Heat treatment method for improving magnetic shielding performance of additive manufacturing magnetically soft alloy-high-strength steel gradient composite material structure

Abstract

The invention provides a heat treatment method for improving the magnetic shielding performance of an additive manufacturing magnetically soft alloy-high-strength steel gradient composite material structure, which comprises the following steps: carrying out vacuum heat treatment on a shielding layer prepared by adopting a laser melting deposition process method, specifically, heating to 630-640 DEG C at a heating rate of 20-25 DEG C / min, carrying out heat preservation for 15-20 minutes, and then cooling in three steps, and cooling to 440-460 DEG C at the furnace cooling speed of 10-15 DEG C / min, cooling to 280-320 DEG C at the furnace cooling speed of 5-8 DEG C / min, and air-cooling to room temperature. According to the heat treatment method for the additive manufacturing magnetically soft alloy-high-strength steel gradient composite material structure, the magnetic conductivity of the FeNi50 magnetically soft alloy can be greatly improved, the integrity and the bonding strength of a gradient material bonding interface are guaranteed, and the magnetic shielding performance is excellent.

Description

Technical Field

[0001] The present invention relates to the field of preparation of gradient material functional structures, and particularly to a heat treatment method for improving the magnetic shielding performance of an additive manufacturing soft magnetic alloy-high strength steel gradient composite material structure. Background Art

[0002] The electromagnetic environment in which aerospace precision instruments and equipment are located is becoming increasingly complex, and their shielding materials need to meet the magnetic shielding requirements in a wide frequency range, such as aerospace fiber optic gyroscopes, satellite rubidium clocks, etc. Existing research focuses on the structural design of single-layer shields. However, limited by manufacturing processes such as traditional diffusion welding and vacuum hot pressing, the prepared shielding structures are large in volume and weight, and it is difficult to adapt to the complex structural shapes of spacecraft products. Based on the principle of multi-layer magnetic conduction layers grading and shunting to attenuate the magnetic field and the gradient structure multiple absorbing and reflecting electromagnetic waves, the multi-layer shielding structure has natural advantages over the single-layer shielding structure. The multi-layer magnetic shielding structure requires clear bonding interfaces and high bonding strength.

[0003] Laser melting deposition forming technology can realize the free forming of complex-shaped structures. The three-dimensional model of the structure is sliced and layered using forming process software. Based on the two-dimensional cross-section of each layer, the powder material synchronously transported is melted by a high-energy beam laser, overlapping track by track and stacking layer by layer to finally form a three-dimensional structure. This technology has been widely used in the production of structural materials and devices. Compared with traditional manufacturing or processing methods, it has the advantages of no mold, not being restricted by part structure and materials, and quickly responding to design changes, providing a technical approach for realizing the "structural design-manufacturing-functional integration" of complex structural functional metal components, and is particularly suitable for the forming manufacturing of gradient structures. However, for the directly formed state structure by additive manufacturing, due to reasons such as tissue anisotropy, complex internal stress state, and intricate grain boundaries, the hindrance to magnetic domain movement is large, and the magnetic properties are usually low.

[0004] In existing research, as described in an additive manufacturing method and device for a multi-wire functional gradient structure, patent number CN107470624A, inventors: Lu Bingheng, Fang Xuewei, Zhang Lijuan, Wang Bowen, this method uses the arc wire feeding additive manufacturing technology to form composition gradient materials, and it is difficult to form precision structures. The formed parts usually have coarse grains and poor performance, a wide bonding area, and it is difficult to improve the product performance to a high level through post-treatment.

[0005] As described in a method for improving the high-frequency magnetic permeability of Fe-based nanocrystalline soft magnetic alloys, patent number CN 113337692A, inventors Zhang Wei, Li Yanhui, Guo Rui, etc., this method provides a method for improving the high-frequency magnetic permeability of Fe-based nanocrystalline soft magnetic alloys, including two aspects of alloy composition and heat treatment process. By increasing the content of pre-transition metal elements (TM) in the alloy and adding C, a heat treatment process is developed to obtain nanocrystalline alloy strips. This method uses the casting and melt spinning process and cannot prepare gradient composite materials.

