Lightweight heat dissipating composite material containing a phase change material

Abstract

The application discloses a light heat-dissipating composite material containing a phase change material, which comprises an outer shell layer with a cavity, a weight-reducing layer arranged in the cavity of the outer shell layer, and a bonding layer connecting the outer shell layer and the weight-reducing layer; wherein the outer shell layer is a metal layer, the weight-reducing layer is a phase change heat-conducting composite material obtained by filling a phase change material in a heat-conducting foam material, and the bonding layer is the phase change material; the application adopts a structure of phase change heat-conducting composite material and metal composite. The phase change heat-conducting composite material has high thermal conductivity and phase change latent heat, can rapidly absorb and store the heat of a heat source, and can ensure that the heat source maintains a low temperature; since the density of the phase change heat-conducting composite material is lower than that of metal material, the weight of a metal device or a metal shell can be effectively reduced.

Description

Technical Field

[0001] This invention relates to a lightweight heat-dissipating composite material containing a phase change material. Background Technology

[0002] Traditional chassis or motor housings are typically solid structures, which are too heavy. Weight reduction can be achieved by drilling holes or making them hollow, but this sacrifices heat dissipation. Patent CN201521032017.1 uses cast aluminum instead of steel to reduce weight and utilizes aluminum's thermal conductivity for heat dissipation, but aluminum's thermal conductivity is limited.

[0003] Therefore, it is necessary to develop new lightweight heat dissipation materials to achieve good heat dissipation while reducing weight. Summary of the Invention

[0004] The purpose of this invention is to provide a lightweight heat-dissipating composite material containing phase change material to solve the problem that it is difficult to achieve both weight reduction and heat dissipation in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A lightweight heat-dissipating composite material containing a phase change material, the lightweight heat-dissipating composite material comprising an outer shell layer with a cavity, a weight-reducing layer disposed within the cavity of the outer shell layer, and a bonding layer connecting the outer shell layer and the weight-reducing layer; wherein, the outer shell layer is a metal layer, the weight-reducing layer is a phase change thermally conductive composite material obtained by filling a thermally conductive foam material with a phase change material, and the bonding layer is the phase change material.

[0007] In the lightweight heat dissipation composite material of the present invention, the outer shell layer is on the outside and is made of metal, and its main function is to provide support; the bonding layer is in the middle and its function is to connect the weight reduction layer and the outer shell layer. It is self-adhesive after the solid-liquid phase change of the phase change material, thereby reducing the interfacial thermal resistance; the weight reduction layer is on the inside and is made of thermally conductive material, and its main function is to reduce the overall density and increase the thermal conductivity.

[0008] In one embodiment of the lightweight heat-dissipating composite material according to the present invention, the thermally conductive foam material is thermally conductive carbon foam and / or copper foam; in another embodiment, preferably, the thermally conductive carbon foam has a density of 0.02-1 g / cm³. 3 For example, 0.05, 0.1, 0.2, 0.3, or 0.5 g / cm³. 3 Thermal diffusivity greater than 20 mm 2 / s, such as 50, 70, 80, 100 or 200mm 2 / s; Thermally conductive copper foam density 0.5-1.8g / cm³ 3 Thermal conductivity greater than 5 W / mK.

[0009] In one embodiment, the thermally conductive foam material is processed to the same size as the cavity; the thermally conductive foam material can be one or both of thermally conductive carbon foam and copper foam. In one embodiment, the thermally conductive foam material accounts for 30-80% of the total volume of the lightweight heat dissipation composite material; the medium in the pores of the thermally conductive foam material is a phase change material.

[0010] In one embodiment, the phase change material is one or more selected from paraffin, decanoic acid, lauric acid, myristic acid, and stearic acid. In another embodiment, when preparing the phase change thermally conductive composite material, the phase change material is heated to a liquid state, and a thermally conductive foam material is immersed in the liquid phase change material under vacuum conditions to adsorb and fill the phase change material, thereby obtaining the phase change thermally conductive composite material.

