Forming method for aluminum-clad sandwich Cf / Al composite fan blade

Abstract

A forming method for an aluminum-clad sandwich Cf / Al composite fan blade according to the present invention belongs to the field of carbon fiber reinforced metal matrix composites. The method steps are as follows: preparing a carbon fiber preform; manufacturing a forming female die for the fan blade; positioning and installing the carbon fiber preform in the female die; placing the female die equipped with the carbon fiber preform in a liquid-solid infiltration extrusion forming device, installing a seal above the extrusion cylinder of the device, and performing an airtightness test on the melting furnace; preparing the fan blade by liquid-solid pressure infiltration; demolding and sampling. The present invention adopts a liquid-solid infiltration extrusion process that integrates alloy melting, transportation, pouring, and forming, and can achieve controllable integrated forming of the aluminum cladding thickness, changing the traditional mode of separately preparing the metal matrix composite and the cladding successively. It solves the technical problems such as surface fiber breakage, cracking, and matrix tearing caused by cutting processing after the forming of the Cf / Al composite fan blade, damaging the surface integrity and continuity of the fan blade, and reducing the dimensional accuracy and corrosion resistance characteristics.

Description

Technical Field

[0001] The present invention belongs to the field of carbon fiber reinforced metal matrix composites (MMCS), and particularly relates to a forming method for an aluminum-clad sandwich Cf / Al composite fan blade. Background Art

[0002] Aero-engines are regarded as the "pearl on the crown of modern industry". As the core component of the fan section, fan blades are regarded as the top priority. To meet the requirements of engines for "higher, faster, quieter, and lower cost", new materials with high strength, high modulus, better heat resistance, lighter weight, and higher impact resistance are needed.

[0003] Currently, aero-engine blades are mainly made of titanium alloys and fiber-reinforced resin matrix composites. Titanium alloy blades are heavy, have a high fuel consumption rate, and are not easy to machine. For carbon fiber-reinforced resin matrix composite fan blades, their forming process is flexible, and their structure and functions are designable. However, resin matrix composite blades have disadvantages such as more processes, poor high-temperature resistance, and easy aging. Carbon fiber-reinforced aluminum matrix composites (Cf / Al) have advantages such as high temperature resistance, low density, high specific strength and specific stiffness, and high dimensional stability. Using them to manufacture aero-engine fan blades can overcome the problems of heavy weight, high fuel consumption, and difficult machining of titanium alloys; at the same time, it also solves the problems of easy aging and moisture absorption of resin matrix composites and difficulty in ensuring strength in high-temperature environments. Currently, boron fiber (Bf), carbon fiber (Cf), and SiC particle-reinforced aluminum matrix composites are more studied and applied in the engineering field. Compared with Cf / Al composites, boron fibers have a larger diameter and higher manufacturing cost, and the processing difficulty of SiC / Al composites (the manufacturing cost is also relatively high) is greater. The working temperature of the fan blades at the low-temperature end of the engine will not be higher than the failure temperature of Cf / Al composites. If Cf / Al composites are used to manufacture the fan blades at the low-temperature end of the engine, their strength and other performance requirements can be met, and it has better economy.

[0004] The prerequisite for the application of Cf / Al composites in aero-engine fan blades is that they must meet the actual dimensions, shapes, and position accuracies. However, research shows that due to the large differences in hardness, plasticity, and machinability between the reinforcement and the matrix of Cf / Al composites, fiber breakage, debonding, interlayer cracking, and matrix tearing will occur during cutting, which destroys the continuity and integrity of the fan blade surface, reduces dimensional accuracy and corrosion resistance characteristics, and generates stress concentration, making them unable to be directly put into use.

[0005] In addition, it is worth noting that although the material has excellent tensile and bending properties, its impact resistance is relatively lower than that of the matrix alloy. The energy absorption process mainly relies on fiber fracture, debonding, and encapsulation, while lightweight alloys (such as Al, Mg, Ti, etc.) can achieve energy absorption through plastic deformation. If this material is directly applied to the fan blade, its performance will be affected. If an alloy layer with a controllable thickness is prepared on its surface layer, this problem can be effectively solved. In the prior art, an aluminum coating was prepared on the surface of the composite material by using the oxyacetylene flame spraying technology. The results show that the preparation of the aluminum coating effectively improves the high-temperature impact resistance and electromagnetic shielding performance of the material. However, before preparing the aluminum coating, the surface of the composite material needs to be processed first to make it flat. Secondly, this process has high requirements for equipment and environment, and the preparation efficiency is relatively low. Most importantly, the thickness of the coating prepared by this technology is only 150μm, and there are microcracks at the interface, which cannot be used for secondary cutting processing.

[0006] Therefore, there is an urgent need in the art to propose a forming method for an aluminum-clad sandwich Cf / Al composite fan blade to achieve the one-time forming of the aluminum cladding and the core Cf / Al composite material, in order to solve the above technical problems. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the present invention provides a forming method for an aluminum-clad sandwich Cf / Al composite fan blade, which uses a liquid-solid infiltration extrusion process to prepare the aluminum-clad sandwich Cf / Al composite fan blade to replace the traditional titanium alloy and resin-based composite fan blades. Among them, the liquid-solid infiltration extrusion process integrates alloy melting, transportation, pouring, and forming, and can realize the controllable integrated forming of the aluminum cladding thickness on the surface of the Cf / Al composite material, changing the traditional mode of separately preparing the metal matrix composite material and the cladding first, and realizing the low-cost and high-efficiency preparation of the fan blade. The present invention solves the technical problems such as the surface fiber breakage, cracking, and matrix tearing of the Cf / Al composite fan blade after forming, which damage the surface integrity and continuity of the fan blade, and reduce the dimensional accuracy and corrosion resistance characteristics.

