Gradient nickel-based corrosion-resistant coating on surface of aluminum alloy and preparation method thereof

Abstract

The invention discloses a gradient nickel-based corrosion-resistant coating on the surface of an aluminum alloy and a preparation method of the gradient nickel-based corrosion-resistant coating, and belongs to the technical field of metal material plating. In order to improve the corrosion resistance of the aluminum alloy surface, the invention provides a gradient nickel-based corrosion-resistant coating on the aluminum alloy surface and a preparation method thereof, and the gradient nickel-based corrosion-resistant coating is prepared by spraying a metal nickel layer on an aluminum alloy matrix and carrying out heat treatment on the metal nickel layer, so that aluminum and nickel react to form the gradient nickel-based corrosion-resistant coating. The gradient structure coating sequentially comprises a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy matrix from the surface to the matrix. According to the method, Ni and Al react to generate a Ni-Al compound in a high-temperature heat treatment environment, the bonding strength between the coatings is effectively improved, and the nickel-based corrosion-resistant coating of the gradient structure has good corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of metal material coating technology, specifically relating to a gradient nickel-based corrosion-resistant coating on the surface of aluminum alloy and its preparation method. Background Technology

[0002] Aluminum alloys are widely used in various fields such as construction, aerospace, and automotive manufacturing due to their advantages such as light weight, high strength, and good machinability. However, aluminum alloys are also susceptible to corrosion. Corrosion not only affects their appearance but also reduces their performance and service life, and may even jeopardize safety in some critical areas (such as aerospace). Surface coatings can provide corrosion protection for aluminum alloy components used in corrosive environments.

[0003] CN 110760782 A discloses a wear-resistant aluminum alloy, which includes an aluminum alloy substrate and a wear-resistant coating plated on the surface of the aluminum alloy substrate. The wear-resistant coating includes an Al / Ni underlayer plated on the aluminum alloy substrate and a metal-ceramic composite coating plated on the Al / Ni underlayer. The Al / Ni underlayer is composed of the following components by mass percentage: Al 2-8%, with the balance being Ni. The metal-ceramic composite coating is composed of the following components by mass percentage: WC 10-30%, with the balance being Ni60.

[0004] CN113089048A discloses an application of a protective coating for welded joints. This protective coating has a double-layer structure consisting of an anodic aluminum oxide layer and a Ni-P plating layer. The coating is applied to the surface of the weld seam in aluminum alloy friction stir welding. The preparation method includes the following steps: 1) pre-treating the aluminum alloy weld seam surface to obtain a smooth and flat surface to be reinforced; 2) anodizing the surface obtained in step 1) to obtain a dense and porous anodic aluminum oxide intermediate layer; 3) activating and expanding the pores of the anodic aluminum oxide intermediate layer obtained in step 2) to obtain a surface to be nickel-plated aluminum alloy weld seam; 4) electrochemically plating nickel onto the surface obtained in step 3) to obtain the protective coating for welded joints.

[0005] CN118835243A discloses a method for preparing a micro-arc oxidation-chemical plating Ni / P electromagnetic shielding coating on aluminum alloy, comprising the following steps: Step 1: Grinding and cleaning the aluminum alloy sample; Step 2: Placing the aluminum alloy sample in an alkaline electrolyte and preparing the micro-arc oxidation coating using a dual-pulse DC power supply; Step 3: Immersing the micro-arc oxidation sample obtained in Step 2 in a sensitizing solution for 1-5 min, and rinsing off the residual liquid with deionized water; Step 4: Activating the sample in an activation solution for 20-50 s, and rinsing off the residual liquid with deionized water; Step 5: Subsequently, reducing the sample in a reducing solution for 10-90 s, removing it and rinsing off the residual liquid with deionized water; Step 6: Performing chemical plating treatment in a water bath; Step 7: Immersing the workpiece obtained in Step 6 in a stearic acid ethanol solution with a concentration of 0.1-1 mol / L, a solution temperature of 50-70℃, and an immersion time of 1-8 h, removing and drying it to obtain a composite coating.

