Method for preparing magnesium-based interpenetrating composite material through circulating negative pressure infiltration

Abstract

The invention discloses a method for preparing a magnesium-based interpenetrating composite material by circulating negative pressure infiltration, which comprises the following steps of: placing a preheated three-dimensional communicated metal lattice framework above molten magnesium liquid, and periodically applying and releasing negative pressure in the infiltration process, so that the molten magnesium liquid is subjected to continuous infiltration under the synergistic effect of multiple times of negative pressure suction and gravity falling, and the magnesium-based interpenetrating composite material is prepared. And residual gas in the pore channel is gradually discharged, and a stable wetting channel is established, so that the complex three-dimensional communicated pore channel is fully permeated and filled. According to the process, external mechanical pressure is not needed, compressive deformation or damage of the lattice framework in the permeation process is avoided, and meanwhile, the permeation uniformity and density are remarkably improved in a circulating negative pressure mode. The obtained magnesium-based interpenetrating composite material is composed of a three-dimensional continuous interpenetrating metal lattice framework and a magnesium matrix phase, interface bonding is compact and continuous, the overall density is larger than or equal to 99%, the magnesium-based interpenetrating composite material has excellent strength, rigidity, toughness and energy absorption capacity, and application of the magnesium-based material in the field of light-weight high-end structures can be remarkably expanded.

Description

Technical Field

[0001] This invention relates to the field of metal matrix composite material preparation technology, and to a method for preparing magnesium-based interpenetrating composite materials by cyclic negative pressure melt infiltration, and more particularly to a method for preparing magnesium-based interpenetrating composite materials by upward suction of molten magnesium liquid and natural fall without the need for external pressure. Background Technology

[0002] Magnesium and its alloys are among the lightest metallic structural materials used in engineering applications, with a density of approximately 1.8 g / cm³. 3 Magnesium alloys possess high specific strength, high specific stiffness, and excellent vibration damping and heat dissipation properties, making them promising for applications in aerospace, transportation, electronic communications, and biomedical fields. However, traditional magnesium alloys still have significant shortcomings in terms of strength, wear resistance, interfacial stability, and ability to withstand complex loads. They struggle to meet the stringent requirements of high-end structural components for load-bearing capacity and service reliability. In particular, under impact or cyclic loading conditions, they are prone to problems such as concentrated localized plastic deformation, premature failure, or insufficient service life, thus limiting their further application.

[0003] To overcome the performance limitations of single magnesium alloy materials, researchers have proposed the design concept of metal-based interpenetrating composite materials. This involves introducing a three-dimensional, continuously connected reinforcing skeleton to create a continuous interpenetrating state between the reinforcing phase and the magnesium matrix phase in space, thereby constructing an efficient load transfer path and significantly improving the overall mechanical properties of the material.

[0004] Compared with traditional particle-reinforced or short fiber-reinforced composite materials, interpenetrating structural composite materials can form a continuous load-bearing network on a macroscopic scale, which not only significantly improves strength and stiffness, but also has good energy absorption capacity and structural stability. Therefore, they have attracted much attention and are suitable for engineering fields that require both lightweight and high performance.

[0005] Currently, common methods for preparing magnesium-based interpenetrating polymer (IPP) composites mainly include vacuum infiltration, pressure infiltration, and centrifugal infiltration. These methods typically require external mechanical pressure or complex vacuum systems to overcome problems such as high surface tension and poor wettability of molten magnesium, thus achieving the filling of the reinforcing skeleton. However, existing methods generally suffer from drawbacks such as complex equipment, high process costs, and narrow parameter control windows. When processing three-dimensional lattice skeletons with fine rods and complex channels, external pressure can easily lead to skeleton deformation or local damage, and unfilled areas, interface defects, or performance fluctuations may still occur during the infiltration process. Furthermore, for fine lattice structures prepared by additive manufacturing, the rods are small in size and have limited stiffness, making them more prone to instability or damage under pressure, thus weakening the performance advantages of the IPP structure. Summary of the Invention

[0006] To address the problems of the existing technology, this invention provides a method for preparing magnesium-based interpenetrating composite materials through cyclic negative pressure melt infiltration. This method establishes a circulating flow path of molten magnesium within the lattice channels by repeatedly applying and releasing negative pressure during the infiltration process, achieving stable and complete infiltration and filling of complex three-dimensional interconnected frameworks. Simultaneously, by combining cyclic negative pressure suction with natural fallback compensation, this method effectively removes residual gas from the channels without external mechanical pressure, significantly improving the wetting continuity and filling integrity of the molten magnesium, and preventing structural deformation or damage to the lattice framework. This solves the shortcomings of existing technologies in preparing magnesium-based interpenetrating composite materials, such as complex equipment, high process costs, and narrow parameter control windows. Furthermore, external pressure can easily lead to framework deformation or localized damage, and the infiltration process may still result in unfilled areas, interface defects, or performance fluctuations. Additionally, the small size and limited stiffness of the rods in the additively manufactured metal framework make it more susceptible to instability or damage under pressure, weakening the performance advantages of the interpenetrating structure.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing magnesium-based interpenetrating composite materials by cyclic negative pressure melt infiltration involves placing a preheated metal skeleton above molten magnesium under a protective atmosphere. A vertically upward attractive force is periodically applied above the metal skeleton, causing the molten magnesium to enter the metal skeleton from bottom to top through the channels within the metal skeleton under the periodic attractive force. The molten magnesium then moves periodically upward or downward within the metal skeleton in a vertical direction until the channels within the metal skeleton are fully filled. Subsequently, the mixture is cooled and solidified to obtain the magnesium-based interpenetrating composite material.

