A preparation method for an anchored microstructure on the surface of structural steel

Abstract

The present invention belongs to the technical field of heterogeneous material connection, and particularly relates to a preparation method for an anchored microstructure on the surface of structural steel. First, the surface of the structural steel is pretreated by shot peening to prefabricate pits. Then, the pretreated surface of the structural steel is subjected to film coating and hole making treatment. Subsequently, chemical pre-etching is carried out to corrode the surface of the structural steel by using a mixed solution containing strong acid. Finally, electrochemical etching is carried out on the surface of the structural steel. Based on the potential difference between different phases in the structural steel, the low-potential tissue is consumed through galvanic corrosion to form holes. By controlling the magnitude of the current and the action time, nano-holes are formed on the basis of micron-scale chemical etching holes. Its principle is scientific and reliable. The surface of the structural steel is controllably etched by an electrochemical method to form an array of concave hole anchoring structures with high controllability and stability and uniform distribution, providing stable mechanical locks and anchor points for the interfacial bonding of structural steel / thermoplastic composites.

Description

Technical Field:

[0001] The present invention belongs to the technical field of heterogeneous material connection, and specifically relates to a method for preparing an anchored microstructure on the surface of structural steel. Based on chemical / electrochemical methods, it provides an anchored microstructure for the mechanical lock of dissimilar materials between structural steel and thermoplastic composites. Background Art:

[0002] Structural steel is the main material for ship structural facilities. It faces severe corrosion damage problems in harsh marine environments. In particular, harsh environments with extreme temperatures, high humidity, high salinity, and high ultraviolet radiation will greatly exacerbate the corrosion of structural steel. Therefore, higher requirements are put forward for the research and development standards of structural steel corrosion protection methods. The current main protection method is to coat organic / inorganic coatings on the surface of structural steel. However, the bonding strength between the structural steel substrate and the coating is relatively low, about 5 - 10 MPa, and it is prone to breakage during application. When an electrical couple is formed between the damaged position and the surrounding area, the probability and speed of pitting corrosion increase, and the mechanical support function of structural steel is severely damaged, increasing the maintenance cost.

[0003] The thickness of organic / inorganic coatings is generally 100 - 2000 μm. In contrast, assembling thermoplastic composites on the metal surface can obtain a greater thickness, which can more effectively hinder the penetration of Cl - ions, thereby reducing the costs of maintenance, rust removal, and coating, extending the maintenance cycle, being particularly suitable for the anti-corrosion of large structural steel, and having been applied in the fields of shipbuilding and marine engineering repair.

[0004] Adhesion and mechanical fastening are the main methods for connecting dissimilar materials. However, adhesion has problems such as interface curing deformation and debonding; mechanical fastening has problems such as stress concentration and contact corrosion of dissimilar metals. Based on this, the mechanical locking connection technology at the interface between resin-based composites and metals has become a new research direction. Among them, increasing the surface roughness of the metal and preparing an anchored structure on the metal surface have become the research key.

[0005] In the prior art, the anchored structures on the metal surface are mainly prepared by methods such as sandpaper grinding, surface sandblasting, and laser processing. However, the surface state of sandpaper grinding and surface sandblasting is difficult to control, and the scale of the prepared anchored structures is usually in the sub-millimeter range, with low density and interface bonding strength; when preparing anchored structures by laser processing, the microstructure of the metal surface after the melting and cooling process changes from the rolling state to the casting state, and it is difficult to avoid the generation of defects such as thermal cracks and pores; in addition, laser processing has high costs, and the processing surface and size are limited, which is not conducive to the surface processing of large structural steel. Therefore, researching and designing a method for preparing an anchored microstructure on the surface of structural steel to solve the deficiencies of mechanical processing and laser processing has positive social and economic benefits. Summary of the Invention:

[0006] The object of the present invention is to overcome the drawbacks existing in the prior art, and research and design a preparation method for the surface anchored microstructure of structural steel. By means of electrochemistry, the surface of the structural steel is controllably etched to form an array of concave hole anchored structures with uniform distribution.

