A pitting-resistant aluminum-based composite coating and its preparation method and application

Abstract

The present invention belongs to the technical field of surface corrosion protection of metal materials, and discloses a pitting-resistant aluminum-based composite coating, a preparation method thereof, and an application thereof. The method comprises the following steps: mechanically mixing aluminum alloy powder, dendritic Ni powder, Cr powder, and spherical Al2O3 powder to obtain a mixed powder; sandblasting the metal substrate with silicon carbide sand particles to achieve a surface roughness Sa of 2.5 on the metal substrate; and performing low-pressure cold spraying on the surface of the sandblasted metal substrate to obtain a pitting-resistant aluminum-based composite coating Al‑Ni‑Cr‑Al2O3. The method is based on cold spraying, mixing Ni and Cr powders of different shapes, exerting the shielding effect of Ni and Cr and promoting the passivation performance of the coating. The method is suitable for surface corrosion protection of various metal substrates, providing long-term and effective corrosion protection for various active metal substrates, and can be applied in the field of corrosion protection of metal materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material surface corrosion protection, and in particular relates to a pitting corrosion resistant aluminum-based composite coating and a preparation method and application thereof. Background Art

[0002] Cold spray technology involves accelerating spray powder in a solid state to supersonic speeds, where it impacts a substrate, causing intense plastic deformation and deposition to form a coating. Cold spray technology can be either high-pressure or low-pressure. Low-pressure cold spray operates at pressures of 0.5 to 1 MPa. This simple, fast, and safe technique is particularly suitable for depositing highly plastic powders such as zinc, aluminum, and copper. It is widely used in anti-corrosion coatings, additive manufacturing, and wear-resistant coatings.

[0003] In terms of corrosion-resistant coatings, single-component metal coatings are prepared by low-pressure cold spraying, among which pure aluminum coatings are widely used. However, due to the poor corrosion fatigue strength of pure aluminum coatings, the fatigue life of the coatings is relatively low. During the anti-corrosion process, pitting corrosion usually occurs, which in turn causes cracking of the coating, allowing the corrosive medium to penetrate and cause severe localized corrosion. In addition, the corrosion resistance of deposited pure metal single coatings is poor. The corrosion resistance of the coating can be improved by preparing a mixed powder composite coating by mixing metal powders with good corrosion resistance. The overall life of cold-sprayed pure aluminum-based coatings is relatively short, and the anti-corrosion effect is not ideal. In the later stages of corrosion, phenomena such as coating damage, perforation, and direct contact of the substrate with the corrosive medium often occur. Summary of the Invention

[0004] In order to address the deficiencies and shortcomings of the above-mentioned prior art, the primary purpose of the present invention is to provide a method for preparing a pitting-resistant aluminum-based composite coating. This method prepares an Al-Ni-Cr composite coating based on cold spraying by mixing Ni / Cr powders of different shapes, which can give full play to the shielding effect of Ni / Cr and its promotion effect on the passivation performance of the coating. It is suitable for surface corrosion resistance of various metal substrates and provides long-term and effective corrosion protection for various active metal substrates.

[0005] Another object of the present invention is to provide a method for preparing a pitting corrosion resistant aluminum-based composite coating. The coating has uniform component distribution, a dense structure, and excellent protection against pitting corrosion.

[0006] Another object of the present invention is to provide an application of the above-mentioned pitting-resistant aluminum-based composite coating.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a pitting-resistant aluminum-based composite coating comprises the following steps:

[0009] S1. Aluminum alloy powder, dendritic Ni powder, Cr powder, and spherical Al2O3 powder were mechanically mixed in a mass ratio of (9 to 21): (3 to 7): (12 to 28): 10 and dried at 50 to 80 ° C in a blast drying to obtain a mixed powder;

[0010] S2. The metal substrate is sandblasted with silicon carbide sand at a pressure of 0.5 to 0.8 MPa to achieve a surface roughness Sa of 2.5.

[0011] S3. Place the mixed powder into a low-pressure cold spraying device and adjust the parameters of the low-pressure cold spraying device: the spray gun pressure is 0.6-0.85 MPa, the operating temperature is 400-600°C, the nozzle movement speed is 800-1200 mm / min, and the powder supply rate is 0.5-0.9 g / s. Run the machine to spray the mixed powder on the surface of the metal substrate that has been sandblasted before, to produce an Al-Ni-Cr-Al2O3 composite coating, which is a pitting-resistant aluminum-based composite coating.

[0012] Preferably, the drying time in step S1 is 4 to 8 hours.

[0013] Preferably, the aluminum alloy powder in step S1 is 5000 series aluminum alloy powder, 6000 series aluminum alloy powder or 7000 series aluminum alloy powder, whose particle size is 20-60 μm, the particle size of Ni powder is 10-30 μm, the purity is more than 99.9%, the particle size of Cr powder is 15-50 μm, the purity is more than 99.9%, and the particle size of Al2O3 powder is 30-70 μm.

[0014] More preferably, the 5000 series aluminum alloy powder is 5052 aluminum alloy powder, 5005 aluminum alloy powder or 5083 aluminum alloy powder; the 6000 series aluminum alloy powder is 6061 aluminum alloy powder; and the 7000 series aluminum alloy powder is 7075 aluminum alloy powder.

[0015] Preferably, the metal substrate in step S2 is a low-carbon steel plate or a magnesium alloy, the particle size of the silicon carbide sand particles is 40-100 mesh, and the sandblasting time is 2-8 minutes.

[0016] Preferably, the thickness of the composite coating in step S3 is 400-1000 μm.

[0017] A pitting corrosion resistant aluminum-based composite coating is prepared by the method.

[0018] The application of the pitting-resistant aluminum-based composite coating in the field of corrosion protection of metal materials.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention improves the deposition rate of Cr powder in the Al-Ni-Cr-Al2O3 composite coating and the density of the coating through the entrainment of dendritic Ni powder and the in-situ compaction of spherical alumina. The large-particle spherical alumina can improve the powder fluidity, compact and densify the coating, and prevent rebound from entering the coating, which is beneficial to improving the corrosion resistance of the coating.

[0021] 2. In the composite coating structure of the present invention, Al, Ni, and Cr are evenly distributed. The passivity of Ni and Cr themselves and the potential difference between them and Al improve the passivation ability of the composite coating and the densification of aluminum corrosion products, so that the overall coating has strong pitting corrosion resistance.

[0022] 3. The regulation of the amount of metal powder in the Al-Ni-Cr-Al2O3 coating prepared by cold spraying in the present invention is greatly affected by its deposition rate, which is related to the type and shape of the powder. It is necessary to select appropriate particle size and shape of nickel powder and chromium powder, as well as the mass ratio of the two. The powder ratio in the coating is regulated through experimental processes to achieve excellent corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM photograph of the microscopic morphology of the powder raw material for preparing the pitting corrosion resistant composite coating in Example 1;

[0024] Figure 2 This is the corrosion morphology of the pitting corrosion resistant composite coating of Example 1 after being corroded in a 3.5% NaCl solution for 25 days;

[0025] Figure 3 Schematic diagram of the structure of the pitting corrosion resistant composite coating of the present invention and its corrosion resistance principle;

[0026] Figure 4 Polarization behavior curves of the pitting corrosion resistant composite coatings of Examples 1-3 and the composite coating of Comparative Example 1 in 3.5% NaCl solution;

[0027] Figure 5 This is the corrosion morphology of the coating of Comparative Example 1 after being corroded in a salt solution for 25 days. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0029] Example 1

[0030] 1. Aluminum alloy powder (7075 aluminum alloy powder with a particle size of 20 to 60 μm), dendritic Ni powder (particle size of 10 to 30 μm, purity of more than 99.9%), Cr powder (particle size of 15 to 50 μm, purity of more than 99.9%), and spherical Al2O3 powder (particle size of 30 to 70 μm) are mechanically mixed in a mass ratio of 21:7:12:10, and dried at 75°C in a forced air drying oven for 6 hours to obtain a mixed powder.

[0031] 2. Using low carbon steel plate as the substrate, sandblasting with 40-100 mesh silicon carbide sand particles was performed at a pressure of 0.7 MPa for 4 minutes to make the surface roughness of the low carbon steel plate (Sa is a roughness evaluation parameter based on regional morphology, 30-70 μm) reach 2.5.

