Thermoplastic carbon fiber reinforced magnesium alloy composite tube differential temperature and air pressure regulation and in-situ reinforcement integrated forming method

Abstract

The invention relates to the technical field of composite material magnesium alloy pipe component forming and manufacturing, in particular to a thermoplastic carbon fiber reinforced magnesium alloy composite pipe differential temperature air pressure regulation and in-situ reinforcement integrated forming method which comprises the steps that a magnesium alloy pipe blank is subjected to heat treatment; magnesium alloy pipe blank surface treatment; assembling a magnesium alloy composite pipe prefabricated body; a differential temperature field is constructed for the magnesium alloy composite pipe, so that the thermoplastic resin in the magnesium alloy composite pipe enters a viscous flow state while the magnesium alloy keeps good plasticity; then air pressure and axial feeding cooperative loading is carried out, and precise forming of the mold is achieved; the magnesium alloy composite pipe component is subjected to differential temperature cooling, thermoplastic resin is promoted to be fully infiltrated by means of radial shrinkage compressive stress generated at the interface by means of thermal expansion difference caused by inner and outer layer temperature difference, and in-situ enhancement of the interface of the magnesium alloy composite pipe is achieved; the requirements of high-end equipment for high-performance and high-efficiency preparation of the magnesium alloy composite pipe are met with high integration level and high strength.

Description

Technical Field

[0001] This invention relates to the field of composite magnesium alloy tube component forming and manufacturing technology, and in particular to an integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature and pressure control and in-situ reinforcement. Background Technology

[0002] Fiber-reinforced metal composite pipes, as a typical type of ultra-hybrid structural material, organically combine lightweight, high-strength fiber composite materials with low-cost, high-ductility metal materials. This synergistically enhances the overall structural impact resistance and energy absorption characteristics while significantly achieving lightweighting. Due to their unique performance advantages, these materials demonstrate significant application value and development prospects in the field of energy-absorbing structures. Magnesium alloys, as commonly used lightweight structural materials, are widely applied in fiber-reinforced metal composites. Thermoplastic carbon fiber reinforced magnesium alloy composite pipes, as an important cutting-edge branch of fiber-reinforced metal composites, offer significant advantages in processing, performance, and applications compared to traditional thermosetting systems: thermoplastic resins can be repeatedly melted, supporting integrated rapid processing of molding, curing, and strengthening, resulting in a shorter process and the ability to recycle waste; their resin matrix exhibits high toughness, stronger impact and fatigue resistance, and stable performance at low temperatures; they possess excellent resistance to damp heat and corrosion, adapting to various harsh environments; the production process is environmentally friendly, aligning with green manufacturing trends, and resulting in lower life-cycle costs.

[0003] The forming process of composite materials has developed rapidly in recent decades. However, the special layered structure of fiber-reinforced metal composite tubes places higher demands on the forming process, and traditional forming techniques are not entirely suitable for fiber-reinforced metal composite tubes. Currently, existing technologies mainly use step-forming-composite processes, hot pressing-resin injection processes, spin forming processes, and hydraulic bulging techniques to prepare fiber-reinforced metal composite tube components.

[0004] Step-by-step forming-composite process: The technology disclosed in Chinese patent CN113787733A uses a process route of "heat treatment of metal tube blank, pre-forming with soft mold, layering of fiber prepreg, and composite pressing" to achieve layered tube preparation by using solid particulate media instead of rigid molds. However, it suffers from numerous steps, cumbersome mold replacement and installation, and low process integration. Autoclave process achieves curing and composite bonding of metal and fiber layers in a high-temperature and high-pressure environment, but it suffers from high equipment investment costs, long production cycles, and difficulty in forming complex shaped components.

[0005] Hot pressing-resin injection process: Chinese patent CN118386578A proposes a composite molding method of hot gas pressure expansion of fiber metal layer tubes / in-situ resin injection, which improves resin wetting efficiency, but lacks effective control over the temperature difference sensitivity of thermoplastic resin and the precipitation behavior of metal reinforcing phase.

[0006] Spin forming, combining multi-pass spinning with curing, can fabricate complex fiber-metal hybrid composite tubes. This process applies progressive pressure to the tube using a rotating die, causing plastic deformation of the outer metal layer while simultaneously bringing the uncured inner fiber prepreg to conform to the die surface. After curing, a composite structure is formed. However, due to the fundamental differences in the deformation mechanisms of the metal and fiber layers—the aluminum alloy layer adapts to the die surface through plastic flow, while the fiber layer primarily undergoes elastic deformation with low elongation—the deformation coordination between the two layers during multi-pass spinning is insufficient. This deformation mismatch easily leads to stress accumulation between layers, especially in areas of abrupt curvature change. Stress concentration often causes wrinkles or delamination in the fiber layer, resulting in delamination defects and affecting the reliability of the component during service.

[0007] Hydraulic bulging technology uses liquid as the force transmission medium. High-pressure liquid pushes the aluminum alloy tube blank to bulge, causing the outer fiber prepreg to adhere to the mold, thus achieving one-time forming of the composite tube. The uniform pressure transmission of the liquid makes it suitable for flexible forming of complex surfaces. However, in this method, the interlayer bonding relies only on the initial impregnation and physical adsorption of resin, resulting in poor interlayer bonding performance between the outer metal layer and the composite material layer.

