Gradient porous copper-aluminum composite material and preparation method and application thereof

Abstract

The invention relates to the field of metal-based composite materials, and discloses a gradient porous copper-aluminum composite material and a preparation method and application thereof. The gradient porous copper-aluminum composite material comprises an aluminum substrate and gradient porous copper arranged on one surface of the aluminum substrate. The gradient porous copper is divided into a small-hole copper layer and a large-hole copper layer which are in contact with the aluminum substrate; wherein the small-hole copper layer is close to the transition part of the aluminum substrate, graphene layers are deposited on the surface, combined with the aluminum substrate, of the small-hole copper layer and the surface of an internal hole, and the hole is filled with silver. Through the gradient pore structure design of the porous copper, the graphene interface is strengthened and filled with the silver colloid, and the composite heat dissipation plate material obtained after compounding with the aluminum substrate has the advantages of high heat conductivity, low interface thermal resistance, high strength, light weight and low cost.

Description

Technical Field

[0001] The present invention relates to the field of metal matrix composites, and particularly to a gradient porous copper-aluminum composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the explosive development of artificial intelligence, high-performance computing, and large model training, the computing power demand has shown exponential growth. The power density of a single cabinet has exceeded 20 kW. Due to the low air thermal conductivity (the thermal conductivity is only 0.024 W·m -1 ·K -1 ), high energy consumption and other problems, traditional air cooling is difficult to meet the heat dissipation requirements of high-power chips. Existing heat dissipation plate materials mostly use pure copper, aluminum alloy, stainless steel, or titanium alloy, and there are significant shortcomings: (1) Pure copper has excellent thermal conductivity (~400 W·m -1 ·K -1 ), but it has a large density and high cost (about 3-5 times that of aluminum), resulting in a sharp increase in the weight and manufacturing cost of the liquid cooling plate; (2) Aluminum alloy has obvious lightweight advantages, but its thermal conductivity is only 200 W·m -1 ·K -1 , and surface anti-corrosion treatment is required. It is easy to fail due to electrolytic corrosion during long-term use; (3) Although the copper-aluminum composite plate takes into account both performance and cost, the interfacial thermal resistance (10 -4 -10 -5 m 2 ·K·W -1 ) causes the overall thermal conductivity to decrease by 30%-50% (CN202421125205.8); (4) Although stainless steel has excellent corrosion resistance, its thermal conductivity is extremely low (~15 W·m -1 ·K -1 ), which cannot meet the heat dissipation requirements of high power density and is only applicable to special corrosion-resistant environments. At the same time, its processing cost is relatively high, and complex process control is required for cold rolling forming; (5) Although titanium alloy has the advantages of light weight, high strength, and corrosion resistance, its thermal conductivity is only 22 W·m -1 ·K -1 , and the processing difficulty is extremely high and the raw material price is expensive (about 5-10 times that of copper), mainly limited to high-end fields such as aerospace and military.

[0003] The above defects have become the key bottleneck restricting the improvement of cooling efficiency. Therefore, it is urgent to develop a new type of heat dissipation plate material with high thermal conductivity, lightweight, and low interfacial thermal resistance. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a gradient porous copper-aluminum composite material, its preparation method and application. Through the design of the gradient pore structure of porous copper, graphene interface strengthening and silver glue filling, the composite heat dissipation plate material obtained after being combined with an aluminum substrate has the advantages of high thermal conductivity, low interface thermal resistance, high strength, light weight and low cost.

[0005] The specific technical solution of the present invention is as follows: In the first aspect, the present invention provides a gradient porous copper-aluminum composite material, which includes an aluminum substrate and gradient porous copper provided on one surface of the aluminum substrate. Among them, the gradient porous copper is divided into a small-hole copper layer and a large-hole copper layer in contact with the aluminum substrate; in the transition part of the small-hole copper layer close to the aluminum substrate, a graphene layer is deposited on the surface of the combination with the aluminum substrate and the inner pore surface, and silver is filled in the pores. Among them, when the gradient porous copper-aluminum composite material is used as a heat dissipation plate, the aluminum substrate is the side in contact with the heat source substance, and the large-hole copper layer is the side for heat diffusion.

[0006] Through the collaborative design of the porous copper gradient pore structure and the graphene interface layer, the present invention systematically optimizes the heat flow path and interface conduction efficiency of the heat dissipation plate. The small-hole copper layer is designed with a low porosity and small pore diameter, retaining the high electronic thermal conductivity of the copper skeleton, while the large-hole copper layer is designed with a high porosity and large pore diameter, which serves as the main channel to reduce the flow resistance and improve the heat dissipation efficiency. The transition part at the bottom of the small-hole copper layer serves as the interface layer combined with the aluminum substrate. Graphene covers the inner surface of the pores of the porous copper. By virtue of the ultra-high intrinsic thermal conductivity of graphene, the pores are transformed from "thermal resistance units" into "extended heat dissipation surfaces", forming a super thermal conduction channel at the interface; at the same time, combined with the filling of nano silver glue, the micro gaps at the copper-aluminum interface are bridged to form a silver-graphene-copper continuous thermal conduction network, synergistically reducing the copper-aluminum interface thermal resistance. Combined with the directional heat flow guidance of the gradient pores, the composite material as a whole has a high thermal conductivity. This transition part can block oxygen erosion and greatly improve the corrosion resistance of the aluminum substrate. The gradient pore structure enables the composite heat dissipation plate material to adapt to high-frequency mechanical vibration and high-frequency thermal shock conditions through mechanical constraint design (its compressive strength is higher than that of non-gradient porous structures) and thermal cycling optimization (extremely low performance attenuation).

