A gradient porous copper-aluminum composite material, a preparation method and application thereof

Abstract

The present application relates to the field of metal matrix composites, and discloses a gradient porous copper-aluminum composite material, a preparation method and application thereof.The gradient porous copper-aluminum composite material comprises an aluminum substrate and a gradient porous copper arranged on one surface of the aluminum substrate; the gradient porous copper is divided into a small-pore copper layer and a large-pore copper layer which are in contact with the aluminum substrate; the transition part of the small-pore copper layer close to the aluminum substrate has a graphene layer deposited on the surface combined with the aluminum substrate and the internal pore surface, and the pores are filled with silver.The present application has the advantages of high thermal conductivity, low interfacial thermal resistance, high strength, lightweight and low cost by designing the gradient pore structure of the porous copper, strengthening the interface with graphene and filling silver glue, and the obtained composite heat dissipation plate material after being combined with the aluminum substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal matrix composites, in particular to a gradient porous copper-aluminum composite material and a preparation method and application thereof. BACKGROUND

[0002] With the explosive development of artificial intelligence, high-performance computing and large model training, the demand for computing power is growing exponentially, and the power density of a single cabinet has broken through 20kW. Traditional air-cooled heat dissipation has problems such as low air heat conduction efficiency (heat conduction coefficient is only 0.024W·m -1 ·K -1 ), high energy consumption, and is difficult to meet the heat dissipation needs of high-power chips. The existing heat dissipation plate materials are mostly pure copper, aluminum alloy, stainless steel or titanium alloy, which have the following significant shortcomings:

[0003] (1) Pure copper has excellent thermal conductivity (~400W·m -1 ·K -1 ), but its density is large and the cost is high (about 3-5 times that of aluminum), which leads to a sharp increase in the weight and manufacturing cost of liquid cooling plates; (2) Aluminum alloy has obvious lightweight advantage, but its thermal conductivity is only 200W·m -1 ·K -1 , and it needs surface corrosion prevention treatment, which is easy to fail due to electrolytic corrosion in long-term use; (3) Copper-aluminum composite plate has both performance and cost, but the interface thermal resistance (10 -4 -10 -5 m 2 ·K·W -1 ) leads to a 30%-50% decrease in overall thermal conductivity (CN202421125205.8); (4) Stainless steel has excellent corrosion resistance, but its thermal conductivity is very low (~15W·m -1 ·K -1 ), which cannot meet the heat dissipation needs of high power density, and is only suitable for special corrosion-resistant environments, and its processing cost is high, and cold rolling forming needs complex process control; (5) Titanium alloy has light weight, high strength and corrosion resistance, but its thermal conductivity is only 22W·m -1 ·K -1 , and its processing difficulty is great and the raw material price is expensive (about 5-10 times that of copper), which is mainly limited to high-end fields such as aerospace and military.

[0004] The above defects become the key bottleneck restricting the improvement of cooling efficiency, so it is urgent to develop a new heat dissipation plate material with high thermal conductivity, lightweight and low interface thermal resistance. SUMMARY

[0005] To solve the above technical problems, the application provides a gradient porous copper-aluminum composite material and a preparation method and application thereof. The gradient porous copper-aluminum composite material has the advantages of high thermal conductivity, low interface thermal resistance, high strength, light weight and low cost.

[0006] The specific technical scheme of the application is as follows:

[0007] In a first aspect, the application provides a gradient porous copper-aluminum composite material, which comprises an aluminum substrate and a gradient porous copper arranged on one surface of the aluminum substrate. The gradient porous copper is divided into a small-pore copper layer and a large-pore copper layer in contact with the aluminum substrate. The transition part of the small-pore copper layer close to the aluminum substrate has a graphene layer deposited on the surface combined with the aluminum substrate and the internal pore surface, and the pores are filled with silver.

[0008] When the gradient porous copper-aluminum composite material is used as a heat sink, the aluminum substrate is in contact with a heat source, and the large-pore copper layer is used to diffuse heat.

[0009] The gradient porous copper-aluminum composite material has the advantages of high thermal conductivity, low interface thermal resistance, high strength, light weight and low cost.

[0010] Preferably, the porosity of the small-pore copper layer is 50-60%, and the pore size is 10-50 μm; the porosity of the large-pore copper layer is 60-70%, and the pore size is 200-500 μm.

