Plating aid process based on super-high strength steel wire aided multi-element alloy immersion plating layer

Abstract

The application relates to the technical field of metal surface treatment, and particularly discloses a plating aid process based on super-high-strength steel wire aided plating of a multicomponent alloy immersion plated layer. The process comprises pretreatment, composite plating aid, preheating, hot immersion plating and controlled cooling; the plating aid liquid comprises zinc chloride, ammonium chloride, stannous chloride and rare earth chloride. The interfacial tension is adjusted by stannous chloride to improve wettability, high-density heterogeneous nucleation is induced by rare earth ions, and the process is combined with atmosphere protection and controlled cooling regulation. The application can obtain a fine-grained and dense multicomponent alloy plated layer, significantly improves corrosion resistance, and effectively retains the strength and toughness of the super-high-strength steel wire matrix. The application solves the problems that a traditional plating aid system cannot simultaneously remove iron, inhibit side reactions and induce nucleation during multicomponent alloy immersion plating.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment technology, and specifically discloses a fluxing process based on a multi-element alloy immersion coating for fluxing ultra-high strength steel wire. Background Technology

[0002] In modern bridge, cable-stayed, and high-strength structural engineering, ultra-high-strength steel wire serves as a core load-bearing component, and its service life and reliability are highly dependent on the integrity and durability of the surface protective coating. Hot-dip galvanizing with multi-alloy technology, due to its excellent corrosion resistance and mechanical compatibility, has become a key means to improve the environmental adaptability of steel wire. The fluxing process, as the core step in the pretreatment for hot-dip galvanizing, directly determines the cleanliness and activation state of the steel wire substrate surface, as well as the nucleation and adhesion behavior of the subsequent coating. Traditional fluxing systems often use zinc chloride (ZnCl2) or ammonium chloride (NH4Cl) as the main salt. Their mechanism of action lies in reacting with the ferrous ions (Fe²⁺) remaining after pickling the steel wire. + The reaction generates soluble complexes (such as Fe(NH4)2Cl4 or FeZnCl4), effectively removing surface oxidation byproducts and activating the interface, laying the foundation for the uniform spreading and metallurgical bonding of the subsequent molten alloy on the steel substrate. This technical approach has demonstrated good process stability and economy in conventional zinc plating systems.

[0003] However, with the increasing demands for coating performance, especially in applications expanding towards multi-element alloy systems such as Zn-Al-Mg-rare earth, traditional fluxing mechanisms have revealed deep-seated inherent contradictions. Specifically, when highly reactive elements such as Al and Mg are introduced into the molten pool to improve the corrosion resistance of the coating, these elements readily react with chloride ions in the flux, generating volatile or high-melting-point chlorides (such as AlCl3 and MgCl2). This not only consumes the active fluxing components but also forms a heterogeneous reaction layer at the interface upon the steel wire's entry into the plating solution, interfering with the wetting process of the alloy melt and leading to defects such as pinholes, porosity, or interface inclusions in the coating. Furthermore, traditional fluxing systems have extremely limited ability to regulate coating nucleation kinetics—their main function focuses on "removal" rather than "promotion," making it difficult to induce a sufficient density of heterogeneous nucleation sites on the low surface energy and high internal stress substrate of ultra-high strength steel wire, thus restricting the formation of a dense, fine-grained coating structure. The reason for this lies in Zn²⁺… + or NH4 + Although cations can effectively complex Fe² + However, it does not catalyze the reduction and deposition of alloying elements (especially Mg and rare earth elements) at the interface, and may even inhibit the interfacial enrichment of beneficial elements due to competitive adsorption.

