Patent Publication Number: US-2022234141-A1

Title: Method for roughening surface of metal material by using laser shock forming technology and application thereof

Description:
TECHNICAL FIELD 
     The present invention relates to the field of technologies for processing surfaces of metal materials, and in particular, to a method for roughening a surface of a metal material by using a laser shock forming technology and an application thereof. 
     BACKGROUND 
     Information of the Related Art part is merely disclosed to increase the understanding of the overall background of the present invention, but is not necessarily regarded as acknowledging or suggesting, in any form, that the information constitutes the prior art known to a person of ordinary skill in the art. 
     A superhydrophobic surface is a special surface layer that has an apparent contact angle greater than 150° and a rolling angle less than 10°. A metal superhydrophobic surface of a metal material has water-proof and self-cleaning properties, and can delay icing, corrosion, and the like during the service of the material. In order to change the wetness of a surface of a metal material, for example, prepare the superhydrophobic surface, technicians often need to roughen a surface of a to-be-processed material. Material surfaces having different roughnesses obtained by using different methods generally have inconsistent functional characteristics. Abrasive papers having different numbers of meshes have different surface shapes and corresponding surface roughness values. Generally, the abrasive papers having different numbers of meshes are used to grind the to-be-processed material, so that the surface of the material can have different roughness. However, during research, the inventors found that the surface of the metal material is easily scratched during the grinding, causing changes in a stress state of the surface of the material, thus affecting mechanical properties of the surface of the material. Thus, researchers are required to seek for a more effective and prospective method for preparing a rough surface. 
     SUMMARY 
     In view of the problem that a rough surface prepared by using a conventional grinding method is likely to cause degraded service performance and the technical obstacle of difficulty in preparing a rough surface for a part of a metal material, the present invention provides a method for roughening a surface of a metal material based on a pulse laser-induced force effect. By means of the method, a micron-structure and a nano-structure can be prepared on a metal surface, and the surface roughness and the preparation scope are accurate and controllable. 
     To achieve the foregoing inventive objectives, the technical means used in the present invention are as follows: 
     First, the present invention discloses a method for roughening a surface of a metal material by using a laser shock forming technology. The method includes: 
     preparation of an imprint mold, including: shocking abrasive papers by using a laser shock forming technology, and reprinting microstructures on surfaces of the abrasive papers having different numbers of meshes and micron-scale structures and nano-scale structures to a surface of a mold material, to obtain a micron-imprint mold and a nano-imprint mold; 
     pre-processing of a to-be-roughened material, including: using a smoothed material as a material having a surface to be roughened, where in order to avoid other components during processing, a material of the imprint mold is required to be same as the material having a surface to be roughened, and if the to-be-roughened material is a block material, that is, the to-be-roughened material has a thickness greater than 0.5 mm, a thickness of the imprint mold is required to be less than the thickness of the material having a surface to be roughened; 
     preparation of a micron-structure on the surface of the to-be-roughened material, including: 
     (a) placing a side of the micron-imprint mold that has a micron-structure on the surface of the to-be-roughened material, and disposing an absorption layer material and a constraint layer material on a side of the imprint mold that is in a pulse laser incident direction; 
     (b) performing single-pulse laser shocking on a to-be-processed area by using the laser shock forming technology, to reprint the micron-scale structure on the surface of the imprint mold to the surface of the to-be-roughened material; and 
     (c) cleaning the to-be-roughened material after the reprinting in step (b) to obtain a surface-micronized material; and 
     preparation of a nano-structure on the surface of the to-be-roughened material, including: 
     (d) paving a material capable of reducing a surface energy on a side of the surface-micronized material that has the micron-structure, placing a side of the nano-imprint mold that has a nano-structure on the material capable of reducing the surface energy, and disposing an absorption layer material and a constraint layer material on a surface of the nano-imprint mold; and 
     (e) performing single-pulse laser shocking on a to-be-processed area by using the laser shock forming technology, to reprint the nano-structure on the surface of the imprint mold to the surface of the to-be-roughed material, and obtain a low-surface-energy coating on the surface; and 
     (f) cleaning the to-be-roughened material finally obtained in step (e), so as to obtain the nano-structure on the surface of the to-be-roughened material. 