[0009] Preferably, the periodic application of an upward vertical gravitational force above the metal frame is achieved in the following manner:

[0010] After applying negative pressure above the metal frame for a period of time, the negative pressure is released for a period of time, allowing the molten magnesium to fall naturally back into the metal frame under the action of gravity and capillary force; then the negative pressure is applied again, and this process is repeated several times.

[0011] Preferably, the negative pressure is applied for 20-30 seconds; the negative pressure is released for 180-300 seconds; after repeating at least twice, the mixture is left to stand for at least 60 seconds before cooling and solidification.

[0012] Preferably, the porosity of the metal skeleton is 10% to 30%.

[0013] Preferably, the protective atmosphere is at least one of a mixed atmosphere of CO2 and SF6 or an inert gas atmosphere.

[0014] Preferably, the volume of the metal skeleton accounts for 20% to 60% of the volume of the magnesium-based interpenetrating composite material, and the pore size is 1 mm to 5 mm.

[0015] Preferably, the metal skeleton has a three-dimensional interconnected channel structure inside.

[0016] Preferably, the metal frame is preheated to 300°C~450°C.

[0017] Preferably, the magnesium liquid is obtained by heating magnesium or a magnesium alloy to above 700°C.

[0018] Preferably, the metal skeleton is made of a metal material with a melting point higher than that of the molten magnesium liquid.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. In the process of researching existing magnesium-based interpenetrating composite material preparation processes, the inventors discovered that the currently mainstream methods such as pressureless infiltration, pressurized infiltration, and vacuum infiltration, although differing in implementation, share a consistent basic technical concept: molten magnesium enters the porous metal framework in a single, continuous, and uncontrollable natural manner during infiltration. Improvements to existing technologies around this fixed infiltration mode mainly focus on optimizing external infiltration conditions, such as applying overall pressure, vacuuming, increasing temperature, or improving wettability. However, these improvements are all based on not changing the magnesium infiltration method itself; their essence remains the parameter enhancement of the existing infiltration mode. When applied to three-dimensional metal frameworks with thin rod structures or complex topologies, overall force can easily cause framework deformation and instability, while pressureless infiltration methods that rely solely on improved wettability struggle to balance structural protection and filling efficiency. The present invention further recognizes that existing technologies generally follow the traditional approach of increasing the strength of the skeleton or enhancing the penetration driving force during the improvement process, forming technological inertia, and do not consider fundamentally solving the above problems by actively designing and controlling the penetration behavior and movement mode of molten magnesium liquid. Moreover, the one-time penetration molding method also reduces the stability and repeatability of complex interpenetrating structure molding.

[0021] 2. To this end, this invention breaks through the traditional improvement logic of existing technologies that focus on overall force application or external condition enhancement, and proposes a new method to drive the penetration of molten magnesium liquid by applying transient negative pressure locally to the pores. This invention discovers that the synergistic effect of local negative pressure, gravity, and capillary force can form a dynamic cycle mechanism of "venting-filling-refilling" during the penetration process, effectively promoting the discharge of residual gas in the pores and guiding the molten magnesium liquid to gradually fall back and replenish the filling along the connected pores. Unlike existing technologies that rely on penetration aids, specific alloy compositions, or high-temperature environments, this invention regulates the penetration process through periodic negative pressure, enabling the filling behavior to actively adapt to metal skeletons with different topologies and pore parameters. This achieves stable filling of complex lattice structures without applying positive pressure to the entire skeleton. Therefore, this invention transforms the filling process from passively adapting to the pore structure to a controllable dynamic process, providing a new technical path to balance structural integrity and filling uniformity.

[0022] 3. The method described in this invention exhibits significant technical advantages in the preparation of magnesium-based interpenetrating composite materials. On one hand, the cyclically applied local negative pressure can continuously expel residual gas from the pores, significantly reducing unfilled defects caused by gas retention. During the natural fall of the molten magnesium, the synergistic effect of gravity and capillary force can effectively compensate for unfilled areas, thereby obtaining a dense and uniformly distributed interpenetrating structure. On the other hand, since this invention does not apply positive pressure to the molten magnesium or the entire metal skeleton, and with appropriate preheating treatment to ensure the thermal stability of the skeleton, it can effectively avoid skeleton deformation or damage caused by external forces during traditional pressurization or vacuum infiltration processes. Even for additive manufacturing lattice skeletons with small rod diameters, complex pores, or special topologies, the original structural morphology can be well maintained, and continuous, dense interfacial bonding can be obtained. Furthermore, this invention can achieve designable control of composite material properties by adjusting parameters such as skeleton topology, volume fraction, and pore size. At the same time, compared with traditional processes that rely on complex vacuum or pressurization equipment, the process flow of this invention is relatively simplified and the equipment requirements are lower, which is conducive to reducing preparation costs and improving process applicability and promotion potential. Attached Figure Description

[0023] Figure 1 A comparative optimization diagram of three infiltration process routes for preparing magnesium-based interpenetrating composites by melt infiltration.

