A method for producing a silicon carbide reinforced aluminum matrix composite

Abstract

The application discloses a preparation method of a silicon carbide reinforced aluminum matrix composite material, and comprises the following steps: mixing raw material powder, a binder and an organic solvent to obtain mixed powder, wherein the raw material powder is composed of silicon carbide powder, sintering aid powder and aluminum alloy powder; the mixed powder is sequentially granulated and sieved to obtain composite powder; the composite powder is molded to obtain a composite material blank; the composite material blank is subjected to degreasing to obtain a degreasing blank; and the degreasing blank is subjected to two-step sintering, wherein the first-step sintering is performed under a nitrogen atmosphere, and the second-step sintering is performed under a vacuum environment. Through the cooperation of various processes in the preparation method, the relative density of the silicon carbide reinforced aluminum matrix composite material can reach more than 98.5%, meanwhile, the silicon carbide particles are uniformly distributed, and the comprehensive mechanical properties of the composite material are excellent.

Description

Technical Field

[0001] This invention belongs to the field of aluminum-based composite material preparation technology, and specifically relates to a method for preparing silicon carbide reinforced aluminum-based composite materials. Background Technology

[0002] Silicon carbide particle-reinforced aluminum matrix composites possess high specific strength and specific modulus, as well as a low coefficient of thermal expansion. This not only meets the high-performance requirements of high-end fields such as aerospace, energy, high-precision machine tools, advanced weaponry, and automobiles, but also allows for processing using traditional metalworking techniques due to their isotropic nature. All these advantages make them promising for applications in high-precision fields and civilian infrastructure. However, current methods for preparing silicon carbide-reinforced aluminum matrix composites mainly involve liquid metal stirring casting, liquid metal impregnation, and powder metallurgy, but these methods suffer from limitations such as uneven microstructure distribution, lengthy processes, low product density, or relatively simple shapes.

[0003] Compared to liquid manufacturing technologies (stirred casting, metal impregnation), powder metallurgy offers advantages such as uniform microstructure (silicon carbide particles uniformly dispersed in an aluminum matrix) and high production efficiency. It involves uniformly mixing powders, cold pressing them into shape, and then sintering to complete the composite process. Its advantages include relatively lower requirements for manufacturing equipment, making it suitable for mass production. However, its disadvantages are also significant. Powder metallurgy products tend to have lower density, higher porosity, and relatively inferior performance. Therefore, for parts with specific mechanical performance requirements, secondary processing (extrusion, rolling, forging, etc.) is necessary for densification.

[0004] Currently, the relatively low sintering density of silicon carbide-reinforced aluminum matrix composites prepared by powder metallurgy is mainly due to two reasons: 1) A dense alumina film exists on the surface of the alumina matrix powder particles, which hinders the metallurgical bonding of the aluminum alloy powder during sintering, making sintering difficult; 2) The aluminum alloy matrix cannot melt during sintering, and the addition of a small amount of sintering aid (such as low-melting-point tin) makes it difficult to achieve complete wetting and filling between particles. To address these two issues, existing processes include hot pressing or hot isostatic pressing, which applies pressure during sintering to break up the oxide film in problem 1), increasing the density of the sintered particles. Many studies also introduce additives that break up the oxide film, such as magnesium, which reacts with the alumina and is consumed, while simultaneously promoting sintering. Other studies introduce nitrogen gas during sintering to induce a nitriding reaction in the surface oxide film, thereby promoting the sintering of aluminum powder particles. Of the solutions mentioned above, hot pressing or hot isostatic pressing can promote sintering and increase sintering density, but it has high energy consumption, and the pressed blank structure is relatively simple (cylindrical ingot, cube, etc.), making it difficult to take advantage of the near-net-shape forming technology of powder metallurgy. Nitrogen sintering can increase the sintering process to a certain extent, but the driving force for subsequent densification is limited, and its sintering density is relatively poor compared with traditional casting and hot pressing methods. Summary of the Invention