[0008] The present invention provides a technical solution: a forming method for an aluminum-clad sandwich Cf / Al composite fan blade, which is characterized in that the specific steps are as follows:

[0009] Step 1: Prepare a carbon fiber preform; use carbon fiber non-woven fabric as the reinforcement, cut and stitch the carbon fiber non-woven fabric according to the model structure of the fan blade body and the tenon, to obtain the carbon fiber preform of the fan blade; and set a shape-preserving positioning structure at both ends of the carbon fiber preform.

[0010] Step 2: Make a forming female die for the fan blade.

[0011] The end face of the female die is provided with a cavity that is consistent with the outer shape structure of the carbon fiber preform and enlarged in equal proportion, and positioning grooves are respectively arranged on the solid parts of the female die at both ends of the cavity;

[0012] Step 3: Positioning and installing the carbon fiber preform in the female die;

[0013] Place the carbon fiber preform in the cavity of the female die, and insert the shape-preserving positioning structures at both ends into the positioning grooves of the female die to ensure that the carbon fiber preform is suspended in the cavity and does not contact the inner wall of the cavity; the width of the gap between the inner wall of the cavity and the carbon fiber preform is the thickness of the aluminum coating layer;

[0014] Step 4: Place the female die with the carbon fiber preform in the liquid-solid infiltration extrusion forming equipment, install a seal above the extrusion cylinder of the equipment, and conduct an airtightness test on the melting furnace;

[0015] Step 5: Prepare the fan blade by liquid-solid pressure infiltration;

[0016] First, melt the aluminum alloy under the protection of an argon atmosphere. When the pouring temperature is reached, open the valve of the argon gas cylinder, transport the molten aluminum in the melting furnace to the extrusion cylinder, and then close the valve of the gas cylinder;

[0017] Then, start the liquid-solid infiltration extrusion forming equipment, control the punch to quickly move downward until it contacts the seal. At the moment of contact, slowly move downward by point pressure, and the pressure shall not be higher than 0.5 - 2 MPa. Keep the pressure for 3 - 5 s to make the molten aluminum first flow into the gap between the preform and the cavity for filling to form an aluminum coating layer to prevent the bending and displacement of the carbon fiber preform; then instantaneously pressurize to 10 - 15 MPa, stop pressurizing, keep the pressure for 3 - 5 s, and then gradually pressurize to 40 - 55 MPa, stop pressurizing, keep the pressure for 10 - 25 s, and then reduce the pressure to 30 - 40 MPa, keep the pressure for 10 hours to infiltrate the molten aluminum into the carbon fiber preform to form a core layer;

[0018] Finally, turn off the power supply of the equipment during the pressure-holding process to form the aluminum-coated sandwich Cf / Al composite fan blade in the forming equipment at one time;

[0019] Step 6: Demold and sample; after the equipment cools down to room temperature, withdraw the female die, and after demolding, obtain the aluminum-coated sandwich Cf / Al composite fan blade.

[0020] A further technical solution of the present invention is that in the above step 1, a T700-12K unidirectional carbon fiber non-woven fabric is used as the reinforcement, and the preforms of the split blade body and the tenon are cut and sewn according to the model structure of the fan blade body and the tenon, and then the split blade body and the tenon are spliced and sewn into an integral carbon fiber preform;

[0021] The method for sewing the carbon fiber non-woven preform is to lay it layer by layer from the inside out, from short to long, that is, when laying, first lay the preform at the small-size central part, and then lay it from the inside out and from small to large in sequence; after the separate laying of the blade body and the tenon head is completed, the overall stitching and fixing are carried out by using the needle punching stitching technology in the transition area of the connection section between the blade body and the tenon head; the stitching process unfolds in a spiral manner from the center to the edge, and the needle punching spacing needs to be kept at 2.0 - 5.0 cm.

[0022] A further technical solution of the present invention is that the shape-preserving positioning structure in the step 1 includes a blade body hanging ear and a tenon head hanging ear. The blade body hanging ear has the same bending curvature as the blade body, and the tenon head hanging ear is a straight line;

[0023] The preparation method of the hanging ear is as follows: First, fold two single-layer carbon cloths respectively. The folded end of the crease is the closed end, and the opposite end of the crease is the open end; then, insert the open ends of the two folded carbon cloths into the interlayer of the carbon fiber preform at the ends of the blade body and the tenon head respectively, and stitch and fix them; then insert metal wires along the crease into the closed ends of the two folded carbon cloths to obtain the blade body hanging ear and the tenon head hanging ear; finally, insert the blade body hanging ear and the tenon head hanging ear into the positioning grooves respectively, and realize the shape preservation and positioning of the carbon fiber preform in the female die through the clamping connection between the folded end inserted with the metal wire and the positioning groove.

[0024] A further technical solution of the present invention is that the female die is a cylindrical structure, and the cavity of its die cavity for accommodating the tenon head is symmetric with respect to the cross-section passing through the central axis of the cylinder; the positioning groove at the tenon head end is arranged along the symmetric plane, including a hanging ear groove arranged parallel to the axial direction on the circumferential surface, and a carbon cloth channel connecting the die cavity to the hanging ear groove; the positioning groove at the blade body end is arranged along the extending direction of the blade body span, including a hanging ear groove arranged parallel to the blade body plane on the circumferential surface, and a carbon cloth channel connecting the die cavity to the hanging ear groove; the hanging ear groove at the blade body end is an arc consistent with the curvature of the blade body.