[0007] Preferably, the porosity of the small-hole copper layer is 50-60%, and the pore diameter is 10-50 μm; the porosity of the large-hole copper layer is 60-70%, and the pore diameter is 200-500 μm.

[0008] For the gradient porous copper, the small pore diameter and low porosity of the small pore copper layer at the bottom layer can reduce the blockage of heat conduction by pores, while the large pore diameter and high porosity of the large pore copper layer at the top layer can reduce weight and flow resistance, and improve the convective heat dissipation efficiency. The present invention discovers that the porosity and pore size of the small pore copper layer and the porosity and pore size of the large pore copper layer are crucial for achieving the above effects. Specifically, for the small pore copper layer: if its porosity is too high or pore diameter is too large (such as porosity > 70%, pore diameter > 50 μm), since the thermal conductivity of air is much lower than that of copper, the equivalent thermal conductivity will drop sharply and the mechanical strength will deteriorate; if the porosity is too low or pore diameter is too small (such as porosity < 50%, pore diameter < 10 μm), the air flow resistance will increase sharply (inversely proportional to the fourth power of the pore diameter), resulting in uneven air flow distribution and increased fan power consumption. For the large pore copper layer: if the porosity is too high or pore diameter is too large (such as porosity > 80%, pore diameter > 500 μm), the continuity of the copper skeleton is damaged, the heat dissipation area is reduced, and the convective heat transfer efficiency is lowered; if the porosity is too low or pore diameter is too small (such as porosity < 60%, pore diameter < 200 μm), the wind resistance will increase significantly (inversely proportional to the square of the pore diameter), easily causing local air flow stagnation and limited heat exchange efficiency.

[0009] Preferably, the thickness of the large pore copper layer is 800 - 2500 μm, the thickness of the small pore copper layer (including the transition part) is 200 - 900 μm, and the thickness of the transition part is 1 / 2 - 1 times the thickness of the small pore copper layer; the thickness of the graphene layer is 0.05 - 0.1 μm; the thickness of the aluminum substrate is 2 - 5 mm, and the surface roughness Ra ≤ 0.8 μm.

[0010] In a second aspect, the present invention provides a method for preparing a gradient porous copper-aluminum composite material, which includes the following steps: 1) Using laser 3D printing to prepare gradient porous copper from spherical copper powder.

[0011] 2) Performing plasma activation treatment on the gradient porous copper.

[0012] Performing plasma activation treatment on the gradient porous copper can remove the surface oxides and generate active sites, which is beneficial for subsequent graphene deposition.

[0013] 3) Immersing the transition part of the gradient porous copper obtained in 2) into a graphene suspension for electrophoretic deposition, and vacuum curing to form a graphene layer.

[0014] 4) Removing the air in the pores of the transition part of the gradient porous copper obtained in 3), injecting silver glue, and vacuum infiltrating to make the nano silver glue fill the pores and the gaps between the graphene layers, and then curing.

[0015] 5) Combining the surface of the transition part of the gradient porous copper obtained in 4) with an aluminum substrate to obtain a gradient porous copper-aluminum composite material.

[0016] Preferably, in step 1), the preparation conditions of the small-hole copper layer are as follows: the particle size of spherical copper powder is 15 - 25 μm, the laser power is 180 - 200 W, the scanning speed is 1000 - 1200 m / s, the single-pass printing layer thickness is 20 - 30 μm, the number of layers is 10 - 30 layers, the checkerboard partition scanning is adopted to disperse heat accumulation, and the energy density is 60 - 80 J / mm 3 .

[0017] By using the above specific process conditions, a small-hole copper layer with the target porosity and pore diameter can be prepared. Among them, the checkerboard partition scanning is adopted to disperse heat accumulation, which can avoid the merging of holes caused by local overheating; the energy density is regulated to 60 - 80 J / mm 3 , which can control the stability of the molten pool.

[0018] Preferably, in step 1), the preparation conditions of the large-hole copper layer are as follows: the particle size of spherical copper powder is 25 - 45 μm, the laser power is 120 - 150 W, the scanning speed is 1500 - 1800 m / s, the single-pass printing layer thickness is 40 - 50 μm, the number of layers is 20 - 50 layers, the unidirectional parallel scanning (tilt angle 15°) is adopted to direct the flow of the molten pool, and the energy density is 30 - 50 J / mm 3 .

[0019] By using the above specific process conditions, a large-hole copper layer with the target porosity and pore diameter can be prepared. Among them, the unidirectional parallel scanning (tilt angle 15°) is adopted to direct the flow of the molten pool, which can form a main channel along the heat flow direction, and the energy density is regulated to 30 - 50 J / mm 3 , and the low energy density can inhibit complete melting and retain pore connectivity.

[0020] Preferably, in step 2), the conditions of the plasma activation treatment are as follows: the plasma gas is argon, the purity is ≥99.99%, the radio frequency power is 250 - 400 W, the treatment time is 5 - 10 min, and the gas flow rate is 20 - 30 sccm.

