阅读说明：本技术 一种纳米金刚石提高镁基复合材料导热性能的方法及镁基复合材料 (Method for improving heat conductivity of magnesium-based composite material by using nano diamond and magnesium-based composite material ) 是由 马鸿斌 王金辉 金培鹏 张鹏 时博 魏福安 于 2019-09-30 设计创作，主要内容包括：本发明公开了一种纳米金刚石提高镁基复合材料导热性能的方法及镁基复合材料,该制备方法首先通过超声分散的方法使纳米金刚石在镁合金基体中的均匀分散,在真空热压烧结炉烧结球磨粉末,得到烧结坯,通过高温高压的处理,使得纳米级别下的金刚石活性增加,进而使得纳米金刚石与镁合金基体之间形成一层碳化物,从而提高界面结合强度,减少界面缺陷,从而提高界面热导率。该制备方法操作简单,易于实现,同时通过高温高压实现了纳米金刚石与镁合金基体之间的轻微的碳化反应。通过该方法制得的镁基复合材料,一方面金刚石颗粒增强的镁基复合材料获得了高的热导率,同时具有与半导体材料相匹配的低的热膨胀系数,具有很好的应用前景。(The invention discloses a method for improving the heat conductivity of a magnesium-based composite material by using nano-diamond and the magnesium-based composite material. The preparation method is simple to operate and easy to realize, and simultaneously realizes slight carbonization reaction between the nano diamond and the magnesium alloy matrix through high temperature and high pressure. The magnesium-based composite material prepared by the method has the advantages that on one hand, the diamond particle reinforced magnesium-based composite material obtains high thermal conductivity, and meanwhile, the magnesium-based composite material has a low thermal expansion coefficient matched with a semiconductor material, and has a good application prospect.)

1. A method for improving the thermal conductivity of a magnesium-based composite material by using nano-diamond is characterized by comprising the following steps:

Step 1, adding magnesium alloy powder into the nano-diamond dispersion liquid, uniformly stirring to obtain a mixed system, and drying the mixed system to obtain mixed powder of nano-diamond and magnesium alloy;

Step 2, ball-milling the mixed powder of the nano-diamond and the magnesium alloy to obtain uniformly dispersed ball-milled powder;

Step 3, sintering the ball-milling powder in a hot pressing manner in a vacuum environment to obtain a sintered blank;

And 4, extruding the sintered blank to obtain an extruded composite material, wherein the extruded composite material is a material obtained by improving the heat conductivity of the magnesium-based composite material through the nano-diamond.

2. The method for improving the thermal conductivity of the magnesium-based composite material by the nano-diamond according to claim 1, wherein in the step 1, the nano-diamond dispersion liquid is prepared by adding the nano-diamond particles into absolute ethyl alcohol and performing ultrasonic dispersion; the solute in the mixed system comprises nano diamond particles and magnesium alloy powder, wherein the mass fraction of the nano diamond particles in the solute is 0.01-0.5%, and the mass fraction of the magnesium alloy powder in the solute is 95-99.9%.

3. The method for improving the thermal conductivity of the magnesium-based composite material by the nano-diamond as claimed in claim 2, wherein in the step 1, the size of the nano-diamond particles is 5-10 nm.

4. The method for improving the thermal conductivity of the magnesium-based composite material by using the nano-diamond as claimed in claim 1, wherein in the step 2, the ball milling is performed by using an intermittent ball milling for 200-400 min; the ball milling process comprises the following steps: rotating forwards, rotating backwards and standing circularly until the set ball milling time is reached; wherein, the time of each forward rotation is 10-20min, the time of each reverse rotation is 10-20min, and the time of each rest is 15 min.

5. The method for improving the thermal conductivity of the magnesium-based composite material through the nano-diamond according to claim 1, wherein in the step 3, the vacuum degree is 10 ^-1 Pa, the sintering pressure is 200-300 MPa, the sintering temperature is 650-700 ℃, and the sintering time is 60-120 min.

6. The method for improving the thermal conductivity of the magnesium-based composite material through the nano-diamond according to claim 1, wherein in the step 4, before the sintered blank is extruded, the sintered blank is heated at the temperature of 300 ℃ for 30-60 min.

