Preparation method for rapidly obtaining La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance

Abstract

The invention relates to the technical field of alloy preparation, in particular to a preparation method for rapidly obtaining La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance. Under the argon protective atmosphere, the BN nanosheet is doped into the La-Fe-Co-Si alloy through the selective laser melting 3D printing technology, and then the La-Fe-Co-Si rare earth magnetic refrigeration alloy with the high magnetocaloric performance is obtained through short-time annealing and air cooling heat treatment. BN nanosheets are doped into the alloy by using a selective laser melting method so as to introduce a B element, promote the formation of a magnetocaloric phase, reduce the content of a second phase, further refine the structure, provide nucleation sites for the subsequent formation of La (Fe, Co and Si) 13, shorten the heat treatment time, improve the mechanical strength, reduce the magnetic lag, improve the magnetocaloric performance and enhance the formability of the alloy; therefore, the problems that the La-Fe-Co-Si magnetic refrigeration alloy is long in high-temperature heat treatment time and difficult to form are effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy preparation, and in particular to a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties. Background Art

[0002] Magnetic refrigeration technology, as an efficient and environmentally friendly alternative to refrigeration, has made significant progress in recent years in materials, system design, and applications. In the field of low-temperature refrigeration, the EU's "MAGNYFIC" project developed a two-stage magnetic refrigeration system with a 20K temperature range, achieving a 20% increase in hydrogen liquefaction efficiency compared to traditional methods. NASA has also developed a 4K ultra-low-temperature magnetic refrigeration prototype for satellite infrared detector cooling. At room temperature, China's Haier, in collaboration with the Chinese Academy of Sciences, launched the first magnetically cooled wine cooler (to be launched in 2023), achieving a temperature difference of 50K and reducing energy consumption by 40%. Furthermore, according to a Tesla patent, using magnetic refrigeration for battery switches can increase response speeds by five times compared to traditional systems. Magnetic refrigeration is a solid-state refrigeration technology based on the magnetocaloric effect, achieving a refrigeration cycle through the heat absorption and release properties of materials during magnetization and demagnetization. Therefore, magnetic refrigeration materials have been a hot topic of research in this field. Among them, La-Fe-Co-Si alloy is one of the most promising magnetic refrigeration materials due to its high magnetocaloric properties, easily adjustable operating temperature range, and low cost. However, the high-temperature heat treatment time required to obtain the magnetocaloric phase is long because the application of traditional melting methods, such as arc melting and induction melting, cannot directly form the magnetocaloric phase (La(Fe,Co,Si) 13 Phase) can only be formed through the peritectic reaction between α-Fe and La-rich phases within the microstructure during high-temperature annealing. Furthermore, the low mechanical properties and poor formability of La-Fe-Co-Si alloys have long been bottlenecks restricting their large-scale practical application.

[0003] Patent publication number CN117535489A proposes a method for rapidly improving the magnetocaloric effect of highly brittle La-Fe-Co-Si rare earth magnetic refrigeration alloy. The method uses high-temperature hot compression technology to achieve high deformation at a low strain rate at high temperature to improve magnetocaloric properties and machinability. -1 , deformation 60% to 80%) promotes the formation of magnetocaloric phase, but it requires high temperature and large deformation treatment, high equipment requirements, high energy consumption, and is difficult to mass produce.

[0004] Patent publication number CN119159095A proposes a method for preparing and heat treating a high-strength and toughness La-Fe-Co-Si rare earth magnetic refrigeration alloy. The Cu element is incorporated into the alloy using selective laser melting 3D printing technology. Although the strength and toughness of the alloy are improved, the main focus is on improving the mechanical properties of the alloy. There is no mention of optimizing the magnetocaloric properties of the alloy and solutions to shorten the magnetocaloric phase formation time. The annealing time is long and the improvement in magnetocaloric performance is limited.

[0005] Patent publication number CN108511142A proposes a giant magnetocaloric La-Fe-Co-Si multiferroic composite material, its preparation method and use. By combining a La-Fe-Co-Si ferromagnetic alloy with a ferroelectric PMN-PT single crystal substrate to form a multiferroic composite material, an electrically controlled magnetic effect and a magnetic memory effect are achieved. However, the magnetocaloric phase formation efficiency and mechanical properties of the alloy itself are not optimized, and the problems of long annealing time and poor formability inherent to the La-Fe-Co-Si alloy cannot be solved.

[0006] Patent publication number CN119008213A proposes a La-Fe-Si-based magnetic refrigeration material and its preparation method. The powder metallurgy process is used to quickly form a magnetocaloric phase and ensure the integrity of the shape and strength of the material after hydrogen charging. However, this method focuses on the powder metallurgy process and composition optimization, has a long sintering time, relies on hydrogen charging treatment, and has low magnetocaloric performance indicators.