[0021] Preferably, in step 3): the conditions of the electrophoretic deposition are as follows: the concentration of the graphene suspension is 0.5 - 1 mg / mL, the anode material is a platinum sheet, the cathode is the gradient porous copper, the electrode spacing is 20 - 30 mm, the deposition voltage is 40 - 60 V, the time is 5 - 15 min, and the temperature is 20 - 30 °C.

[0022] Preferably, in step 3): the conditions of the vacuum curing are as follows: the vacuum degree is ≤10 -2 Pa, the temperature is 70 - 120 °C, and the time is 30 - 60 min.

[0023] Preferably, in step 4): the viscosity of the nano silver glue is 80 - 120 mPa·s, and the silver particle size is 20 - 50 nm.

[0024] Further preferably, the nano silver paste comprises: 60-70 wt% of nano silver particles, 25-30 wt% of epoxy resin, 4-10 wt% of acetone, and 1-2 wt% of diethylenetriamine.

[0025] Preferably, in step 4): the conditions for vacuum infiltration are: the vacuum degree ≤ 10 -2 Pa, the pressure is 0.1-0.5 MPa, and the pressure holding time is 10-30 min.

[0026] Preferably, in step 4): the conditions for curing are: pre-curing: 60-90 °C, 30-60 min; main-curing: 100-120 °C, 120-200 min, post-curing: 150-200 °C, 45-90 min.

[0027] The present invention adopts a three-stage gradient heating design to stepwise control the material phase change and interface bonding process to balance the formation of the thermal conduction network, the improvement of mechanical strength, and the release of residual stress. Specifically: (1) Pre-curing stage: The low temperature reduces the fluidity of the epoxy resin, slows down the gravitational settlement of the nano silver particles, ensures the uniform distribution of the silver paste in the pores, the epoxy resin starts the cross-linking reaction, forms a primary three-dimensional network, fixes the position of the silver particles, and avoids particle agglomeration in the subsequent high-temperature stage. If directly cured at high temperature, the silver particles rapidly settle due to the density difference (silver 10.5 g / cm 3 , epoxy resin 1.2 g / cm 3 ), resulting in uneven distribution of the silver paste in the pores and an increase in the interfacial thermal resistance. (2) Main-curing stage: Heating to above the glass transition temperature of the epoxy resin (Tg≈120 °C) promotes the complete cross-linking of the resin, forms a dense network, wraps the silver particles and fills the micro-gaps. The silver particles self-assemble through surface energy drive in the flowing resin to form a continuous thermal conduction chain, significantly improving the equivalent thermal conductivity. If the medium-temperature stage is skipped and directly cured at high temperature, the resin cross-links too quickly, the silver particles cannot be fully self-organized, and the thermal conduction path is broken, resulting in a decrease in the overall thermal performance. (3) Post-curing stage: At high temperature, the resin molecular chains relax, releasing the interfacial residual stress generated due to the difference in thermal expansion coefficients (copper 17×10 -6 / K, epoxy resin 60×10 -6 / K), preventing delamination during thermal cycling. High temperature promotes the atomic diffusion of silver particles and copper / graphene, forms Ag-Cu eutectic micro-regions, and improves the shear strength. Without post-curing, the interfacial residual stress leads to a decrease in shear strength and is prone to cracking under temperature shock.

[0028] Preferably, in step 5): the aluminum substrate is pre-treated by mechanical grinding and polishing and pickling to remove the surface oxide scale.

[0029] Preferably, in step 5): the bonding method between the aluminum substrate and the gradient porous copper is vacuum diffusion welding, and the conditions are: the vacuum degree ≤ 5×10 -3Pa, first heat it from 5 to 10 °C / min to 250 - 300 °C and pressurize it from 0.5 to 1 MPa / min to 5 - 10 MPa, and keep it for 1 - 10 min for pre - compaction; then heat it from 5 to 10 °C / min to 450 - 500 °C and pressurize it from 3 to 5 MPa / min to 20 - 30 MPa, and keep it for 30 - 60 min; then cool it from 1 to 5 °C / min to 150 - 200 °C, and finally cool it to room temperature.

[0030] In the diffusion welding process, the pressurization rate (i.e., the gradient change speed of pressure application) is a key parameter affecting the interface bonding quality, material deformation, and the integrity of the porous structure. In the initial pressurization stage, it ensures that the materials are in close contact, eliminates the assembly gap, the heating temperature is lower than the aluminum recrystallization temperature, and slow pressurization avoids local stress concentration and reduces the risk of plastic deformation in the subsequent high - pressure stage. In the main pressurization stage, the pressurization is accelerated to shorten the process time, the heating temperature is lower than the aluminum melting point, which drives the migration of interface atoms, promotes the inter - diffusion of Cu / A1 atoms, and forms a metallurgical bond. At the same time, by controlling the pressurization rate, the deformation of the porous copper skeleton is avoided. In the pressure - holding stage, the pressure is maintained stable to ensure sufficient atomic diffusion.

[0031] In the third aspect, the present invention provides the application of the gradient porous copper - aluminum composite material as a heat sink plate.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Through the design of the gradient pore structure of the porous copper, graphene interface strengthening and silver glue filling, the composite heat sink plate material obtained after being compounded with the aluminum substrate has the advantages of high thermal conductivity, low interface thermal resistance, high strength, and light weight.

