CN112111665A - Method for preparing carbon modified aluminum alloy composite material by vacuum pressure infiltration method - Google Patents

Abstract

The invention relates to the technical field of aluminum alloy preparation, and discloses a method for preparing a carbon modified aluminum alloy composite material by a vacuum pressure infiltration method, which comprises the following steps: fully mixing the ceramic particles with a cationic surfactant aqueous solution, and drying to obtain the ceramic particles coated with the cationic surfactant; adding a carbon material and ceramic particles coated with a cationic surfactant into water, carrying out electrostatic self-assembly under stirring, and drying to obtain composite particles; uniformly mixing the composite particles with a foaming agent, and performing hot-pressing sintering to obtain a porous prefabricated body; and melting and impregnating an aluminum alloy ingot into the porous preform in vacuum pressure impregnation equipment, and cooling to obtain the carbon modified aluminum alloy composite material. The method can effectively improve the compatibility between the aluminum alloy and the carbon material, the prefabricated body is not easy to crack in the preparation process, and the aluminum alloy can be fully filled in the pores of the prefabricated body, so that the composite material with better tensile strength and heat-conducting property can be obtained.

Description

A method for preparing carbon-modified aluminum alloy composite material by vacuum pressure infiltration method

technical field

The invention relates to the technical field of aluminum alloy preparation, in particular to a method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method.

Background technique

Aluminum alloy composite material consists of two parts: matrix material (pure aluminum and aluminum alloy) and reinforcing material (fibers, whiskers and particles). Due to its light weight, it belongs to a lightweight metal matrix composite material; it not only has an aluminum matrix It has the advantages of low density, good thermal conductivity and strong corrosion resistance, and also maintains some overall properties of metal matrix composites, such as high specific stiffness and good dimensional stability. It has become the focus of new material research. Carbon-modified aluminum alloy composite material is a general term for a class of composite materials with carbon fibers, carbon nanotubes, graphene and other carbon materials as the reinforcement and aluminum alloy as the matrix. It has high tensile strength and electrical and thermal conductivity. , as a structure and heat dissipation material are widely used in automotive, electronics and communications and other fields. However, due to differences in density and other reasons, the wettability between carbon materials and aluminum matrix is poor, which seriously hinders the preparation of composite materials and has a great impact on the mechanical properties and thermal conductivity of composite materials.

The Chinese patent document with publication number CN106119587A discloses a preparation method of an aluminum alloy composite material with carbon nanotubes effectively added, comprising the following steps: (1) preparation of carbon nanotube aluminum matrix composite powder: The powder and the foaming agent are put into a high-energy ball mill according to a certain proportion, mixed evenly, and cooled to obtain a composite powder; (2) Preparation of carbon nanotube aluminum-based composite ingots: the composite powder obtained in step (1) is mixed. (3) Smelting: after the pure aluminum ingot is melted, the composite ingot obtained in step (2) is added at a certain temperature, and after stirring, Heat preservation and casting to obtain a carbon nanotube aluminum alloy composite material. In the method, by adding a foaming agent to the composite powder, combined with the vacuum hot pressing sintering process, the particles are fused, and the strong mechanical bonding force between the particles is eliminated, and a violent foaming phenomenon occurs after the composite billet is added with aluminum liquid And form fine particles, which solves the problem of wettability between carbon nanotubes and aluminum liquid. But at the same time, this method also has the following problems: (1) the strength of the composite ingot formed by hot pressing and sintering of aluminum and carbon nanotubes is relatively small, and problems such as cracking may occur in the process of stirring and casting, which affects the final production. The strength of the composite material; (2) After the foaming agent is added to the molten aluminum, a large number of bubbles will be generated in the molten aluminum, and the molten aluminum is filled into the composite billet by stirring casting, and the molten aluminum penetrates into the composite billet. The speed of the ingot is slow, which leads to the possibility of pores unfilled with molten aluminum in the final composite material, which affects the strength and thermal conductivity of the composite material; and the carbon material will react with the molten aluminum for a long time, resulting in Al ₄ The thermal conductivity of C ₃ is small (140 W/m·K), which leads to a large interfacial thermal resistance between the carbon material and the aluminum matrix, which affects the thermal conductivity of the composite material.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method. In the process of preparing the composite material by the method, there is no problem of cracking of the preform, and the aluminum alloy can be fully filled in the pores of the preform, so that the composite material with better tensile strength and thermal conductivity can be obtained.