[0007] Currently, the most common solution is to use selective laser melting technology to prepare La-Fe-Co-Si alloy to solve the above problems. The rapid solidification process in selective laser melting technology is used to refine the grains, achieve fine grain strengthening, and improve the mechanical strength of the alloy. The advantage of high forming freedom of this technology is applied to improve the poor formability of the alloy. However, the problem of long high-temperature heat treatment time of La-Fe-Co-Si alloy remains unsolved (about 24 hours). Therefore, on this basis, it is urgent to develop a preparation method that can quickly improve the magnetocaloric properties of La-Fe-Co-Si alloy. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance, and to introduce B element into the alloy by selective laser melting to promote the magnetocaloric phase La (Fe, Co, Si) 13 phase formation, reducing the second phase content and further refining the structure, thus paving the way for subsequent La(Fe,Co,Si) 13The formation of La-Fe-Co-Si magnetic refrigeration alloy provides nucleation sites, shortens the heat treatment time, improves the mechanical strength, reduces the magnetic hysteresis, improves the magnetocaloric properties, and enhances the alloy formability, thereby effectively solving the problems of long high-temperature heat treatment time and difficult forming of La-Fe-Co-Si magnetic refrigeration alloy, and at the same time further improves the mechanical strength of the alloy.

[0009] The technical solution of the present invention is:

[0010] A method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy that can quickly obtain high magnetocaloric properties. In an argon protective atmosphere, BN nanosheets are incorporated into the La-Fe-Co-Si alloy using a selective laser melting 3D printing technology. Subsequently, the La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric properties is obtained through a short-time annealing + air cooling heat treatment.

[0011] The method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance is as follows: the composition of the La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance is La 6.8 Fe 82.8 Co 5.5 Si 4.9 .

[0012] The method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy that rapidly obtains high magnetocaloric properties comprises the following steps:

[0013] (1) Preparation of La using aerosol method 6.8 Fe 82.8 Co 5.5 Si 4.9 Powder, La 6.8 Fe 82.8 Co 5.5 Si 4.9 The alloy rod is heated to liquid state and injected into the tundish located above the atomizing nozzle. The metal liquid flows out from the hole at the bottom of the tundish and meets the high-speed gas ejected when passing through the nozzle and is atomized into fine liquid. After solidification, it forms La 6.8 Fe 82.8 Co 5.5 Si 4.9 powder;

[0014] (2) Mechanical powder mixing method was used to mix BN nanosheets with La 68 Fe 828 Co 55 Si 49 Mix the powder evenly to make La 6.8 Fe 82.8 Co 5.5 Si 4.9 A layer of BN nanosheets is evenly adsorbed on the powder surface;

[0015] (3) Selective laser melting was used to melt BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot, so that BN nanosheets were incorporated into the La-Fe-Co-Si alloy structure. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation.

[0016] (4) Annealing + air cooling heat treatment technology is used to improve the magnetocaloric properties and mechanical strength of La-Fe-Co-Si rare earth magnetic refrigeration alloy.

[0017] The method for preparing La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance rapidly comprises the following steps: before preparing powder by aerosol method in step (1), firstly preparing La with the same composition by arc melting method; 6.8 Fe 82.8 Co 5.5 Si 4.9 Alloy bar: Grind and clean the raw materials to remove the oxide scale on the surface of the pure metal raw materials. Use a high-precision electronic balance to weigh the metal raw materials according to the nominal composition of the alloy. Put the weighed metal raw materials into the melting furnace, place the easily oxidized La and the higher melting point Si in the lower layer, place Co in the middle layer, and place the lower melting point Fe in the upper layer. Evacuate the melting furnace to reduce the pressure in the furnace to 10 - 3 Pa, argon is filled at the same time, and the alloy is homogenized by electromagnetic stirring. The whole melting process is repeated 4 to 5 times to obtain La 6.8 Fe 82.8 Co 5.5 Si 4.9 Alloy bars.

[0018] The method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance is as follows: in step (2), the size of the BN nanosheet is 50 nm, and the La 6.8 Fe 82.8 Co 5.5 Si 4.9 The powder size is 15μm~53μm, BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The mass ratio of the powder is 1:199.

[0019] The method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy that quickly obtains high magnetocaloric properties, in step (3), the specific process of 3D printing into an alloy ingot is as follows: ① powder bed preparation, first evenly spread a thin layer of powder on the substrate to form a uniform particle bed; ② laser scanning and melting, guiding a high-energy laser beam to the powder surface, the laser scans the area according to the set scanning path, selectively melting and fusing the metal particles; ③ layer-by-layer construction, after each layer is melted and solidified, the substrate is lowered, and a new layer of metal powder is evenly spread on the top, and the process is repeated, the laser scans and melts each layer, and the newly melted material is bonded to the previous layer. This layer-by-layer construction process continues until the entire ingot is created.