[0033] (2) The gradient pore structure of the present invention reduces the density of the porous copper to 30 - 50% of that of the dense copper. At the same time, through large - scale 3D printing (copper powder utilization rate > 95%), the material cost is greatly reduced. The nano - silver glue fills the interlayer voids of the graphene to form a continuous heat - conducting network, replacing the high - cost pure silver coating. The comprehensive cost is close to the aluminum alloy solution, but the heat dissipation capacity is greatly improved. This design has a high yield through topology optimization and parametric manufacturing and is suitable for batch production. Through multi - dimensional innovation of materials - structure - process, the present invention overcomes the synergistic problem of high thermal conductivity, light weight, and low cost, provides a heat - dissipating material with both performance and cost - effectiveness for high - power computing devices, and boosts the upgrade of green computing infrastructure. Detailed implementation manners

[0034] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only for further illustration of the present invention, but do not constitute any limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] General Embodiment In a first aspect, a gradient porous copper-aluminum composite material includes an aluminum substrate and a gradient porous copper provided on one surface of the aluminum substrate. Among them, the gradient porous copper is divided into a small-hole copper layer and a large-hole copper layer in contact with the aluminum substrate; the porosity of the small-hole copper layer is 50-60%, and the pore diameter is 10-50 μm. In the transition part of the small-hole copper layer close to the aluminum substrate, graphene layers are deposited on the surface where it combines with the aluminum substrate and the inner pore surfaces, and silver is filled in the pores; the porosity of the large-hole copper layer is 60-70%, and the pore diameter is 200-500 μm.

[0036] In some preferred embodiments, the thickness of the large-hole copper layer is 800-2500 μm, the thickness of the small-hole copper layer (including the transition part) is 200-900 μm, and the thickness of the transition part is 1 / 2-1 of the thickness of the small-hole copper layer; the thickness of the graphene layer is 0.05-0.1 μm; the thickness of the aluminum substrate is 2-5 mm, and the surface roughness Ra ≤ 0.8 μm.

[0037] In a second aspect, a method for preparing a gradient porous copper-aluminum composite material includes the following steps: 1) Using laser 3D printing to prepare gradient porous copper from spherical copper powder.

[0038] In some preferred embodiments, in step 1), the preparation conditions for the small-hole copper layer are: the particle size of the spherical copper powder is 15-25 μm, the laser power is 180-200 W, the scanning speed is 1000-1200 m / s, the single-layer printing thickness is 20-30 μm, the number of layers is 10-30 layers, and the chessboard partition scanning is used to disperse heat accumulation, and the energy density is 60-80 J / mm 3 。

[0039] In some preferred embodiments, in step 1), the preparation conditions for the large-hole copper layer are: the particle size of the spherical copper powder is 25-45 μm, the laser power is 120-150 W, the scanning speed is 1500-1800 m / s, the single-layer printing thickness is 40-50 μm, the number of layers is 20-50 layers, and the unidirectional parallel scanning (tilt angle 15°) is used to direct the flow of the molten pool to form a main channel along the heat flow direction, and the energy density is 30-50 J / mm 3 。

[0040] 2) The gradient porous copper is subjected to plasma activation treatment.

[0041] In some preferred embodiments, in step 2), the conditions of the plasma activation treatment are as follows: the plasma gas is argon with a purity ≥ 99.99%, the radio frequency power is 250 - 400 W, the treatment time is 5 - 10 min, and the gas flow rate is 20 - 30 sccm.

[0042] 3) Immerse the transition part of the gradient porous copper obtained in 2) into the graphene suspension for electrophoretic deposition, and then vacuum cure to form a graphene layer.

[0043] In some preferred embodiments, in step 3): the conditions of the electrophoretic deposition are as follows: the concentration of the graphene suspension is 0.5 - 1 mg / mL, the anode material is a platinum sheet, the cathode is the gradient porous copper, the electrode spacing is 20 - 30 mm, the deposition voltage is 40 - 60 V, the time is 5 - 15 min, and the temperature is 20 - 30 °C.

[0044] In some preferred embodiments, in step 3): the conditions of the vacuum curing are as follows: the vacuum degree ≤ 10 -2 Pa, the temperature is 70 - 120 °C, and the time is 30 - 60 min.

[0045] 4) Exclude the air in the pores of the transition part of the gradient porous copper obtained in 3), inject silver paste, and perform vacuum infiltration to make the nano - silver paste fill the pores and the gaps between the graphene layers, and then cure.

[0046] In some preferred embodiments, in step 4): the viscosity of the nano - silver paste is 80 - 120 mPa·s, and the particle size of the silver particles is 20 - 50 nm. Further preferably, the nano - silver paste includes: 60 - 70 wt% of nano - silver particles, 25 - 30 wt% of epoxy resin, 4 - 10 wt% of acetone, and 1 - 2 wt% of diethylenetriamine.

[0047] In some preferred embodiments, in step 4): the conditions of the vacuum infiltration are as follows: the vacuum degree ≤ 10 -2 Pa, the pressure is 0.1 - 0.5 MPa, and the pressure - holding time is 10 - 30 min.

[0048] In some preferred embodiments, in step 4): the conditions of the curing are as follows: pre - curing: 60 - 90 °C, 30 - 60 min; main - curing: 100 - 120 °C, 120 - 200 min, post - curing: 150 - 200 °C, 45 - 90 min.

