Phosphating treatment method for surface of workpiece with high salt spray corrosion resistance

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a high-salt-spray-corrosion-resistance workpiece surface phosphating treatment method. The method comprises the following working procedures of ultrasonic oil removal, water washing, water washing, activation, dipping phosphorization, water washing, water washing, ultrasonic hot water washing and drying, and dipping phosphorization refers to that an activated workpiece is put into a phosphating solution to be subjected to phosphating treatment; the phosphating solution comprises the following components: 5-8 g / L of organic phosphonic acid, 30-40 g / L of zinc dihydrogen phosphate, 50-55 g / L of calcium nitrate, 2-4 g / L of sodium m-nitrobenzenesulfonate, 1-2 g / L of an accelerant, 0.5-0.8 g / L of a surfactant, 1-3 g / L of sodium molybdate, 2-4 g / L of citric acid and 0.2-0.44 g / L of rare earth salt. Through low-temperature high-efficiency process design and multi-component collaborative innovation, breakthrough is achieved in the aspects of compactness, corrosion resistance, adhesive force and other core performance of the phosphating film, the environment friendliness and economical efficiency are both achieved, and a new solution is provided for metal corrosion prevention in the fields of automobiles, ships, electronics and the like.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment technology, and in particular to a method for phosphating the surface of workpieces with high resistance to salt spray corrosion. Background Technology

[0002] Metal corrosion causes serious damage to the global economy and environment, affecting various industries such as automobiles, ships, and pipelines. Phosphating is one of the most widely used surface treatment methods for preventing metal corrosion. Phosphating includes chemical phosphating and electrolytic phosphating, which involve a chemical or electrochemical reaction occurring during the contact between the metal and the phosphating solution, ultimately depositing an inorganic film layer on the metal surface. The phosphating film possesses excellent hardness and insulation properties. As a surface coating, it provides a certain degree of corrosion protection and lubrication for the metal substrate; as an intermediate coating, the presence of the phosphating film can improve the adhesion between the metal and subsequent organic coatings.

[0003] Traditional high-temperature phosphating processes are energy-intensive, while low-temperature phosphating easily leads to a decline in film performance. Therefore, extending the phosphating time is necessary to ensure phosphating quality, but this leads to reduced phosphating efficiency. Thus, traditional phosphating processes often cannot simultaneously achieve energy saving and high efficiency while maintaining the desired phosphating film effect. However, neither increasing the phosphating temperature nor extending the phosphating time is advantageous for industrial applications. Traditional phosphating accelerators include nitrites, chromates, and fluorides, which easily generate harmful substances during the phosphating process, making them less environmentally friendly. Furthermore, these accelerators can degrade Fe... 2+ Oxidized to Fe 3+ This leads to a large amount of sludge being generated in the later stages of phosphating, increasing the cost of waste treatment. The use of some new accelerators, such as nanoparticles, reduces the stability of the phosphating solution. Nanoparticles in the phosphating solution have high surface energy, making them prone to aggregation and sedimentation, which is detrimental to continuous industrial operations. Therefore, it is crucial to select new, green, and environmentally friendly accelerators to fundamentally avoid the use of harmful accelerators while simultaneously achieving energy-efficient and corrosion-resistant phosphating films. Summary of the Invention

[0004] The purpose of this application is to address the shortcomings of current technology by providing a method for phosphating workpieces with high resistance to salt spray corrosion. This method has the advantages of simple process flow, automated operation and high efficiency. At the same time, the phosphating solution of this application can obtain a uniform and fine phosphating film with excellent corrosion resistance. The phosphating film has strong adhesion to the surface of metal workpieces and is suitable for phosphating workpieces of various materials such as iron, zinc alloy, and stainless steel.

[0005] This application provides a method for phosphating the surface of a workpiece with high resistance to salt spray corrosion, using the following technical solution: A method for phosphating the surface of a workpiece with high resistance to salt spray corrosion includes the following steps: ultrasonic degreasing → water washing → water washing → water washing → activation → immersion phosphating → water washing → water washing → ultrasonic hot water washing → drying. The immersion phosphating refers to immersing the activated workpiece in a phosphating solution for phosphating treatment. The phosphating solution comprises the following components: 5-8 g / L organophosphonic acid, 30-40 g / L zinc dihydrogen phosphate, 50-55 g / L calcium nitrate, 2-4 g / L sodium m-nitrobenzenesulfonate, 1-2 g / L accelerator, 0.5-0.8 g / L surfactant, 1-3 g / L sodium molybdate, 2-4 g / L citric acid, and 0.2-0.44 g / L rare earth salts.