[0020] The method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy that quickly obtains high magnetocaloric properties, in step (3), the laser power range of the selective laser melting method is 200W~240W, the scanning rate is 350mm / s~500mm / s, the layer thickness is 30μm~50μm, and the scanning spacing is 0.09mm~0.12mm.

[0021] In the method for preparing the La-Fe-Co-Si rare earth magnetic refrigeration alloy that rapidly obtains high magnetocaloric properties, in step (4), the annealing temperature is 1323K to 1373K, and the holding time is 10min to 20min.

[0022] The design concept of the present invention is:

[0023] The present invention uses the selective laser melting technology to dope BN nanosheets into La-Fe-Co-Si magnetic refrigeration alloy to introduce B element into the alloy. The alloy is subsequently heat treated by annealing + air cooling technology, which can rapidly improve the magnetocaloric properties of the alloy and at the same time improve the mechanical strength of the alloy. The composition of the magnetic refrigeration alloy is La 6.8 Fe 82.8 Co 5.5 Si 4.9 . Using the selective laser melting method to La 6.8 Fe 82.8 Co 5.5 Si 4.9 The B element is introduced into the alloy to fill the lattice gap to stabilize La(Fe,Co,Si) 13 Phase structure, reducing La(Fe,Co,Si) 13 The formation energy of the phase can be inhibited, the formation of residual α-Fe phase in the alloy is beneficial to the microstructure refinement during the rapid solidification process, the atomic diffusion rate is accelerated, and the La(Fe, Co, Si) 13 Phase formation, La(Fe,Co,Si) during annealing 13The formation of phase provides nucleation sites, greatly shortens the heat treatment time, and reduces La 6.8 Fe 82.8 Co 5.5 Si 4.9 The hysteresis loss generated during the alloy cycle operation increases the operating temperature range.

[0024] The advantages and beneficial effects of the present invention are as follows:

[0025] 1. The present invention provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy that can quickly obtain high magnetocaloric properties and a heat treatment method. The alloy composition is La 6.8 Fe 82.8 Co 5.5 Si 4.9 , the B element is incorporated into the alloy by using the non-equilibrium rapid solidification forming process of selective laser melting. On the one hand, B acts as an interstitial atom to reduce the lattice strain energy and formation energy to promote the La(Fe,Co,Si) 13 Phase generation, which is La(Fe,Co,Si) in the subsequent annealing process 13 On the other hand, the B element can preferentially form with Fe or Co elements, inhibiting the formation of residual α-Fe phase in the alloy and refining the grains, accelerating atomic diffusion, and promoting La(Fe,Co,Si) 13 The annealing time of the alloy was ultimately shortened from several weeks to 10 to 20 minutes, which is much shorter than that of La-Fe-Co-Si ribbons (2 hours), particles (1 hour), and La-Fe-Co-Si alloys not doped with B.

[0026] 2. The preparation method and heat treatment method of the La-Fe-Co-Si rare earth magnetic refrigeration alloy that can quickly obtain high magnetocaloric properties can be applied in the field of magnetic refrigeration, providing theoretical and technical support for shortening the annealing time and formability of magnetic refrigeration materials in magnetic refrigerators.

[0027] 3. The present invention introduces BN nanosheets by selective laser melting (SLM) technology, and adopts SLM power (laser power 200-240W), BN mass ratio (BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9The parameters of the SLM process are designed in a coordinated manner, with a powder mass ratio of 1:199 and annealing (1323-1373K, 10-20min). The SLM bath decomposes the BN nanosheets into B and N, with the B element preferentially combining with Fe / Co to inhibit the formation of the α-Fe phase. The BN mass ratio of 1:199 ensures a moderate B content (excessive B will form brittle borides, impairing toughness). A laser power of 200-240W provides sufficient energy to melt the BN and alloy powder while avoiding composition segregation caused by excessive energy. The annealing temperature is slightly higher than that of La (Fe, Co, Si). 13 The phase formation temperature (~1273K) is kept low, while avoiding the grain coarsening caused by excessive temperatures (>1373K). A short annealing time of 10-20 minutes allows the boron doping to pre-generate nucleation sites, accelerating the phase transformation without the need for long holding times. This results in a uniform distribution of the boron element, forming high-density nucleation sites and grain refinement, achieving breakthroughs in magnetocaloric performance, mechanical strength, and fabrication efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. It can be seen that the following drawings are only part of the experimental embodiments. For ordinary technicians in this field, other related drawings can be obtained based on the following simple diagrams without creative work.

[0029] Figure 1 Schematic diagram of the process of doping BN nanosheets into La-Fe-Co-Si alloy by selective laser melting in Examples 1-8. 6.8 Fe 82.8 Co 5.5 Si 4.9 ), (c) BN nanosheets, (d) scanning images of mixed powder (left) and selective laser melting (right) (numbers in the figure: 1 laser beam, 2 melt pool, 3 substrate), (e) macroscopic image of the final alloy ingot.

