Preparation method and system of continuous fiber reinforced aluminum-based composite material

Abstract

The embodiment of the invention discloses a preparation method and system of a continuous fiber reinforced aluminum-based composite material, and relates to the technical field of metal-based composite material preparation.The method comprises the steps that surface pretreatment is conducted on aluminum oxide fibers so that a composite coating can be formed on the surfaces of the aluminum oxide fibers; applying ultrasonic vibration to a mold in the process of injecting molten aluminum liquid into the mold containing the alumina fibers by using vacuum suction casting; in the vacuum suction casting process, the impregnation pressure in the mold is monitored, and the casting pressure acting on the molten aluminum liquid is dynamically adjusted based on the monitored impregnation pressure; the porosity can be remarkably reduced, and the product stability is improved through closed-loop control.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal matrix composite material preparation, and particularly relates to a preparation method and system of continuous fiber reinforced aluminum matrix composite material. BACKGROUND

[0002] The continuous fiber reinforced aluminum matrix composite material has excellent comprehensive mechanical properties such as light weight, high strength and high modulus, and has broad application prospects in high-end manufacturing fields such as aerospace and precision instruments. The pressure infiltration method is one of the commonly used technologies for preparing the composite material, and the basic principle is to use the external applied pressure to force the molten aluminum matrix liquid to infiltrate into the preform composed of reinforcing fibers, and then form the composite material after cooling and solidification.

[0003] In the current pressure infiltration process, in order to improve the bonding between the non-wetting or poorly wetting reinforcing fibers (such as alumina fibers) and the aluminum matrix, the fibers are usually subjected to surface coating modification treatment in order to obtain good interfacial bonding. However, the existing technical solutions still have inherent defects. First of all, even if the fibers are subjected to surface modification, when the molten aluminum liquid flows in the internal of the preform with high fiber volume fraction or complex structure, it will still be subjected to great flow resistance in the micron-sized complex pore channels, and the surface tension of the aluminum liquid itself also hinders its complete filling of the small gaps. This leads to the fact that the final prepared composite material is prone to have defects such as porosity and shrinkage, which seriously affects the density and mechanical property stability of the material. Secondly, the traditional pressure infiltration equipment usually uses constant pressure or pre-set programmed pressure curve for pressurization, and this open-loop control method cannot real-time sense the dynamic changes of the infiltration state inside the preform, and it is difficult to adaptively adjust according to the actual flow resistance. For example, when there is difficulty in infiltration in a local area, the system cannot timely and effectively apply higher pressure for shrinkage compensation; and if a constant pressure that is too high is blindly applied to the whole system, the reinforcing fibers may be damaged due to the excessive pressure. Therefore, the existing technology generally lacks real-time and accurate feedback control of the infiltration process, which restricts the yield and performance stability of the composite material. SUMMARY

[0004] The main purpose of the present application is to provide a preparation method and system of continuous fiber reinforced aluminum matrix composite material, which can solve the problems of high porosity caused by insufficient infiltration of molten aluminum liquid and unstable performance of the composite material caused by lack of real-time and accurate control of the infiltration process during the preparation of the continuous fiber reinforced aluminum matrix composite material.

[0005] To achieve the above-mentioned purpose, the present application provides a preparation method of continuous fiber reinforced aluminum matrix composite material, comprising: surface pretreatment is performed on the alumina fibers to form a composite coating on the surface of the alumina fibers; applying ultrasonic vibration to the mold during a vacuum suction casting process in which the molten aluminum liquid is injected into the mold containing the alumina fibers; monitoring an impregnation pressure within the mold during the vacuum suction casting process, and dynamically adjusting a casting pressure acting on the molten aluminum liquid based on the monitored impregnation pressure.

[0006] Another aspect of the present application provides a system for preparing a continuous fiber reinforced aluminum matrix composite material, comprising: a mold for containing an alumina fiber preform that has been subjected to surface pretreatment; a vacuum chamber in which the mold is disposed; a heating device for heating an aluminum matrix material into a molten aluminum liquid; an ultrasonic generating device coupled to the mold for applying ultrasonic vibration to the mold during a vacuum suction casting process in which the molten aluminum liquid is injected into the mold containing the alumina fibers; and a dynamic pressure control system, the dynamic pressure control system comprising: a pressure sensor disposed within the mold for monitoring an impregnation pressure within the mold in real time; a controller in signal connection with the pressure sensor; and a pressure adjusting device controlled by the controller for dynamically adjusting a casting pressure acting on the molten aluminum liquid based on the impregnation pressure monitored by the pressure sensor.

