A corrosion-resistant treatment process for the surface of bridge steel

Abstract

The present invention relates to the technical field of anti-corrosion treatment for the surface of steel, and specifically, to an anti-corrosion treatment process for the surface of bridge steel. It includes: S1. Pretreating the substrate by using plasma activation and sandblasting processes; S2. Spraying a Zn-Al-based quaternary alloy onto the surface of the substrate through a spraying and deposition process to form an inner coating for sacrificial anode protection; processing inverted conical micropores on the surface of the inner coating by using femtosecond laser; S3. Electrostatically spraying a fluorocarbon resin composite coating, spraying it twice. After two sprays, the micropores are filled and a dense barrier layer is formed. Through the characteristic micropore process of the inner coating and the secondary spraying process of the outer coating, the present invention forms micropore interlocking to enhance mechanical bonding. At the same time, the sacrificial anode of the inner coating continuously provides cathodic protection, and the self-healing function of the outer coating repairs damages in real time; the graphene oxide and fluorocarbon resin of the outer coating form a dense anti-permeation layer. Secondly, the micropore-filled gradient-cured resin reduces the interfacial residual stress and effectively inhibits the crack propagation caused by dynamic loads.

Description

Technical Field

[0001] The present invention relates to the technical field of steel surface anti-corrosion treatment, in particular to a bridge steel surface anti-corrosion treatment process. Background Art

[0002] Steel structures are the core load-bearing systems of major projects such as bridges, offshore platforms, and chemical storage tanks. Their long-term protection is directly related to structural safety and economic efficiency. The majority of losses caused by metal corrosion are related to coating failure.

[0003] Currently, in the technology for steel structure coating, the penetration defect of a single coating (porosity> 0.3%) allows Cl - Low resistance diffusion path (diffusion rate up to 5×10 -6 cm 2 / s), and lacks a blocking mechanism for already intruded corrosion products. Secondly, conventional technologies use a double coating combination. However, traditional inner coatings (such as zinc-rich primers) and outer coatings (such as fluorocarbon topcoats) are only bonded by intermolecular forces and are easily peeled off under dynamic loads (ASTM D4541 test adhesion <6MPa). Penetration channels are easily formed at the interface of the inner / outer coatings (SEM shows interface porosity >3%), Cl - The diffusion rate along the interface is 2×10 -7 cm 2 / s, which easily creates the risk of corrosive media penetration. Secondly, when the outer coating is partially damaged, traditional inner coatings generally lack the ability to respond quickly and repair, and the corrosion rate of the exposed area of the substrate suddenly increases to 0.5mm / a. Summary of the Invention

[0004] The purpose of the present invention is to provide a surface anti-corrosion treatment process for bridge steel, which forms a three-dimensional interlocking structure through micropore filling, combines the active protection of the inner coating with the passive barrier of the outer coating, and realizes a multi-level protection effect of mechanical anchoring on the interface and self-repair of the failure area, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above objectives, according to Figure 1 As shown, the present invention provides a bridge steel surface anti-corrosion treatment process, comprising the following steps:

[0006] S1. Pre-treat the substrate by using plasma activation (argon flow rate 20L / min, power 800W) combined with a controlled sandblasting process (aluminum oxide sand particle size 40-60μm, sandblasting pressure 0.5-0.8MPa) to form an active interface layer with a roughness of Ra=8-12μm on the steel surface (surface energy increased to 58-65mN / m).

[0007] S2. Prepare an internally coated layer with microstructures, including internal coating spraying and laser micro-hole machining. Specifically:

[0008] Deposit a Zn-Al-based quaternary alloy coating by supersonic arc spraying process, with the coating thickness of 80 - 120 μm, to form an internally coated layer for sacrificial anode protection (open circuit potential -1.05V vs SCE).

[0009] Use femtosecond laser (wavelength 1030 nm, pulse width 300 fs) to process inverted conical micro-holes (hole diameter 200 - 300 μm, ratio of hole bottom diameter to surface diameter 0.5 - 0.7) on the surface of the internally coated layer, with a density of 400 - 600 holes / cm 2 (porosity 15 - 20%) to form a mechanical anchoring structure, and the pore wall presents a gradient heterogeneous interface (EDS shows that the Al / Zn ratio gradually changes from 1:4 at the hole bottom to 1:1 at the hole opening).