[0007] To achieve the above object, the preparation method for the surface anchored microstructure of structural steel involved in the present invention includes the following steps: First, the surface of the structural steel is pretreated by shot peening to prefabricate pits with a pore diameter of 50 - 200 μm. The stress at the pits is relatively concentrated, which can effectively induce the formation of etching holes and facilitate the longitudinal growth of the etching holes. Then, the pretreated surface of the structural steel is subjected to film covering and hole making treatment. The film covering can avoid the problem that the raised parts on the surface of the structural steel are consumed due to the large current during the electrochemical etching process after chemical etching, which is beneficial to increasing the longitudinal depth of the etching holes. Subsequently, chemical pre-etching is carried out to corrode the surface of the structural steel with a mixed solution containing strong acid, effectively removing the metal matrix at the hole making part of the film covering and forming micron-sized etching holes. Finally, electrochemical etching is carried out on the surface of the structural steel. Based on the potential difference between different phases in the structural steel, the low-potential tissue is consumed through galvanic corrosion to form holes. By controlling the magnitude of the current and the action time, nano-sized holes are formed on the basis of the micron-sized chemical etching holes, further enhancing the mechanical anchoring ability.

[0008] The technological process of the preparation method for the surface anchored microstructure of structural steel involved in the present invention includes four steps: pretreatment, film covering and hole making, chemical pre-etching, and electrochemical etching.

[0009] Step 1: Grind and shot peen the surface of the structural steel in sequence, and then clean and dry it.

[0010] Step 2: Carry out film covering and hole making treatment on the pretreated surface of the structural steel.

[0011] Step 3: Carry out chemical pre-etching on the structural steel with film covering and hole making, and form micron-sized etching holes on the surface of the structural steel by controlling the concentration and etching time of the etching solution.

[0012] Step 4: Carry out electrochemical etching on the chemically pre-etched structural steel to form nano-sized holes on the surface of the structural steel.

[0013] Specifically:

[0014] Step 1: Pretreatment:

[0015] First, grind the surface of the structural steel with sandpapers of different meshes until it is clean and has no obvious defects.

[0016] Then, carry out surface treatment by shot peening to form pits with a pore diameter of 50 - 200 μm on the surface of the structural steel.

[0017] Finally, wash with deionized water and ethanol in sequence and dry.

[0018] Among them, the structural steel includes but is not limited to low-carbon steel, medium-carbon steel, high-carbon steel, low-alloy steel, medium-alloy steel and high-alloy steel.

[0019] The shot in the shot peening process includes cast steel shot, the shot peening mesh number is 20 - 50 mesh, the shot peening strength is 0.2 - 0.8 MPa, and the coverage rate is 100%.

[0020] Step 2: Film covering and pore forming:

[0021] Use medium-high density polyethylene film for electrostatic adsorption and attachment to cover the surface of the pretreated structural steel. Among them, the density of the medium-density polyethylene film is 0.93 - 0.94 g / cm 2 , and the density of the high-density polyethylene film is 0.94 - 0.965 g / cm 2 ;

[0022] Use laser or thermal burning to uniformly form pores on the surface of the covered film.

[0023] Among them, the pore diameter of pore forming is 500 - 1000 μm, and the pore density of pore forming is 7000 - 10000 / m 2 ;

[0024] Step 3: Chemical pre-etching:

[0025] Use etching solution for chemical pre-etching. After dissolving the low-potential tissue, micron-level primary etch holes with a pore diameter of 100 - 500 μm are formed on the surface of the structural steel with film-covered pores. After cleaning, there is no obvious corrosion product layer on the surface of the structural steel.

[0026] Among them, the etching solution is a mixed solution composed of one or more of nitric acid solution, hydrochloric acid solution and sulfuric acid solution and hydrofluoric acid. In the mixed solution, the volume ratio of one or more of concentrated nitric acid solution, hydrochloric acid solution and sulfuric acid solution is 10 - 30%, the volume ratio of hydrofluoric acid is 1 - 3%, and the rest is water; the chemical pre-etching time is 10 - 60 min.