[0025] A further technical solution of the present invention is that in the step 3, the gap between the carbon fiber preform and the inner wall of the die cavity is 3 - 8 mm; at the position of the inner wall of the die cavity opposite to the part with the largest thickness of the carbon fiber preform, 6061 aluminum alloy with a width less than 2 - 5 mm is provided to separate the carbon fiber preform from the inner wall of the die cavity.

[0026] A further technical solution of the present invention is that in the step 4, the seal at the upper part of the extrusion cylinder is a graphite block to prevent the oxidation of the aluminum liquid; when checking the air tightness of the equipment, it is required that the vacuum degree is greater than 10 - 15 MPa, close the vacuum pump and wait for 5 - 10 min, and then check the pressure drop. The pressure drop within 10 - 20% meets the requirements.

[0027] A further technical solution of the present invention is as follows: Before performing step 5, first connect the extrusion cylinder with a vacuum pump and an alloy melting and conveying system; then turn on the resistance wire preheating furnace and the silicon carbide rod melting furnace, and when the preheating and melting temperatures reach 450 °C and 780 °C respectively, keep them warm for about 15 - 20 min and 25 - 30 min respectively.

[0028] A further technical solution of the present invention is as follows: In step 6, numerically control process the obtained aluminum-coated sandwich Cf / Al composite fan blade to remove the surface aluminum alloy, and obtain an aluminum-coated Cf / Al composite fan blade with precise dimensions.

[0029] A further technical solution of the present invention is as follows: The preform is continuous 1D, 2D, 2.5D, 3D carbon fiber, continuous silicon carbide, quartz or alumina fiber; the cladding is 6061 aluminum alloy.

[0030] An aluminum-coated sandwich Cf / Al composite fan blade, characterized in that it comprises a core layer and an aluminum cladding; the core layer is a Cf / Al composite material formed by infiltrating a matrix alloy into a carbon fiber preform; the aluminum cladding is a matrix alloy coated on the outer surface of the core layer, and is used for cutting, anti-corrosion and impact resistance after the formation of the aluminum-coated sandwich Cf / Al composite fan blade;

[0031] The thickness of the aluminum cladding is controlled by the gap between the carbon fiber preform and the mold cavity, that is, different cladding thicknesses are prepared by designing carbon fiber preforms and mold cavities of different specifications.

[0032] Beneficial effects:

[0033] The present invention uses Cf / Al composite material to prepare an aero-engine fan blade, and prepares a cladding with a uniform thickness on its surface while preparing the composite material, realizing the integrated forming of Cf / Al composite material + aluminum cladding. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention proposes a forming method for an aluminum-coated sandwich Cf / Al composite fan blade, which is a preparation method based on high-temperature and high-pressure liquid-solid infiltration technology to fully wrap a liquid alloy cladding on the surface of the preform and realize the infiltration forming and local solidification of the alloy under high pressure. It realizes the one-time preparation of the composite material and the cladding, changes the problem of the sequential preparation of existing metal matrix composite materials and claddings; solves the problem that Cf / Al composite materials are not easy to machine, and proposes a preparation method for Cf / Al composite materials applied to fan blades.

[0035] (2) The gap between the carbon fiber preform and the mold cavity is the thickness of the aluminum coating. When the molten aluminum is poured, it seeps along the gap between the carbon fiber preform and the mold cavity under low pressure and fully fills to form the aluminum coating (which is in a liquid state and has not solidified at this time). Then, the molten aluminum coating alloy seeps into the macroscopic to microscopic (from the surface of the carbon fiber preform to the interior) voids during the process of gradually increasing the pressure, and under continuous high pressure, the aluminum coating and the matrix alloy are completely and fully infiltrated, thus obtaining a well-infiltrated aluminum coating sandwich Cf / Al composite fan blade. Then, it is kept under pressure for solidification at high pressure to further achieve the purposes of solidification feeding, grain refinement, and elimination of internal defects.

[0036] (3) The present invention provides a forming method for an aluminum coating sandwich Cf / Al composite fan blade, which can realize the preparation of large-curvature swept metal matrix composite blades. At the same time, this material consists of a super-high-performance core material (Cf / Al composite) and an aluminum coating that is easy to process, corrosion-resistant, and impact-resistant, and the aluminum coating can achieve an all-round wrapping of the core layer. It effectively solves the problems of interlayer cracking and difficult processing of the core layer material.

[0037] (4) The fan blade forming method of the present invention has the advantage of preparing the core layer + aluminum coating at one time, breaking through the problem of sequential preparation of the traditional coating + core layer, and can realize controllable thickness of the aluminum coating, improving the flexibility of composite material preparation. Such a compatible material is one of the development trends of future composite materials. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the preform layup and three-dimensional structure of the blade body and tenon of an aluminum coating sandwich Cf / Al composite fan blade according to an embodiment of the present invention;

[0039] Figure 2 It is a schematic diagram of the stitching process and three-dimensional structure of the blade body and tenon of an aluminum coating sandwich Cf / Al composite fan blade of the present invention;

[0040] Figure 3 It is a schematic diagram of the forming process of an aluminum coating sandwich Cf / Al composite fan blade of the present invention;

[0041] Figure 4 It is a schematic diagram of the three-dimensional structure of an aluminum coating sandwich Cf / Al composite fan blade after forming of the present invention;

[0042] Figure 5 It is a comparison diagram of the surface processing morphologies of Cf / Al composite and aluminum coating sandwich Cf / Al composite.