[0005] To address the issues of low density and poor performance in existing powder metallurgy processes for preparing silicon carbide particle-reinforced aluminum matrix composites, this invention aims to provide a method for preparing silicon carbide-reinforced aluminum matrix composites. This invention employs a two-step sintering method, which avoids the high energy consumption and simple product structure issues associated with hot pressing and hot isostatic pressing. Simultaneously, it can meet the requirements for high-density and highly uniform microstructure in complex composite materials, effectively enhancing the technological competitiveness of powder metallurgy processes for preparing silicon carbide-reinforced aluminum matrix composites. This method is expected to bring a new breakthrough to the next generation of powder metallurgy processes for preparing silicon carbide-reinforced aluminum matrix composites.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a method for preparing a silicon carbide-reinforced aluminum-based composite material. The method involves mixing raw material powder, a binder, and an organic solvent to obtain a mixed powder, wherein the raw material powder consists of silicon carbide powder, sintering aid powder, and aluminum alloy powder. The mixed powder is then granulated and sieved to obtain a composite powder. The composite powder is then molded to obtain a composite material preform. The composite material preform is then degreased to obtain a degreased preform. The degreased preform undergoes a two-step sintering process. The first sintering is carried out under a nitrogen atmosphere at a temperature of 520-550°C for 30-60 minutes. The second sintering is performed under vacuum at a temperature of 600-640°C for 60-90 minutes. After the two-step sintering process, a silicon carbide-reinforced aluminum-based composite material is obtained.

[0008] The preparation method of this invention employs a two-step sintering method. In the first step, during the oxide film removal reaction stage, a relatively low temperature is used, and a high-flow-rate, high-purity nitrogen atmosphere is introduced. This causes a nitriding reaction in the surface oxide film, accelerating the removal of the oxide film and promoting the sintering of aluminum powder particles. Simultaneously, it can suppress secondary oxidation of the aluminum alloy powder, laying the groundwork for subsequent vacuum sintering. After the oxide film is removed, a liquid phase has formed in the silicon carbide-reinforced aluminum matrix composite material. At this point, the second sintering step is performed using a high-vacuum sintering mode. By increasing the temperature, the liquid phase formed at high temperatures has good wettability with the silicon carbide and aluminum alloy matrix, achieving liquid phase sintering densification. The use of high vacuum can enhance the wettability of the liquid phase, increase the capillary force during the sintering process, and allow the liquid phase to penetrate into the matrix, thereby increasing the sintering density of the composite material.

[0009] Of course, the temperature in the first step should not be too low. If it is too low, the alumina film layer cannot be eliminated, which will make it difficult for the liquid phase to form in the second step or the aluminum alloy substrate will be covered by the oxide film, inhibiting the sintering process. In the second step of sintering, if the temperature is too high or too low, it will not promote the sintering process or will cause over-burning.

[0010] In a preferred embodiment, the sintering aid powder is composed of Mg2Si powder, Al2Cu powder, and Sn powder. The raw material powder has the following composition by mass percentage: 5-20 wt% silicon carbide powder, 1-3 wt% sum of Mg2Si powder and Al2Cu powder, 0.5-1.0 wt% Sn powder, and the balance being aluminum alloy powder.

[0011] In this invention, special sintering aids Mg2Si and Al2Cu are introduced. Under high vacuum conditions, they have good wettability with silicon carbide and aluminum alloy powders, which can accelerate the densification process. In addition, the inventors found that Mg2Si powder can react with the oxide film and accelerate the oxide film removal process.

[0012] In the actual exploration process, the inventors also tried a large number of other sintering aids, none of which could achieve the effect of the sintering aids mentioned above in this invention. For example, when aluminum-magnesium alloy and aluminum-silicon alloy powders were added, the inventors found that they could not break the oxide film, and Cu powder was also difficult to react with the oxide film on the aluminum surface at low temperatures.

[0013] Of course, the amount of Mg2Si powder and Al2Cu powder added in this invention also needs to be effectively controlled. If too little is added, it will not have any effect, and if too much is added, it will reduce the performance of the material itself.