[0007] The present application provides a method and system for preparing a continuous fiber reinforced aluminum matrix composite material, in which alumina fibers are subjected to surface pretreatment to form a composite coating on the surface of the alumina fibers; ultrasonic vibration is applied to the mold during a vacuum suction casting process in which the molten aluminum liquid is injected into the mold containing the alumina fibers; an impregnation pressure within the mold is monitored during the vacuum suction casting process, and a casting pressure acting on the molten aluminum liquid is dynamically adjusted based on the monitored impregnation pressure; the present application can significantly reduce porosity and improve product stability through closed-loop control.

[0008] Compared with the prior art, the application has the following beneficial effects: 1. The porosity is significantly reduced, and the denseness is improved. By applying ultrasonic vibration in the infiltration process, the apparent viscosity and flow resistance of the molten aluminum liquid are effectively reduced by using the cavitation effect, the complete filling of the micrometer-level pores between the fiber bundles by the aluminum liquid is promoted, the final porosity of the composite material can be greatly reduced, and a more dense structure is obtained. 2. Precise process control is realized, and the product stability is improved. By introducing a dynamic pressure regulation system based on real-time pressure feedback, closed-loop control of the infiltration process is realized. This method can adaptively adjust the pressure according to the complex and dynamically changing infiltration state inside the preform, effectively solving the contradiction between local underfilling and overpressure damage to the fibers existing in the existing constant pressure or program-controlled pressure technology, and significantly improving the stability of the preparation process, the yield of finished products and the performance consistency of the final products. 3. The interface bonding is improved, and the comprehensive performance is improved. By pre-treating the fiber with a composite coating, the wettability of the fiber with the aluminum matrix is improved, which creates conditions for forming a firm interface bonding. Combined with the ultrasonic-assisted dense filling and the stable process of dynamic pressure regulation, a continuous fiber-reinforced aluminum matrix composite material with good interface bonding, few internal defects and excellent comprehensive mechanical properties can be finally prepared. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0010] Among them: Figure 1 The structural schematic diagram of the preparation method of the continuous fiber-reinforced aluminum matrix composite material provided by the embodiments of the present application; Figure 2 The functional module schematic diagram of the preparation system of the continuous fiber-reinforced aluminum matrix composite material provided by the embodiments of the present application; Figure 3 The structural schematic diagram of the preparation system of the continuous fiber-reinforced aluminum matrix composite material provided by the embodiments of the present application. DETAILED DESCRIPTION

[0011] In order to enable the persons skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0012] The terms "first", "second", and the like in the description and in the claims of the present application and above drawings are used for distinguishing between similar objects, not necessarily described in a particular order. Also, the terms "comprise", "comprising", and the like are to be construed in an open-ended way, meaning that it includes at least the recited steps or elements but not excluding others. For example, a process, method, article, or apparatus that comprises a list of steps or elements is not necessarily limited to the listed steps or elements, but can include further steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

[0013] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of other embodiments. It is expressly understood that the embodiments described herein are merely examples from a whole class of comparable embodiments which those skilled in the art will readily appreciate. It is also expressly understood that the embodiments described herein have a number of applications and the application of that knowledge and of these embodiments applies equally to all functions whether they are supported by prior art inventions or not.

[0014] The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0015] Please refer to Figure 1 A flowchart of a method for preparing a continuous fiber reinforced aluminum matrix composite material is provided in the embodiments of the present application, as shown in Figure 1 The method comprises the following steps: 101. Surface pretreatment is performed on the alumina fibers to form a composite coating on the surface of the alumina fibers; 102. During the process of injecting molten aluminum into a mold containing the alumina fibers by vacuum suction casting, ultrasonic vibration is applied to the mold; 103. During the vacuum suction casting process, the impregnation pressure in the mold is monitored, and the casting pressure acting on the molten aluminum is dynamically adjusted based on the monitored impregnation pressure.

[0016] The embodiments of the present application mainly solve the problems of poor wettability, insufficient penetration, and low process control precision in the prior art by performing composite coating pretreatment on the fibers, applying ultrasonic vibration during vacuum suction casting, and introducing dynamic pressure regulation based on real-time pressure feedback, thereby stably preparing a dense and high-performance composite material.

[0017] Figure 2 A functional module diagram of a system for preparing a continuous fiber reinforced aluminum matrix composite material is provided in the embodiments of the present application.

[0018] Figure 3A structural schematic diagram of a preparation system of continuous fiber reinforced aluminum matrix composite provided by an embodiment of the present application.

[0019] Please also refer to Figure 2 and Figure 3 which respectively show a functional module schematic diagram and a structural schematic diagram of the preparation system for performing the above method. As shown in Figure 3 , the preparation system of the continuous fiber reinforced aluminum matrix composite is mainly built inside a vacuum chamber, which is provided with an interface 1 for connecting a vacuum pump 8 and an interface 3 for introducing protective gas. The core of the system includes a heating device 4 for heating the aluminum matrix material into molten aluminum liquid, a crucible 5 for containing the molten aluminum liquid, and a mold 7 for containing the fiber preform. Wherein 8 is a vacuum pump, and 9 is a PLC controller.

