High-si content cold sprayed al-mg-si composite coating and method of making same

Abstract

The application belongs to the technical field of material corrosion prevention, and particularly relates to a high-Si-content cold-sprayed Al-Mg-Si composite coating and a preparation method thereof. The Al-Mg-Si composite coating is prepared by cold spraying on a pretreated substrate using spherical Al powder, Mg powder, Si powder and Al2O3 ceramic powder as raw materials. The coating is prepared at a low working temperature, has the characteristics of solid-state deposition at a low temperature, has a small thermal influence on the substrate, has no oxidation, grain growth, phase transformation and low residual tensile stress during the spraying process. The addition of Al2O3 ceramic powder can reduce the porosity of the coating and increase the density of the structure. The addition of a proper amount of Si element further enhances the protection effect of the coating, improves the corrosion rate inhibition capacity of the coating and improves the mechanical properties of the composite material. Heat treatment at the selected annealing temperature can enhance the performance of the coating and has no influence on the performance of the substrate itself.

Description

Technical Field

[0001] This invention belongs to the field of materials corrosion protection technology, specifically relating to a high Si content cold-sprayed Al-Mg-Si composite coating and its preparation method. Background Technology

[0002] Corrosion is one of the main causes of steel material failure. For the structural materials of marine equipment that are exposed to harsh environments such as the ocean atmosphere for extended periods, corrosion protection is particularly important. There are many methods for protecting steel, with metal protective coatings being the most widely used. Cold spraying is a spraying technique that utilizes high-pressure gas to carry powder particles axially into a spray gun, generating a supersonic airflow. After being accelerated by the airflow, the powder particles impact the substrate surface in a completely solid state, causing significant plastic deformation and depositing onto the substrate surface to form a coating. Compared to coating technologies such as hot-dip galvanizing, thermal spraying, and laser cladding, cold spraying requires a lower operating temperature, and phenomena such as phase transformation, oxidation, and grain growth during the coating preparation process are effectively improved.

[0003] Due to its abundant reserves and significant passivation properties, Al has become one of the preferred materials for metal protective coatings. However, in seawater, the passivation film of Al coatings will be affected by Cl. - The corrosion eventually develops into pitting corrosion. To improve the anodic properties of Al, elements such as Mg and Si are often added. Adding an appropriate amount of Mg can not only improve the sacrificial capacity of the coating, but also reduce the accumulation of corrosion products, forming a harder shell-like protective layer, which greatly improves the corrosion resistance and service life of the coating. The addition of Si can form a dense protective film, effectively cutting off the contact between water, oxygen and metal, and inhibiting the corrosion rate. Especially in the metal cross-section, since the cut surface exposes the metal substrate, red rust may initially form, but over time, the effect of Si will cause the coating components to dissolve, forming a dense protective film, thereby inhibiting corrosion of the cross-section.

[0004] The Al-Mg-Si materials disclosed in "The effect of Mg and Si content on the microstructure, texture and bendability of Al-Mg-Si alloys" have the following shortcomings:

[0005] (1) Structure stability problem: When the content of certain elements (such as strontium) in the alloy is too high, needle-like phases will be generated. These phases will agglomerate at the grain boundaries, which will reduce the electrical conductivity and mechanical properties of the alloy.

[0006] (2) Poor formability: Aluminum alloys have relatively poor formability, especially when performing certain forming processes (such as 180° flanging), cracking is likely to occur. This is mainly due to the influence of factors such as the texture of the alloy, the morphology, size and quantity of Fe-containing phases, the size of recrystallized grains, and grain boundary precipitates.

[0007] (3) Performance changes during processing: During processing, such as solution treatment and aging treatment, the properties of the alloy will be affected by a variety of factors, such as temperature and time. Inappropriate processing conditions may lead to a decline in alloy properties, such as overheating and uneven distribution of precipitates.

