CN1152969C - Process for preparing particle reinforced Mg-base composite - Google Patents

Abstract

The invention relates to a preparation process of a metal-based composite material, in particular to a preparation process of a designed magnesium-based composite material. The invention provides a method for preparing a particle-reinforced magnesium-based composite material with good comprehensive performance, relatively simple process, low cost, and easy large-scale commercial production. The specific technical plan is: the reaction prefabricated block undergoes self-propagating synthesis reaction under the protection of vacuum or inert gas, so that TiC reinforced particles are formed in situ in metal aluminum, and then the self-propagating reaction product is put into the magnesium alloy melt for dissolution and diffusion, fully After stirring and pouring, the particle-reinforced magnesium-based composite material is prepared. The process includes the preparation of the reaction prefabricated block, the synthesis of reinforced particles by self-propagating high-temperature reaction, the melting and diffusion of self-propagating reaction products in the magnesium alloy matrix, and the use of melt stirring technology. Enhance the dispersion distribution of particles in the magnesium alloy matrix.

Description

Method for preparing particle-reinforced magnesium-based composites by remelting reinforcement-phase carrier

Technical field: The present invention relates to the preparation process of metal matrix composite materials, in particular to the preparation process of magnesium matrix composite materials prepared by remelting reinforcement phase carrier.

Background technology: Metal matrix composites are attracting more and more attention in the automotive and aerospace fields due to their excellent comprehensive properties such as high specific strength, high specific modulus, high hardness, wear resistance and high temperature resistance. So far, the reinforcement methods of magnesium-based composites mainly include continuous fiber (such as carbon fiber, graphite fiber, etc.) reinforcement and discontinuous fiber (such as SiCw whiskers and SiC, B ₄ C and other particles) reinforcement. Due to the complex fiber-reinforced process, high cost, poor wettability with the matrix, and poor machining performance of continuous fiber-reinforced materials, the promotion and application of fiber-reinforced magnesium-based composites are greatly limited, and it is difficult to achieve large-scale production.

In the method of external particle reinforcement, because the surface of the external particle is seriously polluted, the wettability with the matrix is poor, resulting in a series of problems such as poor interfacial bonding between the reinforced particle and the matrix, and a series of problems such as interfacial reactions. At the grain boundary, so the enhancement effect is not ideal.

The preparation methods of particle reinforced metal matrix composites include XD method and contact reaction method. The main process of the XD method (US Patent, U.S.Patent No.4710348) is: powder mixing-powder mixing-compression molding-vacuum degassing-high temperature reaction sintering-extrusion or casting-composite materials. The method can be regarded as two stages: the first stage is to enhance the high-temperature reaction generation of particles, and the second stage is to enhance the dispersion and distribution of particles into the metal matrix. At present, the XD method is mainly used to manufacture particle-reinforced aluminum-based, titanium-based and zinc-based composite materials. The main process of the contact reaction method (Chinese patent, patent number: 93104814) is: powder mixing-powder mixing-compression molding-prefabricated block adding alloy melt-casting. The contact reaction method makes the particle reinforcement phase react in the matrix melt, which simplifies the process. However, due to the strong diffusion of heat into the metal matrix for the self-propagating high-temperature synthesis reaction that generates reinforcing particles in situ in the metal matrix melt, the self-propagating high-temperature synthesis reaction is not complete, and even difficult to maintain. This method is highly skilled in operation, and the process is difficult to master during actual production. The direct contact reaction method is mainly used to manufacture aluminum-based and zinc-based composite materials.

Neither the XD method nor the contact reaction method has ever been used to prepare magnesium matrix composites reinforced with in-situ internal growth particles. At present, for particle-reinforced magnesium-based composites, there are only external particle-reinforced magnesium-based composites, and no report has been seen on the synthesis of reinforced particles by means of self-propagating reactions, and then dissolving and diffusing them into magnesium liquid to prepare particle-reinforced magnesium-based composites. .

Technical content: In order to overcome the above-mentioned shortcomings existing in the prior art, the purpose of the present invention is to provide a method for preparing a particle-reinforced magnesium-based composite material with good comprehensive properties that is relatively simple in process, low in cost, and easy for large-scale commercial production.

The technical solution of the present invention is: the reaction prefabricated block undergoes a self-propagating synthesis reaction under the protection of vacuum or inert gas, so that the TiC reinforced particles are formed in situ in the metal aluminum, and then the self-propagating reaction product is put into the magnesium alloy melt for dissolution and diffusion , fully stirred and poured to prepare particle-reinforced magnesium-based composite materials. The process includes the preparation of reaction prefabricated blocks, the self-propagating reaction generation of reinforced particles, the dissolution, diffusion and dispersion distribution of reinforced particles in the magnesium alloy matrix. The specific steps as follows:

Preparation steps of reaction prefabricated blocks:

a. Composition of prefabricated blocks: prefabricated blocks are composed of Al, C and Ti powders with a particle size ranging from 50nm to 100 μm, Al powder content: weight ratio 5% to 80%; C: Ti=0.8 to 1.2 (atomic ratio);

b. Mixing: Put the above prepared powder into a ball mill, ball mill for 4 to 48 hours, and mix well;

c. Compression molding: Put the uniformly mixed powder into the mold, and press the reaction prefabricated block to 55-95% of the theoretical density at room temperature;

Preparation steps of reinforced particles:

Put the reaction prefabricated block into a vacuum or a heating device with an inert gas protective atmosphere, and heat it to 600-900°C at a heating rate of 5-40°C/min to initiate the self-propagating high-temperature synthesis of TiC reinforced particles and metal aluminum as the reaction product reaction;

Dissolution and diffusion of self-propagating reaction products in magnesium alloy matrix and melt stirring process:

a. Melting of the base alloy: heat the crucible containing an appropriate amount of industrial pure magnesium or magnesium alloy base alloy, which can be protected by protective solvent or protective gas, and the melt temperature is kept at 660-820°C;

For example, in order to prevent the combustion of magnesium alloys during the smelting process, a mixed halogen salt of NaCl, KCl and MgCl can be used as a solvent for protection, and argon can also be used for gas protection, or SF ₆ and CO ₂ composed of a certain proportion can be used. Mixed gas with compressed air for protection, and the melt temperature is kept at 660-820°C.

b. Dissolution and diffusion of self-propagating reaction products: Calculate the amount of self-propagating reaction products containing corresponding TiC-enhanced particle content according to the weight ratio of 1 to 30% TiCp/Mg, and put the self-propagating reaction products into magnesium at 660-820°C In the alloy melt, stir after it dissolves and diffuses;

c. Melt stirring process: the stirring temperature is selected at 660-750°C; the stirring time is selected at 10-45min; the stirring speed is selected at 300-900rpm. The reinforcing particles are evenly dispersed in the magnesium alloy melt by stirring, and then casting is carried out.

d. Cast particle-reinforced magnesium-based composites after refining and degassing.

During the preparation process of the reaction prefabricated block, the optimal composition ratio is: Al content: weight ratio 20%-60%; C:Ti=1.0 (atomic ratio), and the powder particle size is 50nm-44μm.

Ball milling is required for 4 to 24 hours of mixing.

The optimal theoretical density of powder compression molding is 75-85%.

Compared with the existing technology at present, the present invention has the following outstanding advantages:

1) The process is relatively simple, the cost is low, and it is easy to popularize and apply in production. The invention is characterized in that the reinforcing particles are produced in metal aluminum through a self-propagating high-temperature synthesis reaction, and the process is stable and reliable. The reinforced particles are fine, the surface is clean, no pollution, and the wettability with the matrix is good, so it is well combined with the matrix interface, thus improving the comprehensive performance of the composite material. It overcomes the problems of easy oxidation pollution on the surface of the externally reinforced particles, poor wettability with the matrix, and the particles are generally coarse and unevenly distributed, and are easy to segregate at the grain boundary. Unlike the direct contact reaction method, since the reinforcing particles are introduced in the form of self-propagating reaction products, it overcomes the strong diffusion of heat to the metal that is maintained by the self-propagating high-temperature synthesis reaction that generates reinforcing particles in situ in the metal matrix melt. In the matrix, the self-propagating high-temperature synthesis reaction is not carried out completely, and it is even difficult to maintain it, and the technical skills are difficult to master. The metal aluminum in the self-propagating reaction product is the main strengthening element of the magnesium alloy, and has a large solid solubility in magnesium, so the self-propagating reaction product is easy to dissolve and diffuse, and the reinforcing particles react in the metal aluminum through the self-propagating reaction The formed one has good wettability with the matrix, and it is evenly distributed in the matrix after being fully stirred, and the reinforcement effect is remarkable, which greatly improves the mechanical properties of the composite material, as shown in Table 1.

Table 1 Mechanical properties of magnesium alloys and particle-reinforced magnesium matrix composites

Composite material Tensile strength σ _b (Mpa) Yield strength σ _0.2 (Mpa) Elongation (%)

ZM5 230 - 2.0

AZ91D 160 - 3.0

TiC(3% by weight)/ZM5 260 160 6.0

TiC(5% by weight)/AZ91D 240 140 5.0

Note: Metal mold casting is used.

2) Significantly improved casting quality. The existing method of preparing particle-reinforced magnesium-based composites by adding reinforcing particles, because the surface of the reinforcing particles is easy to oxidize and pollute, and has poor wettability with the matrix, the refining agent and degasser cannot be used for sufficient refining and degassing during smelting to prevent the reinforcing particles It is taken away together with slag and air bubbles. The reinforcing particles in the present invention are produced in metal aluminum through self-propagating reaction, and have good wettability with the matrix. Therefore, various refining agents and degassing agents can be used to refine the alloy liquid once or more times to improve the quality of castings. Greatly improved, able to meet the requirements of high-tech products.

3) The size of the reinforced particles prepared by the method of the present invention is between 0.1 μm and 3 μm, generally around 1 μm, the particles are small, round, and nearly spherical, with clean surfaces, good wettability with the matrix, and good interface bonding, significantly improving strengthened by the particles.

4) The reinforcing particles in the particle-reinforced magnesium-based composite material prepared by the method of the present invention are evenly distributed in the matrix, and most of them are distributed in the crystal, so segregation is not easy to occur, and multiple remelting can be performed.

Description of drawings:

Figure 1(a) TiC (50% by weight)/Al self-propagating reaction product microstructure (SEM)

Figure 1(b) XRD pattern of TiC (50% by weight)/Al self-propagating reaction product

Figure 2(a) TiC (10% by weight)/Mg composite microstructure (SEM)

Fig.2(b) Energy spectrum of TiC (10% by weight)/Mg composite

Figure 3TiC (3% by weight)/ZM5 composite microstructure (SEM)

Figure 4 TiC (20% by weight)/AZ91D composite microstructure (SEM)

Detailed ways:

Example 1

Preparation of TiC (20% by weight)/AZ91D composite material

Take Al powder (29 μm, 99.8%), Ti powder (25 μm, 99.5%), carbon powder (50nm, 99.0%), and the matrix magnesium alloy is AZ91D die-casting magnesium alloy ingot. The above three kinds of powders are mixed in the ratio of C: Ti=1.0 (atomic ratio), Al content: 30% by weight in the drum type small ball mill for 24h, and then pressed into a cylindrical reaction of φ55×20 on a 20-ton press For prefabricated blocks, the compaction rate of the green compact is 75% of the theoretical density. The reaction prefabricated block was placed in a vacuum heating device, and the temperature was raised to 800°C at a heating rate of 30°C/min to initiate a self-propagating high-temperature synthesis reaction. The propagating reaction product was added into the AZ91D magnesium alloy liquid at 780°C protected by flux, and fully stirred after the self-propagating reaction product melted and diffused. The stirring temperature was 750°C; the stirring time was 15 minutes; the stirring speed was 350rpm. After the reinforced particles are uniformly dispersed in the magnesium alloy melt, refined and degassed, and finally poured into the metal mold when the melt temperature is 750°C, the particle-reinforced magnesium-based composite material is obtained, and its tensile strength σb≥240MPa.

Example 2,

Preparation of TiC (3% by weight)/ZM5 composite material

Take Al powder (29 μm, 99.8%), Ti powder (25 μm, 99.5%), carbon powder (50nm, 99.0%), and the matrix magnesium alloy is ZM5 cast magnesium alloy. The above three powders are mixed in a drum type small ball mill for 24 hours according to the ratio of C: Ti=1.0 (atomic ratio) and Al content of 60% by weight, and then pressed into a φ55×20 cylindrical reaction prefabrication on a 20-ton press block, the compaction rate of the green compact is 85% of the theoretical density. The reaction prefabricated block is placed in a vacuum heating and pressurizing device, and the temperature is raised to 800°C at a heating rate of 40°C/min to initiate a self-propagating high-temperature synthesis reaction. The self-propagating reaction product is added to the ZM5 magnesium alloy liquid at 750°C protected by flux, and fully stirred after the self-propagating reaction product melts and diffuses. The stirring temperature is 720°C; the stirring time is 40min; the stirring speed is 850rpm. After the reinforced particles are uniformly dispersed in the magnesium alloy melt, refined and degassed, and finally poured into the metal mold when the melt temperature is 720°C, the particle-reinforced magnesium-based composite material is obtained.

Example 3

Preparation of TiC (10% by weight)/Mg composite material

Take Al powder (29 μm, 99.8%), Ti powder (25 μm, 99.5%), carbon powder (50nm, 99.0%), and the matrix magnesium alloy is Industrial No. 1 pure magnesium ingot. The above three powders are mixed in a small roller mill for 24 hours according to the ratio of C: Ti=1.0 (atomic ratio), and the Al content is 45% by weight, and then pressed into a φ55×20 cylindrical reaction prefabrication on a 20-ton press The compaction rate of the compact is 80% of the theoretical density. The reaction prefabricated block is placed in a vacuum heating and pressurizing device, and the temperature is raised to 800°C at a heating rate of 20°C/min to initiate a self-propagating high-temperature synthesis reaction. The self-propagating reaction product is added into the 800°C pure magnesium liquid protected by flux, and fully stirred after the self-propagating reaction product is melted and diffused. The stirring temperature is 750°C; the stirring time is 30min; the stirring speed is 500rpm. After the reinforced particles are evenly distributed in the magnesium alloy melt, they are refined and degassed, and finally poured into the metal mold when the temperature of the melt is 700°C to obtain a particle-reinforced magnesium-based composite material.

Claims (4)

1. The method for preparing particle-reinforced magnesium-based composite materials by remelting the reinforcement phase carrier, which is characterized in that the process includes the preparation of reaction prefabricated blocks, the self-propagating reaction generation of reinforcement particles, the dissolution diffusion and dispersion distribution of reinforcement particles in the magnesium alloy matrix ,Specific steps are as follows: Preparation steps of reaction prefabricated blocks: a. The composition of the prefabricated block: the prefabricated block is composed of Al, C and Ti powders with a particle size range of 50nm to 100 μm, and the weight ratio of the Al powder content is 5% to 80%; C: Ti=0.8 to 1.2 (atomic ratio); b. Mixing: Put the above prepared powder into a ball mill, ball mill for 4 to 48 hours, and mix well; c. Compression molding: Put the uniformly mixed powder into the mold, and press the reaction prefabricated block to 55-95% of the theoretical density at room temperature; Preparation steps of reinforced particles: Put the reaction prefabricated block into a vacuum or a heating device with an inert gas protective atmosphere, and heat it to 600-900°C at a heating rate of 5-40°C/min to initiate the self-propagating high-temperature synthesis of TiC reinforced particles and metal aluminum as the reaction product reaction; Dissolution and diffusion of enhanced particles in magnesium alloy matrix and melt stirring process: a. Melting of the base alloy: heat the crucible containing an appropriate amount of industrial pure magnesium or magnesium alloy base alloy, which can be protected by protective solvent or protective gas, and the melt temperature is kept at 660-820°C; b. Dissolution and diffusion of reinforcing particles: Calculate the amount of self-propagating reaction product containing corresponding TiC reinforcing particle content according to the weight ratio TiCp/Mg of 1-30, and put the self-propagating reaction product into the magnesium alloy melt at 660-820 °C In, stir after it dissolves and diffuses; c. Melt stirring process: the stirring temperature is selected at 660-750°C; the stirring time is selected at 10-45min; the stirring speed is selected at 300-900rpm. Stir to make the reinforced particles uniformly dispersed in the magnesium alloy melt and then cast; d. Cast particle-reinforced magnesium-based composites after refining and degassing. 2. The method for preparing particle-reinforced magnesium-based composite materials according to claim 1, wherein the composition ratio is: Al content: weight ratio 20% to 60%; C:Ti=1.0 (atomic ratio), the powder particle size is 50nm～44μm. 3. The method for preparing particle-reinforced magnesium-based composite materials by remelting the reinforcement phase carrier according to claim 1, characterized in that, ball milling is required for 4 to 24 hours of mixing. 4. The method for preparing particle-reinforced magnesium-based composite materials by remelting the reinforcement phase carrier according to claim 1, characterized in that the theoretical density during powder compaction is 75% to 85%.

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