[0030] Figure 2 (a) is a backscattered scanning image of the longitudinal section of the as-cast BN-doped La-Fe-Co-Si alloy ingot in Example 1, where the dark gray phase is the α-Fe phase and the light gray phase is the magnetocaloric phase La(Fe, Co, Si). 13 phase, and the white phase is La-rich phase. The selective melting process of the alloy is: laser power 220W, scanning speed 450mm / s, scanning spacing 0.09mm, and layer thickness 30μm.

[0031] Figure 2 (b) is the same as that in Example 1 Figure 2(a) Enlarged image of the purple dashed box area, inset is an enlarged image of the red dashed box area, where the dark gray phase is the α-Fe phase and the light gray phase is the magnetocaloric phase La(Fe,Co,Si) 13 phase, and the white phase is La-rich phase. The selective melting process of the alloy is: laser power 220W, scanning speed 450mm / s, scanning spacing 0.09mm, and layer thickness 30μm.

[0032] Figure 2 (c) is a backscattered scanning image of the longitudinal section of the heat-treated BN-doped La-Fe-Co-Si alloy ingot in Example 1, where the dark gray phase is the α-Fe phase and the light gray phase is the magnetocaloric phase La(Fe, Co, Si). 13 phase, the white phase is La-rich phase, the selective melting process of the alloy is: laser power 220W, scanning speed 450mm / s, scanning spacing 0.09mm, layer thickness 30μm, heat treatment process is heat preservation at 1323K for 15min and then air cooling.

[0033] Figure 3 Powder XRD patterns of the BN-doped La-Fe-Co-Si alloy in Example 1 before and after heat treatment. The abscissa (2θ) represents the diffraction angle (degrees), and the ordinate (Intensity) represents the relative intensity (au). The alloy was melted using the following selective melting process: laser power 220 W, scanning speed 450 mm / s, scanning pitch 0.09 mm, and layer thickness 30 μm.

[0034] Figure 4 The hardness of BN-doped La-Fe-Co-Si alloy prepared by selective laser melting method with laser power ranging from 200W to 240W, scanning rate from 350mm / s to 500mm / s, layer thickness from 30μm to 50μm, and scanning spacing from 0.09mm to 0.12mm after annealing at 1323K for 15min and air cooling is shown in Table 1. The horizontal axis represents the selected areas #1, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #14, #16, #19, and #20 of the alloy, and the vertical axis represents the hardness (MPa). The melting process parameters of the selected areas #1, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #14, #16, #19, and #20 of the alloy are shown in Table 1.

[0035] Figure 5Thermomagnetic curves at 0.02 T and 2 T for the La-Fe-Co-Si alloy doped with BN nanosheets prepared by selective laser melting in Example 1 before and after heat treatment. The selective melting process used a laser power of 220 W, a scan speed of 450 mm / s, a scan pitch of 0.09 mm, and a layer thickness of 30 μm. The heat treatment was a 15-min soak at 1323 K.

[0036] Figure 6 This is the isothermal magnetization curve of the La-Fe-Co-Si alloy doped with BN nanosheets after heat treatment, prepared by selective laser melting (SLM) in Example 1. The alloy was melted using the following selective laser melting process: 220 W laser power, 450 mm / s scanning speed, 0.09 mm scanning pitch, 30 μm layer thickness, and a heat treatment temperature range of 250 K to 348 K, holding at 1323 K for 15 min, and a magnetic field range of 0.02 T to 2 T.

[0037] Figure 7 This figure shows the magnetic entropy change curves of the La-Fe-Co-Si alloy doped with BN nanosheets after heat treatment, prepared by selective laser melting (SLM) in Example 1. The alloy was melted using the following conditions: laser power of 220 W, scanning speed of 450 mm / s, scanning pitch of 0.09 mm, layer thickness of 30 μm, and heat treatment at 1323 K for 15 min in magnetic fields of 0.5 T, 1 T, 1.5 T, and 2 T. DETAILED DESCRIPTION

[0038] In the specific implementation process, the present invention quickly obtains a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric performance and a heat treatment method, applies the method of selective laser melting to incorporate BN nanosheets into the La-Fe-Co-Si alloy, and then uses the annealing + quenching heat treatment method to greatly improve the magnetocaloric performance of the alloy, wherein the composition of the magnetic refrigeration alloy is La 6.8 Fe 82.8 Co 5.5 Si 4.9 (at.%).