[0008] (4) Influence of alloying elements: The content and type of elements in an alloy have a significant impact on its properties. For example, an increase in Cu content will reduce its plasticity.

[0009] Therefore, developing Al-Mg-Si materials that combine high strength and excellent corrosion resistance while ensuring excellent formability and casting performance is of great significance to the development of the shipbuilding industry. Summary of the Invention

[0010] To overcome the shortcomings of the prior art, the present invention provides a high Si content cold-sprayed Al-Mg-Si composite coating and its preparation method.

[0011] The preparation method of high Si content cold-sprayed Al-Mg-Si composite coating, the specific steps are as follows:

[0012] (1) Pretreatment of the matrix;

[0013] First, use acetone for ultrasonic cleaning to remove oil stains, then use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate, which includes steel Q235.

[0014] (2) Cold spray composite powder onto the pretreated substrate;

[0015] The composite powder is obtained using spherical Al powder, Mg powder, Si powder and Al2O3 ceramic powder as raw materials (all raw materials were purchased from Beijing Tianchengyu Company);

[0016] The composite powder, by elemental mass percentage, consists of 70-85 wt.% Al, 7-10 wt.% Mg, and 5-20 wt.% Si, with the Al2O3 ceramic powder added at 10% wt% of the total mass of the spherical Al powder, Mg powder, and Si powder.

[0017] The composite powder is obtained by mechanically mixing aluminum powder, magnesium powder, silicon powder and Al2O3 ceramic powder to fully and uniformly mix for no less than 30 minutes. Then, the powder is bagged, vacuum-sealed and dried in a vacuum drying oven at 70°C for 2 hours.

[0018] During the cold spraying process, the powder feeding gas and working gas are compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the gas heating temperature is 400℃, and the powder feeding rate is 50g / min.

[0019] During cold spraying, the distance between the spray gun and the substrate surface is 12mm, and the relative moving speed between the spray gun and the substrate is 5-8mm / s.

[0020] (3) The Al-Mg-Si composite coating is vacuum encapsulated and then subjected to diffusion annealing heat treatment at 400-600℃ for 8 hours. After being taken out and air-cooled to room temperature, the heat-treated coating is obtained.

[0021] The cold-sprayed Al-Mg-Si composite coating obtained by this invention can be used for long-term corrosion protection of steel in various complex environments, including the atmosphere and the ocean.

[0022] Beneficial effects of this invention:

[0023] (1) The present invention uses cold spraying technology to prepare the coating at a low working temperature, which has the characteristics of solid deposition at low temperature, has little thermal impact on the substrate, and has no oxidation, grain growth, or phase transformation during the spraying process, and low residual tensile stress.

[0024] (2) The present invention uses a cold spray process to prepare the target coating, which is simple; the added Al2O3 ceramic phase powder can reduce the porosity of the coating and increase the density of the structure.

[0025] (3) The present invention adds an appropriate amount of Si element, which further enhances the protective effect of the coating, improves the coating’s ability to inhibit corrosion rate and improves the mechanical properties of the composite material.

[0026] (4) In this invention, heat treatment of the coating at the selected annealing temperature can enhance the coating performance without affecting the performance of the body itself. Attached image description:

[0027] Figure 1 This is a cross-sectional scanning electron microscope image of the Al-Mg-8Si coating prepared in Example 1 of the present invention.

[0028] Figure 2 This is a cross-sectional scanning electron microscope image of the Al-Mg-12Si coating prepared in Example 2 of the present invention.

[0029] Figure 3This is a cross-sectional scanning electron microscope image of the Al-Mg-16Si coating prepared in Example 3 of the present invention.

[0030] Figure 4 This is a cross-sectional scanning electron microscope image of the Al-Mg-20Si coating prepared in Example 4 of the present invention.

[0031] Figure 5 This is a cross-sectional scanning electron microscope image of the Al-Mg-12Si coating prepared in Example 5 of the present invention.

