Electrogalvanizing method for weather-resistant steel high-strength bolt

Abstract

The invention discloses an electrogalvanizing method for a weathering-resistant steel high-strength bolt. The electrogalvanizing method comprises the following steps that (1) the weathering-resistant steel high-strength bolt is sequentially subjected to degreasing, rust removing and activating treatment; (2) the bolt is added into an alkaline zincate plating solution to be subjected to electrogalvanizing, and the alkaline zincate plating solution comprises, by concentration, 8-15 g / L of zinc oxide, 80-120 g / L of sodium hydroxide, 12-20 g / L of triethanolamine, 0.5-1 g / L of low-hydrogen composite brightener, 0.5-1 g / L of zinc oxide, 0.5-1 g / L of zinc oxide and the balance zinc oxide. The low-hydrogen composite brightener is prepared from 4-methylbenzalacetone, a polyoxyethylene polyoxypropylene block copolymer, imidazoline quaternary ammonium salt and fatty amine polyoxyethylene ether. And (3) hydrogen removal treatment is conducted, and then sealing treatment is conducted through a chromium-free silicate sealing agent.The obtained electrogalvanized weathering-resistant steel high-strength bolt product has the characteristics of being low in hydrogen embrittlement, high in corrosion resistance, environmentally friendly and the like, and the applicability is wide.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, and specifically relates to an electro-galvanizing method for weather-resistant high-strength bolts. Background Technology

[0002] 390B weathering steel is a low-alloy high-strength steel with good atmospheric corrosion resistance (its weather resistance is 2-5 times that of ordinary steel). It is widely used in the manufacture of high-strength bolts (such as 10.9 grade bolts with tensile strength ≥1000MPa) in steel structure engineering.

[0003] However, the surface protection of 390B weathering steel high-strength bolts still faces the following challenges: 1) Hydrogen embrittlement risk: Grade 10.9 high-strength steel is extremely sensitive to hydrogen embrittlement. Hydrogen evolution reaction products are adsorbed onto the surface of the steel reinforcement in the form of molecular complexes, and penetrate into the steel material through dissolution and diffusion. During the electroplating zinc process, hydrogen (2H+) is released from the cathode reaction. + +2e - →H2) can penetrate into the steel. Once the atomic hydrogen inside the steel bar reaches the threshold, the fracture stress decreases and hydrogen embrittlement occurs, leading to delayed fracture. 2) Surface treatment difficulty: 390B weathering steel is prone to forming a dense oxide scale (composed of Fe2O3, Fe3O4 and alloy oxides) on its surface. If the pretreatment is not thorough, it will lead to poor coating adhesion and incomplete coating. 3) Corrosion resistance requirements: Steel structure engineering requires bolts to have a neutral salt spray test (NSS) life of ≥1000 hours, while the salt spray life of the 12μm pure zinc layer of ordinary alkaline zincate plating is usually only 200-400 hours, which cannot meet the application requirements.

[0004] Electroplating zinc plating forms a zinc film on the surface of bolts through electrochemical principles, using a "sacrificial anode" mechanism to protect the steel surface. However, existing electroplating zinc plating processes still have specific defects: acidic potassium chloride zinc plating has high current efficiency (>90%), but low cathodic polarization, low hydrogen evolution potential, and a high risk of hydrogen embrittlement (10.9 grade steel is prone to breakage); ordinary alkaline zincate zinc plating has a low risk of hydrogen embrittlement, but the coating porosity is high (>5%) and the salt spray life is short; cyanide zinc plating produces a good coating quality, but contains highly toxic cyanide, which does not meet RoHS environmental protection requirements.

[0005] Therefore, there is an urgent need to further develop a method for electroplating zinc onto 390B weathering steel high-strength bolts that is low in hydrogen embrittlement, highly corrosion resistant, and environmentally friendly. Summary of the Invention

[0006] The main objective of this invention is to address the problems and shortcomings of existing electroplating zinc processes for weathering steel high-strength bolts, such as high risk of hydrogen embrittlement, difficulty in surface treatment, and short salt spray life, and to provide an electroplating zinc process for weathering steel high-strength bolts that is suitable for fields such as multi-purpose stadiums and has the characteristics of low hydrogen embrittlement, high corrosion resistance, and environmental friendliness.