[0032] 3. The mixed powder was placed in a low-pressure cold spraying equipment, and the parameters of the low-pressure cold spraying equipment were adjusted: the spray gun pressure was 0.8 MPa, the operating temperature was 500 ° C, the nozzle movement speed was 900 mm / min, and the powder supply rate was 0.6 g / s. The machine was operated to spray on the treated low-carbon steel plate surface to obtain an Al-Ni-Cr-Al2O3 composite coating on the low-carbon steel plate with a thickness of 1000 μm.

[0033] Figure 1 The SEM photos of the microscopic morphology of the powder raw materials for preparing the pitting corrosion resistant composite coating in Example 1; wherein (a) is 7075 aluminum alloy powder, (b) is Cr powder, (c) is Ni powder, and (d) is Al2O3 powder. Figure 1 It can be seen that aluminum powder is spherical with a small particle size, chromium powder is irregular in shape, nickel powder is dendritic with a small particle size, and alumina powder is spherical with a large particle size. Figure 2 The corrosion morphology of the pitting corrosion resistant composite coating of Example 1 after being corroded in 3.5% NaCl solution for 25 days; Figure 2 It can be seen that after the composite coating was fully immersed in 3.5% NaCl solution for 25 days, the corrosion degree was relatively light, the coating did not suffer from severe pitting corrosion, and only shallow tangential corrosion occurred on the coating surface; it can be seen that the composite coating has better corrosion resistance. Figure 3 This is a schematic diagram of the structure of the pitting corrosion resistant composite coating of the present invention and its corrosion resistance principle. Due to the uniform distribution of Al, Ni, and Cr in the composite coating structure, the passivation of Ni and Cr themselves and the potential difference between them and Al, the passivation ability of the composite coating and the densification of aluminum corrosion products are improved, making the overall coating have strong pitting corrosion resistance.

[0034] Example 2

[0035] The difference from Example 1 is that 7075 aluminum alloy powder, dendritic Ni powder, Cr powder, and spherical Al2O3 powder were mechanically mixed in a mass ratio of 15:5:20:10 and dried at 60°C in a forced air dryer for 5 hours to produce a mixed powder. A mild steel plate was used as the substrate and sandblasted with 40-100 mesh silicon carbide sand at a pressure of 0.8 MPa for 3 minutes to achieve a surface roughness Sa of 2.5. The mixed powder was then placed in a low-pressure cold spraying apparatus. The equipment parameters were adjusted to: spray gun pressure of 0.8 MPa, operating temperature of 520°C, nozzle travel speed of 850 mm / min, and powder feed rate of 0.7 g / s. The machine was then operated to spray the sandblasted mild steel plate, resulting in an Al-Ni-Cr-Al2O3 composite coating with a thickness of 900 μm.

[0036] Example 3

[0037] The difference from Example 1 is that 7075 aluminum alloy powder, dendritic Ni powder, Cr powder, and spherical Al2O3 powder were mechanically mixed in a mass ratio of 9:3:28:10 and dried at 60°C in a forced air dryer for 6 hours to produce a mixed powder. A mild steel plate was used as the substrate and sandblasted with 40-100 mesh silicon carbide sand at a pressure of 0.5 MPa for 7 minutes to achieve a surface roughness Sa of 2.5. The mixed powder was placed in a low-pressure cold spraying apparatus. The equipment parameters were adjusted to: spray gun pressure of 0.85 MPa, operating temperature of 600°C, nozzle travel speed of 800 mm / min, and powder feed rate of 0.9 g / s. The machine was then operated to spray the sandblasted mild steel plate, resulting in an Al-Ni-Cr-Al2O3 composite coating with a thickness of 900 μm.

[0038] Comparative Example 1

[0039] 7075 aluminum alloy powder (particle size 20-60 μm) and spherical Al2O3 powder (particle size 30-70 μm) were mechanically mixed in a mass ratio of 4:1 and dried at 60°C in a forced air dryer for 6 hours to produce a mixed powder. A mild steel plate was sandblasted with 40-100 mesh silicon carbide grit at a pressure of 0.5 MPa for 7 minutes to achieve a surface roughness Sa of 2.5. The mixed powder was then applied to a low-pressure cold spraying machine. The machine parameters were adjusted to: gun pressure 0.7 MPa, operating temperature 500°C, nozzle travel speed 1000 mm / min, and powder feed rate 0.6 g / s. The machine was then operated to spray the sandblasted mild steel plate, resulting in an Al-Al2O3 coating with a thickness of 1000 μm.

[0040] Figure 4Figure 2 is the polarization behavior curve of the pitting corrosion resistant composite coating of Examples 1-3 and the composite coating of Comparative Example 1 in 3.5% NaCl solution. Figure 4 It can be seen that the passivation current density of the composite coating of Example 1 in 3.5% NaCl solution is about 3.25×10 -5 A / cm 2 , indicating that the composite coating has good passivation ability and the formed passivation film has good corrosion resistance. The passivation current density of the composite coating of Example 2 in 3.5% NaCl solution is 4.33×10 -5 A / cm 2 After the coating was fully immersed in 3.5% NaCl solution for 25 days, the corrosion degree was relatively light, showing shallow surface corrosion. The passive current density of the composite coating of Example 3 in 3.5% NaCl solution was 7.5×10 -5 A / cm 2 After the coating was fully immersed in 3.5% NaCl solution for 25 days, the corrosion degree was relatively light, showing shallow corrosion on the surface. The passive current density of the Al-Al2O3 coating of comparative example 1 was about 1.04×10 -4 A / cm 2 , which is significantly higher than the passivation current density of the composite coatings in Examples 1 to 3. It can be seen that the Al-Ni-Cr-Al2O3 composite coating of the present invention has a stronger passivation ability, can form a passivation film with better corrosion resistance, and has more excellent pitting corrosion resistance. Figure 5 The corrosion morphology of the coating of Comparative Example 1 after being corroded in salt solution for 25 days. Figure 5 It can be seen that the composite coating of Comparative Example 1 exhibited severe pitting corrosion after being fully immersed in 3.5% NaCl solution for 25 days. The original coating thickness was 1000 μm, and the remaining thickness at the bottom of the corrosion pit of the coating after corrosion was about 100 μm, indicating that the coating had undergone severe corrosion.

[0041] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a pitting-resistant aluminum-based composite coating, characterized in that: The steps include: S1. Mechanically mix 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 dry in a forced air drying oven at 50-80°C to prepare a mixed powder; the aluminum alloy powder is 5000 series aluminum alloy powder, 6000 series aluminum alloy powder, or 7000 series aluminum alloy powder, and has a particle size of 20-60 μm; the dendritic Ni powder has a particle size of 10-30 μm and a purity of 99.9% or greater; the Cr powder has a particle size of 15-50 μm and a purity of 99.9% or greater; and the spherical Al2O3 powder has a particle size of 30-70 μm; S2. The metal substrate is sandblasted with silicon carbide sand at a pressure of 0.5 to 0.8 MPa to a surface roughness Sa of 2.

5. The metal substrate is a low-carbon steel plate or a magnesium alloy, the silicon carbide sand has a particle size of 40 to 100 mesh, and the sandblasting time is 2 to 8 min. S3. Place the mixed powder into a low-pressure cold spraying device and adjust the following parameters: spray gun pressure of 0.6-0.85 MPa, operating temperature of 400-600°C, nozzle movement speed of 800-1200 mm / min, and powder feed rate of 0.5-0.9 g / s. Operate the device to spray the mixed powder onto the surface of a pre-sandblasted metal substrate to produce a pitting-resistant aluminum-based composite coating, namely, an Al-Ni-Cr-Al2O3 composite coating. The thickness of the composite coating is 400-1000 μm.

2. The method for preparing the pitting corrosion resistant aluminum-based composite coating according to claim 1, characterized in that: The drying time in step S1 is 4 to 8 hours.

3. The method for preparing the pitting corrosion resistant aluminum-based composite coating according to claim 1, wherein: In step S1, the 5000 series aluminum alloy powder is 5052 aluminum alloy powder, 5005 aluminum alloy powder or 5083 aluminum alloy powder; the 6000 series aluminum alloy powder is 6061 aluminum alloy powder; and the 7000 series aluminum alloy powder is 7075 aluminum alloy powder.

4. A pitting-resistant aluminum-based composite coating, characterized in that: The composite coating is prepared by the method according to any one of claims 1 to 3.

5. Use of the pitting-resistant aluminum-based composite coating according to claim 4 in the field of corrosion protection of metal materials.

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