[0032] Figure 6 This is a cross-sectional scanning electron microscope image of the Al-Mg-12Si coating prepared in Example 6 of the present invention.

[0033] Figure 7 This is a cross-sectional scanning electron microscope image of the Al-Mg-12Si coating prepared in Example 7 of the present invention.

[0034] Figure 8 This is a cross-sectional scanning electron microscope image of the Al-Mg-1Si coating prepared in Comparative Example 1 of this invention.

[0035] Figure 9 This is a cross-sectional scanning electron microscope image of the Al-Mg-12Si coating prepared in Comparative Example 2 of this invention.

[0036] Figure 10 The electrochemical test results are shown for the Al-Mg-Si composite coatings in the embodiments and comparative examples of the present invention after immersion in 3.5% NaCl solution for 480 h.

[0037] Figure 11 The hardness test results of the Al-Mg-Si composite coatings in the various embodiments and comparative examples of the present invention are shown. Detailed Implementation

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0039] Example 1

[0040] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0041] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0042] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0043] (4) Prepare the ingredients according to the following ratio: Al 85wt.%, Mg 7wt.%, Si 8wt.%, and then add 10%wt of Al2O3 ceramic powder (total mass of spherical Al powder, Mg powder, and Si powder). Mix thoroughly and dry in a vacuum drying oven for 2 hours.

[0044] (5) The powder feeding gas is compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the powder feeding temperature is 400℃, the powder feeding amount is 50g / min, the distance between the spray gun and the substrate is 12mm, and the spray gun moving speed is 6mm / s. Cold spray composite coating is prepared using these parameters.

[0045] (6) After shaping and rigorous inspection, a cold-sprayed Al-Mg-Si composite coating is obtained.

[0046] (7) The sample was sealed in vacuum and subjected to diffusion annealing heat treatment at 500°C for 8 hours, and then taken out and air-cooled to room temperature.

[0047] (8) Solder the wires with a soldering gun and encapsulate them with resin, exposing only the test surface.

[0048] (9) The packaged sample was immersed in a 3.5% NaCl solution for 480 h and then subjected to electrochemical testing.

[0049] (10) Two batches of samples were encapsulated with hot-mounted powder, and only the test surface was exposed to conduct a neutral salt spray test using 5% NaCl solution.

[0050] Hardness testing was performed using a microhardness tester.

[0051] Example 2

[0052] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0053] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0054] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0055] (4) Prepare the ingredients according to the following ratio: Al 81wt.%, Mg 7wt.%, Si 12wt.%, and then add Al2O3 ceramic powder with a total mass of 10%wt of spherical Al powder, Mg powder, and Si powder. After mixing thoroughly, place the mixture in a vacuum drying oven and dry for 2 hours.

[0056] (5)-(10) Same as Example 1;

[0057] Hardness testing was performed using a microhardness tester.

[0058] Example 3

[0059] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0060] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0061] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0062] (4) Prepare the ingredients according to the following ratio: Al 77wt.%, Mg 7wt.%, Si 16wt.%, and then add 10%wt of Al2O3 ceramic powder (total mass of spherical Al powder, Mg powder, and Si powder). Mix thoroughly and dry in a vacuum drying oven for 2 hours.

[0063] (5)-(10) Same as Example 1;

[0064] Hardness testing was performed using a microhardness tester.

[0065] Example 4

[0066] (1) Build the XY automation platform and check the operation of the spraying robot;

[0067] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0068] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0069] (4) Prepare the ingredients according to the following ratio: Al 73wt.%, Mg 7wt.%, Si 20wt.%, and then add 10%wt of Al2O3 ceramic powder (total mass of spherical Al powder, Mg powder, and Si powder). Mix thoroughly and dry in a vacuum drying oven for 2 hours.

[0070] (5)-(10) Same as Example 1;

[0071] Hardness testing was performed using a microhardness tester.