[0014] In a further preferred embodiment, the raw material powder has the following composition by mass percentage: 5-20 wt% silicon carbide powder, 1-2 wt% Mg2Si powder, 0.5-1 wt% Al2Cu powder, 0.5-1.0 wt% Sn powder, with the balance being aluminum alloy powder.

[0015] In a preferred embodiment, the aluminum alloy powder is selected from any one of 2-series aluminum alloys, 6-series aluminum alloys, and 7-series aluminum alloys.

[0016] In a preferred embodiment, the particle size of the silicon carbide powder is 0.2~5.0 μm, more preferably 0.5~3.0 μm. The inventors have found that controlling the particle size of the silicon carbide powder within the above range results in the best performance of the final material. If the particle size is too small, its uniformity in the matrix will decrease, while if the particles are too large, it will affect the sintering densification.

[0017] In a preferred embodiment, the adhesive is selected from at least one of polyethylene glycol, paraffin wax, and rubber, and the amount of adhesive added is 1.0 to 2.0 wt% of the mass of the mixed powder.

[0018] In a preferred embodiment, the organic solvent is selected from at least one of anhydrous ethanol and hexane.

[0019] In a preferred embodiment, the mixing method is ball milling.

[0020] In a preferred embodiment, the granulation method is spray granulation, and the spray granulation temperature is 60~100℃. Spray granulation, because the atomized slurry consists of very fine droplets, has a large specific surface area, resulting in rapid evaporation of moisture from the droplets and quick drying to obtain granulated powder.

[0021] In a preferred embodiment, the average particle size (D50) of the composite powder is 50~100μm.

[0022] In a preferred embodiment, the compression molding pressure is 100~300MPa.

[0023] In a preferred embodiment, the degreasing is carried out under a hydrogen atmosphere at a temperature of 400-450°C, a holding time of 1-3 hours, and a heating rate of 0.5-2°C / min. In this invention, degreasing under a hydrogen atmosphere removes residual carbon from the binder and accelerates the polymer release, allowing it to react completely at a lower temperature.

[0024] In a preferred embodiment, during the first sintering step, the nitrogen flow rate is (1.5~2.0) × V (L / min), where V is the effective volume of the furnace and the positive pressure of the furnace is 1000~2000 Pa. Controlling the nitrogen flow rate within this range in this invention offers two advantages: 1) it accelerates the removal of the oxide film on the surface of the aluminum alloy powder; 2) it eliminates the oxygen atmosphere in the furnace, achieving a low oxygen partial pressure and preventing secondary oxidation of the aluminum alloy powder. For example, if the furnace volume is 5L, the nitrogen flow rate would be (7.5~10) L / min.

[0025] Principles and advantages

[0026] The preparation method of this invention employs a two-step sintering process. In the first step, during the oxide film removal reaction stage, a high-flow-rate, high-purity nitrogen atmosphere is introduced. This causes a nitriding reaction in the surface oxide film, accelerating its removal and promoting the sintering of aluminum powder particles. Simultaneously, it inhibits secondary oxidation of the aluminum alloy powder, paving the way for subsequent vacuum sintering. After the oxide film is removed, a liquid phase has formed in the silicon carbide-reinforced aluminum matrix composite. The second sintering step then takes place using a high-vacuum sintering mode to improve the wettability of the liquid phase and increase capillary forces during sintering, allowing the liquid phase to penetrate into the matrix and increasing the sintering density of the composite material. Secondly, the addition of Mg2Si and Al2Cu components not only helps remove the oxide film but also exhibits good wettability with both silicon carbide and aluminum alloy powders, accelerating the densification process in the second stage. Through the synergistic effect of the various processes in this invention, a silicon carbide-reinforced aluminum matrix composite material with a relative density exceeding 98.5% can be obtained, along with uniform silicon carbide particle distribution and excellent overall mechanical properties. Attached Figure Description

[0027] Figure 1 The morphology and microstructure of the silicon carbide reinforced aluminum matrix composite material obtained by two-step sintering in Example 1.

