angular difference between the actual magnetization direction of the micro-grains inside the NdFeB permanent magnet and the macroscopically designed magnetization direction. There are slight differences in the value of θ at different positions inside the NdFeB permanent magnet, and its overall comprehensive contribution is composed of the volume average value of the remainder. Decide;

[0032] Due to the actual production of NdFeB permanent magnets, parameters A0, θ depends on the production process and is almost unrelated to the composition. Therefore, A0, The process constant A in the production process of neodymium iron boron permanent magnets is integrated to obtain the model (1).

[0033] Preferably, the process of establishing model (2) is as follows:

[0034] The theoretical formula for the coercivity of neodymium iron boron permanent magnets is:

[0035]

[0036] Where K1 represents the magnetocrystalline anisotropy, μ0 represents the free permeability, and μ0 = 4π × 10⁻⁶ -7 H / m, M S That is, J in the models (1) and (2) S , This represents the numerical value after converting the magnetocrystalline anisotropy into equivalent magnetic field strength. That is, H in the model (2). A α ex , α K1 N represents the microstructure coefficients corresponding to exchange coupling, grain orientation, and K1 loss caused by surface defects, respectively. eff N represents the magnetic field dispersion factor. eff The value depends on the phase structure, grain size, and grain shape;

[0037] Because in the actual production of NdFeB permanent magnets, parameter α ex , α K1 Depending on the manufacturing process, therefore, α ex , α K1 The magnetocrystalline anisotropy field coefficient B is determined by the microstructure of the NdFeB permanent magnet, and N... eff The model (2) is further decomposed into the micro-dispersion field coefficient C0 determined by the manufacturing process of NdFeB permanent magnets and C1ω (Non-magnetic Phase) determined by the mass fraction of the non-magnetic phase in NdFeB permanent magnets.

[0038] As a preferred option, J S and H A The constants in the calculation formula are derived from "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology" edited by Zhou Shouzeng, Dong Qingfei, and Gao Xuexu, published by Metallurgical Industry Press in September 2011. The specific method for determining the constants is as follows:

[0039] The saturation magnetic polarization intensities (1.61T, 1.56T, 1.17T, 0.85T, 0.70T, 0.71T, and 0.81T) corresponding to the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho recorded in "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology" were converted to Gaussian units (kGs), where T is the magnetic unit Tesla in the International System of Units (SI). The converted values ​​are 16.1, 15.6, 11.7, 8.5, 7.0, 7.1, and 8.1, respectively. These values ​​were then used as the values ​​of J for the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho. S The impact is reflected in J S In the calculation formula;

[0040] The magnetocrystalline anisotropy fields (5600 kA / m, 5840 kA / m, 3600 kA / m, 4000 kA / m, 17600 kA / m, 12000 kA / m, and 7600 kA / m) corresponding to the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho, as described in "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology," were converted to Gaussian units (kOe), where kA / m is the international standard unit for magnetic magnetism (kiloampere / meter). The converted values ​​are 70.37, 73.39, 45.24, 50.27, 221.17, 150.80, and 95.50, respectively. These values ​​were then used as the values ​​of Nd, Pr, Ce, Gd, Tb, Dy, and Ho relative to H. A The impact is reflected in H A In the calculation formula;

[0041] Since Al has a certain solid solubility in the main phase of NdFeB permanent magnets, and its presence in the crystal lattice reduces the magnetic moment of neighboring Fe atoms, according to "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology," the substitution of one Al atom will lead to a 5.9 μB decrease in the molecular magnetic moment of the NdFeB permanent magnet. This is based on the theoretical density of NdFeB permanent magnets being 7.58 g / cm³. 3 The theoretical saturation magnetic polarization is 16.1 kGs. The molecular magnetic moment of the NdFeB permanent magnet is calculated to be 32.3176 μB. The relative atomic mass of Al is 26.981, and the relative atomic mass of Fe is 55.845. Based on these data, the element Al has a certain influence on J... S The effect is: (32.3176-5.9*14) / 32.3176*(55.845 / 26.981)=-3.2204, and with -3.2204 as element Al, the effect on J is... S The impact is reflected in J S In the calculation formula.