[0049] 5) Bond the surface of the transition part of the gradient porous copper obtained in 4) to an aluminum substrate to obtain a gradient porous copper - aluminum composite material.

[0050] In some preferred embodiments, in step 5): The aluminum substrate is pre-treated by mechanical grinding and polishing and pickling to remove the surface oxide scale. Further preferably, the pickling solution used for pickling is HCl:HF = 3:1 (volume ratio, both hydrochloric acid and hydrofluoric acid are 100% pure acid solutions), and the pickling time is 1 - 5 min.

[0051] In some preferred embodiments, in step 5): The bonding method between the aluminum substrate and the gradient porous copper is vacuum diffusion welding, and the conditions are: the vacuum degree ≤ 5×10 -3 Pa, first heat up to 250 - 300 °C at a rate of 5 - 10 °C / min and apply pressure to 5 - 10 MPa at a rate of 0.5 - 1 MPa / min, and keep it for 1 - 10 min for pre-compression; then heat up to 450 - 500 °C at a rate of 5 - 10 °C / min and apply pressure to 20 - 30 MPa at a rate of 3 - 5 MPa / min, and keep it for 30 - 60 min; then cool down to 150 - 200 °C at a rate of 1 - 5 °C / min, and finally cool down to room temperature.

[0052] Specific examples and comparative examples Example 1: In step 1), using the laser powder bed fusion 3D printing technology, spherical copper powder (≥99.99 wt.%) is used as the raw material to prepare gradient porous copper with a gradient pore structure. 3D printing parameters of the small-hole copper layer (porosity is about 50%, average pore diameter is about 10 μm) located at the bottom layer: the particle size of the copper powder is about 20 μm, and the checkerboard partition scanning is used to disperse the heat accumulation to avoid the merger of pores caused by local overheating, and the energy density is 60 J / mm 3 , controlling the stability of the molten pool, the laser power is 180 W, the scanning speed is 1000 m / s, the layer thickness is about 20 μm, and the number of layers is 25; 3D printing parameters of the large-hole copper layer (porosity is about 70%, average pore diameter is about 400 μm) located at the top layer: the particle size of the copper powder is about 43 um, and the unidirectional parallel scanning (tilt angle 15°) is used to direct the flow of the molten pool to form the main channel along the heat flow direction, and the energy density is 40 J / mm 3 , the low energy density inhibits complete melting and retains the pore connectivity, the laser power is 120 W, the scanning speed is 1800 m / s, the layer thickness is about 50 μm, and the number of layers is 30.

[0053] In step 2), the gradient porous copper prepared in step 1) is placed in a radio frequency plasma cleaner and evacuated (~0.5×10 -2 Pa), and then plasma activation treatment is carried out to remove the surface oxide and generate active sites. The plasma activation process parameters are: the plasma gas is argon, the purity ≥ 99.99%, the radio frequency power is 300 W, the treatment time is 5 min, and the gas flow rate is 22 sccm.

[0054] Step 3), dip the bottom transition part (with a thickness of about 300 μm) of the gradient porous copper processed in Step 2) into a graphene suspension of 0.8 mg / ml for electrophoretic deposition (using a platinum sheet as the anode and the gradient porous copper as the cathode, with an electrode spacing of 20 mm, a deposition voltage of 45 V, a time of 8 min, and a temperature of 25 °C), to form a uniform graphene layer with a thickness of about 0.05 μm on the bottom surface and pore surfaces of the transition part. Then take it out and blow it with nitrogen to remove the residual solvent, and then place it in a vacuum drying oven and cure it at 80 °C for 60 min under a vacuum degree of 5×10 -3 Pa.

[0055] Step 4), place the gradient porous copper prepared in Step 3) in a vacuum pressure impregnation device to evacuate (with a vacuum degree of 0.5×10 -2 Pa) to remove the air in the pores. Then inject a nano-silver glue with a viscosity of 90 mPa·s (including: 60 wt% of nano-silver particles with a particle size of about 30 nm, 30 wt% of epoxy resin, 9 wt% of acetone, and 1 wt% of diethylenetriamine) into the bottom transition part, and keep the pressure at 0.3 MPa for pressure infiltration for 15 min, so that the silver glue fills the pores and the gaps between the graphene layers. Then heat it to 80 °C and keep it warm for 30 min to preliminarily fix the nano-silver particles, then raise the temperature to 100 °C and keep it warm for 120 min to promote the cross-linking of the epoxy resin in the nano-silver glue to form a three-dimensional network to wrap the nano-silver. Finally, raise the temperature to 150 °C and keep it warm for 60 min to improve the interface density and ensure stability.

[0056] Step 5), mechanically grind and polish a 3-mm-thick aluminum substrate to make its surface roughness Ra ≤ 0.8 μm, and put it into an acid solution (HCl:HF volume ratio of 3:1) and soak it for 2 min to remove the surface oxide scale.

[0057] Step 6), align and fix the gradient porous copper prepared in Step 4) and the aluminum substrate processed in Step 5) in a graphite fixture, and then place it in a vacuum diffusion welding furnace for diffusion welding to obtain a composite heat dissipation plate material. The diffusion welding process: a vacuum degree of 2×10 -3 Pa, first heat it at 2 °C / min to 250 °C and pressurize it at 0.5 MPa / min to 5 MPa, and keep it for 3 min for pre-compression. Then heat it at 5 °C / min to 450 °C and pressurize it at 5 MPa / min to 25 MPa, and keep it for 30 min. Finally, cool it at 1 °C / min to 200 °C and then cool it in the furnace to room temperature.