[0006] As described in an iron-nickel based soft magnetic alloy foil and its preparation method and application, patent number CN 116377284 A, inventors Li Chongyang, An Yang, Xu Mingzhou, etc., the invention proposes an iron-nickel based soft magnetic alloy foil and its preparation method and application, and solves the technical problem of poor shielding effectiveness of existing iron-nickel based soft magnetic alloy foil under high frequency strong magnetic field through composition design. The strip is processed by blanking-heat treatment-rolling and other processes, and the process flow is cumbersome and only suitable for preparing single-layer foil, and gradient composite materials cannot be prepared, which does not meet the requirements of both magnetic conductivity and strength of magnetic shielding structure.

[0007] Therefore, there is currently no process and method for preparing a gradient metal composite material magnetic shielding structure with high magnetic conductivity. Summary of the invention

[0008] The purpose of the present invention is to provide a heat treatment method for improving the magnetic shielding performance of an additively manufactured soft magnetic alloy-high-strength steel gradient composite material structure, to solve the problem that the additively manufactured directly morphological gradient multilayer composite magnetic shielding structure still cannot meet the ultra-high shielding requirements, and to maintain the stability of the gradient layer bonding interface and high bonding strength.

[0009] In order to solve the above problems, the present invention provides the following solutions:

[0010] The present invention provides a heat treatment method for improving the magnetic shielding performance of an additively manufactured soft magnetic alloy-high-strength steel gradient composite material structure, comprising vacuum heat treatment of a shielding layer prepared by a laser melting deposition process; firstly heating the temperature to 630-640°C at a heating rate of 20-25°C / min and keeping the temperature for 15-20min, then cooling in three steps, cooling to 440-460°C at a furnace cooling rate of 10-15°C / min, then cooling to 280-320°C at a furnace cooling rate of 5-8°C / min, and then air cooling to room temperature. The heating process needs to make the shielding layer product reach the annealing temperature as soon as possible. If the heating rate is too high, the gradient layer will have the risk of rapid increase in thermal stress and deformation and cracking. The present invention selects the heating rate according to the test results. The annealing and heat preservation temperature is limited by the ordering transformation temperature of the soft magnetic alloy. The temperature is kept for a short time at a temperature close to the top of the Curie temperature (magnetic transition temperature). The dual benefits of eliminating stress and preventing magnetic property loss are desirable. The temperature is kept for a short time in the ordering temperature of 300℃ to 500℃ in steps, mainly avoiding the ordering transformation to form anisotropic magnetic conductivity and reducing magnetic permeability. At the same time, this temperature range can eliminate the residual stress, small-angle grain boundary density, substructure cell wall and other unfavorable factors affecting the movement of magnetic domains in the additive forming process. Long-term heat preservation will also increase the risk of ordering. Therefore, the present invention has determined the aforementioned three-level cooling method after a lot of creative work.

[0011] Furthermore, a shielding layer with a FeNi50-12Cr13-FeNi50 sandwich structure is prepared by a laser melting deposition process method. Among them, the FeNi50 soft magnetic alloy material is used as the magnetic conduction layer, and 12Cr13 high-strength steel is used as the magnetic isolation layer and the structure strengthening layer.

[0012] Furthermore, the gradient structure layer is arranged in the order of FeNi50-12Cr13-FeNi50. Among them, the thickness of the FeNi50 single structure layer is 0.1 mm to 0.5 mm, the thickness of the 12Cr13 single structure layer is 0.2 mm to 1 mm, and the thickness range of the shielding layer is 0.4 mm to 2 mm.

[0013] Furthermore, the composition of the FeNi50 soft magnetic alloy material is Ni: 46.8 - 51.2 wt%, C: 0.002 - 0.006 wt%, O: 0.020 - 0.032 wt%, S: 0.001 - 0.004 wt%, P: 0.005 - 0.012 wt%, Fe: Bal.