[0011] The small-pore copper layer at the bottom has small pore diameter and low porosity, which can reduce the blockage of pores to heat conduction. The large-pore copper layer at the top has large pore diameter and high porosity, which can reduce the weight and flow resistance, and improve the convective heat dissipation efficiency. The present application finds that the porosity and pore diameter of the small-pore copper layer and the porosity and pore diameter of the large-pore copper layer are critical to achieve the above effects. Specifically, for the small-pore copper layer: if the porosity is too high or the pore diameter is too large (e.g., porosity > 70%, pore diameter > 50 μm), the equivalent thermal conductivity will drop sharply due to the much lower thermal conductivity of air than copper, and the mechanical strength will deteriorate; if the porosity is too low or the pore diameter is too small (e.g., porosity < 50%, pore diameter < 10 μm), the air flow resistance will increase dramatically (inversely proportional to the fourth power of the pore diameter), resulting in uneven air distribution and increased fan power consumption. For the large-pore copper layer: if the porosity is too high or the pore diameter is too large (e.g., porosity > 80%, pore diameter > 500 μm), the copper skeleton continuity is destroyed, the heat dissipation area is reduced, and the convective heat transfer efficiency is reduced; if the porosity is too low or the pore diameter is too small (e.g., porosity < 60%, pore diameter < 200 μm), the air resistance will increase significantly (inversely proportional to the square of the pore diameter), which can easily cause local air retention and limit the heat exchange efficiency.

[0012] 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, the thickness of the transition part is 1 / 2-1 of 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 is ≤0.8 μm.

[0013] In a second aspect, the present application provides a preparation method of the gradient porous copper-aluminum composite material, which comprises the following steps: 1) using laser 3D printing to prepare spherical copper powder into gradient porous copper.

[0014] 2) performing plasma activation treatment on the gradient porous copper.

[0015] The plasma activation treatment on the gradient porous copper can remove the surface oxides and generate active sites, which is beneficial to the subsequent graphene deposition.

[0016] 3) electrophoretic deposition of the transition part of the gradient porous copper obtained in 2) into a graphene suspension, vacuum solidification to form a graphene layer.

[0017] 4) removing the air in the pores of the transition part of the gradient porous copper obtained in 3), injecting silver glue, vacuum infiltration to fill the pores and the interstitial space between the graphene layers with nano-silver glue, and solidification.

[0018] 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.

[0019] Preferably, in step 1), the preparation conditions of the small-pore copper layer are as follows: 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 thickness of a single printing layer is 20-30 μm, the number of layers is 10-30, the chessboard partition scanning is used to disperse the heat accumulation, and the energy density is 60-80 J / mm 3 .

[0020] The small-pore copper layer with the target porosity and pore size can be prepared by using the specific process conditions. The chessboard partition scanning is used to disperse the heat accumulation, so that the local overheating and the merging of the holes can be avoided. The energy density is 60-80 J / mm 3 , so that the stability of the molten pool can be controlled.

[0021] Preferably, in step 1), the preparation conditions of the large-pore copper layer are as follows: 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 thickness of a single printing layer is 40-50 μm, the number of layers is 20-50, the unidirectional parallel scanning (with an inclination angle of 15°) is used to direct the flow of the molten pool, and the energy density is 30-50 J / mm 3 .

[0022] The large-pore copper layer with the target porosity and pore size can be prepared by using the specific process conditions. The unidirectional parallel scanning (with an inclination angle of 15°) is used to direct the flow of the molten pool, so that the main channel along the heat flow direction can be formed. The energy density is 30-50 J / mm 3 , so that the complete melting can be inhibited and the connectivity of the pores can be retained.

[0023] Preferably, in step 2), the conditions of the plasma activation treatment are as follows: the plasma gas is argon with a purity of ≥99.99%, the radio frequency power is 250-400 W, the treatment time is 5-10 min, and the gas flow is 20-30 sccm.

[0024] 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 a 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.

[0025] Preferably, in step 3), the conditions of the vacuum solidification are as follows: the vacuum degree is ≤10 -2 Pa, the temperature is 70-120 °C, and the time is 30-60 min.

[0026] Preferably, in step 4), the viscosity of the nano-silver glue is 80-120 mPa·s, and the particle size of the silver particles is 20-50 nm.

[0027] Further preferably, the nano-silver glue comprises: nano-silver particles 60-70wt%, epoxy resin 25-30wt%, acetone 4-10wt%, diethylene triamine 1-2wt%.

[0028] As preferred, in step 4), the conditions of vacuum infiltration are: vacuum degree ≤10 -2 Pa, pressure 0.1-0.5MPa, pressure maintaining time 10-30min.

[0029] As preferred, in step 4), the conditions of curing are: pre-curing: 60-90℃, 30-60min; main curing: 100-120℃, 120-200min, post-curing: 150-200℃, 45-90min.