[0004] Against this backdrop, simply optimizing process parameters such as fluxing temperature or time is no longer sufficient to overcome the aforementioned fundamental bottlenecks. Existing technologies attempt to improve interfacial reaction kinetics by introducing stannous chloride (SnCl2) or rare earth chlorides (such as CeCl3), but these additives, without systematic formulation and synergistic concentration design, are prone to introducing new problems: for example, Sn²⁺… + Rare earth elements are easily oxidized and degraded in air, while excessively high concentrations of rare earth ions can lead to decreased stability of the flux or a significant increase in cost. More importantly, different main salts (ZnCl2, NH4Cl, SnCl2, CeCl3) exhibit significant differences in complexing ability, interfacial adsorption characteristics, and interactions with multiple alloying elements. Using them alone or in simple mixtures often fails to adequately address the Fe²⁺ oxidizing effect. + The goal is to achieve a triple objective: efficient cleaning, deep substrate activation, and enhanced nucleation of multi-element alloys. Accordingly, the rational design of flux components must transcend the traditional single-dimensional approach of "iron removal and activation," and instead focus on constructing a composite flux system that can synergistically regulate the interfacial chemical environment, accelerate the co-deposition and nucleation of multi-element alloys, and effectively suppress the side reactions between highly reactive metals and chloride ions. This requires precise control over the types and proportions of cations and their coupling effect with the process window (temperature, time) to achieve atomic-level cleanliness and high-density nucleation at the coating / substrate interface on the special substrate of ultra-high-strength steel wire.

[0005] Therefore, how to construct a method that can efficiently remove Fe²⁺ through the scientific compounding of multiple main salts and the precise matching of process parameters is a key challenge. + The development of a novel fluxing process that can significantly improve the nucleation rate and film density of Zn-Al-Mg-rare earth multi-element alloys on the surface of ultra-high strength steel wire, while effectively avoiding adverse side reactions between elements such as Al and Mg and the fluxing solution, has become a key challenge and a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating, in order to solve the problem that the existing technology mentioned above cannot achieve efficient removal of Fe²⁺. + The technical challenge is to address the issue of significantly improving the nucleation rate and film density of Zn-Al-Mg-rare earth multi-element alloys on the surface of ultra-high strength steel wire while maintaining the residual properties.

[0007] To address the aforementioned problems, the technical solution adopted in this invention is as follows: a fluxing process based on a multi-element alloy immersion coating for ultra-high strength steel wire, the process sequentially including substrate pretreatment, composite fluxing treatment, preheating and drying, multi-element alloy hot-dip coating, and controlled cooling; wherein, in the composite fluxing treatment step, a multi-element composite fluxing solution containing a first main salt, a second main salt, a third main salt, and a fourth main salt is used, the first main salt being zinc chloride, the second main salt being ammonium chloride, the third main salt being stannous chloride, and the fourth main salt being at least one of cerium chloride or lanthanum chloride; the composite fluxing solution, through the synergistic effect of each main salt, forms a fluxing layer on the surface of the ultra-high strength steel wire substrate that combines interfacial activity regulation and nucleation catalysis functions, thereby achieving efficient complexation and removal of ferrous ions, improvement of the wettability of molten multi-element alloys, and induction of high-density heterogeneous nucleation.

[0008] The beneficial effects of this implementation plan are as follows: First, a multifunctional composite plating system was constructed through the scientific compounding of the first to fourth main salts. This system not only achieved efficient removal of ferrous ions, but also enhanced the surface energy of the ultra-high strength steel wire substrate through the synergistic effect of tin ions and rare earth ions, creating interfacial conditions for the wetting and nucleation of multi-element alloys.

[0009] Secondly, by utilizing the fourth primary salt to regulate nucleation kinetics, high-density heterogeneous nucleation was induced, resulting in a fine-grained and dense microstructure in the Zn-Al-Mg-rare-earth multi-element alloy coating. The enrichment of rare-earth elements at grain boundaries effectively inhibited the intergranular penetration of corrosive media, thereby improving the long-term corrosion resistance of the coating.

[0010] Third, by introducing atmosphere protection and molten pool homogenization technology, the oxidation and burn-off of highly active elements in the atmospheric environment are effectively avoided, ensuring the long-term stability of the molten pool composition, reducing the amount of slag generated during the production process, and improving the material utilization rate.

[0011] Fourth, the implementation of the controlled cooling process enabled precise control over the microstructure and distribution of the coating. Rapid cooling suppressed the precipitation of coarse intermetallic compounds, resulting in an optimized microstructure composed of pre-precipitated phases, chrysanthemum-like structures, and dispersed particles. This improved the coating's hardness and wear resistance while maintaining excellent adhesion.