[0008] Therefore, while the above-mentioned methods can achieve the fabrication of complex-structured magnesium alloy composite tubes, they suffer from the following problems: existing technologies generally suffer from core bottlenecks such as insufficient interlayer bonding strength, poor temperature field control, and low process integration, making it difficult to fully utilize the material advantages of thermoplastic fiber-reinforced magnesium alloy composite tubes. Especially in the fabrication of complex-shaped components, the lack of deformation coordination between the magnesium alloy layer and the intermediate thermoplastic carbon fiber prepreg, the lack of resin impregnation uniformity, and the lack of interfacial strengthening mechanisms make it difficult to balance component reliability and production efficiency. Summary of the Invention

[0009] Therefore, to address the problems existing in the prior art, this invention provides an integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes using differential temperature and pressure control and in-situ reinforcement. This method overcomes the key problems of insufficient interlayer bonding strength, poor temperature field control, and low process integration in the existing thermoplastic fiber reinforced magnesium alloy composite tube forming technology. To achieve the above objective, this invention provides an integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes using differential temperature and pressure control and in-situ reinforcement. This method achieves high-performance fabrication of magnesium alloy composite tubes through the coupling effect of differentiated temperature fields, pressure loading, and in-situ reinforcement. Specifically, it includes the following steps: Step S1: Heat treatment and surface treatment are performed on the inner magnesium alloy tube blank and the outer magnesium alloy tube blank respectively to obtain the inner magnesium alloy tube and the outer magnesium alloy tube. Step S2: The intermediate layer thermoplastic fiber prepreg is laid on the outer surface of the inner layer magnesium alloy tube, and the outer layer magnesium alloy tube is sleeved on the intermediate layer thermoplastic fiber prepreg to form a magnesium alloy composite tube preform. The laying width of the intermediate layer thermoplastic fiber prepreg is smaller than the length of the inner layer magnesium alloy tube blank and the outer layer magnesium alloy tube. Step S3: The magnesium alloy composite tube preform is loaded into the heating chamber of the differential temperature gas pressure forming mold, and the inner magnesium alloy tube and the outer magnesium alloy tube are heated to the corresponding second preset temperature, so that the thermoplastic resin can transfer heat through the inner magnesium alloy tube and the outer magnesium alloy tube to reach the melting temperature and thus enter the viscous flow state. Step S4: Transfer the magnesium alloy composite tube preform, which is in a stable state of differential temperature field, into the mold forming cavity. Use the sealing component in the mold forming cavity to accurately insert into the gap between the inner magnesium alloy tube and the outer magnesium alloy tube for sealing. Turn on the vacuum pump to remove air bubbles from the intermediate layer thermoplastic carbon fiber prepreg. Step S5: After the air inside the magnesium alloy composite tube preform is exhausted, high-pressure gas is introduced into the mold forming cavity to keep the sealing component continuously advancing towards the center of the magnesium alloy composite tube preform, so that the magnesium alloy composite tube preform passively fits the mold surface under the combined action of air pressure loading and axial feeding, so as to complete the forming of thermoplastic carbon fiber reinforced magnesium alloy composite tube. Step S6: After the thermoplastic carbon fiber reinforced magnesium alloy composite pipe is formed, start the mold cooling system, input cooling water into the outer layer of the mold, cool the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component, unload it, and take out the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component.

[0010] Further, step S1 includes: Step S11: Heat treatment is performed on the inner magnesium alloy tube blank 1 and the outer magnesium alloy tube blank 3, wherein the heat treatment includes solution treatment and quenching treatment. Step S12 involves performing surface treatment on the inner surface of the outer magnesium alloy tube and the outer surface of the inner magnesium alloy tube after heat treatment to improve the interfacial adhesion performance. The surface treatment includes pickling to remove the film, alkaline washing to roughen the surface, anodizing, rinsing, and drying.

[0011] Furthermore, in step S2, the thermoplastic carbon fiber prepreg is laid in one or more layers, and each layer is subjected to pressure by a roller press to ensure that the fiber bundles are tightly bonded.

[0012] Furthermore, the inner magnesium alloy tube blank and the outer magnesium alloy tube blank should be made of different types of magnesium alloys, and the strength and coefficient of thermal expansion of the outer magnesium alloy tube blank should be greater than those of the inner magnesium alloy tube blank.

[0013] Further, in step S3, the inner magnesium alloy tube and the outer magnesium alloy tube are heated to a second preset temperature using independent heating systems for the inner and outer layers, wherein... For AZ-series magnesium alloys, the second preset temperature is 180℃ to 260℃, and the holding time is 5-12 minutes. For ZK series magnesium alloys, the second preset temperature is 180℃ to 230℃, and the holding time is 5-15 minutes. For ZM series magnesium alloys, the second preset temperature is 200℃ to 240℃, and the holding time is 5-16 minutes.

[0014] Furthermore, in step S3, if the heat preservation time corresponding to the inner magnesium alloy tube and the outer magnesium alloy tube is different, the heat preservation time of the longer heat preservation time is taken as the heat preservation time of the heating system.

[0015] Furthermore, the melting temperature of the thermoplastic resin used in the thermoplastic carbon fiber prepreg is lower than the minimum of the second preset temperature of the inner magnesium alloy tube and the second preset temperature of the outer magnesium alloy tube.