[0030] The present application adopts three-stage gradient temperature design to control material phase transition and interface combination process step by step, so as to balance the formation of heat conduction network, the improvement of mechanical strength and the release of residual stress. Specifically: (1) pre-curing stage: low temperature reduces the flowability of epoxy resin, slows down the gravity settlement of nano-silver particles, ensures the uniform distribution of silver glue in the pores, the epoxy resin starts crosslinking reaction, forms a primary three-dimensional network, fixes the position of silver particles, and avoids the agglomeration of particles in the subsequent high temperature stage. If direct high temperature curing, silver particles will quickly settle down due to the difference in density (silver 10.5g / cm 3 , epoxy resin 1.2g / cm 3 ), which will lead to uneven distribution of silver glue in the pores and increase of interface thermal resistance. (2) Main curing stage: the temperature is raised to above the glass transition temperature (Tg≈120℃) of the epoxy resin, which promotes the complete crosslinking of the resin, forms a dense network, wraps the silver particles and fills the micro gaps, and the silver particles self-assemble in the flowing resin driven by surface energy to form continuous heat conduction chain, which significantly improves the equivalent thermal conductivity. If the medium temperature stage is skipped and direct high temperature curing is performed, the resin will crosslink too quickly, the silver particles will not be able to fully self-organize, the heat conduction path will be broken, and the overall heat conduction performance will be reduced. (3) Post-curing stage: at high temperature, the molecular chain of the resin relaxes, releasing the interface residual stress generated due to the difference in thermal expansion coefficient (copper 17×10 -6 / K, epoxy resin 60×10 -6 / K), preventing delamination in cold and hot cycles, and high temperature promotes atomic diffusion of silver particles and copper / graphene to form Ag-Cu eutectic micro area, improving shear strength. Without post-curing, the interface residual stress will reduce the shear strength and easily crack under temperature impact.

[0031] As preferred, in step 5), the aluminum substrate is pre-treated by mechanical grinding and polishing and acid pickling to remove surface oxide scale.

[0032] As preferred, in step 5), the combination of the aluminum substrate and the gradient porous copper is vacuum diffusion welding, with a vacuum degree ≤5×10 -3Pa, first 5-10 ℃ / min to 250-300 ℃ and 0.5-1 MPa / min to 5-10 MPa, 1-10 min to maintain pre-pressing; then 5-10 ℃ / min to 450-500 ℃ and 3-5 MPa / min to 20-30 MPa, 30-60 min to maintain; then 1-5 ℃ / min to 150-200 ℃, and finally to room temperature.

[0033] 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. The initial pressurization stage ensures close contact of the materials, eliminates assembly gaps, 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. The main pressurization stage accelerates the pressurization, shortens the process time, and the heating temperature is lower than the aluminum melting point, which drives the interface atomic migration, promotes Cu / Al atomic interdiffusion, and forms a metallurgical bond. At the same time, by controlling the pressurization rate, the deformation of the porous copper skeleton is avoided. The pressure maintaining stage maintains stable pressure to ensure sufficient atomic diffusion.

[0034] In a third aspect, the present application provides the application of the gradient porous copper-aluminum composite material as a heat sink.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] (1) The present application designs a gradient pore structure of porous copper, graphene interface strengthens and fills silver glue, and the composite heat sink material obtained after compounding with an aluminum substrate has the advantages of high thermal conductivity, low interface thermal resistance, high strength, and lightweight.

[0037] (2) The gradient pore structure of the present application reduces the density of porous copper to 30-50% of that of dense copper, and at the same time, through large-scale 3D printing (copper powder utilization rate > 95%), the material cost is greatly reduced. The nanosilver glue fills the interlayer voids of the graphene layer to form a continuous heat conduction network, replacing the high-cost pure silver plating layer, and the comprehensive cost is close to the aluminum alloy scheme, but the heat dissipation capacity is greatly improved. This design, through topology optimization and parameterized manufacturing, has a high yield and is suitable for batch production. Through multi-dimensional innovation of materials-structure-process, the present application solves the coordination problem of high thermal conductivity, lightweight, and low cost, provides a heat dissipation material with performance and cost performance for high-power computing devices, and promotes the upgrading of green computing infrastructure. DETAILED DESCRIPTION

[0038] The technical solutions of the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments only further illustrate the present application but do not constitute any limitation to the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creativity fall within the scope of protection of the present application.