[0028] Figure 2 Morphology and microstructure of silicon carbide reinforced aluminum matrix composite material prepared by two-step sintering in Comparative Example 1. Detailed Implementation

[0029] Example 1

[0030] (1) First, silicon carbide powder, sintering aid powder, and aluminum alloy powder are mixed, and a small amount of binder and organic solvent are added, followed by ball milling. After ball milling, spray granulation is performed. Since the atomized slurry is in the form of very fine droplets, the specific surface area is very large, which makes the water in the droplets evaporate rapidly and the drying ends quickly, resulting in granulated powder. Then, it is sieved to obtain composite spherical powder.

[0031] The composition of the silicon carbide reinforced aluminum matrix composite material is as follows: the mass fraction of silicon carbide powder is 10 wt%; the sintering aid powder consists of 1 wt% Mg2Si and 1 wt% Al2Cu, and contains 0.5 wt% Sn powder; the balance is aluminum alloy powder, which can be 7075 series aluminum alloy.

[0032] The silicon carbide powder has a particle size of 2.0 micrometers.

[0033] The binder is selected from polyethylene glycol, the binder is 1.0 wt% of the composite powder, and the solvent is anhydrous ethanol.

[0034] Preferably, the spray drying temperature is 70°C, and the average particle size (D50) of the composite powder is preferably 50 micrometers.

[0035] (2) Subsequently, the silicon carbide reinforced aluminum-based composite powder is molded under a pressure of 100 MPa, and the resulting composite material blank is obtained.

[0036] (3) Subsequently, the above-mentioned formed blank is degreased in a hydrogen atmosphere at a temperature of 420°C, a holding time of 2 hours, and a heating rate of 0.5°C / min.

[0037] (4) The two-step sintering preparation method of silicon carbide reinforced aluminum matrix composite material described in this case includes the following steps: the above-mentioned degreased composite material blank is sintered in two steps. The first step is sintering in a high nitrogen flow atmosphere, wherein the sintering temperature is 530℃ and the holding time is 60min; then the furnace is evacuated and the nitrogen supply is stopped. The vacuum sintering temperature is 610℃ and the holding time is 90min. After that, silicon carbide particle reinforced aluminum matrix composite material can be obtained.

[0038] In the first step, the nitrogen flow rate for high nitrogen flow atmosphere sintering is 3.0 (L / min), and the effective volume of the furnace is 2L.

[0039] In the second step, the vacuum sintering process requires a vacuum level of 1.0 × 10⁻⁶ to prevent oxidation of the alloy powder. -4 Pa.

[0040] The silicon carbide reinforced aluminum matrix composite material prepared by this technology can achieve a relative density of 98.7%, a yield strength of 420 MPa, a tensile strength of 380 MPa, an elastic modulus of 110 GPa, and an elongation of 7.4%.

[0041] Example 2

[0042] (1) First, silicon carbide powder, sintering aid powder, and aluminum alloy powder are mixed, and a small amount of binder and organic solvent are added, followed by ball milling. After ball milling, spray granulation is performed. Since the atomized slurry is in the form of very fine droplets, the specific surface area is very large, which makes the water in the droplets evaporate rapidly and the drying ends quickly, resulting in granulated powder. Then, it is sieved to obtain composite spherical powder.

[0043] The composition of the silicon carbide reinforced aluminum matrix composite material is as follows: the mass fraction of silicon carbide powder is 15 wt%; the sintering aid powder consists of 2 wt% Mg2Si and 0.5 wt% Al2Cu, and also contains 0.8 wt% Sn powder; the balance is aluminum alloy powder, which can be 6061 series aluminum alloy.

[0044] The silicon carbide powder has a particle size of 5.0 micrometers.

[0045] The binder is selected from paraffin wax, the binder is 2.0 wt% of the composite powder, and the solvent is n-hexane.

[0046] The spray drying temperature is 60°C, and the average particle size (D50) of the composite powder is preferably 100 micrometers.

[0047] (2) Subsequently, the silicon carbide reinforced aluminum-based composite powder is molded under a pressure of 200 MPa, and the molded composite material blank is obtained.