[0014] Furthermore, the thickness range of the magnetic shielding cover structure is 0.4 mm to 2 mm, and the optimal thickness ratio of the gradient structure layer is FeNi50:12Cr13:FeNi50 = 1:2:1.

[0015] Furthermore, the dilution rate range of the bonding interface of the gradient layer after heat treatment does not exceed 0.05 mm.

[0016] The soft magnetic alloy-high strength steel gradient composite material structure obtained by the heat treatment method of the present invention belongs to the protection scope of the present invention.

[0017] The application of the soft magnetic alloy-high strength steel gradient composite material structure obtained by the heat treatment method of the present invention in aerospace precision instruments and equipment also belongs to the protection scope of the present invention.

[0018] Furthermore, the aerospace precision instruments and equipment include aerospace fiber optic gyroscopes, satellite rubidium clocks, etc.

[0019] The principle on which the heat treatment method of the present invention relies is as follows: without solution treatment, only rapidly heat up to a lower temperature below the phase transformation point, and then directly perform stepped cooling. The reason for not performing conventional solution treatment in the present invention is that during high-temperature solution holding for a long time (for example, heating up to 1100 - 1200 °C and holding for 3 - 6 h, etc.), sufficient tissue homogenization and element migration will occur, and the interfacial dilution rate will increase; in order to retain the original bonding interface clear in the present invention, excessive element migration is not allowed. Only rapidly heat up to a lower temperature below the phase transformation point, and then adopting 3-step stepped cooling is beneficial to fully eliminate the influence of residual stress, small-angle grain boundary density, and the change of substructural cell walls on the movement of magnetic domain walls, ensuring the clarity of the bonding interface, improving the magnetic permeability, and being beneficial to fully exert the functions of magnetic field line layered shunting and magnetic isolation.

[0020] Compared with the prior art, the heat treatment method for the structure of the additive manufacturing soft magnetic alloy - high-strength steel gradient composite material provided by the present invention can greatly improve the magnetic permeability of the FeNi50 soft magnetic alloy, ensure the clear integrity and high bonding strength of the bonding interface of the gradient material, and the magnetic shielding performance of the magnetic shielding housing is excellent. Brief Description of the Drawings

[0021] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, objectives, and advantages of the present invention will become more obvious:

[0022] Figure 1 It is a schematic diagram of the heat treatment process curve of a heat treatment method for improving the magnetic shielding performance of the structure of the additive manufacturing soft magnetic alloy - high-strength steel gradient composite material provided by the present invention;

[0023] Figure 2 It is the interfacial dilution rate situation after heat treatment of a typical product prepared by the present invention, and the dilution rate is controlled within the range of 0.01 mm;

[0024] Figure 3 It is a physical diagram of the bonding strength test specimen of the FeNi50 soft magnetic alloy layer and 12Cr13 high-strength steel prepared by the present invention. Detailed Embodiments

[0025] The following further elaborates in detail on a heat treatment method for improving the magnetic shielding performance of the structure of the additive manufacturing soft magnetic alloy - high-strength steel gradient composite material proposed by the present invention in combination with the drawings and specific embodiments. According to the following description and the claims, the advantages and features of the present invention will become clearer. It should be noted that the drawings all use very simplified forms and are supplemented with physical characterizations and performance measurement results to illustrate the operation process and actual effects of the present invention, including but not limited to the proposed material combinations and structural forms.

[0026] Example 1

[0027] In this embodiment, FeNi50 soft magnetic alloy material is used as the magnetic conductive layer, and 12Cr13 high-strength steel is used as the magnetic isolation layer and the structural strengthening layer to form a FeNi50-12Cr13-FeNi50 sandwich structure. The raw material FeNi50 soft magnetic alloy is in powder state, and the main chemical composition test shows Ni: 48.2wt%, C: 0.002wt%, O: 0.022wt%, S: 0.002wt%, P: 0.005wt%, Fe: Bal.