[0039] General embodiment

[0040] In a first aspect, a gradient porous copper-aluminum composite material comprises an aluminum substrate and a gradient porous copper arranged on one surface of the aluminum substrate. The gradient porous copper is divided into a small-pore copper layer in contact with the aluminum substrate and a large-pore copper layer. The small-pore copper layer has a porosity of 50-60% and a pore size of 10-50 μm. The transition part of the small-pore copper layer close to the aluminum substrate has a graphene layer deposited on the surface combined with the aluminum substrate and the internal pore surface, and the pores are filled with silver. The large-pore copper layer has a porosity of 60-70% and a pore size of 200-500 μm.

[0041] In some preferred embodiments, 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, the thickness of the transition part is 1 / 2-1 of the thickness of the small-pore copper layer, the thickness of the graphene layer is 0.05-0.1 μm, and the thickness of the aluminum substrate is 2-5 mm with a surface roughness Ra≤0.8 μm.

[0042] In a second aspect, a method for preparing a gradient porous copper-aluminum composite material comprises the following steps:

[0043] 1) Using laser 3D printing to prepare spherical copper powder into gradient porous copper.

[0044] In some preferred embodiments, in step 1), the preparation conditions of the small-pore copper layer are as follows: 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 thickness of a single printing layer is 20-30 μm, the number of layers is 10-30, the chessboard grid partition scanning is used to disperse heat accumulation, and the energy density is 60-80 J / mm 3 .

[0045] In some preferred embodiments, in step 1), the preparation conditions of the large-pore copper layer are as follows: 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 thickness of a single printing layer is 40-50 μm, the number of layers is 20-50, the unidirectional parallel scanning (inclination 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 .

[0046] 2) Plasma activation treatment of the gradient porous copper.

[0047] In some preferred embodiments, in step 2), the plasma activation treatment is performed under the following conditions: argon gas with purity ≥ 99.99%, radio frequency power 250-400 W, treatment time 5-10 min, and gas flow rate 20-30 sccm.

[0048] 3) Electrophoretic deposition of the transition portion of the gradient porous copper obtained in 2) into a graphene suspension to form a graphene layer by vacuum solidification.

[0049] In some preferred embodiments, in step 3), the electrophoretic deposition is performed under the following conditions: graphene suspension concentration 0.5-1 mg / mL, anode material platinum sheet, cathode gradient porous copper, electrode spacing 20-30 mm, deposition voltage 40-60 V, time 5-15 min, and temperature 20-30 °C.

[0050] In some preferred embodiments, in step 3), the vacuum solidification is performed under the following conditions: vacuum degree ≤ 10 -2 Pa, temperature 70-120 °C, and time 30-60 min.

[0051] 4) Removing air from the pores of the transition portion of the gradient porous copper obtained in 3), injecting silver glue, and filling the pores and interstitial spaces of the graphene layer with nano-silver glue by vacuum infiltration and solidification.

[0052] In some preferred embodiments, in step 4), the nano-silver glue has a viscosity of 80-120 mPa·s and silver particles with a particle size of 20-50 nm. Further preferably, the nano-silver glue comprises: nano-silver particles 60-70 wt%, epoxy resin 25-30 wt%, acetone 4-10 wt%, and diethylene triamine 1-2 wt%.

[0053] In some preferred embodiments, in step 4), the vacuum infiltration is performed under the following conditions: vacuum degree ≤ 10 -2 Pa, pressure 0.1-0.5 MPa, and pressure holding time 10-30 min.

[0054] In some preferred embodiments, in step 4), the solidification is performed under the following conditions: pre-curing at 60-90 °C for 30-60 min, main curing at 100-120 °C for 120-200 min, and post-curing at 150-200 °C for 45-90 min.

[0055] 5) Bonding the surface of the transition portion of the gradient porous copper obtained in 4) to an aluminum substrate to obtain a gradient porous copper-aluminum composite material.

[0056] In some preferred embodiments, in step 5), the aluminum substrate is pre-treated by mechanical grinding and polishing and acid pickling to remove the surface oxide. Further preferably, the acid pickling solution used is HCl:HF = 3:1 (volume ratio, both hydrochloric acid and hydrofluoric acid are 100% pure acid), and the acid pickling time is 1-5 min.

[0057] In some preferred embodiments, in step 5), the aluminum substrate and the gradient porous copper are combined by vacuum diffusion welding, provided that the vacuum degree is ≤5×10 -3 Pa, first heated at 5-10°C / min to 250-300°C and pressurized at 0.5-1 MPa / min to 5-10 MPa for 1-10 min for pre-pressing; then heated at 5-10°C / min to 450-500°C and pressurized at 3-5 MPa / min to 20-30 MPa for 30-60 min; then cooled at 1-5°C / min to 150-200°C, and finally cooled to room temperature.

