A method for brazing large size joints of SiC and Al / SiC composite material with the aid of a three-dimensional grid magnesium aluminate composite interlayer

Abstract

The application discloses a method for brazing large-size joints of SiC and Al / SiC composite materials by using a three-dimensional grid magnesium aluminate composite interlayer, and belongs to the field of brazing connection of space mirrors. The application aims at solving the problem of residual stress in the brazing connection between a large-size SiC space mirror and an Al / SiC composite support. The method comprises the following steps: 1, preparation of a three-dimensional grid MgAl2O4 composite interlayer; 2, compounding of the three-dimensional grid MgAl2O4 composite interlayer and a brazing filler metal; 3, assembling; and 4, brazing. The application is used for brazing large-size joints of SiC and Al / SiC composite materials by using a three-dimensional grid magnesium aluminate composite interlayer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of brazing connection of space mirrors. BACKGROUND

[0002] In view of the urgent need for increasingly complex and precise space observation and exploration missions, the new generation of space mirrors uses SiC as the mirror material due to its light weight, high specific stiffness and good thermal stability, and uses Al / SiC composite material (SiC content > 40%) as the annular support body. Currently, the SiC mirror and the Al / SiC composite material support body are still connected by traditional mechanical flange connection, which not only significantly increases the weight of the optical system, but also easily causes deformation at the connection, thereby damaging the optical precision and thermal stability, and is difficult to meet the increasingly stringent requirements of space missions. In contrast, brazing connection can significantly reduce the weight of the structure, has good connection strength, is not prone to deformation, and helps to improve the precision and thermal stability of the optical system, making it an ideal alternative.

[0003] However, there is relatively little research on the brazing connection between SiC and Al / SiC composite materials, and existing research mainly focuses on the brazing of each of the two materials and their brazing systems with other materials.

[0004] Although domestic research has verified the feasibility of brazing connection of dissimilar materials, the research on brazing connection of SiC and Al / SiC composite materials is still in its infancy, and the connection of the two still faces great difficulties. Due to the large difference in the thermal expansion coefficients of SiC and Al / SiC composite materials (SiC: 4.0 x 10 -6 / K, Al / SiC composite material: 12.0 x 10 -6 / K), the joint will generate a large amount of residual stress after brazing. In particular, the residual stress increases sharply as the size of the joint increases, which easily causes cracks at the brazing interface, greatly weakening the mechanical properties of the joint, and even making it impossible to achieve effective connection. In existing research, the interface size of brazing connection of dissimilar components is mostly less than 100 mm. However, the welding position of the new generation of SiC space mirror and Al / SiC composite material support body dissimilar components has a diameter of 200 mm, and such a large size of brazed joint has great difficulty in residual stress relief, and there are few reports at home and abroad. Therefore, how to relieve the residual stress of the joint is a key problem in achieving high-quality brazing connection of large-size SiC and Al / SiC composite materials. SUMMARY

[0005] The present application solves the problem of residual stress in the brazing connection between the existing large-size SiC space mirror and the Al / SiC composite material support body, and further provides a method of brazing large-size joints of SiC and Al / SiC composite materials assisted by three-dimensional grid magnesium aluminate composite interlayer.

[0006] A method for brazing large-sized joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as an auxiliary is provided, which is carried out in the following steps:

[0007] 1. Preparation of three-dimensional grid MgAl2O4 composite intermediate layer:

[0008] MgAl2O4 particles are added to alcohol to obtain a spraying liquid, which is sprayed on both sides of the porous Nb network skeleton and then sintered to obtain a three-dimensional grid MgAl2O4 composite intermediate layer;

[0009] Composite of 2.3D grid MgAl2O4 composite intermediate layer and solder:

[0010] The three-dimensional grid MgAl2O4 composite intermediate layer and AlSiMg solder powder are placed in a vacuum container, and the three-dimensional grid MgAl2O4 composite intermediate layer is buried in the AlSiMg solder powder, and then a vacuum filling process is performed to obtain the AlSiMg solder-filled composite intermediate layer;

[0011] 3. Assembly:

[0012] Placing the composite intermediate layer filled with AlSiMg brazing filler metal between the SiC reflector and the surface to be welded of the Al / SiC composite material support to obtain a welded part;

[0013] 4. Brazing:

[0014] The parts to be welded are placed in a vacuum furnace to evacuate the vacuum, and then heated for brazing, thereby completing a method for brazing large-size joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as an auxiliary.