[0043] The reference numerals in the figures are as follows: 1. blade body; 1-1. laying form of the preform ply of the blade body; 1-3. preform; 2. blade body twist angle; 3. tenon; 3-1. laying form of the preform ply of the tenon; 4. sewing part of the blade body on the tenon; 5. blade body lug; 5-1. blade body end lug groove; 6. folded carbon cloth (carbon fiber non-woven fabric); 7. needling sewing part of the tenon and the blade body; 7-1. needling sewing position; 8. tenon lug; 8-1. tenon end lug groove; 9. female die; 10. die cavity; 11. punch; 12. graphite block; 13. vacuum tube; 14. aluminum liquid; 15. extrusion cylinder; 16. infusion tube; 17. preheating furnace; 18. gap between the preform and the die cavity; 19. bottom plate; 20. ejector rod. Detailed implementation mode

[0044] The present invention will be further described in detail below in conjunction with specific embodiments, but it does not constitute any limitation to the present invention.

[0045] Based on the technical problems in the prior art that the surface fibers of the Cf / Al composite fan blade are broken, cracked and the matrix is torn after forming due to cutting processing, which destroys the surface integrity and continuity of the fan blade, reduces the dimensional accuracy and corrosion resistance characteristics, etc., the present invention proposes a forming method for an aluminum-coated sandwich Cf / Al composite fan blade, and the specific steps are as follows:

[0046] Step 1: Prepare a carbon fiber preform; use carbon fiber non-woven fabric as the reinforcement, cut and sew the carbon fiber non-woven fabric according to the model structure of the blade body and tenon of the fan blade to obtain a carbon fiber preform for the fan blade; and respectively set shape-preserving positioning structures at both ends of the carbon fiber preform;

[0047] Step 2: Manufacture a forming female die for the fan blade;

[0048] The end face of the female die is provided with a die cavity that is consistent with the outer shape structure of the carbon fiber preform and enlarged in equal proportion, and positioning grooves are respectively arranged on the solid parts of the female die at both ends of the die cavity;

[0049] Step 3: Position and install the carbon fiber preform in the female die;

[0050] Place the carbon fiber preform in the die cavity of the female die, and insert the shape-preserving positioning structures at both ends into the positioning grooves of the female die to ensure that the carbon fiber preform is suspended in the die cavity and does not contact the inner wall of the die cavity; the width of the gap between the inner wall of the die cavity and the carbon fiber preform is the thickness of the aluminum coating;

[0051] Step 4: Place the female die with the carbon fiber preform in the liquid-solid infiltration extrusion forming equipment, install a seal above the extrusion cylinder of the equipment, and perform a airtightness detection on the melting furnace;

[0052] Step 5: Prepare the fan blade by liquid-solid pressure infiltration

[0053] First, melt the aluminum alloy under the protection of an argon atmosphere. After reaching the pouring temperature, open the valve of the argon gas cylinder, transfer the molten aluminum in the melting furnace into the extrusion cylinder, and then close the cylinder valve.

[0054] Then, start the liquid-solid infiltration extrusion forming equipment. Control the punch to quickly move downward until it contacts the seal. At the moment of contact, slowly move downward with point pressure. The pressure shall not be higher than 0.5 - 2 MPa, and keep the pressure for 3 - 5 s, so that the molten aluminum first flows into the gap between the preform and the mold cavity under low pressure for filling to form an aluminum coating, preventing the bending and displacement of the carbon fiber preform. Then, instantaneously pressurize to 10 - 15 MPa, stop pressurizing, keep the pressure for 3 - 5 s, and then gradually pressurize to 40 - 55 MPa, stop pressurizing, keep the pressure for 10 - 25 s, and then reduce the pressure to 30 - 40 MPa, keep the pressure for 10 hours, and infiltrate the molten aluminum into the carbon fiber preform to form a core layer.

[0055] Finally, during the pressure holding process, turn off the power supply of the equipment, and form the aluminum-coated sandwich Cf / Al composite fan blade in the forming equipment at one time.

[0056] Step 6: Demold and sample; after the equipment cools down to room temperature, withdraw the female mold. After demolding, the aluminum-coated sandwich Cf / Al composite fan blade is obtained.

[0057] The present invention is a preparation method based on the high-temperature and high-pressure liquid-solid infiltration technology to comprehensively wrap a liquid alloy coating on the surface of the preform, and realize the infiltration forming and local solidification of the alloy under high pressure. It realizes the one-time preparation of the composite material and the coating, changes the problem of the sequential preparation of the existing metal matrix composite material and the coating, solves the problem that the Cf / Al composite material is not easy to machine, and proposes a preparation method for applying the Cf / Al composite material to the fan blade.

[0058] Example:

[0059] See Figures 1 to 5 The technical solution of the present invention is as follows:

[0060] This example of an aluminum-coated sandwich Cf / Al composite fan blade is composed of a blade body 1 and a tenon 3. The blade body 1 has a twisted equal-size cross-section in the height direction, a symmetric middle-thick and edge-thin swept structure in the width direction, the twisting angle is 20°, and all parts are smoothly transitioned; the tenon 3 is a symmetric structure, as Figure 2As shown. The fan blade includes a core layer A and an aluminum cladding layer B from the inside out; the core layer is composed of a carbon fiber preform and a matrix alloy, where carbon fiber is used as the reinforcement and aluminum alloy is used as the matrix alloy. The matrix alloy liquid infiltrates into the carbon fiber preform under pressure to form a core layer of Cf / Al composite material; the aluminum cladding layer is wrapped on the surface of the core layer and is used for cutting, anti-corrosion and impact resistance after the forming of the aluminum cladding sandwich Cf / Al composite fan blade; the thickness of the aluminum cladding layer is controlled by the gap between the carbon fiber preform and the mold cavity. Specifically, different cladding thicknesses are prepared by designing carbon fiber preforms and mold cavities with different thicknesses.

