Method for preparing SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength through cold spraying

Abstract

The invention discloses a method for preparing a SiCp / Al particle reinforced aluminum-based composite coating with excellent compactness and mechanical strength through cold spraying, and relates to the technical field of material surface engineering, in particular to a method for preparing a SiCp / Al particle reinforced aluminum-based composite coating with excellent compactness and mechanical strength through cold spraying. The invention aims to solve the problems of low density, high defect density and the like in the existing cold spraying process of the SiCp / Al composite coating. The preparation method comprises the following steps: pre-mixing a part of aluminum alloy powder with nano-scale SiC particles by adopting high-speed ball milling to inlay the nano-scale SiC particles on the aluminum alloy powder, then carrying out common mixing with the remaining powder, and then carrying out cold spraying to achieve the purpose of preparing the micron + nano SiCp / Al composite coating. And under the condition that the carrier gas pressure and the gas preheating temperature are not increased, the spraying efficiency of the composite coating reinforcing phase is improved, the porosity of the composite coating is reduced, and the compactness and the mechanical property of the coating are improved.

Description

Technical Field

[0001] The invention relates to the technical field of material surface engineering, in particular to a method for preparing a SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength by cold spraying. Background Art

[0002] In the field of modern materials science and engineering, surface strengthening and repair technology plays a vital role in improving material performance, extending material service life and expanding the scope of material application. As an emerging surface treatment technology, cold spray technology has attracted much attention in recent years and has been widely studied and applied.

[0003] Cold spraying technology is a unique surface strengthening and repair method that uses compressed gas, such as nitrogen, helium, air or their mixed gases as a power source; during the cold spraying process, solid particles are accelerated to extremely high speeds by this power source, and then hit the surface of the substrate at high speed. At the moment of impact, the particles undergo significant plastic deformation, thereby forming a coating. Compared with traditional deposition technologies such as laser, flame, plasma, and arc that require melting materials, the outstanding feature of cold spraying technology is that it can achieve solid deposition of particles at a lower temperature; specifically, during the cold spraying process, the spraying raw material particles will undergo plastic flow due to adiabatic shear instability. This plastic flow allows the particles to firmly adhere to and accumulate on the surface of the substrate, eventually forming a coating; especially for metal particles with good plasticity, such as aluminum, copper, nickel, etc., cold spraying technology can give full play to its advantages and prepare coatings with excellent performance.

[0004] In addition, cold spraying technology has also shown unique advantages in the preparation of aluminum-based composite materials. Aluminum-based composite materials have broad application prospects in many fields due to their excellent comprehensive performance. However, traditional preparation methods often face problems such as material decomposition, oxidation, and grain coarsening when preparing aluminum-based composite materials, which seriously affect the performance and quality of aluminum-based composite materials; cold spraying technology can effectively circumvent these problems, opening up a new path for the research and development of aluminum-based composite coatings, making it possible to prepare high-performance aluminum-based composite coatings.

[0005] As a high-performance material among aluminum-based composite materials, silicon carbide particle reinforced aluminum-based (SiCp / Al) composite material has unique advantages. It breaks through the performance limitations of traditional single materials and achieves an optimized combination of performance through the synergistic effect between the aluminum matrix and the reinforcing phase silicon carbide particles. SiCp / Al composite materials not only have excellent specific strength, specific stiffness and specific modulus, which enable them to maintain good mechanical properties when bearing loads and are not prone to deformation and damage; they also show good thermal conductivity, electrical conductivity, wear resistance and dimensional stability. These excellent properties make SiCp / Al composite materials a representative of outstanding comprehensive performance among aluminum-based composite materials, and have shown great application potential in high-tech manufacturing fields such as aerospace and military industry. For example, in the field of aerospace, SiCp / Al composite materials can be used to manufacture aircraft parts, such as wings, fuselage frames, etc., to reduce the weight of the aircraft, improve fuel efficiency, and enhance the strength and wear resistance of parts. In the military field, it can be used to manufacture key components of weapons and equipment to improve the performance and reliability of equipment.