[0010] Use electrostatic spraying (voltage 50 kV, atomization pressure 0.3 MPa) to apply fluorocarbon resin composite coating [base material: FEVE fluorocarbon resin; filler: flaky graphene oxide (15 wt%) + cerium oxide (CeO2) nanoparticles (5 wt%)], and spray it in two times:

[0011] The first spraying: The coating penetrates into the conical micro-holes and fills the anchoring area through capillary action to form an inverted hook-shaped cured structure inside the micro-holes (SEM shows that the pore filling rate > 92%);

[0012] The second spraying: Spray for surface leveling to a total thickness of 200 - 250 μm to form a continuous and dense barrier layer (the gas permeability measured by helium mass spectrometry < 5×10 -14 Pa·m 3 / s).

[0013] In this invention, through the morphological matching of the inverted conical micro-holes and the filler of the outer coating (the contact area increases by 180%), the bonding strength ≥ 34 MPa (ASTM D3164 standard) is achieved to form mechanical interlocking; chemical bonding: the gradient Al / Zn ratio of the pore wall of the internally coated layer promotes the Lewis acid-base interaction between the C-F bond in the FEVE resin of the outer coating and the metal oxide (FTIR shows a newly generated characteristic peak at 1220 cm -1 ).

[0014] When the outer coating is intact, nano-CeO2 inhibits the initiation of local corrosion through redox reaction (Ce 3+ ⇔Ce 4+ ); when the outer coating is damaged, the Zn-Al alloy of the internally coated layer preferentially dissolves to provide cathodic protection current (polarization resistance Rp > 1×10 6 Ω·cm 2 ). The graphene oxide sheets form a tortuous barrier around the micro-holes (Cl- The diffusion path is extended by 5 times). At the same time, the corrosion inhibitor (benzotriazole) adsorbed between the layers is released when the external pH is greater than 8, repairing microcracks (the self-repair efficiency reaches 78% after 480 hours of salt spray test), realizing self-healing function.

[0015] As a further optimization of this solution, the fluorocarbon resin composite coating adopts a gradient curing process (pre-curing at 80°C for 10 minutes → final curing at 150°C for 30 minutes) to eliminate the interfacial stress (residual stress is reduced from 30 MPa to 8 MPa).

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] Through the unique microporous process of the inner coating and the secondary spraying process of the outer coating, micropores are interlocked to enhance mechanical bonding. At the same time, the sacrificial anode of the inner coating continuously provides cathodic protection, and the self-repair function of the outer coating repairs damage in real time. The graphene oxide and fluorocarbon resin of the outer coating form a dense impermeability layer. Secondly, through laser processing, the pore size, inverted cone ratio and distribution density are adjusted to match the diffusion path of different corrosive media, and for Cl - 、H + Dynamically optimize the corrosion inhibitor and nano-reinforcement phase based on specific failure factors such as freeze-thaw stress. Through mechanical interlocking of inverted tapered micropores, the bond strength between the outer and inner coatings is ≥34 MPa (compared to <6 MPa with traditional processes) (see Table 1). Simultaneously, filling the micropores with a gradient-curing resin reduces interfacial residual stress (from 30 MPa to 8 MPa), effectively inhibiting crack propagation caused by dynamic loads (see Table 5).

[0018] In addition, the process of the present invention can also be expanded to oil pipelines, offshore wind power towers and other scenarios by adjusting the coating components (such as replacing the type of corrosion inhibitor). - Concentration-sensitive repair agent that enables in-situ sensing and response to coating damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flowchart of the overall process of the present invention. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0021] Example 1: This example provides a process for anti-corrosion treatment of bridge steel in a marine environment, comprising the following steps:

[0022] S1. Pretreatment of substrate surface by sandblasting and activation: Use Q345qD bridge steel (size 2000m×500mm×20mm); Alumina sand grains (particle size 50μm, pressure 0.6MPa) are used for sandblasting treatment, and the surface roughness Ra = 10.2μm after sandblasting; The parameters of plasma activation are: argon gas flow rate 20L / min, power 800W, treatment time 5min; The surface energy is increased to 67.3mN / m.