[0016] Furthermore, step S11 also includes step S112, which involves performing a pre-strengthening treatment after heat treatment, transferring the quenched tube blank to a constant temperature drying oven, and holding it at a first preset temperature. For AZ-series magnesium alloys, the first preset temperature is 100℃ to 180℃, and the holding time is 4 to 36 hours. For ZK series magnesium alloys, the first preset temperature is 90℃ to 110℃, and the holding time is 10-24 hours. For ZM series magnesium alloys, the first preset temperature is 80℃ to 120℃, and the holding time is 4-24 hours.

[0017] Furthermore, in step S5, the vacuum pump maintains a negative pressure range of -0.06MPa to -0.08MPa.

[0018] Furthermore, in step S6, the pressure range of the high-pressure gas is 5-50 MPa.

[0019] Compared with the prior art, the beneficial effect of the present invention is that it proposes a novel forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes, namely, a differential temperature and pressure control-in-situ reinforcement integrated forming method. By constructing a differentiated temperature field, implementing precise air pressure loading, and combining the synergistic effect of in-situ reinforcement technology, the overall performance of magnesium alloy composite tubes can be significantly improved.

[0020] Furthermore, the interfacial shrinkage stress field induced by differential temperature cooling ensures thorough resin wetting, improving interlaminar shear strength and anti-delamination ability, thus meeting the stringent interlaminar load-bearing requirements of aerospace components. Current heating aging treatment rapidly raises the temperature, enabling rapid nucleation of the reinforcing phase and shortening the strengthening cycle. This method, through the coupling of differential temperature control, gas pressure loading, and in-situ strengthening, specifically addresses the problems of weak interlaminar bonding, difficult temperature control, and fragmented processes in existing technologies. It integrates forming, curing, and strengthening, shortening the production cycle and reducing energy consumption and costs. These innovations overcome the bottlenecks in the engineering preparation of thermoplastic fiber-reinforced magnesium alloy composite pipes, providing key technical support for their large-scale application in aerospace, new energy vehicles, and other fields. Attached Figure Description

[0021] Figure 1 This is a flowchart of the integrated forming process of differential temperature and pressure control and in-situ reinforcement for thermoplastic carbon fiber reinforced magnesium alloy composite tubes of the present invention. Figure 2 This is an assembly drawing of the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component of the present invention; Figure 3 This is a diagram of the differential temperature control device for the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component of the present invention; Figure 4 This is a diagram of the pneumatic forming apparatus for the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component of the present invention. Figure 5 This is a top view of the lower mold of the integrated forming device for differential temperature and pressure control and in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite pipe of the present invention. Figure 6 This is a diagram of the in-situ reinforcement device for the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component of the present invention; Figure 7 Diagram of the right-side pusher device The attached figures are labeled as follows: 1-Inner magnesium alloy tube, 2-Intermediate thermoplastic fiber prepreg, 3-Outer magnesium alloy tube, 4-Composite tube preform, 5-Differential temperature and pressure control-in-situ reinforcement integrated forming mold, 6-Mold heating cavity, 7-Mold forming cavity, 8-Mold water cooling pipeline, 9-Positive electrode of the inner magnesium alloy tube current heating electrode, 10-Negative electrode of the inner magnesium alloy tube current heating electrode, 11-Positive electrode of the outer magnesium alloy tube current heating electrode, 12-Negative electrode of the outer magnesium alloy tube current heating electrode, 13-Push head, 14-Pressure gauge, 15-Pneumatic forming air path, 16-Sealing ring, 17-Vacuum pump. Detailed Implementation

[0022] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0023] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0025] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] For ease of understanding of the terminology used in this invention: Mg / CFRTP Composite Pipe: Magnesium / Carbon Fiber Reinforced Thermoplastic Composite Pipe, a multi-layered pipe made of magnesium alloy with an outer and inner layer of magnesium alloy and a middle thermoplastic resin-based carbon fiber layer through a composite process.

[0027] Thermoplastic resins are a class of polymeric materials that can melt and flow when heated, solidify and set upon cooling, and can be repeatedly heated and reshaped. In composite tubes, they serve as a matrix, encapsulating fibers and bonding with a magnesium alloy layer. Melt impregnation and curing are achieved through temperature control, and the resins possess recyclability and good processability.

[0028] Solution treatment: The magnesium alloy is heated to the temperature at which its strengthening phase is completely dissolved, and after holding at the temperature, a uniform supersaturated solid solution is formed.

[0029] Quenching treatment: a process in which high-temperature magnesium alloys are cooled to room temperature at a sufficiently fast cooling rate to suppress the precipitation of strengthening phases and to "freeze" solute atoms in the matrix to form a supersaturated solid solution.

[0030] Pre-strengthening treatment: a process step that involves low-temperature aging of quenched magnesium alloy tube blanks to promote the enrichment of solute atoms on the crystal plane to form GP regions.

[0031] GP zone: A metastable transition phase formed during the aging strengthening process of magnesium alloys (such as ZK series and ZM series). It is completely coherent with the matrix and its composition is between that of the matrix and the equilibrium strengthening phase. It is a key precursor for aging strengthening.

[0032] Metastable strengthening phase: A transitional precipitate formed during the aging strengthening process of magnesium alloys. Its structure is semi-coherent with the matrix. It hinders dislocation movement through lattice distortion, thus significantly improving the strength of the material.