[0006] However, in actual application scenarios, the performance of SiCp / Al composite coatings is restricted by many factors, among which the porosity and defect density inside the coating are two key factors; when the porosity of the composite coating is too high or the defect density exceeds the standard, the structural integrity of the coating will be destroyed, and then the coating will fail and lose its original protective function; for example, in some application scenarios that require corrosion resistance, excessively high porosity will make it easier for corrosive media to penetrate into the coating, accelerating the corrosion and damage of the coating; when subjected to mechanical loads, the presence of defects will become stress concentration points, causing the coating to be more susceptible to crack propagation and fracture; therefore, reducing the porosity and defect density of SiCp / Al composite coatings and improving the mechanical properties of the coating are of great significance and practical engineering application value for ensuring the reliability of the coating and extending its service life.

[0007] At present, there are some urgent problems to be solved in the process of depositing SiCp / Al composite coatings by cold spraying technology. Since cold spraying technology forms the coating through plastic deformation induced by high-speed impact of powder particles, a series of defects such as voids and unbonded particle boundaries will inevitably appear in the sprayed coating during this process; the existence of these defects will seriously affect the mechanical properties of the coating and reduce the strength and toughness of the coating. During the deformation process, the aluminum alloy matrix with strong plasticity will produce sufficient plastic deformation and form a mechanical interlocking effect between the particles, which is one of the important mechanisms for the formation of the coating; and the SiC particles in the coating mainly play the role of bearing the load, thereby improving the mechanical properties of the coating; although the irregularly shaped SiC particles will have a certain "compacting" densification effect on the coating due to their high drag coefficient and high acceleration, this effect is still not enough to completely eliminate the void defects in the coating, and some void defects will still exist in the coating.

[0008] In addition, during the spraying process, irregularly shaped SiC particles face some problems during deposition. When these SiC particles collide with hard particles at high speed, due to the high contact pressure generated, the particles often do not deform, but rebound from the surface. This rebound phenomenon not only causes erosion or fracture of SiC particles, but also destroys the structural integrity of the coating, resulting in more defects in the coating; ultimately, these factors combined reduce the overall integrity of the entire coating, seriously affecting the overall performance of the coating, making it difficult for the performance of SiCp / Al composite coatings in practical applications to reach the ideal level.

[0009] In summary, the existing cold spraying SiCp / Al composite coating process has problems such as low density and high defect density, which seriously restricts the application and promotion of SiCp / Al composite coating in practical engineering. Therefore, a new method is urgently needed to solve these problems in order to prepare SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength. Summary of the invention

[0010] The present invention aims to solve the problems of low density and high defect density in the existing cold spraying SiCp / Al composite coating process, and provides a method for cold spraying to prepare SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength.

[0011] The present invention provides a method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying, which is specifically carried out in the following steps:

[0012] 1. Weigh nano-SiC particle powder, micron-SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts: aluminum alloy powder I and aluminum alloy powder II;

[0013] 2. High-energy mechanical mixing of nano-SiC particle powder and aluminum alloy powder I is performed using a ball mill to obtain aluminum alloy powder whose surface is inlaid with nano-SiC particles;

[0014] 3. Mechanically mixing aluminum alloy powder whose surface is inlaid with nano-SiC particles, micron SiC particle powder and aluminum alloy powder II to obtain SiCp / Al composite powder;

[0015] 4. Drying and pre-treating the SiCp / Al composite powder before spraying and loading it into the cold spray powder feeder;

[0016] 5. Pre-treat the surface of the aluminum alloy substrate and place it on the fixture waiting for spraying;

[0017] 6. Set cold spray parameters;

[0018] 7. Start the cold spraying equipment and the gas supply equipment, and use high-pressure cold spraying to spray the SiCp / Al composite powder onto the aluminum alloy substrate to obtain a high-density and high-strength SiCp / Al composite coating.

[0019] Advantages of the present invention:

[0020] The present invention uses high-speed ball milling and mechanical mixing technology to prepare micro-nano SiC / Al composite powders combined with high-pressure cold spraying technology to obtain a micro-nano enhanced SiC / Al composite coating with dense structure and uniform SiC dispersion. It has the following advantages:

[0021] 1. The present invention sprays composite powders by cold spraying. Since a layer of nano-SiC is embedded on the surface of the aluminum alloy, the specific surface area of ​​the deposited particles is increased without increasing the carrier gas pressure and the gas preheating temperature, thereby increasing the drag coefficient and acceleration during the particle acceleration process, and ultimately increasing the particle deposition efficiency during the spraying process.