[0007] To achieve the above objectives, the technical solution adopted by the present invention includes the following: An electro-galvanizing method for high-strength weathering steel bolts includes three key steps: pretreatment, electro-galvanizing, and post-treatment. The specific steps are as follows: 1) Pre-processing; The weathering steel high-strength bolts were sequentially degreased, derusted, and activated; the activation step involved removing the surface passivation film with dilute acid. 2) Electro-galvanizing; An alkaline zincate plating bath was prepared, comprising the following components and their concentrations: zinc oxide 8-15 g / L, sodium hydroxide 80-120 g / L, triethanolamine 12-20 g / L, and a low-hydrogen composite brightener 0.5-1 g / L. The low-hydrogen composite brightener comprises 4-methylbenzyl acetone (0.1-0.3 g / L), polyoxyethylene-polyoxypropylene block copolymer (0.1-0.2 g / L), imidazoline quaternary ammonium salt (0.1-0.2 g / L), and fatty amine polyoxyethylene ether (0.1-0.2 g / L); the total concentration was 0.5-1 g / L. The weathering steel high-strength bolts obtained from the pretreatment in step 1) are added to an alkaline zincate plating solution for electroplating zinc. During the electroplating process, the current density, temperature, electroplating time, and pH value of the plating solution are adjusted. 3) Post-processing After electroplating with zinc, the high-strength weathering steel bolts undergo a dehydrogenation treatment, followed by a sealing treatment with a chromium-free silicate sealant to form a dense silicon film, thus obtaining the final electroplated zinc weathering steel high-strength bolt product.

[0008] In the above scheme, the degreasing step includes: removing oil stains (such as rust-preventive oil, cutting fluid, etc.) from the surface of the bolts with an alkaline degreasing agent to avoid the oil stains affecting the subsequent rust removal and coating adhesion.

[0009] Furthermore, the alkaline degreasing agent contains traditional alkaline degreasing components (inorganic alkali; providing an alkaline environment to saponify oil stains), detergent builders (sodium carbonate, etc., to enhance the degreasing effect), and surfactants (emulsifying and dispersing oil stains), making it suitable for soaking processes.

[0010] Furthermore, the alkaline degreasing agent can also be an environmentally friendly alkaline degreasing agent (using phosphorus-free detergent builders (such as sodium gluconate and sodium citrate) and biodegradable surfactants (such as alkyl glycosides APG and fatty alcohol polyoxyethylene ethers AEO) to reduce environmental impact), phosphorus-free, biodegradable, compliant with RoHS, REACH and other environmental protection requirements, and friendly to human health and the environment.

[0011] Furthermore, the components and their concentrations in the alkaline degreasing agent include: alkaline degreasing component (sodium hydroxide) 20-50 g / L, detergent builder (sodium carbonate) 10-20 g / L, and surfactant (nonionic surfactant OP-10) 3-8 g / L.

[0012] Furthermore, the degreasing step employs an immersion process at a temperature of 40-65℃ for 10-30 minutes.

[0013] In the above scheme, the rust removal step includes: removing oxide scale (rust removal) with hydrochloric acid / hexamethylenetetramine solution, wherein hexamethylenetetramine acts as a corrosion inhibitor to prevent excessive corrosion of the steel substrate by hydrochloric acid.

[0014] In the above scheme, the step of removing oxide scale with hydrochloric acid / hexamethylenetetramine solution must be performed in a single step using a mixed solution. The hydrochloric acid concentration in the hydrochloric acid / hexamethylenetetramine solution is 5-8 vol%, and the hexamethylenetetramine concentration is 0.3-0.4 wt%. The treatment time is 5-15 minutes at room temperature. This process can efficiently dissolve oxide scale (removal rate > 95%) while controlling the substrate corrosion rate below 0.1% (meeting industrial standards).

