High wear resistance cold sprayed al-aln composite coating and method of making same

Abstract

A kind of high wear-resistant cold spraying Al-AlN composite coating and its preparation method. The spherical Al powder with particle size of 15-53 μm is mechanically mixed with irregular AlN powder with particle size of 4-54 μm for 1 h at AlN mass of 10%-50%; the substrate is cleaned and sand blasted to roughness of 1.0-3.0 μm; the cold spraying parameters are: working gas compressed N2, pressure 2 MPa, temperature 400 ℃, powder feeding amount 10 g / min, spraying distance 20 mm, moving speed 2 mm / s, to form a coating with thickness >200 μm. When the AlN content is 50 wt.%, the actual deposition content of AlN in the coating reaches 6.1 wt.%, and the wear rate is as low as 8.05×10 ‑7 mm 3 ·N ‑1 ·m ‑1 The present application breaks through the technical prejudice that ceramic phase is difficult to be deposited at high content by cold spraying, and the coating is dense and non-oxidized, and is suitable for surface wear-resistant protection of light alloys such as magnesium alloy.

Description

Technical Field

[0001] This invention relates to the field of cold spraying technology, specifically to a highly wear-resistant Al-AlN composite coating for lightweight metal substrates such as magnesium alloys and its preparation method. Background Technology

[0002] Magnesium alloys have attracted much attention due to their low density and high specific strength, but their poor wear and corrosion resistance severely limits their widespread application in harsh working conditions. Preparing protective coatings on magnesium alloy surfaces is a common method to improve their surface properties. While traditional methods such as plasma spraying, arc spraying, and supersonic flame spraying can achieve coating deposition, they generally suffer from problems such as cumbersome operation, high cost, the introduction of thermal stress during high-temperature processing, and oxidation or phase transformation of oxygen-sensitive and heat-sensitive materials.

[0003] Cold spraying technology utilizes high-temperature, high-pressure gas to accelerate powder particles, causing them to impact the substrate and deposit through plastic deformation. Due to the low processing temperature, the powder remains below its melting point, exhibiting significant advantages in surface treatment of heat- and oxygen-sensitive materials.

[0004] Pure aluminum (Al) coatings exhibit excellent corrosion resistance due to the easy formation of a dense oxide film on their surface; however, aluminum itself has low hardness and poor wear resistance. To improve the wear resistance of pure Al coatings, current technologies mainly focus on adding ceramic phases (such as SiC, TiC, WC, etc.). Aluminum nitride (AlN) is a high-hardness, chemically stable ceramic material that can compensate for the shortcomings of pure Al coatings. However, research on cold-sprayed Al-AlN composite coatings has not been reported. A search reveals that existing research involving AlN-reinforced coatings or composite materials has the following shortcomings:

[0005] Xie et al. (Al–AlN composite coatings on AZ31 magnesium alloy for surface hardening and corrosion resistance, Vacuum 188 (2021) 110146) prepared Al-AlN composite coatings on AZ31 magnesium alloy using filtered cathodic vacuum arc deposition (FCVAD). The coatings exhibited high hardness (up to 512 HV) and good corrosion resistance, but the coating thickness was only 2.3-3.6 μm, classifying them as physical vapor deposition thin films. These films were ill-suited to withstand frictional wear under heavy loads, and the equipment was costly with low deposition efficiency.

[0006] Fale et al. (The Wear Behavior of In-Situ Al–AlN Metal Matrix Composites, Trans Indian Inst Met (2014) 67(6):841–849 DOI 10.1007 / s12666-014-0407-6) prepared bulk Al-AlN composites in molten aluminum at 700℃ via in-situ melt reaction. This method is mainly for aluminum matrices and suffers from problems such as AlN particle agglomeration with increasing precursor content, leading to uneven distribution and unstable performance. If a similar process is applied to magnesium alloy matrices, the high-temperature melting process may face greater challenges, and it is also difficult to achieve the preparation of surface coatings.