[0023] S2. Preparation of inner coating and construction of micropores on substrate surface: The inner coating material is sprayed onto the substrate surface by the high-velocity arc spraying (HVAS) process; Parameters of high-velocity arc spraying: voltage 32V, current 200A, spraying distance 150mm; Inner coating material: Zn-Al-based quaternary alloy coating (Al: 15%, Mg: 3%, Si: 1%, Zn: 81%), coating thickness 110±5μm, porosity <1%;

[0024] Inverted conical micropores are processed on the surface of the inner coating by femtosecond laser processing (wavelength 1030nm, pulse width 300fs, energy density 1.8J / cm²), with a pore diameter of 250μm, a pore depth of 120μm, an inverted cone ratio (ratio of bottom diameter to surface diameter) of 0.5 - 0.7, and a density of 480 pores / cm 2 , and the Zn / Al atomic ratio at the bottom of the pore is 3.8:1.

[0025] S3. Double-spraying forming of outer coating: Select outer coating material (80wt% FEVE fluorocarbon resin, 15wt% graphene oxide, 5wt% cerium oxide nanoparticles, viscosity 120mPa·s at 25℃); The first spraying uses electrostatic spraying (voltage 50kV), and the outer coating material penetrates into the conical micropores (filling rate 93%), and is pre-cured at 80℃ for 10min to form an inverted hook structure, with a hook curvature radius R = 18±3μm and a hook depth h = 25±5μm, forming a mechanical locking effect; The second spraying covers the entire inner coating, with a total thickness of 220μm, and is finally cured at 150℃ for 30min, with a surface hydrophobic angle of 152° and continuous without defects.

[0026] The bridge steel processed by the process of this embodiment is tested for 4000h according to ASTM B117, with no red rust on the inner coating, no blistering on the outer coating, and a corrosion area of 0.5%. The bonding strength between the coating and the substrate is 34.5MPa (ASTM D4541), which is 475% higher than that of the traditional process (6MPa).

[0027] Example 2: This example provides a steel surface anti-corrosion treatment process for protecting bridge piers in the deicing salt corrosion environment in cold regions. The difference between this example and Example 1 is:

[0028] (1) Inner coating:

[0029] The inner coating material uses a Zn-Al-Mg-Re quaternary alloy coating (Re: 0.5%, Al: 15%, Mg: 3.5%, Zn: 81%) to enhance the anodic activity at low temperatures (polarization resistance at -40°C is 8.3×10 5 Ω·cm 2 );

[0030] The micropore characteristics of the inner coating are that the pore mouth diameter is 200μm, the pore bottom diameter is 120μm (inverted cone ratio 0.6), and the pore depth is designed with a gradient (edge area 80μm → central area 150μm) to adapt to the freeze-thaw stress distribution.

[0031] (2) Outer coating:

[0032] In the outer coating material, pH-responsive microcapsules (shell material: polyurethane; corrosion inhibitor: benzotriazole) are loaded between the graphene oxide layers. When the outer coating cracks during the freeze-thaw cycle at -30°C, the microcapsules rupture and release the corrosion inhibitor (repair efficiency 82%).

[0033] Except for the above differences, the other processes in this embodiment are the same as those in Embodiment 1, and will not be elaborated here. The steel processed by the process of this embodiment undergoes 50 freeze-thaw cycles (-40°C → 25°C), and the coating adhesion retention rate is 89%; the cathode peel radius: 1.2mm (ISO 15711), which is 75% lower than that of the traditional process (4.8mm).

[0034] Embodiment 3: This embodiment provides an anti-corrosion treatment process for high-humidity steel structures in industrial pollution areas. The difference between this embodiment and Embodiment 1 is as follows:

[0035] (1) Inner coating:

[0036] The inner coating material uses a Zn-Al-Ti-B quaternary alloy coating (Ti: 2%, B: 0.1%, Al: 15.8%, Zn: 82.1%), and the wear resistance is improved through the dispersion strengthening of TiB2;

[0037] The micropore structure of the inner coating is a honeycomb hexagonal array (pore spacing 350μm), and a nanocrystalline structure (grain size 85nm) is formed on the pore wall after laser processing.

[0038] (2) Outer coating:

[0039] The flaky graphene oxide used in the outer coating material is modified to have carboxylated edges (XPS shows that the COOH content is 12.6%) to enhance the interfacial bonding with the resin; secondly, the outer coating is cured using a gradient temperature rise (80°C / 20min → 120°C / 40min → 150°C / 30min) to eliminate thermal stress cracks.