[0024] Figure 2 The images show scanning electron microscope images and elemental distribution diagrams of the interface of magnesium-based interpenetrating composite materials; where a is Example 1, b is Example 2, and c is Example 3.

[0025] Figure 3The figures show a comparison of the compressive mechanical properties of magnesium-based and magnesium alloy interpenetrating composites based on crystal lattice topology. Specifically, a) shows the tensile stress-strain curves of composites with different crystal lattice structures (TDC / QDC / DOD) based on an industrial pure magnesium matrix (Mg-based); b) shows the bar chart of tensile yield strength and tensile strength of composites with different crystal lattice structures based on an industrial pure magnesium matrix; c) shows the compressive stress-strain curves of composites with different crystal lattice structures based on a Mg-8.5Gd-3Y-0.5Zr magnesium alloy matrix (GW85K-based); and d) shows the bar chart of compressive yield strength and compressive strength of composites with different crystal lattice structures based on a Mg-8.5Gd-3Y-0.5Zr magnesium alloy matrix. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0027] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0028] I. A method for preparing magnesium-based interpenetrating composite materials by cyclic negative pressure melt infiltration

[0029] In the field of existing magnesium-based interpenetrating polymer (IPP) composite material preparation technology, the inventors discovered during systematic research that although existing technologies have proposed various preparation methods such as vacuum infiltration, pressure infiltration, and centrifugal infiltration, and have made improvements to varying degrees to address their respective problems, their improvement ideas are still generally limited to the traditional technical framework. Specifically, when improving infiltration efficiency, existing technologies typically use external mechanical pressure to force molten metal into the skeleton channels, or improve the wettability between the melt and the skeleton by introducing infiltration aids or controlling the composition of the molten metal. However, to address the problem that pressure infiltration can easily lead to deformation and instability of thin rod structures or complex topological metal skeletons, the focus of improvement shifts to increasing the strength of the metal skeleton itself.

[0030] During the research process, the inventors also attempted the aforementioned improvement ideas, such as enhancing the filling effect by increasing the permeation pressure or improving the wetting conditions. However, experimental results showed that under complex lattice structure conditions, the above methods still struggle to simultaneously ensure the integrity of the framework structure and the uniformity of filling, and the process window is narrow with limited applicability. Therefore, the present invention further recognizes that existing improvements generally neglect the dynamic characteristics of the permeation behavior of molten metal in complex channels, often relying solely on a single permeation pressure parameter for process control, making it difficult to achieve precise regulation of the permeation process.

[0031] Based on the above understanding, this invention starts from the natural infiltration behavior of molten metal driven by physical laws, shifting the research focus from forcibly promoting melt infiltration to actively controlling the dynamic movement process of the melt within the channels. This invention discovers that the periodic flow behavior of molten metal under cyclic negative pressure and the process of residual gas removal within the channels have a significant impact on the density and interfacial quality of the final composite material.

[0032] Based on this, the present invention proposes a process strategy combining cyclic negative pressure control and multi-round infiltration. This strategy guides the molten metal to achieve adaptive filling within complex channels while avoiding mechanical pressure on the entire metal skeleton, thus balancing structural integrity and sufficient filling. Based on fluid dynamics, capillary action, and interface wetting theory, the present invention proposes a method for preparing magnesium-based interpenetrating composite materials through cyclic negative pressure melt infiltration, the specific steps of which are as follows:

[0033] Under a protective atmosphere, a preheated metal skeleton is placed above molten magnesium. A vertically upward attractive force is periodically applied above the metal skeleton, causing the molten magnesium to enter the skeleton from bottom to top through the skeleton's channels under the periodic attractive force. The molten magnesium then moves back and forth vertically inside the skeleton until the channels are fully filled. Subsequently, it is cooled and solidified to obtain a magnesium-based interpenetrating composite material.

[0034] In some embodiments of this invention, to guide the molten magnesium liquid to stably enter the internal channels of the metal framework and achieve bottom-up penetration, this invention periodically applies an upward vertical attraction above the metal framework. While this invention has attempted to improve the filling effect of the internal channels of the metal framework using vacuum or negative pressure infiltration methods during the optimization of the preparation method, it has been found that the vacuum / negative pressure infiltration process used in the prior art is essentially a one-time, continuous pressure difference application molding method. The core problem hindering the full and uniform filling of complex three-dimensional lattice frameworks lies not in the introduction of vacuum or negative pressure conditions themselves, but in the fact that the prior art has not recognized the need for periodic, phased, and dynamic control of the infiltration behavior of the molten metal within the channels. Existing vacuum or negative pressure infiltration processes typically employ continuous pressure holding or single vacuuming, maintaining a unidirectional, static pressure-driven mode throughout the entire infiltration process. In this process, the pressure difference can only drive the molten magnesium liquid to advance unidirectionally along the channel direction. However, for the complex channel structure with spatial interlacing and tortuous paths that are common within the crystal lattice framework, the gas in some dead corners of the channels is easily trapped after being compressed and is difficult to be discharged during the advancement of the magnesium liquid. At the same time, the unidirectional advancement of the magnesium liquid front is prone to forming a liquid seal effect in the narrow or converging regions of the channels, sealing the residual gas inside the channels, which eventually forms pores or interface defects after cooling and solidification.