[0061] The laying scheme of the blade body 1 and the tenon 3 of the carbon fiber preform is as Figure 1 shown Figure 1 In it, 1-1 is the single-layer carbon cloth laying method of the blade body 1 section, 7-1 is the needling and stitching position, and 3-1 is the single-layer carbon-carbon cloth method of the tenon section. After the blade body 1 and the tenon 3 of the preform are separately laid, the two are stitched along the stitching part 4 (tenon connection part) (as Figure 2 shown), to obtain the carbon fiber preform 1-3 of the fan blade. At both ends of the blade body 1 and the tenon 3, a folded carbon cloth 6 with the same width as them is stitched respectively. The folded carbon cloth 6 includes an opening (opposite side of the crease end) and a closing (crease end). The opening end is inserted into the carbon fiber preform layer between the ends of the blade body 1 or the tenon 3 to form a lap joint structure. Then the lap joint part is stitched. Then a steel wire is inserted into the closing end to form a blade body lug 5 and a tenon lug 8. Finally, the preform 1-3 is placed into the split mold cavity 10, and the blade body lug 5 and the tenon lug 8 are respectively inserted into the blade body lug groove 5-1 and the tenon lug groove 8-1. Through the clamping connection between the crease end inserted with the steel wire and the lug groove, the carbon fiber preform is suspended in the concave mold, playing the role of shape retention and positioning.

[0062] As Figure 3 shown, the forming process of the fan blade adopts a liquid-solid high-pressure infiltration and extrusion forming device, which mainly includes a punch 11, a graphite block 12, a vacuum tube 13, aluminum liquid 14, an extrusion cylinder 15, a concave mold 10, an infusion tube 16, a preheating furnace 17, a bottom plate 19, and a ejector rod 20.

[0063] The specific steps of the forming process of a kind of liquid-solid infiltration and extrusion aluminum cladding sandwich Cf / Al composite fan blade in this embodiment are as follows:

[0064] Step 1: Preparation of the fan blade preform: The fan blade preform 1-3 includes a blade body 1 and a tenon 3. The T700-12K unidirectional carbon fiber non-woven fabric (abbreviation: carbon cloth) treated with acetone solution is selected as the reinforcement, that is, the lay-up material of the preform. The Volume Fill module in the composite material design software Fibersim is used to complete the volume filling and lay-up design of the fan blade, and then the carbon cloth is cut according to the model structure of the blade body and tenon of the fan blade. After that, the cut carbon cloth is laid and stitched layer by layer, and finally the stitched blade body and tenon are stitched at the tenon connection part to form the carbon fiber preform of the fan blade.

[0065] The specific sewing method of the preform is to adopt the split design of the blade body and tenon of the fan blade, overall stitching, from inside to outside, from short to long, and layer-by-layer laying scheme; that is, when laying, first lay the preform of the small-size part in the center, and lay it from inside to outside and from small to large in turn; after the split laying of the blade body and tenon is completed, the needle punching stitching technology is used to integrally stitch and fix at the tenon connection part (the transition area of the connection section between the blade body and the tenon), and the stitching process is carried out in a spiral manner from the center to the edge, and the needle punching spacing needs to be kept at 2.0-5.0 cm. It should be noted that in order to ensure the accuracy of the laying angle and size, every 1-3 layers of carbon cloth are laid, and it needs to be placed in the mold cavity 10 of the female mold 9 for laying position correction. Since the scheme of laying from short to long and layer by layer is adopted, the carbon cloth laid later will wrap the carbon cloth laid first in turn, and the thickness will increase by 0.3 mm every time it is wrapped. Therefore, the laying curved surface or variable cross-section transition can be realized by designing carbon cloth of different lengths and numbers of insertion layers. The feature of the insertion layer is the carbon cloth with small size, which is used for the laying of the preform at the shoulder and variable cross-section parts.

[0066] Preferably, after the laying of the blade body 1 of the preform is completed, it is twisted about 20°-25°, and then needle punching stitching is carried out.

[0067] Preferably, the shoulder structure of the tenon 3 of the preform can be realized by the insertion layer. After each laying of the insertion layer structure is completed, 2-5 layers of structural layer carbon cloth need to be laid on its surface. The long-size carbon cloth is called the structural layer. When all the carbon cloth is laid, the tenon 3 is integrally needle punched and stitched. The stitching process needs to be carried out in a spiral manner from the center of the tenon 3 to the edge, and the needle punching spacing needs to be kept at 1-2.5 cm. Too dense needle punching will damage the internal structure of the carbon cloth and reduce the mechanical properties of the blade. Too sparse is not conducive to the fixation of the preform 1-3.

[0068] One end of the blade body 1 of the preform is placed on the upper part of the tenon 3, and stitching is carried out according to the pre-set stitching part 4, and finally the fan blade preform 1-3 is obtained, as Figure 2 shown.