[0011] In one embodiment of the lightweight heat-dissipating composite material according to the present invention, the weight-reducing layer further comprises thermally conductive carbon blocks; the thermally conductive carbon blocks are arrayed within the cavity, and the phase change thermally conductive composite material is processed into a structure complementary to the array of thermally conductive carbon blocks to fill the cavity. Preferably, the density of the thermally conductive carbon blocks is 1.7-2.0 g / cm³. 3 The carbon content is greater than 90%, the horizontal thermal conductivity is 300-600 W / mK, and the vertical thermal conductivity is 10-50 W / mK. When the weight-reducing layer is a combination of thermally conductive carbon blocks and thermally conductive foam materials, the low density of the thermally conductive foam materials can effectively reduce weight, while the high thermal conductivity of the thermally conductive carbon blocks can enhance thermal conductivity. Combining the two can achieve two benefits at once: weight reduction and pre-heat conduction.

[0012] In one embodiment, during the processing of the weight-reducing layer, holes are drilled in the phase change thermally conductive composite material block, with the shape and size of the holes matching those of the thermally conductive carbon block. The thermally conductive carbon block is then placed into the phase change thermally conductive composite material and heated to melt the phase change material, thus bonding the thermally conductive carbon block and the phase change thermally conductive composite material together. To effectively transfer heat, the thermally conductive carbon block is positioned so that its horizontal thermal conductivity corresponds to the vertical direction of the carbon block column, i.e., it aligns with the heat transfer direction of the carbon block (i.e., the direction of greatest temperature difference). The thermally conductive carbon block can be processed into a cylinder or a square column.

[0013] In this invention, when a lightweight heat-dissipating composite material is obtained by combining a metal with a phase change thermally conductive composite material, the phase change thermally conductive composite material is placed in the outer shell metal cavity, and the metal cavity can be sealed by welding, flanges, or other methods. The outer shell metal can be copper, aluminum, stainless steel, or an alloy, and is a shell with a certain cavity. In one embodiment, the volume ratio of the outer shell layer in the entire lightweight heat-dissipating composite material is 20-70%, that is, the metal volume of the outer shell layer accounts for 20-70% of the total volume of the outer shell layer, for example, 30%.

[0014] In one embodiment of the lightweight heat-dissipating composite material according to the present invention, the thermally conductive foam material is thermally conductive carbon foam, and the preparation method of the thermally conductive carbon foam includes the following steps:

[0015] (1) The asphalt component is crushed and then dry-mixed with porous graphite and optionally thermally conductive reinforcing material to achieve uniform mixing, and then pressed into shape.

[0016] (2) The preform obtained in step (1) is treated at 450-700℃ for more than 10 minutes under normal pressure to obtain the molding material;

[0017] (3) The molding material obtained in step (2) is subjected to high temperature treatment at a temperature above 900°C under normal pressure and in a protective atmosphere to obtain foamed carbon material.

[0018] The asphalt component is mesophase asphalt; in the preform, porous graphite accounts for 30%-60% by mass, mesophase asphalt accounts for 40-70% by mass, and thermally conductive reinforcing material accounts for 0-20% by mass.

[0019] In step (1), the asphalt component is pulverized and then mixed uniformly with porous graphite and optionally a thermally conductive reinforcing material. In one embodiment, the asphalt component is pulverized and then dry-mixed with porous graphite and optionally a thermally conductive reinforcing material to achieve uniform mixing, for example, by dry mixing at room temperature.

[0020] In one embodiment, the mesophase content of the mesophase asphalt is not less than 60%, such as 80% or 100%; in another embodiment, the softening point of the mesophase asphalt is 150-400℃, such as 180, 220, 250, 280, 300, 350 or 380℃, preferably 200-360℃; in this invention, the mesophase asphalt is pulverized before mixing to ensure thorough mixing; in one embodiment, after pulverization, the particle size of the mesophase asphalt is not less than 100 mesh (Taylor standard sieve), preferably not less than 200 mesh, such as 200-1000 mesh, such as 300, 500 or 800 mesh, to facilitate the subsequent formation of multi-level pores.