[0035] On the other hand, traditional vacuum / negative pressure infiltration processes lack a phased, reversible, and feedback control mechanism for the infiltration process. Molten magnesium relies solely on a one-time pressure difference to complete the filling. After the vacuum or negative pressure is released, it cannot re-drive or compensate for the filling of incompletely wetted or unfilled pore areas. When the pore paths are complex or the degree of interlacing of the rods is high, it easily leads to discontinuous filling in local areas, weak interfacial bonding, and low overall density. Furthermore, under continuous negative pressure, the wetting behavior of molten magnesium on the surface of the titanium alloy lattice framework depends entirely on the natural interfacial reaction process, lacking active intervention in the wetting state. The magnesium's ability to damage the oxide film on the framework surface is limited, easily forming weak bonding zones at the interface. In contrast, this invention does not simply introduce vacuum or negative pressure conditions, but for the first time utilizes negative pressure as a periodically applied gravitational force. Through a dynamic permeation mode of cyclical negative pressure upward suction and natural fall back after negative pressure is released, the two functional stages of "negative pressure suction to expel gas" and "release and fill after negative pressure are released" are alternately introduced during the permeation process. This distinguishes the permeation mechanism from the one-time vacuum / negative pressure impregnation method of the prior art and effectively overcomes its inherent defects.

[0036] This attraction is achieved through the periodic application and release of negative pressure. During the negative pressure phase, molten magnesium is driven to permeate upwards along the channels and expel residual gas. During the negative pressure release phase, gravity and capillary forces compensate for and fill in the incompletely filled areas. Through the cyclical action of the above-mentioned suction and fall process, continuous filling of complex channels can be achieved without applying mechanical pressure to the entire metal framework, thereby improving the filling integrity while effectively avoiding structural deformation or damage to the crystal framework.

[0037] In some embodiments of the present invention, the negative pressure application time is 20–30 s, and the negative pressure release time is 180–300 s. The above-mentioned negative pressure suction-return process is repeated at least twice, and then left to stand for at least 60 s for cooling and solidification. Through multiple rounds of cyclic negative pressure, the molten magnesium liquid enters the internal channels of the metal skeleton in stages during the penetration process, and in the negative pressure release stage, gravity and capillary forces are used to compensate for and fill the incompletely filled areas.

[0038] The negative pressure used in this invention is not a micro negative pressure, but a medium negative pressure range that can effectively generate a suction effect and will not cause a liquid seal effect due to excessively fast advancement. This ensures that the molten magnesium liquid can smoothly enter the channel, while facilitating the discharge of residual gas in the channel and the stable progress of the fallback and filling process.

[0039] Unlike existing technologies that use a single injection of molten metal into the skeleton to complete the filling process, this invention achieves dynamic control of the permeation process through multiple rounds of cyclic negative pressure, which significantly improves the filling uniformity and process stability of complex pore structures. Preferably, the negative pressure suction-fall process is repeated 2 to 5 times.

[0040] According to the ideal gas law ,in The pressure inside the air chamber before suction (approximately atmospheric pressure). This represents the volume of a localized air cavity above the metal frame before suction. This represents the air chamber pressure after suction. , The volume of air extracted each time is denoted as . With a local air cavity volume of several hundred milliliters above the metal frame and an air extraction volume of 30–50 mL each time, a negative pressure range of approximately −5 kPa to −10 kPa can be formed above the frame. This negative pressure range effectively drives the molten magnesium liquid to permeate upwards along the channels, while avoiding excessive negative pressure that could cause the magnesium liquid to advance too quickly and create a liquid seal effect, thus balancing extraction efficiency and filling stability. Therefore, this invention uses an extraction rate of 1 mL / s to 5 mL / s to extract the molten magnesium liquid. The liquid falls back naturally due to gravity, but pressure can also be used to control the fall, with the fall time controlled between 3 and 5 minutes.

[0041] In some embodiments of the present invention, the porosity of the metal skeleton is 10% to 30%, and the volume of the metal skeleton accounts for 20% to 60% of the total volume of the magnesium-based interpenetrating composite material, with a pore size of 1 mm to 5 mm. By rationally selecting the porosity, pore size, and skeleton volume fraction, the mechanical properties of the composite material can be designed and controlled while ensuring smooth penetration of molten magnesium.

[0042] In some embodiments of the present invention, the protective atmosphere is at least one of a mixed atmosphere of CO2 and SF6 or an inert gas atmosphere. The protective atmosphere is used to suppress the oxidation reaction of magnesium or magnesium alloys during heating and infiltration, thereby ensuring the fluidity of the molten magnesium and the continuity of interfacial wetting, which is beneficial for obtaining an interpenetrating composite structure with a dense interface and fewer defects.

[0043] In some embodiments of the present invention, the metal framework has a three-dimensional interconnected channel structure. The method of the present invention is applicable to metal lattice frameworks with three-dimensional interconnected channels, such as three-diameter staggered structures, four-diameter intersecting structures, dodecahedral structures, or other lattice forms with three-dimensional interconnected channel characteristics. Because the present invention employs a permeation method combining cyclic negative pressure driving and natural fallback compensation, it has good adaptability to channel topologies and is particularly suitable for complex lattice structures that are difficult to fully fill using traditional processes.

[0044] In some embodiments of the present invention, the metal skeleton is preheated to 300°C to 450°C to maintain thermal stability during subsequent melting and infiltration. Preheating effectively reduces the temperature difference between the molten magnesium and the metal skeleton, minimizing the adverse effects of thermal stress on the skeleton structure, thereby further improving structural integrity and interfacial bonding quality.