[0006] CN118308715A discloses a method for preparing a pitting-resistant aluminum-based composite coating, comprising the following steps: S1. Mechanically mixing aluminum alloy powder, dendritic Ni powder, Cr powder, and spherical Al2O3 powder in a mass ratio of 9–21:3–7:12–28:10, and drying in a forced-air drying environment at 50–80°C to obtain a mixed powder; S2. Sandblasting a metal substrate with silicon carbide abrasive particles under a pressure of 0.5–0.8 MPa to roughen the surface of the metal substrate. The roughness Sa reaches 2.5; S3. The mixed powder is put into a low-pressure cold spraying equipment, and the parameters of the low-pressure cold spraying equipment are adjusted: the spray gun pressure is 0.6~0.85MPa, the working temperature is 400~600℃, the nozzle moving speed is 800~1200mm / min, and the powder feeding rate is 0.5~0.9g / s. The machine is run to spray on the surface of the metal substrate that has been pretreated by sandblasting to obtain a pitting corrosion resistant aluminum-based composite coating, which is the Al-Ni-Cr-Al2O3 composite coating.

[0007] CN215680143U discloses a pure nickel conductive composite material that is cold- and hot-sprayed onto the surface of an aluminum alloy, comprising an aluminum alloy substrate (1), wherein a Ni layer (2) is sprayed onto the surface of the aluminum alloy substrate (1), the Ni layer (2) being Ni powder with a size of 2μm to 20μm, and a conductive and corrosion-resistant coating of 0.001mm to 0.50mm is formed on the surface of the aluminum alloy substrate (1) after spraying.

[0008] It is evident that a large amount of research has been conducted both domestically and internationally on corrosion-resistant coatings for aluminum alloy surfaces. Nickel-based corrosion-resistant coatings are mainly used for surface protection of metal substrates (such as 7075 aluminum alloy), and can extend service life, especially in corrosive environments such as deep-sea equipment and chemical machinery, and have received extensive research. However, most of the research on nickel-based coatings for aluminum alloy surfaces focuses on different preparation processes and the addition of reinforcing phases, while there are few reports on gradient nickel-based coatings for aluminum alloy surfaces and their corrosion resistance. Summary of the Invention

[0009] To address the limited research on the corrosion resistance of gradient nickel-based coatings in existing technologies, this invention provides a gradient nickel-based corrosion-resistant coating for aluminum alloy surfaces and its preparation method.

[0010] This invention involves spraying a nickel layer onto the surface of an aluminum alloy substrate and then heat-treating it. In this process, nickel and aluminum can sequentially form Ni, Ni3Al, and NiAl layers at high temperatures, thereby improving the bonding strength of the coating, hindering the penetration of corrosive media, and enhancing the corrosion resistance of the coating.

[0011] In a first aspect, the present invention provides a method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface, comprising the following steps:

[0012] A. Sandblasting is performed on the surface of the aluminum alloy substrate to obtain a roughened aluminum alloy substrate.

[0013] B. After heating and heat preservation, the nickel powder is sprayed onto the roughened aluminum alloy substrate surface using plasma spraying to obtain a nickel layer; in step B, the thickness of the obtained nickel layer is 100~300μm.

[0014] C. The aluminum alloy substrate coated with a nickel layer is heated to 300℃~500℃ at a heating rate of 4℃ / min~6℃ / min and held at that temperature, and then cooled in the furnace to obtain a gradient nickel-based corrosion-resistant coating consisting of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate; In step C, the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer in the obtained gradient structure coating is 1:0.2~0.5:0.2~0.5.

[0015] Preferably, in the above-mentioned method for preparing a gradient nickel-based corrosion-resistant coating on the surface of aluminum alloy, the thickness of the obtained nickel layer in step B is 250~300μm.

[0016] Preferably, in the above-mentioned method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface, in step C, the temperature is raised to 450℃~500℃, and the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer in the resulting gradient structure coating is 1:0.4~0.5:0.4~0.5.