[0042] For non-rare earth functional elements, they are usually enriched in the non-magnetic phase, which affects the J of the main phase of NdFeB permanent magnets. S or H A There is no significant effect, but Al is a notable exception; therefore, the method of this invention takes into account the effect of Al on J. S The influence of Co on J. Besides Al, Co can also dissolve significantly into the main phase, but in the current mainstream composition system of NdFeB permanent magnets, Co has a relatively small effect on J. S Almost no impact.

[0043] Compared with existing technologies, this invention has the following advantages: The method for predicting the room-temperature magnetic properties of NdFeB permanent magnets in this invention is a prediction method based on practical and theoretical analysis. This prediction method transforms existing theoretical formulas for remanence and coercivity from a theoretical phenomenological form to a form that includes phase composition parameters. This invention's prediction method establishes a calculation model for remanence and coercivity by calculating the ratio of the main phase (NdFeB) to the non-magnetic phase, achieving a simple, efficient, and accurate prediction of the room-temperature magnetic properties of NdFeB permanent magnets. It bypasses the non-magnetic phase composition and its components, which cannot be quantitatively analyzed, and concisely demonstrates and calculates the influence of NdFeB permanent magnet composition on performance from a more macroscopic perspective. It provides a general-purpose, quantitative, and rapid solution for the composition and process design of various NdFeB permanent magnets. Attached Figure Description

[0044] Figure 1 This is the fitting result of the relationship between the main phase and T;

[0045] Figure 2 Comparison of calculated and measured remanence values ​​for NdFeB permanent magnet samples with different compositions; Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0047] A method for predicting the room-temperature magnetic properties of neodymium iron boron permanent magnets includes the following steps:

[0048] S1. Establish a residual magnetism calculation model:

[0049] Jr=A×J S [1-ω(Non-magnetic Phase)] (1)

[0050] Where Jr represents the remanence of the NdFeB permanent magnet, A represents the process constant in the production of the NdFeB permanent magnet, and J S J represents the saturation magnetic polarization intensity of the main phase in a NdFeB permanent magnet, determined based on composition calculations. S The unit is kGs, and ω (Non-magenetic Phase) represents the mass fraction of the non-magnetic phase in a NdFeB permanent magnet.

[0051] J S The formula for calculation is:

[0052]

[0053] Wherein, ω(Nd), ω(Pr), ω(Ce), ω(Gd), ω(Tb), ω(Dy), ω(Ho), ω(Fe), ω(Co), and ω(Al) represent the mass fractions of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho, Fe, Co, and Al in the formulation design of NdFeB permanent magnets, respectively.

[0054] Specifically, the process of establishing the above model (1) is as follows:

[0055] The theoretical formula for the remanence of neodymium iron boron permanent magnets is:

[0056]

[0057] Where A0 represents the volume fraction of the positive domains in the NdFeB permanent magnet, β is ω (Non-magnetic Phase) in models (1) and (2), and d 磁体 d represents the actual density of the neodymium iron boron permanent magnet. 理论 This represents the theoretical density of neodymium iron boron permanent magnets; This indicates the effect of the density of the sintered NdFeB permanent magnet on its remanence. A value of 100% indicates that the interior of the NdFeB permanent magnet is completely dense; in reality... The value is slightly less than 100%; θ represents the grain orientation degree. The value of θ reflects the angular difference between the actual magnetization direction of the micro-grains inside the NdFeB permanent magnet and the macroscopically designed magnetization direction. There are slight differences in the value of θ at different positions inside the NdFeB permanent magnet, and its overall comprehensive contribution is composed of the volume average value of the remainder. Decide;