[0033] Please see Figures 1-7 As shown, Figure 1 This is a flow chart of the integrated forming process of differential temperature and pressure control and in-situ reinforcement of the present invention. An embodiment of the present invention provides a method for integrated forming of thermoplastic carbon fiber reinforced magnesium alloy composite tubes using differential temperature and pressure control and in-situ reinforcement, comprising: Step S1: Heat treatment and surface treatment are performed on the inner magnesium alloy tube blank and the outer magnesium alloy tube blank respectively to obtain the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3. Step S11: Heat treat the inner magnesium alloy tube blank and the outer magnesium alloy tube blank. Specifically, heat treatment includes solution treatment and quenching treatment. Step S111: Solution treatment and quenching. Solution treatment: The inner magnesium alloy tube blank and the outer magnesium alloy tube blank are placed in a box-type resistance furnace, heated to the solution temperature, and held for a certain time to allow the strengthening phase to dissolve fully. Then, they are immediately immersed in 20°C deionized water for quenching to obtain a supersaturated solid solution.

[0034] Specifically, for AZ-based magnesium alloys (Mg-Al-Zn), the solution treatment temperature is 380℃ to 420℃, with a holding time of 2–18 hours. For ZK-based magnesium alloys (Mg-Zn-Zr), the solution treatment temperature is 390℃ to 450℃, with a holding time of 1–10 hours. For ZM-based magnesium alloys (Mg-Zn-Mn), the solution treatment temperature is 360℃ to 540℃, with a holding time of 4–14 hours. The specific temperature and holding time depend on the specific alloy type and will not be elaborated further here.

[0035] Step S112, pre-strengthening treatment; Pre-strengthening treatment: The quenched inner and outer magnesium alloy tube blanks are transferred to a constant temperature drying oven and kept at the first preset temperature to promote the enrichment of solute atoms on the crystal surface to form GP regions or solute atom segregation regions, which provide nucleation sites for subsequent metastable strengthening phase precipitation.

[0036] Specifically, for AZ-based magnesium alloys, the first preset temperature is 100℃ to 180℃, and the holding time is 4 to 36 hours. Solute atoms undergo uniform segregation in the matrix, forming dispersed solute atom segregation regions, which provide nucleation sites for the subsequent precipitation of the metastable strengthening phase β′.

[0037] Specifically, for ZK-based magnesium alloys, the first preset temperature is 90℃ to 110℃, and the holding time is 10-24 hours, which precipitates the GP zone and provides nucleation sites for the subsequent precipitation of the metastable strengthening phase β′.

[0038] Specifically, for ZM-based magnesium alloys, the first preset temperature is 80℃ to 120℃, and the holding time is 4-24 hours, which precipitates the GP zone and provides nucleation sites for the subsequent precipitation of the metastable strengthening phase β′.

[0039] Step S12 involves surface treatment of the inner surface of the outer magnesium alloy tube blank and the outer surface of the inner magnesium alloy tube blank after heat treatment to improve interfacial adhesion performance. This includes the following steps: Pickling to remove oxide film: Immerse the tube blank in a 5% hydrochloric acid solution for 5 minutes to remove the natural oxide film on the surface and expose the fresh magnesium alloy substrate; Alkaline washing and roughening: Transfer to a 10% sodium hydroxide solution for 3 minutes to neutralize residual acid and etch the surface, forming a micron-level uneven structure; Anodizing: Using oxalic acid electrolyte, with the tube blank as the anode and the lead plate as the cathode, a constant current is applied to generate a porous oxide film; Rinse and dry: Rinse repeatedly with deionized water until neutral, and dry in an 80°C oven to ensure no residual electrolyte remains on the surface.

[0040] It is understandable that the surface treatment process of pickling, alkali washing, anodizing and rinsing and drying is used to remove the oxide film on the surface of the tube blank and form a porous structure, thereby improving the surface energy matching degree between the magnesium alloy layer and the fiber resin layer and providing conditions for interfacial molecular diffusion and mechanical interlocking.

[0041] Step S2: The intermediate layer thermoplastic fiber prepreg 2 is laid on the outer surface of the inner layer magnesium alloy tube 1, and the outer layer magnesium alloy tube 3 is sleeved on the intermediate layer thermoplastic fiber prepreg 2 to form a magnesium alloy composite tube preform 4. The laying width of the intermediate layer thermoplastic fiber prepreg 2 is smaller than the length of the inner layer magnesium alloy tube 1 and the outer layer magnesium alloy tube 3. Prepreg Layup: The thermoplastic carbon fiber prepreg 2 is laid in one or more layers, and each layer is subjected to pressure by a roller press to ensure that the fiber bundles are tightly bonded.

[0042] Specifically, the intermediate layer of thermoplastic carbon fiber prepreg 2 is laid on the inner layer of magnesium alloy tube 1 in one or more layers. Each layer is pressurized by a roller press to ensure that the fiber bundles are tightly bonded. Then, the outer layer of magnesium alloy tube 3 is sleeved on the outside of the intermediate layer of thermoplastic carbon fiber prepreg 2, so that there is a gap of about 0.2-0.5 mm between the intermediate layer of thermoplastic carbon fiber prepreg 2 and the inner wall of the outer layer of magnesium alloy tube 3, forming a magnesium alloy composite tube preform 4 with a sandwich structure of "inner magnesium alloy - carbon fiber prepreg - outer magnesium alloy", which provides a stable initial interlayer state for subsequent differential temperature control and air pressure forming.