[0015] The beneficial effects of the present invention are:

[0016] 1. Aiming at the problem of brazing connection between SiC reflector and Al / SiC composite support in space observation and detection missions, the three-dimensional grid MgAl2O4 composite intermediate layer auxiliary brazing method proposed in this invention can effectively alleviate the residual stress caused by the difference in thermal expansion coefficient between SiC and Al / SiC composite, especially in large-scale joints with welding area exceeding 200mm. The thermal expansion coefficient of MgAl2O4 spinel is close to that of SiC and Al / SiC composite (8.5×10 -6 / K), making it a critical component of the brazing process. By regulating the gradient transition of the thermal expansion coefficient, stresses in the joint area are dispersed, significantly reducing the risk of cracks and deformation. This is an effective means of addressing the problem of high residual stresses in large-scale joints.

[0017] 2. MgAl2O4 spinel has extremely high chemical activity, high temperature stability, and excellent wettability. In particular, it can form a good interface bond with Al-based solder, which can effectively improve the wettability of Al-based solder. It does not react with Al-based solder, and can effectively avoid the formation of pores, inclusions and cracks in the joint.

[0018] 3. Porous Nb has a moderate thermal expansion coefficient (7.5×10 -6 / K) and has good mechanical properties. It is used as a skeleton material to effectively support the reinforcement phase while maintaining the stability and uniformity of the joint.

[0019] 4. Compared to traditional mechanical flange connections, this method significantly reduces structural weight. This significantly reduces the mass of the optical system, helping to lower launch costs and improve maneuverability and stability during space missions. It also reduces mechanical deformation at the joint, significantly improving the accuracy of the optical system. Brazed joints offer greater stability than traditional mechanical connections, effectively preventing optical errors caused by joint deformation and ensuring the mirror maintains optimal operating conditions even in high-temperature environments or those subject to sudden temperature fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 To compare the interface between the brazing filler metal and SiC in the large-scale joint of SiC and Al / SiC composite materials without adding the three-dimensional grid magnesium aluminate composite intermediate layer in Experiment 1;

[0021] Figure 2 The interface between the brazing filler metal and SiC in a large-scale joint of SiC and Al / SiC composite materials based on a three-dimensional grid magnesium aluminate composite intermediate layer in Example 1, (a) the interface between the brazing filler metal and SiC, (b) the polycrystalline diffraction spots of SiC, (c) the inverse Fourier transform of Figure (a), (d) the diffraction spots of the brazing filler metal in Figure (c), (e) the geometric phase analysis orientation, (f) ε xx The strain of the joint in the direction, (g)ε yy The strain of the joint in the direction;

[0022] Figure 3 The stress-strain curves of large-scale joints of SiC and Al / SiC composite materials prepared in Example 1 and Comparative Experiments 1 and 2;

[0023] Figure 4 2. Simulated strain changes of large-scale joints of SiC and Al / SiC composite materials prepared in Example 1 and Comparative Experiment 1. (a) is Comparative Experiment 1, and (b) is Example 1. DETAILED DESCRIPTION

[0024] Specific embodiment one: the method of the embodiment is a method for brazing a large-size joint of SiC and Al / SiC composite material with the aid of a three-dimensional grid magnesium aluminate composite interlayer, which is performed according to the following steps:

[0025] I. Preparation of the three-dimensional grid MgAl2O4 composite interlayer:

[0026] MgAl2O4 particles are added to alcohol to obtain a spraying liquid, the spraying liquid is sprayed on both sides of the porous Nb network skeleton, and then sintering treatment is performed to obtain the three-dimensional grid MgAl2O4 composite interlayer;

[0027] II. Compounding of the three-dimensional grid MgAl2O4 composite interlayer and the filler metal:

[0028] The three-dimensional grid MgAl2O4 composite interlayer and the AlSiMg filler metal powder are placed in a vacuum container, and the three-dimensional grid MgAl2O4 composite interlayer is buried in the AlSiMg filler metal powder, and then vacuum filling treatment is performed to obtain the AlSiMg filler metal filled composite interlayer;

[0029] III. Assembly:

[0030] The AlSiMg filler metal filled composite interlayer is placed between the SiC mirror and the Al / SiC composite material support to be welded to obtain a to-be-welded piece;

[0031] IV. Brazing:

[0032] The to-be-welded piece is placed in a vacuum furnace for vacuumizing, and then heating and brazing are performed, thereby completing the method of brazing a large-size joint of SiC and Al / SiC composite material with the aid of a three-dimensional grid magnesium aluminate composite interlayer.

[0033] To realize the gradient transition of the thermal expansion coefficient of the joint area, it is crucial to select the reinforcing phase and the grid skeleton with a matching thermal expansion coefficient. The thermal expansion coefficient of porous Nb is 7.5×10 -6 / K, which is between SiC and Al / SiC composite material, and is the ideal grid skeleton of the embodiment. As the reinforcing phase of Al-based filler metal, MgAl2O4 spinel has a series of unique advantages, making it have potential in improving the performance of filler metal. First, MgAl2O4 spinel has very good high-temperature stability and can maintain structural stability in high-temperature environments. The melting point of MgAl2O4 spinel is very high, about 2000°C, which enables it to withstand high temperatures during the brazing process of Al-based filler metal without degradation or reaction. Second, MgAl2O4 spinel can improve the wettability of Al-based filler metal and does not react with Al-based filler metal, which can help the filler metal flow better and reduce the formation of pores, inclusions and cracks, thereby improving the quality of the brazed joint. In addition, the thermal expansion coefficient of MgAl2O4 spinel is 8.5×10-6 / K, which is similar to porous Nb, can effectively reduce the stress caused by temperature changes, thereby reducing the risk of cracks and deformation during the cooling process. It is an ideal particle reinforcement phase for Al-based solders.

[0034] This specific embodiment proposes a novel method for brazing SiC and Al / SiC composite materials using a three-dimensional grid MgAl2O4 composite intermediate layer to achieve a gradient transition in the thermal expansion coefficient of the joint region, thereby alleviating high residual stress in large-scale joints. This specific embodiment selects MgAl2O4 with matching thermal expansion coefficients as the reinforcing phase and porous Nb as the grid skeleton. Leveraging the advantages of the reinforcing phase properties and uniform dispersion of the network structure, this method regulates the stress distribution state of the joint, improves the joint mechanical properties, and achieves high-quality brazing of heterogeneous components between large-scale SiC space reflectors and Al / SiC composite support bodies. This provides core applied basic theory and key technical support for the development of a new generation of space reflectors.

[0035] The beneficial effects of this embodiment are:

[0036] 1. To address the brazing connection problem between SiC reflectors and Al / SiC composite supports in space observation and detection missions, the three-dimensional grid MgAl2O4 composite intermediate layer assisted brazing method proposed in this embodiment can effectively alleviate the residual stress caused by the difference in thermal expansion coefficient between SiC and Al / SiC composites, especially in large-scale joints with a welding area exceeding 200mm. The thermal expansion coefficient of MgAl2O4 spinel is close to that of SiC and Al / SiC composites (8.5×10 -6 / K), making it a critical component of the brazing process. By regulating the gradient transition of the thermal expansion coefficient, stresses in the joint area are dispersed, significantly reducing the risk of cracks and deformation. This is an effective means of addressing the problem of high residual stresses in large-scale joints.

