Whether the preparation process of carbon fiber reinforced magnesium matrix composites is appropriate or not determines the properties, structural characteristics, application scope and prospect of the composites to a certain extent. At present, the commonly used preparation processes of carbon fiber reinforced magnesium matrix composites mainly include powder metallurgy, liquid infiltration, stirring casting and so on.
1. Powder metallurgy method.
Powder metallurgy method is based on the principle of powder metallurgy, the matrix powder and reinforced fiber are mechanically mixed according to the proportion required by the design. Then the method of pressing, sintering or directly hot pressing, hot rolling and hot extrusion of the mixture to prepare magnesium matrix composites. The main advantage of magnesium matrix composites prepared by powder metallurgy is that the matrix pure magnesium or magnesium alloy does not have to go through the high temperature state of full melting, so it can avoid the strong oxidation of magnesium alloy caused by casting method. Serious reactions occur at the interface between the matrix and the reinforcements. In addition, the fibers are uniformly distributed in the matrix, which makes the magnesium matrix composites have better comprehensive mechanical properties. .
Another advantage of powder metallurgy is that it has no restriction on the type of reinforcement and can change the ratio of reinforcement to matrix to prepare magnesium matrix composites with high volume fraction reinforced phase. However, the manufacturing cost of powder metallurgy process is high, the production equipment is complex, and it is difficult to manufacture billets and parts with too large size. Therefore, powder metallurgy method is widely used in laboratory research, and it is difficult to be widely used in practical production.
two。. Liquid infiltration method.
Liquid infiltration method, also known as melt infiltration method, is a preparation method of solidifying composite materials by infiltrating liquid metal into the pores of porous preforms of reinforced materials under certain conditions. Liquid metal infiltration with or without external pressure, commonly used can be divided into non-pressure infiltration, vacuum infiltration and vacuum pressure infiltration.
2.1 pressure infiltration method.
Pressure infiltration, also known as extrusion casting, is a method of making composite materials by making reinforced particles into preforms, adding liquid magnesium alloy and then pressing the molten magnesium alloy into the preform. The characteristics of the pressure infiltration method are as follows: under the action of high pressure, the liquid metal can infiltrate into the fiber preform, promote the wetting between the magnesium alloy melt and the fiber, and effectively eliminate the defects such as micropores and shrinkage holes in the composites. The obtained composites have dense microstructure and better mechanical properties. The preparation period of this method is short and the quality of the parts is good. Its disadvantage is that the preparation process of prefabrication system is complex and the cost is high. .
2.2 pressureless infiltration method.
Pressureless infiltration method is a method for the preparation of metal matrix composites by spontaneous infiltration of reinforced fiber preforms without external pressure. The pressure-free infiltration method has the advantages of simple process, low cost and controllable volume of reinforcements. However, the pressure-free infiltration method needs to be carried out at a relatively high temperature, and the infiltration rate is low, the process cost is higher, at the same time, there are interface reactions, there are many micro-defects, which reduces the properties of the material.
2.3 vacuum pressure immersion method.
Vacuum pressure immersion method is a method to prepare metal matrix composite products by pressing liquid metal into the pores of preforms made of reinforced materials under the combined action of vacuum and high pressure inert gas. It is characterized in that dipping is carried out in vacuum and solidified under pressure, so the products have no casting defects such as porosity, porosity and shrinkage, compact structure and mechanical properties of composites. In addition, the process parameters of this method can be easily controlled and serious interfacial reactions can be avoided. However, its equipment is more complex, the process cycle is long, the efficiency is low, the preparation of large-size parts requires large-scale equipment. .
3. Stirring casting method.
The stirring casting method is that the fiber reinforcement is directly added to the matrix metal melt, the fiber is uniformly dispersed by stirring, and then cast into ingot or casting to produce fiber reinforced magnesium matrix composites. It is often combined with other methods to prepare composite materials.
The stirring casting method has the advantages of low equipment input, simple process, convenient operation, low production cost, and can produce large volume composite materials, which is suitable for large-scale production. However, as-cast composites are easy to form pores. Therefore, it is necessary to adopt appropriate follow-up technology for as-cast composites, such as extrusion, which can reduce the porosity, make the microstructure dense and the fiber distribution more uniform, which is helpful to improve the mechanical properties of the composites.