The specific technical scheme of the present invention is:

A method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method, comprising the following steps:

(1) fully mixing the ceramic particles with the aqueous cationic surfactant solution, and drying to obtain ceramic particles coated with the cationic surfactant;

(2) adding the carbon material and the ceramic particles coated with the cationic surfactant into water, performing electrostatic self-assembly under stirring, and drying to obtain composite particles;

(3) after the composite particles and the foaming agent are evenly mixed, hot-press sintering is performed to obtain a porous preform;

(4) In the vacuum pressure infiltration equipment, the aluminum alloy ingot is melted and infiltrated into the porous preform, and the carbon-modified aluminum alloy composite material is obtained after cooling.

In the present invention, the porous preform is prepared by mixing ceramic particles and carbon material, and the characteristics of high compressive strength and high shear strength of the ceramic material can be used to improve the strength of the preform and prevent it from cracking during the subsequent infiltration of aluminum liquid. Thereby, the carbon material and ceramic particles are distributed more uniformly in the composite material, so as to improve the tensile strength and thermal conductivity of the composite material. At the same time, in the present invention, the surface of the ceramic particles is positively charged by coating the cationic surfactant on the surface of the ceramic particles, so as to realize the effective combination with the carbon material with negative charge on the surface through electrostatic attraction, which can further improve the strength of the preform and prevent the prefabrication. The body deformed and collapsed during the vacuum pressure infiltration process.

In addition, in the present invention, a foaming agent is added to the preform, and the latter plays a role in the process of hot pressing and sintering to form pores in the preform, and then the aluminum alloy melt is infiltrated into the pores by a vacuum pressure infiltration method. It can prevent the wettability between the preform and the aluminum alloy melt from being improved, and improve the interface bonding between the two, thereby improving the tensile strength and thermal conductivity of the composite material. Compared with the patent with the publication number of CN106119587A, the foaming agent of the present invention plays a role during hot pressing There are pores of unfilled aluminum alloy in the final composite material, which can improve the tensile strength and thermal conductivity of the composite material, and at the same time can reduce the reaction between the carbon material and the aluminum liquid to generate Al ₄ C ₃ , thereby reducing the interface thermal resistance, Improve the thermal conductivity of composite materials.

Preferably, in step (2), the carbon material is at least one of carbon nanotubes, graphene, fullerenes, nano-carbon black, nano-graphite, and short carbon fibers; the length of the short carbon fibers is 30-50 μm , with a diameter of 4 to 7 μm.

Preferably, in step (1), the ceramic particles are at least one of nano-alumina, nano-sodium silicate, nano-feldspar, and nano-quartz.

Preferably, in step (1), the cationic surfactant is at least one of fatty amine, polyoxyethylene fatty amine, quaternary ammonium salt, and polyoxyethylene quaternary ammonium salt.

Preferably, in step (1), the mass fraction of the cationic surfactant aqueous solution is 5-50 wt.%.

Preferably, the amount of the ceramic particles in step (1) is 5-10 wt.% of the amount of carbon material in step (2).

Preferably, in step (3), the amount of the foaming agent is 1-5 wt.% of the amount of the composite particles.

Preferably, in step (3), the foaming agent is at least one of calcium carbonate, magnesium carbonate and sodium bicarbonate.

Preferably, in step (3), the temperature of the hot pressing sintering is 1500-2000°C.

Preferably, in step (3), the pressure of the hot pressing sintering is 5-10 MPa.

Preferably, in step (4), the pressure of the impregnation is 1-5 Mpa.

Preferably, the short carbon fiber includes a core and a skin layer wrapped around the core; the core is carbon, and the skin is a carbon/aluminum composite material.

The short carbon fiber is designed into a skin-core structure, and the existence of the carbon core can increase the carbon content in the short carbon fiber, so as to better exert the reinforcing effect of the short carbon fiber on the composite material; the aluminum/carbon composite material skin is used as the carbon core and aluminum. The transition layer between the substrates can improve the compatibility between the short carbon fiber and the aluminum substrate, and improve the interfacial bonding between the two, which can effectively transfer the load from the aluminum substrate to the carbon fiber, preventing the two from Delamination occurs during tension, thereby improving the tensile properties of the composite material, and the improvement of the interfacial bonding can also reduce the interfacial thermal resistance and improve the thermal conductivity of the composite material.

