阅读说明：本技术 具有非均匀结构的高强韧碳纳米管增强铝复合材料及其制备方法 (High-strength and high-toughness carbon nano tube reinforced aluminum composite material with non-uniform structure and preparation method thereof ) 是由 刘振宇 马宗义 肖伯律 王全兆 王东 倪丁瑞 张星星 于 2019-10-30 设计创作，主要内容包括：本发明公开了一种具有非均匀结构的高强韧碳纳米管增强铝基复合材料及其制备方法,属于复合材料制备技术领域。采用在球磨过程中先预磨高含量的碳纳米管/铝复合材料粉末,再每隔一段时间添加较低含量的碳纳米管/铝复合材料粉末球磨,最后添加铝合金粉末,由此在冷焊作用下复合材料微区形成碳纳米管含量的梯度变化。此外,由于后加入的复合材料粉末经历球磨时间短,晶粒细化程度小,从而形成微区的晶粒尺寸梯度分布。将粉末进行后续致密化及二次加工得到最终的复合材料,表现出远高于均匀结构复合材料的强韧性。(The invention discloses a high-strength and high-toughness carbon nano tube reinforced aluminum-based composite material with a non-uniform structure and a preparation method thereof, belonging to the technical field of composite material preparation. The method comprises the steps of pre-grinding high-content carbon nanotube/aluminum composite material powder in a ball milling process, adding low-content carbon nanotube/aluminum composite material powder at intervals for ball milling, and finally adding aluminum alloy powder, so that gradient change of the content of the carbon nanotubes is formed in a micro area of the composite material under the cold welding effect. In addition, the composite material powder added later has short ball milling time and small grain refining degree, so that the grain size gradient distribution of the micro-area is formed. The powder is subjected to subsequent densification and secondary processing to obtain the final composite material, which shows the toughness far higher than that of the composite material with a uniform structure.)

1. A preparation method of a high-strength and high-toughness carbon nano tube reinforced aluminum composite material with a non-uniform structure is characterized by comprising the following steps of: the method comprises the following steps:

(1) preparing n parts of mixed powder consisting of carbon nanotubes and aluminum alloy powder, wherein the content of the carbon nanotubes in the 1 st part to the nth part of the mixed powder is A in sequence₁vol.％、A₂vol.％、……、A_nvol.％，A₁>A₂>…A_n-1>A_n(ii) a The mixed powder is obtained by putting aluminum alloy powder and carbon nanotube powder into a mixer and uniformly mixing;

(2) with mass m₁The 1 st mixed powder is put into a ball mill for ball milling h₁Hours; then the mass is m₂Adding the 2 nd part of mixed powder into a ball mill on the 1 st part of mixed powder, and ball-milling the 1 st part of mixed powder together for h₂Hours; sequentially until the mass is m_nThe nth part of the mixed powder is added to the (n-1) th part of the mixed powder in the ball mill, and all the previous powder is ball milled together for h_nHours; finally adding m mass_n+1Ball milling the aluminum alloy powder with all the previous powder h_n+1H, obtaining final composite material powder;

(3) performing powder metallurgy densification on the final composite material powder obtained in the step (2) to obtain a compact composite material billet;

(4) and carrying out secondary plastic deformation processing on the obtained composite material billet to further improve the microstructure, and finally obtaining the high-strength and high-toughness carbon nano tube reinforced aluminum composite material with the non-uniform structure.

2. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1, wherein the method comprises the following steps: in the step (2), the aluminum alloy powder added finally in the ball milling is alloyed aluminum alloy powder or pre-alloyed aluminum powder consisting of element powder; the average grain diameter of the aluminum alloy powder added in the ball milling is between 5 and 100 mu m.

3. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1 or 2, wherein the method comprises the following steps: an aluminum alloy powder whose nominal composition is selected from the group consisting of 1 xxx series to 8 xxx series aluminum alloy compositions is added during ball milling.

4. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1, wherein the method comprises the following steps: the carbon nano tube is of a single-wall or multi-wall carbon nano tube structure, the diameter is less than 100nm, and the length is less than 500 mu m.

5. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1, wherein the method comprises the following steps: in the step (2), a process control agent is added in the ball milling process, and the process control agent is one of methanol, ethanol, petroleum ether, stearic acid, oleic acid and liquid paraffin.

6. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1, wherein the method comprises the following steps: in the step (2), the ball material in the ball milling processThe ratio of 5:1-30:1, the rotating speed of 100-_nvol.% is 0.5-6 vol.%, and the time h of each ball milling is_nIs 0.5-4 hours.

7. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 6, wherein the method comprises the following steps: in the step (2), the ball material ratio is 10:1-15:1, the rotating speed is 200-_nFor 1-3 hours.

8. The method for preparing the high-strength and high-toughness carbon nanotube reinforced aluminum composite material with the non-uniform structure as claimed in claim 1, wherein the method comprises the following steps: in the step (4), the secondary plastic deformation processing is hot extrusion, hot rolling or unidirectional forging.

9. A high-toughness carbon nanotube reinforced aluminum composite material having a non-uniform structure prepared by the method of any one of claims 1 to 8, wherein: the composite material has a non-uniform structure and is formed by dispersing carbon nanotubes in an aluminum matrix, wherein: the content and the grain size of the carbon nano tube are distributed in a gradient way in the micro area.

10. The high strength and toughness carbon nanotube reinforced aluminum composite material with non-uniform structure as claimed in claim 9, wherein: the carbon nano tubes are distributed in a gradient manner at the local part of the matrix, and the grain size is also changed in a gradient manner in the area where the carbon nano tubes are distributed in a gradient manner.

Technical Field

The invention relates to the technical field of composite material preparation, in particular to a high-strength and high-toughness carbon nano tube reinforced aluminum composite material with a non-uniform structure and a preparation method thereof.

Background

Carbon Nanotubes (CNTs) have extremely high mechanical properties (tensile strength >10GPa, elastic modulus-1 GPa) and a large aspect ratio, and are considered to be ideal reinforcements of composite materials. A small amount of carbon nano tubes are added into the aluminum alloy matrix, so that the high-strength and high-modulus aluminum matrix composite is expected to be prepared, and the preparation method has wide application prospect in the field of aerospace. However, the addition of the carbon nanotubes improves the strength and modulus of the composite material, and also inevitably deteriorates the toughness of the composite material, mainly for two reasons, namely that the carbon nanotubes dispersed in the aluminum matrix have a strong function of nail-rolling grain boundaries, so that the matrix grains are seriously refined, and the capability of storing dislocation is greatly reduced; secondly, the uniformly dispersed carbon nano tube distribution is sought to be obtained in the past, but the free path of the microcrack expansion is greatly reduced by the distribution, and the capability of the composite material for inhibiting the microcrack expansion is seriously reduced.

One of the current methods for preparing high strength and toughness aluminum-based composites is by adding coarse matrix powder to the composite [ Mater Sci Eng a, 1999; 259, p 296-; 49, p 405-417], thereby constructing a non-uniform structure with grain-free regions and grain-enriched regions, utilizing the good toughness of the grain-free regions to inhibit crack propagation in the composite material. However, the size of the constructed toughness zone is more than dozens of micrometers, so that the stress concentration of the toughness zone on the brittle zone cannot be effectively relaxed, the toughness is not obviously improved, and the strength, particularly the yield strength, of the composite material is greatly reduced due to the introduction of a large amount of low-strength toughness zones.