7. The method as claimed in claim 1, wherein the extrusion ratio in step 4 is 20: 1.

8. The method as claimed in claim 1, further comprising step 5 of annealing the extruded composite material covered with carbon powder or alumina.

9. The method as claimed in claim 8, wherein the annealing temperature is 350 ℃ and the annealing time is 90 min.

10. A magnesium-based composite material obtained by the production method according to any one of claims 1 to 9.

[ technical field ] A method for producing a semiconductor device

The invention belongs to the scientific field of magnesium-based alloy materials, and particularly relates to a method for improving the heat conductivity of a magnesium-based composite material by using nano-diamond and the magnesium-based composite material.

[ background of the invention ]

Although magnesium and magnesium alloys can effectively realize light weight in the fields of 3C products, communication electronics and aerospace, the heat dissipation of used devices becomes a key for hindering the rapid development of the devices, a light weight material with small linear expansion coefficient and high heat conductivity is needed to ensure and improve the service life and the working stability of the products, the density of magnesium is 1.74g/cm ³, which is about 2/3 of aluminum and 1/4 of iron, the heat conductivity of magnesium at room temperature is 156W/(m.K), the thermal conductivity is only inferior to that of copper and aluminum, the specific heat conductivity (namely the unit mass) is equivalent to that of aluminum, so that the magnesium and magnesium alloys are expected to replace the field of the aluminum alloys widely used at present, and the commercial heat conductivity of pure magnesium alloys is limited by the practical mechanical property of the magnesium and the heat radiator.

At present, the main research on the thermal conductivity of magnesium alloy includes the aspects of thermal expansion coefficient, thermal conductivity coefficient and the like: the heat conductivity coefficients of the as-cast Mg-Al and Mg-Sc alloys are researched, and the heat conductivity coefficients are found to be continuously reduced along with the increase of the content of solute elements and increased along with the increase of the temperature; the heat conductivity coefficient of the Mg-Gd-Y-Zn-Zr alloy at room temperature is 23W/(m.K) through experiment measurement; studies have shown that the thermal conductivity of AZ31 and AZ61 magnesium alloys increases with increasing temperature from-125 ℃ to 400 ℃; beck et al showed that different alloying elements have different effects on the thermal conductivity of magnesium alloys: the heat conductivity of the magnesium alloy is relatively less influenced by the addition of Cu, Ni and Zn, and the heat conductivity of the magnesium alloy is remarkably reduced by the addition of Al. On the other hand, the study on the thermal conductivity of the magnesium-based composite material mainly uses carbon fibers, carbon nanotubes, SiCp and the like as the thermal conductivity of the reinforcement, and it is found that the thermal expansion performance of the composite material decreases with the increase in temperature. Judri et al believe that the effect of the reinforcement on the coefficient of thermal expansion of the composite is primarily in the near-interface region, and that a decrease in particle size increases the reinforcement/matrix interface area, resulting in an increase in the constraining force for matrix deformation, and difficulty in thermal expansion, resulting in a decrease in the coefficient of thermal expansion of the magnesium-based composite. The addition of the nano particles into the magnesium alloy can obviously improve the comprehensive performance of the magnesium alloy, so that the magnesium-based composite material not only can inherit the excellent performance of the magnesium alloy, but also can break through the limitations of low high-temperature mechanical property and poor normal-temperature wear resistance of the magnesium alloy, so that the magnesium-based composite material has high elastic modulus and lower thermal expansion coefficient, and becomes a hotspot of the research in the current material field.

The diamond has many excellent properties, such as high hardness, good chemical stability, thermal conductivity and thermal stability, etc., the thermal conductivity of the diamond is the highest among known materials, 2000W/(m.K) at room temperature, which is about 5 times of that of good conductor copper, the thermal expansion coefficient of the diamond is in direct proportion to the temperature, and linearly increases with the rise of the temperature, generally 1.5 × 10 ^-6 -4.8 × 10 ^{- 6} K ^-1. the nano-diamond has some basic properties of nano-diamond and diamond, such as large chemical activity, low Debye temperature, etc., so the nano-diamond is compounded with high thermal conductivity metal as an enhanced phase, and theoretically should have excellent thermal conductivity.