[0006] By employing the above technical solutions, ultrasonic degreasing removes oil and mechanical impurities from the workpiece surface through the ultrasonic cavitation effect, ensuring full contact between the subsequent treatment solution and the substrate. This provides a clean surface for subsequent activation and phosphating, preventing oil from hindering the film-forming reaction. Three water rinses progressively remove residual degreasing agents and contaminants, preventing cross-contamination. This ensures the purity of the solution between each process, preventing impurities from interfering with subsequent chemical reactions. It activates the micro-etched substrate surface, exposing the metal lattice and enhancing the adhesion of the phosphating film. It provides an active surface for the phosphating solution, promoting metal dissolution and crystal nucleation. Immersion phosphating forms a dense phosphating film at low temperatures using the phosphating solution. The synergistic effect of the components accelerates film formation, and low-temperature operation reduces energy consumption, avoiding high temperatures that could lead to a porous film. Ultrasonic hot water rinsing uses ultrasound to remove residual solution from the micropores of the phosphating film, reducing salt crystallization residue. This improves the film's density and reduces the risk of later corrosion. Drying thoroughly removes moisture, preventing residual water vapor from causing film oxidation or localized corrosion. This stabilizes the film structure and enhances corrosion resistance. The role of phosphating solution components: Organophosphonic acids (such as ethylenediaminetetramethylenephosphonic acid, EDTMP) chelate metal ions (such as Zn). 2+ Fe 2+ It stabilizes the phosphating solution system and inhibits the precipitation of free metal ions. Combined with zinc dihydrogen phosphate, it controls the growth rate of phosphate crystal nuclei and refines the grains. Zinc dihydrogen phosphate is the main film-forming substance, providing Zn. 2+ and PO4 3- It reacts with the Fe substrate to form a Zn₂Fe(PO₄)₂·4H₂O phosphating film. Calcium nitrate adjusts the film hardness, and organophosphonic acid stabilizes its dissolution equilibrium. Calcium nitrate provides Ca. 2+ , with PO4 3- The formation of Ca3(PO4)2 enhances the film's hardness and corrosion resistance. It forms a composite phosphate film with zinc dihydrogen phosphate, optimizing the film structure. Sodium m-nitrobenzenesulfonate accelerates anolyte dissolution and promotes Fe... 2+Release. Adsorbed onto active sites on the metal surface, inhibiting localized over-corrosion. Promotes crystal nucleation with rare earth salts, shortening phosphating time. Accelerators (such as enalapril maleate + hydroxylamine sulfate): Enalapril maleate: Multiple active sites (O, N, heterocyclic rings) in its molecular structure adsorb onto the metal surface, forming high-density crystal nuclei. Refines grains and reduces porosity. Hydroxylamine sulfate: Low-temperature oxidation of Fe. 2+ →Fe 3+ This accelerates the phosphating reaction. It provides active sites and promotes crystal nucleus growth. The two work synergistically to optimize crystal nucleus density and oxidation capacity, balancing film formation speed and density. Surfactants reduce solution surface tension, improve wettability, and ensure uniform coverage of the substrate by the phosphating solution. They adsorb at the interface to form a molecular film, inhibiting H2 precipitation and reducing film porosity. Combined with sodium m-nitrobenzenesulfonate, it enhances solution permeability and accelerates film formation. Sodium molybdate forms a molybdate passivation film, filling the micropores of the phosphating film. It forms a composite passivation layer with calcium nitrate and phosphate. Citric acid complexes excess metal ions, preventing precipitation. It adjusts the solution pH and stabilizes the reaction system. It works synergistically with organophosphonic acids to maintain solution stability. Rare earth salts (such as cerium sulfate + lanthanum nitrate), Ce... 3+ La preferentially adsorbs at metal defect sites, inhibiting localized corrosion. 3+ Promote PO4 3- The orderly arrangement and refined grain structure, along with the synergistic effect of rare earth ions, enhance the film density and salt spray resistance. In summary, through the synergistic effect of these multi-component and multi-step processes, this technology achieves efficient and uniform phosphating film formation under low-temperature conditions, significantly improving the salt spray corrosion resistance of the workpiece.

[0007] Preferably, the accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 3:1-3.

[0008] Preferably, the accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 2:1.