[0037] 2. MgAl2O4 spinel has extremely high chemical activity, high temperature stability, and excellent wettability. In particular, it can form a good interface bond with Al-based solder, which can effectively improve the wettability of Al-based solder. It does not react with Al-based solder, and can effectively avoid the formation of pores, inclusions and cracks in the joint.

[0038] 3. Porous Nb has a moderate thermal expansion coefficient (7.5×10 -6 / K) and has good mechanical properties. It is used as a skeleton material to effectively support the reinforcement phase while maintaining the stability and uniformity of the joint.

[0039] 4. Compared to traditional mechanical flange connections, this method significantly reduces structural weight. This significantly reduces the mass of the optical system, helping to lower launch costs and improve maneuverability and stability during space missions. It also reduces mechanical deformation at the joint, significantly improving the accuracy of the optical system. Brazed joints offer greater stability than traditional mechanical connections, effectively preventing optical errors caused by joint deformation and ensuring the mirror maintains optimal operating conditions even in high-temperature environments or those subject to sudden temperature fluctuations.

[0040] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass percentage of the alcohol in step 1 is 50% to 80%. Other aspects are the same as specific embodiment 1.

[0041] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the mass ratio of MgAl2O4 particles to alcohol in step 1 is 1:(5-10). Other aspects are the same as specific embodiment 1 or 2.

[0042] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the particle size of the MgAl2O4 particles in step 1 is 5 μm to 15 μm. Other aspects are the same as those of specific embodiment 3.

[0043] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the PPI of the porous Nb network skeleton in step 1 is 30 ppi to 70 ppi and the thickness is 0.5 mm to 3 mm. Other aspects are the same as specific embodiments 1 to 4.

[0044] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: in step 1, the spraying liquid is sprayed on the porous Nb network skeleton, specifically according to the following steps: spraying at a spraying pressure of 0.5MPa to 2MPa and a spraying distance of 10cm to 20cm, and the spraying load is 0.1g / cm 2 ~0.5g / cm 2 The rest is the same as the specific implementation modes 1 to 5.

[0045] In this embodiment, MgAl2O4 particles are loaded onto the porous Nb lattice skeleton by spraying. Precise control of the spraying pressure and spraying time ensures uniform distribution of the reinforcement phase and enables effective coverage without destroying the lattice skeleton structure.

[0046] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the sintering treatment described in step 1 is specifically to increase the temperature to 300°C to 500°C at a heating rate of 5°C / min to 10°C / min, and to maintain the temperature at 300°C to 500°C for 5 to 10 minutes. Then, the temperature is increased to 1000°C to 1400°C at a heating rate of 5°C / min to 10°C / min, and to maintain the temperature at 1000°C to 1400°C for 1 to 4 hours. Other aspects are the same as specific embodiments 1 to 6.

[0047] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the vacuum filling process described in step 2 is specifically performed as follows: vacuuming to a pressure of 0.01 MPa to 0.1 MPa, then maintaining the pressure at 0.01 MPa to 0.1 MPa for 5 to 10 minutes, and then releasing the vacuum at a rate of 0.05 MPa / min to 0.1 MPa / min until the pressure returns to normal. Other aspects are the same as Specific Embodiments 1 to 7.

[0048] Specific Embodiment 9: This embodiment differs from Specific Embodiments 1 to 8 in that the SiC reflector and Al / SiC composite material support described in step 3 are pretreated SiC reflector and Al / SiC composite material support. The pretreatment is performed according to the following steps: the surfaces to be welded of the SiC reflector and Al / SiC composite material support are mechanically polished to a surface roughness Ra of 0.2 μm to 0.5 μm after polishing, and then ultrasonically cleaned for 10 to 15 minutes at room temperature and an ultrasonic power of 50 W to 100 W. Other aspects are the same as Specific Embodiments 1 to 8.