[ summary of the invention ]

The invention aims to overcome the defects of the prior art and provides a method for improving the heat conductivity of a magnesium-based composite material by using nano-diamond and the magnesium-based composite material; the preparation method is used for solving the problem of how to improve the thermal conductivity of the magnesium-based alloy by adding diamond into the magnesium-based alloy.

in order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

A method for improving the thermal conductivity of a magnesium-based composite material by using nano-diamond comprises the following steps:

Step 1, adding magnesium alloy powder into the nano-diamond dispersion liquid, uniformly stirring to obtain a mixed system, and drying the mixed system to obtain mixed powder of nano-diamond and magnesium alloy;

step 2, ball-milling the mixed powder of the nano-diamond and the magnesium alloy to obtain uniformly dispersed ball-milled powder;

Step 3, sintering the ball-milling powder in a hot pressing manner in a vacuum environment to obtain a sintered blank;

And 4, extruding the sintered blank to obtain an extruded composite material, wherein the extruded composite material is a material obtained by improving the heat conductivity of the magnesium-based composite material through the nano-diamond.

The invention is further improved in that:

Preferably, in step 1, the nano-diamond dispersion liquid is prepared by adding nano-diamond particles into absolute ethyl alcohol and performing ultrasonic dispersion; the solute in the mixed system comprises nano diamond particles and magnesium alloy powder, wherein the mass fraction of the nano diamond particles in the solute is 0.01-0.5%, and the mass fraction of the magnesium alloy powder in the solute is 95-99.9%.

Preferably, in the step 1, the size of the nano-diamond particles is 5-10 nm.

Preferably, in the step 2, intermittent ball milling is adopted for ball milling, and the ball milling time is 200-400 min; the ball milling process comprises the following steps: rotating forwards, rotating backwards and standing circularly until the set ball milling time is reached; wherein, the time of each forward rotation is 10-20min, the time of each reverse rotation is 10-20min, and the time of each rest is 15 min.

Preferably, in the step 3, the vacuum degree is 10 ^-1 Pa, the sintering pressure is 200-300 MPa, the sintering temperature is 650-700 ℃, and the sintering time is 60-120 min.

Preferably, in the step 4, before the sintered blank is extruded, the sintered blank is heated at the temperature of 300 ℃ for 30-60 min.

Preferably, in step 4, the extrusion ratio is 20: 1.

Preferably, the method further comprises a step 5 of covering the extruded composite material with carbon powder or aluminum oxide and carrying out annealing treatment.

Preferably, the annealing temperature is 350 ℃ and the annealing time is 90 min.

A magnesium-based composite material obtained by any one of the above-mentioned production methods.

compared with the prior art, the invention has the following beneficial effects:

the invention discloses a method for improving the thermal conductivity of a magnesium-based composite material by nano-diamond, which comprises the steps of uniformly dispersing the nano-diamond in a magnesium alloy matrix by an ultrasonic dispersion method, sintering ball-milling powder in a vacuum hot-pressing sintering furnace to obtain a sintered blank, and increasing the activity of the diamond at a nano level by high-temperature and high-pressure treatment to form a layer of carbide (magnesium carbide) between the nano-diamond and the magnesium alloy matrix, so that the interface bonding strength is improved, the interface defects are reduced, and the interface thermal conductivity is improved. Compared with the traditional method, the preparation method is simple to operate and easy to realize, and simultaneously realizes the slight carbonization reaction between the nano diamond and the magnesium alloy matrix through high temperature and high pressure.

Furthermore, the proportion of the nano-diamond particles in the total mixed powder is limited to be small, when the proportion of the nano-diamond particles is large, on one hand, the preparation cost of the whole composite material is high, and on the other hand, the nano-diamond particles in the nano-diamond dispersion liquid are easy to agglomerate and have poor dispersibility, so that the final uniform mixing of the nano-diamond particles and the magnesium alloy powder is influenced.

Furthermore, the size of the nano diamond particles is limited to be about 5-10 nm, the unit cell constant is increased compared with that of the conventional bulk diamond, the chemical activity is increased, and the carbonization reaction between the nano diamond particles and a magnesium matrix in the preparation process of the material is facilitated.