[0045] In some embodiments of the present invention, the molten magnesium is obtained by heating magnesium or a magnesium alloy to above 700°C. The method of the present invention does not depend on a specific magnesium alloy composition; the synergistic effect of cyclic negative pressure and natural settling significantly improves the wetting continuity and filling integrity of the molten magnesium, thus exhibiting good material adaptability.

[0046] In some embodiments of the present invention, the metal framework is made of a metal material with a melting point higher than that of the molten magnesium liquid, and is prepared by a metal additive manufacturing process, including but not limited to selective laser melting, electron beam melting, or other layer-by-layer forming processes, to obtain a metal lattice framework with a predetermined topological structure and porosity distribution. The metal framework material is selected from stainless steel, titanium alloy, aluminum alloy, or other high-temperature resistant metal materials, thereby enabling the method of the present invention to be applied to different material systems and performance requirements.

[0047] II. Examples and Comparative Examples

[0048] Example 1

[0049] A TC4 titanium alloy lattice framework with a three-diameter staggered topology (TDC) was selected as the reinforcing phase. The lattice framework was fabricated using laser melting additive manufacturing, exhibiting a regular cubic structure internally composed of multiple sets of spatially staggered rods forming three-dimensional interconnected channels. The rod diameter of the lattice framework was 1 mm, and the overall porosity was controlled at 20%.

[0050] After the crystal lattice is formed, it is subjected to a combination of mechanical vibration and airflow to remove powder residues in the pores. Then, it is ultrasonically cleaned with anhydrous ethanol for 20 minutes to remove surface impurities and is allowed to air dry naturally.

[0051] The cleaned crystal lattice framework was placed in a box-type resistance furnace for preheating treatment. The preheating temperature was set at 350℃, and the holding time was 15 min. Preheating treatment reduces the temperature gradient when the molten magnesium enters the lattice channels, avoiding localized rapid solidification. It also improves the wettability of the molten magnesium on the titanium alloy surface.

[0052] Industrial pure magnesium was selected as the matrix material and placed in a high-temperature resistant crucible. It was heated to a molten state under the protection of a mixed atmosphere of CO2 and SF6. The melting temperature was controlled at 720℃ and held at this temperature for 10 min to ensure that the molten magnesium liquid has good fluidity.

[0053] The preheated crystal lattice framework is slowly inserted into the molten magnesium from top to bottom, ensuring that the lower end of the framework is completely submerged while maintaining communication between the upper end and the outside environment. Subsequently, a suction device positioned above the framework periodically opens and closes the suction channel, creating multiple cycles of negative pressure above the framework.

[0054] In this embodiment, the volume of the local air cavity formed above the metal frame is approximately 300 mL, and the volume of air extracted during each round of suction is approximately 40 mL, according to the ideal gas law. Calculations show that under the above conditions, a negative pressure zone of approximately -10 to -12 kPa can be formed above the crystal lattice framework, effectively driving the molten magnesium liquid to penetrate upwards along the channels and avoiding the liquid seal effect. The suction rate is controlled between 1 mL / s and 5 mL / s.

[0055] Under negative pressure, molten magnesium enters the crystal framework from bottom to top through the three-dimensional interconnected channels. This upward suction process lasts for 20 seconds. During this process, the original gas in the crystal lattice channels is effectively expelled, and the molten magnesium gradually establishes a continuous wetting channel.

[0056] After each round of negative pressure suction, the negative pressure is released and the crystal lattice framework is kept still, allowing the molten magnesium liquid to fall back naturally under the action of gravity and capillary force, compensating for the areas in the pores that are not completely filled; the above negative pressure suction-fall process is repeated 5 times.

[0057] During the natural fall-through infiltration process, the crystal lattice framework was kept static for 60 seconds to ensure that the molten magnesium could fully fill the complex pore structure. Subsequently, the entire system was subjected to controlled cooling to solidify the molten magnesium inside the crystal lattice framework, resulting in a magnesium-based interpenetrating composite material.

[0058] Density testing and cross-sectional observation of the obtained composite material showed that the overall density was approximately 99.5%. Interface scanning electron microscopy revealed a continuous interface between the magnesium matrix and the TC4 titanium alloy lattice framework, with no obvious impermeable regions or through-hole defects. These results demonstrate that the upward suction-natural fallback negative pressure melt infiltration method described in this invention can achieve full infiltration and stable forming of a three-diameter staggered lattice structure without the need for external mechanical pressure.

[0059] Example 2

[0060] A TC4 titanium alloy lattice framework with a four-diameter cross topology (QDC) was selected as the reinforcing phase. Its rods are orthogonally distributed in space, the channel structure is relatively regular, the rod diameter is 1 mm, and the porosity is about 23%.

[0061] The cleaning, drying and preheating treatment of the crystal lattice framework were the same as in Example 1, with the preheating temperature set at 350°C and held for 15 minutes.

[0062] Industrial pure magnesium is heated to a molten state under a protective atmosphere, and a preheated QDC lattice framework is inserted into the molten magnesium. Subsequently, a suction device positioned above the lattice framework periodically opens and closes the suction channel, creating a multi-cycle negative pressure environment above the framework.

[0063] In this embodiment, the formation method of negative pressure, the volume of local air cavity, the volume of extracted air, and the corresponding negative pressure range are all the same as in Embodiment 1.

