Method for preparing durable aviation aluminum alloy super-hydrophobic surface through liquid nitrogen assisted laser peening

Abstract

The invention provides a method for preparing a durable aviation aluminum alloy super-hydrophobic surface through liquid nitrogen assisted laser peening, which comprises the following steps: a pretreated aluminum alloy workpiece is fixed on an impact platform, and the impact platform is positioned in a sealed protective cover; flowing liquid nitrogen is continuously input into the to-be-machined surface of the aluminum alloy workpiece; the liquid nitrogen layer serves as a restraint layer; the to-be-machined surface of the aluminum alloy workpiece is subjected to laser peening treatment without an absorption layer; a to-be-processed surface is irradiated through short pulse laser, and a super-hydrophobic micro-nano multilevel structure with the surface containing nitrogen is formed; and placing in a vacuum drying box for drying treatment, so as to obtain the super-hydrophobic surface of the aviation aluminum alloy. The aviation aluminum alloy super-hydrophobic surface with high durability is prepared in one step, the nitride improves the hardness of the structure, the capability of preventing damage of foreign objects is improved, and the durability of the super-hydrophobic surface is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy surface processing, and in particular to a method for preparing a durable aviation aluminum alloy super-hydrophobic surface by liquid nitrogen-assisted laser shot peening. Background Art

[0002] Due to their excellent strength-to-weight ratio, high toughness, good plasticity, and lightweight properties, aviation aluminum alloys have become important structural materials in the aerospace industry and are widely used in the manufacture of key components such as aircraft skins and wing ribs. When aircraft are exposed to the extreme temperature fluctuations of the ocean, icing easily forms on the surfaces of aviation aluminum alloys, adversely affecting the aircraft's service safety and performance. Research has shown that constructing a superhydrophobic structure on the surface of aviation aluminum alloys can effectively mitigate icing. Therefore, imparting superhydrophobic properties to aluminum alloy surfaces is of great significance for improving the safety of aircraft in extreme weather conditions.

[0003] There are many methods for preparing super-hydrophobic surfaces on aluminum alloys, such as electrochemical deposition, vapor deposition, and chemical etching. Among them, the method of using nanosecond lasers to construct super-hydrophobic microstructures on the surface of aluminum alloys has the obvious advantages of high preparation efficiency and environmental friendliness compared to other preparation methods. This technology uses laser etching to form a regular array structure, which reduces the surface energy and gives the surface of the aluminum alloy material good hydrophobic properties. However, due to the processing characteristics of laser etching, which is hot and quenching, it is easy to induce high-amplitude residual tensile stress on the surface of the material, greatly reducing the mechanical properties of the base material of aviation aluminum alloy components.

[0004] Therefore, the existing preparation methods of metal superhydrophobic surfaces are limited by defects such as complex manufacturing process, high cost, damage to the mechanical properties of the base material, and inability to prepare on a large scale, making them difficult to apply in the complex force-bearing aviation field. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening. On the basis of the existing laser shot peening process for preparing a super-hydrophobic surface, a flowing liquid nitrogen layer is used as a constraining layer to perform non-absorbing layer shot peening on the pre-treated aluminum alloy surface. In a liquid nitrogen environment, laser irradiation is applied to the aluminum alloy surface, and the liquid nitrogen and the aluminum alloy surface absorb the laser energy to form a high-temperature and high-pressure plasma and generate a high-pressure shock wave. Under the action of the shock wave, the material dislocations near the surface of the aviation aluminum alloy multiply, the grains are refined, and high residual compressive stress is introduced to improve the mechanical properties of the material; at the same time, under high temperature and high pressure environments, nitrogen ions react with the remelted material on the surface of the aluminum alloy to form nitrides, thereby constructing a micro-nano multi-level structure with super-hydrophobic properties and a high nitrogen content. In a low-temperature environment, the heat generated on the surface during the laser shot peening process is rapidly conducted to the surroundings, avoiding excessive accumulation of thermal effects and potential thermal damage. The present invention prepares a highly durable super-hydrophobic surface of an aviation aluminum alloy in one step. On the one hand, the nitride increases the hardness of the structure, increases the ability to prevent damage from foreign objects, and improves the durability of the super-hydrophobic surface. On the other hand, the near-surface layer is affected by the GPa-level plasma shock wave, and the near-surface layer of the matrix material forms beneficial microstructure evolution and residual compressive stress, thereby increasing the service life of aluminum alloy super-hydrophobic surface components in complex aerospace environments. An innovative method for preparing a highly durable super-hydrophobic surface of an aviation aluminum alloy by a liquid nitrogen-assisted absorption layer-free laser shot peening process is proposed.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A method for preparing a durable super-hydrophobic surface of an aviation aluminum alloy by liquid nitrogen-assisted laser shot peening comprises the following steps:

[0008] Pre-treat the surface of aluminum alloy workpiece;

[0009] The pre-treated aluminum alloy workpiece is fixed on an impact platform, which is located inside a sealed protective cover. Liquid nitrogen is continuously injected into the surface to be processed of the aluminum alloy workpiece. By controlling the flow of liquid nitrogen, the temperature of the processing area is reduced and maintained at a low temperature.

[0010] By adjusting the distance between the surface to be processed of the aluminum alloy workpiece and the protective cover, the thickness of the liquid nitrogen layer is controlled to form a stable and uniform liquid nitrogen layer as a constraining layer; the surface to be processed of the aluminum alloy workpiece is subjected to laser shot peening without an absorption layer; and the surface to be processed is irradiated with a short-pulse laser to form a nitrogen-containing super-hydrophobic micro-nano multi-level structure on the surface;

[0011] Ultrasonic cleaning is used to remove the attached residues on the surface of the micro-nano multi-level structure, and then the structure is placed in a vacuum drying oven for drying. The operating temperature of the vacuum drying oven gradually increases from low temperature to room temperature to reduce the release of residual compressive stress caused by the ultra-high strain rate plastic deformation of the laser shot peening substrate material without an absorption layer, thereby obtaining a super-hydrophobic surface of the aviation aluminum alloy.

[0012] Furthermore, by controlling the liquid nitrogen gas flow rate to 20 to 30 L / min, the surface temperature of the aluminum alloy workpiece to be processed is controlled within the range of -130°C to -110°C.

[0013] Furthermore, in a low-temperature environment, a short-pulse laser is used to directly irradiate the surface of aviation aluminum alloy with the assistance of a liquid nitrogen confinement layer. The liquid nitrogen and the surface to be processed of the aluminum alloy workpiece absorb the plasma generated by the laser energy. The expanding plasma generates a GPa-level shock wave under the action of the liquid nitrogen confinement layer, which propagates toward the interior of the surface to be processed, causing surface dislocations to multiply and high-amplitude residual compressive stress to be generated inside the grain-refined material. The remelted material on the surface to be processed reacts with nitrogen ions to form nitrides, which are used to improve the strength of the superhydrophobic micro-nanostructure.

[0014] Furthermore, the surface to be processed of the aluminum alloy workpiece is polished step by step using sandpaper of different mesh sizes to control the surface roughness of the workpiece to be 100 μm; the surface to be processed of the aluminum alloy workpiece is placed in anhydrous ethanol for ultrasonic cleaning to remove surface impurities.

[0015] Furthermore, by adjusting the distance between the surface to be processed of the aluminum alloy workpiece and the protective cover, the thickness of the liquid nitrogen layer is controlled to be 1.5 mm to 2.5 mm.

[0016] Furthermore, the aluminum alloy workpiece after ultrasonic cleaning was placed in a vacuum drying oven with an initial temperature of -50°C. During the drying process, the temperature rate was controlled so that the temperature of the vacuum drying oven was raised from -50°C to 30°C.

[0017] Furthermore, the short pulse laser parameters are specifically as follows: wavelength 1064nm, laser energy 1J~3J, flat top distribution, circular spot diameter 1~3mm, repetition frequency 5Hz~15Hz, and pulse width 10ns~20ns.

[0018] Furthermore, the nitrogen content on the surface of the aluminum alloy workpiece after machining is 4.95~6.25 wt%.

[0019] The beneficial effects of the present invention are:

[0020] 1. The method described in this invention for producing a durable super-hydrophobic surface on an aviation aluminum alloy by liquid nitrogen-assisted laser peening involves direct irradiation of the aluminum alloy surface with a high-energy, short-pulse laser, assisted by liquid nitrogen. The liquid nitrogen and the aluminum alloy surface absorb energy to form a high-temperature, high-pressure plasma. Remelted materials on the aluminum alloy surface react fully with nitrogen ions to form nitrides, effectively enhancing the strength of the super-hydrophobic surface micro- and nanostructures. The rapidly expanding plasma, under the influence of a liquid nitrogen confinement layer, generates GPa-level shock waves that propagate into the substrate material, causing ultra-high strain-rate plastic deformation near the surface layer. This increases dislocation density, refines grains, and generates high-amplitude residual compressive stresses within the material, thereby improving the mechanical properties of the super-hydrophobic aluminum alloy substrate. This fabrication process can simultaneously enhance the mechanical properties of the super-hydrophobic micro- and nano-hierarchical structure of the aviation aluminum alloy and the substrate material.