Furthermore, because magnesium-based alloy is active metal, the ball milling adopts intermittent ball milling, so as to ensure safety and prevent explosion in the ball milling process.

Furthermore, the activity of the nano-grade diamond is improved by limiting the sintering pressure, temperature and time, and a layer of carbide can be formed between the nano-diamond and the magnesium alloy substrate, so that the interface bonding strength is improved, the interface defects are reduced, and the interface thermal conductivity is improved.

furthermore, because the magnesium alloy has poor plasticity, the plasticity can be improved by heating treatment before extrusion, and the material forming is facilitated.

Furthermore, smaller grain size can be obtained by limiting the extrusion ratio, so that the composite material has high thermal conductivity and high mechanical property.

Furthermore, the extruded composite material is covered by carbon powder or aluminum oxide, so that the material can be uniformly heated, and the heat preservation effect is improved. The annealing treatment can eliminate the internal stress and dislocation of the material in the extrusion process. In addition, after the bar is extruded, the composite material is annealed, so that the phenomenon that internal defects, dislocation and the like generated in the extrusion process generate strong scattering on the movement of electrons and phonons is eliminated, the heat conduction performance is improved, and meanwhile, the thermal expansion coefficient of the magnesium-based composite material can be reduced to a certain degree through annealing treatment.

The invention also discloses the magnesium-based composite material prepared by the method, on one hand, the diamond particle reinforced magnesium-based composite material obtains high thermal conductivity, and meanwhile, the magnesium-based composite material has low thermal expansion coefficient matched with a semiconductor material, and has good application prospect. Therefore, the heat-conducting property of the magnesium-based composite material is improved by adding the nano-diamond, the application of the light magnesium-based composite material in the engineering field with mechanical-thermal dual-property requirements can be realized, and the application research range of the magnesium-based composite material is expanded.

[ description of the drawings ]

Fig. 1 is a flow chart of the method for improving the thermal conductivity of the magnesium-based composite material by using the nano-diamond of the invention.

FIG. 2 is a microstructure analysis diagram of a matrix magnesium alloy according to example 1 of the present invention. In the figure, (a), (b) and (c) are respectively a magnesium matrix crystal grain transmission electron microscope picture, a magnesium matrix electron diffraction picture and an interface high resolution picture of the nano-diamond and the magnesium matrix.

FIG. 3 is a microstructure analysis chart of the magnesium-based composite material of example 1 of the present invention. In the figure, (a), (b) and (c) are respectively a magnesium matrix crystal grain transmission electron microscope picture, a magnesium matrix electron diffraction picture and an interface high resolution picture of the nano-diamond and the magnesium matrix.

FIG. 4 is a graph showing the dimensional changes and temperature responses of the matrix magnesium alloy and the Mg-based composite material in example 1 of the present invention. In the figure, (a), (b), (c) and (d) are respectively prepared ZK60 magnesium alloy, ZK60+ 0.05% nanodiamondMagnesium-based composite A composite material,ZK60+ 0.1% nanodiamondA magnesium-based composite material,ZK60+ 0.15% nanodiamondMagnesium-based composite material and the like The change curve of strain with temperature under the action of thermal cycle.

FIG. 5 is a graph showing the effect of the amount of nanodiamond added on the thermal expansion properties of the materials of example 1 of the present invention.

FIG. 6 is a heat conductivity test chart of the matrix Mg-based composite material in example 1 of the present invention.

FIG. 7 is a graph showing the tensile properties of the matrix magnesium alloy and the magnesium-based composite material in example 1 of the present invention.

FIG. 8 is a graph showing the hardness test of the matrix magnesium alloy and the magnesium-based composite material in example 1 of the present invention.