[0039] The BN nanosheets were incorporated into the La-Fe-Co-Si rare earth magnetic refrigeration alloy by the selective laser melting method. The specific parameters are as follows: the laser power range is 200W~240W, the scanning rate is 350mm / s~500mm / s, the layer thickness is 30μm~50μm, and the scanning spacing is 0.09mm~0.12mm. The subsequent annealing + air cooling heat treatment technology was used to improve the magnetocaloric properties of the alloy. The specific parameters are as follows: the annealing temperature is 1323K~1373K, and the heat treatment time is 10min~15min. It should be noted that by further optimizing the process parameters of selective laser melting, the La(Fe,Co,Si)13 The increased generation of the phase provides more nucleation sites during the subsequent annealing process, shortening the annealing time. By processing the La-Fe-Co-Si rare earth magnetic refrigeration alloy within the above parameter range, it is possible to effectively ensure that the alloy achieves high magnetocaloric properties in a short period of time. In other embodiments of the present invention, the process parameters can also be adjusted as needed.

[0040] To further clarify the objectives, technical solutions, and advantages of the embodiments of the present invention, the following provides a clear and complete description of the technical solutions in the embodiments of the present invention. It should be apparent that the description is only a portion of the embodiments, not all of them. The following describes in detail the preparation method and heat treatment process for a La-Fe-Co-Si rare earth magnetic refrigeration alloy that rapidly achieves high magnetocaloric properties, as provided in the embodiments of the present invention.

[0041] Example 1

[0042] This embodiment provides a preparation and heat treatment process of a high-strength and toughness La-Fe-Co-Si rare earth magnetic refrigeration alloy, which is prepared and heat treated by the following method:

[0043] (1) Preparation of La using aerosol method 68 Fe 828 Co 55 Si 49 powder

[0044] Before preparing powder by aerosol method, La with the same composition was prepared by arc melting method. 6.8 Fe 82.8 Co 5.5 Si 4.9 Alloy bar: First, grind and clean the raw materials to remove the oxide scale on the surface of the pure metal raw materials. Use a high-precision electronic balance to weigh the metal raw materials according to the nominal composition of the alloy. Put the weighed metal raw materials into the melting furnace, place the easily oxidized La and the higher melting point Si in the lower layer, place Co in the middle layer, and the lower melting point Fe in the upper layer. Evacuate the melting furnace to reduce the pressure in the furnace to 10 -3 Pa, and high-purity argon (volume purity 99.999%) is filled in at the same time, and the alloy is homogenized by electromagnetic stirring. The entire smelting process is repeated 5 times to obtain alloy rods, which are then heated to liquid and injected into a tundish located above the atomizing nozzle. The metal liquid flows out from the leak at the bottom of the tundish, meets the ejected high-speed gas when passing through the nozzle, and is atomized into fine liquid, which forms powder after solidification.

[0045] (2) Mechanical powder mixing method was used to mix BN nanosheets with La 6.8 Fe 82.8 Co 5.5 Si4.9 Powder mixed evenly

[0046] A small amount of BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The powders were mixed evenly by mechanical mixing, and the BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The mass ratio of the powder is 1:199, making La 6.8 Fe 82.8 Co 5.5 Si 4.9 A layer of BN nanosheets is evenly adsorbed on the powder surface.

[0047] (3) BN was incorporated into the La-Fe-Co-Si alloy structure by selective laser melting

[0048] BN and La were melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder is 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process is carried out under an argon protective atmosphere to prevent powder oxidation. The specific process is: ① Powder bed preparation: First, a thin layer of powder is evenly spread on the substrate to form a uniform particle bed. The thickness of each layer of powder is 30μm; ② Laser scanning and melting: A laser beam with a power of 220W is guided to the powder surface. The laser scans the area according to the set scanning path, with a scanning spacing of 0.09mm and a scanning speed of 450mm / s, selectively melting and fusing metal particles; ③ Layer-by-layer construction: After each layer is melted and solidified, the substrate is lowered and a new layer of metal powder is evenly spread on the top. The layer thickness is still 30μm. The process is repeated. The laser scans and melts each layer, bonding the newly melted material to the previous layer. This layer-by-layer construction process continues until the entire ingot is created.

[0049] (4) Using annealing + air cooling heat treatment technology to improve the magnetocaloric effect of La-Fe-Co-Si rare earth magnetic refrigeration alloy

[0050] The alloy ingot prepared by selective laser melting was annealed and air-cooled at a temperature of 1323 K for 15 min. The magnetic entropy change at 2 T increased to 3.2 J / kg·K.

[0051] Example 2

[0052] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0053] In step (3), BN and La are melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. During the laser scanning and melting process, the power of the selective laser melting was 210W, the final heat treatment time was shortened to 10min, and the magnetic entropy change at 2T was increased to 3.0J / kg·K.

[0054] Example 3

[0055] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0056] In step (3), BN and La are melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. During the laser scanning and melting process, the scanning rate of the selective laser melting was 400mm / s. The final heat treatment time was shortened to 12min, and the magnetic entropy change at 2T was increased to 3.1J / kg·K.