[0015] In the above scheme, the activation step includes: the dilute acid used is preferably dilute sulfuric acid (concentration of 3-5wt%), dilute hydrochloric acid (concentration of 2-4wt%), or a mixed acid (mass ratio of hydrochloric acid to sulfuric acid of 1:0.8-1.2, total concentration of 2-4wt%), which can effectively remove the passivation film containing alloying elements, control the corrosion rate, and ensure the effect of subsequent electroplating.

[0016] Furthermore, the activation step should be performed at a temperature of 20-30℃ to remove the surface passivation film, expose the fresh metal surface, and improve the adhesion of the coating.

[0017] In the above scheme, the activation treatment time is 5-15 min.

[0018] Furthermore, the molecular weight of the polyoxyethylene-polyoxypropylene block copolymer is 2000-8000, preferably 3000-5000; the molecular weight of the fatty amine polyoxyethylene ether is 1000-3000, preferably 1500-2500.

[0019] Preferably, the concentration of the low-hydrogen composite brightener in the zinc plating solution is 0.6-1.0 g / L.

[0020] The low-hydrogen composite brightener described in this invention, combined with sulfur-free components, low-concentration design, and a special chemical structure, promotes a synergistic effect of "refined grains + low hydrogen embrittlement + high density," which is key to solving the hydrogen embrittlement problem in high-strength bolt zinc plating. It reduces hydrogen generation and penetration at the source (sulfur-free, low hydrogen evolution) while optimizing the coating structure (refined grains, reduced porosity), thereby achieving the goal of low hydrogen embrittlement. Furthermore, this invention employs an alkaline zincate plating solution system, introducing zincate ions ([Zn(OH)4]). 2- Maintaining a pH of 12-13 further effectively inhibits hydrogen evolution; the introduced triethanolamine can complex Zn. 2+ It improves cathode polarization and coating uniformity (especially suitable for complex shapes such as threads); the introduced low-hydrogen brightener can refine the grains (grain size ≤10μm), reduce coating porosity (≤2%), and avoid sulfur-containing components (which aggravate hydrogen embrittlement).

[0021] Furthermore, the synergistic effect of the low-hydrogen brightener and triethanolamine introduced in this invention can achieve a good grain refinement effect: 1) Increase cathode polarization: Increase the cathode polarization value from 100-150mV in conventional processes to 200-300mV; 2) Promotes nucleation: With increased cathodic polarization, the overpotential for zinc ion nucleation increases (from the conventional 50mV to 150mV), and the nucleation rate increases by 4 times (more crystal nuclei are formed, inhibiting grain growth). 3) Uniform adsorption: The low-hydrogen brightener components can be uniformly adsorbed on the cathode surface (including current-concentrated areas such as thread grooves), avoiding "coarse grains caused by excessive local current" (in conventional processes, the grain size at the top of the thread is usually 30% larger than that on the plane, while in this invention the difference is ≤10%).

[0022] In addition, grain refinement can directly improve the density and corrosion resistance of the coating.

[0023] This invention successfully achieves a grain size ≤10μm through the synergistic effect of a low-hydrogen brightener and triethanolamine, meeting industrial standard requirements (GB / T 13298-2015) and significantly outperforming conventional processes (average grain size reduction of 55%). Grain refinement not only improves the density and corrosion resistance of the coating but also provides protection against hydrogen embrittlement risk (fine grains create more "hydrogen traps," reducing hydrogen diffusion).

[0024] In the above scheme, the current density used in the electroplating zinc step is 2-2.5 A / dm². 2(Threaded parts); Too low a current density will prolong the zinc plating time, while too high a current density will cause thread "ablation" (over-deposition) and increase the risk of hydrogen embrittlement. The operating temperature is 20-25℃ (room temperature). Too high a temperature will accelerate additive decomposition and reduce coating toughness; too low a temperature will reduce current efficiency (<70%) and prolong the plating time. The electroplating time is 10-15 min. pH value: 12.0-13.0 (maintained by NaOH). When pH < 12, [Zn(OH)4] 2 ⁻ It will decompose into Zn(OH)2 precipitate, resulting in a rough coating or even failure to deposit; when pH>13, hydrogen evolution intensifies, and excessive hydrogen atoms penetrate into the coating and substrate, significantly increasing the risk of hydrogen embrittlement of workpieces such as high-strength bolts.