[0048] (3) Subsequently, the above-mentioned formed blank is degreased in a hydrogen atmosphere at a temperature of 400°C, a holding time of 2 hours, and a heating rate of 1°C / min.

[0049] (4) The two-step sintering preparation method of silicon carbide reinforced aluminum matrix composite material described in this case includes the following steps: the above-mentioned degreased composite material blank is subjected to two-step sintering. The first step is sintering in a high nitrogen flow atmosphere, wherein the sintering temperature is 520℃ and the holding time is 60min; then the furnace is evacuated and the nitrogen gas supply is stopped. The vacuum sintering temperature is 630℃ and the holding time is 60min. After that, silicon carbide particle reinforced aluminum matrix composite material can be obtained.

[0050] In the first step, the nitrogen flow rate for high nitrogen flow atmosphere sintering is 4.0 (L / min), and the effective volume of the furnace is 2L.

[0051] In the second step, the vacuum sintering process requires a vacuum level of 3.0 × 10⁻⁶ to prevent oxidation of the alloy powder. -4 Pa.

[0052] The silicon carbide-reinforced aluminum-based composite material prepared by this technique has a relative density of 98.9%, a yield strength of 450 MPa, a tensile strength of 410 MPa, an elastic modulus of 130 GPa, and an elongation of 6.5%.

[0053] Example 3

[0054] (1) First, silicon carbide powder, sintering aid powder, and aluminum alloy powder are mixed, and a small amount of binder and organic solvent are added, followed by ball milling. After ball milling, spray granulation is performed. Since the atomized slurry is in the form of very fine droplets, the specific surface area is very large, which makes the water in the droplets evaporate rapidly and the drying ends quickly, resulting in granulated powder. Then, it is sieved to obtain composite spherical powder.

[0055] The composition of the silicon carbide reinforced aluminum matrix composite material is as follows: the mass fraction of silicon carbide powder is 20 wt%; the sintering aid powder consists of 2 wt% Mg2Si and 1 wt% Al2Cu, and also contains 1.0 wt% Sn powder; the balance is aluminum alloy powder, which can be 7075 series aluminum alloy.

[0056] The silicon carbide powder has a particle size of 3.0 micrometers.

[0057] The binder is selected from polyethylene glycol, the binder is 1.5 wt% of the composite powder, and the solvent is anhydrous ethanol.

[0058] The spray drying temperature is 80°C, and the average particle size (D50) of the composite powder is preferably 80 micrometers.

[0059] (2) Subsequently, the silicon carbide reinforced aluminum-based composite powder is molded under a pressure of 150 MPa, and the resulting composite material blank is obtained.

[0060] (3) Subsequently, the above-mentioned formed blank is degreased in a hydrogen atmosphere at a temperature of 450°C, a holding time of 2 hours, and a heating rate of 0.5°C / min.

[0061] (4) The two-step sintering preparation method of silicon carbide reinforced aluminum matrix composite material described in this case includes the following steps: the above-mentioned degreased composite material blank is sintered in two steps. The first step is sintering in a high nitrogen flow atmosphere, wherein the sintering temperature is 520℃ and the holding time is 120min; then the furnace is evacuated and the nitrogen gas is stopped. The vacuum sintering temperature is 640℃ and the holding time is 60min. After that, silicon carbide particle reinforced aluminum matrix composite material can be obtained.

[0062] In the first step, the nitrogen flow rate for high nitrogen flow atmosphere sintering is 3.0 (L / min), and the effective volume of the furnace is 2L.

[0063] In the second step, the vacuum sintering process requires a vacuum level of 1.0 × 10⁻⁶ to prevent oxidation of the alloy powder. -4 Pa.

[0064] The silicon carbide reinforced aluminum matrix composite material prepared by this technology can achieve a relative density of 98.5%, a yield strength of 430 MPa, a tensile strength of 390 MPa, an elastic modulus of 150 GPa, and an elongation of 5.4%.