Preferably, the diameter of the core is 3-5 μm, and the thickness of the skin layer is 1-2 μm; the preparation method of the short carbon fiber is as follows:

(A) Spinning: melt spinning the pitch to make carbon fiber precursor;

(B) Pre-oxidation: pre-oxidize the carbon fiber strands at 200-400° C. in an air atmosphere;

(C) impregnation: the carbon fiber precursor is immersed in the mixed solution of aluminum sol and molten pitch, and dipped for 30 to 40 minutes to obtain carbon fibers coated with aluminum sol and molten pitch; the mass ratio of the aluminum sol and molten pitch is 1: 3 to 5;

(D) Pre-oxidation: pre-oxidize the carbon fibers after the impregnation treatment at 200-400° C. in an air atmosphere;

(E) Carbonization: carbonize the pre-oxidized carbon fibers at 800-1200° C. in a nitrogen atmosphere;

(F) Electrolysis: The carbon fiber after carbonization is spread on the bottom of the electrolytic cell as the cathode, and the carbon material is used as the anode, and the molten cryolite is used as the electrolyte for electrolysis; after the electrolysis is completed, the carbon fiber is taken out, and the skin-core structure is obtained after cooling. carbon fiber;

(G) Cutting: The skin-core structure carbon fibers are radially cut to obtain short carbon fibers.

The present invention realizes the coating of the carbon/aluminum composite material outside the carbon core through the process of impregnation and electrolysis, and the specific mechanism is as follows: after the carbon fiber precursor is pre-oxidized (stabilized), it is coated on the outer surface of the precursor by the dip coating method. Mixed layer of aluminum sol and molten asphalt; in the subsequent pre-oxidation process, the asphalt in the mixed layer of the outer layer undergoes a series of complex reactions and is transformed into a pyridine ring trapezoidal structure that is thermally stable and has a semiconductor resistance value. The aluminum sol is also dried and solidified; after carbonization, the aluminum oxide of the outer layer is converted into aluminum by electrolysis. The specific process of electrolysis is as follows: during the electrolysis process, the alumina in the outer layer of carbon fiber reacts with AlF ₆ ^3- in the molten cryolite to form Al ₂ OF ₆ ^2- , and Al ₂ OF ₆ ^2- enters the electrolyte, and in the outer layer of carbon fiber Form pores, AlF ₆ ^3- is reduced to aluminum at the cathode, and filled into the pores of the outer layer of the carbon fiber in the form of aluminum liquid. After cooling, a skin-core structure carbon fiber with a carbon core and an aluminum/carbon composite material can be obtained . During electrolysis, the anode generates carbon dioxide, and it can be judged whether the electrolysis is complete by whether there are bubbles coming out of the anode.

In step (B), the reason why aluminum sol is used instead of directly using aluminum is that the melting point of aluminum is relatively low (660° C.), which will be lost due to melting during carbonization, and the aluminum in the aluminum sol is in the form of alumina. Exist, the melting point of alumina is as high as 2054 ℃, and it can still exist stably when carbonized at high temperature. In addition, the porosity of the aluminum sol enables it to form a porous framework in the skin layer, which increases the contact area between aluminum and carbon materials in the skin layer, thereby better improving the compatibility between the short carbon fibers in the composite material and the aluminum matrix.

Preferably, the skin layer includes an inner layer, a middle layer and an outer layer whose aluminum content increases sequentially from the inside to the outside; the diameter of the core portion is 2-4 μm, and the thicknesses of the inner layer, the middle layer and the outer layer are all 0.5-1 μm ; The preparation method of described short carbon fiber is as follows:

(a) Spinning: melt spinning the pitch to make carbon fiber precursors;

(b) Pre-oxidation: pre-oxidize the carbon fiber strands at 200-400° C. in an air atmosphere;

(c) Coating the inner layer: Immerse the carbon fiber strands in a mixture of aluminum sol and molten asphalt, the mass ratio of the aluminum sol and molten asphalt being 1:4.5-6.5, and dipping for 18-23 minutes; The carbon fiber is pre-oxidized at 200-400°C in an air atmosphere to obtain a carbon fiber covered with an inner layer;

(d) Coating the middle layer and the outer layer: change the mass ratio of the aluminum sol to the molten asphalt in step (c) to 1:2-4.5 and 1:1-2, repeat step (c), and sequentially coat the upper middle layer and outer layer;

(e) Carbonization: carbonize the carbon fiber coated with the outer layer at 800-1200° C. in a nitrogen atmosphere;

(f) Electrolysis: The carbon fiber after carbonization is spread on the bottom of the electrolytic cell as the cathode, and the carbon material is used as the anode, and the molten cryolite is used as the electrolyte for electrolysis; after the electrolysis is completed, the carbon fiber is taken out, and the skin-core structure is obtained after cooling. carbon fiber;

(g) Cutting: The skin-core structure carbon fibers are radially cut to obtain short carbon fibers.