[0043] Specifically, the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 should be made of different types of magnesium alloys, and the strength and coefficient of thermal expansion of the outer magnesium alloy tube 3 are greater than those of the inner magnesium alloy tube 1.

[0044] Step S3: The magnesium alloy composite tube preform 4 is placed into the heating chamber 6 of the differential temperature gas pressure forming mold, and the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are heated to the corresponding second preset temperature, so that the thermoplastic resin can transfer heat through the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 to reach the melting temperature and thus enter the viscous flow state.

[0045] Specifically, the magnesium alloy composite tube preform 4 is installed into the heating chamber 6 of the differential temperature gas pressure forming mold, and the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are heated by the inner independent heating power electrodes 9 and 10 and the outer independent heating power electrodes 11 and 12, respectively, so as to achieve independent temperature control of the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3.

[0046] By using independent heating systems for the inner and outer layers, the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are heated to their corresponding second preset temperatures, causing them to rapidly precipitate metastable reinforcing phases. The temperature difference between the inner and outer heating systems, which can be independently controlled, is then used to heat the intermediate thermoplastic carbon fiber prepreg 2 to a temperature that allows the thermoplastic resin to enter a viscous flow state. It is understood that the specific temperature and holding time of the second preset temperature are determined according to the specific alloy type. When the holding time required for the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are different, the one with the longer holding time should be used. Among them, for AZ series magnesium alloys, the second preset temperature is 180℃ to 260℃, and the holding time is 5-12 minutes. For ZK series magnesium alloys, the second preset temperature is 180℃ to 230℃, and the holding time is 5-15 minutes. For ZM series magnesium alloys, the second preset temperature is 200℃ to 240℃, and the holding time is 5-16 minutes.

[0047] Specifically, the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3, which can be independently heated, are used for differential temperature control to heat the intermediate thermoplastic carbon fiber prepreg 2 to the temperature at which the thermoplastic resin enters the viscous flow state. When deformation occurs between the layers, shear stress can be released and a certain strength can be maintained inside the resin layer, thereby improving the deformation margin of the composite material layer.

[0048] In this embodiment, the specific steps for implementing differential temperature control are as follows: the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are simultaneously heated to their respective second preset temperatures and then held at those temperatures. The intermediate thermoplastic carbon fiber prepreg 2 is placed between the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3, and is heated by heat transfer between the inner and outer magnesium alloy tubes. Differential temperature refers to the fact that the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are made of different materials, thus requiring different second preset temperatures. Furthermore, the melting temperature of the thermoplastic resin is lower than the minimum of the second preset temperatures of the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3. Therefore, differential temperature control can be achieved by heating the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 individually.

[0049] Specifically, the thermoplastic resin can be selected from polypropylene (PP) with a melting temperature of about 170°C, polymethyl methacrylate (PMMA) with a melting temperature of about 180°C, polyoxymethylene (POM) with a melting temperature of about 165°C, polyvinyl chloride (PVC) with a melting temperature of about 180°C, nylon 6 (PA6) with a melting temperature of about 220°C, etc. Those skilled in the art can select the corresponding material according to the specific scenario. The thermoplastic resin can be selected as long as its melting temperature is compatible with the second preset temperature of the magnesium alloy. This invention does not limit the selection, and all of them are within the protection scope of this invention.

[0050] Step S4: The magnesium alloy composite tube preform 4, which is in a stable state of differential temperature field, is transferred into the mold forming cavity 7. The sealing component in the mold forming cavity 7 is precisely inserted into the gap between the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 to seal it. The vacuum pump 17 is turned on to remove air bubbles in the intermediate thermoplastic carbon fiber prepreg 2.

[0051] Specifically, the magnesium alloy composite pipe preform 4, which is in a stable state of differential temperature field, is quickly transferred into the mold forming cavity 7. The mold forming cavity 7 has a built-in concave mold, and the upper and lower molds of the mold forming cavity 7 are quickly closed. The push heads 13 at both ends of the cavity are fed towards the mold, and the sealing ring 16 is used to seal the magnesium alloy composite pipe preform 4.

[0052] The annular inclined sealing component on the pusher head 13 is precisely inserted into the gap between the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3. It achieves a seal by plastic deformation through pushing and squeezing. At the same time, the pusher head 13 is equipped with an annular pipe, which is connected to the vacuum pump 17. The vacuum pump 17 is turned on and the negative pressure range is maintained at -0.06 to -0.08 MPa to remove air bubbles trapped in the interlayer, reduce dense pore defects, and improve the forming quality. At this time, a negative pressure is generated between the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3, which is conducive to the removal of air bubbles in the fiber layer during the forming process, reducing porosity and improving the forming quality.

[0053] Step S5: After the air inside the magnesium alloy composite tube preform 4 is exhausted, high-pressure gas is introduced into the mold forming cavity 7, and the sealing component is continuously pushed toward the center of the magnesium alloy composite tube preform 4, so that the magnesium alloy composite tube preform 4 passively fits the mold surface under the combined action of air pressure loading and axial feeding, so as to complete the forming of thermoplastic carbon fiber reinforced magnesium alloy composite tube.