[0058] Example 2: Compared with Example 1, the difference is that the porosity of the small-hole copper layer at the bottom layer of the gradient porous copper is about 55%, the porosity of the large-hole copper layer at the top layer is about 65%, the thickness of the graphene layer is about 0.1 μm, and the thickness of the aluminum substrate is 5 mm.

[0059] Example 3: Compared with Example 1, the differences are as follows: (1) The nano-silver glue includes: 70 wt% of nano-silver particles with a particle size of about 30 nm, 25 wt% of epoxy resin, 4 wt% of acetone, and 1 wt% of diethylenetriamine.

[0060] (2) The vacuum diffusion welding temperature is 500 °C (align and fix the gradient porous copper prepared in step 4) and the aluminum substrate treated in step 5) in a graphite fixture, and then place it in a vacuum diffusion welding furnace for diffusion welding to obtain the composite heat dissipation plate material. The diffusion welding process: the vacuum degree is 2×10 -3 Pa, first heat up to 250 °C at a rate of 2 °C / min and pressurize to 5 MPa at a rate of 0.5 MPa / min, hold for 3 min for pre-compression, then heat up to 500 °C at a rate of 5 °C / min and pressurize to 25 MPa at a rate of 5 MPa / min, hold for 30 min, and finally cool down to 200 °C at a rate of 1 °C / min and then cool with the furnace to room temperature) Example 4: Compared with Example 1, the differences are as follows: The porosity of the small-hole copper layer at the bottom layer of the gradient porous copper is about 50%, the porosity of the large-hole copper layer at the top layer is about 60%, and the thickness of the aluminum substrate is 2 mm.

[0061] Comparative Example 1: Compared with Example 1, the differences are as follows: The porous copper has a non-gradient pore structure, the porosity is about 70%, and the average pore diameter is about 100 μm.

[0062] Comparative Example 2: Compared with Example 1, the differences are as follows: The porosity of the small-hole copper layer at the bottom layer of the gradient porous copper is about 40%, and the porosity of the large-hole copper layer at the top layer is about 80%.

[0063] Comparative Example 3: Compared with Example 1, the differences are as follows: There is no graphite layer and no nano-silver glue is filled (that is, not processed through step 3) and step 4)), and the gradient porous copper and the aluminum substrate are directly diffusion welded.

[0064] Comparative Example 4: Compared with Example 1, the differences are as follows: Only the graphene layer is electrophoretically deposited, and no nano-silver glue is filled (that is, not processed through step 4)).

[0065] Comparative Example 5: Compared with Example 1, the differences are as follows: The laser 3D printing parameters are different: the laser power is 300 W for both, the bottom small-hole copper layer does not use checkerboard partition scanning, and the top large-hole copper layer does not use unidirectional parallel scanning.

[0066] Comparative Example 6: Compared with Example 1, the difference lies in that the preparation process of the graphene layer is different. The graphene layer is prepared by spraying, and the steps are as follows: Step 3) Use a high-pressure airless spray gun to spray the graphene dispersion (40 wt% graphene powder + 59.5 wt% solvent ethanol + 0.5 wt% dispersant sodium dodecyl sulfate) on the surface of the small-hole copper layer (spraying pressure 0.5 MPa, nozzle distance 10 cm). Since the graphene layer is relatively thin, it is difficult to control the layer thickness and uniformity by the spraying method. After spraying, it needs to be dried in an oven at 80 °C for 1 hour to remove the residual solvent, and then annealed at 250 °C for 1 hour in an inert atmosphere (Ar) to remove the dispersant and enhance the binding between the graphene and the substrate. The spraying method has unique advantages in the low-cost and rapid preparation of graphene coatings, but its uniformity and interfacial properties are difficult to meet the high-power heat dissipation requirements.

[0067] Comparative Example 7: Compared with Example 1, the difference lies in that the silver paste infiltration process is different, and the atmospheric pressure infiltration method is adopted.

[0068] Comparative Example 8: Compared with Example 1, the difference lies in that non-gradient porous copper (porosity about 70%, average pore diameter about 100 μm) + no graphene layer + atmospheric pressure infiltration of nano silver paste are used.

[0069] Performance Test Perform various performance tests on the materials obtained in each example and each comparative example. The test standards or test methods for the performance indicators involved are as follows: (1) Thermal conductivity test: Refer to the national standard "Determination of Steady-State Thermal Resistance and Related Characteristics of Thermal Insulation Materials: Guarded Hot Plate Method" (GB / T 10294-2008) (2) Interface thermal resistance test: Refer to the international standard "Properties, Thermal Transmission, of Thermally Conductive Electrical Insulation Materials" (ASTM D5470) (3) Areal density test: Use the weighing method. Cut 5 square samples, remove the edge burrs, clean them by ultrasonic cleaning with alcohol and dry them at room temperature in vacuum for 24 h, then weigh the sample mass m (precision electronic balance, 0.001 g), and measure the sample area A (vernier caliper, 0.01 mm). The areal density