By repeating the steps of impregnation and pre-oxidation, three layers of aluminum/carbon composite material are wrapped around the carbon core, and the aluminum content from the inner layer to the outer layer is increased in turn. Through this gradient transition, the core, skin and The compatibility between the aluminum matrix improves the interfacial bonding between the short carbon fibers and the aluminum matrix, thereby improving the tensile strength and thermal conductivity of the composite.

Preferably, in step (F) or (g), the mass ratio of the cathode to the molten cryolite is 1:2-2.5.

Preferably, in step (C) or step (c), the immersion time is 30-40 min.

Preferably, in step (B) or step (D) or step (b) or step (c), the pre-oxidation time is 30-40 min.

Preferably, in step (E) or step (e), the carbonization time is 3-6h.

Preferably, in step (F) or step (f), the voltage of the electrolysis is 3.5-4.5V.

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

(1) The strength of the porous preform in the preparation process is relatively large, and problems such as cracking will not occur in the process of infiltrating the aluminum alloy melt, and the final composite material has high tensile strength and thermal conductivity;

(2) The combination of foaming agent, hot pressing sintering and vacuum pressure infiltration method can improve the wettability between the aluminum alloy melt and the carbon material, so that the two can be better combined, which is beneficial to improve the tensile strength of the composite material. strength and thermal conductivity;

(3) The short carbon fiber with skin-core structure can improve the compatibility between the carbon material and the aluminum matrix, and further improve the tensile strength and thermal conductivity of the composite material.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the examples.

General Example

A method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method, comprising the following steps (as shown in Figure 1):

(1) After fully mixing the ceramic particles with an aqueous solution of a cationic surfactant with a mass fraction of 5-50 wt.%, drying them to obtain ceramic particles coated with a cationic surfactant; the ceramic particles are nano-alumina, At least one of nano-sodium silicate, nano-feldspar, and nano-quartz; the cationic surfactant is at least one of fatty amine, polyoxyethylene fatty amine, quaternary ammonium salt, and polyoxyethylene quaternary ammonium salt;

(2) adding the carbon material and the ceramic particles coated with the cationic surfactant into water, performing electrostatic self-assembly under stirring, and drying to obtain composite particles; the carbon material is carbon nanotube, graphene, fullerene , at least one of nano-carbon black, nano-graphite, and short carbon fibers; the length of the short carbon fibers is 30-50 μm, and the diameter is 4-7 μm; the amount of ceramic particles in step (1) is the carbon material in step (2). 5～10wt.% of the dosage;

(3) After mixing the composite particles and the foaming agent uniformly, hot-press sintering at 1500-2000 ° C and 5-10 MPa to obtain a porous preform; the foaming agent is calcium carbonate, magnesium carbonate and sodium bicarbonate. At least one of the foaming agents; the amount of the foaming agent is 1 to 5 wt.% of the amount of the composite particles;

(4) In the vacuum pressure infiltration equipment, the aluminum alloy ingot is melted, and infiltrated into the porous preform at 1-5 Mpa, and the carbon-modified aluminum alloy composite material is obtained after cooling.

Optionally, in step (2), the carbon material is a short carbon fiber with a length of 30-50 μm and a diameter of 4-7 μm; the short carbon fiber includes a core and a skin wrapped around the core; the core is carbon, with a diameter of 4-7 μm. The thickness is 3-5 μm; the skin layer is carbon/aluminum composite material, and the thickness is 1-2 μm. The preparation method of the short carbon fiber is as follows:

(A) Spinning: melt spinning the pitch to make carbon fiber precursor;

(B) Pre-oxidation: pre-oxidize the carbon fiber strands at 200 to 400° C. in an air atmosphere for 30 to 40 minutes;

(C) impregnation: the carbon fiber precursor is immersed in the mixed solution of aluminum sol and molten pitch, and dipped for 30 to 40 minutes to obtain carbon fibers coated with aluminum sol and molten pitch; the mass ratio of the aluminum sol and molten pitch is 1: 3 to 5;

(D) Pre-oxidation: pre-oxidize the dipped carbon fibers at 200-400° C. in an air atmosphere for 30-40 minutes;

(E) Carbonization: carbonize the pre-oxidized carbon fibers at 800-1200° C. in a nitrogen atmosphere for 3-6 hours;

(F) Electrolysis: The carbonized carbon fibers are laid on the bottom of the electrolytic cell as a cathode, and the mass ratio of the cathode to the molten cryolite is 1:2 to 2.5. The carbon material is used as the anode, and the molten cryolite is used as the electrolyte. Electrolysis is carried out at a voltage of 3.5-4.5V; after the anode has no bubbles, the carbon fiber is taken out, and the skin-core structure carbon fiber is obtained after cooling;

(G) Cutting: The skin-core structure carbon fibers are radially cut to obtain short carbon fibers.