[0021] In this invention, the porous graphite can be one or more of graphene, expanded graphite, high thermal conductivity carbon felt, foamed graphite, and carbon nanotubes; in one embodiment, the bulk density of the porous graphite is not less than 100, preferably not less than 200, such as 220, 250, 300, 330, or 350; in another embodiment, the porous graphite is preferably one or more of expanded graphite and carbon nanotubes, and the bulk density is preferably 200-350, which is beneficial for the mixing and dispersion of mesophase pitch and for generating hierarchical pores that are more conducive to filling phase change materials.

[0022] In this invention, when the porous graphite in step (1) is a combination of multiple components, its bulkiness refers to the average bulkiness of the porous graphite composition, which is equal to the sum of the products of the weight parts of each component and the bulkiness divided by the sum of the weight parts of each component. For example, when the porous graphite is composed of expanded graphite and carbon nanotubes, its bulkiness is equal to (Z1*P1+Z2P2) / (Z1+Z2); where Z1 is the weight part of expanded graphite, Z2 is the weight part of carbon nanotubes, P1 is the bulkiness of expanded graphite, and P2 is the bulkiness of carbon nanotubes.

[0023] In step (1), the mixed raw materials are pressed and molded to obtain a preform, which serves as the basis for subsequent processing in this invention. In one embodiment, the molding pressure is preferably 3-20 MPa, such as 5, 8, 10, 15, or 18 MPa, which helps to reduce the adverse foaming effects in subsequent steps. In this invention, after molding, the density of the preform can be 0.035-0.5 g / cm³. 3 For example, 0.04, 0.05, 0.1, 0.2, 0.4 or 0.45; during molding, the holding time can be 1-10 minutes, such as 2, 5 or 8 minutes.

[0024] In one embodiment, the preform contains 40%-60% porous graphite by mass, such as 42%, 45%, 50%, 55%, or 58%, 30%-45% asphalt material by mass, such as 32%, 35%, 40%, or 43%, and 0-10% thermally conductive reinforcing material by mass, such as 2%, 5%, or 8%. The thermally conductive reinforcing material, used to enhance the thermal conductivity of the thermally conductive carbon foam, is well-known in the art and can be one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride, wherein high thermal conductivity carbon fiber refers to carbon fiber with a thermal conductivity ≥2000 W / mK. It should be understood that in this invention, when the mass percentage of a component is 0, it means that the component is not present. For example, in this invention, when the high-temperature treatment in subsequent step (3) is sufficiently high, such as above 3000°C, allowing the carbon foam to be fully graphitized, since graphite itself has good thermal conductivity, the addition of the thermally conductive reinforcing material can be considered unnecessary.

[0025] In step (2), the preform obtained in step (1) is treated at 450-700℃ for at least 10 minutes under normal pressure to allow the preform to solidify and significantly reduce foaming, thereby obtaining the molded material. In one embodiment, the treatment temperature is 450-650℃, such as 470, 500, 550, 600, or 620℃, and the treatment time can be 10-60 minutes, such as 20, 30, or 50 minutes. Excessive time is not conducive to improving efficiency. In this invention, during the heat treatment in step (2), the treatment atmosphere can be an air atmosphere or a protective atmosphere. For cost considerations, an air atmosphere can be chosen. In this invention, unless otherwise specified, the above-mentioned treatment atmosphere is an air atmosphere.