[0017] In the preparation method of the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, in step B, the plasma spraying conditions are as follows: voltage of 50~70V, current of 500~550A, main gas Ar and auxiliary gas H2 flow rates of 60~65L / min and 2~4L / min respectively, powder feeding gas Ar flow rate of 6~7L / min, spraying distance of 110~120mm, and travel speed of 12~14cm / s.

[0018] In the method for preparing the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, in step A, the aluminum alloy substrate is 7075 aluminum alloy, 7055 aluminum alloy, 6061 aluminum alloy or 2024 aluminum alloy.

[0019] In the method for preparing the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, in step A, the sandblasting time is 5-15 minutes.

[0020] In the preparation method of the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, in step B, the particle size of the nickel powder is 45~150μm.

[0021] In the preparation method of the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, in step B, the temperature of heating and holding the nickel powder is 80~100℃ and the time is 0.5~2h.

[0022] In the method for preparing the gradient nickel-based corrosion-resistant coating on the surface of the aluminum alloy, the heat preservation time in step C is 1~3h.

[0023] Secondly, the present invention also provides a gradient nickel-based corrosion-resistant coating consisting of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate, which is prepared by the above-mentioned method for preparing gradient nickel-based corrosion-resistant coatings on aluminum alloy surfaces.

[0024] Thirdly, the present invention also provides the application of the above-mentioned gradient nickel-based corrosion-resistant coating, which consists of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate, in the preparation of corrosion-resistant aluminum alloys.

[0025] Among the above applications, the gradient nickel-based corrosion-resistant coating on the surface of corrosion-resistant aluminum alloy can resist corrosion from any of the corrosive salts, NaCl and MgCl2, and is also particularly suitable for seawater corrosion resistance.

[0026] In actual production, the coating process of this invention can be selectively applied as needed, for example, coating only one side or coating all sides.

[0027] The beneficial effects of this invention are:

[0028] This invention employs a plasma spraying + heat treatment composite technology to prepare a gradient nickel-based composite coating. First, a nickel layer is sprayed onto the aluminum alloy surface and then heat-treated. Under high-temperature heat treatment, Ni and Al react to form Ni-Al compounds, effectively improving the coating's bonding strength. Furthermore, the dense structure of the reaction layer effectively hinders the penetration of corrosive media. Under corrosive conditions, the nickel-based corrosion-resistant coating generates a NiO-Al2O3 composite oxide, which deposits in the corrosion micropores, thus preventing the inward diffusion of corrosive media and exhibiting excellent corrosion resistance. This invention features a simple production process, high bonding strength, selective area preparation, and demonstrates excellent corrosion resistance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the gradient nickel-based corrosion-resistant coating structure on the aluminum alloy surface of the present invention.

[0030] Figure 2 This is an image of the surface of the gradient nickel-based coating sprayed in Embodiment 1 of the present invention.

[0031] Figure 3 This is a comparison image of the nickel-based coating on the aluminum alloy surface before and after heat treatment in Example 1 of the present invention.

[0032] Figure 4 This is a cross-sectional morphology diagram of the gradient nickel-based coating in Embodiment 3 of the present invention. Detailed Implementation

[0033] Specifically, a method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface includes the following steps:

[0034] A. Sandblasting is performed on the surface of the aluminum alloy substrate to obtain a roughened aluminum alloy substrate.

[0035] B. After heating and heat preservation, the nickel powder is sprayed onto the roughened aluminum alloy substrate surface using plasma spraying to obtain a nickel layer; in step B, the thickness of the obtained nickel layer is 100~300μm.

[0036] C. The aluminum alloy substrate coated with a nickel layer is heated to 300℃~500℃ at a heating rate of 4℃ / min~6℃ / min and held at that temperature, and then cooled in the furnace to obtain a gradient nickel-based corrosion-resistant coating consisting of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate; In step C, the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer in the obtained gradient structure coating is 1:0.2~0.5:0.2~0.5.

