In recent years, there is an increasing demand for the development of super materials with ultra-light, high hardness and high strength in the fields of aviation, aerospace and automobile. Because high damping materials are effective in controlling noise and enhancing the stability of vehicles and equipment, and magnesium alloys have the best vibration absorption properties of all commercial metal materials, Magnesium and magnesium alloys have attracted more and more interest from researchers.
Magnesium has low density, high specific strength and specific modulus, good thermal conductivity and excellent damping and damping performance, and is rich in metal deposits, salt lakes and oceans in the surface of the earth's crust. Magnesium is one of the most potential materials in the modern high-tech field. However, the corrosion resistance, wear resistance, high temperature performance, creep resistance and strength of magnesium alloys are poor. These defects limit the further application of magnesium alloys.
Therefore, researchers began to seek a new material with good mechanical properties and damping properties at the same time, magnesium matrix composites become one of the best choices. Through the design of reinforcement, the properties of magnesium alloy can be effectively improved, and the prepared magnesium matrix composites can show excellent properties that any component does not have, such as high specific stiffness and specific strength. Good dimensional stability and excellent damping performance. In addition, magnesium matrix composites also have electromagnetic shielding and hydrogen storage characteristics, which is an excellent structural and functional material, and it is also one of the composites with great application potential in the field of high and new technology.
Since the research of magnesium matrix composites was carried out in the late 1980s, magnesium matrix composites have become another light metal matrix composites with broad application prospects and competitiveness after aluminum matrix composites. It has been more and more widely used in aerospace, automobile, electronics, transportation industry and other fields.
According to the types of reinforcements, magnesium matrix composites can be divided into particle reinforced, whisker reinforced, short fiber reinforced, carbon nanotube reinforced, discontinuous fiber reinforced and continuous fiber reinforced magnesium matrix composites.
Cf/Mg Composites and their advantages in Properties.
Carbon fiber reinforced magnesium matrix (Cf/Mg) composite is a kind of metal matrix composite with high specific strength, high specific modulus and good thermal stability, which is based on magnesium or magnesium alloy and reinforced by carbon fiber. Cf/Mg composites have high specific strength, specific stiffness and good damping properties, thermoelectric conductivity and thermal stability. The material has the advantages of light weight, high structural efficiency and good dimensional stability, and can meet the requirements of aerospace structural materials. It is an ideal material for aerospace, weapons, electronics and other high-tech industries.
Compared with other metal materials or carbon fiber resin matrix composites, Cf/Mg composites have the following advantages:
1. Low density.
Magnesium alloy is the lowest density alloy in common engineering metals. Compared with other commonly used alloys, such as iron, copper, zinc, nickel, titanium, aluminum and so on, magnesium alloy has lower density and higher specific strength. The composites prepared by using it as matrix alloy have lower density than those with other alloy matrix. Table 1 shows that 50% volume fraction of carbon fiber is combined with different alloys, and the density of carbon fiber composites is calculated, in which the density of Cf/Mg composites is much lower than that of other metal-based carbon fiber composites. It is slightly higher than that of resin matrix composites, which greatly reduces the density of the whole metal matrix composites on the premise of ensuring the metal properties.
Compared with carbon fiber resin matrix composites, high density has always been the soft rib of carbon fiber metal matrix composites, and the low density of Cf/Mg composites makes its advantages in weight loss become as prominent as resin based carbon fiber composites.
2. High specific strength and specific modulus.
Cf/Mg composite is a composite made of carbon fiber and magnesium, in which excellent mechanical properties of carbon fiber is the main force in the composite, magnesium alloy as the matrix alloy mainly plays the role of connecting carbon fiber and transferring load. Because of the excellent high specific strength and high specific modulus of carbon fiber, Cf/Mg composites can be endowed with the same high specific strength and modulus.
3. Heat conduction and conductivity.
Carbon fiber has good conductive and thermal conductivity, and the higher the degree of graphitization, the better its conductive and thermal conductivity. Taking the carbon fiber product of Toray Company of Japan as an example, the thermal conductivity of Toray T300 high strength medium mold carbon fiber is 6.5W/ (m / K). The thermal conductivity of M55J high strength and high modulus carbon fiber is as high as 150W/ (m / K). Table 2 shows the thermal conductivity of different materials. It is found that the thermal conductivity of M55J high strength and high modulus carbon fiber is superior to that of some metals and similar to that of magnesium.
4. Low coefficient of expansion.
Carbon fiber has a very low coefficient of thermal expansion along the fiber direction, and its axial thermal expansion coefficient is negative. Therefore, adding a certain amount of carbon fiber to the magnesium matrix can not only greatly improve the strength and modulus of the material. At the same time, the thermal expansion coefficient of the material can be reduced obviously. .
In terms of specific modulus and thermal stability, high strength and high modulus carbon fiber reinforced magnesium matrix composites are the highest among all kinds of materials. When the content of high strength and high modulus carbon fiber is about 50%, the thermal expansion coefficient of carbon fiber reinforced magnesium composites is almost zero.
5. Stable performance and high machining accuracy.
Compared with resin-based carbon fiber composites, C/Mg composites do not have the problems of aging, decomposition, moisture absorption, natural degradation of properties and high fatigue resistance. Space use will not decompose low molecular substances that pollute the instrument and the environment. Due to the effect of resin withdrawal, the machining accuracy of carbon fiber resin matrix composites is not high, but in Cf/Mg composites, due to the existence of alloy stiffness, the machining accuracy of carbon fiber matrix composites is much higher than that of resin based carbon fiber composites. It changes the limited situation of carbon fiber composites in the situation of high dimensional accuracy, and makes carbon fiber composites suitable for higher precision requirements.