[0012] Fifth, this process, taking advantage of the special mechanical properties of ultra-high strength steel wire, preserves the high strength and high toughness of the substrate by shortening the heat-affected time, thus solving the problem that traditional hot-dip galvanizing processes easily lead to substrate performance degradation.

[0013] In summary, this invention constructs a complete and rigorous multi-element alloy immersion plating technology system for ultra-high strength steel wire from four dimensions: chemical regulation of the fluxing system, physical protection of the molten pool environment, kinetic intervention of the solidification process, and systematic evaluation of the finished product performance.

[0014] Furthermore, the composite flux also contains a nonionic surfactant with a mass fraction of 0.05% to 0.15%, which is used to reduce the surface tension of the flux to below 30 mN / m, enhance the penetration ability of the flux components on the micro-rough surface of the ultra-high strength steel wire substrate, cover microcracks and micropores, and prevent pinhole defects in the subsequent coating.

[0015] Furthermore, in the composite flux, the mass concentration of zinc chloride is 200 g / L to 350 g / L, the mass concentration of ammonium chloride is 100 g / L to 180 g / L, the mass concentration of stannous chloride is 5 g / L to 15 g / L, and the mass concentration of rare earth chloride is 2 g / L to 8 g / L; the concentration ratio of each component satisfies the complexation equilibrium relationship.

[0016] Furthermore, the tin ions in the third main salt adsorb onto the surface of the ultra-high strength steel wire matrix to form a tin-based activation layer, and its adsorption behavior follows the Langmuir adsorption isotherm model:

[0017] in, The amount of adsorption per unit area, expressed in mol / m². 2 ; max denoted as saturated adsorption capacity; b is the adsorption equilibrium constant; and C is the mass concentration of stannous chloride in the flux, thereby inducing a micro-displacement reaction upon entry into the plating solution, reducing interfacial tension, and improving wettability.

[0018] Furthermore, the rare earth ions in the fourth main salt accumulate at defect sites on the surface of the ultra-high strength steel wire matrix, forming rare earth-induced nucleation centers, which reduce the critical nucleation work during the solidification process of the multi-element alloy. The expression for the nucleation work is as follows:

[0019] in, The critical nucleation work; It is the liquid-solid interface energy; This represents the change in free energy per unit volume. This is a geometric factor related to the contact angle. Because rare earth ions adsorb onto the steel wire surface, the contact angle between the molten alloy and the matrix is ​​reduced. This reduces The value of promotes high-density heterogeneous nucleation.

[0020] Furthermore, the substrate pretreatment includes multi-stage continuous pickling and ultrasonic cleaning. The pickling uses a hydrochloric acid solution with a mass fraction of 15% to 20% and adds 0.1% to 0.3% imidazoline corrosion inhibitor. The ultrasonic cleaning frequency is 25kHz to 40kHz. The preheating and drying are carried out in a circulating hot air drying oven at a drying temperature of 120°C to 180°C and a drying time of 45 seconds to 90 seconds to form a continuous solid flux coating film without crystallization water.

[0021] Furthermore, the controlled cooling step employs a ring-array structure of cooling jet nozzles, mixing a low-temperature cold source with a preset-pressure airflow at the nozzle tip to form a uniform cooling jet that acts on the circumferential surface of the steel wire; the cooling rate is controlled between 30℃ / s and 50℃ / s by adjusting the flow regulating valve, and its heat exchange process follows the heat balance equation:

[0022] in, Total heat exchange; Where A is the convective heat transfer coefficient; A is the surface area of ​​the steel wire. This refers to the real-time surface temperature of the coating. The initial temperature of the cooling jet; The mass flow rate of the cold source; This refers to the latent heat of vaporization of atomized water droplets. Detailed Implementation

[0023] The following detailed description illustrates the specific implementation method: This invention provides a fluxing process for plating a multi-alloy immersion coating based on ultra-high strength steel wire. The process comprises a complete technical system, from microscopic interface activation to macroscopic process control. During the process, the ultra-high strength steel wire substrate undergoes core steps including substrate pretreatment, composite fluxing treatment, preheating and drying, multi-alloy hot-dip plating, and controlled cooling. Ultimately, a multi-alloy coating with high bonding strength and excellent corrosion resistance is formed on the substrate surface.