[0058] Due to the actual production of NdFeB permanent magnets, parameters A0, θ depends on the production process, therefore, A0, The process constant A in the production process of neodymium iron boron permanent magnets is integrated to obtain the model (1);

[0059] S2. Establish a coercivity calculation model:

[0060] Hcj=B×H A -J S ×[C0+C1ω(Non-magnetic Phase)] (2)

[0061] Where Hcj represents the coercivity of the NdFeB permanent magnet, B represents the magnetocrystalline anisotropy field coefficient determined by the microstructure of the NdFeB permanent magnet, and H A H represents the magnetocrystalline anisotropy field determined by rare earth elements in neodymium iron boron permanent magnets. AThe unit is kOe. C0 represents the micro-dispersive magnetic field coefficient that is independent of the phase composition of NdFeB permanent magnets and only related to the production process of NdFeB permanent magnets. C1 represents the micro-dispersive magnetic field coefficient that is related to the mass fraction of non-magnetic phase in NdFeB permanent magnets. C0 + C1ω (Non-magnetic Phase) constitutes the complete micro-dispersive magnetic field coefficient.

[0062] H A The formula for calculation is:

[0063]

[0064] Specifically, the process of establishing the above model (2) is as follows:

[0065] The theoretical formula for the coercivity of neodymium iron boron permanent magnets is:

[0066]

[0067] Where K1 represents the magnetocrystalline anisotropy, μ0 represents the free permeability, and μ0 = 4π × 10⁻⁶ -7 H / m, M S That is, J in the models (1) and (2) S , This represents the numerical value after converting the magnetocrystalline anisotropy into equivalent magnetic field strength. That is, H in the model (2). A α ex , α K1 N represents the microstructure coefficients corresponding to exchange coupling, grain orientation, and K1 loss caused by surface defects, respectively. eff N represents the magnetic field dispersion factor. eff The value depends on the phase structure, grain size, and grain shape;

[0068] Because in the actual production of NdFeB permanent magnets, parameter α ex , α K1 Depending on the manufacturing process, therefore, α ex , α K1 The magnetocrystalline anisotropy field coefficient B is determined by the microstructure of the NdFeB permanent magnet, and N... eff The model (2) is further decomposed into the micro-dispersion field coefficient C0 determined by the production process of NdFeB permanent magnets and C1ω (Non-magnetic Phase) determined by the mass fraction of non-magnetic phase in NdFeB permanent magnets.

[0069] S3. Based on statistical analysis of literature and production practice data, the following values ​​were determined: A = 0.985, B = 0.65, C0 = 2.4233, C1 = -4.2798. The process constant A was determined using a constant of 7.58 g / cm³. 3 As the theoretical density of NdFeB permanent magnets, in actual production, the actual density of NdFeB permanent magnets after sintering is 99.5% to 99.9% of the theoretical density, i.e. The grain orientation degree θ is 0–15°. The value ranges from 0.985 to 0.995. Based on the above data, A = 0.985 is determined.

[0070] Define parameter T to satisfy:

[0071] T = ω(Fe) + ω(Co) - 1.9ω(Ga)

[0072] Wherein, ω(Ga) represents the mass fraction of element Ga in the formulation design of neodymium iron boron permanent magnets;

[0073] The mass fraction of the non-magnetic phase in a neodymium iron boron permanent magnet is defined to satisfy:

[0074] ω(Non-magnetic Phase)=1-(0.0160×T-0.1650)

[0075] Statistical fitting was performed on the measured data collected in production practice to obtain the relationship between ω (Non-magnetic Phase) and T, where the mass fraction of the main phase is (0.0160×T-0.1650). The fitting results of the relationship between the main phase and T are shown in [the table below]. Figure 1 . Figure 1 In this context, x represents T, and y represents the principal phase.