[0049] To ensure the strength of the brazed joint, this embodiment must ensure that the surface roughness of the weld area is sufficient to promote wetting and adhesion of the solder. Surface treatment with an Ra value within the range of 0.2μm to 0.5μm ensures good wettability while avoiding uneven solder flow caused by excessive surface roughness.

[0050] Specific embodiment 10: The difference between this embodiment and the first to ninth embodiments is that in step 4, the workpiece to be welded is placed in a vacuum furnace and vacuumed for 10 to 20 minutes until the vacuum degree is 1×10 -3 Pa~5×10 -3Pa, then heated to 200-300℃ at a heating rate of 5-10℃ / min, and kept at the temperature of 200-300℃ for 5-10min, then heated to 550-650℃ at a heating rate of 5-10℃ / min, and kept at the temperature of 550-650℃ for 5-60min, and finally cooled to room temperature at a cooling rate of 5-10℃ / min. The other steps are the same as those in Embodiment 1-9.

[0051] The present embodiment is performed in a vacuum environment, which can prevent the oxide in the air from contaminating the welding area and ensure the purity of the joint. The setting of the vacuum degree and the appropriate vacuum time help the filler metal to be fully filled in the composite layer and achieve good wetting.

[0052] The beneficial effects of the present application are verified by the following examples:

[0053] Example 1:

[0054] A method for assisting the brazing of a large-size joint of SiC and Al / SiC composite material by a three-dimensional grid MgAl2O4 composite interlayer, which is performed according to the following steps:

[0055] I. Preparation of a three-dimensional grid MgAl2O4 composite interlayer:

[0056] MgAl2O4 particles are added to alcohol to obtain a spraying liquid, and the spraying liquid is sprayed on both sides of the porous Nb network skeleton under the conditions of a spraying pressure of 0.5MPa and a spraying distance of 10cm, and the spraying load is 0.1g / cm 2 at a heating rate of 5℃ / min to 300℃, and kept at the temperature of 300℃ for 5min, then heated to 1200℃ at a heating rate of 5℃ / min, and kept at the sintering temperature of 1200℃ for 1h to obtain a three-dimensional grid MgAl2O4 composite interlayer;

[0057] The mass percentage of the alcohol is 80%;

[0058] The mass ratio of the MgAl2O4 particles to the alcohol is 1:5;

[0059] The particle size of the MgAl2O4 particles is 5μm;

[0060] The PPI of the porous Nb network skeleton is 30ppi, the shape is annular, the inner diameter is 200mm, the outer diameter is 200.5mm, and the thickness is 0.5mm;

[0061] II. The combination of the three-dimensional grid MgAl2O4 composite interlayer and the filler metal:

[0062] The three-dimensional grid MgAl2O4 composite interlayer and AlSiMg solder powder are placed in a vacuum container, and the three-dimensional grid MgAl2O4 composite interlayer is buried in the AlSiMg solder powder. The container is then evacuated to a pressure of 0.1 MPa, and then maintained at a pressure of 0.1 MPa for 5 minutes. The vacuum is then released at a rate of 0.05 MPa / min until the pressure returns to normal, thereby obtaining a composite interlayer filled with AlSiMg solder.

[0063] 3. Assembly:

[0064] Placing the composite intermediate layer filled with AlSiMg brazing filler metal between the SiC reflector and the surface to be welded of the Al / SiC composite material support to obtain a welded part;

[0065] The SiC reflector is circular with a diameter of 200 mm; the Al / SiC composite material support is annular with an inner diameter of 200.5 mm and an outer diameter of 220 mm; the SiC reflector and the Al / SiC composite material support are pretreated SiC reflector and Al / SiC composite material support; the pretreatment is performed according to the following steps: mechanically polishing the surfaces to be welded of the SiC reflector and the Al / SiC composite material support to a surface roughness Ra of 0.2 μm after polishing, and then ultrasonically cleaning them at room temperature and an ultrasonic power of 50 W for 10 minutes;