     A first feature of the preparation method of the present invention is as follows: The pulse laser can cause a plasma explosion on the surface of the material, forming a shocking pressure at a GPa level. When the imprint mold having a specific surface roughness is disposed on the surface of the material having a surface to be roughened, a shock wave effect induced by the pulse laser can reprint the surface shapes of the imprint mold on the material having a surface to be roughened. By means of the prepared imprint molds having micron-structures and nano-structures, the surface of the material can be easily, efficiently, accurately, and controllably micronized and nanosized in advance. The conventional methods lack these advantages. In addition, by means of the method of the present invention, the roughening of a part of the surface of the metal material can be realized without scratches. 
     A second feature of the preparation method of the present invention is as follows: In the present invention, abrasive papers having different numbers of meshes are used as templates of the imprint molds. By means of laser shocking, the surface of the material can generate surface shapes of the abrasive papers having corresponding numbers of meshes. Then the micron-structures and the nano-structures of the abrasive papers are reprinted on the surface of the material having a surface to be roughened. Such a physical preparation process is significantly different from a convention chemical preparation process and a convention mechanical grinding process. 
     A third feature of the preparation method of the present invention is as follows: A double-scale rough surface and a low-surface-energy coating material are important factors for preparing a hydrophobic surface. In order to obtain a metal hydrophobic surface, abrasive papers having different surface roughnesses are used for reprinting, so as to process the micron-structures and the nano-structures on the surface of the metal material step by step. In addition, the material capable of reducing surface energy is added to the reprint molds and then compressed into the material having a surface to be roughened by means of shocking, so as to reduce the surface energy. In this way, the micron-structures and the nano-structures having reduced surface energy are obtained. Therefore, a common surface of the material is converted into a hydrophobic surface. 
     Finally, the present invention discloses applications of a product prepared by using the method for roughening a surface of a metal material by using a laser shock forming technology in anti-snow accumulation and anti-icing of an outdoor metal article, anti-fouling and anti-corrosion of a ship shell, and anti-adhesion and anti-blocking of an inner wall of an oil pipeline in fields such as aerospace, military industries, and transportation. 
     Compared with the prior art, the present invention achieves the following beneficial effects: According to the method provided in the present invention based on a pulse-laser-induced force effect, a micron-imprint mold and a nano-imprint mold are first prepared, and then the molds are used as a template to present surface microstructures of the imprint molds on a surface of a to-be-processed material. By means of the method, the roughing of the part of the surface of the metal material is realized without scratches. In addition, compared with a conventional method, by means of the method of the present invention, micron-structures and nano-structures can be quantitatively prepared on a metal surface, and the surface roughness and the preparation scope are accurate and controllable and can be pre-designed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary examples of the present invention and descriptions thereof are used to explain the present invention, and do not constitute an improper limitation of the present invention. 
         FIG. 1  is a schematic diagram of preparing an imprint mold according to Embodiment 1 of the present invention. 
         FIG. 2  is a schematic diagram of preparing an imprint mold according to Embodiment 2 of the present invention. 
     
    
    
     Reference Numerals:  1 ,  8 : Pulse laser beam;  2 ,  9 : Constraint layer;  3 ,  10 : Absorption layer;  4 ,  12 : Imprint mold material;  5 ,  11 : Abrasive paper;  6 ,  13 : Mechanical arm or workbench;  7 ,  14 : Rough surface of imprint mold. 
     DETAILED DESCRIPTION 
     It should be pointed out that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those usually understood by a person of ordinary skill in the art to which the present invention belongs. 
     It should be noted that the terms used herein are merely used for describing specific implementations, and are not intended to limit exemplary implementations of the present invention. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise. In addition, it should further be understood that terms “comprise” and/or “include” used in this specification indicate that there are features, steps, operations, devices, components, and/or combinations thereof. 