[0064] After each round of negative pressure suction, the negative pressure is released and the crystal lattice framework is kept still, allowing the molten magnesium liquid to fall back naturally under the action of gravity and capillary force; the above negative pressure suction-fall process is repeated 5 times.

[0065] Magnesium-based interpenetrating composite material was obtained after cooling and solidification. Density test results showed that the overall density of the composite material was approximately 99.6%, slightly higher than that of Example 1.

[0066] The results show that in a four-diameter intersecting lattice structure with relatively regular channels, the method of the present invention can also achieve rapid and stable negative pressure melt penetration with good penetration uniformity.

[0067] Example 3

[0068] A dodecahedral topological (DOD) TC4 titanium alloy lattice framework was selected as the reinforcing phase. This structure exhibits high spatial symmetry, with diverse channel orientations and complex paths, placing higher demands on the penetration ability of molten metal. The lattice framework has a rod diameter of 1 mm and a porosity of approximately 15%.

[0069] The DOD lattice framework was subjected to the same cleaning, drying and preheating treatment as in Example 1, with a preheating temperature of 350°C and a holding time of 15 min.

[0070] The temperature of the molten magnesium liquid is controlled at 720 ℃. The preheated crystal lattice skeleton is inserted into the molten magnesium liquid, and the suction device is turned on. Then, the suction channel is periodically opened and closed by the suction device set above the crystal lattice skeleton to form a multi-round negative pressure environment above the skeleton.

[0071] In this embodiment, the formation method of negative pressure, the volume of local air cavity, the volume of extracted air, and the corresponding negative pressure range are all the same as in Embodiment 1.

[0072] After each round of negative pressure suction, the negative pressure is released and the crystal lattice framework is kept still, allowing the molten magnesium liquid to fall back naturally under the action of gravity and capillary force; the above negative pressure suction-fall process is repeated 5 times.

[0073] After cooling and solidification, a magnesium-based interpenetrating composite material was obtained. Density testing showed that the overall density of the composite material was approximately 99.2%. Cross-sectional observation revealed no obvious non-permeable areas, indicating that the method of this invention has good adaptability to complex pore structures.

[0074] Example 4

[0075] The same dodecahedral topology (DOD) TC4 titanium alloy lattice framework as in Example 3 was selected as the reinforcing phase. The preparation method, geometric morphology and structural parameters of the lattice framework were the same as in Example 1. The rod diameter of the lattice framework was 1 mm and the overall porosity was 20%.

[0076] After the crystal lattice framework is formed, it is subjected to a combination of mechanical vibration and airflow to remove powder, and then ultrasonically cleaned with anhydrous ethanol for 20 minutes to remove residual powder and surface impurities in the pores. Finally, it is allowed to air dry naturally.

[0077] The cleaned crystal skeleton was placed in a box-type resistance furnace for preheating treatment. The preheating temperature was set at 350 ℃ and the holding time was 15 min to reduce the temperature gradient when the molten metal enters the channel and to ensure the thermal stability of the crystal skeleton during the infiltration process.

[0078] Mg-8.5Gd-3Y-0.5Zr magnesium alloy was selected as the matrix material. It was placed in a high-temperature resistant crucible and heated to the molten state under the protection of a mixed atmosphere of CO2 and SF6. The melting temperature was controlled at 730 ℃ and held at this temperature for 10 min to obtain a molten magnesium alloy with good fluidity.

[0079] The preheated crystal lattice framework is slowly inserted into the molten magnesium alloy from top to bottom, ensuring that the lower end of the framework is completely submerged in the molten metal while maintaining communication between the upper end and the outside environment. Subsequently, a suction device positioned above the crystal lattice framework periodically opens and closes the suction channel, creating multiple cycles of negative pressure above the framework.

[0080] In this embodiment, the formation method of negative pressure, the volume of local air cavity, the volume of extracted air, and the corresponding negative pressure range are all the same as in Embodiment 1.

[0081] Under negative pressure, molten Mg-8.5Gd-3Y-0.5Zr alloy enters the crystal lattice from bottom to top through the three-dimensional interconnected channels. Each upward suction lasts for 20 seconds, gradually expelling the original gas in the channels and establishing continuous wetting channels. After each round of negative pressure suction, the negative pressure is released and the crystal lattice is left to stand, allowing the molten magnesium alloy to fall back naturally under the action of gravity and capillary force, compensating for and filling the incompletely filled channel areas. This negative pressure suction-natural fall process is repeated 5 times.

[0082] During the final natural fall-off process, the lattice framework is kept static for 60 seconds to ensure that the molten magnesium alloy fully fills the complex pore structure. Then, the entire system is cooled in a controlled manner to solidify the molten magnesium alloy inside the lattice framework, thus obtaining a magnesium-based interpenetrating composite material.

[0083] Density tests and cross-sectional morphology observations were conducted on the obtained composite material. The results showed that the overall density of the magnesium alloy-based interpenetrating composite material was stable at over 99%. The interface between the magnesium alloy matrix and the TC4 titanium alloy lattice framework was continuous and dense, and no obvious non-penetrating areas or through-type pore defects were observed.

[0084] The above results show that the cyclic negative pressure upward suction-natural fall melt infiltration method of the present invention is not only applicable to industrial pure magnesium, but also to magnesium alloy systems such as Mg-8.5Gd-3Y-0.5Zr (GW83K), and the infiltration effect does not depend on the specific alloy composition of the metal melt, which proves the good adaptability and versatility of the method of the present invention in different magnesium-based material systems.