[0058] Specific embodiments and comparative examples

[0059] Example 1:

[0060] Step 1), using laser powder bed fusion 3D printing technology, spherical copper powder (≥99.99wt.%) as raw material, gradient porous copper with gradient porosity structure is prepared. The 3D printing parameters of the small-pore copper layer (porosity about 50%, average pore size about 10 μm) located at the bottom layer are as follows: copper powder particle size about 20 μm, chessboard grid partition scanning is adopted to disperse heat accumulation and avoid local overheating leading to hole merging, energy density 60 J / mm 3 , control the stability of the molten pool, laser power 180 W, scanning speed 1000 m / s, layer thickness about 20 μm, and layer number 25; the 3D printing parameters of the large-pore copper layer (porosity about 70%, average pore size about 400 μm) located at the top layer are as follows: copper powder particle size about 43 um, unidirectional parallel scanning (inclination angle 15°) is adopted to direct the flow of the molten pool, forming the main channel along the heat flow direction, energy density 40 J / mm 3 , low energy density inhibits complete melting, preserves the connectivity of the pores, laser power 120 W, scanning speed 1800 m / s, layer thickness about 50 μm, and layer number 30.

[0061] Step 2), the gradient porous copper prepared in step 1) is placed in a radio frequency plasma cleaning machine and vacuumized (~0.5×10 -2 Pa), and then subjected to plasma activation treatment to remove surface oxides and generate active sites. The plasma activation process parameters are as follows: the plasma gas is argon with a purity of ≥99.99%, the radio frequency power is 300 W, the treatment time is 5 min, and the gas flow is 22 sccm.

[0062] Step 3), the bottom transition part (thickness of about 300 μm) of the gradient porous copper treated in step 2) was immersed in a 0.8 mg / ml graphene suspension for electrophoretic deposition (with a platinum sheet as anode and the gradient porous copper as cathode, electrode spacing of 20 mm, deposition voltage of 45 V, time of 8 min, and temperature of 25 °C), forming a uniform graphene layer with a thickness of about 0.05 μm on the bottom surface of the transition part and the pore surface, and then removed and blown with nitrogen to remove residual solvent, and then placed in a vacuum drying oven at a vacuum degree of 5 x 10 -3 Pa) for 60 min at 80 °C.

[0063] Step 4), the gradient porous copper prepared in step 3) was placed in a vacuum pressure impregnation device and vacuumed (vacuum degree of 0.5 x 10 -2 Pa) to remove air in the pores, and then the viscosity of 90 mPa s nano-silver glue (including: nano-silver particles with a particle size of about 30 nm 60 wt%, epoxy resin 30 wt%, acetone 9 wt%, diethylene triamine 1 wt%) was injected into the bottom transition part, and the silver glue was infiltrated for 15 min at 0.3 MPa to fill the pores and the interstices between the graphene layers, and then heated to 80 °C for 30 min to preliminarily fix the nano-silver particles, and then heated to 100 °C 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, and finally heated to 150 °C for 60 min to improve the interface density and ensure stability.

[0064] Step 5), a 3 mm thick aluminum substrate was mechanically ground and polished to have a surface roughness Ra≤0.8 μm, and then immersed in an acid solution (HCl:HF volume ratio of 3:1) for 2 min to remove the surface oxide skin.

[0065] Step 6), the gradient porous copper prepared in step 4) and the aluminum substrate treated in step 5) were aligned and fixed in a graphite clamp, and then placed in a vacuum diffusion welding furnace to perform diffusion welding to obtain a composite heat sink material, wherein the diffusion welding process was as follows: vacuum degree of 2 x 10 -3 Pa, first heated to 250 °C at a rate of 2 °C / min and pressurized to 5 MPa at a rate of 0.5 MPa / min, held for 3 min for pre-pressing, then heated to 450 °C at a rate of 5 °C / min and pressurized to 25 MPa at a rate of 5 MPa / min, held for 30 min, and finally cooled to 200 °C at a rate of 1 °C / min and then cooled to room temperature with the furnace.

[0066] Example 2:

[0067] Compared with example 1, the difference is that the porosity of the small-pore copper layer at the bottom layer in the gradient porous copper is about 55%, the porosity of the large-pore 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.

[0068] Example 3:

[0069] Compared with Example 1, the difference is that:

[0070] (1) The nano-silver glue comprises: nano-silver particles with a particle size of about 30 nm 70 wt%, epoxy resin 25 wt%, acetone 4 wt%, diethylene triamine 1 wt%.