[0069] In order to suspend the preform in the cavity of the female mold, lugs need to be provided at the blade body and the end of the tenon of the fan blade preform. The two lugs are respectively installed in cooperation with the lug grooves of the female mold 9 so that the preform is suspended in the cavity. The lugs are divided into the blade body lug 5 and the tenon lug 8. The blade body lug 5 has the same bending curvature as the blade body, while the tenon lug 8 is straight. The lugs are formed by folding a single layer of carbon cloth. After folding, the carbon cloth forms an open end (the opposite sides of the crease end) and a closed end (the crease end). Then, the open end is inserted into the interlayer of the carbon fiber preform at the blade body and the end of the tenon to form a lap joint structure. After that, it is sewn. Finally, a steel wire with a diameter of 1-2 mm is placed at the closed end to form the blade body lug and the tenon lug. Finally, the lugs are placed in the hanging grooves, and the position of the preform in the female mold is adjusted to ensure that the preform is suspended in the cavity.

[0070] Step 2: Installation of the preform:

[0071] S2.1: Fabricate the female mold 9 for forming the fan blade; the female mold 9 is of a cylindrical structure, and its end face is provided with a cavity that is consistent with the outer shape structure of the carbon fiber preform and enlarged in equal proportion. Positioning grooves are respectively provided at the solid parts of the female mold at both ends of the cavity; the cavity 10 for accommodating the tenon is symmetric with respect to the cross-section passing through the central axis of the cylinder. The female mold 9 adopts a split structure and is made of die steel, which has the advantages of facilitating the installation of the carbon fiber preform and being easy to demold after the blade is formed.

[0072] The positioning groove at the tenon end is arranged along the symmetry plane, including a lug groove (the radial cross-section is semi-circular) arranged parallel to the axial direction on the circumferential surface, and a carbon cloth channel connecting the cavity to the lug groove; the positioning groove at the blade body end is arranged along the extending direction of the blade body, including a lug groove arranged parallel to the blade body plane on the circumferential surface, and a carbon cloth channel connecting the cavity to the lug groove; the lug groove at the blade body end is an arc that is consistent with the curvature of the blade body.

[0073] S2.2: Install the preform in the cavity of the female mold for positioning;

[0074] When installing the preform 1-3, first separate the female mold 9, put the preform 1-3 into the cavity 10, then combine the female mold 9, and then insert the blade body lug 5 and the tenon lug 8 into the blade body lug groove 5-1 and the tenon lug groove 8-1. The steel wire in the tenon lug 8 is rotated to drive the carbon cloth to wind to form a pre-tightening force, and the pre-tightening force is used to tighten the preform 1-3 so that it is suspended in the cavity 10 and does not contact the inner wall of the cavity; then the female mold 9 with the preform 1-3 installed is put into the extrusion cylinder 15.

[0075] The gap between the carbon fiber preform and the inner wall of the mold cavity is 3-8 mm, which is the thickness of the aluminum cladding layer; this width is the thickness of the aluminum cladding layer of the aluminum cladding layer sandwich Cf / Al composite fan blade. When this thickness is too thin, the core Cf / Al composite material will be exposed during machining. When it is too thick, the density of the fan blade is large, and the volume fraction of the high-strength Cf / Al composite material inside is too small to fully exert the synergistic effect between the aluminum cladding layer and the core layer. At the position of the inner wall of the mold cavity opposite to the thickest part of the carbon fiber preform, 6061 aluminum alloy with a width less than 2-5 mm is provided to separate the carbon fiber preform from the inner wall of the mold cavity.

[0076] Step 3: Place the female mold containing the carbon fiber preform in the liquid-solid infiltration extrusion forming equipment, install a graphite block above the extrusion cylinder of the equipment to prevent oxidation of the aluminum liquid; and conduct airtightness detection on the melting furnace and preheat the mold.

[0077] The method for checking the airtightness of the device is as follows: First, connect the extrusion cylinder 15, the vacuum pump 13, and the alloy melting and conveying system 16. Then start checking the airtightness of the device. It is required that the vacuum degree > 10-15 MPa. Close the vacuum pump and wait for 5-10 minutes, and then check the pressure drop. As long as the pressure drop is within 10-20%, it meets the requirements.

[0078] The method for preheating the mold: Turn on the resistance wire preheating furnace 17 and the silicon carbide rod melting furnace. When the preheating and melting temperatures reach 450°C and 780°C respectively, keep them warm for about 15-20 minutes and 25-30 minutes.

[0079] Step 4: Conduct alloy pouring; melt the aluminum alloy under the protection of an argon atmosphere. When the pouring temperature is reached, open the valve of the argon gas cylinder to allow argon to enter the melting furnace and send the alloy liquid 14 into the extrusion cylinder 15 along the infusion pipe 16, and then close the valve of the gas cylinder.

[0080] Step 5: Liquid-solid high-pressure infiltration forming.

[0081] First, turn on the hydraulic press. When the punch 11 moves quickly downward and contacts the graphite block 12, control it to move slowly downward by point pressing. The pressure shall not be higher than 0.5 - 2 MPa. When the pressure instantaneously increases to about 2 - 5 MPa, it indicates that the graphite block 12 contacts the liquid alloy 14, and immediately stop pressurizing; keep the pressure for 3 - 5 s to ensure that the aluminum liquid 14 fully fills along the gap between the preform 3 and the mold cavity 10 under low pressure. The said gap is the thickness of the aluminum cladding of the aluminum cladding sandwich Cf / Al composite fan blade. The quality of the aluminum liquid filling will affect the uniformity of the cladding thickness. At the same time, the low pressure is also to prevent the preform 1 - 3 from bending and offsetting. Then gradually pressurize to 40 - 55 MPa, stop pressurizing, keep the pressure for 10 - 25 s, and then reduce the pressure to 30 - 40 MPa and keep the pressure for 10 hours. Keep the pressure for 10 hours to infiltrate the aluminum liquid into the carbon fiber preform to form the core layer; turn off the power supply of the equipment during the pressure holding process to form the aluminum cladding sandwich Cf / Al composite fan blade in the forming equipment at one time. The pressure holding process can achieve the effects of forced feeding of the alloy liquid, grain refinement, and full infiltration. After the pressure holding is over, reduce the pressure to 10 - 25 MPa, and then turn off the power supply of the preheating furnace 14 and other equipment to solidify the composite material under this pressure, which has the effect of forced feeding.

