(1) Powder metallurgy composite method

The basic principle of the powder metallurgy composite method is the same as the conventional powder metallurgy method, including sintering forming method, sintering blanking and plasticizing method, processing forming method, etc. Suitable for the preparation and molding of dispersion-reinforced composite materials (particle-reinforced or fiber-reinforced composite materials). The main advantages of the powder metallurgy composite method are: the composition of the base metal or alloy can be freely selected, and the reaction between the base metal and the strengthening particles is not easy to occur; the type and size of the strengthening particles can be freely selected, and a variety of particles can be strengthened; the strengthening particles The range of addition amount is large; it is easier to achieve particle uniformity. Disadvantages are: complex process and high cost; product shape and size are limited; uniform dispersion of fine reinforced particles is difficult; the interface between particles and matrix is ??not as good as cast composite materials, etc.

(2) Casting solidification forming method

The casting solidification forming method is to composite the base metal in a molten state. The main methods include stirring casting method, liquid phase infiltration method and *** spray deposition method. Cast solidification molded composite materials have the characteristics of simple process and good product quality, and are widely used in industry.

1. Primary casting compound method

The primary casting compound method (also known as liquid contact reaction synthesis technology Liquid Contact Reaction: LCR) is to add the raw materials for producing reinforced particles to the molten matrix In metals, chemical reactions at high temperatures are used to strengthen the phase, which is then shaped by casting. The characteristics of this process are that the bonding state between the particles and the matrix material is good, the particles are small (0.25 ~ 1.5 μm), uniformly dispersed, and the content can be as high as 40%, so high-performance composite materials can be obtained. Commonly used element powders include titanium, carbon, boron, etc., and compound powders include Al2O3, TiO2, B2O3, etc. This method can be used to prepare A1-based, Mg-based, Cu-based, Ti-based, Fe-based, and Ni-based composite materials. The strengthening phase can be boride, carbide, nitride, etc.

2. Stirring casting method

Stirring casting method, also known as blending casting method, etc., is to add ceramic particles to the molten metal, stir it evenly and then pour it into the mold to obtain the product or Secondary processing of blanks, this method is easy to implement, can be produced in large quantities, and the cost is low. This method is widely used in the preparation of aluminum-based composite materials, but its main disadvantage is that the combination of matrix metal and reinforcing particles is limited. There are two reasons: ① It is easy for chemical reactions to occur between the reinforced particles and the base metal of the melt; ② The reinforced particles are not easily dispersed evenly in alloy melts such as aluminum alloys. This is due to the poor lubricity of ceramic particles and aluminum alloys. , another problem is that ceramic particles are prone to segregation between dendrites together with solute atoms.

3. Semi-solid composite casting method

The semi-solid composite casting method is developed from the semi-solid casting method. Usually when metal solidifies, primary crystals grow in the form of dendrites. When the solid phase ratio reaches about 0.2%, the dendrites form a continuous network skeleton and lose macroscopic fluidity. If the liquid metal is strongly stirred during the cooling process from the liquid phase to the solid phase, the dendritic network skeleton will be broken and the dispersed granular tissue shape will be retained, suspended in the remaining liquid phase. This granular non-dendritic microstructure will The tissue still has certain rheology when the solid phase ratio reaches 0.5% to 0.6%. The semi-solid alloy remaining in the liquid-solid phase can be rheologically cast due to its rheology; the semi-solid slurry also has thixotropy, and the rheological ingot can be reheated to the solid and liquid phase change points to soften. Due to the die-casting The shearing action at the gate and the mold wall can restore the rheology and fill the mold. Reinforced particles or short fiber reinforced materials are added to the semi-solid alloy that is subject to strong stirring. Due to the dispersion and capture effect of the spherical broken grains of the semi-solid slurry on the added particles, it not only prevents the agglomeration and segregation of the particles, but also makes the particles uniform in the slurry. distribution, improves wettability and promotes interfacial bonding.

4. Impregnation solidification method (MI technology)

The impregnation solidification method is a method of immersing a pre-prepared reinforced phase formed body containing higher porosity into the molten base metal. , a method of preparing composite materials by allowing the matrix metal to penetrate into the preform and then solidify it. There are two methods: pressure impregnation and non-pressure impregnation. The impregnation method is suitable for the preparation of composite materials with poor wettability between the strengthening phase and the molten matrix metal. The content of the strengthening phase can be as high as 30% to 80%; the reaction between the strengthening phase and the molten metal is suppressed, making deflection less likely to occur. However, when particles are used as the reinforcing phase, the preparation of the preform is more difficult, and whiskers and short fibers are usually used to prepare the preform. It is difficult for molten metal to penetrate into the interior of the preform, making it difficult to prepare large-size composite materials.