[0037] Current research indicates that NiAl exhibits good corrosion resistance, but most methods employ thermal spraying or electroplating, which present challenges in phase control and weak bonding during preparation, leading to galvanic cell effects (accelerated corrosion) during subsequent corrosion. This invention addresses this issue by considering Ni's inherent chemical stability and corrosion resistance, as well as its tendency to react with Al. The proposed method involves spraying Ni onto the aluminum alloy surface, utilizing subsequent heat treatment to enhance bonding through reaction, stabilizing the phase through diffusion, and ensuring a gradient phase distribution to reduce galvanic cell effects.

[0038] For Ni powder spraying, after screening tests, the plasma spraying conditions in step B of this invention are as follows: voltage 50~70V, current 500~550A, main gas Ar and auxiliary gas H2 flow rates 60~65L / min and 2~4L / min respectively, powder feeding gas Ar flow rate 6~7L / min, spraying distance 110~120mm, and travel speed 12~14cm / s.

[0039] In order to form a gradient structure with a reasonable thickness distribution after heat treatment, in step B of the present invention, the thickness of the obtained nickel layer is controlled to be 100~300μm, preferably 250~300μm.

[0040] In this invention, NiAl3 may be formed in the early stage of heat treatment, but it is a low-temperature initial phase and will transform into NiAl as the heat treatment progresses.

[0041] In this invention, the formation of the gradient structure is highly correlated with the heat treatment parameters. Experiments have shown that this invention strictly controls the heating rate during heat treatment to be 4℃ / min~6℃ / min and the holding temperature to be 300℃~500℃, thereby achieving a thickness ratio of 1:0.2~0.5:0.2~0.5 for the Ni layer, Ni3Al layer, and NiAl layer in the gradient structure coating. Pure Ni and Al have a large potential difference; direct contact would form a strong electrical couple, accelerating the corrosion of the aluminum alloy substrate. The layered structure can form a potential gradient buffer layer; the continuous and dense intermetallic compound layer in the middle can act as a physical barrier to prevent the intrusion of corrosive media; and the Ni solid solution region near the substrate can also inhibit intergranular corrosion of the aluminum alloy. This invention strictly controls the thickness ratio, achieving a smooth transition of the potential gradient, a continuous and intact dense barrier layer, and effective release of interfacial stress. This avoids both strong Ni / Al galvanic corrosion and the formation of corrosion channels through cracking of brittle intermetallic phases, while also preventing excessive Ni diffusion from degrading the substrate's corrosion resistance. Consequently, the coating system exhibits comprehensive corrosion resistance with high stability, low defects, and long lifespan in corrosive environments. Furthermore, excessively low temperatures result in a long formation time for the gradient structure, which is detrimental to engineering applications; while excessively high temperatures, although requiring less time, can cause softening or melting of the aluminum alloy substrate and make it difficult to form the gradient structure. Moreover, experiments have shown that when heat-treated at 450℃~500℃, the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer in the resulting gradient structure coating is 1:0.4~0.5:0.4~0.5, further significantly improving corrosion resistance.

[0042] In step A of this invention, the aluminum alloy matrix is ​​7075 aluminum alloy, 7055 aluminum alloy, 6061 aluminum alloy or 2024 aluminum alloy.

[0043] In step A of this invention, the sandblasting treatment time is 5~15 minutes.

[0044] In step B of this invention, the particle size of the nickel powder is 45~150μm.

[0045] In step B of this invention, the temperature for heating and holding the nickel powder is 80~100℃, and the time is 0.5~2h.

[0046] In step C of this invention, the heat preservation time is 1 to 3 hours.

[0047] Secondly, the present invention also provides a gradient nickel-based corrosion-resistant coating consisting of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate, which is prepared by the above-mentioned method for preparing gradient nickel-based corrosion-resistant coatings on aluminum alloy surfaces.

[0048] Thirdly, the present invention also provides the application of the above-mentioned gradient nickel-based corrosion-resistant coating, which consists of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate, in the preparation of corrosion-resistant aluminum alloys.

[0049] In the above applications of the present invention, the gradient nickel-based corrosion-resistant coating on the surface of the corrosion-resistant aluminum alloy can resist corrosion from any of the corrosive salts, NaCl and MgCl2, and is also particularly suitable for seawater corrosion resistance.