[0025] Preferably, the alkaline zincate plating bath system uses a current density of 2 A / dm³. 2 Temperature 25℃, pH 12.5.

[0026] Furthermore, the electroplating time t is determined based on the bolt surface area S, as shown in Formula I; I; Where δ is the coating thickness, μm; ρ is the zinc density (7.14), g / cm³. 3 S is the bolt surface area dm. 2 ; k is the electrochemical equivalent of zinc (1.22), g / (A·h); η is the current efficiency; J is the current density, A / dm³ 2 .

[0027] Furthermore, the designed coating thickness is 10-14 μm.

[0028] Furthermore, the bolt surface area takes into account a thread enlargement factor of 1.1-1.2.

[0029] In the above scheme, the process conditions for hydrogen removal treatment include: 190-220℃, 2-3h (the preferred conditions for 10.9s grade steel are 200±2℃ and 2.5h; without affecting the steel properties, the hydrogen that has seeped in can be efficiently removed, preventing hydrogen embrittlement fracture); it can effectively remove the hydrogen that has seeped in during the galvanizing process and prevent hydrogen embrittlement fracture.

[0030] In the above scheme, the sealing treatment process conditions include: using a chromium-free silicate sealant with a concentration of 5-10%; immersing the dehydrogenated bolts in the chromium-free silicate sealant for 5-10 minutes, then removing them and sealing them at a temperature of 80-100℃ for 15-30 minutes. Using the sealing treatment process described in this invention, a dense silicon film can be formed by filling the pores of the coating, significantly improving salt spray life; simultaneously, by controlling the concentration and temperature, the wettability of the sealant on the zinc coating is effectively improved (contact angle reduced to <70°), and the adhesion between the sealant film and the zinc coating is improved to level 0 (cross-cut test), achieving a synergy between chromium-free environmental protection and high corrosion resistance, avoiding the environmental pollution risks of traditional chromate sealing.

[0031] In the above scheme, the selection of the chromium-free silicate sealant is based on the criteria of chromium-free environmental protection requirements, film density, process parameter compatibility (5-10% total concentration, 80-100℃ temperature), and functional objectives (filling pores, improving salt spray life). A chromium-free silicate sealant system based on a silicate matrix, film-forming aid, chromium-free corrosion inhibitor, and wetting agent is selected. Specifically, the silicate matrix preferably uses one or more of sodium silicate, potassium silicate, etc.; the film-forming aid uses one or more of polyols, alkanolamines, etc.; the chromium-free corrosion inhibitor uses one or more of molybdate, tungstate, sodium citrate, etc.; and the wetting agent can be a nonionic surfactant.

[0032] Furthermore, in the chromium-free silicate sealant, the components and their mass percentages include: silicate main body 42-50%, film-forming aid 18-25%, chromium-free corrosion inhibitor 5-10%, wetting agent 2-5%, and the balance being water.

[0033] Preferably, the chromium-free silicate sealant comprises the following components and their mass percentages: silicate main body 44-46%, film-forming aid 18-22%, chromium-free corrosion inhibitor 7-9%, and wetting agent 2-4%; which can effectively balance film-forming properties, corrosion resistance and wettability, and further adapt to the 80-100℃ sealing process, promoting the formation of a dense silicon film with a bonding strength of 0.

[0034] The chromium-free silicate sealant used in this invention meets the requirements of chromium-free environmental protection, and through synergistic effect, it achieves the effects of "effectively filling the pores of the coating, forming a dense silicon film, and improving the salt spray life" (salt spray life > 1000 hours, which is 1.5-2 times that of traditional chromate sealants), and is fully compatible with the process conditions of this invention (5-10% concentration, 80-100℃ temperature, 15-30min time).