[0040] Except for the above differences, the other processes in this embodiment are the same as those in Embodiment 1, and will not be elaborated herein. The steel processed by the process of this embodiment is in a mixed solution of H2SO4 + NaCl with pH = 3 (Cl - concentration 1M), and is spray-circulated for 2000 h; the result shows that the corrosion rate is 0.003 mm / a (the traditional coating is 0.12 mm / a), and the protection efficiency is increased by 40 times.

[0041] Comparative Example 1: This comparative example adopts the traditional double-coating process. Specifically:

[0042] The inner coating uses an epoxy zinc-rich primer (Zn content 80%), with a thickness of 80 μm; the outer coating uses a polyurethane topcoat, with a thickness of 200 μm; there is no microporous structure, and it only relies on physical adsorption to combine.

[0043] Test Example 1: Comparison of coating bond strength

[0044] The purpose of this test example is to verify the improvement effect of the interface micro-anchoring structure of the present invention on the bond strength. The test method is as follows:

[0045] (1) Specimen groups: Test Group 1 uses the coating style prepared in Embodiment 1; Control Group 1 uses the coating specimen prepared in Comparative Example 1.

[0046] (2) Test standard: ASTM D4541 (pull-off test for bond strength); Equipment: PosiTest AT-A automatic adhesion tester.

[0047] Table 1

[0048]

[0049] As shown in Table 1, the inverted conical micropores of the present invention significantly improve the bond strength through mechanical interlocking, and the failure mode changes from interfacial peeling to material self-fracture, achieving a three-dimensional anchoring effect.

[0050] Test Example 2: Salt spray corrosion acceleration test

[0051] The purpose of this test example is to compare the Cl - penetration resistance of the present invention and the traditional process in a harsh marine environment. The test method is as follows:

[0052] (1) Specimen groups: 5 groups each for Test Group 1 (Embodiment 1) and Control Group 1 (Comparative Example 1);

[0053] (2) Test standard: ASTM B117 neutral salt spray test, 5% NaCl solution, 35 °C, 4000 h; Evaluation indicators include corrosion area (analyzed by ImageJ software), time to appearance of red rust, and outer coating blistering grade.

[0054] Table 2

[0055]

[0056] As shown in Table 2, the graphene oxide barrier of the outer coating of the present invention and the sacrificial anode of the inner coating act synergistically to reduce the Cl - diffusion rate to 1 / 60 (calculated value) of the traditional process, significantly prolonging the corrosion initiation time.

[0057] Test Example 3: Freeze-thaw cycle aging resistance test

[0058] The purpose of this test example is to verify the protection ability of the self-healing microcapsules in Example 2 under freeze-thaw conditions in cold regions. The test method is as follows:

[0059] (1) Specimen groups: Test group 2 (coating pattern prepared in Example 2) and control group 1, control group 2 (inner coating of Example 2 with a uniform pore depth of 100 μm).

[0060] (2) Test standard: GB / T 9268 standard, cycle program (-40°C × 4 h → soak in water at 25°C for 4 h), repeat 50 times; test items include adhesion retention rate, cathodic disbondment radius (ISO 15711).

[0061] Table 3

[0062]

[0063] As shown in Table 3, the benzotriazole released by the microcapsules in Example 2 of the present invention can effectively inhibit the corrosion of the substrate at the freeze-thaw cracks, and the cathodic disbondment radius is reduced by 66% compared with the prior art. Secondly, the gradient pore depth design adopted in Example 2 has a further effect compared with the uniform pore depth.

[0064] Test Example 4: Acidic industrial precipitation simulation test

[0065] The purpose of this test example is to verify the anti-permeation performance of carboxylated graphene oxide in Example 3 in an acidic environment. The test method is as follows:

[0066] (1) Specimen groups: Test group 3 (coating pattern prepared in Example 3) and control group 3 (similar coatings with ordinary graphene fillers).

[0067] (2) Test standard: Use a mixed solution of H2SO4 + 1M NaCl with pH = 3, and cycle spray at 40°C (10 min / h); evaluation indexes include electrochemical impedance spectroscopy (EIS) test of polarization resistance (Rp), corrosion rate (Tafel fitting).

[0068] Table 4

[0069]

[0070] As shown in Table 4, the carboxylated graphene provided in the coating of Example 3 of the present invention enhances the interlayer chemical bonding, enabling the coating to have a barrier efficiency for H + and SO3 2- which is improved by about 40 times.