[0024] In the substrate pretreatment stage, this invention employs a composite scheme combining multi-stage continuous pickling and ultrasonic cleaning, targeting the high-strength physical properties and surface microstructure of the ultra-high-strength steel wire substrate. The pickling tank is filled with a pre-concentrated inorganic acid solution, specifically a hydrochloric acid solution with a mass fraction of 15% to 20%, and an imidazoline corrosion inhibitor with a mass fraction of 0.1% to 0.3% is added to the solution. The addition of the corrosion inhibitor aims to form a dense molecular protective film by adsorbing onto active sites on the steel wire surface, thereby efficiently removing oxide scale while inhibiting the diffusion of hydrogen atoms into the steel wire substrate, preventing hydrogen embrittlement fracture of the ultra-high-strength steel wire. After the pickling process, the steel wire enters an ultrasonic cleaning tank equipped with an ultrasonic transducer with a frequency of 25kHz to 40kHz. Through the cavitation effect generated by ultrasound in the liquid, residual acid, iron salt particles, and grease residues remaining in the micropores and microcracks of the steel wire after pickling can be completely removed.

[0025] After pretreatment, the ultra-high-strength steel wire substrate enters the composite fluxing treatment step. This step is crucial for achieving high wettability and high-density nucleation of the subsequent multi-element alloy. The composite fluxing solution used in this invention is a multi-element aqueous solution system composed of a first main salt, a second main salt, a third main salt, a fourth main salt, and a nonionic surfactant. Specifically, the first main salt is zinc chloride, with a mass concentration controlled between 200 g / L and 350 g / L. It is mainly responsible for building a zinc ion complexation environment on the steel wire surface, providing the zinc source required for subsequent reactions. The second main salt is ammonium chloride, with a mass concentration set between 100 g / L and 180 g / L. Utilizing its volatility at high temperatures and strong complexing ability with metal ions, it works synergistically with the first main salt to remove residual ferrous ions from the steel wire surface.

[0026] In the chemical equilibrium control of fluxing solutions, the complexation state of ferrous ions directly affects the purity of the coating interface. This invention adjusts the ratio of each main salt to ensure that the complexation equilibrium of ferrous ions in the fluxing system follows the following formula:

[0027] In this formula, The overall complexation constant of the fluxing system for ferrous ions; [Fe 2+ [M] represents the molar concentration of ferrous ions in the interface layer on the surface of the steel wire; z+ The symbol ] represents the activity of different cations (such as zinc ions, stannous ions, rare earth ions, etc.) in the flux; n and m represent the number of coordinating atoms, respectively. By precisely adjusting the ratio of zinc chloride to ammonium chloride, the desired fluxing activity is ensured. Maintain at 10 12 Up to 10 15 Within a certain range, ferrous ions are firmly complexed in the liquid phase, preventing the formation of brittle iron-zinc compound inclusions when subsequently entering the molten pool.

[0028] Furthermore, as a core innovation of this invention, a third primary salt, stannous chloride, is introduced into the composite plating solution at a concentration of 5 g / L to 15 g / L. The introduction of stannous chloride not only utilizes its reducing properties to prevent the oxidation of ferrous ions, but more importantly, stannous ions exhibit specific adsorption kinetics on the surface of ultra-high strength steel wire. The adsorption of stannous ions on the steel wire surface follows the Langmuir adsorption isotherm model:

[0029] in, The amount of adsorption per unit area, expressed in mol / m². 2 ; max denoted as saturated adsorption capacity; b is the adsorption equilibrium constant; and C is the mass concentration of stannous chloride in the flux. By controlling the concentration C within the aforementioned preset range, the adsorption capacity is maximized. Approaching saturation, a molecular-level tin-based activation layer is formed on the surface of the steel wire. This activation layer induces a micro-regional displacement reaction the moment the steel wire enters the molten multi-element alloy pool at around 450°C, releasing additional chemical potential energy, significantly reducing the interfacial tension between the molten metal and the steel wire matrix, and improving the wetting rate.