[0035] The process described in this invention can significantly reduce the risk of hydrogen embrittlement: through precise dehydrogenation (temperature and time control), the residual hydrogen content is <2ppm and the hydrogen embrittlement fracture rate is <1%, solving the fatal problem of galvanized 10.9 grade steel; significantly improve salt spray life: further combined with optimized sealing process (5-10% chromium-free silicate sealant, 80-100℃), the salt spray life is >1000 hours, meeting the requirements of harsh outdoor environments; maintain the mechanical properties of high-strength steel: by controlling the dehydrogenation temperature, the tensile strength decreases by <3%, meeting the standard of 10.9 grade steel; chromium-free and environmentally friendly with superior performance compared to traditional processes: using chromium-free silicate sealant instead of chromate avoids heavy metal pollution, while the salt spray life exceeds that of traditional chromate sealant; improve the adhesion of the galvanized layer: the dilute acid activation process (3-8%) improves the adhesion of the galvanized layer to level 0, preventing the coating from peeling off.

[0036] Furthermore, the electroplated galvanized weathering steel high-strength bolts obtained from the above scheme can be applied to fields such as multi-purpose stadiums.

[0037] Compared with the prior art, the beneficial effects of the present invention include: 1) Low hydrogen embrittlement: Using alkaline zincate solution (high cathodic polarization) and combined with dehydrogenation treatment (low hydrogen brightener with low hydrogen embrittlement combined with dehydrogenation treatment process), the hydrogen residue is reduced from the conventional >10ppm to <2ppm (far below the critical value of 5ppm); delayed fracture test (maintaining 80% of yield strength for 24 hours) shows no fracture. 2) High corrosion resistance: The low-hydrogen brightener introduced into the optimized zinc plating solution system can further exert the effect of uniform adsorption and grain refinement, resulting in a coating porosity of ≤2%. Combined with chromium-free sealing treatment, it can significantly improve the salt spray life of the coating (salt spray life ≥1000 hours, corrosion area ≤5%). 3) Environmentally friendly: Cyanide-free and RoHS compliant; 4) Stable: The solution does not easily generate impurities (such as Fe). 3+ Cu 2+ It has low maintenance costs and only needs to be filtered 1-2 times per week. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the electroplating zinc process described in this invention. Detailed Implementation

[0039] The technical solutions adopted in this invention are described in detail below through specific implementation examples. These descriptions are merely a part of the invention and do not represent all embodiments. Unless otherwise specified, the experimental methods used in this invention are conventional methods, and the instruments and equipment used are commercial products in this technical field.

[0040] In the following examples, the bolt samples used are Φ24×50mm 10.9s grade 390B weathering steel high-strength bolt samples, and the specific sample parameters are as follows: Dimensions: Φ24×50mm (thread diameter 24mm, length 50mm); Material: 390B weathering steel (yield strength ≥ 390MPa); Performance grade: 10.9s grade (tensile strength ≥1000MPa); Surface area: Considering a thread enlargement factor of 1.15, we get 0.537 dm. 2 .