Optionally, in step (2), the carbon material is a short carbon fiber with a length of 30-50 μm and a diameter of 4-7 μm; the short carbon fiber includes a core and a skin wrapped around the core; the core is carbon, with a diameter of 4-7 μm. The thickness of the inner layer, the middle layer and the outer layer is 0.5 to 1 μm. The preparation method of the short carbon fiber is as follows:

(a) Spinning: melt spinning the pitch to make carbon fiber precursors;

(b) Pre-oxidation: pre-oxidize the carbon fiber strands at 200 to 400° C. in an air atmosphere for 30 to 40 minutes;

(c) Coating the inner layer: Immerse the carbon fiber strands in a mixture of aluminum sol and molten asphalt, the mass ratio of the aluminum sol and molten asphalt being 1:4.5-6.5, and dipping for 18-23 minutes; The carbon fiber is pre-oxidized at 200-400° C. in an air atmosphere for 30-40 minutes to obtain a carbon fiber covered with an inner layer;

(d) Coating the middle layer and outer layer: change the mass ratio of the aluminum sol and molten asphalt in step (c) to 1:2-4.5 and 1:1-2, repeat step (c), and coat the upper middle layer in turn and outer layer;

(e) Carbonization: carbonize the carbon fiber coated with the outer layer at 800 to 1200° C. in a nitrogen atmosphere for 3 to 6 hours;

(f) Electrolysis: The carbon fiber after carbonization is spread on the bottom of the electrolytic cell as the cathode, and the carbon material is used as the anode. The mass ratio of the cathode to the molten cryolite is 1:2 to 2.5. Electrolysis is carried out at a voltage of 3.5-4.5V; after the anode has no bubbles, the carbon fiber is taken out, and the skin-core structure carbon fiber is obtained after cooling;

(g) Cutting: The skin-core structure carbon fibers are radially cut to obtain short carbon fibers.

Example 1

A method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method, comprising the following steps:

(1) After fully mixing the nano-alumina particles with an aqueous solution of octadecyldimethylhydroxyethyl quaternary ammonium nitrate with a mass fraction of 30 wt.%, and drying, obtaining ceramic particles coated with a cationic surfactant ;

(2) adding carbon nanotubes and ceramic particles coated with a cationic surfactant into water, performing electrostatic self-assembly under stirring, and drying to obtain composite particles; the amount of ceramic particles in step (1) is step (2) 8wt.% of the amount of medium carbon material;

(3) After the composite particles and calcium carbonate are evenly mixed, hot-press sintering at 1800° C. and 10 MPa to obtain a porous preform; the amount of the foaming agent is 3wt.% of the amount of the composite particles;

(4) In the vacuum pressure infiltration equipment, the 6061 aluminum alloy ingot is melted and infiltrated into the porous preform under 4Mpa, and the carbon-modified aluminum alloy composite material is obtained after cooling.

Example 2

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is nano carbon black.

Example 3

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is nano-graphite.

Example 4

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is graphene.

Example 5

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is a short carbon fiber with a length of 40 μm and a diameter of 5.5 μm, and the preparation method is as follows:

A) Spinning: melt spinning the pitch to make carbon fiber precursor;

B) Pre-oxidation: pre-oxidize the carbon fiber strands at 300° C. in an air atmosphere for 35 minutes;

C) Carbonization: carbonize the pre-oxidized carbon fibers at 1000°C in a nitrogen atmosphere for 5h;

D) Cutting: radially cutting the skin-core structure carbon fibers to obtain short carbon fibers with a length of 40 μm.

Example 6

Prepared according to the steps of Example 1, the difference from Example 1 is that the ceramic particles in step (1) are sodium carbonate.

Example 7

Prepared according to the steps of Example 1, the difference from Example 1 is that the ceramic particles in step (1) are feldspar.

Example 8

Prepared according to the steps of Example 1, the difference from Example 1 is that the ceramic particles in step (1) are quartzite.

Example 9

It was prepared according to the steps of Example 1, and the difference from Example 1 was that the hot-pressing sintering temperature in step (3) was 1600°C.

Example 10

It was prepared according to the steps of Example 1, and the difference from Example 1 was that the hot pressing sintering temperature in step (3) was 1700°C.

Example 11

It was prepared according to the steps of Example 1, and the difference from Example 1 was that the hot pressing sintering temperature in step (3) was 1900°C.

Example 12

Prepared according to the steps of Example 1, the difference from Example 1 is that the impregnation pressure in step (4) is 2 MPa.