[0076] Place A and J S Substituting the values ​​of ω (Non-magnetic Phase) into model (1), the predicted value of the remanence Jr of the NdFeB permanent magnet is obtained; B and H are then used to... A J S Substituting the values ​​of C0, C1, and ω (Non-magnetic Phase) into model (2), the predicted value of the coercivity Hcj of the neodymium iron boron permanent magnet is obtained.

[0077] In the above models (1) and (2), J S and H A The constants in the calculation formula are derived from "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology" edited by Zhou Shouzeng, Dong Qingfei, and Gao Xuexu, published by Metallurgical Industry Press in September 2011. The specific method for determining the constants is as follows:

[0078] The saturation magnetic polarization intensities (1.61T, 1.56T, 1.17T, 0.85T, 0.70T, 0.71T, and 0.81T) corresponding to the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho recorded in "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology" were converted to Gaussian units in kGs. The converted values ​​were 16.1, 15.6, 11.7, 8.5, 7.0, 7.1, and 8.1 (see Table 1 for a summary table of the converted values). These values ​​were then used as the values ​​for the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho relative to J. S The impact is reflected in J S In the calculation formula;

[0079] The magnetocrystalline anisotropy fields (5600 kA / m, 5840 kA / m, 3600 kA / m, 4000 kA / m, 17600 kA / m, 12000 kA / m, and 7600 kA / m) corresponding to the elements Nd, Pr, Ce, Gd, Tb, Dy, and Ho, as described in "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology," were converted to Gaussian units (kOe). The converted values ​​are 70.37, 73.39, 45.24, 50.27, 221.17, 150.80, and 95.50, respectively (see Table 1 for a summary table of the converted values). These values ​​were then used as the values ​​of Nd, Pr, Ce, Gd, Tb, Dy, and Ho relative to H. A The impact is reflected in H A In the calculation formula;

[0080] Table 1

[0081]

[0082] The influence of rare earth element composition design on remanence and coercivity was confirmed based on Table 1.

[0083] Since Al has a certain solid solubility in the main phase of NdFeB permanent magnets, and its presence in the crystal lattice reduces the magnetic moment of neighboring Fe atoms, according to "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology," the substitution of one Al atom will lead to a 5.9 μB decrease in the molecular magnetic moment of the NdFeB permanent magnet. This is based on the theoretical density of NdFeB permanent magnets being 7.58 g / cm³. 3 The theoretical saturation magnetic polarization is 16.1 kGs. The molecular magnetic moment of the NdFeB permanent magnet is calculated to be 32.3176 μB. The relative atomic mass of Al is 26.981, and the relative atomic mass of Fe is 55.845. Based on these data, the element Al has a certain influence on J... S The effect is: (32.3176-5.9*14) / 32.3176*(55.845 / 26.981)=-3.2204, and with -3.2204 as element Al, the effect on J is... SThe impact is reflected in J S In the calculation formula.

[0084] Taking remanence as an example, for NdFeB permanent magnet samples with different compositions, their remanence was calculated according to the above model (1), and the remanence of the samples was actually measured. The comparison results of the calculated and measured remanence values ​​of NdFeB permanent magnet samples with different compositions are shown in the figure. Figure 2 . Figure 2 In the graph, the horizontal axis represents the measured value of remanence, and the vertical axis represents the calculated value of remanence. (From...) Figure 2 It can be seen that the calculated and measured values ​​of remanence have a high degree of fit, indicating that the prediction method of the present invention has high accuracy.

[0085] The following describes a neodymium iron boron permanent magnet with a specific composition. Its room temperature magnetic properties are predicted using the method of this invention, and compared with the measured values ​​of its room temperature magnetic properties.