[0066] 4. Brazing:

[0067] Place the workpiece to be welded in a vacuum furnace and evacuate for 10 minutes until the vacuum degree is 5×10 -3 Pa, then heated to 200°C at a heating rate of 10°C / min, and kept warm at 200°C for 10 minutes, then heated to 620°C at a heating rate of 10°C / min, and kept warm at 620°C for 10 minutes, and finally cooled to room temperature at a cooling rate of 5°C / min to obtain a large-scale joint of SiC and Al / SiC composite materials based on a three-dimensional grid magnesium aluminate composite intermediate layer.

[0068] Comparative Experiment 1: This comparative experiment differs from Example 1 in that a three-dimensional magnesium aluminate composite interlayer was not used. Instead, the SiC reflector and the Al / SiC composite support were brazed directly using AlSiMg brazing filler metal. This resulted in a large-scale SiC-Al / SiC composite joint without the addition of a three-dimensional magnesium aluminate composite interlayer. All other aspects were the same as in Example 1.

[0069] Comparative Experiment 2: The difference between this comparative experiment and Example 1 is that: the spraying in Step 1 is cancelled; the porous Nb network skeleton and the AlSiMg filler powder are placed in a vacuum container in Step 2, and the porous Nb network skeleton is buried in the AlSiMg filler powder. The others are the same as Example 1.

[0070] Figure 1 The interface between the filler and SiC of the SiC and Al / SiC composite material large-size joint without adding the three-dimensional grid magnesium aluminate composite interlayer in Comparative Experiment 1. It can be seen from the figure that the wettability of the filler to the SiC interface is poor, and the interface has many pores.

[0071] Figure 2 The interface between the filler and SiC of the SiC and Al / SiC composite material large-size joint based on the three-dimensional grid magnesium aluminate composite interlayer in Example 1, (a) the interface between the filler and SiC, (b) the polycrystalline diffraction spot of SiC, (c) the inverse Fourier transform of figure (a), (d) the diffraction spot of the filler in figure (c), (e) the geometric phase analysis direction, (f) ε xx the strain of the joint in the x direction, (g) the strain of the joint in the y direction; it can be seen from the figure that there is no pore, inclusion and crack in the joint, the interface between AlSiMg and SiC presents interdiffusion between atoms, it can be found from the inverse Fourier transform that there is dispersed MgAl2O4 in the weld, which indicates that it improves the wettability of the joint. The geometric phase analysis of the joint shows that the strain occurring at the interface is less than 5%, and the three-dimensional grid MgAl2O4 composite interlayer effectively relieves the large deformation after welding. yy

[0072] Test according to GB / T 11363-2008 standard; Figure 3 The stress-strain curve of the SiC and Al / SiC composite material large-size joint prepared in Example 1 and Comparative Experiments 1-2. It can be seen that when no interlayer is added (Original), the joint presents the characteristics of brittle fracture, the joint shear strength is 51.7 MPa, and the fracture strain is 12%. After adding the porous Nb interlayer (Porous-Nb), the joint shear strength is 58.0 MPa, and the fracture strain is 26%. Although the toughness of the joint is increased, the joint still presents the characteristics of brittle fracture. After adding the three-dimensional grid MgAl2O4 composite interlayer (Porous-Nb@MgAl2O4), the joint shear strength reaches 90.1 MPa, and the fracture strain is 27%. At this time, the fracture mode changes from brittle fracture to ductile fracture. The joint strength is obviously improved.

[0073] Figure 4 ​Figure 1 shows the simulated strain changes of a large-scale joint of SiC and Al / SiC composites prepared in Example 1 and Comparative Experiment 1. (a) is Comparative Experiment 1, and (b) is Example 1. As can be seen, without the addition of an interlayer, the SiC exhibits significant strain near the weld. Adding the three-dimensional mesh MgAl2O4 composite interlayer significantly reduces this strain, significantly improving the accuracy of the optical system.