[0054] Specifically, after the air inside the magnesium alloy composite tube preform 4 is exhausted and the negative pressure is stabilized, the high-pressure forming air passage 15 is introduced with adjustable high-pressure gas. The air pressure intensity is monitored by the air pressure gauge 14. At the same time, the pusher head 13 continues to advance towards the mold. By utilizing the synergistic effect of "air pressure loading and axial feeding", the magnesium alloy composite tube preform 4 is driven to fit against the mold surface of the mold forming cavity 7, so as to make the magnesium alloy composite tube preform 4 fit against the concave mold surface to complete the complex surface forming.

[0055] It is understandable that the matching relationship between air pressure and axial feed needs to be determined based on the complexity of the mold shape and the characteristics of the composite tube material, while temperature control mainly depends on the type of the inner magnesium alloy 1 and the outer magnesium alloy 3, as well as the type of the thermoplastic resin. In specific implementation, the forming stage adopts pressure ramp-axial feeding coordinated control to achieve precise control, and its control law satisfies... , ( (This is the sum of the material displacements at both ends), corresponding to , The final pressure is controlled within the range of 5–50 MPa, and the pressure is held for 10–20 seconds after reaching the target pressure to ensure shaping.

[0056] Step S6: After the thermoplastic carbon fiber reinforced magnesium alloy composite pipe is formed, start the mold cooling system, input cooling water into the outer layer of the mold, cool the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component, unload it, and take out the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component.

[0057] Specifically, after the thermoplastic carbon fiber reinforced magnesium alloy composite tube is formed, the mold cooling system is immediately activated. The outer magnesium alloy tube 3 adheres to the inner wall of the forming mold, and cooling water is input through the outer water-cooling channel 8 of the mold, causing the outer magnesium alloy tube 3 to cool down rapidly. The contraction of the outer magnesium alloy tube 3 causes shrinkage stress in the resin layer. The inner magnesium alloy 1 cools naturally under continuous internal pressure. The inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are simultaneously cooled by temperature difference under continuous gas internal pressure. Utilizing the shrinkage stress field caused by the temperature difference between the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3, a shrinkage stress field is formed, such as... Figure 6 As shown, the composite tube has a strong interlayer bond, achieving in-situ interface reinforcement in the thermoplastic carbon fiber reinforced magnesium alloy composite tube component. The component is removed after the outer layer of the thermoplastic carbon fiber reinforced magnesium alloy composite tube component cools to room temperature.

[0058] Specifically, the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component has a huge quality difference compared to the mold, and the rapid cooling can be achieved by relying on the large contact area of ​​the outer wall. Specifically, because the coefficient of thermal expansion of the outer magnesium alloy is greater than that of the inner metal, and because the cooling rate of the outer magnesium alloy tube 3 is greater than that of the inner magnesium alloy tube 1, the shrinkage stress is more pronounced.

[0059] Specifically, when the temperature difference control time required for the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 is different, the one with the longer time should be processed.

[0060] It is understandable that the differential temperature control time is the time required to maintain the temperature at the second preset temperature. Because the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 are made of different materials, the required heat preservation time may also differ (the difference may be a few minutes). The heat preservation of the inner magnesium alloy tube 1 and the outer magnesium alloy tube 3 needs to be carried out simultaneously, so the heat preservation time with the longer heat preservation time should be used.

[0061] In addition, since the forming temperature is lower than the solution temperature of magnesium alloy, dislocations are difficult to fully recover when the outer tube is deformed, resulting in a significant work hardening effect. At the same time, differential temperature control promotes the precipitation of metastable strengthening phases, and the synergistic effect of the two further improves the strength of the composite tube.

[0062] The working principle of this invention is as follows: First, the magnesium alloy tube blank undergoes solution quenching, pre-strengthening, and surface treatment to increase surface roughness and improve the adhesion between the magnesium alloy layer and the carbon fiber resin layer. Then, thermoplastic carbon fiber prepreg is laid on the inner magnesium alloy tube and coaxially assembled with the outer magnesium alloy tube, forming a sandwich structure prefabricated body of "inner magnesium alloy - carbon fiber prepreg - outer magnesium alloy". The inner and outer magnesium alloy tubes are heated by electric current to maintain the precipitation temperature of the metastable strengthening phase, rapidly precipitating the metastable strengthening phase. The intermediate fiber layer is heated to the viscous flow temperature of the thermoplastic resin, allowing the resin to melt and impregnate the fibers. The composite tube is initially fitted with the rough surface structure of the magnesium alloy tube. Next, a pusher-type annular inclined sealing assembly is precisely inserted into the magnesium alloy interlayer, and the composite tube is subjected to vacuum negative pressure treatment. Then, pneumatic loading combined with axial feeding drives the composite tube to conform to the mold surface, achieving complex surface forming. After forming, the outer mold is rapidly water-cooled, causing the outer magnesium alloy tube to cool drastically, while the inner magnesium alloy tube cools naturally and slowly. Utilizing the difference in thermal expansion coefficients between magnesium alloy and resin, as well as the temperature difference cooling between the inner and outer magnesium alloy tubes, shrinkage stress is induced at the interface, forming a strong bond between the composite tube layers, achieving in-situ interface reinforcement. Simultaneously, dislocations accumulate and metastable strengthening phases precipitate during deformation of the magnesium alloy tube, achieving synergistic reinforcement through work hardening and precipitation strengthening, ultimately producing a high-strength, strongly interfacially bonded thermoplastic fiber-reinforced magnesium alloy composite tube.