[0086] Neodymium iron boron permanent magnet design composition (Pr 0.25 Nd 0.75 ) 30.5 Gd 1.0 Ho 0.6 Ga 0.15 Al 0.95 (Co,Fe) 65.4 (Ti,Zr,Nb,B,Cu) 1.4 The relevant calculation results based on this design component are as follows:

[0087] Saturation magnetic polarization J S =14.652 kGs;

[0088] Parameter T = 65.4 - 1.9 * 0.15 = 65.115%;

[0089] The mass fraction of the non-magnetic phase ω = 1 - (0.0160 × T - 0.1650) = 12.32%;

[0090] Remanence Jr = 0.985 * 14.652 * (1 - 0.1232) = 12.654 kGs;

[0091] Magnetocrystalline anisotropic field H A =72.37kOe;

[0092] Coercivity Hcj=0.65*72.37-14.652*[2.4233-4.2798*0.1232]=19.260kOe.

[0093] NdFeB permanent magnets were sintered according to the above-designed composition to obtain samples. The samples were tested and found to have Br = 12.64~12.67kGs and Hcj = 19.57~19.68kOe, which showed good matching with the calculated values, indicating that the prediction method of the present invention has high accuracy.

Claims

1. A method of predicting the room temperature magnetic properties of a neodymium-iron-boron permanent magnet, characterized in that, The method comprises the following steps: S1, establishing a residual magnetism calculation model: (1) wherein represents the remanence of a neodymium-iron-boron permanent magnet, represents a process constant in the production of a neodymium-iron-boron permanent magnet, represents the saturation magnetic polarization of the main phase in a neodymium-iron-boron permanent magnet determined on the basis of a composition calculation, is in kGs, represents the mass fraction of non-magnetic phases in a neodymium-iron-boron permanent magnet; The calculation formula is: ， wherein, , , , , , , , , , respectively represent the mass fraction of elements Nd, Pr, Ce, Gd, Tb, Dy, Ho, Fe, Co, Al in the formula design of neodymium-iron-boron permanent magnet. S2, establishing a coercivity calculation model: (2) wherein, Hcj represents the coercivity of the Nd-Fe-B permanent magnet, K1 represents the magnetocrystalline anisotropy field coefficient determined by the microstructure of the Nd-Fe-B permanent magnet, Hk represents the magnetocrystalline anisotropy field determined by the rare earth elements in the Nd-Fe-B permanent magnet, The unit of Hk is kOe, K2 represents the micro-dispersion magnetic field coefficient which is split out from the microstructure of the Nd-Fe-B permanent magnet and is irrelevant to the phase composition of the Nd-Fe-B permanent magnet and only related to the production process of the Nd-Fe-B permanent magnet, K3 represents the micro-dispersion magnetic field coefficient related to the mass fraction of the non-magnetic phase in the Nd-Fe-B permanent magnet, K2 and K3 constitute the complete micro-dispersion magnetic field coefficient; The calculation formula is: ， S3, based on literature and statistical analysis of production practice data, determine: = 0.985, = 0.65, = 2.4233, = -4.2798; Definition parameters satisfies: ， wherein, represents the mass fraction of the element Ga in the formulation design of the neodymium-iron-boron permanent magnet; The mass fraction of the non-magnetic phase in the Nd-Fe-B permanent magnet satisfies: ， Substituting the values of , , into the model (1) gives the predicted value of the remanence of the Nd-Fe-B permanent magnet; substituting the values of , , , , , into the model (2) gives the predicted value of the coercivity of the Nd-Fe-B permanent magnet.

2. The method of predicting the room temperature magnetic properties of a Nd-Fe-B permanent magnet according to claim 1, characterized in that The establishment process of the model (1) is as follows: The residual magnetism theoretical formula of the Nd-Fe-B permanent magnet is: ， in, This represents the volume fraction of positive domains in a neodymium iron boron permanent magnet. That is, in the models (1) and (2) , This indicates the actual density of the neodymium iron boron permanent magnet. This represents the theoretical density of neodymium iron boron permanent magnets; This indicates the effect of the density of the sintered NdFeB permanent magnet on its remanence. A value of 100% indicates that the interior of the NdFeB permanent magnet is completely dense; in reality... The value is slightly below 100%; Indicates grain orientation degree. The value reflects the angular difference between the actual magnetization direction and the macroscopically designed magnetization direction of the microcrystalline grains inside the NdFeB permanent magnet, and the magnetization direction at different locations inside the NdFeB permanent magnet. The values ​​vary slightly, and their overall contribution is determined by the volume average of the cosine values. Decide; Since in the actual production of Nd-Fe-B permanent magnets, parameters , , depend on the production process, therefore, the , , process constants in the production process of Nd-Fe-B permanent magnets are integrated , to obtain the model (1).