[0070] (4) Shear strength test: Refer to the international standard "Test Method for Shear Strength of the Surface of Metal Specimens in Single-Lap Adhesive Bonds by Tensile Loading (Metal to Metal)" (ASTM D1002-2010) (5) 500 W / cm 2Junction Temperature Test: Integrate the liquid-cooled plate into the test fixture, make the liquid-cooled plate in close contact with the heat source, connect it to the liquid-cooling system, coat the surface of the heat source with high-emissivity black paint (ε≥0.95), scan the surface with an infrared thermal imager to ensure the temperature distribution uniformity (temperature difference ≤ 2°C), and gradually apply power up to 500 W / cm 2 , wait for the system to reach thermal equilibrium (temperature fluctuation < 1°C / min) and record the temperature after 15 minutes of continuous operation, which is the junction temperature at 500 W / cm 2 .

[0071] The test results are shown in Table 1 as follows: Table 1: Performance test data of the heat dissipation plate materials prepared in each example and comparative example It can be seen from the data comparison in the above table that: The difference between Comparative Example 1 and Example 1 lies in the use of porous copper with a non-gradient pore structure. It is found that the thermal conductivity, interfacial thermal resistance, and 500 W / cm 2 junction temperature data of the heat dissipation plate material in Comparative Example 1 are poor. The reason is that the non-gradient structure leads to uneven heat flow distribution, the thermal conductivity decreases by 45%, and the junction temperature increases by 15°C.

[0072] The difference between Comparative Example 2 and Example 1 lies in that the porosity of the small-hole copper layer is relatively low and the porosity of the large-hole copper layer is relatively high. It is found that the thermal conductivity, interfacial thermal resistance, shear strength, and 500 W / cm 2 junction temperature data of the heat dissipation plate material in Comparative Example 2 are poor. The reason is that the porosity of the small-hole copper layer is relatively low, the heat conduction path is broken, and the equivalent thermal conductivity drops significantly; the porosity of the large-hole copper layer is relatively high, the structure is loose, the compressive strength drops suddenly, resulting in a high risk of flow channel collapse, and local hot spots cause the junction temperature to soar.

[0073] The difference between Comparative Example 3 and Example 1 lies in the absence of a graphite layer and the non-filling of nano-silver paste. It is found that the interfacial thermal resistance data of the heat dissipation plate material in Comparative Example 3 are poor. The reason is that when the silver paste is not filled, the pore heat conduction path is broken and the thermal conductivity decreases.

[0074] The difference between Comparative Example 4 and Example 1 lies in the electrophoretic deposition of only graphene layer and the non-filling of nano-silver paste. It is found that the interfacial thermal resistance and 500 W / cm 2 junction temperature data of the heat dissipation plate material in Comparative Example 4 are poor. The reason is that the interfacial thermal resistance surges by 317% and the shear strength drops by 33% without graphene.

[0075] The difference between Comparative Example 5 and Example 1 lies in that the laser power is too high during the laser 3D printing process, the small-hole copper layer is not scanned in a checkerboard partition, and the large-hole copper layer is not scanned in a unidirectional parallel manner. It is found that the thermal conductivity, interfacial thermal resistance, shear strength, and 500 W / cm 2The junction temperature data is poor. The reason is that the same power of 300W is used for the preparation of the large / small hole copper layers, resulting in relatively small porosity and pore diameter of both the large / small hole layers. At the same time, in Comparative Example 5, the small hole copper layer did not adopt checkerboard partition scanning, resulting in local heat accumulation and inducing pore coalescence. The large hole copper layer did not adopt unidirectional parallel scanning, resulting in the molten pool failing to flow directionally, forming a chaotic main channel, and partial pore closure, resulting in poor channel connectivity.

[0076] The difference between Comparative Example 6 and Example 1 lies in the use of spraying method to prepare the graphene layer. It is found that the thermal conductivity, interfacial thermal resistance, shear strength, 500W / cm 2 The junction temperature data is poor. The reason is that the graphene only covers part of the surface and the thickness is uneven. At the same time, the sprayed graphene agglomerates, the local thermal resistance surges, the unbonded area is prone to oxidation, and the thermal conductivity decays after thermal cycling.

[0077] The difference between Comparative Example 7 and Example 1 lies in the use of atmospheric pressure infiltration method to infiltrate silver paste. It is found that the thermal conductivity, interfacial thermal resistance, areal density, shear strength, 500W / cm 2 The junction temperature data is poor. The reason is that the pores of the graphene layer are not all filled with silver paste, and the air gap thermal resistance dominates; the silver paste does not penetrate deep into the pores, the interfacial bonding depends on physical adsorption, and the delamination risk is high; the atmospheric pressure infiltration needs to be repeated multiple times, increasing the time consumption and cost.

[0078] The difference between Comparative Example 8 and Example 1 lies in the use of non-gradient porous copper + no graphene layer + atmospheric pressure infiltration of nano-silver paste. It is found that the thermal conductivity, interfacial thermal resistance, shear strength and 500W / cm 2 The junction temperature data is poor. The reason is that multiple parameters deviate, and the junction temperature exceeds the standard when there are non-gradient pores or the graphene is missing. The deviation of process parameters leads to insufficient mechanical strength.