[0063] The workflow of this invention achieves efficient fabrication of thermoplastic fiber-reinforced magnesium alloy composite tubes through multi-field coupling control. The core of this workflow is "pretreatment – ​​assembly – differential temperature forming – in-situ strengthening," which utilizes electro-thermal and thermo-mechanical synergy to achieve integrated fabrication of composite tubes through forming, curing, and strengthening. Surface modification technology in the pretreatment stage enhances interfacial bonding strength; differential temperature control technology enables rapid precipitation of metastable strengthening phases; the coupling effect of gas pressure and axial feed ensures the forming accuracy of complex surfaces; and the differential temperature cooling strategy forms strong interlayer bonds through a contraction stress field, achieving in-situ interface strengthening. Through the integrated innovation of these key technologies, the overall performance and fabrication efficiency of the composite tube are significantly improved. Example

[0064] A method for integrated forming of thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature pressure control and in-situ reinforcement is disclosed, with the specific configuration and process parameters as follows: The outer magnesium alloy is grade ZK60 and has a thickness of 1.6 mm; The inner magnesium alloy is grade AZ80 and has a thickness of 1.2 mm; The resin matrix of the intermediate layer thermoplastic fiber prepreg is polymethyl methacrylate (PMMA), with a total thickness of 0.8 mm; the layup sequence is ±45° / 0° / 90° / 0° / ±45°, with a total of 5 layers, and the actual measured thickness of a single layer is approximately 0.16 mm.

[0065] Assembly parameters: radial clearance of prefabricated body 0.2 mm, target bulge ratio η = 115%; Tube blank dimensions: inner tube inner diameter 22.4 mm, outer tube outer diameter 30 mm, total tube length 220 mm; Segmented design: effective bulging section length 80 mm, transition section 2×10 mm, clamping section 2×60 mm; Target morphology: After bulging, the maximum outer diameter of the component is 34.5 mm.

[0066] Step S1: The outer magnesium alloy tube blank is solution treated at approximately 435°C for 10 hours, followed by quenching with deionized water at 20°C. The inner magnesium alloy tube blank is solution treated at approximately 410°C for 4 hours, followed by quenching with deionized water at 20°C. Next, the outer magnesium alloy tube blank is pre-strengthened by holding at approximately 90°C for 24 hours, and the inner magnesium alloy tube blank is pre-strengthened by holding at approximately 170°C for 6 hours. Subsequently, the inner and outer magnesium alloy tube blanks are pickled, alkali-washed, anodized, and dried, respectively.

[0067] Step S2: The multilayer thermoplastic fiber prepreg is laid on the outer surface of the inner magnesium alloy tube blank after the surface has been treated. Each layer is compacted by applying pressure with a roller press. Then the outer magnesium alloy tube is put on, so that there is a gap of about 0.2-0.5 mm between the carbon fiber prepreg and the inner wall of the outer magnesium alloy tube, forming a magnesium alloy composite tube preform. Step S3: The magnesium alloy composite tube preform is placed into the heating chamber of the differential pressure forming mold. The inner magnesium alloy tube and the outer magnesium alloy tube are rapidly heated by the independent heating power electrodes inside and outside, so that the inner magnesium alloy tube is heated to about 220°C and the outer magnesium alloy tube is heated to about 210°C. The temperature is maintained for 15 minutes. The thermoplastic resin polymethyl methacrylate is heated to a melting temperature of over 180°C through the inner and outer magnesium alloy tubes. Step S4: The magnesium alloy composite tube preform, which is in a stable state of differential temperature field, is quickly transferred into the mold forming cavity. The mold forming cavity is quickly closed, and the pushers at both ends of the cavity are fed towards the mold. The vacuum pump is turned on to maintain a negative pressure of -0.08MPa to seal the magnesium alloy composite tube preform. Step S5: High-pressure gas is introduced into the mold, and pressure ramp-axial feeding is used for coordinated control. The pressure is maintained at about 10MPa for 30 seconds to make the preform completely fit the mold surface. Step S6: After the pressure holding is completed, start the mold cooling system. After the component cools and solidifies, unload and remove the final thermoplastic carbon fiber reinforced magnesium alloy composite pipe component.

[0068] Experiments showed that the thermoplastic carbon fiber reinforced magnesium alloy composite pipe prepared in this embodiment exhibits excellent interfacial bonding quality, specifically: peel strength ≥ 4.0 N / mm, interfacial shear strength ≥ 22 MPa, and interlaminar fracture toughness (G_I ≥ 0.60 kJ / m², G_II ≥ 5.0 kJ / m²), while the porosity of the composite layer is effectively controlled at a low level of ≤ 1.5%. These data fully demonstrate the significant effect of this process in achieving strong interfacial bonding and low-defect forming.