[0071] Test Example 5: Dynamic Load Fatigue Test

[0072] The purpose of this test example is to evaluate the anti-peeling ability of the coating under high-frequency vibration. The test method is as follows:

[0073] (1) Specimen groups: Test Group 1 and Control Group 1.

[0074] (2) Test conditions: Three-point bending fatigue test (stress amplitude Δσ = 150 MPa, frequency 5 Hz, number of cycles 1×10 6 times); Observation indicators include the length of interfacial crack propagation (measured by SEM).

[0075] Table 5

[0076]

[0077] As shown in Table 5, the mechanical anchoring structure of the present invention completely inhibits crack initiation under dynamic loads, while the coating of the traditional process fails rapidly due to weak interfacial bonding.

[0078] In summary, the surface corrosion treatment process for bridge steel provided by the present invention utilizes the mechanical anchoring effect of inverted conical micropores. The coating bonding strength reaches 34.5 MPa (6.2 MPa for the traditional process), and the interfacial failure mode changes from "substrate peeling" to "coating body fracture". The three-dimensional interlocking design fundamentally improves the interfacial stability. In terms of environmental tolerance, after 4000 h salt spray test, the corrosion area is only 0.5% (34.8% for the traditional process), and the Cl - penetration rate is reduced by 98%. After 50 freeze-thaw cycles, the adhesion retention rate is 89%. The self-healing microcapsules reduce the cathode peeling radius by 66% (1.2 mm vs 3.5 mm). The dense barrier of the carboxylated graphene filler reduces the corrosion rate to 0.003 mm / a (0.12 mm / a for the traditional process), and the polarization resistance is increased by 26 times. Under 1×10 6 cycles of cyclic load, there is no crack propagation in the coating (the crack propagation of the traditional coating reaches 850 μm), proving that the microporous structure effectively disperses stress. Therefore, it can be seen that the process of the present invention solves the three major technical problems of weak interfacial bonding, poor environmental adaptability, and easy dynamic failure of traditional anti-corrosion coatings through special structural design and material modification, providing further optimization for the long life of steel in harsh corrosion environments.

[0079] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A bridge steel surface anti-corrosion treatment process, characterized in that: The following steps are involved: S1. Pre-treating the substrate using plasma activation and sandblasting processes; S2. Spraying a Zn-Al-based quaternary alloy onto the substrate surface through a spray deposition process to form an inner coating for sacrificial anode protection; using a femtosecond laser to machine inverted tapered micropores on the inner coating surface, with the pore walls presenting a gradient heterogeneous interface; S3. Use electrostatic spraying to apply fluorocarbon resin composite coating to the inner coating in two steps: The first spraying of the fluorocarbon resin composite coating penetrates into the interior of the inverted cone-shaped micropores to form a barbed hook-shaped solidified structure within the micropores; The second time, the surface is leveled and sprayed to form a continuous and dense barrier layer; The fluorocarbon resin composite coating comprises: Base material: 80wt% fluorocarbon resin; Filler: 15 wt% of flake graphene oxide or one of the pH-responsive microcapsules loaded between graphene oxide layers, and 5 wt% of cerium oxide nanoparticles; The pH-responsive microcapsules loaded between graphene oxide layers are made of polyurethane as the shell material and benzotriazole as the corrosion inhibitor. When the outer coating cracks during a freeze-thaw cycle at -30°C, the pH-responsive microcapsules loaded between graphene oxide layers rupture and release the corrosion inhibitor. In S3, the fluorocarbon resin composite coating adopts a gradient curing process to eliminate interfacial stress; The gradient curing process is: pre-curing at 80° C. for 10 minutes → final curing at 150° C. for 30 minutes.

2. The bridge steel surface anti-corrosion treatment process according to claim 1, characterized in that: The Zn-Al based quaternary alloy coating includes, in addition to Zn-Al, one of Mg-Si, Mg-Re and Ti-B.

3. The bridge steel surface anti-corrosion treatment process according to claim 1, characterized in that: The inverted tapered micropores have a pore diameter of 200-300 μm, a bottom diameter / surface diameter ratio of 0.5-0.7, and a density of 400-600 pores / cm 3 .

4. The bridge steel surface anti-corrosion treatment process according to claim 1, characterized in that: In the S2, the thickness of the inner coating layer is 80-120 μm.

5. The bridge steel surface anti-corrosion treatment process according to claim 1, characterized in that: In the above-mentioned S3, the surface is leveled and sprayed to a total thickness of 200-250 μm.

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