     As described above, scratches are easily caused during roughening of a surface of a metal material by means of mechanical grinding, causing changes in a stress state of the surface of the material, thus affecting mechanical properties of the surface of the material. Thus, the present invention provides a method for roughening a surface of a metal material by using a laser shock forming technology based on a pulse-laser-induced force effect. 
     In some typical embodiments, a method for preparing a micron-imprint mold includes: using an abrasive paper having a micron-scale microstructure as a base plate, superimposing the mold material with a surface of the base plate that has a micron-structure, disposing an absorption layer material and a constraint layer material on a side in a pulse laser incident direction, and performing shock imprinting by using the laser shock forming technology to reprint the micron-scale microstructure on a surface of the base plate to the surface of the mold material, so as to obtain the micron-imprint mold. 
     In some typical embodiments, a method for preparing a nano-imprint mold includes: using an abrasive paper having a nano-scale microstructure as a base plate, superimposing the mold material with a surface of the base plate that has a nano-structure, disposing an absorption layer material and a constraint layer material on a side in a pulse laser incident direction, and performing shock imprinting by using the laser shock forming technology to reprint the nano-scale microstructure on a surface of the base plate to the surface of the mold material, so as to obtain the nano-imprint mold. 
     In some typical embodiments, the micron-structure and the nano-structure on the surfaces of the imprint molds are reprinted by using the abrasive papers having a relatively small number of meshes and a relatively large number of meshes respectively, to obtain a rough surface having a double-scale structure. 
     Further, an abrasive paper having a relatively small number of meshes is used to reprint the micron-structure, and the imprint mold using an abrasive paper having a relatively large number of meshes is required to form the nano-microstructure. It is to be noted that, the relatively small number of meshes herein are only required to meet a required scale of micron-structure, and the relatively large number of meshes of the abrasive paper are relative to the relatively small number of meshes, and may be selected according to a required scale of nano-structure. 
     Optionally, a surface roughness of the abrasive paper having a relatively small number of meshes is in a range of Ra0.5 to Ra1, and a surface roughness of the abrasive paper having a relatively large number of meshes is not higher than Ra0.2. 
     In some typical embodiments, if a to-be-roughened material is a block material having a thickness greater than 0.5 mm, when the imprint mold is foil, a thickness of the imprint mold is required to be less than the thickness of the material having a surface to be roughened, to ensure that the surface of the to-be-processed material can be deformed during laser shocking, so as to reprint the micron-structures and the nano-structures on the surfaces of the imprint molds to the material having a surface to be roughened. If the thickness of the imprint mold is greater than the thickness of the material having a surface to be roughened, the shock wave strength on the surface of the to-be-processed material is excessively high or excessively low. 
     In some typical embodiments, if a hydrophobic surface or a surface having other functional characteristics is to be prepared on a part of the to-be-roughened material having a thickness less than 0.5 mm, a rough surface of the abrasive paper may be directly reprinted on the foil of the same material as the to-be-roughened material. Then the foil having the rough surface is used as the imprint mold to prepare a rough surface by directly shocking the surface of the to-be-roughened material. 
     When the imprint mold uses foil, which is generally thin, damage may be caused to the imprint mold as a result of the weaker plastic deformation strength of the imprint mold compared to the to-be-processed material. Therefore, an ultra-thin hard coating is required to be selectively deposited on the rough surface of the imprint mold according to actual processing situations. The ultra-thin hard coating can protect the rough surface of the foil material used as the imprint mold from being damaged. 
     Thus, in some typical embodiments, if a functional rough surface is to be formed on a sheet material or a block material having thickness greater than 0.5 mm, the rough surface of the abrasive paper is required to be reprinted on the foil same as a material of to-be-processed sheet material, and then a hard coating (for example, an alumina coating) is required to be deposited on the rough surface of the foil, so that the rough surface of the foil material used as the imprint mold is not damaged. 
     In some typical embodiments, the laser shock forming technology includes one movement by a mechanical arm followed by one shocking by a laser, that is, point-by-point processing. 