[0082] The specific forming process is as follows: The gap between the carbon fiber preform and the mold cavity is the thickness of the aluminum cladding. When the aluminum liquid is poured, it seeps along the gap between the carbon fiber preform and the mold cavity under low pressure and fully fills to form the aluminum cladding (at this time, it is liquid and has not solidified). Then the aluminum cladding alloy liquid infiltrates into the voids from macroscopic to microscopic (from the surface of the carbon fiber preform to the inside) during the process of gradually increasing the pressure, and under continuous high pressure, the aluminum cladding and the matrix alloy are fully infiltrated, so as to obtain a well-infiltrated aluminum cladding sandwich Cf / Al composite fan blade. Then it is pressure held and solidified under high pressure to further achieve the purposes of solidification feeding, grain refinement, and elimination of internal defects.

[0083] Step 6: Demold and sample; After the mold cools to room temperature, turn on the hydraulic press, the ejector rod 20 moves upward and acts on the bottom plate 19, and then withdraw the female mold 9. After demolding, the aluminum cladding sandwich Cf / Al composite fan blade is obtained, as Figure 4 shown. Then numerically control process the obtained aluminum cladding Cf / Al composite fan blade to remove the surface aluminum alloy to obtain the aluminum cladding Cf / Al composite fan blade with precise dimensions.

[0084] Preferably, the preform includes continuous 1D, 2D, 2.5D, 3D carbon fibers, or continuous silicon carbide, quartz, alumina fibers; the cladding is 6061 aluminum alloy.

[0085] Preferably, the female die is a split female die structure made of die steel; the distance between the preform and the cavity of the female die is the thickness of the aluminum coating. The thickness of the aluminum coating is controlled by the gap between the carbon fiber preform and the cavity, that is, different coating thicknesses are prepared by designing carbon fiber preforms and cavities of different specifications.

[0086] The forming method of the aluminum-coated sandwich Cf / Al composite fan blade proposed by the present invention effectively solves the technical problems such as the surface fiber breakage, cracking and matrix tearing caused by cutting processing after the forming of the Cf / Al composite fan blade, which destroys the surface integrity and continuity of the fan blade, and reduces the dimensional accuracy and corrosion resistance.

[0087] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principle and spirit of the present invention.

Claims

1. A forming method for an aluminum-clad sandwich Cf / Al composite aeroengine fan blade, characterized in that the specific steps are as follows: Step 1: Prepare a carbon fiber preform; use carbon fiber non-woven fabric as the reinforcement, cut and sew the carbon fiber non-woven fabric according to the model structure of the fan blade airfoil and tenon, and obtain the carbon fiber preform of the fan blade; And set conformal positioning structures at both ends of the carbon fiber preform respectively; Step 2: Manufacture a forming female die for the fan blade; The end face of the female die is provided with a die cavity that is consistent with the outer shape structure of the carbon fiber preform and enlarged in equal proportion, and positioning grooves are respectively arranged on the solid parts of the female die at both ends of the die cavity; Step 3: Position and install the carbon fiber preform in the female die; Place the carbon fiber preform in the die cavity of the female die, and insert the conformal positioning structures at both ends into the positioning grooves of the female die to ensure that the carbon fiber preform is suspended in the die cavity and does not contact the inner wall of the die cavity; the gap width between the inner wall of the die cavity and the carbon fiber preform is the thickness of the aluminum cladding layer; Step 4: Place the female die equipped with the carbon fiber preform in a liquid-solid infiltration extrusion forming device, install a seal above the extrusion cylinder of the device, and perform a airtightness test on the melting furnace; Step 5: Prepare the fan blade by liquid-solid pressure infiltration; First, melt the aluminum alloy under the protection of an argon atmosphere. When the pouring temperature is reached, open the valve of the argon gas cylinder, transport the aluminum liquid in the melting furnace to the extrusion cylinder, and then close the valve of the argon gas cylinder; Then, start the liquid-solid infiltration extrusion forming device, control the punch to quickly move downward until it contacts the seal, and then slowly move downward by point pressure. The pressure is 0.5-2 MPa, and the pressure is maintained for 3-5 s, so that the aluminum liquid first flows into the gap between the preform and the die cavity under low pressure for filling to form an aluminum cladding layer, preventing the bending and displacement of the carbon fiber preform; then instantaneously pressurize to 10-15 MPa, stop pressurizing, maintain the pressure for 3-5 s, and then gradually pressurize to 40-55 MPa, stop pressurizing, maintain the pressure for 10-25 s, and then reduce the pressure to 30-40 MPa, maintain the pressure for 10 hours, and infiltrate the aluminum liquid into the carbon fiber preform to form a core layer; Finally, turn off the power supply of the device during the pressure maintaining process, and form the aluminum-clad sandwich Cf / Al composite fan blade in the forming device at one time; Step 6: Demold and sample; after the device cools to room temperature, withdraw the female die, and obtain the aluminum-clad sandwich Cf / Al composite fan blade after demolding.