[0050] Exemplary embodiments of the present invention will now be described in detail. However, it should be understood that the present invention should not be limited to the described embodiments. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0051] The aluminum alloy substrates used in the embodiments of this invention are all 7075 aluminum alloys, and the sample size is 12mm × 12mm × 6mm (e.g. Figure 2 Its chemical composition is as follows: silicon (Si): 0.40 wt%, iron (Fe): 0.50 wt%, copper (Cu): 1.2-2.0 wt%, manganese (Mn): 0.30 wt%, magnesium (Mg): 2.1-2.9 wt%, chromium (Cr): 0.18-0.28 wt%, zinc (Zn): 5.1-6.1 wt%, titanium (Ti): 0.20 wt%, aluminum (Al): balance.

[0052] Example 1

[0053] A gradient nickel-based corrosion-resistant coating for aluminum alloy surfaces, wherein the gradient nickel-based corrosion-resistant coating is obtained by spraying a nickel layer onto an aluminum alloy substrate and then heat-treating it.

[0054] The nickel-based coating is obtained by spraying metallic nickel powder, followed by heat treatment to allow Ni and Al to diffuse and react, forming a gradient nickel-based coating containing Ni, Ni3Al, and NiAl.

[0055] The method for preparing the above-mentioned gradient nickel-based corrosion-resistant coating on the surface of aluminum alloy includes the following steps:

[0056] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0057] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 100μm. After preparation, take it out and let it stand at room temperature for later use.

[0058] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0059] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 300°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0060] Figure 1 This is a schematic diagram of the gradient nickel-based corrosion-resistant coating structure on the surface of an aluminum alloy. Figure 2 This is an image of the surface coated with a gradient nickel-based coating in Example 1. Figure 3 These are comparison images of the nickel-based coating on the aluminum alloy surface before and after heat treatment in Example 1. Figure 3 The color change of the surface coating is clearly visible, indicating the formation of a gradient coating.

[0061] Example 2

[0062] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0063] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0064] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 100μm. After preparation, take it out and let it stand at room temperature for later use.

[0065] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0066] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 400°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0067] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.3:0.4.

[0068] Example 3

[0069] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0070] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0071] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 100μm. After preparation, take it out and let it stand at room temperature for later use.

[0072] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0073] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 500°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0074] The microstructure was observed using a scanning electron microscope. Figure 4 The image shows the cross-sectional morphology of the gradient nickel-based coating in Example 3. There are basically clear boundaries between the Ni layer, Ni3Al layer and NiAl layer, and the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer is 1:0.5:0.5.

[0075] Example 4

[0076] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0077] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0078] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 200μm. After preparation, take it out and let it stand at room temperature for later use.

[0079] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0080] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 300°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0081] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.2:0.3.

[0082] Example 5

[0083] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0084] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0085] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 200μm. After preparation, take it out and let it stand at room temperature for later use.

[0086] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0087] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 400°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0088] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.3:0.4.

[0089] Example 6

[0090] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0091] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0092] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 200μm. After preparation, take it out and let it stand at room temperature for later use.

[0093] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0094] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 500°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0095] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.5:0.4.

[0096] Example 7

[0097] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0098] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0099] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 300μm. After preparation, take it out and let it stand at room temperature for later use.

[0100] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0101] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 300°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0102] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.2:0.3.

[0103] Example 8

[0104] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0105] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0106] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 300μm. After preparation, take it out and let it stand at room temperature for later use.

[0107] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0108] S3. Place the aluminum alloy substrate with the metallic nickel layer into a muffle furnace, heat it to 400°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0109] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.3:0.3.

[0110] Example 9

[0111] The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface in this embodiment includes the following steps:

[0112] S1. Sandblast the surface of the aluminum alloy substrate for 10 minutes to obtain the surface roughened aluminum alloy substrate.

[0113] S2. Place the nickel powder in an oven and keep it at 80°C for 1 hour. Then, take out the powder and put it into a powder feeder. Use plasma spraying to spray the nickel powder onto the surface of the aluminum alloy substrate to obtain a nickel layer with a thickness of 300μm. After preparation, take it out and let it stand at room temperature for later use.