[0020] In the embodiment, the mold 7 is specifically a porous graphite mold D, as shown in Figure 2 , in order to realize accurate temperature control of different regions, the system adopts a partitioned heating device J, which can independently control the temperature of the smelting area A (mainly including the crucible 5) and the suction casting area B (mainly including the mold 7).

[0021] In order to provide auxiliary penetration energy during the infiltration process, the system is equipped with an ultrasonic generating device, which is specifically a piezoelectric transducer 6 (represented as piezoelectric transducer E in the functional module diagram) tightly coupled with the outer wall of the mold 7 in the embodiment. The piezoelectric transducer E can convert electrical energy into high-frequency mechanical vibration and transmit it to the mold 7.

[0022] In order to realize accurate closed-loop control of the infiltration process, the system also includes a dynamic pressure control system. The system consists of three key parts: The pressure sensor 2 (represented as pressure sensor G in the functional module diagram) arranged inside the mold 7 is used to monitor the infiltration pressure inside the mold in real time; The PLC controller 9 (represented as PLC controller H in the functional module diagram) as the control center is signal connected with the pressure sensor 2 for receiving and processing pressure data; The pressure regulating device as the actuator, which is specifically a multi-stage vacuum pump I (represented as vacuum pump 8 in the structural diagram) in the embodiment, is controlled by the PLC controller 9.

[0023] Through real-time monitoring by the pressure sensor G, logical judgment and instruction issuing by the PLC controller H, and action execution by the multi-stage vacuum pump I, a complete "monitoring-feedback-control" closed loop is formed, which can dynamically adjust the casting pressure acting on the molten aluminum liquid.

[0024] In the following Figure 1 , Figure 2 andFigure 3 The detailed preparation process of the embodiment is described in detail.

[0025] For step 101, in the embodiment of the application, the purpose of fiber pretreatment and preform preparation is to improve the wettability between the reinforcement (continuous alumina fiber) and the matrix (aluminum) and to create conditions for forming a good interface bond. Taking Example 1 as an example, the specific operation can be as follows: First, the surface of the continuous alumina fiber is cleaned and activated. The coiled continuous alumina fiber is placed in a special plasma treatment chamber, and high-purity argon gas is introduced as the working gas. The radio frequency power supply is started, and under the condition that the power is 300 W and the chamber pressure is maintained at 50 Pa, the fiber surface is bombarded and cleaned by low-temperature argon plasma, and the duration is 10 minutes. This step can effectively remove organic contaminants and physically adsorbed water vapor that may exist on the surface of the fiber, and more importantly, it can activate the fiber surface, increase the surface energy and active sites, and provide a clean and high-adhesion substrate for subsequent coating deposition. This preferred plasma cleaning step can significantly improve the bonding strength of the subsequent composite coating.

[0026] Second, a composite coating is formed on the surface of the activated alumina fiber. In this embodiment, the composite coating is composed of an inner aluminum layer and an outer copper layer. First, the plasma-cleaned fiber is loaded into the winding system of the direct current magnetron sputtering device. High-purity aluminum target is used as the target material, and sputtering is carried out in an argon atmosphere. By precisely controlling the winding speed and sputtering power, a 400-500 nm thick aluminum layer is uniformly deposited on the surface of the fiber. The aluminum layer serves as a transition layer and has good physical compatibility with the alumina fiber. Subsequently, the aluminum-coated fiber is removed from the sputtering device and immersed in a constant-temperature water bath for chemical copper plating. The plating solution is copper sulfate solution, and by adding complexing agents and adjusting agents, the pH value of the solution is precisely controlled at 12, and the temperature is maintained at 60°C. The fiber stays in the plating solution for enough time until a copper layer with a thickness of about 100 nm is deposited on its surface. The copper layer as the outermost wetting layer can instantaneously react with the subsequent molten aluminum liquid, greatly improving the wetting angle and promoting the occurrence of infiltration. Thus, a multilayer structure composite coating of "alumina-aluminum-copper" is formed on the surface of the alumina fiber.

[0027] Third, the preform is prepared. The fiber with Al / Cu composite coating is unidirectionally arranged or woven into a specific fabric structure according to needs, and then stacked and compacted to form a preform with a fiber volume fraction of 40% to 60%. The preform has a determined shape and size and retains a pore network for the infiltration of molten aluminum liquid. Finally, the preform is carefully placed in the porous graphite mold D (i.e., mold 7).

[0028] Subsequently, the aluminum ingot melting can be performed. Quantitative pure aluminum ingots or aluminum alloy ingots are placed in the crucible 5 in the melting zone A of the system. The melting zone A is heated by the zoned heating device J, while the flow-stable high-purity argon gas is introduced into the vacuum chamber from the interface of the protective gas 3 to prevent the aluminum from being oxidized at high temperature. The aluminum ingots are heated to 750°C, and are completely melted to form molten aluminum liquid with good fluidity.