     In some typical embodiments, the smoothing includes mechanical polishing or electrochemical polishing, and is required to be performed before the preparation of a rough surface. In the present invention, a surface roughness value of the surface of the to-be-roughed material is required to be low, that is, the surface roughness of the to-be-roughed material is required to be not greater than a desired surface roughness. 
     In some typical embodiments, the to-be-processed material is cleaned by means of ultrasonic cleaning. 
     In some typical embodiments, the absorption layer material is a black paint or a black tape. The absorption layer material is coated or pasted on a surface of a corresponding material that faces a pulse laser incident direction for use. 
     In some typical embodiments, the constraint layer material is K9 glass or deionized water. The constraint layer material is placed or coated on a surface of the absorption layer. 
     In some typical embodiments, the material capable of reducing the surface energy includes any of stearic acid, palmitic acid, and N-dodecyl mercaptan. 
     For example, a hydrophobic surface is prepared on a pure aluminum sample in an area irradiated by a single pulse laser by means of laser shocking. The present invention is further described with reference to  FIG. 1  and  FIG. 2 . 
     Embodiment 1 
     Referring to  FIG. 1 , a method for roughening a surface of a metal material by using a laser shock forming technology includes the following steps. 
     (I) Preparation of an imprint mold, including the following steps: 
     (1) A pure aluminum foil material having a thickness about 0.05 mm is selected as an imprint mold material, and a pure aluminum plate having a thickness of 2 mm is selected as a material having a surface to be roughed. Surfaces of the pure aluminum foil and the pure aluminum plate are both mechanically polished to be smooth. Before laser shocking, a black paint having a thickness about 0.5 mm is selected as an absorption layer, and K9 glass having a thickness about 3 mm is selected as a constraint layer. A used pulse laser is a circular beam having the following parameters: a wave length of 1064 nm, an energy of 1.2 J, a pulse width of 16 ns, and a diameter of 2 mm. A rough abrasive paper having 200 meshes is used to prepare a micron-imprint mold. 
     (2) First, the rough abrasive paper  5  having 200 meshes is fixed on a workbench  6  in a laser shock processing system, where a rough side of the abrasive paper is disposed upward. Then a to-be-processed side of the pure aluminum foil (an imprint mold material  4 ) is placed on a rough surface  7  on a surface of an imprint mold using the abrasive paper. After the above operation is finished, a layer of black paint is coated on an other side of the pure aluminum foil as the absorption layer  3 , and then the K9 glass is placed on a surface of the absorption layer as a constraint layer  2 . 
     (3) Single-pulse laser shocking is performed on a to-be-processed area of the to-be-processed aluminum foil by using a laser shock forming technology (a laser beam first reaches the aluminum foil, and then reaches the abrasive paper). The laser shock forming technology includes one movement by a mechanical arm followed by one shocking by a pulse laser beam  1 , that is, point-by-point processing. 
     (4) After the laser shocking, the absorption layer material and the constraint layer material on the surface of the aluminum foil are peeled off. When a surface of the aluminum foil that is in contact with the rough abrasive paper finally becomes a rough surface having a micron-structure of a size of a single laser spot, and a surface state of the obtained rough surface is same as that of the used rough abrasive paper having 200 meshes, a micron-imprint mold is obtained. 
     (II) Preparation of a nano-imprint mold, including the following steps: 
     (5) A pure aluminum foil material having a thickness about 0.05 mm and a smooth surface is selected as an imprint mold material. Before laser shocking, a black paint having a thickness about 0.5 mm is selected as an absorption layer, and K9 glass having a thickness about 3 mm is selected as a constraint layer. A used pulse laser is a circular beam having the following parameters: a wave length of 1064 nm, an energy of 1.2 J, a pulse width of 16 ns, and a diameter of 2 mm. A fine abrasive paper having 1000 meshes is used to prepare a nano-imprint mold. 