[0026] In step (3), the molding material obtained in step (2) is subjected to high-temperature treatment at a temperature above 900°C under normal pressure and a protective atmosphere to obtain foamed carbon material; the protective atmosphere can be a nitrogen atmosphere or an inert gas atmosphere. In one embodiment, the high-temperature treatment temperature is 1000-3200°C, such as 1200, 1500, 2000, 2500 or 3000°C. Different treatment temperatures can yield foamed carbon materials with different thermal diffusivity. Therefore, the corresponding treatment temperature can be selected according to the target thermal diffusivity. For example, to obtain a better thermal diffusivity, the high-temperature treatment temperature can be increased, such as to 2800°C or even 3000°C or 3200°C, so as to facilitate full graphitization; or, the foamed carbon material obtained by the present invention through high-temperature treatment (such as below 2000°C, 2500°C or even below 2800°C) is further treated at a temperature above 2800°C, such as 3000°C or 3200°C, to improve the thermal diffusivity, so as to facilitate full graphitization.

[0027] In this invention, the thermally conductive foam carbon prepared according to the above preparation method has a multi-level pore size distribution. Specifically, the pore size distribution in the range of 0.01-5 μm (excluding 5 μm) is not less than 20%, preferably 22-60%, such as 25%, 30%, 40%, 45%, 50%, 55%, or 58%; the pore size distribution in the range of 5-150 μm is not less than 10%, preferably 12-45%, such as 15%, 20%, 25%, 30%, 35%, 40%, or 42%; and the pore size distribution in the range of 150-1000 μm (excluding 150 μm) is not less than 8%, preferably 10-60%, such as 12%, 15%, 20%, 30%, 40%, 45%, 50%, 55%, or 58%. In one embodiment, the density of the thermally conductive foam carbon of this invention is 0.03-0.4 g / cm³. 3 For example, 0.05, 0.1, 0.2, 0.3, or 0.35 g / cm³. 3In one embodiment, the thermally conductive foam carbon is composed of graphite and amorphous carbon components, wherein the graphite content can be 40%-100%, such as 60%, 80%, 90%, or 95%, and the amorphous carbon content can be 0-60%. In another embodiment, the graphite content of the thermally conductive foam carbon is 90% or even 95% or higher, so as to have a relatively higher thermal diffusivity at its low density level.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The lightweight heat dissipation composite material or structure of the present invention consists of an outer shell layer, a weight-reducing layer, and a bonding layer. The outer shell layer is on the outside and is made of metal, mainly for support. The bonding layer is in the middle and is a phase change material, which achieves self-bonding after a solid-liquid phase change, mainly for reducing interfacial thermal resistance. The weight-reducing layer is on the inside and is a phase change thermally conductive composite material composed of a thermally conductive skeleton and a phase change material, mainly for reducing overall density and increasing thermal conductivity and heat absorption capacity. To enhance thermal conductivity, thermally conductive carbon blocks can be inserted inside the phase change thermally conductive composite material. Under a certain heat source, the outer shell layer transfers heat to the weight-reducing layer. The phase change material in the weight-reducing layer absorbs heat and undergoes a solid-liquid phase change. The temperature does not change or remains within a very narrow range during the phase change process, thereby keeping the entire lightweight heat dissipation composite material at a low temperature for a certain period of time. Compared with a solid metal structure, the weight can be reduced by 25%-55%. The phase change temperature of the phase change material in the weight-reducing layer can be selected as needed to maintain the temperature near the phase change temperature (for a certain period of time). By selecting an appropriate phase transition temperature, the temperature can be reduced by 5-20°C or even more than that of solid metal within a certain period of time.