[0030] The four main salts are rare earth chlorides, specifically cerium chloride or lanthanum chloride, with a mass concentration of 2 g / L to 8 g / L. The role of rare earth ions is to alter the nucleation kinetics at the interface of the multi-element alloy. Due to their large ionic radii and unique 4f electron orbitals, rare earth ions preferentially accumulate at defect sites on the steel wire surface, forming rare earth-induced nucleation centers. According to the heterogeneous nucleation theory, the presence of rare earth ions significantly reduces the critical nucleation work, the degree of which is expressed by the following formula:

[0031] in, The critical nucleation work; It is the liquid-solid interface energy; This represents the change in free energy per unit volume. This is a geometric factor related to the contact angle. Because rare earth ions adsorb onto the steel wire surface, the contact angle between the molten alloy and the matrix is ​​reduced. This reduces The value of this property allows for the induction of high-density heterogeneous nucleation in the early stages of solidification of the multi-element alloy, thereby refining the coating structure and inhibiting the growth of coarse columnar crystals.

[0032] To further enhance the penetration of the flux into the micro-rough surface of ultra-high strength steel wire, a nonionic surfactant, such as fatty alcohol polyoxyethylene ether (AEO-9), is added to the composite flux at a mass fraction of 0.05% to 0.15%. This surfactant can reduce the surface tension of the flux to below 30 mN / m, ensuring that the flux salt components can completely cover the tiny scratches on the steel wire surface and the micropores left during the production process, eliminating "missed plating" defects caused by localized lack of wetting.

[0033] During the composite fluxing process, the temperature of the flux solution is maintained at a first preset temperature of 50°C to 70°C, and the fluxing time is set to a first preset duration of 30 to 60 seconds. This temperature range ensures that the salt components have sufficient diffusion kinetic activity while preventing the rapid decomposition of ammonium chloride from causing an imbalance in the solution composition.

[0034] After the fluxing process is complete, the steel wire enters the preheating and drying step. The drying process is completed in a circulating hot air drying oven, with the drying temperature (second preset temperature) set between 120℃ and 180℃, and the drying time (second preset duration) between 45 and 90 seconds. By precisely controlling the airflow and temperature gradient, the moisture on the surface of the steel wire evaporates rapidly, forming a uniform, continuous, and water-free solid flux film. This film effectively isolates the steel wire from air before it enters the molten pool, preventing secondary oxidation of the steel wire surface.

[0035] Subsequently, the steel wire enters the multi-alloy hot-dip galvanizing bath. The chemical composition of the bath is: aluminum 3.0% to 6.0%, magnesium 1.0% to 3.0%, rare earth elements (cerium and lanthanum) 0.05% to 0.2%, with the balance being zinc. The bath temperature is strictly controlled between 430℃ and 460℃. During the immersion plating process, in order to suppress the violent side reaction between highly reactive elements such as aluminum and magnesium and chloride ions in the flux film to generate aluminum chloride or magnesium chloride slag, this invention utilizes a tin-based activation layer and rare earth induction centers in the flux to construct an interfacial reaction inhibition mechanism. The reaction rate is controlled according to the following Arrhenius modified equation:

[0036] in, Indicates the rate of side reactions; Pre-exponential factors; The activation energy of the elementary reaction; The interfacial energy barrier is generated by the composite adsorption film formed by tin subions and rare earth ions; R is the gas constant; and T is the absolute temperature of the molten pool. The interfacial layer constructed by this process significantly increases the... This reduces the rate of harmful side reactions by more than 60%, ensuring that the metallurgical bond between the coating and the substrate is based on brittle salts generated by atomic diffusion rather than chemical reactions.