[0041] Example 1 An electro-galvanizing method for high-strength weathering steel bolts includes three key steps: pretreatment, electro-galvanizing, and post-treatment. The specific steps are as follows: 1) Preprocessing Degreasing: Place the bolts in an alkaline degreasing agent (NaOH 50g / L + sodium carbonate 15g / L + nonionic surfactant OP-10 (octylphenol polyoxyethylene ether-10) 5g / L), immerse at 65℃ for 12 minutes, and then rinse twice with clean water. Rust removal: Immerse the degreased bolts in a hydrochloric acid mixture (7vol%HCl + 0.35g / L hexamethylenetetramine) at room temperature for 8 minutes. After rinsing, remove the bolts and rinse them twice with clean water. At the same time, check whether the oxide scale has been completely removed. Activation: Immerse the rust-removed bolts in a dilute hydrochloric acid solution (3wt%) at room temperature (20-30℃) for 10 minutes, then rinse them three times with clean water to avoid residual acid; 2) Electro-galvanizing Preparation of alkaline zincate plating solution: Dissolve 100g NaOH in 1L deionized water, add 12g ZnO, and stir until completely dissolved; then add 15g triethanolamine and 0.8g low-hydrogen brightener components (0.2g 4-methylbenzyl acetone + 0.2g polyoxyethylene polyoxypropylene block copolymer + 0.2g imidazoline quaternary ammonium salt + 0.2g fatty amine polyoxyethylene ether), and stir evenly; adjust the pH value to 12.5 with NaOH; thus obtaining the alkaline zincate plating solution; wherein, the synergistic effect of 4-methylbenzyl acetone + triethanolamine introduced in this invention reduces the total concentration of brightener to 0.8g / L (far lower than the traditional concentration), which maintains high brightness (coating brightness ≥90%, conforming to GB / T 13312-2002 standard) while avoiding "excessive hydrogen evolution" (hydrogen evolution <7%). Electroplating zinc process parameter settings: Current density 2.5A / dm³ 2 (Current = 2.5A / dm) 2 ×0.537dm 2=1.34A), temperature 22℃, time 15min; Electroplating zinc operation: Connect the bolt to the cathode of the steel bar and place it in a zinc plating bath containing alkaline zincate plating solution (pure zinc plate is used as the anode). Turn on the power to start electroplating zinc. Stir the solution every 15 minutes during the zinc plating process to ensure uniformity. 3) Post-processing Dehydrogenation treatment: Place the galvanized bolts in an oven and heat them at 200℃ for 2.5 hours to remove hydrogen, then let them cool naturally to room temperature; Sealing treatment: After hydrogen removal treatment, the bolts are placed in a chromium-free silicate sealant, wherein the components and their mass percentages are as follows: sodium silicate 45%, ethylene glycol 20%, sodium citrate 8%, Tween-80 3%, and the balance is water (24%). After soaking for 5 minutes, the bolts are removed and placed in an 85℃ oven for sealing treatment for 20 minutes. A dense silicon film is formed on the surface of the galvanized bolts, thus obtaining the final electro-galvanized weathering steel high-strength bolt product.

[0042] The bolt product obtained in this embodiment was subjected to performance testing, as detailed below: Coating thickness: The bolt surface (thread, head, screw) was inspected using a magnetic thickness gauge (Fischer MP0). The average thickness was 12.1 μm, with a deviation of ±0.9 μm (meeting the requirement of ≥12 μm). Porosity: Tested using the filter paper method (GB / T 17722-2018), porosity 1.8% (≤2%). Grain size testing: Three different regions (thread top, thread side, and bolt plane) were observed under SEM, with five photos taken for each region (magnification 5000×). ImageJ software was used to measure 100 grains in each photo (totaling 1500 grains). The results showed: average grain size: 8.2 μm; maximum grain size: 9.8 μm (≤10 μm requirement); grain size distribution: more than 95% of the grains were between 6-10 μm; the grains were fine, uniform, and had clear boundaries.

[0043] Salt spray test: Conduct a neutral salt spray test according to GB / T 10125-2012. Check after 1000 hours, and the corrosion area should be 2.3% (≤5%).

[0044] Hydrogen embrittlement test: Delayed fracture test was conducted according to GB / T 3098.1-2010 (holding the load at 80% of the yield strength for 24 hours), with no fracture (meeting the requirements for 10.9s grade steel).

[0045] Thread fit: Tested with GB / T 193-2003 thread go and no-go gauges. The go gauge passes, but the no-go gauge fails (the sealing film thickness is ≤5μm, which does not affect the thread fit).