[0065] Comparative Example 1

[0066] The preparation method of this comparative example is basically the same as that of Example 1, except that the silicon carbide powder and sintering aid powder are selected in this comparative example. The sintering aid only uses Sn, omitting Mg2Si and Al2Cu. Other process conditions and parameters are the same as in Example 1. The composite material obtained has a relative density of 97.2%, a yield strength of 320 MPa, a tensile strength of 270 MPa, an elastic modulus of 100 GPa, and an elongation of 4.6%.

[0067] Comparative Example 2

[0068] The preparation method of this comparative example is basically the same as that of Example 1, except that only a nitrogen atmosphere is used for sintering during the sintering process in this comparative example, and nitrogen is still introduced during the subsequent vacuum sintering process without vacuuming. Other process conditions and parameters are the same as those in Example 1. The composite material can be obtained with a relative density of 97.5%, a yield strength of 360 MPa, a tensile strength of 320 MPa, an elastic modulus of 105 GPa, and an elongation of 5.2%.

[0069] Comparative Example 3

[0070] The preparation method of this comparative example is basically the same as that of Example 1, except that the nitrogen flow rate during sintering in this comparative example is only 1.0 L / min. Other process conditions and parameters are the same as those of Example 1. The composite material can be obtained with a relative density of 98.0%, a yield strength of 350 MPa, a tensile strength of 330 MPa, an elastic modulus of 110 GPa, and an elongation of 5.5%.

[0071]

Claims

1. A method for preparing a silicon carbide reinforced aluminum matrix composite material, characterized in that: Raw material powder, binder, and organic solvent are mixed to obtain a mixed powder, wherein the raw material powder consists of silicon carbide powder, sintering aid powder, and aluminum alloy powder. The mixed powder is granulated and sieved to obtain a composite powder. The composite powder is then molded to obtain a composite material blank. The composite material blank is then degreased to obtain a degreased blank. The degreased blank is then subjected to two-step sintering. The first step of sintering is carried out in a nitrogen atmosphere at a temperature of 520~550℃ for 30~60 minutes. The second step of sintering is carried out in a vacuum environment at a temperature of 600~640℃ for 60~90 minutes. After the two-step sintering is completed, a silicon carbide reinforced aluminum matrix composite material is obtained. The sintering aid powder is composed of Mg2Si powder, Al2Cu powder, and Sn powder. The raw material powder has the following composition by mass percentage: 5-20 wt% silicon carbide powder, 1-3 wt% sum of Mg2Si powder and Al2Cu powder, 0.5-1.0 wt% Sn powder, and the balance is aluminum alloy powder.

2. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The raw material powder has the following composition by mass percentage: 5-20 wt% silicon carbide powder, 1-2 wt% Mg2Si powder, 0.5-1 wt% Al2Cu powder, 0.5-1.0 wt% Sn powder, with the balance being aluminum alloy powder.

3. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The aluminum alloy powder is selected from any one of 2-series aluminum alloys, 6-series aluminum alloys, and 7-series aluminum alloys; The silicon carbide powder has a particle size of 0.2~5.0 μm. The binder is selected from at least one of polyethylene glycol, paraffin wax, and rubber, and the amount of binder added is 1.0~2.0 wt% of the mass of the mixed powder. The organic solvent is selected from at least one of anhydrous ethanol and hexane.

4. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The mixing method is ball milling.

5. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The granulation method is spray granulation, and the spray granulation temperature is 60~100℃.

6. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The average particle size of the composite powder is 50~100μm.

7. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The pressure for compression molding is 100~300MPa.

8. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: The degreasing is carried out in a hydrogen atmosphere at a temperature of 400-450°C, for a holding time of 1-3 hours, and at a heating rate of 0.5-2°C / min.

9. The method for preparing a silicon carbide reinforced aluminum matrix composite material according to claim 1, characterized in that: During the first sintering step, the nitrogen flow rate is (1.5~2.0)×V (L / min), where V is the effective volume of the furnace and the positive pressure of the furnace is 1000~2000Pa.

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