[0037] In terms of the engineering management of the molten pool, this invention includes an atmosphere protection auxiliary system. A lightweight cover made of high-temperature resistant ceramic fiber material covers the molten pool, and high-purity nitrogen (≥99.99% purity) is introduced between the cover and the molten pool surface to maintain a slight positive pressure of 0.05 MPa to 0.1 MPa, creating an oxygen-free environment. Simultaneously, a ceramic impeller-type forced convection device is installed inside the molten pool. A PID control system adjusts the pump power to ensure that the temperature difference between different areas of the molten pool is less than ±2℃, and the composition fluctuation is controlled within 0.05%.

[0038] The wire feed speed in the molten pool needs to be dynamically adjusted according to the wire diameter to ensure an appropriate immersion time. The wire feed speed, immersion time, and molten pool length satisfy the following logical relationship:

[0039] in, For effective immersion time, The effective immersion zone length of the molten pool The speed at which the steel wire passes through the molten pool; for ultra-high strength steel wire with a diameter of 5mm, this time should be controlled between 3 and 6 seconds. If the time is too short, the interfacial diffusion will be insufficient, resulting in poor bonding; if the time is too long, it will lead to excessive iron-zinc reaction, forming an excessively thick brittle intermetallic compound layer.

[0040] After immersion coating, the steel wire immediately enters a controlled cooling process. This process uses a ring-array cooling jet nozzle to uniformly cool the steel wire leaving the molten pool using a low-temperature cold source (such as a mixture of -10°C compressed air and atomized water). The cooling rate is controlled according to the following heat balance equation:

[0041] in, Total heat exchange; Where A is the convective heat transfer coefficient; A is the surface area of ​​the steel wire. This refers to the real-time surface temperature of the coating. The initial temperature of the cooling jet; The mass flow rate of the cold source; The latent heat of vaporization of the atomized water droplets is used. The cooling rate is controlled between 30℃ / s and 50℃ / s by adjusting the flow regulating valve. This rapid cooling method effectively shortens the heat-affected zone, preventing the ultra-high strength steel wire matrix from recovering and recrystallizing due to prolonged exposure to high temperatures, thus preserving the matrix's ultra-high strength. Simultaneously, rapid cooling promotes the refinement of the Zn-Al-Mg eutectic structure in the coating, forming a multi-level structure consisting of a first precipitated zinc-rich phase, a fine chrysanthemum-like eutectic structure, and dispersed rare-earth intermetallic compounds.

[0042] Finally, the steel wire enters the finished product processing unit for environmentally friendly chromium-free passivation treatment, which further enhances the initial resistance to white rust of the coating.

[0043] To verify the technical superiority of the process of the present invention, the following detailed description is provided in conjunction with specific embodiments and comparative examples.

[0044] In Example 1, ultra-high strength steel wire with a strength grade of 1860 MPa and a diameter of 5.0 mm was selected as the substrate. Pretreatment involved 18% hydrochloric acid with 0.2% corrosion inhibitor, combined with 35 kHz ultrasonic cleaning. The composite flux composition was: zinc chloride 280 g / L, ammonium chloride 150 g / L, stannous chloride 10 g / L, cerium chloride 5 g / L, and nonionic surfactant AEO-9 0.1 g / L. The fluxing temperature was 60°C, and the time was 45 seconds. The preheating and drying temperature was 150°C. The multi-element alloy bath composition was Zn-5.5Al-2.0Mg-0.1RE, and the temperature was 450°C. The wire feed speed was set to 15 meters per minute, and the cooling rate was controlled at 40°C / s.

[0045] In Comparative Example 1, a conventional fluxing process was used. The fluxing solution contained only 250 g / L zinc chloride and 150 g / L ammonium chloride, and did not contain stannous chloride, rare earth chloride, or surfactants. Other parameters, such as pickling, drying, immersion bath composition and temperature, and cooling method, were completely consistent with those in Example 1.