[0072] Example 5

[0073] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0074] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0075] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0076] (4) Prepare the ingredients according to the following ratio: Al 79wt.%, Mg 9wt.%, Si 12wt.%, and then add 10%wt of Al2O3 ceramic powder (total mass of spherical Al powder, Mg powder, and Si powder). Mix thoroughly and dry in a vacuum drying oven for 2 hours.

[0077] (5)-(10) Same as Example 1;

[0078] Hardness testing was performed using a microhardness tester.

[0079] Example 6

[0080] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0081] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0082] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0083] (4) Prepare the ingredients according to the following ratio: Al 81wt.%, Mg 7wt.%, Si 12wt.%, and then add Al2O3 ceramic powder with a total mass of 10%wt of spherical Al powder, Mg powder, and Si powder. After mixing thoroughly, place the mixture in a vacuum drying oven and dry for 2 hours.

[0084] (5) The powder feeding gas is compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the powder feeding temperature is 400℃, the powder feeding amount is 50g / min, the distance between the spray gun and the substrate is 12mm, and the spray gun moving speed is 6mm / s. Cold spray composite coating is prepared using these parameters.

[0085] (6) After shaping and rigorous inspection, a cold-sprayed Al-Mg-Si composite coating is obtained.

[0086] (7) The sample was sealed in a vacuum and subjected to diffusion annealing heat treatment at 400°C for 8 hours, and then taken out and air-cooled to room temperature.

[0087] (8)-(10) Same as Example 1;

[0088] Hardness testing was performed using a microhardness tester.

[0089] Example 7

[0090] (1) Set up the XY automation platform and check the operation of the spraying robot;

[0091] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0092] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0093] (4) Prepare the ingredients according to the following ratio: Al 81wt.%, Mg 7wt.%, Si 12wt.%, and then add Al2O3 ceramic powder with a total mass of 10%wt of spherical Al powder, Mg powder, and Si powder. After mixing thoroughly, place the mixture in a vacuum drying oven and dry for 2 hours.

[0094] (5) The powder feeding gas is compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the powder feeding temperature is 400℃, the powder feeding amount is 50g / min, the distance between the spray gun and the substrate is 12mm, and the spray gun moving speed is 6mm / s. Cold spray composite coating is prepared using these parameters.

[0095] (6) After shaping and rigorous inspection, a cold-sprayed Al-Mg-Si composite coating is obtained.

[0096] (7) The sample was sealed in a vacuum and subjected to diffusion annealing heat treatment at 600°C for 8 hours, and then taken out and air-cooled to room temperature.

[0097] (8)-(10) Same as Example 1;

[0098] Hardness testing was performed using a microhardness tester.

[0099] Comparative Example 1

[0100] (1) Build the XY automation platform and check the operation of the spraying robot;

[0101] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0102] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0103] (4) Prepare the ingredients according to the following ratio: Al 92wt.%, Mg 7wt.%, Si 1wt.%, and then add 10%wt of Al2O3 ceramic powder (total mass of spherical Al powder, Mg powder, and Si powder). Mix thoroughly and dry in a vacuum drying oven for 2 hours.

[0104] (5) The powder feeding gas is compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the powder feeding temperature is 400℃, the powder feeding amount is 50g / min, the distance between the spray gun and the substrate is 12mm, and the spray gun moving speed is 6mm / s. Cold spray composite coating is prepared using these parameters.

[0105] (6) After shaping and rigorous inspection, a cold-sprayed Al-Mg-Si composite coating is obtained.

[0106] (7) The sample was sealed in vacuum and subjected to diffusion annealing heat treatment at 500°C for 8 hours, and then taken out and air-cooled to room temperature.

[0107] (8) Solder the wires with a soldering gun and encapsulate them with resin, exposing only the test surface.

[0108] (9) The packaged sample was immersed in a 3.5% NaCl solution for 480 h and then subjected to electrochemical testing.

[0109] (10) Two batches of samples were encapsulated with thermally embedded powder, and only the test surface was exposed to conduct a neutral salt spray test using a 5% NaCl solution.