[0021] 2. The method described in this invention for producing a durable super-hydrophobic surface on aviation aluminum alloys using liquid nitrogen-assisted laser peening adjusts the distance between the workpiece and the protective cover, thereby precisely controlling the thickness of the liquid nitrogen confinement layer. Furthermore, in a low-temperature environment, the heat generated by high-energy, short-pulse laser irradiation on the aluminum alloy surface is rapidly transferred to the surrounding area, preventing excessive accumulation of thermal stress and potential thermal damage, making it more suitable for the complex and demanding environments of aerospace. Furthermore, due to the low temperature of liquid nitrogen in existing techniques, its rapid diffusion rate at room temperature or low temperatures prevents it from forming an effective confinement layer. This invention utilizes a cryogenically resistant protective cover and controls the gap between the cover and the workpiece surface, creating a defined liquid nitrogen flow channel that limits its diffusion.

[0022] 3. The liquid nitrogen-assisted laser peening method described herein for producing a durable super-hydrophobic surface on aviation aluminum alloys utilizes a flat-top pulse laser. Compared to conventional circular-spot Gaussian pulse laser peening, stress waves are primarily longitudinally propagating plane compression waves, with a lower energy contribution from surface transverse waves. This characteristic eliminates complex interference between the residual stress fields induced by adjacent peening points during flat-top laser peening, significantly reducing stress field nonuniformity caused by the order of peening. The resulting macroscopic surface morphology is relatively flat, reducing drag on the falling droplet.

[0023] 4. The method described in this invention for producing a durable super-hydrophobic surface on aviation aluminum alloys using liquid nitrogen-assisted laser shot peening is simple to operate, low-cost, and has great potential for large-scale industrial production. It also significantly improves the wear resistance and mechanical stability of the super-hydrophobic surface's micro-nano hierarchical structure, while effectively enhancing the strength of the aluminum alloy substrate. These excellent properties make this technology highly adaptable for key components in the aerospace industry, demonstrating broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, it is obvious that other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Schematic diagram of the preparation of a durable super-hydrophobic surface of aviation aluminum alloy by laser shot peening according to the present invention.

[0026] Figure 2 This is an SEM image of the porous micro-nano multi-level structure on the super-hydrophobic surface of a durable aviation aluminum alloy prepared by laser shot peening as described in Example 1 of the present invention.

[0027] Figure 3 A comparison of the contact angles of liquid droplets on super-hydrophobic surfaces prepared in various embodiments of the present invention.

[0028] Figure 4 This is a comparison chart of the nitrogen content near the surface of the super-hydrophobic surface prepared in various embodiments of the present invention.

[0029] Figure 5 A comparison chart of the near-surface microhardness of the super-hydrophobic surface prepared in various embodiments of the present invention.

[0030] Figure 6 Graph showing the maximum amplitude of residual stress near the surface of the super-hydrophobic surface prepared in various embodiments of the present invention.

[0031] Figure 7 This is the change curve of the droplet contact angle after the super-hydrophobic surface prepared in Example 1 of the present invention has been subjected to different friction distances.

[0032] In the picture:

[0033] 1-Impact platform; 2-Aluminum alloy workpiece; 3-Protective cover. DETAILED DESCRIPTION

[0034] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "axial", "radial", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0036] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0037] like Figure 1 As shown, the method of preparing a high-durability super-hydrophobic surface of an aviation aluminum alloy by liquid nitrogen-assisted laser shot peening according to the present invention comprises the following steps:

[0038] S01: Pre-treating the surface of the aluminum alloy workpiece 2, grinding and polishing the aluminum alloy surface step by step to make the surface roughness of the workpiece 100 μm; placing the aluminum alloy surface in anhydrous ethanol for ultrasonic cleaning to remove surface impurities.

[0039] S02: The pretreated aluminum alloy workpiece 2 is fixed on an impact platform 1, which is located inside a sealed, transparent, low-temperature-resistant protective cover 3. The impact platform 1 is perpendicular to the horizontal plane and has liquid nitrogen inlets and outlets at its upper and lower ends. Liquid nitrogen is continuously supplied to the surface to be processed of the aluminum alloy workpiece 2, and the temperature of the processing area is reduced and maintained at a low temperature by controlling the liquid nitrogen flow rate.