[0046] Example 2 An electro-galvanizing method for high-strength weathering steel bolts, the specific steps of which are as follows: 1) Preprocessing Degreasing: Place the bolts in an alkaline degreasing agent (NaOH 30g / L + sodium carbonate 20g / L + nonionic surfactant OP-10 (octylphenol polyoxyethylene ether-10) 6g / L), immerse at 60℃ for 15 minutes, then remove and rinse twice with clean water. Rust removal: Immerse the degreased bolts in a hydrochloric acid mixture (6 vol% HCl + 0.3 g / L hexamethylenetetramine) at room temperature for 7 minutes. After immersion, rinse twice with clean water and check whether the oxide scale has been completely removed. Activation: Immerse the rust-removed bolts in a dilute hydrochloric acid solution (4wt%) at room temperature (20-30℃) for 6 minutes, then rinse them three times with clean water to avoid residual acid; 2) Electro-galvanizing Preparation of alkaline zincate plating solution: Dissolve 90g NaOH in 1L deionized water, add 10g ZnO, and stir until completely dissolved; then add 16g triethanolamine and 0.7g low-hydrogen brightener components (0.3g 4-methylbenzyl acetone + 0.2g polyoxyethylene polyoxypropylene block copolymer + 0.1g imidazoline quaternary ammonium salt + 0.1g fatty amine polyoxyethylene ether), and stir evenly; adjust the pH value to 12 with NaOH; thus obtaining the alkaline zincate plating solution. Electroplating zinc process parameter settings: Current density 2.4A / dm³ 2 Temperature 23℃, time 15min; Electroplating zinc operation: Connect the bolt to the cathode of the steel bar and place it in a zinc plating bath containing alkaline zincate plating solution (pure zinc plate is used as the anode). Turn on the power to start electroplating zinc. Stir the solution every 15 minutes during the zinc plating process to ensure uniformity. 3) Post-processing Dehydrogenation treatment: Place the galvanized bolts in an oven and heat them at 210℃ for 2.2 hours to remove hydrogen, then let them cool naturally to room temperature; Sealing treatment: After hydrogen removal treatment, the bolts are placed in a chromium-free silicate sealant, wherein the components and their mass percentages are as follows: sodium silicate 44%, ethylene glycol 21%, sodium citrate 7%, Tween-80 4%, and the balance is water (24%). After soaking for 5 minutes, the bolts are removed and placed in an 80℃ oven for sealing treatment for 25 minutes. A dense silicon film is formed on the surface of the galvanized bolts, thus obtaining the final electro-galvanized weathering steel high-strength bolt product. Comparative Example 1 An electroplating zinc method for weather-resistant high-strength bolts is largely the same as in Example 1, except that: In the electroplating zinc process: Plating solution formula: ZnO 10 g / L, NaOH 100 g / L, triethanolamine 10 g / L, low-hydrogen brightener 1.0 g / L; The current density set for electroplating zinc is 2.2 A / dm³. 2 The time was 12 minutes, and the rest was the same as in Example 1.

[0047] In the sealing step: the components and their mass percentages in the chromium-free silicate sealant are as follows: sodium silicate 40%, ethylene glycol 15%, sodium citrate 8%, Tween-80 3%, and the remainder is water (34%). The temperature is 95℃ and the time is 25 min.

[0048] The performance test results of the electroplated zinc weathering steel high-strength bolts obtained in this embodiment are shown in Table 1.

[0049] Table 1 shows the performance test results of the electroplated zinc weathering steel high-strength bolts obtained in Comparative Example 1.

[0050] Comparative Example 2 An electroplating zinc method for weather-resistant high-strength bolts is largely the same as in Example 1, except that: In the activation step, the concentration of dilute hydrochloric acid was 2 wt%, and the activation time was 2%. In the electroplating zinc process, the current density used is 1.8 A / dm³. 2 The time is 18 minutes.

[0051] The performance test results of the electroplated galvanized weathering steel high-strength bolts obtained in this comparative example are shown in Table 1.

[0052] Table 2 shows the performance test results of the electroplated zinc weathering steel high-strength bolts obtained in Comparative Example 2.

[0053] Comparative Example 3 A method for electroplating zinc on weathering steel high-strength bolts is largely the same as in Example 1, except that no dehydrogenation treatment is performed.

[0054] The test results are as follows: Hydrogen embrittlement fracture rate: 18% (fractured after 24 hours of delayed fracture test); Tensile strength decreased by 8% (original strength 1000MPa → 920MPa).

[0055] Conclusion: The dehydrogenation process is the key to solving hydrogen embrittlement in grade 10.9 steel; its absence directly leads to mechanical property failure.