[0029] Then, the preform preheating is performed. Before the suction casting is performed, in order to avoid the molten aluminum liquid from being blocked in the infiltration channel due to rapid solidification when the molten aluminum liquid is in contact with the low-temperature mold, the porous graphite mold D loaded with the preform needs to be preheated. The suction casting zone B is independently heated by the zoned heating device J, and the temperature of the mold 7 is raised to 550°C and is kept for a period of time to ensure that the temperature of the entire preform is uniform.

[0030] Subsequently, the key infiltration stage, i.e., the vacuum suction casting, step 102 and step 103 (ultrasonic and dynamic pressure synergistic infiltration) is entered. These steps can be closely connected and simultaneously performed in operation.

[0031] Firstly, the vacuum system is started. The PLC controller 9 instructs the vacuum pump 8 to pump the entire vacuum chamber through the connecting interface 1 until the vacuum degree in the chamber reaches 10 -2 Pa or lower. At this time, the melting zone A and the suction casting zone B are both in a high-vacuum environment.

[0032] Then, the vacuum suction casting is started. The molten aluminum liquid in the crucible 5 is connected to the bottom of the mold 7 in the suction casting zone B through a specific mechanical structure (not shown) or pressure control. Since the inside of the mold 7 is in a high-vacuum state, and a certain inert gas pressure (or atmospheric pressure) can be applied above the molten aluminum liquid, under the action of a large pressure difference, the molten aluminum liquid is rapidly sucked into the mold 7, and starts to infiltrate into the pore network of the fiber preform. At this time, an initial casting pressure of 0.5 MPa is set.

[0033] During the entire process of the molten aluminum liquid being injected and infiltrating the preform, the synergistic effect of step 102 and step 103 starts to play a key role: In one aspect, ultrasonic assistance is initiated. The PLC controller 9 applies a high-frequency alternating voltage to the piezoelectric transducer E (i.e., the piezoelectric transducer 6) coupled to the mold 7, causing it to generate ultrasonic vibrations at a frequency of 20-25 kHz. The vibrations are transmitted through the walls of the mold 7 to the molten aluminum being infiltrated. Ultrasonic waves propagate in a liquid and produce a well-known acoustic cavitation effect, i.e., in the rarefaction phase of the acoustic wave, the liquid is locally stretched to produce tiny bubbles or cavities, which collapse rapidly in the subsequent compression phase, generating micro-jets with high temperatures of several thousand degrees Celsius and high local pressures of several hundred megapascals. This intense physical effect acts on the molten aluminum, effectively breaking and peeling off the oxide film that hinders flow, significantly reducing the apparent viscosity of the aluminum, and producing strong stirring and impact effects, thereby greatly enhancing the flow and filling capacity of the aluminum in the micron-sized narrow gaps between the fiber bundles.

[0034] In another aspect, dynamic pressure regulation is initiated. At the same time as the infiltration begins, the pressure sensor G (i.e., the pressure sensor 2) embedded inside the mold 7 begins to work, it collects the infiltration pressure at a specific location inside the mold at an extremely high frequency (e.g., several hundred times per second), and sends the real-time pressure data to the PLC controller H (i.e., the PLC controller 9) in the form of an electrical signal. The PLC controller H has a set of control logic pre-set inside it, including a key pressure threshold, for example 0.3 MPa, and a pressure upper limit, for example 3 MPa. The controller compares the received pressure value with the pre-set 0.3 MPa threshold in real time. During the infiltration process, if the fiber arrangement in a certain area is particularly tight, or the flowability of the aluminum is poor due to local cooling, the flow resistance of this area will increase sharply, causing the infiltration pressure monitored by the sensor to drop significantly. Once the PLC controller H detects that the pressure value is lower than 0.3 MPa, it immediately determines that there is a problem with infiltration or insufficient feeding. At this time, the controller will immediately issue an instruction to the multi-stage vacuum pump I (i.e., the vacuum pump 8) as the pressure regulating device, instructing it to increase operating power. The increase in vacuum pump power will further increase the pressure difference of the entire vacuum system, thereby rapidly increasing the casting pressure acting on the molten aluminum in the crucible 5. The pressure continues to rise until the pressure value fed back by the pressure sensor G inside the mold reaches the pre-set pressure upper limit of 3 MPa. This high pressure state forces the molten aluminum to break through the obstacles and complete the filling and feeding of the difficult areas. When the area is filled, the flow resistance decreases, and the pressure naturally rises. The PLC controller H can continue to stabilize the casting pressure in a more appropriate range, for example 1-2 MPa, based on real-time pressure feedback, until the entire infiltration process is complete. This closed-loop dynamic regulation based on real-time feedback ensures that the entire preform is fully and densely filled, while avoiding the potential damage to the fibers caused by applying excessively high constant pressure for a long time.