[0022] 2. Since the nano-SiC particles are on the surface of the aluminum alloy particles, when forming the coating, the nano-SiC is mainly distributed at the particle boundaries of the aluminum alloy particles. The filling effect reduces defects such as unbonded particle boundaries and gaps, making the coating denser.

[0023] 3. Since the nano-SiC particles are on the surface of the aluminum alloy particles, when forming the coating, the nano-SiC is mainly distributed at the particle boundaries of the aluminum alloy particles. This diffuse distribution at the particle boundaries can disperse strengthen the overall coating and increase the strength of the overall coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Comparative Example 1: SEM morphology of the surface before and after spherical graphite and the cross-section of the aluminum alloy powder whose surface is inlaid with nano-SiC particles, and EDS energy spectrum; wherein (a) SEM of the aluminum alloy surface before ball milling; (b) SEM of the aluminum alloy surface after ball milling; (c) EDS energy spectrum of the aluminum alloy surface after ball milling - Al; (d) EDS energy spectrum of the aluminum alloy surface after ball milling - Si; (e) SEM of the cross-section of the aluminum alloy after ball milling; (f) EDS energy spectrum of the cross-section of the aluminum alloy after ball milling - Si;

[0025] Figure 2 The surface SEM morphology of the SiCp / Al composite powder obtained in Comparative Example 1; (a) low magnification SEM; (b) high magnification SEM;

[0026] Figure 3 The cross-sectional SEM, porosity and thickness change comparison diagram of the micron SiCp / Al composite coating obtained in Comparative Example 2 and the micro-nano enhanced SiCp / Al coating obtained in Example 1; wherein (a) low-magnification SEM of the micro-nano enhanced SiCp / Al coating; (b) thickness and porosity change of the micro-nano enhanced SiCp / Al coating; (c) high-magnification SEM of the micro-nano enhanced SiCp / Al coating; (d) low-magnification SEM of the micro-enhanced SiCp / Al coating; (e) thickness and porosity change of the micro-enhanced SiCp / Al coating; (f) high-magnification SEM of the micro-enhanced SiCp / Al coating;

[0027] Figure 4 The cross-sectional microscopic morphology comparison diagram of the micron SiCp / Al composite coating obtained in comparative example 3 and the micro-nano enhanced SiCp / Al coating obtained in example 2; (a) SEM of micron enhanced SiCp / Al coating; (b) SEM of micro-nano enhanced SiCp / Al coating. DETAILED DESCRIPTION

[0028] Specific implementation method 1: In this implementation method, a method for cold spraying to prepare a SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength is specifically carried out in the following steps:

[0029] 1. Weigh nano-SiC particle powder, micron-SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts: aluminum alloy powder I and aluminum alloy powder II;

[0030] 2. High-energy mechanical mixing of nano-SiC particle powder and aluminum alloy powder I is performed using a ball mill to obtain aluminum alloy powder whose surface is inlaid with nano-SiC particles;

[0031] 3. Mechanically mixing aluminum alloy powder whose surface is inlaid with nano-SiC particles, micron SiC particle powder and aluminum alloy powder II to obtain SiCp / Al composite powder;

[0032] 4. Drying and pre-treating the SiCp / Al composite powder before spraying and loading it into the cold spray powder feeder;

[0033] 5. Pre-treat the surface of the aluminum alloy substrate and place it on the fixture waiting for spraying;

[0034] 6. Set cold spray parameters;

[0035] 7. Start the cold spraying equipment and the gas supply equipment, and use high-pressure cold spraying to spray the SiCp / Al composite powder onto the aluminum alloy substrate to obtain a high-density and high-strength SiCp / Al composite coating.

[0036] This embodiment adopts high-speed ball milling technology to pre-mix a part of aluminum alloy powder with nano-scale SiC particles, so that the nano-particles are embedded in the aluminum alloy powder, and then mixed with the remaining powder in a normal way. Through this multiple mixing technology, the nano-particles are successfully deposited on the substrate during the spraying process, and the purpose of preparing the micron + nano-SiCp / Al composite coating is achieved. The small particle filling effect of the nano-particles effectively reduces the porosity of the overall composite coating, making the coating more dense. Secondly, since the nano-SiC particles are on the surface of the aluminum alloy particles, when forming the coating, the nano-SiC is mainly distributed at the particle boundary position of the aluminum alloy particles. The overall coating is dispersed and strengthened by this dispersed distribution at the particle boundary, and the strength of the coating is further improved, so that it has excellent mechanical and wear resistance.