[0027] Step 4: Electrochemical etching:

[0028] Use a DC regulated power supply, with the electrochemical electrolyte as a mixed salt solution, to perform electrochemical etching on the chemically pre-etched structural steel. Wash with deionized water and ethanol in sequence. Nano-holes with a pore diameter of 100 - 500 nm are formed on the surface of the structural steel. On the basis of the micron-level primary holes on the surface of the structural steel, the growth of nano-level etch holes is continuously induced, ensuring the formation of nano-level holes, avoiding the problem of matrix shedding due to over-corrosion connection between etch holes, effectively controlling the pore size and distribution density. In addition, the micron-nano dual-level structure can improve the mechanical anchoring effect.

[0029] Among them, the electrochemical etching process is adjusted by controlling the current magnitude and action time. The electrolyte is a mixed solution of one or more of NaCl, NaNO3, Na2SO4, Na2S2O3, and NH4Cl. The mass percentage concentration of the solute is 10 - 30%, the etching voltage is 2 - 6V, and the etching time is 10 - 60min.

[0030] Compared with the prior art, the present invention uses a chemical / electrochemical method to prepare an anchored structure array on the surface of structural steel, which is not limited by the size and shape of the structural steel, facilitating the processing and preparation of anchored microstructures on the surface of non-planar and large-sized structural steel in ships. It has low processing costs, is suitable for large-scale industrial production, can avoid the problem of reduced mechanical strength caused by internal stress generated by pure mechanical processing, and the generation of defects such as thermal cracks and holes caused by high heat during laser processing, thereby significantly improving the interface stability and interface bonding strength after connection; its principle is scientific and reliable. By electrochemically etching the surface of the structural steel, a uniformly distributed concave hole anchored structure array with high controllability and stability is formed, providing stable mechanical locks and anchor points for the interface bonding of structural steel / thermoplastic composites. Description of the drawings:

[0031] Figure 1 It is a scanning electron microscope photograph of the surface of low-carbon steel after shot peening in Example 1 of the present invention.

[0032] Figure 2 It is a scanning electron microscope photograph of the surface of low-carbon steel after chemical pre-etching in Example 1 of the present invention.

[0033] Figure 3 It is a scanning electron microscope photograph of the surface of low-carbon steel after electrochemical etching in Example 1 of the present invention. Specific implementation method:

[0034] The present invention will be further described below in conjunction with the drawings and specific implementation methods.

[0035] Example 1:

[0036] The specific process of the method for preparing the anchored microstructure on the surface of the structural steel involved in this example is as follows:

[0037] Step 1: Polish the surface of the low-carbon steel with sandpaper and perform shot peening. The shot peening mesh number is 20 - 30 mesh, the shot peening strength is 0.2 - 0.4MPa, and the coverage rate is 100%. The scanning electron microscope photograph of the surface of the low-carbon steel after shot peening is as Figure 1 shown, and the pit aperture is 150 - 200μm;

[0038] Step 2: Use medium-density polyethylene film to coat the surface of the low-carbon steel after shot peening, and uniformly create holes on the film-coated low-carbon steel surface by thermal burning. The pore diameter of the holes is 500 - 700 μm, and the pore density is 7000 - 8000 / m 2 ;

[0039] Step 3: Use a mixed solution composed of concentrated hydrochloric acid solution with a volume ratio of 20%, hydrofluoric acid with a volume ratio of 1%, and water as the chemical etching solution. At room temperature, perform chemical pre-etching on the low-carbon steel after film coating and hole making for 10 - 20 minutes, and ultrasonically clean it successively with ethanol and deionized water. The scanning electron microscope photo of the surface of the low-carbon steel after chemical pre-etching is as Figure 2 shown, and the pore diameter of the primary etching holes is 100 - 200 μm;

[0040] Step 4: Use a NaCl solution with a mass percentage concentration of 10% as the electrolyte, and perform electrochemical etching on the low-carbon steel after chemical pre-etching at room temperature. The etching voltage is 2 - 3 V, and the etching time is 10 minutes. Remove the film, ultrasonically clean it successively with ethanol and deionized water, and then dry it. The scanning electron microscope photo of the surface of the low-carbon steel after electrochemical etching is as Figure 3 shown, and the nano-scale holes are located inside the primary etching holes, with a pore diameter of 100 - 200 nm.