Example 13

Prepared according to the steps of Example 1, the difference from Example 1 is that the impregnation pressure in step (4) is 3 MPa.

Example 14

Prepared according to the steps of Example 1, the difference from Example 1 is that the impregnation pressure in step (3) is 5MPa.

Example 15

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is short carbon fiber, and the preparation method is as follows:

(A) Spinning: melt spinning the pitch to make carbon fiber precursors;

(B) Pre-oxidation: pre-oxidize the carbon fiber strands at 300° C. in an air atmosphere for 35 minutes;

(C) dipping: the carbon fiber precursor is immersed in the mixed solution of aluminum sol and molten pitch, and dipped for 35min to obtain carbon fibers coated with aluminum sol and molten pitch; the mass ratio of the aluminum sol and molten pitch is 1:4;

(D) Pre-oxidation: pre-oxidize the impregnated carbon fibers in an air atmosphere at 300° C. for 35 minutes;

(E) Carbonization: carbonize the pre-oxidized carbon fibers at 1000° C. in a nitrogen atmosphere for 5 hours;

(F) Electrolysis: The carbon fiber after carbonization treatment is spread on the bottom of the electrolytic cell as a cathode, the mass ratio of the cathode to the molten cryolite is 1:2, the graphite is used as the anode, and the molten cryolite is used as the electrolyte. Electrolysis; after the anode has no bubbles, take out the carbon fiber, and get the skin-core structure carbon fiber after cooling;

(G) Cutting: The skin-core structure carbon fibers were radially cut to obtain short carbon fibers with a length of 40 μm.

The obtained short carbon fibers had a core diameter of 4 μm and a skin thickness of 1.5 μm.

Example 16

Prepared according to the steps of Example 1, the difference from Example 1 is that the carbon material in step (2) is short carbon fiber, and the preparation method is as follows:

(a) Spinning: melt spinning the pitch to make carbon fiber precursors;

(b) Pre-oxidation: pre-oxidize the carbon fiber strands at 300° C. in an air atmosphere for 35 minutes;

(c) Coating the inner layer: Immerse the carbon fiber strands in a mixture of aluminum sol and molten pitch, the mass ratio of the aluminum sol and molten pitch being 1:5.5, for 18 min; , Pre-oxidation in air atmosphere for 35min to obtain carbon fiber covered with inner layer;

(d) coating the middle layer and the outer layer: the mass ratio of the aluminum sol in the step (c) to the molten asphalt is changed to 1:3 and 1:1.5, and the step (c) is repeated to coat the upper middle layer and the outer layer in turn;

(e) Carbonization: the carbon fiber coated with the outer layer was carbonized for 5h at 1000°C in a nitrogen atmosphere;

(f) Electrolysis: The carbon fiber after carbonization is spread on the bottom of the electrolytic cell as the cathode, with graphite as the anode, the mass ratio of the cathode to the molten cryolite is 1:2, and the molten cryolite is used as the electrolyte. Electrolysis; after the anode has no bubbles, take out the carbon fiber, and obtain the skin-core structure carbon fiber after cooling;

(g) Cutting: The skin-core structure carbon fibers were radially cut to obtain short carbon fibers with a length of 40 μm.

The core diameter of the obtained short carbon fiber was 4 μm, and the thickness of the inner layer, the middle layer and the outer layer in the skin layer were all 0.5 μm.

Comparative example 1 (the surface of ceramic particles is not coated with cationic surfactant)

A method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method, comprising the following steps:

(1) adding carbon nanotubes and nano-alumina particles into water, and mixing them uniformly to obtain composite particles;

(2) After uniformly mixing the composite particles and calcium carbonate, hot-press sintering at 1800° C. and 10 MPa to obtain a porous preform;

(3) In the vacuum pressure infiltration equipment, the 6061 aluminum alloy ingot is melted and infiltrated into the porous preform under 4Mpa, and the carbon-modified aluminum alloy composite material is obtained after cooling.

Comparative example 2 (foaming agent works after adding aluminum alloy melt)

A method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method, comprising the following steps:

(1) fully mixing the nano-alumina particles with a quaternary ammonium salt aqueous solution with a mass fraction of 30 wt.%, and drying to obtain ceramic particles coated with a cationic surfactant;

(2) adding carbon nanotubes and ceramic particles coated with a cationic surfactant into water, performing electrostatic self-assembly under stirring, and drying to obtain composite particles;

(3) After mixing the composite particles and calcium carbonate uniformly, hot-press sintering at 500 ° C and 10 MPa to obtain a preform;

(4) In the vacuum pressure infiltration equipment, the 6061 aluminum alloy ingot is melted and infiltrated into the preform at 4Mpa and 900°C, and the carbon-modified aluminum alloy composite material is obtained after cooling.