[0037] This embodiment adopts nano-SiC particle powder and micron SiC particle powder to mix in a specific ratio, and the nano-SiC particles can be filled into the tiny gap between the micron SiC particles and the aluminum alloy powder, which plays a role in refining the microstructure and reducing the pores. The micron SiC particles provide the main reinforcement, bear the load, and improve the overall mechanical properties of the coating. The two cooperate with each other to help improve the density and mechanical strength of the coating. At the same time, the aluminum alloy powder is divided into two parts and distributed according to a specific mass ratio, one of which is first ball-milled with nano-SiC particles, so that the nano-SiC particles are embedded on the surface of the aluminum alloy powder, increasing the bonding force between the aluminum alloy and the SiC particles; the remaining aluminum alloy powder is subsequently mixed with other powders and ball-milled, which further ensures the uniform distribution of the aluminum alloy in the composite powder, which is conducive to the aluminum alloy matrix to give full play to the plastic deformation ability during the cold spraying process, and form a good mechanical interlocking with the SiC particles, thereby improving the density of the coating and reducing defects.

[0038] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass ratio of the nano-SiC particle powder, micron-SiC particle powder and aluminum alloy powder in step 1 is 3:(15-17):(80-82). Others are the same as specific embodiment 1.

[0039] Specific implementation method three: This implementation method is different from specific implementation method one in that the mass ratio of the aluminum alloy powder I to the aluminum alloy powder II in step one is 25:55. The rest is the same as specific implementation method one.

[0040] Specific embodiment 4: This embodiment differs from specific embodiment 1 in that the particle size of the nano-SiC particle powder in step 1 is 100-999 nm, and the particle size of the micron SiC particle powder is 30-100 μm. Others are the same as specific embodiment 1.

[0041] In this embodiment, the particle size of the aluminum alloy powder is 30 to 100 μm.

[0042] Specific embodiment 5: This embodiment is different from specific embodiment 1 in that: the high-energy mechanical mixing described in step 2 is to mix the nano-SiC particle powder and the aluminum alloy powder I and then put them into the ball mill; first evacuate and then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is (5-10):1, the ball milling speed is 100-400r / min, the ball milling time is 1-10h, bidirectional rotation, the rotation direction is changed every 15min, and the ball milling stops for 5min every 25min. Others are the same as specific embodiment 1.

[0043] Specific implementation example 6: This implementation example is different from the specific implementation example 1 in that the mass fraction of the nano-SiC particles in the aluminum alloy powder whose surface is inlaid with nano-SiC particles in step 2 is 2-25%. The rest is the same as the specific implementation example 1.

[0044] Specific embodiment 7: This embodiment is different from the specific embodiment 1 in that: the mechanical mixing described in step 3 is to mix the aluminum alloy powder with nano-SiC particles embedded on the surface, the micron SiC particle powder and the aluminum alloy powder II and put them into the ball mill; first evacuate and then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is (1-3):1, the ball milling speed is 50-200r / min, the ball milling time is 1-5h, bidirectional rotation, the rotation direction is changed every 15min, and the ball milling stops for 10min every 1h. The rest is the same as the specific embodiment 1.

[0045] Specific embodiment 8: This embodiment differs from specific embodiment 1 in that the mass fraction of the micron SiC particle powder in the SiCp / Al composite powder in step 3 is 5-50%. The rest is the same as specific embodiment 1.

[0046] Specific embodiment 9: This embodiment is different from specific embodiment 1 in that: the surface pretreatment in step 5 is to use 24 mesh white corundum sand to sandblast the aluminum alloy substrate under 0.8 MPa air pressure, then use 99.5% anhydrous ethanol to clean it, and finally dry it with a hair dryer. The rest is the same as specific embodiment 1.

[0047] Specific embodiment 10: This embodiment differs from specific embodiment 1 in that the working carrier gas in the cold spraying parameters in step 6 is nitrogen, the carrier gas pressure is 3.5-7 MPa, the carrier gas preheating temperature is 400-800°C, and the powder feeder speed is 0.5-3 r / min. The rest is the same as specific embodiment 1.