[0041] Example 2:

[0042] The specific process of the method for preparing the surface-anchored microstructure of the structural steel involved in this example is as follows:

[0043] Step 1: Use sandpaper to polish the surface of medium-carbon steel, and perform shot peening. The shot peening mesh number is 30 - 40 mesh, the shot peening strength is 0.4 - 0.6 MPa, and the coverage rate is 100%. Pits with a pore diameter of 100 - 150 μm are formed on the surface of medium-carbon steel;

[0044] Step 2: After using high-density polyethylene film to coat the surface of the medium-carbon steel after shot peening, uniformly create holes on the film-coated medium-carbon steel surface by laser. The pore diameter of the holes is 700 - 800 μm, and the pore density is 8000 - 9000 / m 2 ;

[0045] Step 3: Use a mixed solution composed of concentrated sulfuric acid solution with a volume ratio of 20%, hydrofluoric acid with a volume ratio of 2%, and water as the chemical etching solution. At room temperature, perform chemical pre-etching on the medium-carbon steel after film coating and hole making for 20 - 30 minutes. Primary etching holes with a pore diameter of 200 - 300 μm are formed on the surface of medium-carbon steel, and ultrasonically clean it respectively with ethanol and deionized water;

[0046] Step 4: Using a Na2SO4 solution with a mass percentage concentration of 20% as the electrolyte, electrochemically etch the medium carbon steel after chemical pre-erosion at room temperature. The etching voltage is 3 - 4V, and the etching time is 20 min to remove the coating film, and holes with a pore diameter of 200 - 300 nm are formed on the surface of the medium carbon steel.

[0047] Example 3:

[0048] The specific process of the method for preparing the surface anchored microstructure of the structural steel involved in this example is as follows:

[0049] Step 1: Polish the surface of the high carbon steel with sandpaper and perform shot peening. The shot peening mesh number is 40 - 50 mesh, the shot peening strength is 0.6 - 0.8 MPa, and the coverage rate is 100%. Pits with a pore diameter of 50 - 100 μm are formed on the surface of the high carbon steel.

[0050] Step 2: After coating the surface of the shot-peened high carbon steel with a high-density polyethylene film, uniformly create holes on the coating film on the surface of the high carbon steel by thermal burning. The pore diameter of the holes is 800 - 900 μm, and the hole density is 8000 - 9000 / m 2 ;

[0051] Step 3: Using a mixed solution composed of a concentrated nitric acid solution with a volume ratio of 30%, hydrofluoric acid with a volume ratio of 3% and water as the chemical etching solution, perform chemical pre-etching on the medium carbon steel after coating film hole creation at room temperature for 20 min. Primary etching holes with a pore diameter of 300 - 400 μm are formed on the surface of the high carbon steel, and ultrasonic cleaning is performed with ethanol and deionized water respectively.

[0052] Step 4: Using a Na2SO4 solution with a mass percentage concentration of 30% as the electrolyte, electrochemically etch the high carbon steel after chemical pre-erosion at room temperature. The etching voltage is 4 - 6V, and the etching time is 30 - 40 min to remove the coating film, and holes with a pore diameter of 300 - 400 nm are formed on the surface of the high carbon steel.

[0053] Example 4:

[0054] The specific process of the method for preparing the surface anchored microstructure of the structural steel involved in this example is as follows:

[0055] Step 1: Polish the surface of the low alloy steel with sandpaper and perform shot peening. The shot peening mesh number is 40 - 50 mesh, the shot peening strength is 0.4 - 0.6 MPa, and the coverage rate is 100%. Pits with a pore diameter of 50 - 100 μm are formed on the surface of the low alloy steel.