[0007] Zhou et al. (Wear and corrosion properties of Cu–AlN composite coatings deposited by cold spray, Journal of Materials Research and Technology 30(2024) 3986–3995) prepared Cu-AlN composite coatings on copper alloy substrates using cold spraying. While this study confirmed that introducing AlN into soft metals can improve wear resistance, its results showed that when the AlN content in the raw material powder was 30 vol.%, the actual AlN deposition content in the coating was only a maximum of 3.8 vol.% (deposition efficiency less than 13%). This is because the AlN ceramic phase has extremely poor plastic deformation ability and extremely high hardness, making it prone to particle breakage and rebound during the high-speed impact of cold spraying, hindering effective embedding into the metal matrix for co-deposition. This literature essentially presents a technical bias that "cold spraying cannot achieve stable deposition of high-content ceramic phases," leading to a lack of technical motivation for those skilled in the art to further increase the ceramic phase content. Furthermore, the wear rate of this Cu-AlN coating was still as high as 1.69 × 10⁻⁶. -3 mm 3 N -1 m -1 The absolute improvement in wear resistance is limited, and copper-based coatings cannot provide effective cathodic protection for magnesium alloys.

[0008] In summary, although there have been studies on Al-AlN composite materials or coatings, no reported technical solutions have been found for preparing thick and dense Al-AlN composite coatings on magnesium alloy substrates using cold spraying technology, and achieving high deposition rates and low wear rates by optimizing AlN content. The wear resistance of existing cold-sprayed Al-based coatings (pure Al or with the addition of other ceramic phases) still has significant room for improvement. Summary of the Invention

[0009] This invention aims to overcome the shortcomings of existing cold-sprayed Al-based coatings and PVD films in terms of wear resistance, coating thickness, and ceramic phase deposition efficiency, and provides a high-wear-resistant cold-sprayed Al-AlN composite coating and its preparation method. By designing the particle size of Al and AlN powders, optimizing the mechanical mixing process, and synergistically controlling cold-spraying parameters, this invention overcomes the technical bias that "cold spraying is difficult to achieve effective deposition of high-content AlN," significantly improving the actual deposition content and distribution uniformity of AlN in the coating. This results in a thick-section composite coating that combines high hardness and ultra-low wear rate, making it particularly suitable for surface protection of soft, heat-sensitive substrates such as magnesium alloys.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0011] A method for preparing a highly wear-resistant cold-sprayed Al-AlN composite coating includes the following steps:

[0012] (1) Al powder and AlN powder are mixed by mechanical mixing to obtain Al-AlN mixed powder; the Al powder is spherical with a particle size of 15-53 μm; the AlN powder is irregular in shape with a particle size of 4-54 μm. The mass percentage of AlN powder in the mixed powder is 10%-50%; the mechanical mixing time is 1 h and the speed is 200 rpm.

[0013] Preferably, the particle size ranges of the Al powder and AlN powder overlap (approximately 15–54 μm). This particle size matching design is beneficial for achieving similar acceleration behavior and flight trajectory in the high-speed airflow field of cold spraying, reducing segregation and deposition efficiency imbalance caused by excessive particle size differences, thereby improving the actual deposition content and distribution uniformity of the AlN ceramic phase in the coating.

[0014] (2) Pretreatment of the substrate surface: clean with acetone and dry, then perform sandblasting (No. 6 corundum sand, compressed air pressure 0.4MPa) to remove the oxide layer and make the surface roughness reach 1.0-3.0μm to enhance the mechanical interlocking between the coating and the substrate.

[0015] (3) The mixed powder was sprayed onto the pretreated substrate surface using cold spraying technology to form an Al-AlN composite coating. The cold spraying process parameters were as follows: both the working gas and the powder feeding gas were compressed nitrogen (N2), the gas pressure was 2 MPa, the heating temperature was 400℃, the powder feeding rate was 10 g / min, the distance between the spray gun and the substrate was 20 mm, and the relative moving speed of the spray gun was 2 mm / s. The final Al-AlN composite coating had a thickness greater than 200 μm.

[0016] As a preferred embodiment, the mass percentage of AlN powder in the Al-AlN mixed powder in step (1) is 50%. Under this preferred ratio, through the above-mentioned particle size matching and process synergistic optimization, the actual deposition content of AlN in the coating can reach 6.1 wt.% (far higher than the existing cold-sprayed AlN reinforced coating), and the hardness and wear resistance of the coating achieve the optimal balance.

[0017] This invention also protects a highly wear-resistant cold-sprayed Al-AlN composite coating prepared by any of the above-described preparation methods. The composite coating has a thickness greater than 200 μm, low porosity, uniform Al and AlN distribution within the coating, and only Al and AlN phases are detected, with no oxidation products.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Significantly improved wear resistance: Experiments show that when the AlN content is 50 wt.%, the wear rate is as low as 8.05 × 10⁻⁶. - 7 mm 3 ·N -1 ·m -1 It has excellent wear resistance.

[0020] (2) Surpassing existing cold-sprayed composite coatings: Compared with the Cu-AlN coating reported by Zhou et al. (actual AlN content is only 3.8 vol.%, wear rate is 1.69 × 10⁻⁶), the coating is superior to the Cu-AlN coating reported by Zhou et al. (actual AlN content is only 3.8 vol.%, wear rate is 1.69 × 10⁻⁶). -3 mm 3 Compared to AlN powder (15–53 μm), this invention, through particle size design of Al powder (15–53 μm) and AlN powder (4–54 μm), optimization of mechanical mixing methods, and synergistic control of cold spraying process parameters, successfully achieved stable deposition of AlN with an actual deposition content of 6.1 wt.% (equivalent to more than 4 times the actual content in the prior art after mass / volume conversion), effectively overcoming the aforementioned technical bottlenecks. This breakthrough is not something that those skilled in the art could easily foresee through conventional parameter adjustments.

[0021] (3) Overcoming the thickness limitation of PVD film: Compared with the FCVAD film (thickness <4μm) reported by Xie et al., the coating thickness of the present invention is >200μm, which can withstand greater load and longer wear time, and meet the heavy load requirements of engineering.

[0022] (4) Reasonable composition design and strong process adaptability: The influence of 10%-50% AlN content on coating performance was systematically studied, and the optimal ratio was optimized. The mechanical mixing method is simple and efficient, and the low-temperature cold spraying process avoids oxidation and phase transformation, resulting in a dense coating with low porosity.

[0023] (5) Wide range of applications: It can be used not only for magnesium alloys, but also for other metal parts that require surface wear protection. It has broad application prospects in mechanical seals, bearings, molds and other fields. Attached Figure Description

[0024] Figure 1 These are scanning electron microscope (SEM) images of the Al-AlN mixed powder used in Examples 1-5 of this invention.

[0025] Figure 2 This is a particle size distribution diagram of the Al-AlN mixed powder used in Examples 1-5 of the present invention.

[0026] Figure 3 These are X-ray diffraction (XRD) phase diagrams of Al-AlN composite coatings with different AlN contents (Al-10AlN-C, Al-20AlN-C, Al-30AlN-C, Al-40AlN-C and Al-50AlN-C correspond to AlN contents of 10%, 20%, 30%, 40% and 50%, respectively) prepared in Examples 1 to 5 of this invention.

[0027] Figure 4 This is a cross-sectional SEM image of the 10% AlN content Al-AlN composite coating prepared in Example 1 of the present invention, and a distribution diagram of Al, AlN and Mg elements in the coating and the matrix.

[0028] Figure 5 This is a cross-sectional SEM image of the 20% AlN content Al-AlN composite coating prepared in Example 2 of the present invention, and a distribution diagram of Al, AlN and Mg elements in the coating and the matrix.

[0029] Figure 6 This is a cross-sectional SEM image of the 30% AlN content Al-AlN composite coating prepared in Example 3 of the present invention, and a distribution diagram of Al, AlN and Mg elements in the coating and the matrix.

[0030] Figure 7 This is a cross-sectional SEM image of the 40% AlN content Al-AlN composite coating prepared in Example 4 of the present invention, and a distribution diagram of Al, AlN and Mg elements in the coating and the matrix.

[0031] Figure 8 This is a cross-sectional SEM image of the Al-AlN composite coating with 50% AlN content prepared in Example 5 of the present invention, and a distribution diagram of Al, AlN and Mg elements in the coating and the matrix.

[0032] Figure 9These are friction coefficient curves and average friction coefficient histograms of Al-AlN composite coatings with different AlN contents prepared in Examples 1-5 of the present invention; wherein (a) to (e) are friction coefficient curves for AlN contents of 10%, 20%, 30%, 40%, and 50%, respectively, and (f) is an average friction coefficient histogram.

[0033] Figure 10 These are SEM images of the wear marks of the Al-AlN composite coating with 10 wt.% AlN prepared in Example 1 of this invention; where (a), (b), (c), and (d) are magnifications of 100 μm, 50 μm, 10 μm, and 5 μm, respectively.

[0034] Figure 11 These are SEM images of the wear marks of the Al-AlN composite coating with 20 wt.% AlN prepared in Example 2 of this invention; where (a), (b), (c), and (d) are magnifications of 100 μm, 50 μm, 10 μm, and 5 μm, respectively.

[0035] Figure 12 These are SEM images of the wear marks of the Al-AlN composite coating with 30 wt.% AlN prepared in Example 3 of this invention; where (a), (b), (c), and (d) are magnifications of 100 μm, 50 μm, 10 μm, and 5 μm, respectively.

[0036] Figure 13 These are SEM images of the wear marks of the Al-AlN composite coating with 40 wt.% AlN prepared in Example 4 of this invention; where (a), (b), (c), and (d) are magnifications of 100 μm, 50 μm, 10 μm, and 5 μm, respectively.

[0037] Figure 14 These are SEM images of the wear marks of the Al-AlN composite coating with 50 wt.% AlN prepared in Example 5 of this invention; where (a), (b), (c), and (d) are magnifications of 100 μm, 50 μm, 10 μm, and 5 μm, respectively.

[0038] Figure 15 The images show the three-dimensional morphology and cross-sectional profile curve of the wear track of the Al-AlN composite coating with 10 wt.% AlN prepared in Example 1 of this invention.

[0039] Figure 16 The images show the three-dimensional morphology and cross-sectional profile curve of the wear track of the Al-AlN composite coating with 20 wt.% AlN prepared in Example 2 of this invention.

[0040] Figure 17 The images show the three-dimensional morphology and cross-sectional profile curve of the wear track of the Al-AlN composite coating with 30 wt.% AlN prepared in Example 3 of this invention.

[0041] Figure 18 The images show the three-dimensional morphology and cross-sectional profile curve of the wear track of the Al-AlN composite coating with 40 wt.% AlN prepared in Example 4 of this invention.

[0042] Figure 19 The images show the three-dimensional morphology and cross-sectional profile curve of the wear track of the Al-AlN composite coating with 50 wt.% AlN prepared in Example 5 of this invention.

[0043] Figure 20 These are images showing the wear volume and wear rate of the Al-AlN composite coatings prepared in Examples 1-5 of this invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0045] Example 1

[0046] This embodiment provides a cold-sprayed Al-AlN composite coating with an AlN content of 10 wt.%, and the preparation method is as follows:

[0047] S1. Powder mixing: Weigh 90% spherical Al powder (particle size 15-53μm) and 10% irregular AlN powder (particle size 4-54μm) by weight and mechanically mix for 1 hour.

[0048] S2. Substrate pretreatment: Clean the surface of the metal substrate (such as AZ31 magnesium alloy) with acetone and dry it. Then, use No. 6 corundum sand to perform sandblasting under a compressed air pressure of 0.4 MPa to remove the oxide layer and make the surface roughness reach 1.0-3.0 μm.

[0049] S3. Cold spray deposition: Using cold spray equipment, compressed N2 is used as the working gas and powder feeding gas. Under the conditions of gas pressure of 2MPa, heating temperature of 400℃, powder feeding rate of 10g / min, spray gun distance from the substrate of 20mm, and spray gun moving speed of 2mm / s, the mixed powder is sprayed onto the pretreated substrate surface to form a coating with a thickness greater than 200μm.