     (6) First, the fine abrasive paper  5  having 1000 meshes is fixed on the workbench  6  in the laser shock processing system, where a rough side of the abrasive paper is disposed upward. Then a to-be-processed side of the pure aluminum foil (an imprint mold material  4 ) is placed on a rough surface  7  on a surface of an imprint mold using the abrasive paper. After the above operation is finished, a layer of black paint is coated on an other side of the pure aluminum foil as the absorption layer  3 , and then the K9 glass is placed on a surface of the absorption layer as a constraint layer  2 . 
     (7) Step (3) and step (4) are repeated, and the nano-imprint mold is obtained after steps are finished. 
     (III) Preparation of a hard coating, including the following steps: 
     After the laser shocking, an alumina coating of 0.1 mm is deposited on the microstructure rough surfaces of the micron-imprint mold and the nano-imprint mold, to increase the strength of the micron-structure rough surface and the nano-structure rough surface of the aluminum foil. 
     (IV) Micronization of a surface of a pure aluminum plate, including the following steps: 
     (a) The pure aluminum plate is fixed on the workbench of the laser shock processing system. A side of the micron-imprint mold prepared in step (4) that has the micron-structure is placed on the surface of the pure aluminum plate. Then, a layer of black paint is coated on a side of the imprint mold in a pulse laser incident direction, and the K9 glass is placed on the black paint. 
     (b) Single-pulse laser shocking is performed on a to-be-processed area by using the laser shock forming technology (a laser beam first reaches the imprint mold, and then reaches the pure aluminum plate), to reprint the micron-structure on the surface of the imprint mold to the surface of the pure aluminum plate. 
     (c) The pure aluminum plate after the reprinting in step (b) is cleaned to obtain a surface-micronized material. 
     (V) Nanonization of the surface of the pure aluminum plate, including the following steps: 
     (d) The surface-micronized material obtained in step (c) is fixed on the workbench of the laser shock processing system. A layer of stearic acid is paved on a surface of the surface-micronized material that has the micron-structure, then the nano-imprint mold prepared in step (7) is placed on the stearic acid, a layer of black paint is coated on a side of the imprint mold that is in a pulse laser incident direction, and then the K9 glass is placed on the black paint. 
     (e) Single-pulse laser shocking is performed on a to-be-processed area by using the laser shock forming technology (a laser beam first reaches the imprint mold, and then reaches the pure aluminum plate), to reprint the nano-structure on the surface of the imprint mold to the surface of the surface-micronized material, and a low-surface-energy coating is pressed on the surface. 
     (f) The pure aluminum plate after the reprinting in step (e) is cleaned to obtain a surface-micronized and nanonized functional aluminum plate. 
     Embodiment 2 
     Referring to  FIG. 2 , a method for roughening a surface of a metal material by using a laser shock forming technology includes the following steps. 
     (I) Preparation of an imprint mold, including the following steps: 
     (1) A pure aluminum foil material having a thickness about 0.05 mm is selected as an imprint mold material, and a pure aluminum sheet having a thickness of 0.45 mm is selected as a material having a surface to be roughed. Surfaces of the pure aluminum foil and the pure aluminum sheet are both electrochemically polished to be smooth. Before laser shocking, a black tape having a thickness about 0.5 mm is selected as an absorption layer, and K9 glass having a thickness about 3 mm is selected as a constraint layer. A used pulse laser is a circular beam having the following parameters: a wave length of 1064 nm, an energy of 3.2 J, a pulse width of 16 ns, and a diameter of 2 mm. A rough abrasive paper having 200 meshes is used to prepare a micron-imprint mold. 
     (2) First, the pure aluminum foil (an imprint mold material  12 ) is fixed on a workbench  13  in a laser shock processing system. The rough abrasive paper  11  having 200 meshes is placed on a to-be-processed side of the imprint mold material  12 . After the above operation is finished, a layer of black tape is pasted on an other side of the rough abrasive paper  11  as the absorption layer  10 , and then the K9 glass is placed on a surface of the absorption layer as the constraint layer  9 . 