[0046] The steel wires prepared in Example 1 and Comparative Example 1 were subjected to performance testing. The testing items included: coating surface quality (visual inspection and scanning electron microscopy), coating thickness uniformity, adhesion (180° bending and torsion tests), corrosion resistance (neutral salt spray test, NSS), and retention rate of substrate mechanical properties. The test data are summarized in the table below:

[0047] Table 1: Comparison of Performance Test Results between Example 1 and Comparative Example 1 As can be clearly observed from the data in Table 1, the fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating described in this invention exhibits significant technical advantages in multiple dimensions. Specifically, in terms of corrosion resistance, the red rust appearance time in Example 1 reached 2800 hours, while that in Comparative Example 1 was only 950 hours. This improvement is attributed to the induced nucleation effect of rare earth ions in the fourth main salt, resulting in an extremely dense Zn-Al-Mg eutectic structure in the coating. The enrichment of rare earth elements at the grain boundaries effectively blocks the intergranular penetration of corrosive ions such as Cl⁻.

[0048] Regarding the retention of mechanical properties, the tensile strength of the matrix in Example 1 showed almost no decrease (1852 MPa, compared to 1860 MPa initially), while the decrease was more significant in Comparative Example 1. This demonstrates that the controlled cooling system and the optimized fluxing layer work synergistically in this process, shortening the effective heat treatment time and successfully solving the problem of strength degradation after hot-dip galvanizing of ultra-high strength steel wire.

[0049] Further analysis of the interface microstructure, observed using scanning electron microscopy (SEM), revealed that an extremely thin and uniform iron-zinc-aluminum ternary intermetallic layer, approximately 1.5 μm thick, was formed between the coating and the substrate in Example 1. According to the modified form of Fick's first law:

[0050] Where J is the ion flux and D is the diffusion coefficient; C represents the ion concentration gradient; z represents the charge number; u represents the mobility; and F represents the Faraday constant. The potential gradient is the interface potential gradient.

[0051] In the process of this invention, due to the rare earth ion Ce 3+ Or La 3+ The presence of this material alters the potential gradient at the interface. This allows elements such as aluminum and magnesium to preferentially migrate to the matrix surface and participate in nucleation, thereby forming a stable mutually soluble layer in a very short time and rapidly entering the eutectic solidification stage, effectively suppressing the excessive diffusion of iron atoms into the molten pool.

[0052] Furthermore, the process of this invention also exhibits excellent production stability. Due to the application of the atmosphere protection auxiliary system and the forced convection device, the amount of slag generated on the surface of the molten pool is reduced by more than 75% compared to traditional processes, and the burn-off rate of aluminum and magnesium elements is controlled within 3%. The real-time elemental analysis system for the molten pool automatically samples and analyzes the composition of the molten pool every 30 minutes using spectral analysis. When the aluminum or magnesium content is detected to be lower than a preset threshold, the replenishment device automatically adds Zn-Al-Mg master alloy ingots preheated to 400℃ to the molten pool, achieving closed-loop precise compensation of the composition.

[0053] During the controlled cooling stage, the arrangement of the annular array nozzles ensures that the temperature difference along the circumference of the steel wire is kept within 5°C. This highly symmetrical cooling field prevents the steel wire from bending and deforming due to uneven radial thermal stress during high-speed operation, thus ensuring the straightness of the finished product.

[0054] In summary, this invention, through the reconstruction of the chemical composition of the fluxing solution combined with precise thermal control and atmosphere protection, not only solves the wetting and nucleation problems of ultra-high strength steel wire in the multi-element alloy immersion plating process, but also achieves a perfect balance between high-performance coating and high-strength substrate through refined microstructure control. This process has extremely high engineering application value in fields such as cable wire for extra-long span bridges and ultra-high strength steel wire rope for marine engineering.

[0055] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating, characterized in that, The process sequentially includes substrate pretreatment, composite fluxing treatment, preheating and drying, multi-element alloy hot-dip plating, and controlled cooling. In the composite fluxing treatment step, a multi-element composite fluxing solution containing a first main salt, a second main salt, a third main salt, and a fourth main salt is used. The first main salt is zinc chloride, the second main salt is ammonium chloride, the third main salt is stannous chloride, and the fourth main salt is at least one of cerium chloride or lanthanum chloride. Through the synergistic effect of the main salts, the composite fluxing solution forms a fluxing layer on the surface of the ultra-high strength steel wire substrate that combines interfacial activity regulation and nucleation catalysis, thereby achieving efficient complexation and removal of ferrous ions, improved wettability of the molten multi-element alloy, and induction of high-density heterogeneous nucleation.

2. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The composite flux also contains a nonionic surfactant with a mass fraction of 0.05% to 0.15%, which is used to reduce the surface tension of the flux to below 30 mN / m, enhance the penetration ability of the flux components on the micro-rough surface of the ultra-high strength steel wire substrate, cover microcracks and micropores, and prevent pinhole defects in the subsequent coating.

3. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: In the composite flux, the mass concentration of zinc chloride is 200 g / L to 350 g / L, the mass concentration of ammonium chloride is 100 g / L to 180 g / L, the mass concentration of stannous chloride is 5 g / L to 15 g / L, and the mass concentration of rare earth chloride is 2 g / L to 8 g / L; the concentration ratio of each component satisfies the complexation equilibrium relationship.

4. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The tin ions in the third main salt adsorb onto the surface of the ultra-high strength steel wire matrix to form a tin-based activation layer, and its adsorption behavior follows the Langmuir adsorption isotherm model: in, The amount of adsorption per unit area, expressed in mol / m². 2 ; max denoted as saturated adsorption capacity; b is the adsorption equilibrium constant; and C is the mass concentration of stannous chloride in the flux, thereby inducing a micro-displacement reaction upon entry into the plating solution, reducing interfacial tension, and improving wettability.

5. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The rare earth ions in the fourth main salt accumulate at defect sites on the surface of the ultra-high strength steel wire matrix, forming rare earth-induced nucleation centers, which reduce the critical nucleation work during the solidification process of the multi-element alloy. The expression for the nucleation work is as follows: in, The critical nucleation work; It is the liquid-solid interface energy; This represents the change in free energy per unit volume. This is a geometric factor related to the contact angle. Because rare earth ions adsorb onto the steel wire surface, the contact angle between the molten alloy and the matrix is ​​reduced. This reduces The value of promotes high-density heterogeneous nucleation.

6. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The substrate pretreatment includes multi-stage continuous pickling and ultrasonic cleaning. The pickling uses a hydrochloric acid solution with a mass fraction of 15% to 20% and adds 0.1% to 0.3% imidazoline corrosion inhibitor. The ultrasonic cleaning frequency is 25kHz to 40kHz. The preheating and drying are carried out in a circulating hot air drying oven at a drying temperature of 120℃ to 180℃ and a drying time of 45 seconds to 90 seconds to form a continuous solid flux coating film without crystallization water.

7. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The multi-element alloy hot-dip galvanizing is carried out in a multi-element alloy molten pool, which consists of: 3.0% to 6.0% aluminum, 1.0% to 3.0% magnesium, 0.05% to 0.2% rare earth elements, with the balance being zinc. An inert gas cover is provided above the molten pool, which is filled with high-purity nitrogen or argon to maintain a slight positive pressure of 0.05 MPa to 0.1 MPa. A forced convection device is also provided to ensure uniform temperature and concentration fields in the molten pool. The molten pool is also equipped with a real-time elemental analysis system and a replenishment device to achieve closed-loop composition compensation.

8. The fluxing process based on ultra-high strength steel wire fluxing multi-alloy immersion coating according to claim 1, characterized in that: The controlled cooling step employs a ring-array cooling jet nozzle structure, mixing a low-temperature cold source with a preset-pressure airflow at the nozzle tip to form a uniform cooling jet that acts on the circumferential surface of the steel wire. The cooling rate is controlled between 30°C / s and 50°C / s by adjusting the flow rate valve, and its heat exchange process follows the heat balance equation. in, Total heat exchange; Where A is the convective heat transfer coefficient; A is the surface area of ​​the steel wire. This refers to the real-time surface temperature of the coating. The initial temperature of the cooling jet; The mass flow rate of the cold source; This refers to the latent heat of vaporization of atomized water droplets.

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