[0114] The nickel powder particle size is 45~150μm; the parameters for plasma spraying are: voltage 50V, current 500A, main gas Ar and auxiliary gas H2 flow rates 60L / min and 2L / min respectively, powder feeding gas Ar flow rate 6L / min, spraying distance 120mm, and travel speed 12cm / s.

[0115] S3. Place the aluminum alloy substrate with the nickel layer into a muffle furnace, heat it to 500°C at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it with the furnace and take out the sample to obtain a gradient nickel-based corrosion-resistant coating with Ni layer, Ni3Al layer, NiAl layer and aluminum alloy substrate in sequence from the surface to the substrate.

[0116] The microstructure was observed using a scanning electron microscope, and the thickness ratio of the Ni layer, Ni3Al layer, and NiAl layer was 1:0.4:0.4.

[0117] The above Examples 1 to 9 all prepared a gradient nickel-based corrosion-resistant coating on the surface of aluminum alloy. The corrosion performance of the gradient nickel-based corrosion-resistant coating on the surface of aluminum alloy was measured below.

[0118] The gradient coating prepared in the examples was used as the experimental sample, and electrochemical corrosion tests were performed on it according to GB / T 24196-2009. The corrosion medium was 3.5% NaCl, and the data are shown in Table 1.

[0119] Table 1 Corrosion voltage and corrosion current of gradient coatings sprayed onto aluminum alloy substrates in the examples

[0120] As can be seen from Table 1, the gradient coating of the present invention exhibits relatively low corrosion tendency and corrosion rate, indicating its good corrosion resistance. Furthermore, regarding corrosion resistance, a lower corrosion current and higher corrosion voltage indicate better corrosion resistance of the material; therefore, Example 9 demonstrates the best corrosion resistance.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface, characterized in that: Includes the following steps: A. Sandblasting is performed on the surface of the aluminum alloy substrate to obtain a roughened aluminum alloy substrate. B. After heating and heat preservation, the nickel powder is sprayed onto the roughened aluminum alloy substrate surface using plasma spraying to obtain a nickel layer; in step B, the thickness of the obtained nickel layer is 100~300μm. C. The aluminum alloy substrate coated with a nickel layer is heated to 300℃~500℃ at a heating rate of 4℃ / min~6℃ / min and held at that temperature, and then cooled in the furnace to obtain a gradient nickel-based corrosion-resistant coating consisting of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate; In step C, the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer in the obtained gradient structure coating is 1:0.2~0.5:0.2~0.

5.

2. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step B, the thickness of the obtained nickel layer is 250~300μm.

3. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step C, the temperature is raised to 450℃~500℃, and the thickness ratio of the Ni layer, Ni3Al layer and NiAl layer in the resulting gradient structure coating is 1:0.4~0.5:0.4~0.

5.

4. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step B, the conditions for plasma spraying are as follows: voltage 50~70V, current 500~550A, main gas Ar and auxiliary gas H2 flow rates 60~65L / min and 2~4L / min respectively, powder feeding gas Ar flow rate 6~7L / min, spraying distance 110~120mm, and travel speed 12~14cm / s.

5. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step A, the aluminum alloy matrix is ​​7075 aluminum alloy, 7055 aluminum alloy, 6061 aluminum alloy or 2024 aluminum alloy.

6. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step A, the sandblasting process takes 5 to 15 minutes.

7. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step B, the particle size of the nickel powder is 45~150μm.

8. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step B, the nickel powder is heated and kept at a temperature of 80~100℃ for 0.5~2h.

9. The method for preparing a gradient nickel-based corrosion-resistant coating on an aluminum alloy surface according to claim 1, characterized in that: In step C, the heat preservation time is 1 to 3 hours.

10. A gradient nickel-based corrosion-resistant coating for aluminum alloy surface prepared by the method described in any one of claims 1 to 9, wherein the coating consists of a Ni layer, a Ni3Al layer, a NiAl layer and an aluminum alloy substrate in sequence from the surface to the substrate.

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