[0110] Hardness testing was performed using a microhardness tester.

[0111] The scanning electron microscope (SEM) image of the cross-section of the heat-treated cold-sprayed Al-Mg-Si composite coating obtained in step (7) of Comparative Example 1 is shown below. Figure 8 As shown, scanning electron microscopy results indicate that after prolonged heat treatment, the coating with low Si content becomes porous and exhibits obvious cracks.

[0112] Comparative Example 2

[0113] (1) Build the XY automation platform and check the operation of the spraying robot;

[0114] (2) Use acetone to ultrasonically clean the Q235 steel substrate to remove oil stains;

[0115] (3) Use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate;

[0116] (4) Prepare the ingredients according to the following ratio: Al 81wt.%, Mg 7wt.%, Si 12wt.%, mix them thoroughly and evenly, and then put them into a vacuum drying oven to dry for 2 hours.

[0117] (5) The powder feeding gas is compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the powder feeding temperature is 400℃, the powder feeding amount is 50g / min, the distance between the spray gun and the substrate is 12mm, and the spray gun moving speed is 6mm / s. Cold spray composite coating is prepared using these parameters.

[0118] (6) After shaping and rigorous inspection, a cold-sprayed Al-Mg-Si composite coating is obtained.

[0119] (7) The sample was sealed in vacuum and subjected to diffusion annealing heat treatment at 500°C for 8 hours, and then taken out and air-cooled to room temperature.

[0120] The scanning electron microscope (SEM) image of the cross-section of the heat-treated cold-sprayed Al-Mg-Si composite coating obtained in step (7) of Comparative Example 2 is shown below. Figure 9 As shown, a comparison of the scanning electron microscope results with those of Example 2 reveals that the coating without Al2O3 ceramic powder exhibits significantly more and more pores, indicating a higher porosity.

[0121] Performance testing:

[0122] The relevant performance tests were conducted on the embodiments and comparative examples of the present invention, and the test results are shown below.

[0123] (1) Vickers hardness test: The test standard is GB / T 4340.1-2024. Take one hot-mounted sample from each of the examples and comparative examples in step (10), and use 400-grit, 1000-grit and 2000-grit sandpaper to polish the surface of the sample coating in turn to make the sample surface flat and free of scratches.

[0124] Then, a microhardness tester was used to perform hardness testing. Five points were selected and the average value was calculated. The results are shown in Table 1 and 2. Figure 11 As shown.

[0125] Table 1

[0126]

[0127] Conclusion: The hardness of the cold-sprayed Al-Mg-Si composite coatings showed a trend of first increasing and then decreasing with the increase of Si content. The hardness of the coatings prepared in Example 2 was not significantly different from that of the coatings prepared in Example 7 due to the increase of heat treatment temperature. However, it can be seen that the hardness of the coatings prepared in the examples was higher than that of the coating in Comparative Example 1.

[0128] The coating prepared in Example 2 had the highest hardness when the Si content was 12 wt.%.

[0129] (2) Neutral salt spray test: The test standard is GB / T 10125-2021. The hot-mounted samples in step (10) of the examples and comparative examples are cleaned with anhydrous ethanol and dried. The weight of the sample is weighed using an electronic balance. A 5wt.% NaCl solution is prepared and added to the salt spray chamber. The sample is placed in the salt spray chamber for testing.

[0130] The salt spray chamber temperature was maintained at 35±1℃, pH = 6.5~7.2, and the corrosion time was 480 hours. The results are shown in Table 2.