2. The forming method for an aluminum-clad sandwich Cf / Al composite aeroengine fan blade according to claim 1, characterized in that: In the step 1, use T700-12K unidirectional carbon fiber non-woven fabric as the reinforcement, cut and sew according to the model structure of the fan blade airfoil and tenon to obtain preforms of the split airfoil and tenon, and then splice and sew the split airfoil and tenon into an integrated carbon fiber preform; The method for sewing the carbon fiber non-woven preform is to lay it layer by layer from the inside to the outside and from short to long, that is, when laying, first lay the preform at the small-sized central part, and then lay it from the inside to the outside and from small to large in sequence; after the separate laying of the blade body and the tenon head is completed, the overall stitching and fixing are carried out by using the needle punching stitching technology in the transition area of the connection section between the blade body and the tenon head; the stitching process unfolds in a spiral manner from the center to the edge, and the needle punching spacing needs to be maintained at 2.0 - 5.0 cm.

3. The forming method of an aluminum-clad sandwich Cf / Al composite material aeroengine fan blade according to claim 1, characterized in that: in the step 1, the shape-preserving positioning structure includes a blade body lug and a tenon head lug, the blade body lug has the same bending curvature as the blade body, and the tenon head lug is a straight line; the preparation method of the lug is as follows: first, fold two single-layer carbon cloths respectively, the folded end of the fold is the closed end, and the opposite end of the fold is the open end; then, insert the open ends of the two folded carbon cloths into the carbon fiber preform layers at the ends of the blade body and the tenon head respectively, and stitch and fix them; then insert metal wires along the fold into the closed ends of the two folded carbon cloths, and the blade body lug and the tenon head lug are obtained; finally, insert the blade body lug and the tenon head lug into the positioning grooves respectively, and through the clamping connection between the folded end with the inserted metal wire and the positioning groove, the shape preservation and positioning of the carbon fiber preform in the female die are realized.

4. The forming method of an aluminum-clad sandwich Cf / Al composite material aeroengine fan blade according to claim 3, characterized in that: the female die is a cylindrical structure, and the cavity of its die cavity for accommodating the tenon head is symmetric with respect to the cross-section passing through the central axis of the cylinder; the positioning groove at the tenon head end is arranged along the symmetric plane, including a lug groove arranged parallel to the axial direction on the circumferential surface, and a carbon cloth channel connecting the die cavity and the lug groove; the positioning groove at the blade body end is arranged along the extending direction of the blade body span, including a lug groove arranged parallel to the blade body plane on the circumferential surface, and a carbon cloth channel connecting the die cavity and the lug groove; the lug groove at the blade body end is an arc consistent with the curvature of the blade body.

5. The forming method of an aluminum-clad sandwich Cf / Al composite material aeroengine fan blade according to claim 1, characterized in that: in the step 3, the gap between the carbon fiber preform and the inner wall of the die cavity is 3 - 8 mm; at the position of the inner wall of the die cavity opposite to the part with the largest thickness of the carbon fiber preform, 6061 aluminum alloy with a width of 2 - 5 mm is arranged to separate the carbon fiber preform from the inner wall of the die cavity.

6. The forming method of an aluminum-clad sandwich Cf / Al composite material aeroengine fan blade according to claim 1, characterized in that in the step 4, the seal at the upper part of the extrusion cylinder is a graphite block to prevent the oxidation of the aluminum liquid; when checking the airtightness of the equipment, it is required that the vacuum degree is greater than 10 MPa, close the vacuum pump and wait for 5 - 10 min, and then check the pressure drop. The pressure drop within 10 - 20% meets the requirements.

7. The forming method of an aluminum-clad sandwich Cf / Al composite material aeroengine fan blade according to claim 1, characterized in that: Before performing the said step 5, first connect the extrusion cylinder with the vacuum pump and the alloy melting and conveying system; then turn on the resistance wire preheating furnace and the melting furnace, where the melting furnace is a silicon carbide rod melting furnace. When the preheating and melting temperatures reach 450°C and 780°C respectively, keep them warm for 15 - 20 minutes and 25 - 30 minutes respectively.

8. A method for forming a fan blade of an aeroengine made of an aluminum - clad sandwich Cf / Al composite material according to claim 1, characterized in that: In the said step 6, numerically control the processed aluminum - clad sandwich Cf / Al composite material fan blade to remove the surface aluminum alloy, and obtain a fan blade of aluminum - clad Cf / Al composite material with precise dimensions.

9. A method for forming a fan blade of an aeroengine made of an aluminum - clad sandwich Cf / Al composite material according to claim 1, characterized in that: The preform is made of continuous 1D, 2D, 2.5D, 3D carbon fibers, continuous silicon carbide, quartz or alumina fibers; the cladding is 6061 aluminum alloy.

10. A fan blade prepared by using the method for forming a fan blade of an aeroengine made of an aluminum - clad sandwich Cf / Al composite material according to any one of claims 1 - 9, characterized in that: It includes a core layer and an aluminum cladding layer; the core layer is a Cf / Al composite material formed by infiltrating a matrix alloy into a carbon fiber preform; The aluminum cladding layer is a matrix alloy coated on the outer surface of the core layer, and is used for cutting processing, anti - corrosion and impact resistance after the formation of the aluminum - clad sandwich Cf / Al composite material fan blade; The thickness of the aluminum cladding layer is controlled by the gap between the carbon fiber preform and the mold cavity, that is, different thicknesses of the cladding layer are prepared by designing carbon fiber preforms and mold cavities with different specifications.

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