[0028] The additive manufacturing method of this magnetic shielding structure includes: First, form the first layer of FeNi50 soft magnetic alloy layer. The laser melting deposition forming process parameters used are laser power = 600W, spot diameter = 0.3mm, lift = 0.1mm, the thickness of the formed part is 0.4mm, and the magnetic properties of the formed part are tested to have a saturation magnetic induction intensity of B S = 1.1T and a maximum magnetic permeability of μ m = 4.88mH / m; Then laser melt deposit and form the 12Cr13 high-strength steel magnetic isolation layer. The forming process parameters are laser power = 1000W, spot diameter = 0.4mm, lift = 0.2mm. Multiple passes are overlapped to form the intermediate layer, and the forming thickness is 0.8mm; Finally, form the second layer of FeNi50 soft magnetic alloy layer. The laser melting deposition forming process parameters used are laser power = 800W, spot diameter = 0.4mm, lift = 0.2mm, and the forming thickness is 0.4mm. The final shielding layer forms a sandwich structure with 12Cr13 high-strength steel in the middle and FeNi50 soft magnetic alloy on both sides. The total thickness is 1.6mm. The middle 12Cr13 high-strength steel layer has good structural strength, and the FeNi50 soft magnetic alloys on both sides have excellent magnetic conductive properties. The double magnetic conductive layer structure can achieve the function of hierarchical shunt attenuation of the magnetic field, and the gradient structure interface can achieve multiple absorption and reflection of electromagnetic waves.

[0029] Verify the bonding strength between the FeNi50 soft magnetic alloy layer and the 12Cr13 high-strength steel (the physical object of the bonding strength test specimen is as Figure 3 described). Using the above process parameters, form a substrate of 12Cr13 high-strength steel and a cladding layer of FeNi50 soft magnetic alloy with thicknesses of 20mm and 5mm respectively. Prepare and test the pull-off specimens according to GB / T 12948—1991. The average pull-off strength is measured to reach 352MPa, indicating that the bonding interface has good bonding strength.

[0030] Then heat-treat the above shielding structure using a vacuum heat treatment furnace. The heat treatment process curve refers to Figure 1; First, it is heated to 630 °C at a heating rate of 20 °C / min and held for 15 min, then cooled in three steps. It is cooled to 450 °C at a furnace cooling rate of 15 °C / min, then cooled to 300 °C at a furnace cooling rate of 5 °C / min, and finally air-cooled to room temperature. The interface dilution rate after heat treatment is as shown in Figure 2 . After magnetic property testing, the saturation magnetic induction intensity of the directly formed FeNi50 soft magnetic alloy is B S = 1.15 T, and the maximum magnetic permeability is μ m = 0.69 mH / m. After heat treatment, the saturation magnetic induction intensity is B S = 1.11 T, and the maximum magnetic permeability is μ m = 5.93 mH / m. At the same time, as a comparative experiment of the heat treatment scheme, new specimens are prepared according to the above preparation process. In the heat treatment process, it is first heated to 1100 °C for high-temperature solution treatment and held for 4 h, and then the heat treatment is continued according to the above heat treatment process. After testing, its saturation magnetic induction intensity is B S = 1.1 T, and the maximum magnetic permeability is μ m = 4.88 mH / m. The magnetic properties are slightly reduced compared with the heat treatment method proposed in the present invention. The heat treatment method proposed in the present invention greatly improves the magnetic permeability of the magnetic conduction layer. At the same time, the clear bonding interface has a multi-layer reflection and attenuation effect on electromagnetic waves, and the performance of the magnetic shielding layer is greatly improved. In the case of the present invention, the magnetic shielding performance is tested by the shielding cover method, and the magnetic shielding coefficient (Shielding Factor, SF) is used to characterize the magnetic shielding effect of the structure. The definition of the magnetic shielding coefficient is as follows:

[0031]

[0032] Among them, H0 is the magnetic field intensity measured without a shielding cover, and H S is the magnetic field intensity measured with a magnetic shielding cover. The magnetic field intensity is measured using the FVM-400 type fluxgate meter produced by MEDA Company. The magnetic field intensity at the same point is tested. The measured SF after heat treatment is 24.8. Compared with the shielding cover structure in the directly formed state, the magnetic shielding effect is improved by about 87%.