[ detailed description ] embodiments

The invention is described in further detail below with reference to the figures and the specific embodiments; the invention discloses a method for improving the thermal conductivity of a magnesium-based composite material by using nano-diamond, which specifically comprises the following steps of:

Step 1, weighing and mixing powder. And respectively weighing the nano diamond particles and the magnesium alloy powder, wherein the size of the nano diamond is 5-10 nm, and the size of the magnesium matrix powder is 40-70 mu m. Adding the nano-diamond with the mass accounting for 0.01-5% of the total powder mass, uniformly dispersing the nano-diamond particles into absolute ethyl alcohol by using an ultrasonic stirrer, ultrasonically mixing for 20min to prepare nano-diamond dispersion liquid, wherein the amount of the absolute ethyl alcohol is only required to uniformly disperse the nano-diamond particles, adding the weighed magnesium alloy powder into the nano-diamond dispersion liquid, and uniformly stirring to obtain a mixed system; the magnesium alloy powder is preferably ZK60, and the mixed system is placed in a drying oven, is subjected to heat preservation at 30 ℃ and then is subjected to ventilation drying for 24-30h, so that the mixed powder with the nano-diamond uniformly dispersed in the magnesium alloy can be obtained.

and 2, ball-milling the mixed powder obtained in the step 1 by a planetary ball mill, wherein the ball-material ratio is 20:1, adding alcohol simultaneously to prevent the powder from bonding, and ensuring the powder to be uniformly mixed. Introducing argon gas into the ball milling tank, and removing air in the ball milling tank to prevent magnesium alloy powder from being oxidized; setting the rotation speed of the ball mill to be 200rmp/min, ball milling time to be 200-.

And 3, sintering the ball-milling powder in a vacuum hot-pressing sintering furnace, wherein the vacuum degree is 10 ^-1 Pa, the sintering pressure is 200-300 MPa, the sintering temperature is 650-700 ℃, and sintering is carried out for 60-120 min to obtain a sintered blank, and a layer of carbide is formed between the nano diamond and the magnesium alloy matrix through high-temperature and high-pressure treatment, so that the interface bonding strength is improved, the interface defects are reduced, and the interface thermal conductivity is improved.

And 4, placing the sintered blank obtained in the step 3 in a vacuum heat treatment furnace, heating to 300 ℃, and preserving heat for 30-60 min. The mold is heated to 350 ℃ and kept warm for 60 min. The material was placed in a mold and the sintered compact was hot extruded by a four-column hydraulic press at a rate of 5mm/s and an extrusion ratio of 20:1, the extrusion temperature being 300 ℃. After the extrusion is finished, the rod-shaped composite material with the diameter of phi 10mm is obtained.

And 5, covering the composite material obtained in the step 4 with carbon powder or aluminum oxide, placing the composite material in a vacuum furnace, keeping the temperature at 350 ℃ for 90min for annealing treatment, and cooling the composite material along with the furnace after the annealing treatment is finished, so that the internal stress, dislocation and the like of the material in the hot extrusion process are eliminated.

The method for testing the thermal expansion performance of the magnesium-based composite material comprises the following steps:

Processing the extruded bar of the magnesium-based composite material into a cylindrical small short bar with the diameter of 6 multiplied by 25mm, carrying out a thermal cycle experiment on the bar by using a thermal expansion instrument, setting the experimental cycle temperature to be 30-300 ℃, setting the temperature rise and fall rates to be 5K/min, and carrying out five times of thermal cycles on the magnesium-based composite material samples enhanced by the nano-diamond with different mass fractions. And analyzing and processing the data obtained by the experiment. The thermal expansion performance of the material refers to the change of the material performance caused by the change of the length or the volume of the material along with the change of the temperature, and the addition of the reinforcing phase nano diamond leads the thermal expansion coefficient of the magnesium-based composite material to be lower than that of the Mg matrix.

The method for testing the heat conductivity of the magnesium-based composite material comprises the following steps:

the small round piece processed by the extrusion bar of the nano-diamond reinforced magnesium-based composite material is tested for the heat conductivity coefficient and the thermal diffusion coefficient at different temperatures by a laser heat conductivity test method. The specific method for testing the thermal conductivity coefficient by the laser method comprises the following steps: the thermal diffusivity of a sample is tested, and the thermal conductivity (thermal conductivity) and the thermal diffusivity have the following conversion relation: λ (T) ═ α (T) × Cp (T) × ρ (T), and the thermal conductivity can be calculated with the thermal diffusion coefficient α, specific heat Cp and density ρ at a known temperature T.

the invention is further illustrated by the following specific examples: