CN1073636C - Aluminium-bath self-overgrowth reaction process - Google Patents

Abstract

The invention relates to a method for preparing particle-reinforced aluminum-based composite materials, which is characterized in that: the aluminum or aluminum alloy melt is used as a heat source and a protective medium to generate self-propagating reaction to synthesize reinforcement phase particles or to form a coating on the surface of reinforcement phase particles. The aluminum-based composite material with SiC, graphite, TiC, _TiB2 , etc. as the reinforcement phase not only expands the types of reinforcement phases, but also makes the prepared materials have excellent properties, and simplifies the preparation process and related equipment, reducing production costs .

Description

Method for preparing particle-reinforced aluminum matrix composites by self-propagating reaction in aluminum bath

The invention relates to a method for preparing particle-reinforced aluminum-based composite materials.

There are many preparation processes for particle-reinforced aluminum matrix composites. According to whether the reinforcing phase particles are added from the outside or generated inside the matrix, these processes can be roughly divided into two categories: one is the forced external addition method; the other is the in-situ reaction composite method. .

The so-called forced external addition method means that the reinforcement phase particles are added to the matrix from the outside. At present, the processes commonly used in this type of method mainly include: powder metallurgy method, spray deposition method, stirring casting method, etc.

The preparation process of powder metallurgy and spray deposition is complex and costly, and it shows extremely high cost barriers even in the field of aerospace and defense with high performance requirements.

The stirring casting method disperses the reinforcing phase particles into the aluminum alloy melt through strong mechanical stirring, and its cost is relatively low. Since the reinforcing phase particles are often non-wettable with the aluminum alloy melt, external force must be applied to overcome the thermodynamic surface barrier and viscous resistance, so that the particles are dispersed in the melt. Dural has realized the industrial production of aluminum matrix composites by using vacuum stirring technology, but the complicated mechanical stirring device and vacuum technology increase the difficulty of operation (see US Patent 4,786,467). This method has great limitations on the particle size and volume fraction of the reinforcement phase. The particle diameter is generally greater than 10 μm and the volume fraction is less than 40%. The particles are prone to specific gravity segregation in the melt, and dendrite segregation is easy to form during solidification, resulting in uneven particles. distributed.

The coating method is to form a coating wetted with the aluminum alloy on the surface of the reinforcement phase particles by certain processes, thereby improving the wettability of the reinforcement phase particles and the metal melt. For example, electroless plating is used to form Cu and Ni coatings on the surface of graphite or SiC particles, and then mechanical stirring is used to disperse the coated graphite, SiC and other reinforcement phase particles into the aluminum alloy melt. However, this method increases the coating process and significantly increases the cost, and the formed Cu coating is easily oxidized and melted at high temperature, and the oxidized or melted coating cannot improve the wettability of the particles and the aluminum alloy melt. However, the electroless Ni coating is easy to react with aluminum to form brittle phases such as NiAl ₃ , which reduces the performance of the composite material.

The in-situ reaction composite method uses two or more elements to react with each other in the matrix to generate reinforcing phase particles inside the matrix to achieve the purpose of strengthening the matrix. Compared with the forced external addition method, it has the following advantages: ①The reinforcement phase is generated inside the matrix, and the surface is clean and free of pollutants; ②The interface between the reinforcement phase and the matrix is clean and well combined; ③The in-situ-generated reinforcement phase has fine particles and uniform distribution; ④The amount of reinforcement phase can be adjusted within a wide range. However, the in-situ reaction method cannot currently prepare aluminum matrix composites with graphite, SiC, etc. as the reinforcing phase.

The in-situ reaction composite method to prepare particle-reinforced aluminum matrix composites mainly includes the VLS technology proposed by Koczak et al. (see M.J.Koczak, M.K.PremkumarJOM.January 1993 44-48); .Shtessel; Mater.Sci.Eng.; A187(1994) 189~119) and the XD technology of American Martin Company (see Tao Chunhu, Zhang Shaoqing, etc., Materials Engineering, 1994, No. 11, 10~12).

The principle of VLS technology is to pass an inert gas containing carbon or/and nitrogen into a high-temperature aluminum alloy melt, and use the carbon or/and nitrogen generated by gas decomposition to undergo a rapid chemical reaction with Ti in the alloy to synthesize fine TiC or/and TiN particles. However, this method needs to use an inert gas as a carrier, and because the reaction heat of the synthesis reaction is not used, the temperature of the aluminum alloy melt must be very high to decompose the gas and carry out the synthesis reaction. In addition, the types of reinforcement phase particles are limited, and currently only aluminum-based composite materials such as TiC and TiN as reinforcement phases can be prepared.

The SHS technology is about mixing the various powders required to form the product in proportion and compacting the compact, placing the compact in an inert atmosphere, and igniting it to cause a self-propagating reaction to synthesize a composite material. This method has been used to prepare Al-matrix composites with TiC and _TiB2 as reinforcing phases. The reaction process of this method needs to be carried out under the protection of an inert atmosphere. The prepared material has more pores and needs subsequent processing, which increases the preparation cost of the material. When the content of the reinforcing phase is low, it cannot be synthesized by reaction, which undoubtedly increases The difficulty of the process operation. In addition, this method cannot prepare aluminum-based composite materials with graphite, SiC, etc. as the reinforcing phase.

XD technology is the development of SHS technology, that is, the various powders required to form the product are mixed in proportion and compacted, and then the mixture is placed in an inert atmosphere and heated at a certain heating rate to allow the reaction to occur spontaneously. Occurs throughout the mixture to synthesize reinforcing phase particles. The XD technique differs from the SHS technique in the way the reaction proceeds. In the SHS technology, the reaction process relies on the spread of the combustion wave to proceed successively, while in the XD technology, the reaction basically occurs simultaneously in the entire mixture. Due to the simultaneous release of reaction heat, XD technology can usually reach higher adiabatic temperatures than SHS technology. It solves the problem that when the SHS technology is used, due to the low heat release of the intermetallic reaction, the system cannot be maintained because the high adiabatic temperature cannot be reached, but it cannot solve the problem that the inert atmosphere needs to be used for protection in the SHS technology. The prepared material contains pores and needs subsequent processing. It is also unable to prepare aluminum-based composite materials with graphite, SiCp, etc. as reinforcement phases.

Chen Ziyong of Harbin Institute of Technology and others proposed a melt direct reaction synthesis process, that is, adding TiO ₂ and flux mixture to aluminum or aluminum alloy melt to prepare A1 ₃ Ti/aluminum composite materials, or adding TiO ₂ , KBF ₄ and Flux mixture to prepare TiB ₂ /aluminum composites. But this method has the following disadvantages: due to the use of oxides and salts as reaction raw materials, the reaction process is very complicated and difficult to control; the volatilization of low melting point salts makes the operating environment worse; the reaction is carried out at the interface between the slag layer and the aluminum melt, and the reaction speed Limited, increasing the difficulty of operation.

The purpose of the present invention is to provide a preparation process of aluminum-based composite material, which not only expands the types of reinforcing phases, but also simplifies the preparation process and related equipment, and reduces production costs.

In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: use aluminum or aluminum alloy melt as heat source and protection medium, produce self-propagating reaction to synthesize reinforcement phase particles or form a coating on the surface of reinforcement phase particles to produce SiC, graphite , TiC, TiB ₂ etc. are the aluminum-based composite materials of the reinforcing phase, the method comprising:

① Aluminum bath self-propagating reaction synthesis: first melt aluminum or aluminum alloy and overheat to 750°C~1050°C, then mix Ti powder, B ₄ C powder, and aluminum powder in a weight ratio of 3:1:(2~4) Mix or mix Ti powder, graphite powder, and Al powder according to the weight ratio of 4:1:(2～3), and press into a compact; then press the compact into the above melt, 1- After 2 minutes, the outer layer of the compact is heated to the melt temperature, triggering the synthesis reaction, and in-situ synthesis of TiB ₂ and TiC reinforced particles; the heat generated by the reaction further increases the temperature of the compact, so that the reaction continues until the entire The reaction of the compact is completed; the aluminum powder in the compact is used as a diluent to make the reaction easy to control, to avoid the interruption of the reaction due to the bursting of the briquette due to the excessive reaction, and the addition of aluminum powder is conducive to the dispersion of the reaction product; after the reaction is completed, Stir gently to disperse the reaction product in the melt, and then cast it to produce an aluminum-based composite material with TiC and _TiB2 as the reinforcing phase; the volume of the reinforcing phase in the composite material can be adjusted by changing the number of briquettes added Fraction.

② Aluminum bath self-propagating reaction coating: firstly, aluminum or aluminum alloy is melted and overheated to 750°C-1050°C; then Ti powder and graphite powder are mixed according to weight ratio (0.3-1): 2 and pressed into a compact, Or mix Ti powder and SiC powder according to the weight ratio (0.3~1): 2 and press it into a compact; then add the compact to the melt, and after 1 to 2 minutes, the outer layer of the compact is heated to the melt temperature, triggering the synthesis reaction, and the heat generated by the reaction further increases the temperature of the compact, so that the reaction continues until the entire compact reaction is completed. Due to the excessive amount of graphite and SiC in the compact and the small amount of Ti, the surface layer of graphite or SiC participates in the reaction, thereby forming a coating on the surface of these reinforcing phases. Excessive graphite, SiC, like aluminum powder, acts as a dilution to make the reaction process go on smoothly. Gently stir to make the reaction product evenly disperse into the melt, and then cast to make TiC-coated graphite or SiC particle-reinforced aluminum-based composite material; changing the amount of briquettes can adjust the reinforcement phase in the composite material. Volume fraction.

In the present invention, since the self-propagating reaction occurs inside the aluminum alloy melt, the reinforcement phase particles or the coating on the surface of the reinforcement phase particles are generated inside the melt, and compared with the above-mentioned existing methods, it has the following significant advantages:

① Using aluminum melt as a heat source and protective medium, the self-propagating reaction occurs in a closed aluminum melt, avoiding the ignition device and protective atmosphere required for general self-propagating reactions.

② By changing the amount of compacts added, the content of reinforcement phase can be adjusted in a wide range, which solves the problem that the general self-propagating reaction method can only prepare composite materials with high content of reinforcement phase.

③Adjust the composition and proportion of the powder in the compact to realize the in-situ formation of coatings on the surface of graphite or SiC reinforcement phase particles, so that the coating preparation process is simple and effective, making these particles that cannot be synthesized in situ by XD technology and SHS technology It can also be easily and uniformly dispersed in the aluminum alloy melt.

④ Due to the good wettability of the reinforcement phase particles or coatings generated in situ by the self-propagating reaction with the metal melt, the reinforcement phase particles can be dispersed into the melt by stirring at a low speed in the air, avoiding the agitation casting method. Complicated vacuum stirring device and inert gas protection system, the process is simple and the cost of material preparation is low.

⑤ The in-situ-generated reinforcement phase particles or the coating on the surface of the reinforcement phase particles are well bonded to the interface of the matrix, and the prepared material has excellent performance.

The present invention will be further described in detail according to the examples below.

Example:

Aluminum bath self-propagating reaction synthesis:

① Evenly mix Ti powder, B ₄ C powder and Al powder with a particle size of 20 μm in a weight ratio of 3:1:3 and press into a compact, and press the compact into an aluminum melt that is superheated to 850°C to 950°C . After 1 minute, the briquette undergoes a self-propagating reaction, according to the reaction formula , in situ generation of TiC, TiB ₂ enhanced phase. After the reaction is complete, stir to disperse the reaction product, and then cast it into shape. Viewed from the fracture of the casting, the particles are evenly distributed. TiC and TiB ₂ particle-reinforced Al composites with volume fractions of 4% and 10% respectively were prepared by changing the amount of compacts added.

② Evenly mix Ti powder, 20μm B ₄ C powder, and lead powder in a weight ratio of 3:1:4 and press into a compact, and press the compact into an Al-Cu or Al-Si alloy overheated to 850°C to 950°C in the melt. After 1 minute, the briquette undergoes a self-propagating reaction, and TiC and TiB ₂ reinforcement phases are formed in situ. After the reaction is completed, the product is stirred to disperse, and then cast into shape. Viewed from the fracture of the casting, the particles are evenly distributed. By changing the number of briquettes added, the composite materials with volume content of 4% and 10% TiC and TiB ₂ reinforced aluminum alloy matrix were prepared.

③ Evenly mix Ti powder, graphite powder, and 20-30 μm aluminum powder in a weight ratio of 4:1:3 and press into a compact, and press the compact into an aluminum melt at 850°C-950°C. After 1 minute, the compact was induced by the aluminum melt to undergo a self-propagating reaction, and TiC particles were formed in situ. After the reaction is complete, stir to disperse the briquette and cast it into shape. Seen from the casting fracture, the particle distribution is uniform. TiC/aluminum composites with TiC volume fractions of 4% and 10% were prepared by changing the amount of compacts added.

④ Evenly mix Ti powder, graphite powder, and aluminum powder in a weight ratio of 4:1:2 and press into a compact, and press the compact into an Al-Cu or Al-Si alloy melt that is superheated to 850°C to 950°C middle. After 1 minute, a self-propagating reaction occurred in the compact, and TiC particles were generated in situ in the aluminum alloy melt. After the reaction is complete, stir to disperse the briquette and cast it into shape. Seen from the casting fracture, the particle distribution is uniform. TiC/Al alloy composites with TiC volume fractions of 4% and 10% were prepared by changing the amount of compacts added.

Aluminum bath self-propagating reactive coating

⑤ Evenly mix Ti powder and 20-30 μm graphite powder in a weight ratio of 0.5:2, press into a compact, and press the compact into an aluminum melt superheated to 850°C to 950°C. After 1 to 2 minutes, the outer layer of the compact reacts, and then spreads to the entire compact, forming a TiC coating on the surface of the graphite particles. Stir with a graphite rod to evenly disperse the compact into the melt, and then cast it into shape. From the perspective of the casting fracture, the graphite is evenly distributed. Grp/Al composites with graphite volume fractions of 4%, 8%, and 12% were prepared by changing the amount of briquettes added.

⑥ Evenly mix Ti powder and 20-30 μm graphite powder in a weight ratio of 1:2, and press into a compact, and press the compact into an Al-Si or Al-Cu melt overheated to 750-850 °C, After 1 to 2 minutes, the self-propagating reaction occurs, and a TiC coating is formed in situ on the surface of the graphite particles. Stir with a graphite rod, and then cast into shape. From the perspective of the casting fracture, the graphite is evenly distributed. The graphite-aluminum alloy composites with graphite volume fractions of 4%, 8%, and 12% were prepared by changing the amount of briquettes added, so that the briquettes were evenly dispersed into the melt.

⑦ Evenly mix Ti powder and 14-20 μm SiC powder at a weight ratio of 0.5:2 and press into a compact, and press the compact into an aluminum melt superheated to 950°C to 1050°C. After 1 to 2 minutes, the outer layer of the compact reacts, and then spreads to the entire compact, forming a coating in situ on the surface of the SiC particles. Stir to disperse the compact into the melt, and then cast it into shape. Seen from the fracture surface of the casting, SiC is evenly distributed. SiC/Al composites with SiC volume fractions of 4%, 8%, 12%, and 20% were prepared by changing the amount of compacts added.

⑧ Mix Ti powder and 14-20μm SiC powder uniformly in a weight ratio of 1:2 and press into a compact, and press the compact into an Al-Si or Al-Cu melt overheated to 850°C-950°C. After 2 minutes, the briquette undergoes a self-propagating reaction to generate a coating in situ on the surface of the SiC particles. Stir to disperse SiC particles into the melt, and then cast into shape. Seen from the fracture surface of the casting, SiC is evenly distributed, and SiC/Al alloy composites with SiC volume fractions of 4%, 8%, 12%, and 20% are prepared.

Claims (2)

1. The method for preparing particle-reinforced aluminum-based composite materials by aluminum bath self-propagating reaction is characterized in that: using aluminum or aluminum alloy melt as a heat source and a protective medium, a self-propagating reaction is generated to synthesize reinforcement phase particles to prepare SiC, graphite, TiC, Aluminum-based composite materials such as TiB ₂ as the reinforcing phase: first melt the aluminum or aluminum alloy and overheat it to 750°C~1050°C, then mix Ti powder, B ₄ C powder, and aluminum powder in a weight ratio of 3:1:(3~ 4) or mix Ti powder, graphite powder, and Al powder in a weight ratio of 4:1:(2-3), press into compacts, and then press the compacts into the above melt. After 1-2 minutes, the outer layer of the compact is heated to the melt temperature, triggering the synthesis reaction, and the reaction heat generated by the reaction further increases the temperature of the compact, so that the reaction continues until the entire compact is completed; The aluminum powder in the billet is used as a diluent, which makes the reaction easy to control and facilitates the dispersion of the reaction product; lightly stirs to disperse the reaction product in the melt; and then casts to obtain an aluminum base with TiC and _TiB2 as the reinforcing phase. Composite material; adjust the volume fraction of the reinforcing phase in the composite material by changing the amount of green compact added. 2. The method for preparing particle-reinforced aluminum-based composite materials by self-propagating reaction in an aluminum bath is characterized in that: using aluminum or aluminum alloy melt as a heat source and a protective medium, a self-propagating reaction is generated to form a coating on the surface of the reinforcing phase particles to prepare SiC, Aluminum-based composite materials with graphite, TiC, _TiB2 , etc. as the reinforcing phase: first melt the aluminum or aluminum alloy and overheat it to 750 ° C ~ 1050 ° C, then mix Ti powder and graphite powder in a weight ratio (0.5 ~ 1): 2 ratio Mixing and pressing into a compact, or mixing Ti powder and SiC powder in a weight ratio (0.5-1): 2 and pressing into a compact, and then adding the compact to the melt. After 1-2 minutes, the outer layer of the compact is heated to the melt temperature, triggering the synthesis reaction, and the reaction heat generated by the reaction further increases the temperature of the compact, so that the reaction continues until the entire compact is completed; There is too much graphite or SiC in the compact, and the amount of Ti is small. Only the surface layer of graphite or SiC is consumed, so that a coating is formed on the surface of these reinforcement phases. Excessive graphite, SiC, like aluminum powder, acts as a dilution to make the reaction process stable. Carry out; slightly stir, so that the particles after the reaction are evenly dispersed in the melt, and then cast, that is, the coated graphite or SiC particle reinforced aluminum matrix composite material is obtained; change the amount of the briquette to adjust the reinforcement phase in the composite material volume fraction.