[0030] (2) The novel foamed carbon proposed in this invention has a non-porous structure, which differs from the traditional foamed structure. In this invention, powdered asphalt is dispersed and mixed in loose porous graphite and molded under certain pressure. Subsequent heating effectively reduces foaming, and the asphalt material adheres to the porous graphite material. Effective overlap between the porous graphite particles results in a multi-level pore size distribution, forming a low-density porous structure. The pore size distribution is multi-level, with abundant distribution even at 50 micrometers, for example, 5 micrometers. Therefore, even when filled with a large amount of phase change material, the liquid phase change material can be effectively bound. After five cycles of "melting-solidification" for the phase change thermally conductive composite material, the mass loss is less than 10%. Simultaneously, the fine thermally conductive skeleton of the foamed carbon in this invention also gives the entire composite material a high thermal conductivity. For example, when the density of the foamed carbon is 0.045 g / cm³... 3 At that time, 10 grams of foamed carbon filled with 115 grams of paraffin phase change material had a thermal conductivity of 6.5 W / mK;

[0031] (3) The present invention adopts an atmospheric pressure preparation process, which is simple and has low cost. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of one embodiment of the lightweight heat dissipation composite material of the present invention;

[0033] Figure 2 A schematic diagram of a weight reduction layer without thermally conductive carbon blocks;

[0034] Figure 3 A schematic diagram showing a weight-reducing layer with a heat-conducting carbon block. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the present invention is not limited to the listed embodiments and drawings.

[0036] like Figure 1 and 2 The lightweight heat-dissipating composite material shown is divided into an outer shell layer 1, a weight-reducing layer 2, and a bonding layer. The outer shell layer 1 is on the outside and is a hollow metal shell structure. The weight-reducing layer, located inside the cavity of the outer shell layer 1, is a composite material of thermally conductive foam and phase change material, wherein the thermally conductive foam is one or more of foamed copper and foamed carbon. The bonding layer, located between the outer shell layer 1 and the weight-reducing layer 2, is a phase change material that achieves self-bonding through a solid-liquid phase change. Figure 2 As shown, the weight-reducing layer 2 is a phase change thermally conductive composite material obtained by combining thermally conductive foam material and phase change material. In preparing the phase change composite thermally conductive material, the phase change material is heated to a liquid state, and the thermally conductive foam material is immersed in the liquid phase change material under vacuum conditions to allow for the adsorption and filling of the phase change material, thereby obtaining the phase change composite thermally conductive material.

[0037] The phase change thermally conductive composite material is processed into the size of a metal cavity, thus forming a structure with a metal exterior and a phase change thermally conductive composite material interior. Phase change material is added to the joint and heated to melt it, or the phase change thermally conductive composite material of the weight-reducing layer 2 is directly heated to cause a small amount of phase change material to flow out from the carbon foam skeleton, automatically filling the gap between the outer shell layer 1 and the weight-reducing layer 2, forming a bonding layer and reducing interfacial thermal resistance.

[0038] like Figure 3As shown, to enhance thermal conductivity, thermally conductive carbon blocks 2-2 can be interspersed within the phase change thermally conductive composite material 2-1. The thermally conductive carbon blocks 2-2 are evenly distributed in an array within the thermally conductive foam material or the phase change composite thermally conductive material. The phase change composite thermally conductive material is processed into a structure complementary to the array of thermally conductive carbon blocks to fill the cavities. The thermal conductivity of the thermally conductive carbon blocks 2-2 is directional, with high thermal conductivity in the horizontal direction and low thermal conductivity in the vertical direction. Aligning the horizontal thermal conductivity with the vertical direction of the carbon block array achieves optimal heat transfer. During the processing of the weight-reducing layer 2, holes are drilled in the phase change thermally conductive composite material 2-1 block. The shape and size of the holes are consistent with the thermally conductive carbon blocks. The thermally conductive carbon blocks 2-2 are placed into the phase change composite thermally conductive material and heated to melt the phase change material, thus bonding the thermally conductive carbon blocks and the phase change thermally conductive composite material together.

[0039] Example 1 of the preparation of thermally conductive carbon foam material

[0040] Asphalt with a softening point of 360℃ and a mesophase content of 100% was pulverized and passed through a 200-mesh sieve. 50 parts of asphalt, 40 parts of expanded graphite (bulkness 200, carbon content 99.9%), and 10 parts of high thermal conductivity carbon fiber (thermal conductivity approximately 2000 W / mK) were mixed. The mixture was pressed into shape in a mold at a pressure of 7 MPa for 3 minutes. It was then fired at 600℃ for 30 minutes to obtain the molded material. The molded material was then subjected to high-temperature treatment at 1600℃ in a protective atmosphere to obtain foamed carbon material.