[0071] (2) The vacuum diffusion welding temperature is 500℃ (align and fix the gradient porous copper prepared in step 4) with the aluminum substrate treated in step 5) in the graphite clamp, and then place it in the vacuum diffusion welding furnace to obtain the composite heat sink material by diffusion welding, wherein the diffusion welding process: vacuum degree 2×10 -3 Pa, first heat up to 250℃ at 2℃ / min and pressurize to 5MPa at 0.5MPa / min, keep 3min for pre-pressing, then heat up to 500℃ at 5℃ / min and pressurize to 25MPa at 5MPa / min, keep 30min, finally cool down to 200℃ at 1℃ / min and cool to room temperature with the furnace)

[0072] Example 4:

[0073] Compared with Example 1, the difference is that: the porosity of the small-pore copper layer at the bottom of the gradient porous copper is about 50%, the porosity of the large-pore copper layer at the top is about 60%, and the thickness of the aluminum substrate is 2mm.

[0074] Comparative Example 1:

[0075] Compared with Example 1, the difference is that: the porous copper is a non-gradient porous structure, the porosity is about 70%, and the average pore size is about 100μm.

[0076] Comparative Example 2:

[0077] Compared with Example 1, the difference is that: the porosity of the small-pore copper layer at the bottom of the gradient porous copper is about 40%, and the porosity of the large-pore copper layer at the top is about 80%.

[0078] Comparative Example 3:

[0079] Compared with Example 1, the difference is that: there is no graphite layer and no nano-silver glue is filled (i.e. not treated in step 3) and step 4), and the gradient porous copper is directly diffusion welded with the aluminum substrate.

[0080] Comparative Example 4:

[0081] Compared with Example 1, the difference is that: only the graphene layer is electrophoretically deposited, and no nano-silver glue is filled (i.e. not treated in step 4).

[0082] Comparative Example 5:

[0083] Compared with Example 1, the difference lies in that the laser 3D printing parameters are different: the laser power is 300 W, the small hole copper layer at the bottom is not scanned by the chessboard partition, and the large hole copper layer at the top is not scanned by the one-way parallel scanning.

[0084] Comparative Example 6:

[0085] Compared with Example 1, the difference lies in that the preparation process of the graphene layer is different, and the graphene layer is prepared by spraying, and the steps are as follows:

[0086] Step 3) The graphene dispersion liquid (graphene powder 40wt% + solvent ethanol 59.5wt% + dispersant sodium dodecyl sulfate 0.5wt%) is sprayed on the surface of the small hole copper layer by using a high-pressure airless spray gun (spraying pressure 0.5 MPa, nozzle distance 10 cm). Due to the thinness of the graphene layer, it is difficult to control the layer thickness and uniformity by spraying, so after spraying, it needs to be dried in an 80°C oven for 1 hour to remove residual solvents, and then annealed at 250°C in an inert atmosphere (Ar) for 1 hour to remove the dispersant and enhance the bonding between graphene and the substrate. Spraying has unique advantages in low-cost and rapid preparation of graphene coating, but its uniformity and interface performance are difficult to meet the high-power heat dissipation demand.

[0087] Comparative Example 7:

[0088] Compared with Example 1, the difference lies in that the silver glue infiltration process is different, and the normal pressure infiltration method is used.

[0089] Comparative Example 8:

[0090] Compared with Example 1, the difference lies in that non-gradient porous copper (porosity about 70%, average pore size about 100 μm) + no graphene layer + normal pressure infiltration of nano-silver glue is used.

[0091] Performance test

[0092] The materials obtained in each example and each comparative example are subjected to various performance tests, and the performance index test standards or test methods involved are as follows:

[0093] (1) Thermal conductivity test: reference national standard "Determination of Steady-state Thermal Resistance and Related Properties of Thermal Insulation Materials: Guarded Hot Plate Method" (GB / T10294-2008)

[0094] (2) Interface thermal resistance test: reference international standard "Properties, Thermal Transmission, of Thermally Conductive Electrical Insulation Materials" (ASTM D5470)

[0095] (3) Area density test: 5 square samples were cut, the burrs were removed, and the samples were cleaned with alcohol by ultrasonic and dried in vacuum at room temperature for 24 h, then the sample mass m (precision electronic balance, 0.001 g) was measured, the sample area A (vernier caliper, 0.01 mm) was measured, and the area density was calculated

[0096] (4) Shear strength test: reference to international standard "Test Method for Shear Strength of Adhesively Bonded Metal Specimens by Tension Load Parallel to the Plane of Bond (Metal to Metal)" (ASTM D1002-2010)

[0097] (5) 500W / cm 2 Junction temperature test: the liquid cooling plate was integrated into the test fixture to make the liquid cooling plate closely contact with the heat source, the liquid cooling system was connected, the high-emissivity black paint (ε≥0.95) was coated on the surface of the heat source, the surface was scanned by an infrared thermal imager to ensure the uniformity of temperature distribution (temperature difference ≤2℃), the power was gradually applied to 500W / cm by adjusting the voltage / current 2 , and the temperature was recorded after the system reached thermal equilibrium (temperature fluctuation <1℃ / min) and lasted for 15 min, which was the 500W / cm 2 junction temperature.