[0131] Table 2

[0132]

[0133] This study uses the weight gain method to measure the corrosion rate of the samples, and the calculation formula is as follows:

[0134] V = (W2 - W1)·S -1 ·T -1

[0135] In the formula, V represents the corrosion rate of the galvanized sheet, expressed in g·m³.-2 ·h -1

[0136] W1: Weight of the sample before corrosion, in grams

[0137] W2: Weight of the sample after corrosion, in grams

[0138] S: Exposed area of ​​the sample, m 2

[0139] T: Corrosion cycle, h

[0140] Conclusion: The corrosion rate of the cold-sprayed Al-Mg-Si composite coating showed a trend of first decreasing and then increasing with increasing Si content. Increasing the Mg content and decreasing the heat treatment temperature did not significantly change the corrosion rate compared to Example 2. However, increasing the heat treatment temperature in Example 7 accelerated the corrosion rate. Furthermore, in Comparative Example 1, when the Si content was only 1 wt.%, the coating corrosion rate was 2.2869 g / (m²). 2 .h), corrosion is too rapid;

[0141] The Al-Mg-Si composite coating prepared in Example 2 had a salt spray corrosion rate of 1.181 g / (m²). 2 At this point, the corrosion rate is the lowest (.h).

[0142] (3) Electrochemical testing: The testing standard was GB / T 40299-2021. Electrochemical impedance spectroscopy and potentiodynamic polarization curve testing were performed on the samples soaked in step (9) of the examples and comparative examples. The results are shown in Table 3 and... Figure 9 As shown.

[0143] Table 3

[0144]

[0145] Conclusion: Among the examples and comparative examples, the coating prepared in Example 2 has the highest self-corrosion potential and the lowest self-corrosion current density, so it has the least corrosion tendency, the slowest corrosion rate, and the best corrosion resistance.

[0146] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A high-Si-content cold-sprayed Al-Mg-Si composite coating, characterized in that: The high Si content cold-sprayed Al-Mg-Si composite coating is obtained by cold-spraying a mixture of spherical Al powder, Mg powder, Si powder and Al2O3 ceramic powder onto a pretreated substrate, followed by heat treatment. The high-Si content cold-sprayed Al-Mg-Si composite coating has the following composition by elemental mass percentage: Al 70-85 wt.%, Mg 7 wt-10.%, Si 12-16 wt.%, and the amount of Al2O3 ceramic powder added is 10% wt of the total mass of spherical Al powder, Mg powder, and Si powder.

2. A method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 1, characterized in that: The preparation method steps are as follows: (1) Pretreatment of the matrix; (2) Cold spraying composite powder onto the pretreated substrate; (3) The Al-Mg-Si composite coating is vacuum encapsulated, and then subjected to diffusion annealing heat treatment. After cooling, the heat-treated coating is obtained.

3. The method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 2, characterized in that: The pretreatment of the substrate in step (1) is as follows: first, use acetone for ultrasonic cleaning to remove oil stains, and then use white corundum for sandblasting to remove rust and increase the surface roughness of the substrate. The substrate includes steel Q235.

4. The method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 2, characterized in that: The composite powder in step (2) is obtained by mechanically mixing aluminum powder, magnesium powder, silicon powder and Al2O3 ceramic powder, then packaging the powder in a bag, vacuuming it and drying it in a vacuum drying oven at 70°C for 2 hours.

5. The method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 2, characterized in that: In the cold spraying process described in step (2), the powder feeding gas and working gas are compressed air, the spraying angle is 90°, the gas pressure is 0.99MPa, the gas heating temperature is 400℃, and the powder feeding rate is 50g / min.

6. The method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 2, characterized in that: In step (2), during the cold spraying process, the distance between the spray gun and the substrate surface is 12mm, and the relative moving speed between the spray gun and the substrate is 5~8mm / s.

7. The method for preparing a high-Si-content cold-sprayed Al-Mg-Si composite coating as described in claim 2, characterized in that: The diffusion annealing heat treatment in step (3) is performed at 400-600℃ for 8 hours.

8. An application of the high Si content cold-sprayed Al-Mg-Si composite coating as described in claim 1, characterized in that: The composite coating is used for long-term corrosion protection of steel in complex atmospheric and marine environments.

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