[0041] Tests showed that the density of the foamed carbon material was 0.1 g / cm³, and its thermal diffusivity was 45 mm². 2 / s, graphite content 55%, amorphous carbon content 45%. Pore size distribution: 0.01-5μm 35%, 5-150μm 40%, 150-1000μm 25%.

[0042] Example 2 of preparation of thermally conductive carbon foam material

[0043] Asphalt with a softening point of 300℃ and a mesophase content of 80% was pulverized and passed through a 500-mesh sieve. 55 parts asphalt, 40 parts carbon nanotubes (300% bulk), and 5 parts natural graphite were mixed. The mixture was pressed into shape in a mold at a pressure of 15 MPa for 3 minutes. It was then fired at 500℃ for 20 minutes to obtain the molded material. Finally, it was treated at 3000℃ in a protective atmosphere to obtain foamed carbon material.

[0044] Tests showed that the density of the foamed carbon material was 0.2 g / cm³. 3 Thermal diffusivity 200 mm 2 / s, graphite content 99.5%, amorphous carbon content 0.5%. Pore size distribution: 0.01-5μm 55%, 5-150μm 35%, 150-1000μm 10%.

[0045] Example 3 of preparation of thermally conductive carbon foam material

[0046] Asphalt with a softening point of 250℃ and a mesophase content of 60% was pulverized and passed through a 300-mesh sieve. 60 parts of asphalt and 40 parts of expanded graphite (bulk density 250) were mixed. The mixture was then pressed into shape in a mold at a pressure of 3 MPa for 1 minute. It was then fired at 450℃ for 25 minutes to obtain the molded material. Finally, it was treated at 1000℃ in a protective atmosphere to obtain foamed carbon material.

[0047] Tests showed that the density of the foamed carbon material was 0.05 g / cm³. 3 Thermal diffusion system 20mm 2 / s, graphite content 40%, amorphous carbon content 60%. Pore size distribution: 0.01-5μm 25%, 5-20μm 15%, 20-250μm 15%, 250-1000μm 45%.

[0048] Example 4 of preparation of phase change thermally conductive composite material

[0049] The foamed carbon obtained in Example 2 was composited with a phase change material (the phase change material was phase change paraffin, with a phase change temperature of 38°C). The composite process was as follows: the phase change material was heated to a liquid state, and 10 grams of thermally conductive foamed carbon was immersed in the liquid phase change material under vacuum conditions until adsorption saturation (adsorption amount 65 grams) was achieved, resulting in a foamed carbon phase change composite material. The thermal conductivity of the foamed carbon phase change composite material at room temperature was 30 W / mK. Testing showed that after five cycles of melting and solidification, the mass loss of the phase change composite material was less than 5%, indicating that it could form effective binding.

[0050] Example 5 of preparation of phase change thermally conductive composite materials

[0051] The foamed carbon prepared in Example 3 was subjected to graphitization treatment at 3000℃ to obtain a foamed carbon material with a density of 0.045 g / cm³. 3 Thermal diffusion system 45mm 2 / s. Then, it is composited with a phase change material (the phase change material is phase change paraffin, phase change temperature 38℃). The composite process is as follows: the phase change material is heated to a liquid state, and 10 grams of thermally conductive carbon foam is immersed in the liquid phase change material under vacuum conditions until adsorption saturation (adsorption amount 115 grams), resulting in a phase change composite carbon foam material. The thermal conductivity of the phase change composite carbon foam material at room temperature is 6.5 W / mK. Testing showed that after 5 cycles of "melting-solidification," the mass loss of the phase change composite material was less than 10%, indicating that it can form effective binding.