[0098] The test results are shown in Table 1:

[0099] Table 1: Performance test data of the heat dissipation plate materials prepared in each example and comparative example

[0100]

[0101] From the comparison of the data in the above table, it can be seen that:

[0102] The difference between Comparative Example 1 and Example 1 is that the porous copper with non-gradient pore structure is used, and it is found that the thermal conductivity, interfacial thermal resistance, 500W / cm 2 junction temperature data of the heat dissipation plate material of Comparative Example 1 are poor, and 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℃.

[0103] The difference between Comparative Example 2 and Example 1 is that the porosity of the small-pore copper layer is low and the porosity of the large-pore copper layer is high, and it is found that the thermal conductivity, interfacial thermal resistance, shear strength, 500W / cm 2 junction temperature data of the heat dissipation plate material of Comparative Example 2 are poor, and the reason is that the porosity of the small-pore copper layer is low, the thermal conduction path is broken, the equivalent thermal conductivity decreases greatly, the porosity of the large-pore copper layer is high, the structure is loose, the compressive strength decreases sharply, leading to high risk of flow channel collapse, and local hot spots cause the junction temperature to soar.

[0104] The difference between Comparative Example 3 and Example 1 is that there is no graphite layer and no nano-silver glue filling. It is found that the interface thermal resistance data of the heat sink material of Comparative Example 3 is poor, and the reason is that when the silver glue is not filled, the pore thermal conduction path is broken, and the thermal conductivity decreases.

[0105] The difference between Comparative Example 4 and Example 1 is that only the graphene layer is electrophoretically deposited, and no nano-silver glue is filled. It is found that the interface thermal resistance and 500W / cm 2 junction temperature data are poor, and the reason is that when there is no graphene, the interface thermal resistance increases by 317%, and the shear strength decreases by 33%.

[0106] The difference between Comparative Example 5 and Example 1 is that the laser power is too high during laser 3D printing, and the small-pore copper layer is not scanned by chessboard partitioning, and the large-pore copper layer is not scanned by one-way parallel scanning. It is found that the thermal conductivity, interface thermal resistance, shear strength, and 500W / cm 2 junction temperature data are poor, and the reason is that the same power of 300W is used to prepare the large-pore and small-pore copper layers, resulting in small porosity and pore size of the large-pore and small-pore layers. At the same time, in Comparative Example 5, the small-pore copper layer is not scanned by chessboard partitioning, which causes local heat accumulation to induce hole merging. The large-pore copper layer is not scanned by one-way parallel scanning, which causes the molten pool to not flow in a directional manner, forming chaotic main channels, and some pores are closed, resulting in poor channel connectivity.

[0107] The difference between Comparative Example 6 and Example 1 is that the graphene layer is prepared by spraying. It is found that the thermal conductivity, interface thermal resistance, shear strength, and 500W / cm 2 junction temperature data are poor, and the reason is that the graphene only covers part of the surface and has uneven thickness, and the sprayed graphene is agglomerated, the local thermal resistance is increased, and the non-bonding area is easily oxidized, resulting in thermal decay after cold and hot cycles.

[0108] The difference between Comparative Example 7 and Example 1 is that silver glue is infiltrated by atmospheric pressure infiltration. It is found that the thermal conductivity, interface thermal resistance, surface density, shear strength, and 500W / cm 2 junction temperature data are poor, and the reason is that the pores of the graphene layer are not all filled with silver glue, and the air gap thermal resistance dominates; the silver glue does not penetrate into the pores, and the interface bonding relies on physical adsorption, with high delamination risk; atmospheric pressure infiltration needs to be repeated multiple times, increasing the time consumption and cost.

[0109] The difference between Comparative Example 8 and Example 1 is that non-gradient porous copper is used, there is no graphene layer, and nano-silver glue is infiltrated by atmospheric pressure infiltration. It is found that the thermal conductivity, interface thermal resistance, shear strength, and 500W / cm 2 junction temperature data are poor, and the reason is that multiple parameters deviate, and when there is no gradient pore or no graphene, the junction temperature exceeds the standard, and process parameter deviation leads to insufficient mechanical strength.