[0040] S03: By adjusting the distance between the surface to be processed of the aluminum alloy workpiece 2 and the protective cover 3, the thickness of the liquid nitrogen layer is controlled to form a stable and uniform liquid nitrogen layer as a constraining layer; when the ambient temperature in the protective cover 3 reaches a preset value, the surface to be processed of the aluminum alloy workpiece 2 is subjected to laser shot peening without an absorption layer; a circular spot flat-top nanosecond pulse laser is used, the pulse parameters and path are set, and the liquid nitrogen layer is used as the constraining layer to perform laser shot peening without an absorption layer on the aluminum alloy surface, and the light beam is always kept perpendicular to the material surface. The surface to be processed is irradiated by short-pulse laser to form a nitrogen-containing super-hydrophobic micro-nano multi-level structure on the surface;

[0041] S04: Remove the attached residues on the surface of the micro-nano multi-level structure through ultrasonic cleaning, and then place it in a low-temperature vacuum drying oven for drying. During the drying process, the temperature is precisely controlled so that the working temperature of the vacuum drying oven gradually rises from low temperature to room temperature, so as to reduce the release of residual compressive stress caused by the ultra-high strain rate plastic deformation of the laser shot peening substrate material without an absorption layer, thereby obtaining a highly durable aviation aluminum alloy super-hydrophobic surface.

[0042] like Figure 1 As shown, a lifting mechanism is installed at the bottom of the protective cover 3. By changing the height of the protective cover 3, the distance between the surface to be processed of the aluminum alloy workpiece 2 and the protective cover 3 is adjusted. There is flowing liquid nitrogen in the gap, which ensures the thickness of the liquid nitrogen constraint layer; by controlling the flow rate of liquid nitrogen, the low-temperature laser shot peening environment temperature without absorption layer is maintained.

[0043] The method of preparing a high-durability super-hydrophobic surface of an aviation aluminum alloy by liquid nitrogen-assisted laser shot peening of the present invention comprises the following steps: a flat-top nanosecond pulse laser is used to directly irradiate the surface of the aviation aluminum alloy with a high-energy short-pulse laser under the auxiliary effect of liquid nitrogen; the liquid nitrogen and the aluminum alloy surface absorb the laser energy to generate a high-temperature and high-pressure plasma; the remelted material on the aluminum alloy surface fully reacts with the nitrogen ions to form nitrides, effectively improving the strength of the super-hydrophobic micro-nanostructure; the rapidly expanding plasma generates a GPa-level shock wave under the action of the liquid nitrogen confinement layer, which propagates into the interior of the matrix material, multiplies surface dislocations, and generates high-amplitude residual compressive stress inside the grain-refined material, thereby improving the mechanical properties of the matrix material of the aviation aluminum alloy super-hydrophobic component; at the same time, under a low-temperature environment, the heat generated during the high-energy short-pulse laser irradiation process is rapidly conducted to the surrounding area, avoiding excessive accumulation of thermal stress and potential thermal damage; the flat-top pulse laser is used, and the surface macroscopic surface morphology of the prepared surface is relatively flat, which is conducive to reducing the resistance when the droplets roll down. The present invention adopts the preparation process of liquid nitrogen-assisted laser shot peening to prepare a high-durability super-hydrophobic surface on an aviation aluminum alloy material.

[0044] In order to make the purpose, technical solutions and advantages of the present invention clearer, 2024-T351 aviation aluminum alloy is selected as the research object and the present invention is described in detail in combination with specific embodiments.

[0045] Example 1

[0046] The method for preparing a highly durable super-hydrophobic surface of an aviation aluminum alloy by liquid nitrogen-assisted laser shot peening as described in Example 1 comprises the following steps:

[0047] S01: The surface of 2024-T351 aviation aluminum alloy was ground using 400#, 800#, 1000#, and 1500# sandpaper, and then polished on a grinder and polisher to a surface roughness of 100μm. The surface of the workpiece was ultrasonically cleaned in anhydrous ethanol for 5 minutes and then dried for later use.