The thermal conductivity of the carbon-modified aluminum alloy composite materials prepared in Examples 1-16 and Comparative Examples 1-2 was tested, and the test results are shown in Table 1.

Table 1 Thermal conductivity and mechanical properties of the products of Examples 1-16 and Comparative Examples 1-2

Example 1 On the basis of Comparative Example 1, the ceramic particles were coated with cationic surfactant and then mixed with carbon nanotubes, and the thermal conductivity and tensile strength of the obtained composite material were significantly increased. The ceramic particles are coated with a cationic surfactant, so that the surface of the ceramic particles is positively charged, which can be effectively combined with the negatively charged carbon material through electrostatic attraction, so as to improve the strength of the preform and prevent it from being impregnated in the subsequent aluminum liquid. During the process, cracking occurs, so that the distribution of carbon materials and ceramic particles in the composite material is more uniform, so the tensile strength and thermal conductivity of the composite material can be improved.

The difference between Example 1 and Comparative Example 2 is that in Example 1, the foaming agent plays a role in the process of hot-pressing sintering, while in Comparative Example 2, the foaming agent plays a role after adding the aluminum alloy melt. Example 1 The thermal conductivity and tensile strength of the prepared composite material are obviously larger, because the foaming agent plays a role in the addition of the aluminum alloy melt, which will generate a large number of bubbles in the melt, resulting in that the melt cannot be fully filled into the prefabricated material. In the pores of the body, it affects the tensile strength and thermal conductivity of the composite material.

In Examples 2 to 14, on the basis of Example 1, one of the types of carbon materials, the types of ceramic particles, the hot-pressing sintering temperature, and the infiltration pressure were respectively changed, and the composite materials prepared in Examples 1 to 14 were compared. The test results show that the thermal conductivity of the aluminum alloy obtained by using the process parameters in Example 1 can reach 0.95, and the tensile strength can reach 705 MPa, which are better than other examples. Therefore, the formulation and process parameters in Example 1 can be selected as the optimal choice.

Example 15 On the basis of Example 5, short carbon fibers with a skin-core structure were used, and the thermal conductivity and tensile strength of the obtained composite material were significantly increased, because the skin layer of the aluminum/carbon composite material was used as the carbon core. The transition layer between the aluminum matrix and the aluminum matrix can improve the compatibility between the short carbon fiber and the aluminum matrix, and improve the interface bonding between the two, which can effectively transfer the load from the aluminum matrix to the carbon fiber, preventing the two. In addition, the improvement of the interface bonding can also reduce the thermal resistance of the interface and improve the thermal conductivity of the composite material.

In Example 16, on the basis of Example 15, the skin layer was designed as three layers, and the aluminum content increased sequentially from the inside to the outside, and the tensile strength and thermal conductivity of the obtained composite material increased significantly. , The gradient transition of aluminum content between the inner layer, middle layer, outer layer and aluminum matrix of the skin layer can further improve the compatibility between the core, the skin layer and the aluminum matrix, and improve the interface between the short carbon fiber and the aluminum matrix. Improve tensile strength and thermal conductivity of composites.

The raw materials and equipment used in the present invention, unless otherwise specified, are the common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are the conventional methods in the art.

The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the technical solutions of the present invention. scope of protection.

Claims (10)