[0110] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form or in essence. It should be noted that those skilled in the art can make some improvements and supplements without departing from the method of the present application, and these improvements and supplements should also be considered as the protection scope of the present application. For those skilled in the art, some slight changes, modifications and equivalent changes made by using the disclosed technical content without departing from the spirit and scope of the present application are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution made according to the essential technology of the present application to the above embodiments are still within the scope of the technical solutions of the present application.

[0111] The raw materials and equipment used in the present application are conventional raw materials and equipment in the art unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

Claims

1. A gradient porous copper-aluminum composite material, characterized by: The gradient porous copper-aluminum composite material comprises an aluminum substrate and a gradient porous copper arranged on one surface of the aluminum substrate. The gradient porous copper is divided into a small-pore copper layer and a large-pore copper layer in contact with the aluminum substrate. The small-pore copper layer has a porosity of 50-60% and a pore size of 10-50 μm, wherein the transition part of the small-pore copper layer close to the aluminum substrate has a graphene layer deposited on the surface combined with the aluminum substrate and the internal pore surface, and the pores are filled with silver. The large-pore copper layer has a porosity of 60-70% and a pore size of 200-500 μm.

2. The gradient porous copper-aluminum composite material according to claim 1, wherein: the thickness of the large-pore copper layer is 800-2500 μm, the thickness of the small-pore copper layer is 200-900 μm, wherein the thickness of the transition part is 1 / 2-1 of 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 is ≤0.8 μm.

3. A method for producing the gradient porous copper-aluminum composite material according to claim 1 or 2, characterized by The preparation method comprises the following steps: 1) preparing the spherical copper powder into the gradient porous copper by using the laser 3D printing; 2) plasma activating the gradient porous copper; 3) electrophoretically depositing the transition part of the gradient porous copper obtained in step 2) in a graphene suspension to form a graphene layer by vacuum solidification; 4) removing the air in the pores of the transition part of the gradient porous copper obtained in step 3), injecting silver glue, and vacuum infiltrating to fill the pores and the interstitial space between the graphene layers with the nano-silver glue, and solidifying; 5) combining the surface of the transition part of the gradient porous copper obtained in step 4) with the aluminum substrate.

4. The method of 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 thickness of single printing layer is 20-30 μm, the chessboard grid partition scanning is adopted, and the energy density is 60-80 J / mm 3 ; The preparation conditions of the large-pore copper layer are as follows: the particle size of spherical copper powder is 25-45 mu m, the laser power is 120-150 W, the scanning speed is 1500-1800 m / s, the single printing layer thickness is 40-50 mu m, the unidirectional parallel scanning is adopted, and the energy density is 30-50 J / mm 3 .

5. The method of claim 3, wherein: In step 2), the plasma activation treatment is performed under the following conditions: the plasma gas is argon, the radio frequency power is 250-400 W, the treatment time is 5-10 min, and the gas flow is 20-30 sccm.

6. The method of claim 3, wherein: In step 3): The electrophoretic deposition is performed under the following conditions: the concentration of the graphene suspension is 0.5-1 mg / mL, the anode material is platinum, 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; The conditions for the vacuum solidification are: vacuum degree ≤ 10 -2 Pa, temperature 70-120°C, time 30-60 min.

7. The method of claim 3, wherein: In step 4): The viscosity of the nano-silver glue is 80-120 mPa·s, and the silver particle size is 20-50 nm; The conditions of the vacuum infiltration are: vacuum degree ≤10 -2 Pa, pressure 0.1-0.5 MPa, pressure maintaining time 10-30 min; The solidification is performed under the following conditions: pre-solidification: 60-90 °C, 30-60 min; main solidification: 100-120 °C, 120-200 min, and post-solidification: 150-200 °C, 45-90 min.

8. The method of claim 3, wherein: In step 5), the aluminum substrate is pre-treated by mechanical grinding and polishing and acid washing.

9. The method of manufacturing according to claim 3 or 8, wherein: In step 5), the combination of the aluminum substrate and the gradient porous copper is vacuum diffusion welding, with a vacuum degree of ≤5×10 -3 Pa, first 5-10°C / min to 250-300°C and 0.5-1 MPa / min to 5-10 MPa, 1-10 min for pre-pressing; then 5-10°C / min to 450-500°C and 3-5 MPa / min to 20-30 MPa, 30-60 min; then 1-5°C / min to 150-200°C, and finally to room temperature.

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

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