[0048] The beneficial effects of the present invention are verified by the following examples:

[0049] Comparative Example 1: A method for preparing SiCp / Al composite powder is specifically carried out according to the following steps:

[0050] 1. Weigh nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts, aluminum alloy powder I and aluminum alloy powder II; the mass ratio of the nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder is 3:17:80; the mass ratio of the aluminum alloy powder I to the aluminum alloy powder II is 25:55; the particle size of the nano-SiC particle powder is 100-999nm, and the particle size of the micron SiC particle powder is 30-100μm;

[0051] 2. Mix the nano-SiC particle powder and the aluminum alloy powder I in a mass ratio of 3:25 and put them into a ball mill; first evacuate the mixture, then introduce argon gas, and perform dry milling. The ball-to-material ratio is 8:1, the ball milling speed is 300r / min, the ball milling time is 2h, and the rotation direction is changed every 15min. The ball milling stops for 5min after every 25min of ball milling, to obtain an aluminum alloy powder with the surface inlaid with nano-SiC particles;

[0052] 3. Mix aluminum alloy powder with nano-SiC particles on the surface, micron SiC particle powder and aluminum alloy powder II and put them into a ball mill; first evacuate the vacuum, then introduce argon gas, the ball milling process is dry grinding, the ball-to-material ratio is 2:1, the ball milling speed is 200r / min, the ball milling time is 2h, bidirectional rotation, the rotation direction is changed every 15min, and the ball milling is stopped for 10min after every 1h to obtain SiCp / Al composite powder; the mass fraction of micron SiC particle powder in the SiCp / Al composite powder is 17%.

[0053] In order to prevent the aluminum alloy powder from oxidizing during the mixing process, we evacuated the mixing tank and introduced argon gas in advance. Figure 1b It can be seen that the mixed powder is composed of approximately spherical aluminum alloy powder and small-particle SiC powder. Figure 1 Compared with the original aluminum alloy powder of a, no obvious deformation occurred after ball milling. Figure 1 b From the observation, the surface of the spherical aluminum alloy powder is inlaid with some fine particles. The surface of the particles is scanned and analyzed by EDS energy spectrum. As shown in the figure, the surface of the aluminum alloy powder is attached with nano-SiC particles. This is because during the high-speed ball milling process, the hard nano-SiC particles have a mutual mechanical bonding effect similar to pinning and inlaying with the aluminum alloy powder under the action of the grinding ball, and gradually and evenly bond to the surface of the alloy powder as the ball milling time increases. After the ball milling treatment, the composite powder is mixed with the remaining micron-sized SiC and micron-sized aluminum alloy powder to finally obtain a mixed powder.

[0054] After ball milling, the composite powder is mixed with the remaining micron-sized SiC and micron-sized aluminum alloy powders to obtain a mixed powder such as Figure 2 As shown. Figure 2 a It can be seen that the micron SiC particles are evenly distributed in the mixed powder after mixing. Figure 2 b It can be seen that the mixed powder is composed of spherical, irregular and some fine particles.

[0055] Comparative Example 2: A method for preparing SiCp / Al composite powder by cold spraying is specifically carried out in the following steps:

[0056] A pure aluminum plate with a size of 100*100*5mm was taken as the base material, and sandblasted with 24# white corundum sand at an air pressure of 0.8MPa to improve the surface roughness and remove the surface oxide skin, and then cleaned with 99.5% anhydrous ethanol and then dried with a hair dryer; 20wt% micron SiC particle powder and 80wt% aluminum alloy were mechanically mixed to obtain a mixed powder. Then, a high-pressure cold spray method was used to prepare a micron-enhanced SiCp / Al coating, the cold spray carrier gas (nitrogen) pressure was 5MPa, the powder preheating temperature was 650℃, the powder was SiCp / Al composite powder with a mass fraction of 20% micron SiC, and the spray gun moving speed was 200mm / s.