Disclosure of Invention

The invention aims to provide a high-toughness carbon nano tube reinforced aluminum composite material (CNT/Al) with a non-uniform structure and a preparation method thereof aiming at the defect of the existing toughness of the CNT/Al composite material. The prepared composite material has gradient distribution of carbon nano tube content and grain size in a micro area, not only can effectively exert the strengthening effect of the carbon nano tube, but also can ensure that the composite material keeps good toughness.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a preparation method of a high-strength and high-toughness carbon nano tube reinforced aluminum composite material with a non-uniform structure comprises the following steps:

(1) preparing n parts of mixed powder consisting of carbon nanotubes and aluminum alloy powder, wherein the content of the carbon nanotubes in the 1 st part to the nth part of the mixed powder is A in sequence₁vol.％、A₂vol.％、……、A_nvol.％，A₁>A₂>…A_n-1>A_n(ii) a The mixed powder is obtained by putting aluminum alloy powder and carbon nanotube powder into a mixer and uniformly mixing;

(2) with mass m₁Part 1 of the mixed powder (A)₁vol.% carbon nanotubes) in a ball mill, ball milling h₁Hours; then the mass is m₂Part 2 of the mixed powder (A)₂vol.% carbon nanotubes) was added to the ball mill above the 1 st portion of the mixed powder and the 1 st portion of the mixed powder was co-milled h₂Hours; sequentially until the mass is m_nThe nth part of the mixed powder (A)_nvol.% carbon nanotubes) was added to the ball mill on top of the (n-1) th mixed powder and all the previous powders were ball milled together h_nHours; finally adding m mass_n+1Ball milling the aluminum alloy powder with all the previous powder h_n+1H, obtaining final composite material powder;

(3) performing powder metallurgy densification on the final composite material powder obtained in the step (2) to obtain a compact composite material billet;

(4) and carrying out secondary plastic deformation processing on the obtained composite material billet to further improve the microstructure, and finally obtaining the high-strength and high-toughness carbon nano tube reinforced aluminum composite material with the non-uniform structure.

In the step (2), the aluminum alloy powder added finally in the ball milling is alloyed aluminum alloy powder or pre-alloyed aluminum powder consisting of element powder; the average grain diameter of the aluminum alloy powder added in the ball milling is between 5 and 100 mu m.

In the above step (2), the aluminum alloy powder added in the ball milling is selected from various types of aluminum alloy compositions of 1 xxx series to 8 xxx series, and among them, 2 xxx series, 5 xxx series, 6 xxx series, and 7 xxx series aluminum alloys are preferable.

The carbon nano tube is of a single-wall or multi-wall carbon nano tube structure, the diameter is less than 100nm, and the length is less than 500 mu m.

In the step (2), a process control agent is added in the ball milling process, and the process control agent is one of methanol, ethanol, petroleum ether, stearic acid, oleic acid and liquid paraffin.

In the step (2), in order to enable the local structure of the final composite material to have the characteristics of carbon nanotube content and grain size gradient change, the ball-material ratio, the rotating speed and the time need to be regulated and controlled, so that the powder is in the deformation-cold welding stage without severe crushing, and the powder added in the (n + 1) th time is subjected to cold welding with the powder in the previous ball-milling tank after deformation. In order to achieve the effect, the ball-material ratio in the ball milling process is designed to be 5:1-30:1, the rotating speed is 100-_nvol.% is 0.5-6 vol.%, and the time h of each ball milling is_nIs 0.5-4 hours. The ball-material ratio is preferably 10:1-15:1, the rotating speed is preferably 200-_nPreferably 1-3 hours.

In the step (4), the secondary plastic deformation processing is hot extrusion, hot rolling or unidirectional forging, preferably hot extrusion and hot rolling. When hot extrusion is used, the nominal extrusion ratio is not less than 10: 1; when hot rolling is used, the nominal rolling reduction is not less than 60%.

The high-strength and high-toughness carbon nano tube reinforced aluminum composite material with the non-uniform structure, which is prepared by the invention, has the non-uniform structure and is formed by dispersing carbon nano tubes in an aluminum matrix, wherein: the composite material presents gradient distribution of carbon nanotube content and grain size in a micro area), the carbon nanotubes are locally distributed in a gradient manner in a matrix, and the grain size is also changed in a gradient manner in an area where the carbon nanotubes are distributed in a gradient manner.