[0035] Optionally, the method further comprises: After the impregnation is completed, the composite material in the mold is slowly cooled; and The mold wrapped around the composite material is removed by chemical etching.

[0036] Finally, cooling and post-processing can be performed. When the readings of the pressure sensor G reach stability throughout the mold area and are maintained for a period of time, it can be judged that the impregnation process has been completed. At this time, the application of ultrasonic waves and casting pressure is stopped, and the cooling program is started. In order to reduce the residual thermal stress of the composite material due to the mismatch of the thermal expansion coefficients of the matrix and the fibers during solidification, the embodiment adopts slow cooling treatment. By precisely controlling the power of the heating device 4, the mold 7 is slowly cooled to 300℃ at a rate of 10℃ / min in the vacuum chamber. After that, the vacuum chamber can be opened, the mold 7 is taken out, and naturally cooled to room temperature in the air.

[0037] After the composite material is completely cooled, the demolding process is performed. Since the graphite mold has a complex structure, mechanical demolding may damage the product. Therefore, the embodiment can adopt a chemical etching method to remove the mold wrapped around the composite material. The entire graphite mold with the composite material is immersed in a concentrated nitric acid solution with a concentration of 65wt%, and the nitric acid will react with the graphite to oxidize and etch it away, while having little effect on the internal aluminum-based composite material. After a period of corrosion, the graphite mold is completely removed, and the final product of the continuous aluminum oxide fiber reinforced aluminum matrix composite material with a clean surface and a dense interior is obtained.

[0038] Table 1 is a table of parameters and effects of some key process steps involved in the embodiment of the present application.

[0039]

[0040] Table 1 As shown in Table 1, some key process parameters involved in the method are included, in which the direct current magnetron sputtering device is used for magnetron sputtering aluminum deposition, which can realize the condition of sputtering rate to ensure constant rate deposition and improve material wettability; the ultrasonic wave is generated by a piezoelectric transducer, which can emit a frequency range of 20-25kHz; and the programmable tube furnace temperature control is used to achieve slow cooling at a constant cooling rate, so as to realize a cooling rate of 10℃ / min.

[0041] Table 2 is a table of dynamic pressure adjustment parameters involved in the embodiment of the present application.

[0042]

[0043] Table 2 The composite material prepared by the above method is detected to have internal porosity less than 1%, uniform fiber distribution, no macroscopic defects, good interface bonding between the fiber and the matrix, and excellent comprehensive mechanical properties.

[0044] The following describes Example 2 of the present application, which is a variant of Example 1, the main difference being the type of composite coating formed by the fiber surface pretreatment, which is intended to show that the technical solution of the present application is not limited to a specific coating system. In this example, the remaining preparation steps, including the preparation of the preform, the smelting of the aluminum ingot, the preheating of the preform, the ultrasonic and dynamic pressure assisted infiltration (steps 102 and 103), and the cooling and post-treatment, are all exactly the same as described in Example 1. The preparation system used can also be consistent with the system shown in Figure 2 and Figure 3 .

[0045] In this example, the fiber pretreatment of step 101 is performed as follows: First, the continuous alumina fibers are also subjected to plasma cleaning, with the same parameters and operations as in Example 1, to obtain a clean and activated fiber surface. Subsequently, a Ti / Ni composite coating is formed on the fiber surface by using a magnetron sputtering technique to sequentially deposit two different metal layers. Specifically, the plasma cleaned fiber is loaded into a multi-target magnetron sputtering device.

[0046] In the first step, a high-purity titanium target is used as the target material, and a 50-nanometer-thick titanium layer is deposited on the fiber surface by sputtering in an argon atmosphere. Titanium is an active metal that can react weakly with the alumina fiber surface during the subsequent high-temperature infiltration process, forming intermetallic compounds such as TiAl3, thereby achieving strong chemical and metallurgical bonding.

[0047] In the second step, without breaking the vacuum, the target material is switched to a high-purity nickel target, and a 150-nanometer-thick nickel layer is deposited on the titanium layer by sputtering. The nickel layer, as the outer layer, has excellent wettability with molten aluminum, which can significantly reduce the wetting angle and guide the rapid spreading and infiltration of the aluminum liquid. Through the above steps, a "alumina-titanium-nickel" composite coating structure is formed on the surface of the alumina fiber.

[0048] After completing the above fiber pretreatment, the fiber with the Ti / Ni composite coating is made into a preform with the same specifications as in Example 1 and placed in the porous graphite mold D. All subsequent processes, including smelting, preheating, vacuum suction casting, ultrasonic assistance (frequency 20-25 kHz), dynamic pressure regulation (pressure threshold 0.3 MPa, pressure upper limit 3 MPa), and cooling and chemical corrosion demolding, are carried out according to the parameters and procedures described in Example 1.