[0056] Comparative Example 4 A method for electroplating high-strength weathering steel bolts is largely the same as in Example 1, except that a common sulfur-containing brightener (traditional brightener N,N'-di-n-butylthiourea DBTU) is used at a concentration of 0.8 g / L; the remaining steps are the same as in Example 1.

[0057] The specific test results are as follows: 1) Coating porosity: 8.5%; 2) Grain size test: According to the method described in Example 1, the average grain size is 18.5 μm; the maximum grain size is 25.3 μm; the grain size distribution is that more than 60% of the grains are between 15-25 μm; the grains are coarse and irregular, with obvious "columnar" structure.

[0058] 3) Salt spray lifespan: 350 h.

[0059] 4) Hydrogen embrittlement fracture rate: 5%.

[0060] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for electroplating zinc onto high-strength weathering steel bolts, characterized in that, Includes the following steps: 1) Pretreatment; the weathering steel high-strength bolts are subjected to degreasing, rust removal and activation treatment in sequence; the activation treatment step uses dilute acid; 2) Electro-galvanizing; An alkaline zincate plating bath is prepared, and the components and their concentrations are as follows: zinc oxide 8-15 g / L, sodium hydroxide 80-120 g / L, triethanolamine 12-20 g / L, and low-hydrogen composite brightener 0.5-1 g / L. The low-hydrogen composite brightener comprises 4-methylbenzyl acetone, polyoxyethylene polyoxypropylene block copolymer, imidazoline quaternary ammonium salt, and fatty amine polyoxyethylene ether. The weather-resistant high-strength bolts obtained from the pretreatment in step 1) are added to an alkaline zincate plating solution for electroplating with zinc. 3) Post-treatment: Dehydrogenation treatment is performed, followed by sealing treatment with chromium-free silicate sealant to obtain the final electroplated zinc weathering steel high-strength bolt product.

2. The electroplating zinc method according to claim 1, characterized in that, The degreasing step uses an alkaline degreasing agent, which includes alkaline degreasing components, detergent additives, and surfactants.

3. The electroplating zinc method according to claim 1, characterized in that, The rust removal step uses a hydrochloric acid / hexamethylenetetramine solution; wherein the concentration of hydrochloric acid in the hydrochloric acid / hexamethylenetetramine solution is 5-8 vol%, and the concentration of hexamethylenetetramine is 0.3-0.4 wt%.

4. The electroplating zinc method according to claim 1, characterized in that, The activation step uses dilute sulfuric acid, dilute hydrochloric acid, or a mixture of hydrochloric acid and sulfuric acid.

5. The electroplating zinc method according to claim 1, characterized in that, The low-hydrogen composite brightener comprises the following components and their concentrations in the alkaline zincate plating bath: 4-methylbenzyl acetone 0.1-0.3 g / L, polyoxyethylene polyoxypropylene block copolymer 0.1-0.2 g / L, imidazoline quaternary ammonium salt 0.1-0.2 g / L, and fatty amine polyoxyethylene ether 0.1-0.2 g / L.

6. The electroplating zinc method according to claim 1, characterized in that, The current density used in the electroplating zinc process is 2-2.5 A / dm³. 2 The temperature is 20-25℃, the time is 10-15min, and the pH value is 12.0-13.

0.

7. The electroplating zinc method according to claim 1, characterized in that, The dehydrogenation process conditions include: 190-220℃, 2-3h.

8. The electroplating zinc method according to claim 1, characterized in that, The sealing process conditions include: using a chromium-free silicate sealant; a temperature of 80-100℃; and a time of 15-30 minutes.

9. The electroplating zinc method according to claim 1, characterized in that, The chromium-free silicate sealant comprises a silicate matrix, a film-forming aid, a chromium-free corrosion inhibitor, and a wetting agent.

10. The electroplating zinc method according to claim 9, characterized in that, The chromium-free silicate sealant comprises the following components and their mass percentages: silicate main body 42-50%, film-forming aid 18-25%, chromium-free corrosion inhibitor 5-10%, and wetting agent 2-5%.

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