Claims

1. A method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer, characterized in that It is carried out in the following steps:

1. Preparation of three-dimensional grid MgAl2O4 composite intermediate layer: MgAl2O4 particles are added to alcohol to obtain a spraying liquid, which is sprayed on both sides of the porous Nb network skeleton and then sintered to obtain a three-dimensional grid MgAl2O4 composite intermediate layer; Composite of 2.3D grid MgAl2O4 composite intermediate layer and solder: The three-dimensional grid MgAl2O4 composite intermediate layer and AlSiMg solder powder are placed in a vacuum container, and the three-dimensional grid MgAl2O4 composite intermediate layer is buried in the AlSiMg solder powder, and then a vacuum filling process is performed to obtain the AlSiMg solder-filled composite intermediate layer; 3. Assembly: Placing the composite intermediate layer filled with AlSiMg brazing filler metal between the SiC reflector and the surface to be welded of the Al / SiC composite material support to obtain a welded part; 4. Brazing: The parts to be welded are placed in a vacuum furnace to evacuate the vacuum, and then heated for brazing, thereby completing a method for brazing large-size joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as an auxiliary.

2. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The mass percentage of the alcohol described in step 1 is 50% to 80%.

3. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The mass ratio of the MgAl2O4 particles to the alcohol described in step 1 is 1:(5-10).

4. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The particle size of the MgAl2O4 particles described in step 1 is 5 μm to 15 μm.

5. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The porous Nb network skeleton described in step 1 has a PPI of 30 ppi to 70 ppi and a thickness of 0.5 mm to 3 mm.

6. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that In step 1, the spraying liquid is sprayed on the porous Nb network skeleton, specifically according to the following steps: spraying at a spraying pressure of 0.5MPa to 2MPa and a spraying distance of 10cm to 20cm, and the spraying load is 0.1g / cm 2 ~0.5g / cm 2 .

7. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The sintering treatment described in step 1 is specifically to heat up to 300°C~500°C at a heating rate of 5°C / min~10°C / min, and keep it at 300°C~500°C for 5min~10min, then heat up to 1000°C~1400°C at a heating rate of 5°C / min~10°C / min, and keep it at sintering temperature of 1000°C~1400°C for 1h~4h.

8. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The vacuum filling process described in step 2 is specifically carried out in the following steps: vacuuming to a pressure of 0.01MPa to 0.1MPa, then maintaining the pressure at 0.01MPa to 0.1MPa for 5min to 10min, and then releasing the vacuum at a speed of 0.05MPa / min to 0.1MPa / min until the pressure returns to normal.

9. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that The SiC reflector and Al / SiC composite material support described in step 3 are pretreated SiC reflector and pretreated Al / SiC composite material support; the pretreatment is carried out according to the following steps: mechanically polishing the surfaces to be welded of the SiC reflector and the Al / SiC composite material support, and the surface roughness Ra after polishing is 0.2μm to 0.5μm, and then ultrasonically cleaning for 10min to 15min at room temperature and an ultrasonic power of 50W to 100W.

10. The method for brazing large-scale joints of SiC and Al / SiC composite materials using a three-dimensional grid magnesium aluminate composite intermediate layer as claimed in claim 1, characterized in that In step 4, the workpiece to be welded is placed in a vacuum furnace and vacuumed for 10 to 20 minutes until the vacuum degree reaches 1×10 -3 Pa~5×10 -3 Pa, then heat to 200℃~300℃ at a heating rate of 5℃ / min~10℃ / min, and keep warm at 200℃~300℃ for 5min~10min, then heat to 550℃~650℃ at a heating rate of 5℃ / min~10℃ / min, and keep warm at 550℃~650℃ for 5min~60min, and finally cool to room temperature at a cooling rate of 5℃ / min~10℃ / min.

Images