Application and Development of Carbon Nanotubes Magnesium Matrix Composites

There are many common composite materials in life . The traditional composite materials include reinforced concrete, fiberglass fishing rods, integrally formed shoes, and synthetic resin for switch insulation. The new composite material is a material with higher performance, high specific strength, high specific modulus, low density, etc. It includes high-performance reinforcements such as carbon, aramid, ceramic and other fibers and crystals with good heat resistance. A high performance polymer composite composed of a thermosetting and thermoplastic resin matrix. It is of great significance to study the practical application of magnesium alloy composites.

Composite materials are a kind of new materials with great vitality that emerged from the development of modern science and technology. From the 1970s to the present, magnesium-based composite materials have become an important research hotspot in the field of metal matrix composites. Magnesium-based composite materials are valued in the fields of aerospace, automotive, machinery and electronics. They have greater market potential and value than traditional single metal and aluminum-based composite materials in new high-tech applications.

I. Overview

Magnesium is silvery white, melting point is 649 ° C, light weight, density is 1.74g/cm3, about 1/4 of copper (Cu), 2/3 of aluminum (Al); it has strong chemical activity and strong affinity with oxygen. , commonly used as a reducing agent. Powdery or thin strips of magnesium, which are easily burned in the air, emit glare white light when burned, but are easily soluble in organic and inorganic acids. Magnesium can be directly combined with nitrogen, sulfur and halogen. Magnesium metal is non-magnetic and has good heat dissipation, soft and low melting point.

Magnesium alloy is one of the lightest structural materials and has unparalleled advantages over other metals. Magnesium and magnesium alloys have special properties such as low density, high specific strength and specific stiffness, good vibration damping, excellent electromagnetic shielding performance, good machinability and thermoformability, etc., making them suitable for mobile communication, laptop computers, etc. It has important application value and broad application prospects in the body structure and in the fields of automobile, electronics, electrical appliances, aerospace, defense and military, transportation and so on.

Second, the research status of magnesium alloy composites

The main characteristics of magnesium-based composite materials are low density, high specific strength and specific stiffness, good wear resistance, good high temperature resistance, good impact resistance, excellent shock absorption, good dimensional stability, and good Castability and excellent electromagnetic shielding performance. Due to the low melting point, high chemical activity, flammability, easy oxidation, etc., the preparation process suitable for magnesium-based composite materials has been a hot spot for people to study and solve. Since the melting point of magnesium is close to the melting point of aluminum, many preparation methods are promoted and improved on the basis of research on aluminum-based composite materials. The more traditional methods are common casting method, stirring casting method, extrusion casting method and powder metallurgy method. In addition, many new preparation methods have appeared, such as mechanical alloying method, melt infiltration method, spray deposition method, and Spread high temperature synthesis method, remelting dilution method and repeated plastic deformation method [8]. In recent years, research on new reinforcements such as quasicrystals, carbon fibers and graphene has made great progress. The problem of interfacial wettability between reinforcements and magnesium and magnesium alloys has also been gradually solved by different processes. This is a magnesium-based composite. The researchers brought new inspiration.

Han Li from Qinghai University used sol-gel method to prepare copper oxide (CuO) coated magnesium borate (Mg2B2O5) whisker reinforced magnesium matrix composites and studied its interface structure. It was found that CuO coating can improve the interface. The bond strength, tensile strength and elongation after fracture increased by 37.6% and 35.7%, respectively, compared to before uncoating. Li Kun et al. also prepared a uniform and crack-free silica (SiO2) coating on the surface of carbon fiber by sol-gel method, and prepared SiO2 coated carbon fiber reinforced magnesium matrix composite. The ultimate tensile strength value is only 527 MPa, which is far from the theoretical value, but the SiO2 coating on the surface of carbon fiber can significantly promote the wetting of carbon fiber by liquid magnesium. The bulk graphene particle reinforced magnesium matrix composites were successfully prepared by liquid ultrasonic combined with solid state stirring. The graphene was uniformly distributed in the matrix, and the performance of the composite was strengthened. The microhardness of the 1.2% graphene composite was up to 66kg/mm2, the performance of pure magnesium is 78% higher than the same process conditions.

Third, the research status of carbon nanotubes / magnesium matrix composites

With the continuous advancement of magnesium alloy research, based on the excellent physical and chemical properties of carbon nanotubes, people have also tried to introduce carbon nanotubes into metal matrix composites, and it is expected to enhance the performance of metal matrix by using one or some of its properties. . At present, many literatures have mentioned the use of carbon nanotubes to strengthen metal substrates such as Al, Cu, and nickel (Ni), and the carbon nanotubes have a good strengthening effect on the above metal substrates.