5. Centrifugal casting method

The centrifugal casting method is widely used in the casting and forming of hollow parts. Bimetallic layered composite materials can be formed through two casting methods. This method is simple. It has the advantages of low cost and high casting density, but the interface quality is difficult to control and it is difficult to form continuous long-dimension composite materials.

6. Pressurized solidification casting method

This method is to pour the molten metal into the mold and then apply pressure to solidify the molten metal under pressure. The metal is under high pressure from liquid to solidification, so it can be fully impregnated, fed and prevented from producing pores, resulting in dense castings. The method of combining casting and forging is also called squeeze casting, liquid die forging, forging and casting, etc. The pressurized solidification casting method can prepare more complex MMCs parts and can also be partially reinforced.

Since composite materials are easy to be combined under pressure in the molten state, the combination is very strong and parts with high mechanical properties can be obtained. The composite billet made at this high temperature is more convenient for secondary molding and can be subjected to various heat treatments to meet various requirements for materials.

7. Hot dip plating and reverse solidification method

Hot dip plating and reverse solidification methods are both methods used to prepare continuous long-dimension cladding materials. Hot dip plating is mainly used for continuous coating of wires, mainly controlling the length of the coating area and the speed of the core wire passing through the area. The reverse solidification method uses a thin strip as the master strip and passes through the reverse solidifier at a certain pulling speed. Since the speed of the master strip is much lower than the speed of the molten metal, a sufficiently large supercooling zone is formed near the surface of the master strip. degree, the molten metal begins to solidify and grow on the surface of the master strip, and a pair of rollers arranged above the reverse solidifier play the role of flattening and welding at the same time.

8. Vacuum casting method

The vacuum casting method is to first wind the continuous fiber on a winding machine, and then use decomposable organic polymer compounds such as polymethacrylic acid to make a semi-cured fiber. belt, put the preform into the mold, and heat it to 500°C to decompose the organic polymer. One end of the mold is immersed in the matrix metal liquid, and the other end is evacuated to suck the metal liquid into the mold cavity and soak the fibers.

(3) Spray forming method

Spray forming, also known as spray deposition (Spray Forming), uses inert gas to atomize metal into tiny droplets and make them move in a certain direction. During the injection process, it meets the enhanced fine particles sent by another route of inert gas. Together with the injection, they are deposited on a platform with a water-cooled substrate and solidified into a composite material. The solidification process is relatively complex and is related to the atomization of the metal, the deposition and solidification conditions, or the feeding angle of the reinforcement. Premature solidification cannot recombine, and too late solidification will cause the reinforcement to float and sink and become unevenly distributed. The advantage of this method is that the process is fast, large-scale metal segregation and grain coarsening can be suppressed, interface reactions in the composite material are avoided, and the reinforcements are evenly distributed. The disadvantages are that the raw materials are taken away by the air flow and deposited on the effector wall, resulting in greater losses. There is also the porosity of the composite material and easy looseness. There are two preparation processes using the spray forming principle: additive method (inert spray form-ing) and reaction method (reactive spray forming). The Osprey process studied by Osprey Metals is a representative of the injection molding method. The contact time between the reinforced particles and the molten metal is short, and the interface reaction is effectively suppressed. The reactive spray deposition method is a method that automatically generates reinforced ceramic particles in metal mist or matrix.

(4) Laminated composite method

Laminated composite method is to first composite different metal plates by diffusion bonding method, and then use ion sputtering or molecular beam epitaxy method to alternately combine them. Thin layers of different metals or metals and ceramics are laminated together to form metal matrix composites. This kind of composite material has good performance, but the process is complicated and difficult to put into practical use. At present, the application of this material is not widespread. In the past, it was mainly used in small quantities or on trials in aviation, aerospace and other military equipment. Now it is trying to transfer to the civilian direction, especially in the automobile industry, which has good development prospects.