[0049] The embodiment can also prepare a composite material with very low porosity and dense structure. Compared with Example 1, the interface bonding mechanism and strength can be different due to the formation of chemical reaction products at the interface, but the purpose of improving wettability and strengthening interface bonding is achieved, which proves the wide applicability of the technical feature of "composite coating" in the method of the application.

[0050] Example 3 is introduced below, which is another variant of Example 1, the main difference being the specific implementation of the pressure regulating device in the dynamic pressure control system, aiming to illustrate that the core of the dynamic pressure regulation of the application is the closed-loop feedback logic, and the actuator can have various forms.

[0051] In this embodiment, the hardware structure of the preparation system is adjusted. Specifically, Figure 2 and Figure 3 The pressure regulating device in the dynamic pressure control system shown in the above formula is no longer a multi-stage vacuum pump I (or a vacuum pump 8), but is replaced by a high-temperature-resistant graphite pressure head (not shown in the figure) driven by a servo motor. The graphite pressure head is installed in the vacuum chamber, located directly above the molten aluminum liquid in the crucible 5, and can accurately move up and down to exert mechanical pressure on the aluminum liquid. Other parts of the system, such as the mold 7, the pressure sensor 2, the PLC controller 9, the heating device 4, the piezoelectric transducer 6, etc., are exactly the same as in Example 1.

[0052] In the preparation method of this embodiment, the fiber pretreatment (using the Al / Cu coating of Example 1), the preparation of the preform, the melting of the aluminum ingot, the preheating of the preform, the ultrasonic assistance, and the cooling and post-treatment steps are all exactly the same as in Example 1. The core difference lies in the specific execution process of dynamically adjusting the casting pressure in step 103: After the vacuum suction casting starts, the main role of the vacuum pump 8 is to establish and maintain a high vacuum non-oxidizing environment for the system, and to provide a basic suction pressure difference, the power of which remains relatively constant during the infiltration process. During the infiltration process, the pressure sensor 2 also monitors the infiltration pressure in the mold 7 in real time and sends a signal to the PLC controller 9. The control logic (pressure threshold 0.3 MPa, pressure upper limit 3 MPa) inside the PLC controller 9 is also the same as that of embodiment 1. When the PLC controller 9 monitors that the infiltration pressure is lower than 0.3 MPa, it no longer issues instructions to the vacuum pump 8, but issues instructions to the servo motor controlling the graphite pressure head. After receiving the instructions, the servo motor accurately drives the graphite pressure head to move downward at a set speed and stroke, directly applying a controllable mechanical pressure to the molten aluminum liquid in the crucible 5. This pressure is quickly transmitted to the entire liquid phase, including the infiltration front being infiltrated, through the Pascal principle. The PLC controller 9 continuously adjusts the output torque of the servo motor and the depth of the pressure head according to the real-time feedback of the pressure sensor 2, so as to accurately raise the infiltration pressure in the mold to the target value of 3 MPa, realizing forced feeding. When the pressure returns, the controller can instruct the pressure head to maintain a stable pressure or slightly retreat.

[0053] Compared with the method of changing the pressure difference by adjusting the vacuum pump, using a mechanical pressure head for pressure adjustment has the advantages of faster response speed, more direct pressure control, and higher upper limit of the pressure that can be applied. This method is especially suitable for preparing composite components with larger size, more complex structure, or higher fiber volume fraction, and can achieve more rapid and powerful dynamic feeding. This embodiment proves that as long as the pressure regulation device is a vacuum pump or a mechanical pressure head, as long as it constitutes a closed-loop feedback system of "sensor monitoring-controller decision-actuator regulation", it falls within the protection concept of the present application.

[0054] Further optionally, embodiment 4 is introduced below, which is another variant of embodiment 1, the main difference being that the specific type of ultrasonic generator used in step 102 is different, aiming to illustrate that the purpose of applying ultrasonic vibration is to utilize its physical effect, and the type of transducer used to achieve this purpose is not unique.

[0055] In this embodiment, the piezoelectric transducer E (or the piezoelectric transducer 6) coupled with the mold 7 of the preparation system is replaced by a large-power magnetostrictive transducer (not shown in the figure). The vibration head of the magnetostrictive transducer is rigidly connected and acoustically coupled with the bottom or side wall of the mold 7. All other parts of the system, including the fibers with Al / Cu coating, the dynamic pressure control system (consisting of a pressure sensor, a PLC controller and a vacuum pump), etc., are exactly the same as those of embodiment 1.