[0052] Examples 6-7 and Comparative Example 1

[0053] Comparative Example 1: Made of solid aluminum alloy, with dimensions of 185*185*30mm.

[0054] Example 6: See Figure 1 and Figure 2 The outer shell is made of aluminum alloy, accounting for 30% of the volume, and its dimensions are the same as Comparative Example 1. The weight-reducing layer uses the phase change thermally conductive composite material prepared in Example 4; wherein the phase change material is paraffin wax, and the phase change temperature is 38°C. The bonding layer is also made of paraffin wax phase change material. Compared with the solid structure of Comparative Example 1, the weight is reduced by 45%.

[0055] Example 7: See Figure 1 and Figure 3 The outer shell is made of aluminum alloy, accounting for 30% of the volume. Weight-reduction layers include... Figure 3 The image shows a composite of the phase change thermally conductive composite material prepared in Example 4 and a thermally conductive carbon block. The thermally conductive carbon block has a horizontal thermal conductivity of 600 W / mK and a vertical thermal conductivity of 20 W / mK, with the horizontal thermal conductivity direction corresponding to the thickness direction of the structural layer. The phase change material is paraffin wax, and the phase change temperature is 38°C. The bonding layer is also made of paraffin wax phase change material. Compared to the solid structure in Comparative Example 1, the weight is reduced by 30%.

[0056] Temperature control application test: An 80W heat source was attached to the lower surface of Comparative Example 1, Example 6, and Example 7, and the upper surface temperature was tested after heating for 1 hour. Because Examples 6 and 7 use thermally conductive materials for heat transfer and phase change materials for temperature control, the upper surface temperature is 18-21℃ lower than that of Comparative Example 1. See Table 1 for details.

[0057] Table 1

[0058]

[0059]

Claims

1. A lightweight heat-dissipating composite material containing phase change material, characterized in that, The lightweight heat dissipation composite material includes an outer shell layer with a cavity, a weight-reducing layer disposed within the cavity of the outer shell layer, and a bonding layer connecting the outer shell layer and the weight-reducing layer; wherein, the outer shell layer is a metal layer, the weight-reducing layer is a phase change thermally conductive composite material obtained by filling a phase change material into a thermally conductive foam material, and the bonding layer is the phase change material; In the preparation of the phase change thermally conductive composite material, the phase change material is heated to a liquid state, and a thermally conductive foam material is immersed in the liquid phase change material under vacuum conditions to adsorb and fill the phase change material, thereby obtaining the phase change thermally conductive composite material.

2. The lightweight heat-dissipating composite material according to claim 1, characterized in that, The outer shell layer accounts for 20-70% of the total volume of the lightweight heat-dissipating composite material; the thermally conductive foam material is thermally conductive carbon foam and / or copper foam; the phase change material is one or more of paraffin wax, decanoic acid, lauric acid, myristic acid, and stearic acid.

3. The lightweight heat-dissipating composite material according to claim 2, characterized in that, The thermally conductive carbon foam has a density of 0.02-1 g / cm3 and a thermal diffusivity greater than 20 mm2 / s; the thermally conductive copper foam has a density of 0.5-1.8 g / cm3 and a thermal conductivity greater than 5 W / mK.

4. The lightweight heat-dissipating composite material according to any one of claims 1-3, characterized in that, The weight-reducing layer is further provided with thermally conductive carbon blocks.

5. The lightweight heat-dissipating composite material according to claim 4, characterized in that, The thermally conductive carbon blocks are arranged in an array within the cavity, and the phase change thermally conductive composite material is processed into a structure complementary to the array of thermally conductive carbon blocks to fill the cavity.

6. The lightweight heat-dissipating composite material according to claim 5, characterized in that, The thermally conductive carbon block has a density of 1.7-2.0 g / cm3, a carbon content greater than 90%, a horizontal thermal conductivity of 300-600 W / mK, and a vertical thermal conductivity of 10-50 W / mK. When setting the thermally conductive carbon block, the horizontal thermal conductivity is aligned with the vertical direction of the thermally conductive carbon block column.