[0057] Example 4

[0058] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0059] In step (3), BN and La are melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. During the laser scanning and melting process, the scanning pitch of the selective laser melting was 0.1mm. The final heat treatment time was shortened to 13min, and the magnetic entropy change at 2T was increased to 3.2J / kg·K.

[0060] Example 5

[0061] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0062] In step (3), BN and La are melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. In the laser scanning and melting process, the power of the selective laser melting was 200W. In the end, the mixed powder did not melt and the ingot failed to form. The reason is that the laser power is too low and the energy provided is difficult to melt the powder and fuse it, resulting in the failure of the ingot to form.

[0063] Example 6

[0064] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0065] In step (3), BN and La are melted by selective laser melting. 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot with a size of 4mm×4mm×8mm. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. During the laser scanning and melting process, the scanning rate of the selective laser melting was 600mm / s. The final alloy required 2h of annealing to achieve a magnetic entropy change of 3.1J / kg·K. The reason for this is that the scanning rate was too fast, resulting in insufficient energy absorption by the metal powder, making it difficult to achieve the La(Fe,Co,Si) 13 The formation energy required for phase formation, therefore La(Fe,Co,Si) cannot be directly generated in the cast alloy 13 phase, so no nucleation sites can be generated during the annealing process, resulting in a prolonged heat treatment time.

[0066] Example 7

[0067] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0068] In step (4), annealing + air cooling heat treatment technology is used to improve the magnetocaloric effect of the La-Fe-Co-Si rare earth magnetic refrigeration alloy. The annealing temperature is 1353K, and the final magnetic entropy change is increased to 3.0J / kg·K.

[0069] Example 8

[0070] This embodiment provides a method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy and a heat treatment process for rapidly obtaining high magnetocaloric properties. The only difference between this method and embodiment 1 is that:

[0071] In step (4), annealing + air cooling heat treatment technology is used to improve the magnetocaloric effect of La-Fe-Co-Si rare earth magnetic refrigeration alloy. The annealing time is 5 minutes, and the final magnetic entropy change is reduced to 1.9 J / kg·K. The reason is that the heat treatment time is too short and a large amount of La(Fe, Co, Si) 13 phase, resulting in a decrease in magnetic entropy change.

[0072] Reference Figure 1 As shown, the mechanical powder mixing method can be used to mix (c) BN nanosheets and (a)-(b) La 6.8 Fe 82.8 Co 5.5 Si 4.9 Mix the powder evenly to make La 6.8 Fe 82.8 Co 5.5 Si 4.9 A layer of BN nanosheets is uniformly adsorbed on the powder surface. Figure 1 As shown in (d), the basic process flow of selective laser melting is as follows: a high-energy laser beam 1 is directed onto the surface of the mixed powder. The laser scans the area according to the set scanning path, selectively melting and fusing the metal particles to form a molten pool 2. After each layer is melted and solidified, the base plate 3 is lowered and a new layer of metal powder is evenly spread on the top. The process is repeated, and the laser scans and melts each layer, bonding the newly melted material to the previous layer until the entire ingot is created (e).

[0073] Reference Figure 2 As shown in (a), the backscattered image of the BN-doped La-Fe-Co-Si cast alloy ingot prepared by selective laser melting has the following structural features in the longitudinal section: the interior of some grains is a fine dendrite structure composed of α-Fe and La-rich phase, and the interior of other grains is La(Fe, Co, Si) 13 Mutually.

[0074] Reference Figure 2 As shown in (b), there are a large number of equiaxed crystals inside the BN-doped La-Fe-Co-Si cast alloy ingot prepared by selective laser melting. 13The phase size is about 10 μm, and the La(Fe, Co, Si) 13 The formation of the phase provides a large number of sites, accelerating the La(Fe,Co,Si) 13 The formation of the phase shortens the annealing time. In addition, the dendrite size of α-Fe and La-rich phase is only 2μm, the atomic diffusion distance is shortened, and the peritectic reaction occurs.

[0075] Reference Figure 2 As shown in (c), after annealing at 1323K for only 15min, a large amount of magnetocaloric phase La(Fe,Co,Si) is formed inside the BN-doped La-Fe-Co-Si alloy ingot prepared by selective laser melting. 13 Phase (light gray area), the volume fraction can reach 90 vol.%, and the content of residual α-Fe phase is only 10 vol.%.