[0033] Example 2

[0034] In this example, the shielding structure prepared in Example 1 is heat-treated using a vacuum heat treatment furnace. First, it is heated to 640 °C at a heating rate of 25 °C / min and held for 15 min, then cooled in three steps. It is cooled to 450 °C at a furnace cooling rate of 10 °C / min, then cooled to 300 °C at a furnace cooling rate of 8 °C / min, and finally air-cooled to room temperature. The magnetic field intensity is measured using the FVM-400 type fluxgate meter produced by MEDA Company. The magnetic field intensity at the same point is tested. The measured SF after heat treatment is 22.1.

[0035] Example 3

[0036] In this example, the shielding structure obtained in Example 1 was heat-treated. Using a vacuum heat treatment furnace, it was first heated to 635 °C at a heating rate of 22 °C / min and held for 15 min, and then cooled in three steps. It was cooled to 450 °C at a furnace cooling rate of 12 °C / min, then cooled to 300 °C at a furnace cooling rate of 7 °C / min, and finally air-cooled to room temperature. The magnetic field strength was measured using an FVM-400 type fluxgate meter produced by MEDA Company. The magnetic field strength at the same point was tested, and the measured SF after heat treatment was 20.8.

[0037] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A heat treatment method for improving the magnetic shielding performance of the structure of an additive manufacturing soft magnetic alloy-high strength steel gradient composite material, characterized in that, Including: The shielding layer prepared by the laser melting deposition process method is first heated to 630 - 640 °C at a heating rate of 20 - 25 °C / min and held for 15 - 20 min, then cooled in 3 steps. It is cooled to 440 - 460 °C at a furnace cooling rate of 10 - 15 °C / min, then cooled to 280 - 320 °C at a furnace cooling rate of 5 - 8 °C / min, and then air-cooled to room temperature.

2. The heat treatment method according to claim 1, characterized in that, The shielding layer of the FeNi50-12Cr13-FeNi50 sandwich structure is prepared by the laser melting deposition process method, where the FeNi50 soft magnetic alloy material is used as the magnetic conductive layer, and 12Cr13 high-strength steel is used as the magnetic isolation layer and the structure strengthening layer.

3. The heat treatment method according to claim 2, wherein The gradient structure layer is arranged in the order of FeNi50-12Cr13-FeNi50. The thickness of the FeNi50 single structure layer is 0.1 mm - 0.5 mm, the thickness of the 12Cr13 single structure layer is 0.2 mm - 1 mm, and the thickness range of the shielding layer is 0.4 mm - 2 mm.

4. The heat treatment method according to claim 2, characterized in that The composition of the FeNi50 soft magnetic alloy material is Ni: 46.8 - 51.2 wt%, C: 0.002 - 0.006 wt%, O: 0.020 - 0.032 wt%, S: 0.001 - 0.004 wt%, P: 0.005 - 0.012 wt%, Fe: Bal.

5. The heat treatment method according to claim 1, characterized in that, The dilution rate range of the combined interface of the gradient layer after heat treatment does not exceed 0.05 mm.

6. A soft magnetic alloy-high strength steel gradient composite material structure obtained by the heat treatment method according to claim 1.

7. An application of the soft magnetic alloy-high strength steel gradient composite material structure as claimed in claim 6 in aerospace precision instruments and equipment.

8. The application according to claim 7, characterized in that, The aerospace precision instruments and equipment include aerospace fiber optic gyroscopes and satellite rubidium clocks.

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