[0050] Example 2

[0051] This embodiment is basically the same as embodiment 1, except that in step S1: 80% Al powder and 20% AlN powder by weight are weighed.

[0052] Example 3

[0053] This embodiment is basically the same as Embodiment 1, except that in step S1: 70% Al powder and 30% AlN powder by weight are weighed.

[0054] Example 4

[0055] This embodiment is basically the same as embodiment 1, except that in step S1: 60% Al powder and 40% AlN powder by weight are weighed.

[0056] Example 5

[0057] This embodiment is basically the same as Embodiment 1, except that in step S1: 50% Al powder and 50% AlN powder are weighed.

[0058] Performance characterization and testing

[0059] The coatings obtained in Examples 1-5 above were subjected to the following tests:

[0060] (1) Powder morphology and particle size: SEM (Structured Electron Microscopy) was used to determine the morphology and particle size of the powder. Figure 1 ) and laser particle size analyzer ( Figure 2 Observation results showed that Al powder was nearly spherical and AlN powder was irregular in shape, with particle size within the suitable range for cold spraying.

[0061] (2) Coating phase: XRD analysis ( Figure 3 The results showed that only Al and AlN diffraction peaks were detected in all coatings, and no oxide peaks were found, indicating that the cold spraying process of the present invention effectively avoids oxidation.

[0062] (3) Coating cross-section: SEM and EDS ( Figure 4-8 The results showed that all coatings were dense, had low porosity, and exhibited uniform Al and AlN distribution. The density of the coatings increased with increasing AlN content.

[0063] (4) Friction and wear performance: The test was conducted using a reciprocating friction and wear tester (with Φ6mm GCr15 steel balls, load 1N, time 30min).

[0064] Coefficient of friction: such as Figure 9 As shown, the average friction coefficient generally increases with increasing AlN content.

[0065] Wear morphology: such as Figure 10-14 As shown, when the AlN content is low (10-20%), the coating is mainly subjected to abrasive wear, and the furrows are obvious; when the AlN content is high (40-50%), the furrows become shallower or disappear, and a friction layer and small particles appear, and the wear mechanism changes to slight abrasive wear.

[0066] Wear rate: such as Figure 20As shown in Table 1, the wear volume and wear rate decreased significantly with increasing AlN content. Among them, Example 5 (50 wt.% AlN) exhibited the lowest wear rate, at 8.05 × 10⁻⁶. -7 mm 3 ·N -1 ·m -1 It has the best wear resistance.

[0067] Table 1 Wear volume and wear rate of coatings in different embodiments

[0068]

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly wear-resistant cold-sprayed Al-AlN composite coating, characterized in that, Includes the following steps: Step (1): Al powder and AlN powder are mixed by mechanical mixing to obtain Al-AlN mixed powder; the Al powder is spherical with a particle size of 15-53μm; the AlN powder is irregular in shape with a particle size of 4-54μm; the mass percentage of AlN powder in the mixed powder is 10%-50%; the mechanical mixing time is 1h and the rotation speed is 200rpm; Step (2): Pre-treatment of the substrate surface: clean with acetone and dry, then perform sandblasting to remove the oxide layer and make the surface roughness reach 1.0-3.0μm; Step (3): Using cold spraying technology, the Al-AlN mixed powder obtained in step (1) is sprayed onto the substrate surface after pretreatment in step (2) to form an Al-AlN composite coating. The cold spraying process parameters are: the working gas and the powder feeding gas are both compressed nitrogen, the gas pressure is 2MPa, the heating temperature is 400℃, the powder feeding rate is 10g / min, the distance between the spray gun and the substrate surface is 20mm, and the relative moving speed between the spray gun and the substrate is 2mm / s. The thickness of the Al-AlN composite coating is greater than 200μm.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass percentage of AlN powder in the Al-AlN mixed powder is 50%.

3. The preparation method according to claim 1, characterized in that, The sandblasting process in step (2) uses No. 6 corundum sand and the compressed air pressure is 0.4 MPa.

4. A highly wear-resistant cold-sprayed Al-AlN composite coating, characterized in that, It is prepared by the preparation method according to any one of claims 1-3.

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