[0076] Reference Figure 3 As shown, the interior of the BN-doped La-Fe-Co-Si cast alloy ingot prepared by selective laser melting is the magnetocaloric phase La(Fe, Co, Si) 13 phase and non-magnetocaloric phase α-Fe and La-rich phase coexist, and the magnetocaloric phase La(Fe,Co,Si) 13 The phase peak intensity is low, indicating that the content is low, which is consistent with the scanning image. However, after annealing at 1323K for only 15min, La(Fe,Co,Si) 13 The phase peak intensity is significantly improved, the La-rich phase diffraction peak disappears, and only the diffraction peak of the α-Fe phase remains, indicating that the La (Fe, Co, Si) inside the alloy is 13 The phase content increases significantly, the non-magnetocaloric La-rich phase disappears, and only a small amount of α-Fe remains, which is consistent with the scanning image.

[0077] Reference Figure 4 As shown in the figure, the hardness of the BN-doped La-Fe-Co-Si cast alloy prepared by selective laser melting ranges from 280 MPa to 450 MPa, which is higher than the hardness of the Cu-doped La-Fe-Co-Si cast alloy prepared by selective laser melting (250 MPa to 300 MPa) and the hardness of the La-Fe-Co-Si cast alloy (200 MPa to 280 MPa), indicating that the incorporation of BN into La-Fe-Co-Si alloy can significantly improve the hardness of the alloy. The reason is that the doping of B element can effectively refine the grains, stimulate fine grain strengthening, and can enter the lattice as an interstitial atom to stimulate solid solution strengthening.

[0078] Table 1 is Figure 4 Selective laser melting (SLM) preparation process of BN nanosheets doped with La-Fe-Co-Si alloy.

[0079] Table 1 Process parameters of selective laser melting of BN nanosheets doped with La-Fe-Co-Si alloy

[0080] Sample number Laser power (W) Scanning speed (mm / s) <![CDATA[Energy density (J / mm 3 )]]> #1 200 350 211.64 #3 200 450 164.61 #4 200 500 148.15 #5 210 350 222.22 #6 210 400 194.44 #7 210 450 172.84 #8 210 500 155.56 #9 220 350 232.80 #10 220 400 203.70 #11 220 450 181.07 #12 220 500 162.96 #14 230 400 212.96 #16 230 500 170.37 #19 240 450 197.53 #20 240 500 177.78

[0081] The data in Table 1 show that by rationally adjusting the laser power and scanning speed, the energy density can be optimized, thereby significantly improving the hardness, mechanical properties, and magnetothermal properties of the BN nanosheet-doped La-Fe-Co-Si alloy. At the same time, it provides a better foundation for subsequent heat treatment and achieves rapid and efficient alloy preparation.

[0082] Reference Figure 5 As shown in the figure, at 0.02T and 2T, the magnetization intensity of the BN-doped La-Fe-Co-Si cast alloy prepared by selective laser melting decreases with increasing temperature and suddenly changes at its Curie temperature of 285K, indicating the generation of magnetic phase transition behavior and magnetic entropy change. After annealing at 1323K for 15min, the degree of sudden change in magnetization intensity increases, indicating that the degree of magnetic phase transition of the alloy increases after annealing. The reason is that the magnetocaloric phase La(Fe,Co,Si) in the organization 13 The content of the phase increases rapidly. At the same time, the Curie temperature of the alloy increases to 300K, indicating that the magnetic phase transition temperature range increases. The reason is that B atoms occupy the La(Fe,Co,Si) 13 The phase gap position induces lattice expansion, reduces the overlap between the 3d electron wave functions of Fe, narrows the 3d energy band, enhances the ferromagnetic interaction, and thus increases the Curie temperature.

[0083] Reference Figure 6 As shown in the figure, when the temperature is lower than 300K, the BN-doped La-Fe-Co-Si alloy after annealing at 1323K for 15min is rapidly magnetized under the action of the magnetic field, that is, the magnetization intensity increases rapidly, indicating that the alloy is in a ferromagnetic state at this time. When the temperature is higher than 300K, the magnetization speed of the annealed alloy slows down, and the magnetization intensity is low at 2T, indicating that the alloy is in a paramagnetic state at this time. Therefore, it can be concluded that 300K is the Curie temperature of the alloy, which is consistent with the Figure 5 The results obtained are consistent.

[0084] Reference Figure 7 As shown in the figure, after only 15 minutes of annealing, the magnetic entropy changes of BN-doped La-Fe-Co-Si alloy at 0.5T, 1T, 1.5T and 2T can reach 0.9J / kg·K, 1.7J / kg·K, 2.4J / kg·K and 3.2J / kg·K, respectively. This value is much higher than that of Cu-doped La-Fe-Co-Si alloy prepared by selective laser melting process with annealing time of 12h (1.4J / kg·K), and close to that of La-Fe-Co-Si alloy with annealing time of 24h (3.5J / kg·K). In addition, the operating temperature range at 2T can reach 36K.