[0057] Embodiment 1: A method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying is specifically carried out in the following steps:

[0058] 1. Weigh nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts, aluminum alloy powder I and aluminum alloy powder II; the mass ratio of the nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder is 3:17:80; the mass ratio of the aluminum alloy powder I to the aluminum alloy powder II is 25:55; the particle size of the nano-SiC particle powder is 100-999nm, and the particle size of the micron SiC particle powder is 30-100μm;

[0059] 2. Mix the nano-SiC particle powder and the aluminum alloy powder I in a mass ratio of 3:25 and put them into a ball mill; first evacuate the mixture, then introduce argon gas, and perform dry milling. The ball-to-material ratio is 8:1, the ball milling speed is 300r / min, the ball milling time is 2h, and the rotation direction is changed every 15min. The ball milling stops for 5min after every 25min of ball milling, to obtain an aluminum alloy powder with the surface inlaid with nano-SiC particles;

[0060] 3. Mix aluminum alloy powder with nano-SiC particles embedded on the surface, micron SiC particle powder and aluminum alloy powder II and put them into a ball mill; first evacuate the vacuum, then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is 2:1, the ball milling speed is 200r / min, the ball milling time is 2h, the rotation direction is changed every 15min, and the ball milling is stopped for 10min every 1h to obtain SiCp / Al composite powder; the mass fraction of micron SiC particle powder in the SiCp / Al composite powder is 17%;

[0061] 4. Drying and pre-treating the SiCp / Al composite powder before spraying and loading it into the cold spray powder feeder;

[0062] 5. Take a pure aluminum plate with a size of 100*100*5mm as the base material, use 24-mesh white corundum sand to sandblast the aluminum alloy substrate under 0.8MPa air pressure, then use 99.5% anhydrous ethanol to clean it, and finally dry it with a hair dryer, and place it on the fixture to wait for spraying;

[0063] 6. Set the cold spray parameters: the working carrier gas is nitrogen, the carrier gas pressure is 5MPa, the carrier gas preheating temperature is 650℃, the powder feeder speed is 0.5~3r / min; the spray gun moving speed is 200mm / s;

[0064] 7. Start the cold spraying equipment and the gas supply equipment, and use high-pressure cold spraying to spray the SiCp / Al composite powder onto the aluminum alloy substrate to obtain a micro-nano enhanced SiCp / Al coating.

[0065] Finally, the sprayed samples were inlaid, ground, polished and etched, and the coating morphology of the samples was observed under different magnifications using a scanning electron microscope (200 FEG field emission SEM). Figure 3 ). The phase composition of the coating and the mechanical properties of the coating were tested and finally compared.

[0066] Figure 3 The coating thickness, porosity and cross-sectional morphology of the micro-nano reinforced composite coating and the micron reinforced composite coating were compared. Figure 3 b and Figure 3 e comparison shows that the porosity of the micro-nano reinforced SiCp / Al coating is significantly lower than that of the micron reinforced SiCp / Al coating, while the thickness of the micro-nano reinforced SiCp / Al coating is significantly higher than that of the micron reinforced SiCp / Al coating. Figure 3 c and Figure 3 f comparison shows that a large number of nano-SiC particles appearing in the micro-nano enhanced composite coating are dispersed in the composite coating, while the single micron enhanced composite coating contains more pores. In comparison, the porosity of the micro-nano enhanced composite coating is reduced by an order of magnitude.

[0067] The measurement results show that the hardness of the micro-nano reinforced coating prepared with the same process parameters is significantly higher than that of the single micron-enhanced composite coating. Under the same gas pressure, the hardness of the micro-nano reinforced composite coating is increased by 13.98% compared with the micron-enhanced coating. This is because the addition of nano-SiC particles increases the density of the composite coating and reduces the defect density of the coating on the one hand, and increases the deposition rate of the particles on the other hand, thereby increasing the deformation of the particles and increasing the overall work hardening degree of the coating. Through calculation, we concluded that the fracture toughness of the micro-nano composite coating is 1.95±0.05MPa·m 1 / 2 , while the fracture toughness of pure micron-reinforced composite coating is 1.75±0.04MPa·m 1 / 2 , compared with the pure micron-reinforced composite coating, the fracture toughness of the micro-nano composite coating increased by 11.4%.

[0068] In this example, by introducing nanoparticles, the spraying efficiency of the reinforcing phase of the composite coating is increased, the porosity of the composite coating is reduced, and the density and mechanical properties of the coating are improved without increasing the carrier gas pressure and the gas preheating temperature.