[0069] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for integrated forming of thermoplastic carbon fiber reinforced magnesium alloy composite tubes using differential temperature gas pressure control and in-situ reinforcement, characterized in that... Includes the following steps: Step S1: Heat treatment and surface treatment are performed on the inner magnesium alloy tube blank and the outer magnesium alloy tube blank respectively to obtain the inner magnesium alloy tube and the outer magnesium alloy tube. Step S2: The intermediate layer thermoplastic fiber prepreg is laid on the outer surface of the inner layer magnesium alloy tube, and the outer layer magnesium alloy tube is sleeved on the intermediate layer thermoplastic fiber prepreg to form a magnesium alloy composite tube preform. The laying width of the intermediate layer thermoplastic fiber prepreg is smaller than the length of the inner layer magnesium alloy tube and the outer layer magnesium alloy tube. Step S3: The magnesium alloy composite tube preform is loaded into the heating chamber of the differential temperature gas pressure forming mold, and the inner magnesium alloy tube and the outer magnesium alloy tube are heated to the corresponding second preset temperature, so that the thermoplastic resin can transfer heat through the inner magnesium alloy tube and the outer magnesium alloy tube to reach the melting temperature and thus enter the viscous flow state. Step S4: Transfer the magnesium alloy composite tube preform, which is in a stable state of differential temperature field, into the mold forming cavity. Use the sealing component in the mold forming cavity to accurately insert into the gap between the inner magnesium alloy tube and the outer magnesium alloy tube for sealing. Turn on the vacuum pump to remove air bubbles from the intermediate layer thermoplastic carbon fiber prepreg. Step S5: After the air inside the magnesium alloy composite tube preform is exhausted, high-pressure gas is introduced into the mold forming cavity to keep the sealing component continuously advancing towards the center of the magnesium alloy composite tube preform, so that the magnesium alloy composite tube preform passively fits the mold surface under the combined action of air pressure loading and axial feeding, so as to complete the forming of thermoplastic carbon fiber reinforced magnesium alloy composite tube. Step S6: After the thermoplastic carbon fiber reinforced magnesium alloy composite pipe is formed, start the mold cooling system, input cooling water into the outer layer of the mold, cool the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component, unload it, and take out the thermoplastic carbon fiber reinforced magnesium alloy composite pipe component.

2. The integrated forming method for differential temperature gas pressure regulation and in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite tubes according to claim 1, characterized in that, Step S1 includes: Step S11: Heat treatment is performed on the inner magnesium alloy tube blank and the outer magnesium alloy tube blank, wherein the heat treatment includes solution treatment and quenching treatment. Step S12 involves performing surface treatment on the inner surface of the outer magnesium alloy tube blank and the outer surface of the inner magnesium alloy tube blank after heat treatment to improve the interfacial adhesion performance. The surface treatment includes pickling to remove film, alkaline washing and roughening, anodizing, rinsing and drying.

3. The integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature gas pressure control and in-situ reinforcement according to claim 2, characterized in that, In step S2, the thermoplastic carbon fiber prepreg is laid in one or more layers, and each layer is subjected to pressure by a roller press to ensure that the fiber bundles are tightly bonded.

4. The integrated forming method for differential temperature gas pressure regulation and in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite tubes according to any one of claims 1-3, characterized in that, The inner magnesium alloy tube blank and the outer magnesium alloy tube blank should be made of different types of magnesium alloy, and the strength and coefficient of thermal expansion of the outer magnesium alloy tube blank should be greater than those of the inner magnesium alloy tube blank.

5. The integrated forming method for differential temperature and pressure regulation-in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite tubes according to claim 1, characterized in that, In step S3, the inner magnesium alloy tube and the outer magnesium alloy tube are heated to a second preset temperature using independent heating systems for the inner and outer layers, respectively. For AZ-series magnesium alloys, the second preset temperature is 180℃ to 260℃, and the holding time is 5-12 minutes. For ZK series magnesium alloys, the second preset temperature is 180℃ to 230℃, and the holding time is 5-15 minutes. For ZM series magnesium alloys, the second preset temperature is 200℃ to 240℃, and the holding time is 5-16 minutes.

6. The integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature gas pressure control and in-situ reinforcement according to claim 5, characterized in that, In step S3, if the heat preservation time corresponding to the inner magnesium alloy tube and the outer magnesium alloy tube is different, the heat preservation time of the longer heat preservation time shall be used as the heat preservation time of the heating system.

7. The integrated forming method for differential temperature and pressure regulation-in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite tubes according to claim 6, characterized in that, The melting temperature of the thermoplastic resin used in the thermoplastic carbon fiber prepreg is lower than the minimum of the second preset temperature of the inner magnesium alloy tube and the second preset temperature of the outer magnesium alloy tube.

8. The integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature and pressure control and in-situ reinforcement according to claim 2, characterized in that, Step S11 further includes step S112, which involves performing a pre-strengthening treatment after heat treatment, by holding the quenched tube blank at a first preset temperature. For AZ-series magnesium alloys, the first preset temperature is 100℃ to 180℃, and the holding time is 4 to 36 hours. For ZK series magnesium alloys, the first preset temperature is 90℃ to 110℃, and the holding time is 10-24 hours. For ZM series magnesium alloys, the first preset temperature is 80℃ to 120℃, and the holding time is 4-24 hours.

9. The integrated forming method for thermoplastic carbon fiber reinforced magnesium alloy composite tubes with differential temperature and pressure control and in-situ reinforcement according to claim 8, characterized in that, In step S5, the vacuum pump maintains a negative pressure range of -0.06MPa to -0.08MPa.

10. The integrated forming method for differential temperature and pressure regulation-in-situ reinforcement of thermoplastic carbon fiber reinforced magnesium alloy composite tubes according to claim 9, characterized in that, In step S6, the pressure range of the high-pressure gas is 5-50 MPa.

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