[0056] The preparation method of this embodiment is different from that of embodiment 1 in that the equipment and parameters for applying ultrasonic waves are different. All other steps, including fiber pretreatment, preform preparation, smelting, preheating, dynamic pressure regulation, and post-processing, are completely consistent with those of embodiment 1. During the combined infiltration process of steps 102 and 103, when the PLC controller 9 issues an instruction to start the ultrasonic waves, an electric current is applied to the coil of the magnetostrictive transducer, causing the magnetostrictive material (such as a rod of iron-based or rare earth-based alloy) inside to expand and contract in an alternating magnetic field, thereby generating strong mechanical vibrations. In this embodiment, the applied ultrasonic frequency is 18-22 kHz. This vibration is transmitted to the molten aluminum through the vibration head and mold 7, and can also produce strong acoustic cavitation and acoustic streaming effects in the aluminum melt, with the same mechanism and final effect (reducing flow resistance and promoting infiltration) as the piezoelectric transducer in embodiment 1.

[0057] Compared with piezoelectric transducers, magnetostrictive transducers can generally withstand higher power input, produce larger vibration amplitudes and acoustic intensities, and work more stably in high-temperature environments. Therefore, for scenarios that require stronger ultrasonic energy to assist infiltration, such as processing preforms with very high fiber volume fractions (e.g., more than 65%) or complex components with extremely small infiltration channels, using a magnetostrictive transducer can be a more preferred technical choice. This embodiment demonstrates that the technical solution of the present application encompasses the use of ultrasonic devices with different working principles, as long as they can apply ultrasonic vibrations to the mold during the infiltration process.

[0058] The following specific examples and experimental data are presented to further illustrate the technical solutions and effects of the present application.

[0059] 1. Introduction This embodiment is based on the preparation of alumina fiber reinforced aluminum matrix composites and thermal-mechanical coupling finite element analysis project, the main purpose is to realize a kind of higher performance alumina fiber reinforced aluminum matrix composite material preparation, for subsequent project development lay a foundation and condition.

[0060] The composite material prepared by the continuous alumina fiber reinforced aluminum matrix composite ultrasonic assisted composite coating vacuum suction casting method in this embodiment not only meets the needs of the basic research project, but also greatly improves the performance of this traditional composite material, including strength, stiffness and other mechanical properties.

[0061] 2. Required equipment and materials Table 3 is a list of required equipment and materials provided by the present application. The list of equipment and materials required to carry out this embodiment is shown in Table 3:

[0062] Table 3 3. Operation and application steps The preparation of the composite material is carried out according to the process of the ultrasonic-assisted composite coating vacuum suction casting method of continuous aluminum oxide fiber reinforced aluminum matrix composite material. The detailed operation process is as follows: 1-1: Take the argon plasma chamber, put 50 grams of aluminum oxide fiber in the chamber, and adjust the internal gas pressure to 50 Pa by electrifying. Maintain the argon plasma chamber environment for 10 minutes to remove the surface contaminants of the fiber and achieve surface molecular activation.

[0063] 1-2: Take out the aluminum oxide fiber after plasma cleaning, start the direct current magnetron sputtering device, and start the aluminum plating operation. Set the sputtering rate to 5 nm / min. After one and a half hours of sputtering and plating aluminum, the aluminum layer on the surface of the aluminum oxide fiber is 450 nm thick.

[0064] 1-3: Heat the prepared copper sulfate solution to 60°C, then immerse the aluminum-plated fiber into the copper sulfate solution, and start the copper plating. According to the reaction rate of copper sulfate, take out the aluminum fiber after 20 minutes of copper plating. The average thickness of the copper plating layer is about 99.5 nm measured by a plating thickness gauge.

[0065] 2-1: Take out the prepared porous graphite mold, place the aluminum / copper composite plated fiber in the mold according to the unidirectional arrangement, use a temperature control device to heat the porous graphite mold to 550°C, and prepare the preform. At the same time, the fiber volume fraction needs to be controlled at 40-60 vol%.

[0066] 3-1: Prepare a sealed heating device, put 100 grams of pure aluminum into the sealed heating device, and flush with argon to protect the aluminum liquid from oxidation. Use a temperature control device to heat to 750°C and maintain until all the pure aluminum is completely melted.

[0067] 3-2: During the heating of pure aluminum, the upper and lower chambers of the porous graphite mold are heated to 550°C and 750°C respectively, and the current temperature is maintained. Then use a vacuum pump to evacuate the chamber until the vacuum degree is less than 10-2Pa. After the pure aluminum is completely melted, the aluminum liquid is injected into the mold through the plunger pressurizing device, and the initial injection pressure is 0.5 MPa.

[0068] 3-3: When the aluminum liquid starts to inject into the mold, turn on the piezoelectric transducer array on the outer wall of the mold until the entire injection molding process is completed. Set the ultrasonic vibration frequency to 22 kHz, so that the ultrasonic cavitation effect can fully penetrate the aluminum liquid into the gaps between the fibers and break the oxide film.