[0069] Comparative Example 3: A cold spraying preparation method of SiCp / Al composite powder is specifically carried out according to the following steps:

[0070] A pure aluminum plate with a size of 50*50*5mm is taken as a base material, and sandblasted with 24# white corundum sand at an air pressure of 0.8MPa to improve the surface roughness and remove the surface oxide scale, and then cleaned with 99.5% anhydrous ethanol and then dried with a hair dryer; 18wt% micron SiC particle powder and 82wt% aluminum alloy are mechanically mixed to obtain a mixed powder; then a high-pressure cold spraying method is used to prepare a micron-reinforced SiCp / Al coating, the cold spraying carrier gas (nitrogen) pressure is 5MPa, the powder preheating temperature is 650℃, the powder is SiCp / Al composite powder with a mass fraction of 18% micron SiC, and the spray gun moving speed is 200mm / s.

[0071] Embodiment 2: A method for preparing a SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength by cold spraying is specifically carried out in the following steps:

[0072] 1. Weigh nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts, aluminum alloy powder I and aluminum alloy powder II; the mass ratio of the nano-SiC particle powder, micron SiC particle powder and aluminum alloy powder is 3:15:82; the mass ratio of the aluminum alloy powder I to the aluminum alloy powder II is 25:55; the particle size of the nano-SiC particle powder is 100-999nm, and the particle size of the micron SiC particle powder is 30-100μm;

[0073] 2. Mix the nano-SiC particle powder and the aluminum alloy powder I in a mass ratio of 3:25 and put them into a ball mill; first evacuate the mixture, then introduce argon gas, and perform dry milling. The ball-to-material ratio is 8:1, the ball milling speed is 300r / min, the ball milling time is 2h, and the rotation direction is changed every 15min. The ball milling stops for 5min after every 25min of ball milling, to obtain an aluminum alloy powder with the surface inlaid with nano-SiC particles;

[0074] 3. Mix aluminum alloy powder with nano-SiC particles embedded on the surface, micron SiC particle powder and aluminum alloy powder II and put them into a ball mill; first evacuate the vacuum, then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is 2:1, the ball milling speed is 200r / min, the ball milling time is 2h, the rotation direction is changed every 15min, and the ball milling is stopped for 10min every 1h to obtain SiCp / Al composite powder; the mass fraction of micron SiC particle powder in the SiCp / Al composite powder is 15%;

[0075] 4. Drying and pre-treating the SiCp / Al composite powder before spraying and loading it into the cold spray powder feeder;

[0076] 5. Take a pure aluminum plate with a size of 50*50*5mm as the base material, use 24-mesh white corundum sand to sandblast the aluminum alloy substrate under 0.8MPa air pressure, then use 99.5% anhydrous ethanol to clean it, and finally dry it with a hair dryer, and place it on the fixture to wait for spraying;

[0077] 6. Set the cold spray parameters: the working carrier gas is nitrogen, the carrier gas pressure is 5MPa, the carrier gas preheating temperature is 650℃, the powder feeder speed is 0.5~3r / min; the spray gun moving speed is 200mm / s;

[0078] 7. Start the cold spraying equipment and the gas supply equipment, and use high-pressure cold spraying to spray the SiCp / Al composite powder onto the aluminum alloy substrate to obtain a micro-nano enhanced SiCp / Al coating.

[0079] Finally, the sprayed samples were inlaid, ground, polished and etched, and the coating morphology of the samples was observed under different magnifications using a scanning electron microscope (200 FEG field emission SEM). Figure 4 ). The phase composition of the coating and the mechanical properties of the coating were tested and finally compared.

[0080] Figure 4 The cross-sectional morphologies of micro-nano reinforced composite coatings and micron reinforced composite coatings were compared. Figure 4 It can be seen that the cross section of the micro-nano enhanced composite coating is mainly composed of deformed aluminum alloy particles, micron-sized SiC particles and nano-sized SiC particles. Further observation revealed that the main distribution area of ​​nano-sized SiC particles is at the boundary of the deformed aluminum alloy particles. Most of the gaps at the boundary are also filled with nano-sized SiC particles. Figure 4 The main components of the micron-reinforced composite coating in b are deformed aluminum alloy particles and micron-sized SiC particles. Figure 4 a The difference is that there are no nano-sized SiC particles at the boundaries of the deformed particles, but they are composed of a large number of unbonded boundaries and voids.