[0056] Step 2: After covering the surface of the shot-peened low-alloy steel with a high-density polyethylene film, uniformly create holes on the film-covered surface of the low-alloy steel through thermal burning. The pore diameter of the holes is 900 - 1000 μm, and the hole density is 9000 - 10000 / m 2 ;

[0057] Step 3: Use a mixed solution composed of a concentrated nitric acid solution with a volume ratio of 10%, a concentrated sulfuric acid solution with a volume ratio of 10%, hydrofluoric acid with a volume ratio of 1%, and water as the chemical etching solution. At room temperature, perform chemical pre-etching on the film-covered and hole-created low-alloy steel for 40 - 50 minutes. Primary etching holes with a pore diameter of 400 - 500 μm are formed on the surface of the low-alloy steel, and ultrasonic cleaning is performed using ethanol and deionized water respectively;

[0058] Step 4: Use a mixed solution of NaCl with a mass percentage concentration of 10% and NH4Cl with a mass percentage concentration of 10% as the electrolyte. At room temperature, perform electrochemical etching on the chemically pre-etched low-alloy steel. The etching voltage is 2 - 3 V, and the etching time is 40 - 60 minutes to remove the film. Holes with a pore diameter of 400 - 500 nm are formed on the surface of the low-alloy steel.

[0059] Example 5:

[0060] The specific process of the method for preparing the surface-anchored microstructure of the structural steel involved in this example is as follows:

[0061] Step 1: Polish the surface of the medium-alloy steel with sandpaper and perform shot peening. The shot peening mesh number is 40 - 50 mesh, the shot peening strength is 0.6 - 0.8 MPa, and the coverage rate is 100%. Pits with a pore diameter of 100 - 150 μm are formed on the surface of the medium-alloy steel;

[0062] Step 2: After covering the surface of the shot-peened medium-alloy steel with a high-density polyethylene film, uniformly create holes on the film-covered surface of the medium-alloy steel through thermal burning. The pore diameter of the holes is 900 - 1000 μm, and the hole density is 9000 - 10000 / m 2 ;

[0063] Step 3: Use a mixed solution composed of a concentrated nitric acid solution with a volume ratio of 10%, a concentrated hydrochloric acid solution with a volume ratio of 10%, hydrofluoric acid with a volume ratio of 2%, and water as the chemical etching solution. At room temperature, perform chemical pre-etching on the film-covered and hole-created medium-alloy steel for 50 - 60 minutes. Primary etching holes with a pore diameter of 300 - 400 μm are formed on the surface of the medium-alloy steel, and ultrasonic cleaning is performed using ethanol and deionized water respectively;

[0064] Step 4: Using a mixed solution of 10% NaCl and 10% NH4Cl by mass percentage concentration as the electrolyte, electrochemically etch the medium alloy steel after chemical pre-etching at room temperature. The etching voltage is 4 - 5V, and the etching time is 40 - 50 min to remove the coating film, and holes with a pore diameter of 400 - 500 nm are formed on the surface of the medium alloy steel.

[0065] Example 6:

[0066] The specific process of the method for preparing the surface-anchored microstructure of the structural steel involved in this example is as follows:

[0067] Step 1: Polish the surface of the high alloy steel with sandpaper and perform shot peening. The shot peening mesh number is 40 - 50 mesh, the shot peening strength is 0.6 - 0.8 MPa, and the coverage rate is 100%. Pits with a pore diameter of 100 - 150 μm are formed on the surface of the high alloy steel.

[0068] Step 2: After covering the surface of the shot-peened high alloy steel with a high-density polyethylene film, uniformly create holes on the coating film on the surface of the high alloy steel by thermal burning. The pore diameter of the holes is 900 - 1000 μm, and the hole density is 9000 - 10000 / m 2 ;

[0069] Step 3: Using a mixed solution composed of 20% concentrated nitric acid solution by volume, 10% concentrated hydrochloric acid solution by volume, 3% hydrofluoric acid, and water as the chemical etching solution, perform chemical pre-etching on the high alloy steel after hole-making on the coating film at room temperature for 50 - 60 min. Primary etching holes with a pore diameter of 400 - 500 μm are formed on the surface of the high alloy steel, and ultrasonic cleaning is performed with ethanol and deionized water respectively.

[0070] Step 4: Using a mixed solution of 20% NaNO3 and 10% NH4Cl by mass percentage concentration as the electrolyte, electrochemically etch the chemically pre-etched high alloy steel at room temperature. The etching voltage is 5 - 6V, and the etching time is 50 - 60 min to remove the coating film, and holes with a pore diameter of 400 - 500 nm are formed on the surface of the high alloy steel.