[0048] S02: Clamp the aluminum alloy workpiece 2 to the designated position and tighten it. Adjust the distance between the surface to be machined of the aluminum alloy workpiece 2 and the protective cover 3 to control the thickness of the liquid nitrogen confinement layer to 1.5 mm. Continuously inject liquid nitrogen into the surface to be machined of the aluminum alloy workpiece 2 at a controlled flow rate of 20 L / min, maintaining the ambient temperature inside the protective cover 3 at -110°C.

[0049] S03: The surface to be processed of the aluminum alloy workpiece 2 is subjected to laser shot peening without an absorption layer. A Nd:YAG high-frequency, high-energy nanosecond laser is selected, and a circular spot flat-top pulse nanosecond laser is used. The specific parameters of laser shot peening are: wavelength 1064nm, laser energy 1J, flat-top distribution, circular spot diameter 1mm, repetition frequency 5Hz, pulse width 10ns, and a multi-point overlapping large-area impact method with a spot overlap rate of 60% between rows and columns is adopted. The scanning path adopts a "bow" motion trajectory; flowing liquid nitrogen is used as the constraining layer.

[0050] S04: After laser shot peening, ultrasonic cleaning is used to remove residual attachments on the surface of the micro-nanostructure. The aviation aluminum alloy workpiece is placed in a low-temperature vacuum drying oven for 2 hours. During the drying process, the temperature is precisely controlled to raise the temperature of the vacuum drying oven from -50°C to 30°C to achieve the preparation of the super-hydrophobic surface of the aviation aluminum alloy.

[0051] The highly durable aviation aluminum alloy super hydrophobic surface prepared in Example 1 is as follows: Figure 2 As shown in the figure, a high-density micro-nano porous structure is generated on the surface of the aviation aluminum alloy, which can retain a large amount of air when in contact with the droplets, forming an air cushion, which greatly reduces the contact area between the droplets and the aviation aluminum alloy surface, making the aviation aluminum alloy surface exhibit superhydrophobic properties; Figure 3 As shown in FIG, the water contact angle is 159° and the rolling angle is 5° as measured by an angular contact measuring instrument; Figure 4 As shown in Figure 2, the nitrogen content of the micro-nanostructure on the surface of the aluminum alloy is 4.95 wt%. The nitrogen content on the surface of the material is greatly increased, which greatly improves the microhardness of the aviation aluminum alloy. Figure 5As shown in Figure 2, the microhardness value reaches 191HV, which is 46.9% higher than the average hardness value of 130HV on the untreated workpiece surface. Figure 6 As shown in FIG1 , the maximum amplitude of the residual stress near the surface of the aviation aluminum alloy prepared in Example 1 is -176.7 MPa; Figure 7 As shown in Figure 1, the contact angle of the aviation aluminum alloy super-hydrophobic surface prepared in Example 1 after friction. A 10N load was applied to 400-grit sandpaper, causing it to perform a 10CM linear reciprocating friction with the workpiece surface. The contact angle was measured after each friction. The results showed that the workpiece still maintained super-hydrophobic properties, exhibiting good wear resistance and super-hydrophobic stability.

[0052] Example 2

[0053] On the basis of Example 1, the liquid nitrogen flow rate in Example 2 is set to 20 L / min, the laser shot peening energy is set to 2 J, the liquid nitrogen confinement layer thickness is 2 mm, the circular spot diameter is 2 mm, the repetition frequency is 10 Hz, and the pulse width is 15 ns.

[0054] The highly durable aviation aluminum alloy super hydrophobic surface prepared in Example 2 is as follows: Figure 3 As shown in the figure, the water contact angle is 164° and the rolling angle is 4° as measured by the angular contact measuring instrument; the nitrogen content near the surface of the aluminum alloy material is increased, which greatly improves the microhardness of the aviation aluminum alloy. Figure 4 As shown in Figure 2, the surface nitrogen content is 5.43 wt%. Figure 5 As shown in Figure 2, the microhardness value reaches 201HV, which is 54.6% higher than the average hardness value of 130HV on the untreated workpiece surface. Figure 6 As shown, the maximum amplitude of the near-surface residual stress of the aviation aluminum alloy prepared in Example 2 is -190.1 MPa.

[0055] Example 3

[0056] On the basis of Example 1, the liquid nitrogen flow rate in Example 2 is set to 30 L / min, the laser shot peening energy is set to 3J, the liquid nitrogen confinement layer thickness is 3mm, the circular spot diameter is 3mm, the repetition frequency is 15Hz, and the pulse width is 20ns.