[0079] As mentioned above, the above are only the preferred embodiments of the present invention, and do not impose any formal or substantial restrictions on the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. Those skilled in the art, without departing from the spirit and scope of the present invention, when making some equivalent changes, modifications and evolutions using the technical content disclosed above, are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solutions of the present invention.

[0080] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

Claims

1. A gradient porous copper-aluminum composite material, characterized in that: It includes an aluminum substrate and a gradient porous copper provided on one surface of the aluminum substrate; The gradient porous copper is divided into a small-hole copper layer and a large-hole copper layer in contact with the aluminum substrate; The porosity of the small-hole copper layer is 50 - 60%, and the pore diameter is 10 - 50 μm. In the transition part of the small-hole copper layer close to the aluminum substrate, graphene layers are deposited on the surface where it combines with the aluminum substrate and on the inner pore surfaces, and the pores are filled with silver; The porosity of the large-hole copper layer is 60 - 70%, and the pore diameter is 200 - 500 μm.

2. The gradient porous copper-aluminum composite material according to claim 1, characterized in that: The thickness of the large-hole copper layer is 800 - 2500 μm, The thickness of the small-hole copper layer is 200 - 900 μm, and the thickness of the transition part is 1 / 2 - 1 of the thickness of the small-hole copper layer; The thickness of the graphene layer is 0.05 - 0.1 μm; The thickness of the aluminum substrate is 2 - 5 mm, and the surface roughness Ra ≤ 0.8 μm.

3. A method for preparing the gradient porous copper-aluminum composite material according to claim 1 or 2, characterized in that It includes: 1) Using laser 3D printing to prepare gradient porous copper from spherical copper powder; 2) Performing plasma activation treatment on the gradient porous copper; 3) Immersing the transition part of the gradient porous copper obtained in 2) into a graphene suspension for electrophoretic deposition, and vacuum curing to form a graphene layer; 4) Removing the air in the pores of the transition part of the gradient porous copper obtained in 3), injecting silver paste, and performing vacuum infiltration to make the nano silver paste fill the pores and the gaps between the graphene layers, and curing; 5) Bonding the surface of the transition part of the gradient porous copper obtained in 4) with the aluminum substrate.

4. The preparation method according to claim 3, wherein: In step 1), The preparation conditions of the small-hole copper layer are as follows: the particle size of spherical copper powder is 15 - 25 μm, the laser power is 180 - 200 W, the scanning speed is 1000 - 1200 m / s, the single-pass printing layer thickness is 20 - 30 μm, checkerboard zoning scanning is adopted, and the energy density is 60 - 80 J / mm 3 ; The preparation conditions of the macroporous copper layer are as follows: the particle size of spherical copper powder is 25 - 45 μm, the laser power is 120 - 150 W, the scanning speed is 1500 - 1800 m / s, the single-pass printing layer thickness is 40 - 50 μm, unidirectional parallel scanning is adopted, and the energy density is 30 - 50 J / mm 3 .

5. The preparation method according to claim 3, characterized in that: In step 2), the conditions of the plasma activation treatment are: the plasma gas is argon, the radio frequency power is 250 - 400 W, the treatment time is 5 - 10 min, and the gas flow rate is 20 - 30 sccm.

6. The preparation method according to claim 3, characterized in that: In step 3): The conditions of the electrophoretic deposition are: the concentration of the graphene suspension is 0.5 - 1 mg / mL, the anode material is a platinum sheet, the cathode is the gradient porous copper, the electrode distance is 20 - 30 mm, the deposition voltage is 40 - 60 V, the time is 5 - 15 min, and the temperature is 20 - 30 °C; The conditions for vacuum curing are as follows: the degree of vacuum ≤ 10 -2 Pa, the temperature is 70 - 120 °C, and the time is 30 - 60 min.

7. The preparation method according to claim 3, characterized in that: In step 4): The viscosity of the nano silver paste is 80 - 120 mPa·s, and the silver particle size is 20 - 50 nm; The conditions for the vacuum infiltration are as follows: the degree of vacuum ≤ 10 -2 Pa, the pressure is 0.1 - 0.5 MPa, and the pressure holding time is 10 - 30 min; The conditions of the curing are: pre-curing: 60 - 90 °C, 30 - 60 min; main-curing: 100 - 120 °C, 120 - 200 min, post-curing: 150 - 200 °C, 45 - 90 min.

8. The preparation method according to claim 3, characterized in that: In step 5): The aluminum substrate is pre-treated by mechanical grinding and polishing and pickling.

9. The preparation method according to claim 3 or 8, characterized in that: In step 5), the bonding method between the aluminum substrate and the gradient porous copper is vacuum diffusion welding, and the conditions are as follows: the vacuum degree ≤ 5×10 -3 Pa. First, heat it from room temperature to 250-300°C at a rate of 5-10°C / min and apply pressure from 0.5-1 MPa / min to 5-10 MPa, and hold for 1-10 min for pre-compression; then heat it to 450-500°C at a rate of 5-10°C / min and apply pressure from 3-5 MPa / min to 20-30 MPa, and hold for 30-60 min; then cool it to 150-200°C at a rate of 1-5°C / min, and finally cool it to room temperature.

10. The application of the gradient porous copper-aluminum composite material according to claim 1 or 2 or the gradient porous copper-aluminum composite material obtained by the preparation method according to any one of claims 3 - 9 as a heat dissipation plate.

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