3. The method of predicting the room temperature magnetic properties of a Nd-Fe-B permanent magnet according to claim 1, characterized in that, The establishment process of the model (2) is as follows: The coercivity theoretical formula of the Nd-Fe-B permanent magnet is: ， wherein, represents the magnetocrystalline anisotropy energy, represents the vacuum permeability, = 4π x 10 -7 H / m, is the value of the magnetic field strength equivalent to the , magnetocrystalline anisotropy energy, is the value of the magnetic field strength equivalent to the , respectively represent the microstructure coefficients corresponding to the exchange coupling, the degree of grain orientation, the surface defect-induced loss, represents the demagnetizing field factor, the value of which depends on the phase structure, the grain size, the grain shape; Due to the parameters in the actual production of NdFeB permanent magnets Depending on the production process, therefore, The magnetocrystalline anisotropy field coefficient determined by the microstructure of neodymium iron boron permanent magnets and will Further breakdown into the microscopic magnetic field coefficient determined by the manufacturing process of NdFeB permanent magnets And determined by the mass fraction of the non-magnetic phase in NdFeB permanent magnets. Thus, the model (2) is obtained.

4. The method of claim 1, wherein the method is characterized by: and The specific determination method of the constant in the calculation formula is: The saturation magnetic polarization strength 1.61T, 1.56T, 1.17T, 0.85T, 0.70T, 0.71T, 0.81T of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho are converted into values in kGs of the Gaussian unit system, and the converted values are 16.1, 15.6, 11.7, 8.5, 7.0, 7.1, 8.1, respectively. These values are used as the influence of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho on the calculation formula of the magnetic field intensity H. of the magnetic field intensity H.​ The magnetocrystalline anisotropy field 5600 kA / m, 5840 kA / m, 3600 kA / m, 4000 kA / m, 17600 kA / m, 12000 kA / m, 7600 kA / m of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho are converted into values expressed in kOe of the Gaussian unit system, the converted values are respectively: 70.37, 73.39, 45.24, 50.27, 221.17, 150.80, 95.50, and these values are taken as the influence of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho on the calculation formula of the magnetic field of the permanent magnet. The influence of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho is reflected in the calculation formula of the magnetic field of the permanent magnet. The influence of the elements Nd, Pr, Ce, Gd, Tb, Dy, Ho is reflected in the calculation formula of the magnetic field of the permanent magnet. Since Al has a certain solid solubility in the main phase of the Nd-Fe-B permanent magnet, and when it exists in the crystal lattice, it will reduce the magnetic moment of the adjacent Fe atoms in the crystal lattice, 1 Al atom substitution will cause the molecular magnetic moment of the Nd-Fe-B permanent magnet to decrease by 5.9μB, and the theoretical density of the Nd-Fe-B permanent magnet is 7.58g / cm 3 , the theoretical saturation magnetic polarization strength is 16.1kGs, so the molecular magnetic moment of the Nd-Fe-B permanent magnet is 32.3176μB, the relative atomic mass of Al is 26.981, the relative atomic mass of Fe is 55.845, and based on the above data, the influence of element Al on is: (32.3176-5.9 14) / 32.3176 (55.845 / 26.981)=-3.2204, and -3.2204 is taken as the influence of element Al on , which is reflected in the calculation formula of .

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