7. The lightweight heat-dissipating composite material according to claim 6, characterized in that, During the processing of the weight-reducing layer, holes are drilled in the phase change thermally conductive composite material block so that the shape and size of the holes are consistent with the thermally conductive carbon block. The thermally conductive carbon block is placed into the phase change thermally conductive composite material and heated to melt the phase change material, so that the thermally conductive carbon block and the phase change thermally conductive composite material are bonded together.

8. The lightweight heat-dissipating composite material according to any one of claims 1-3 and 5-7, characterized in that, The thermally conductive foam material is thermally conductive foam carbon, and the preparation method of the thermally conductive foam carbon includes the following steps: (1) After the asphalt component is crushed, it is dry-mixed with porous graphite and optionally thermally conductive reinforcing material to achieve uniform mixing, and then pressed into shape; (2) The preform obtained in step (1) is treated at 450-700℃ for more than 10 minutes under normal pressure to obtain the molding material; (3) The molding material obtained in step (2) is subjected to high temperature treatment at a temperature above 900°C under normal pressure and in a protective atmosphere to obtain foamed carbon material; In the preform, porous graphite accounts for 30%-60% of the mass, mesophase pitch accounts for 40-70% of the mass, and thermally conductive reinforcing material accounts for 0-20% of the mass; the pitch component is mesophase pitch.

9. The lightweight heat-dissipating composite material according to claim 8, characterized in that, The porous graphite has a bulk density of not less than 100; the porous graphite is one or more of graphene, expanded graphite, high thermal conductivity carbon felt, foamed graphite and carbon nanotubes; The thermally conductive enhancement material includes one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride.

10. The lightweight heat-dissipating composite material according to claim 8, characterized in that, The porosity of the porous graphite is not less than 200; the porous graphite is one or more of expanded graphite and carbon nanotubes. The thermally conductive enhancement material includes one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride.

11. The lightweight heat-dissipating composite material according to any one of claims 8-10, characterized in that, The mesophase asphalt has a mesophase content of not less than 60%, a softening point of 150-400℃, and a particle size of not less than 100 mesh.

12. The lightweight heat-dissipating composite material according to claim 11, characterized in that, The softening point of the mesophase pitch is 200-360℃, and the particle size is 200-1000 mesh.

13. The lightweight heat-dissipating composite material according to claim 11, characterized in that, The preform contains 40%-60% porous graphite, 30%-45% asphalt components, and 0-10% thermally conductive reinforcing materials.

14. The lightweight heat-dissipating composite material according to any one of claims 8-10 and 12-13, characterized in that, In step (1), the molding pressure is 3-20 MPa and the molding time is 1-10 min; The processing time in step (2) is 10-60 min, and the processing temperature is 450-650℃; In step (3), the protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere; the high-temperature treatment temperature is 1000-3200℃.

15. The lightweight heat-dissipating composite material according to claim 14, characterized in that, The density of the preform is 0.035-0.5 g / cm3.

16. The lightweight heat-dissipating composite material according to any one of claims 8-10, 12-13 and 15, characterized in that, The density of the thermally conductive foam carbon is 0.05-0.4 g / cm3; The thermally conductive carbon foam has a multi-level pore size distribution, wherein the pore size distribution in the range of 0.01-5μm is not less than 20%; the pore size distribution in the range of 5-150μm is not less than 10%; and the pore size distribution in the range of 150-1000μm is not less than 8%.

17. The lightweight heat-dissipating composite material according to claim 16, characterized in that, The pore size distribution is 22-60% for pore sizes ranging from 0.01 to 5 μm; 12-45% for pore sizes ranging from 5 to 150 μm; and 10-60% for pore sizes ranging from 150 to 1000 μm.

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