Compared with the prior strengthening and toughening technology, the invention has the advantages that:

1. the method has simple process, easy control and large-scale production capacity. Compared with the common ball milling process, the invention sequentially adds the mixed powder of the carbon nano tube and the aluminum alloy from high content to low content, and enables the powder to be in the deformation and cold welding stage without violent crushing by controlling the ball milling rotating speed and the ball milling time, so that the powder added later is subjected to cold welding with the powder in the previous ball milling tank after deformation. And finally, a non-uniform structure with the local carbon nanotube content and the grain size in gradient distribution is reserved.

2. The composite material prepared by the method has a non-uniform structure in a micro-area, the content of the carbon nano tube and the size of the crystal grain are in gradient distribution, the non-uniform structure can effectively inhibit local strain concentration, not only can effectively exert the strengthening effect of the carbon nano tube, but also can keep good toughness of the composite material, namely the overall toughness of the composite material is improved.

3. On the basis of toughening research of the existing particle-reinforced metal-based composite material, the invention is favorable for realizing coordinated deformation of different areas by constructing a non-uniform structure-gradient structure with the micro-area CNT content and the grain size in gradient distribution in the composite material, thereby inhibiting local strain concentration and ensuring that the reinforcing advantage of the CNT is fully exerted. In addition, the grain size is distributed in a gradient manner, the reduction of the yield strength can be compensated to a certain extent by regulating the content of large-size grains, and finally the high-strength and high-toughness CNT/Al composite material is obtained, and is expected to be applied to the aerospace field requiring light weight and high strength.

Drawings

FIG. 1 is a schematic view of the micro-domain structure of the non-uniform CNT/Al composite of the invention.

FIG. 2 is a microstructure of a non-uniform structure CNT/Al composite prepared according to the present invention; wherein: (b) and (c) is an enlarged view of the different regions in (a).

Detailed Description

The invention is described in detail below with reference to the figures and examples.

The invention adopts the steps of pre-grinding high-content carbon nano tube/aluminum composite material powder in the ball milling process, adding low-content carbon nano tube/aluminum composite material powder at intervals, and finally adding aluminum alloy powder, so that gradient change of the content of the carbon nano tube is formed in a micro area of the composite material under the cold welding action. In addition, the composite material powder added later has short ball milling time and small grain refining degree, so that the grain size gradient of a micro-area is formed. The composite powder is densified and secondary processed to obtain the final non-uniform CNT/Al composite. The method has simple process, and the prepared CNT/Al composite material has excellent toughness and large-scale application potential.

The invention comprises the following steps:

(1) mixing aluminum alloy powder with A_nvol.% carbon nanotube powder was placed in a blender and mixed to obtain a_nvol.% carbon nanotube/aluminum composite powder;

(2) with mass m₁A of (A)₁Putting the vol.% carbon nano tube/aluminum composite material powder into a ball mill, adding a proper amount of process control agent, and ball milling for h₁Hours; with mass m₂A of (A)₂vol.% of the carbon nanotube/aluminum composite powder was added to a ball mill and co-milled with the previous powder h₂Hours; … has mass m_nA of (A)_nvol.% of the carbon nanotube/aluminum composite powder was added to a ball mill and co-milled with the previous powder h_nAnd (4) hours. Finally adding m mass_n+1Ball milling the aluminum alloy powder together_n+1And (4) hours. Obtaining final composite material powder;

(3) performing densification treatment on the final composite material powder to obtain a compact composite material billet;

(4) the composite material billet is subjected to conventional forging, extrusion or rolling type thermal secondary processing treatment to further improve the microstructure, so that the carbon nanotube/aluminum composite material with the non-uniform structure and the gradient distribution of the carbon nanotube content and the grain size in a local area is obtained (figure 1).