1. a method for preparing carbon-modified aluminum alloy composite material by vacuum pressure infiltration method, is characterized in that, comprises the following steps: (1) After fully mixing the ceramic particles with the aqueous solution of the cationic surfactant, and drying, to obtain the ceramic particles coated with the cationic surfactant; (2) adding the carbon material and the ceramic particles coated with the cationic surfactant into water, performing electrostatic self-assembly under stirring, and drying to obtain composite particles; (3) After mixing the composite particles and the foaming agent uniformly, hot-press sintering to obtain a porous preform; (4) In the vacuum pressure infiltration equipment, the aluminum alloy ingot is melted and infiltrated into the porous preform, and the carbon-modified aluminum alloy composite material is obtained after cooling. 2. The method for preparing carbon-modified aluminum alloy composite material by vacuum pressure infiltration method according to claim 1, wherein in step (2), the carbon material is carbon nanotube, graphene, rich At least one of lerene, nano-carbon black, nano-graphite, and short carbon fibers; the short carbon fibers have a length of 30-50 μm and a diameter of 4-7 μm. 3. the method for preparing carbon-modified aluminum alloy composite material by a kind of vacuum pressure infiltration method as claimed in claim 1, is characterized in that: In step (1), the ceramic particles are at least one of nano-alumina, nano-sodium silicate, nano-feldspar, and nano-quartz; and/or In step (3), the foaming agent is at least one of calcium carbonate, magnesium carbonate and sodium bicarbonate. 4. the method for preparing carbon-modified aluminum alloy composite material by a kind of vacuum pressure infiltration method as claimed in claim 1, is characterized in that: In step (1), the cationic surfactant is at least one of fatty amine, polyoxyethylene fatty amine, quaternary ammonium salt, and polyoxyethylene quaternary ammonium salt; and/or In step (1), the mass fraction of the cationic surfactant aqueous solution is 5-50 wt.%. 5. the method for preparing carbon-modified aluminum alloy composite material by a kind of vacuum pressure infiltration method as claimed in claim 1, is characterized in that: The amount of the ceramic particles in step (2) is 5~10wt.% of the amount of carbon material in step (1); and/or In step (3), the amount of the foaming agent is 1-5 wt.% of the amount of the composite particles. 6. the method for preparing carbon-modified aluminum alloy composite material by a kind of vacuum pressure infiltration method as claimed in claim 1, is characterized in that: In step (3), the temperature of the hot pressing sintering is 1500-2000°C; and/or In step (3), the pressure of the hot pressing sintering is 5-10 MPa. 7 . The method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method according to claim 1 , wherein in step (4), the pressure of the infiltration is 1-5 Mpa. 8 . 8. The method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method as claimed in claim 2, wherein the short carbon fiber comprises a core and a skin layer wrapped outside the core; the core The core is carbon, and the skin is carbon/aluminum composite. 9. The method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method as claimed in claim 8, wherein the diameter of the core is 3 to 5 μm, and the thickness of the skin layer is 1 to 2 μm; The preparation method of the short carbon fiber is as follows: (A) Spinning: melt spinning the pitch to make carbon fiber precursors; (B) Pre-oxidation: pre-oxidize carbon fiber strands at 200-400 °C in an air atmosphere; (C) Impregnation: the carbon fiber precursor is immersed in the mixed solution of aluminum sol and molten pitch, and dipped for 30 to 40 minutes to obtain carbon fibers coated with aluminum sol and molten pitch; the mass ratio of the aluminum sol and molten pitch is 1: 3~5; (D) Pre-oxidation: pre-oxidize the impregnated carbon fibers in an air atmosphere at 200-400 °C; (E) Carbonization: carbonize the pre-oxidized carbon fibers at 800-1200°C in a nitrogen atmosphere; (F) Electrolysis: The carbon fiber after carbonization is spread on the bottom of the electrolytic cell as the cathode, the carbon material is used as the anode, and the molten cryolite is used as the electrolyte for electrolysis; after the electrolysis is completed, the carbon fiber is taken out, and the skin-core structure is obtained after cooling. carbon fiber; (G) Cutting: radially cutting the skin-core carbon fibers to obtain short carbon fibers. 10. The method for preparing a carbon-modified aluminum alloy composite material by a vacuum pressure infiltration method as claimed in claim 8, wherein the skin layer comprises an inner layer, a middle layer and a Outer layer; the diameter of the core is 2-4 μm, the thickness of the inner layer, the middle layer and the outer layer are all 0.5-1 μm; the preparation method of the short carbon fiber is as follows: (a) Spinning: melt spinning the pitch to make carbon fiber precursors; (b) Pre-oxidation: pre-oxidize carbon fiber strands at 200-400 °C in an air atmosphere; (c) Coating the inner layer: Immerse the carbon fiber strands in a mixture of aluminum sol and molten asphalt, the mass ratio of the aluminum sol and molten asphalt being 1:4.5~6.5, and dipping for 18~23 minutes; The carbon fiber is pre-oxidized at 200~400°C in an air atmosphere to obtain a carbon fiber covered with an inner layer; (d) Coating the middle layer and the outer layer: Change the mass ratio of the aluminum sol to the molten asphalt in step (c) to 1:2~4.5 and 1:1~2, repeat step (c), and sequentially coat the upper middle layer and outer layer; (e) Carbonization: carbonize the carbon fiber coated with the outer layer at 800~1200°C in a nitrogen atmosphere; (f) Electrolysis: The carbonized carbon fibers are laid on the bottom of the electrolytic cell as the cathode, the carbon material is used as the anode, and the molten cryolite is used as the electrolyte for electrolysis; after the electrolysis is completed, the carbon fibers are taken out and cooled to obtain a skin-core structure carbon fiber; (g) Cutting: radially cutting the skin-core carbon fibers to obtain short carbon fibers.

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