[0085] Implementation results demonstrate that, building on existing technologies, this method innovatively combines selective laser melting with the incorporation of boron nitride (BN) nanosheets to achieve efficient preparation and improved performance of La-Fe-Co-Si alloys. By introducing the boron element and leveraging the rapid solidification characteristics of selective laser melting, this method effectively addresses key challenges inherent in conventional methods, such as the long magnetocaloric phase formation time and poor mechanical properties. The alloy's annealing time is shortened to 10 to 15 minutes, significantly improving magnetocaloric performance and mechanical strength. In particular, the magnetic entropy change at 2 T is increased to 3.2 J / kg·K, and the alloy's formability is enhanced, making it a promising candidate for magnetic refrigeration.

[0086] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy that rapidly obtains high magnetocaloric properties, characterized in that: Under argon protective atmosphere, BN nanosheets were doped into La-Fe-Co-Si alloy using selective laser melting 3D printing technology, and then La-Fe-Co-Si rare earth magnetic refrigeration alloy with high magnetocaloric properties was obtained through short-time annealing + air cooling heat treatment.

2. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy that rapidly obtains high magnetocaloric properties according to claim 1, characterized in that: In terms of atomic percentage, the composition of the high magnetocaloric performance La-Fe-Co-Si rare earth magnetic refrigeration alloy is La 6.8 Fe 82.8 Co 5.5 Si 4.9 .

3. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 1, characterized in that: The steps include: (1) Preparation of La using aerosol method 6.8 Fe 82.8 Co 5.5 Si 4.9 Powder, La 6.8 Fe 82.8 Co 5.5 Si 4.9 The alloy rod is heated to liquid state and injected into the tundish located above the atomizing nozzle. The metal liquid flows out from the hole at the bottom of the tundish and meets the high-speed gas ejected when passing through the nozzle and is atomized into fine liquid. After solidification, it forms La 6.8 Fe 82.8 Co 5.5 Si 4.9 powder; (2) Mechanical powder mixing method was used to mix BN nanosheets with La 6.8 Fe 82.8 Co 5.5 Si 4.9 Mix the powder evenly to make La 6.8 Fe 82.8 Co 5.5 Si 4.9 A layer of BN nanosheets is uniformly adsorbed on the powder surface; (3) Selective laser melting was used to melt BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The mixed powder was 3D printed into an alloy ingot, so that BN nanosheets were incorporated into the La-Fe-Co-Si alloy structure. The printing process was carried out under an argon protective atmosphere to prevent powder oxidation. (4) Annealing + air cooling heat treatment technology is used to improve the magnetocaloric properties and mechanical strength of La-Fe-Co-Si rare earth magnetic refrigeration alloy.

4. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 3, characterized in that: Before preparing powder by aerosol method in step (1), La with the same composition was prepared by arc melting method. 6.8 Fe 82.8 Co 5.5 Si 4.9 Alloy bar: Grind and clean the raw materials to remove the oxide scale on the surface of the pure metal raw materials. Use a high-precision electronic balance to weigh the metal raw materials according to the nominal composition of the alloy. Put the weighed metal raw materials into the melting furnace, place the easily oxidized La and the higher melting point Si in the lower layer, place Co in the middle layer, and place the lower melting point Fe in the upper layer. Evacuate the melting furnace to reduce the pressure in the furnace to 10 -3 Pa, argon is filled at the same time, and the alloy is homogenized by electromagnetic stirring. The whole melting process is repeated 4 to 5 times to obtain La 6.8 Fe 82.8 Co 5.5 Si 4.9 Alloy bars.

5. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 3, characterized in that: In step (2), the size of the BN nanosheet is 50 nm, and the La 6.8 Fe 82.8 Co 5.5 Si 4.9 The powder size is 15μm~53μm, BN nanosheets and La 6.8 Fe 82.8 Co 5.5 Si 4.9 The mass ratio of the powder is 1:

199.

6. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 3, characterized in that: In step (3), the specific process of 3D printing into an alloy ingot is as follows: ① powder bed preparation, first a thin layer of powder is evenly spread on the substrate to form a uniform particle bed; ② laser scanning and melting, a high-energy laser beam is directed to the powder surface, and the laser scans the area according to the set scanning path, selectively melting and fusing the metal particles; ③ layer-by-layer construction, after each layer is melted and solidified, the substrate is lowered and a new layer of metal powder is evenly spread on the top, and the process is repeated, the laser scans and melts each layer, and the newly melted material is bonded to the previous layer. This layer-by-layer construction process continues until the entire ingot is created.

7. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 3 or 6, characterized in that: In step (3), the laser power range of the selective laser melting method is 200W to 240W, the scanning rate is 350mm / s to 500mm / s, the layer thickness is 30μm to 50μm, and the scanning spacing is 0.09mm to 0.12mm.

8. The method for preparing a La-Fe-Co-Si rare earth magnetic refrigeration alloy capable of rapidly obtaining high magnetocaloric properties according to claim 3, characterized in that: In step (4), the annealing temperature is 1323K to 1373K, and the holding time is 10min to 20min.

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