     (3) Single-pulse laser shocking is performed on a to-be-processed area of the to-be-processed aluminum foil by using a laser shock forming technology (a laser beam first reaches the abrasive paper, and then reaches the aluminum foil). The laser shock forming technology includes one movement by a mechanical arm followed by one shocking by a pulse laser beam  8 , that is, point-by-point processing. 
     (4) After the laser shocking, the absorption layer material and the constraint layer material on the surface of the aluminum foil are peeled off. When a surface of the aluminum foil that is in contact with the rough abrasive paper finally becomes a rough surface having a micron-structure of a size of a single laser spot, and a surface state of the obtained rough surface is same as that of the used rough abrasive paper having 200 meshes, a micron-imprint mold is obtained. 
     (II) Preparation of a nano-imprint mold, including the following steps: 
     (5) A pure aluminum foil material having a thickness about 0.05 mm and a smooth surface is selected as an imprint mold material. Before laser shocking, a black tape having a thickness about 0.5 mm is selected as an absorption layer, and K9 glass having a thickness about 3 mm is selected as a constraint layer. A used pulse laser is a circular beam having the following parameters: a wave length of 1064 nm, an energy of 2.4 J, a pulse width of 16 ns, and a diameter of 2 mm. A fine abrasive paper having 1000 meshes is used to prepare a nano-imprint mold. 
     (6) First, the pure aluminum foil (an imprint mold material  4 ) is fixed on a workbench  13  in the laser shock processing system. The fine abrasive paper  5  having 1000 meshes is placed on a rough surface  14  of the imprint mold material  4 . After the above operation is finished, a layer of black tape is pasted on an other side of the fine abrasive paper  5  as the absorption layer  3 , and then the K9 glass is placed on a surface of the absorption layer as the constraint layer  2 . 
     (7) Step (3) and step (4) are repeated, and the nano-imprint mold is obtained after steps are finished. 
     (III) Preparation of a hard coating, including the following steps: 
     After the laser shocking, an alumina coating of 0.1 mm is deposited on the microstructure rough surfaces of the micron-imprint mold and the nano-imprint mold, to increase the strength of the micron-structure rough surface and the nano-structure rough surface of the aluminum foil. 
     (IV) Micronization of a surface of a pure aluminum sheet, including the following steps: 
     (a) The micron-imprint mold prepared in step (4) is fixed on the workbench in the laser shock processing system. A side of the imprint mold that has the micron-structure is placed on the surface of the pure aluminum sheet. Then, a layer of black tape is pasted on a side of the pure aluminum sheet that is in a pulse laser incident direction, and the K9 glass is placed on the black tape. 
     (b) Single-pulse laser shocking is performed on a to-be-processed area by using the laser shock forming technology (a laser beam first reaches the pure aluminum sheet, and then reaches the imprint mold), to reprint the micron-structure on the surface of the imprint mold to the surface of the pure aluminum sheet. 
     (c) The pure aluminum sheet after the reprinting in step (b) is cleaned to obtain a surface-micronized material. 
     (V) Nanonization of the surface of the pure aluminum sheet, including the following steps: 
     (d) The surface-micronized material obtained in step (c) is fixed on the workbench of the laser shock processing system. A layer of stearic acid is paved on a surface of the surface-micronized material that has the micron-structure, then the nano-imprint mold prepared in step (7) is placed on the stearic acid, a layer of black tape is pasted on a side of the imprint mold that is in a pulse laser incident direction, and then the K9 glass is placed on the black tape. 
     (e) Single-pulse laser shocking is performed on a to-be-processed area by using the laser shock forming technology (a laser beam first reaches the imprint mold, and then reaches the pure aluminum sheet), to reprint the nano-structure on the surface of the imprint mold to the surface of the surface-micronized material, and a low-surface-energy coating is pressed on the surface. 
     (f) The pure aluminum plate after the reprinting in step (e) is cleaned to obtain a surface-micronized and nanonized functional aluminum sheet. 
     The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. A person skilled in the art may make various alterations and variations to the present invention. Any modification, equivalent replacement, or improvement made and the like within the spirit and principle of the present invention shall fall within the protection scope of the present invention.