1. Structure and properties of carbon nanotubes

Carbon nanotubes are a new type of carbon-bonded steel with a complete molecular structure. The carbon nanotubes arranged in a hexagonal shape form a number of layers to dozens of coaxial tubes, and the layer maintains a fixed distance between the layers. It is 0.34 nm and has an average diameter of 2 to 20 nm and is classified into single-walled carbon nanotubes and multi-walled carbon nanotubes. Carbon nanotubes are one-dimensional materials, and the hexagonal structure is perfectly connected with many excellent mechanical, electrical and chemical properties. In recent years, with the in-depth study of carbon nanotubes, its broad application prospects are constantly being revealed.

Carbon nanotubes have the following properties: 1 Mechanical properties: high strength, good toughness, high elongation, low density, it is an ideal reinforcement [13]; 2 thermal properties: single theoretical thermal conductivity up to 6 600 W / ( m·K), reaching 3 215 W/(m·K) during the experiment; 3 electrical properties: having a conductivity close to metal, which can be a good material for semiconductors; 4 magnetic properties: its absorbing properties are remarkable , frequency bandwidth; 5 hydrogen storage performance: because of the carbon nano hollow structure, the theoretical hydrogen storage weight ratio reached 15%.

2. Research status of carbon nanotube/magnesium composites

The addition of carbon nanotubes as a reinforcement in the magnesium matrix is ​​a feasible method for improving the linear thermal stability of the magnesium alloy and improving the tensile strength of the alloy without increasing the proportion of the magnesium alloy. However, since the chemical nature of magnesium itself is relatively active, it is easy to chemically react during the preparation process. Therefore, for composite materials with magnesium or magnesium alloy as the matrix, the process parameters in the preparation process should be strictly controlled to prevent defects at the interface. reaction. At present, the preparation process of magnesium-based composite materials has yet to be improved and improved, and its constructive research on accurate composite mechanism and strengthening mechanism at the interface is not comprehensive. For carbon nanotube-reinforced magnesium-based composites, the morphology of carbon nanotubes in the magnesium matrix is ​​flake-shaped, so research on this aspect will be a new direction.

Carbon nanotubes are modified as reinforcing magnesium or magnesium alloys. The obtained magnesium matrix composites have the advantages of high strength, corrosion resistance and wear resistance. Carbon nanotubes and magnesium-based composite materials have been widely used in many fields. application. The magnesium-based composite material was prepared by using nickel-plated multi-walled carbon nanotubes by stirring casting method. It was found that the carbon nanotubes became the nucleus of the heterogeneous crystal during the solidification process, which can cause grain refinement and improve the combination of carbon nanotubes and matrix. The modulus of elasticity and tensile strength of the composite are improved compared to the matrix. Y. Shimizu et al. prepared a carbon nanotube-reinforced AZ91D magnesium matrix composite by powder metallurgy. When the carbon nanotubes were added in an amount of 1.0% ( mass fraction), the tensile strength of the composite reached 388 MPa. The mechanical properties of the carbon nanotube-reinforced magnesium matrix composites prepared by Qianqian Li et al. were significantly improved. It can be seen that the carbon nanotube magnesium-based composite material not only can refine the grain to improve the mechanical properties, but also can improve the corrosion resistance. The carbon nanotube magnesium-based composite material provides a broad field for the selection of engineering materials.

Fourth, the problem of carbon nanotube / magnesium matrix composites

Since the chemical nature of magnesium itself is relatively active, it is easy to chemically react during the preparation process. Therefore, for composite materials with magnesium or magnesium alloy as the matrix, the process parameters in the preparation process should be strictly controlled to prevent adverse reactions at the interface. .

At present, due to the disadvantages of low strength, low modulus, poor plasticity and perishability of magnesium and magnesium alloys, the preparation process of magnesium-based composite materials needs to be improved and improved, and its exact composite mechanism and strengthening mechanism at the interface. Constructive research is not yet comprehensive.

Two major challenges are faced in the preparation of carbon nanotubes-based composites: uniform dispersion of carbon nanotubes and poor wettability with the matrix. Since the carbon nanotubes have a large specific surface area and a high surface energy, they have a strong tendency to agglomerate. Most of the carbon nanotubes do not wet, so it is difficult to form a stronger bonding interface with the metal matrix.

V. Conclusion

At present, there are many researches on carbon nanotube-reinforced magnesium-based composite materials. However, if we thoroughly study the respective aspects of carbon nanotubes and magnesium alloys, and then optimize the advantages of both, we will achieve very good results. In view of the current research, the author believes that the research of carbon nanotube/magnesium-based composite materials will mainly develop in the following directions:

First, the computer simulation technology for studying the thermodynamics and kinetics of carbon nanotubes and magnesium-based composite materials can not only bring convenience and benefits to production, but also provide a good platform for more researchers.

Second, in-depth study of the interface behavior of carbon nano- and magnesium-based composites to obtain a composite with good interface.

Third, more research and application of various aspects of the internal structural properties of materials have been carried out in the preparation process, composite material regeneration and recycling technology.

Fourth, research on space and transportation, hydrogen storage materials and ultra-light structural materials for elderly aids.