Claims

1. A method for preparing an anchored microstructure on the surface of structural steel, characterized in that, First, perform film coating and pore formation on the surface of structural steel; then, chemically pre-etch the structural steel with film coating and pore formation to form micron-sized primary etching holes with a pore diameter of 100 - 500 μm; finally, electrochemically etch the surface of the structural steel to form nano-pores inside the micron-sized primary etching holes. The electrochemically etching process is adjusted by controlling the voltage magnitude and action time. The electrolyte is a mixed solution of one or more of NaCl, NaNO3, Na2SO4, and NH4Cl, and the mass percentage concentration of the solute is 10 - 30%. The etching voltage is 2 - 6V, and the etching time is 10 - 60 min; the etching solution is a mixed solution composed of one or more of nitric acid solution, hydrochloric acid solution, and sulfuric acid solution and hydrofluoric acid. The former accounts for 10 - 30% by volume, the latter is 1 - 3%, and the rest is water.

2. The preparation method of the surface-anchored microstructure of structural steel according to claim 1, characterized in that, Before performing film coating and pore formation on the surface of structural steel, use shot peening process to pre-treat the surface of structural steel and prefabricate pits.

3. A method for preparing an anchored microstructure on the surface of structural steel according to claim 2, characterized in that, The technological process includes four steps: pre-treatment, film coating and pore formation, chemical pre-etching, and electrochemical etching. Step 1: Grind and shot peen the surface of structural steel in sequence, then clean and dry. Step 2: Perform film coating and pore formation on the pre-treated surface of structural steel. Step 3: Chemically pre-etch the structural steel with film coating and pore formation, and form micron-sized etching holes on the surface of structural steel by controlling the concentration and etching time of the etching solution. Step 4: Electrochemically etch the chemically pre-etched structural steel to form nano-pores on the surface of structural steel.

4. A method for preparing an anchored microstructure on the surface of structural steel according to claim 3, characterized in that Step 1: Pre-treatment: First, grind the surface of structural steel with sandpapers of different mesh numbers until it is clean and has no obvious defects. Then, perform surface treatment by shot peening process to form pits with a pore diameter of 50 - 200 μm on the surface of structural steel. Finally, clean and dry with deionized water and ethanol in sequence. Step 2: Film coating and pore formation: Use medium-density polyethylene film or high-density polyethylene film for electrostatic adsorption and attachment to coat the surface of the pre-treated structural steel. Use laser or thermal burning to uniformly form pores on the coated surface. Step 3: Chemical pre-etching: Perform chemical pre-etching with the etching solution. After dissolving the low-potential tissue, form micron-sized primary etching holes on the surface of the structural steel with film coating and pore formation. After cleaning, there is no obvious corrosion product layer on the surface of the structural steel. Step 4: Electrochemical etching: Use a DC regulated power supply to electrochemically etch the chemically pre-etched structural steel in the electrochemical electrolyte, and continue to induce the growth of nano-sized etching holes on the basis of the micron-sized primary etching holes on the surface of the structural steel. Clean with deionized water and ethanol in sequence, and nano-pores with a pore diameter of 100 - 500 nm are formed on the surface of the structural steel.

5. A method for preparing an anchored microstructure on the surface of structural steel according to claim 4, characterized in that, In Step 1, the structural steel includes low-carbon steel, medium-carbon steel, high-carbon steel, low-alloy steel, medium-alloy steel, and high-alloy steel; the shot peening media of the shot peening process includes cast steel shots, the shot peening mesh number is 20 - 50 mesh, the shot peening strength is 0.2 - 0.8 MPa, and the coverage rate is 100%.

6. The preparation method of the surface-anchored microstructure of structural steel according to claim 4, characterized in that In Step 2, the density of the medium-density polyethylene film is 0.93 - 0.94 g / cm 2 , and the density of the high-density polyethylene film is 0.94 - 0.965 g / cm 2 ; the pore diameter for pore formation is 500 - 1000 μm, and the pore density for pore formation is 7000 - 10000 / m 2 .

7. A method for preparing an anchored microstructure on the surface of structural steel according to claim 4, characterized in that, In Step 3, the chemical pre-etching time is 10 - 60 min.

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