(5) In-situ generation composite method

The in-situ generation composite method is also called reaction synthesis technology. The reaction synthesis method of metal matrix composite materials refers to the use of chemical reactions to produce materials under certain conditions. A composite method that generates one or several thermodynamically stable reinforcing phases in situ in the matrix metal. This reinforcing phase is generally ceramic particles with high hardness, high elastic modulus and high temperature strength, that is, oxides, carbides, chlorides, borides, and even silicides. They are often combined with traditional metal materials, such as Al, Mg , Ti, Fe, Cu and other metals and their alloys, or (NiTi) (, AlTi) and other intermetallic compounds are compounded to obtain structural materials or functional materials with excellent properties.

The in-situ composite process of metal matrix composites can basically overcome a series of problems that often occur in other processes, such as poor infiltration of the matrix and reinforcements, brittleness caused by interface reactions, uneven distribution of reinforcements, and problems with tiny components. (submicron and nanoscale) reinforcements are extremely difficult to composite, etc. It has received widespread attention as a breakthrough new process method, including direct oxidation method, self-propagation method and in-situ crystal growth method.

1. Direct oxidation (DIMON) method

The direct oxidation method uses oxidizing gas to directly oxidize metal alloy liquid under certain process conditions to form composite materials. Usually the temperature of the direct oxidation method is relatively high, and adding an appropriate amount of alloy elements such as Mg, Si, etc. can speed up the reaction speed. The strength and toughness of this type of composite material depend on the state of the particles and the final microstructure morphology. Since the formed reinforcements can be judged by alloying and reaction thermodynamics, composite materials with different types of reinforcements can be produced through alloying and furnace atmosphere control.

2. Exothermic dispersion (XD) method

The basic principle of exothermic dispersion composite technology (Exothermic Dispersion) is to uniformly mix the reinforced phase reaction materials and metal-based powders in a certain proportion Mix, cold press or hot press molding to form a compact, which is heated at a certain heating rate and kept at a certain temperature (usually higher than the melting point of the matrix and lower than the melting point of the reinforcement phase) to make each component of the reinforcement phase An exothermic chemical reaction occurs between them to generate an enhanced phase. The reinforcement phase is small in size and dispersedly distributed. XD technology has many advantages: ① There are many types of reinforcing phases that can be synthesized, including borides, carbides, silicides, etc.; ② The volume percentage of reinforcing phase particles can be controlled by controlling the proportion and content of reinforcing phase component materials; ③ Reinforcement The size of the phase particles can be controlled by adjusting the heating temperature; ④ Various MMCs can be prepared; ⑤ Since the reaction is carried out in the molten state, it can be further formed near the final shape. XD technology is one of the most effective processes for synthesizing particle-reinforced metal-based and intermetallic compound-based composite materials. However, products made by the XD process have the problem of larger porosity. Currently, direct compaction during the reaction process is generally used to increase density.

3. SHS-cast infiltration method

SHS-cast infiltration method is a combination of self-propagating high temperature synthesis technology (Self-Propagating High Temperature Synthesis) and liquid casting method of metal matrix composite materials A new technology that combines the two processes of in-situ synthesis of reinforced particles and casting molding. Currently, the SHS-cast infiltration method is one of the competitive reaction synthesis processes, but process control is very difficult. The typical process is: using the high temperature of the alloy melt to ignite the solid SHS system in the casting mold, and forming a composite coating on the surface of the casting by controlling the positions of the reactants and products. It can synthesize and densify the SHS material and make the casting The forming and surface coating preparation are completed simultaneously.

4. Reactive Spray Deposition Technology (RSD)

The reactions used to generate ceramic particles by the Reactive Spray Deposition process include gas-liquid reaction, liquid-liquid reaction, and solid- liquid reaction and salt addition reaction. It combines the advantages of rapid solidification and powder metallurgy, and overcomes the shortcomings in the spray deposition process, such as the close mechanical combination of particles and matrix, and the volume fraction of the reinforcement phase cannot be too high. It has become an important direction in the current research on metal matrix composite materials. one. The reactive spray deposition process is as follows: before the metal liquid is atomized, highly active solid particles are sprayed into the liquid to cause a liquid-solid reaction, causing the sprayed particles to dissolve during the atomization process and react with one or more elements in the matrix to form a stable The size of the dispersed phase can be controlled by controlling the cooling rate of the spray and subsequently the cooling rate of the blank.