[0085] Comparative Example 1

[0086] The same three-dimensional connected lattice metal framework as in the embodiment was selected, and its material, geometry, and porosity parameters were kept consistent with those in the embodiment. Figure 1 Method 1 involves placing a cleaned and preheated metal framework in molten magnesium and performing a pressureless static infiltration process under a protective atmosphere of CO2 and SF6. During the infiltration process, no external mechanical pressure, negative pressure, or vacuum is applied to the molten magnesium or the metal framework; the infiltration is carried out solely by the gravity and capillary action of the molten magnesium itself, allowing it to penetrate the internal pores of the metal framework. This is a conventional technique for preparing interpenetrating materials in the prior art.

[0087] After being kept in a static state for a certain period of time, the system was cooled and solidified to obtain a magnesium-based interpenetrating composite material. Observation of the cross-sectional morphology of the obtained sample revealed that there were pores in some areas of the metal framework that were not fully filled by the molten magnesium, and residual gas entrapment defects were still observed in some channels. In the complex channel intersection areas, the filling continuity of the molten magnesium was poor, and discontinuities were observed in the interface bonding areas. These results indicate that it is difficult to achieve sufficient and uniform filling of complex three-dimensional lattice structures by simply relying on the pressureless static infiltration method.

[0088] Comparative Example 2

[0089] Based on Comparative Example 1, to improve the fluidity of molten magnesium, a container containing molten magnesium and a metal skeleton was placed on a shaking device. External mechanical vibration was used to assist in the treatment of the system, aiming to promote the molten magnesium to enter the channels of the metal skeleton. Figure 1 Method 2 in the text. No negative pressure or vacuum condition is applied to the system during the oscillation process, which is still a pressureless permeation method.

[0090] The composite material obtained after oscillation treatment and cooling solidification exhibits a relatively complete shape macroscopically. However, cross-sectional observation shows that although the filling of some channels has improved, there are still incompletely filled areas and local porosity defects inside the skeleton, and the uniformity of filling is significantly affected by the lattice topology. In areas with complex channels or intersecting rods, it is still difficult to achieve continuous and dense interfacial bonding.

[0091] A comparison with the aforementioned pressureless static infiltration and pressureless oscillation-assisted infiltration examples reveals that the circulating negative pressure upward suction-natural fall-back infiltration method employed in this embodiment effectively removes residual gas from the lattice channels during infiltration and guides the molten magnesium liquid to fill the complex pore structure in a staged and controllable manner. This results in a more continuous and dense filling morphology and a more stable interface bonding quality in the microstructure. In contrast, the pressureless infiltration method used in the comparative examples, lacking active control over the infiltration process, is prone to gas retention and insufficient local filling, which is more pronounced in lattice frameworks with complex topologies.

[0092] Further analysis of the results from Examples 1-4 shows that the negative pressure melt infiltration method proposed in this invention is applicable to lattice framework structures with varying degrees of topological complexity. Consistent filling effects were achieved in multiple experiments, demonstrating good process stability and repeatability. Therefore, the negative pressure melt infiltration method based on an upward suction-natural fallback mechanism proposed in this invention can achieve full infiltration of molten magnesium into complex three-dimensional lattice frameworks without the need for external mechanical pressure, balancing structural integrity and sufficient filling, and has promising engineering application prospects.

[0093] Table 1. Statistical results of density and compactness of magnesium-based interpenetrating composites with different crystal structures

[0094]

[0095] In Table 1, m1 is the mass of the molded sample block, m2 is the mass of the molded sample block after immersion in water, m3 is the mass of TC4 in the molded sample block, m4 is the mass of Mg in the molded sample block, V1 is the theoretical volume of the molded sample block, and V2 is the actual volume of the molded sample block.

[0096] From the perspectives of filling effect and density, the magnesium-based interpenetrating composite materials prepared by the method of this invention in Examples 1-4 all maintained a stable density of over 99%, with the composite material of the four-diameter cross-topology (QDC) reaching the highest density of 99.6%. A comparison of the theoretical volume (V1) and actual volume (V2) values ​​in Table 1 shows that the actual volume of each composite material is highly close to the theoretical volume. Cross-sectional observation further confirms that the interface between the magnesium matrix and the TC4 titanium alloy lattice framework is continuous and dense, with no obvious impermeable areas or through-hole defects. (See [reference]). Figure 1 In contrast, neither of the two existing technologies—pressureless static infiltration in Comparative Example 1 and mechanical oscillation-assisted pressureless infiltration in Comparative Example 2—can achieve sufficient filling of the lattice framework channels. The composite material exhibits pore defects caused by residual gas retention, and interfacial discontinuities occur in complex channel intersection regions. (See [link to relevant documentation]). Figure 1 This comparison directly demonstrates that the method of the present invention, by actively expelling gas from the pores through negative pressure suction and then compensating for the filling by gravity and capillary force through a natural fall-off process, can effectively solve the problems of gas retention and insufficient filling in pressureless permeation methods, and achieve stable forming of high-density composite materials without the need for external mechanical pressure.