[0069] 3-4: In the process of molten aluminum injection, the high-temperature piezoresistive sensor (temperature resistance ≥800℃) is embedded in the mold to monitor the immersion pressure in real time. When the internal pressure is observed to be lower than 0.3 MPa, the power of the vacuum pump is adjusted to increase the pressure to 3 MPa to achieve forced flow of molten aluminum.

[0070] 4-1: The program of the programmable tubular furnace temperature control device is adjusted to achieve slow cooling of the mold at 10℃ / min, and then the temperature control device is turned off to air cool the mold to room temperature.

[0071] 4-2: Take out the prepared concentrated nitric acid solution, and immerse the cooled mold into it. After the graphite mold is corroded, immediately take out the prepared composite material.

[0072] 4, Experimental test results In addition, the traditional method is used to prepare aluminum-based composite materials. The performance of the composite materials prepared by the traditional method and the method of the application is measured and counted. The counting method is to count the number of pores in different cross sections of the material. The coating thickness gauge is used to measure the coating thickness of different points after aluminum plating and copper plating. Five cross sections of the final material are taken to count the pores (a certain radial length greater than 0.2mm). The results are shown in Table 4.

[0073]

[0074] Table 4 Table 4 is a comparison table of the number of pores of a traditional method and the method of the application provided by the application. As can be seen from Table 4, the number of pores in the same position cross section of the composite material prepared by the method of the application is significantly lower than that of the composite material prepared by the traditional method. Therefore, the method of the application can effectively reduce the porosity of the composite material.

[0075] The same 8 points are taken, and the coating thickness gauge is used to measure the thickness of the material after aluminum plating and copper plating. The results are shown in Table 5.

[0076] Table 5 Table 5 is a comparison table of the thickness of the material after aluminum plating / copper plating of a traditional method and the method of the application provided by the application. As can be seen from Table 5, at the same position, the thickness variance of the aluminum plating layer and the copper plating layer of the composite material obtained by the traditional method is significantly greater than the thickness variance of the aluminum plating layer and the copper plating layer of the composite material obtained by the method of the application. That is, the uniformity of the plating layer obtained by the method of the application is significantly improved.

[0077] Any combination of the technical features in the above embodiments can be made, and for the sake of brevity, not all possible combinations are described above, however, as long as the combination of the technical features does not exist in contradiction, it shall be considered within the scope of the present disclosure.

[0078] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the patent scope of the present application. It shall be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for preparing a continuous fiber-reinforced aluminum matrix composite material, characterized in that, include: The alumina fibers are pretreated to form a composite coating on the surface of the alumina fibers. During the process of injecting molten aluminum into a mold containing alumina fibers using vacuum casting, ultrasonic vibration is applied to the mold. During the vacuum casting process, the immersion pressure inside the mold is monitored, and the casting pressure acting on the molten aluminum is dynamically adjusted based on the monitored immersion pressure.

2. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 1, characterized in that, The method further includes: The alumina fibers are plasma cleaned before the composite coating is formed.

3. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 1 or 2, characterized in that, The composite coating comprises an aluminum layer and a copper layer sequentially disposed on the surface of the alumina fiber.

4. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 1 or 2, characterized in that, The composite coating comprises a titanium layer and a nickel layer sequentially disposed on the surface of the alumina fiber.

5. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 1, characterized in that, The frequency of the ultrasonic vibration is 18 kHz to 25 kHz.

6. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 5, characterized in that, The step of dynamically adjusting the casting pressure specifically includes: When the detected impregnation pressure is lower than a preset pressure threshold, the casting pressure is increased to a preset pressure upper limit.

7. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 6, characterized in that, The increase in casting pressure is achieved by adjusting the power of the vacuum pump to increase the pressure difference of the vacuum system.

8. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 6, characterized in that, The increase in casting pressure is achieved by driving a mechanical pressure head to apply mechanical pressure to the molten aluminum.

9. The method for preparing the continuous fiber reinforced aluminum matrix composite material according to claim 8, characterized in that, The method further includes: After impregnation, the composite material inside the mold is subjected to slow cooling treatment; and The mold encapsulating the composite material is removed by chemical corrosion.

10. A preparation system for continuous fiber reinforced aluminum matrix composites, characterized in that, include: A mold for holding a surface-pretreated alumina fiber preform; The mold is disposed within the vacuum chamber. A heating device for heating an aluminum substrate into molten aluminum. An ultrasonic generator, coupled to the mold, is used to apply ultrasonic vibration to the mold during vacuum casting. as well as A dynamic pressure control system, comprising: A pressure sensor installed inside the mold is used to monitor the immersion pressure inside the mold in real time. The controller is connected to the pressure sensor signal; and The pressure regulating device, controlled by the controller, is used to dynamically adjust the casting pressure acting on the molten aluminum liquid based on the immersion pressure monitored by the pressure sensor.

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