[0081] Image pro plus measurement shows that the porosity of the micro-nano reinforced SiC / Al coating (0.21±0.08%) is significantly lower than that of the single micro-enhanced SiC / Al coating (1.72±0.07%). When the gas pressure is the same as 4MPa, the hardness of the micro-nano reinforced composite coating is increased by 13.98% compared with the micro-enhanced coating.

[0082] In this example, by introducing nanoparticles, the spraying efficiency of the reinforcing phase of the composite coating is increased, the porosity of the composite coating is reduced, and the density and mechanical properties of the coating are improved without increasing the carrier gas pressure and the gas preheating temperature.

Claims

1. A method for cold spraying a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength, characterized in that The method for cold spraying to prepare SiCp / Al particle reinforced aluminum-based composite coating with excellent density and mechanical strength is specifically carried out in the following steps:

1. Weigh nano-SiC particle powder, micron-SiC particle powder and aluminum alloy powder as raw materials, and divide the aluminum alloy powder into two parts: aluminum alloy powder I and aluminum alloy powder II; 2. High-energy mechanical mixing of nano-SiC particle powder and aluminum alloy powder I is performed using a ball mill to obtain aluminum alloy powder whose surface is inlaid with nano-SiC particles; 3. Mechanically mixing aluminum alloy powder whose surface is inlaid with nano-SiC particles, micron SiC particle powder and aluminum alloy powder II to obtain SiCp / Al composite powder; 4. Drying and pre-treating the SiCp / Al composite powder before spraying and loading it into the cold spray powder feeder; 5. Pre-treat the surface of the aluminum alloy substrate and place it on the fixture waiting for spraying; 6. Set cold spray parameters; 7. Start the cold spraying equipment and the gas supply equipment, and use high-pressure cold spraying to spray the SiCp / Al composite powder onto the aluminum alloy substrate to obtain a high-density and high-strength SiCp / Al composite coating.

2. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The mass ratio of the nano-SiC particle powder, the micron-SiC particle powder and the aluminum alloy powder in step 1 is 3:(15-17):(80-82).

3. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The mass ratio of the aluminum alloy powder I and the aluminum alloy powder II in step 1 is 25:

55.

4. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The particle size of the nano-SiC particle powder in step 1 is 100-1000 nm, and the particle size of the micron SiC particle powder is 30-100 μm.

5. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The high-energy mechanical mixing described in step 2 is to mix the nano-SiC particle powder and the aluminum alloy powder I and then load them into a ball mill; first evacuate the vacuum, then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is (5-10):1, the ball milling speed is 100-400r / min, the ball milling time is 1-10h, bidirectional rotation, the rotation direction is changed every 15min, and the ball milling is stopped for 5min every 25min.

6. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that In step 2, the mass fraction of nano-SiC particles in the aluminum alloy powder whose surface is inlaid with nano-SiC particles is 2-25%.

7. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The mechanical mixing described in step three is to mix the aluminum alloy powder with nano-SiC particles inlaid on the surface, the micron SiC particle powder and the aluminum alloy powder II and then put them into the ball mill; first evacuate the vacuum, then introduce argon gas, the ball milling process is dry milling, the ball-to-material ratio is (1-3):1, the ball milling speed is 50-200r / min, the ball milling time is 1-5h, bidirectional rotation, the rotation direction is changed every 15min, and the ball milling is stopped for 10min every 1h.

8. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that Step 3: The mass fraction of the micron SiC particle powder in the SiCp / Al composite powder is 5-50%.

9. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The surface pretreatment in step 5 is to use 24-mesh white corundum sand to sandblast the aluminum alloy substrate under an air pressure of 0.8 MPa, then use 99.5% anhydrous ethanol to clean it, and finally use a hair dryer to dry it.

10. The method for preparing a SiCp / Al particle reinforced aluminum-based composite coating having excellent density and mechanical strength by cold spraying according to claim 1, characterized in that The working carrier gas in the cold spraying parameters in step six is ​​nitrogen, the carrier gas pressure is 3.5-7 MPa, the carrier gas preheating temperature is 400-800° C., and the powder feeder speed is 0.5-3 r / min.

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