[0097] From the perspective of adaptability of lattice topology, Examples 1-3 selected lattice frameworks with increasing channel complexity: three-diameter staggered topology (TDC), four-diameter intersecting topology (QDC), and dodecahedral topology (DOD). Among them, the DOD structure has diverse channel directions and complex paths, requiring the highest penetration capability of molten metal. Experimental results show that the density of the composite materials corresponding to the three structures is not lower than 99.2%, and no obvious unpenetrated areas are observed in the cross-sections. This indicates that the method of the present invention has good adaptability to three-dimensional lattice frameworks of different complexities. Its staged and controllable penetration mechanism can adapt to various topologies from regular to complex channels, breaking through the limitations of existing pressureless penetration methods on the complexity of lattice structures.

[0098] From the perspective of the versatility of the material system, Examples 1-3 used industrial pure magnesium as the matrix, while Example 4 used GW83K magnesium alloy as the matrix. After adjusting the melting temperature to 730℃, the composite materials prepared using the same cyclic negative pressure infiltration process still achieved a density of 99.4%, and the interfacial bonding quality was comparable to that of the pure magnesium matrix composite material. This result confirms that the infiltration effect of the method of the present invention does not depend on the specific alloy composition of the magnesium-based material, and is applicable to both industrial pure magnesium and multi-element alloyed magnesium alloys, possessing versatility across material systems.

[0099] from Figure 3 It can be seen that the magnesium-based interpenetrating composite material prepared by the cyclic negative pressure upward suction-natural fall-back infiltration process of this invention exhibits significant advantages in mechanical properties. This advantage is directly and closely related to the high density data (over 99%) shown in Table 1: the density of Mg-QDC in Table 1 reaches 99.6% (the highest among the three lattice structures in pure magnesium matrix), corresponding to... Figure 3 In component b, its tensile strength (255.4 MPa) is also the best value in the pure magnesium matrix system; even for Mg-DOD with diverse pore orientations and more complex paths, Table 1 shows that its density remains stable at 99.2%. Figure 3 In sample b, its tensile strength also remained at a high level of 235.7 MPa. This not only echoes the conclusion in Example 3 that the preparation method of the present invention has good adaptability to complex pore structures, but also stands in stark contrast to the insufficient mechanical properties caused by pore defects in the pressureless permeation in the comparative example.

[0100] When the matrix was replaced with GW83K magnesium alloy, the density of GW85K-DOD in Table 1 remained stable at 99.4%, corresponding to... Figure 3 In d, its compressive strength reached 474.2 MPa, and GW85K-QDC achieved a compressive strength of 523.5 MPa with a density of over 99%. This not only confirms the conclusion in Example 4 that the preparation method of the present invention is applicable to different magnesium-based material systems, but also shows that the high density and defect-free structure achieved by the preparation method of the present invention can effectively cooperate with the strengthening effect of the alloy itself to further expand the upper limit of the mechanical properties of the material.

[0101] In summary, the correspondence of these data clearly shows that it is the preparation method described in this invention that achieves high-density filling of different lattice topologies and different magnesium-based systems (Table 1), which ensures the uniform transfer of load between the matrix and the TC4 titanium alloy lattice framework from the structural level. Ultimately, it exhibits excellent tensile and compressive properties that far exceed those of traditional pressureless infiltration processes, and also highlights the comprehensive technical advantages of the preparation method described in this invention in terms of structural adaptation, material versatility, and performance enhancement.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing magnesium-based interpenetrating composite materials by cyclic negative pressure melt infiltration, characterized in that, Under a protective atmosphere, a preheated metal skeleton is placed above molten magnesium. A vertically upward attractive force is periodically applied above the metal skeleton, causing the molten magnesium to enter the metal skeleton from bottom to top through the channels within the metal skeleton under the periodic attractive force. The molten magnesium then moves periodically upward or downward within the metal skeleton in the vertical direction until the channels within the metal skeleton are fully filled. Subsequently, the skeleton is cooled and solidified to obtain a magnesium-based interpenetrating composite material.

2. The method according to claim 1, characterized in that, The upward vertical force is periodically applied above the metal frame in the following way: After applying negative pressure above the metal frame for a period of time, the negative pressure is released for a period of time, allowing the molten magnesium to fall naturally back into the metal frame under the action of gravity and capillary force. Then apply negative pressure again and repeat several times.

3. The method according to claim 2, characterized in that, The negative pressure is applied for 20-30 seconds; the negative pressure is released for 180-300 seconds; repeat at least twice, let stand for at least 60 seconds, and then cool and solidify.

4. The method according to claim 1, characterized in that, The porosity of the metal skeleton is 10% to 30%.

5. The method according to claim 1, characterized in that, The protective atmosphere is at least one of a mixed atmosphere of CO2 and SF6 or an inert gas atmosphere.

6. The method according to claim 1, characterized in that, Based on volume percentage, the metal skeleton accounts for 20% to 60% of the volume of the magnesium-based interpenetrating composite material, and the pore size is 1 mm to 5 mm.

7. The method according to claim 1, characterized in that, The metal skeleton has a three-dimensional interconnected channel structure inside.

8. The method according to claim 1, characterized in that, The metal frame is preheated to 300℃~450℃.

9. The method according to claim 1, characterized in that, The magnesium liquid is obtained by heating magnesium or magnesium alloy to above 700°C.

10. The method according to claim 1, characterized in that, The metal skeleton is made of a metal material with a melting point higher than that of the molten magnesium liquid.

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