[0057] The highly durable aviation aluminum alloy super hydrophobic surface prepared in Example 1 is as follows: Figure 3 As shown in the figure, the water contact angle is 162° and the rolling angle is 4° as measured by the angular contact measuring instrument; the nitrogen content near the surface of the aluminum alloy material is increased, which greatly improves the microhardness of the aviation aluminum alloy. Figure 4 As shown, its surface nitrogen content is 6.25 wt%, as shown in Figure 5 As shown in Figure 2, the microhardness value reaches 211HV, which is 62.3% higher than the average hardness value of 130HV on the untreated workpiece surface. Figure 6 As shown, the maximum amplitude of the near-surface residual stress of the aviation aluminum alloy prepared in Example 2 is -210.4 MPa.

[0058] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0059] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening, characterized in that: The following steps are involved: Pre-treating the surface of the aluminum alloy workpiece (2); The pre-treated aluminum alloy workpiece (2) is fixed on an impact platform (1), and the impact platform (1) is located inside a sealed protective cover; liquid nitrogen is continuously input into the surface to be processed of the aluminum alloy workpiece (2), and the temperature of the processing area is reduced and maintained at a low temperature by controlling the flow rate of the liquid nitrogen; By adjusting the distance between the surface to be processed of the aluminum alloy workpiece (2) and the protective cover, the thickness of the liquid nitrogen layer is controlled to form a stable and uniform liquid nitrogen layer as a constraint layer; performing laser shot peening treatment without an absorption layer on the surface to be processed of the aluminum alloy workpiece (2); and forming a nitrogen-containing super-hydrophobic micro-nano multi-level structure on the surface by irradiating the surface to be processed with a short-pulse laser. Ultrasonic cleaning is used to remove the attached residues on the surface of the micro-nano multi-level structure, and then the structure is placed in a vacuum drying oven for drying. The operating temperature of the vacuum drying oven gradually increases from low temperature to room temperature to reduce the release of residual compressive stress caused by the ultra-high strain rate plastic deformation of the laser shot peening substrate material without an absorption layer, thereby obtaining a super-hydrophobic surface of the aviation aluminum alloy.

2. The method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: By controlling the liquid nitrogen gas flow rate to 20 to 30 L / min, the surface temperature of the aluminum alloy workpiece (2) to be processed is controlled within the range of -130°C to -110°C.

3. The method for preparing a durable aviation aluminum alloy super-hydrophobic surface by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: In a low-temperature environment, a short-pulse laser is directly irradiated on the surface of an aviation aluminum alloy with the assistance of a liquid nitrogen confinement layer. The liquid nitrogen and the surface to be processed of the aluminum alloy workpiece (2) absorb the plasma generated by the laser energy. The expanded plasma generates a shock wave of the order of GPa under the action of the liquid nitrogen confinement layer and propagates into the interior of the surface to be processed, causing surface dislocations to multiply and grain refinement to produce high-amplitude residual compressive stress inside the material. The remelted material on the surface to be processed reacts with nitrogen ions to form nitrides, which are used to improve the strength of the superhydrophobic micro-nanostructure.

4. The method for preparing a durable aviation aluminum alloy super-hydrophobic surface by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: The surface to be processed of the aluminum alloy workpiece (2) is polished step by step using sandpaper of different mesh sizes, so that the surface roughness of the workpiece is controlled at 100 μm; the surface to be processed of the aluminum alloy workpiece (2) is placed in anhydrous ethanol for ultrasonic cleaning to remove surface impurities.

5. The method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: By adjusting the distance between the surface to be processed of the aluminum alloy workpiece (2) and the protective cover, the thickness of the liquid nitrogen layer is controlled to be 1.5 mm to 2.5 mm.

6. The method for preparing a durable aviation aluminum alloy super-hydrophobic surface by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: The aluminum alloy workpiece (2) after ultrasonic cleaning is placed in a vacuum drying oven with an initial temperature of -50°C. During the drying process, the temperature rate is controlled so that the temperature of the vacuum drying oven is raised from -50°C to 30°C.

7. The method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: The specific parameters of the short pulse laser are: wavelength 1064nm, laser energy 1J~3J, flat top distribution, circular spot diameter 1~3mm, repetition frequency 5Hz~15Hz, and pulse width 10ns~20ns.

8. The method for preparing a durable super-hydrophobic surface of aviation aluminum alloy by liquid nitrogen-assisted laser shot peening according to claim 1, characterized in that: The surface nitrogen content of the treated aluminum alloy workpiece (2) is 4.95-6.25 wt%.

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