[0009] By employing the above technical solution, enalapril maleate molecules contain multiple active sites (such as O, N, heterocyclic rings, and benzene rings), which preferentially adsorb onto metal surfaces, forming high-density adsorption sites that serve as nucleation centers for phosphate crystals. Its macromolecular structure can inhibit excessive grain growth, significantly refine the phosphating film grains (particle size can reach the nanometer scale), thereby reducing porosity and enhancing film density. The benzene rings and heterocyclic structures in the molecule can adsorb onto metal defect sites through π-π stacking or hydrophobic interactions, inhibiting localized electrochemical corrosion. Hydroxylamine sulfate, under low-temperature conditions of 25-35℃, oxidizes Fe by releasing reactive oxygen species (such as ·OH radicals). 2+ →Fe 3+It accelerates the dissolution of the metal matrix and promotes the kinetics of phosphate deposition. The reducing property of hydroxylamine can activate active sites on the metal surface, while its decomposition products (such as NH3) regulate the local pH and promote the uniform distribution of phosphate crystal nuclei. The synergistic mechanism of the two is: 1) Oxidation-adsorption equilibrium: The oxidation of Fe by hydroxylamine sulfate accelerates the dissolution of the metal matrix and promotes the kinetics of phosphate deposition. 2 + Dissolution, while enalapril maleate regulates Fe through adsorption. 3+ / Zn 2+ The distribution at the interface avoids localized over-deposition leading to a porous film. 2) Nucleus-growth synergy: Enalapril maleate provides nuclei (high-density sites), while hydroxylamine sulfate continuously supplies Fe through oxidation. 3+ This allows the crystal nuclei to grow rapidly into a continuous film at low temperatures. 3) Enhanced low-temperature adaptability: The increased proportion of hydroxylamine sulfate enhances the low-temperature oxidation capacity, compensating for the limitation of reaction rate at low temperatures. Enalapril maleate maintains sufficient adsorption site density, ensuring that the grain refinement effect is not interfered with by excessive oxidant. 4) Synergistic defect repair: The adsorption layer of enalapril maleate can capture byproducts (such as NH4) generated by the oxidation of hydroxylamine sulfate. + To prevent film defects caused by its accumulation, while rare earth salts (Ce) 3+ / La 3+ Together with both, it repairs grain boundary micropores. With sodium m-nitrobenzenesulfonate: The oxidizing effect of hydroxylamine sulfate and the depolarizing effect of sodium m-nitrobenzenesulfonate are superimposed, further accelerating the anodic reaction. With rare earth salts: The adsorption layer of enalapril maleate is Ce. 3+ / La 3+ It provides anchoring points, enhancing the segregation effect of rare earth elements at grain boundaries. With surfactants: the promoter adsorption layer and surfactant molecular film form a composite interface structure, synergistically reducing surface tension. In summary, when enalapril maleate and hydroxylamine sulfate are mixed in a 2:1 ratio, a balance between rapid film formation and a highly dense phosphating film is achieved at low temperatures through a triple synergistic mechanism of oxidation-adsorption-nucleation. Simultaneously, it forms a multi-scale synergistic network with other components of the phosphating solution (such as rare earth salts and sodium m-nitrobenzenesulfonate), ultimately endowing the workpiece with excellent salt spray corrosion resistance.

[0010] Preferably, the rare earth salt is composed of cerium sulfate and lanthanum nitrate in a mass ratio of 2:3.

[0011] By adopting the above technical solution, the Ce in cerium sulfate (Ce(SO4)2) is reduced. 4+ CePO4 precipitates preferentially accumulate at defect sites (such as grain boundaries and scratches) in the metal substrate through chemical adsorption, reacting with phosphate to form CePO4 precipitate, which fills the micropores of the phosphating film and inhibits the penetration of corrosive media such as Cl-. 4+ It has strong oxidizing properties in acidic environments and can accelerate the oxidation of Fe. 2+ →Fe 3+ The conversion promotes the forward phosphating reaction. Ce4+ Adsorbed at phosphate grain boundaries, it lowers grain boundary energy, inhibits abnormal grain growth, and improves film continuity. Lanthanum nitrate (La(NO3)3) contains La... 3+ With PO4 3 - The combination of LaPO4 microcrystals and their formation serves as a heterogeneous nucleation substrate, significantly increasing the nucleus density. 3+ By controlling the preferred orientation of Zn2Fe(PO4)2 crystals through electrostatic interaction, the film exhibits a dominant growth of the (002) crystal plane (which offers superior corrosion resistance). 3+ It can compensate for cation vacancies in the phosphating film, reduce the electronic conductivity of the film, and inhibit electrochemical corrosion. With organophosphonic acid (EDTMP): Ce 4+ / La 3+ It forms a complex with EDTMP, enabling the directional release of rare earth ions at the solution / metal interface, thus achieving precise nucleation control. It also interacts with sodium molybdate (Ce). 4+ With MoO4 2- A Ce2(MoO4)3 composite passivation layer is generated, filling the micropores of the phosphating film and synergistically improving pitting corrosion resistance. With accelerator: La 3+ Coordination with the carboxyl group of enalapril maleate enhances its adsorption stability on metal surfaces and increases crystal nucleation density. In summary, when cerium sulfate and lanthanum nitrate are combined in a 2:3 mass ratio, a triple synergistic mechanism of defect repair, crystal nucleation induction, and electronic regulation is employed to control the crystal structure of the phosphating film at the nanoscale, while simultaneously optimizing film formation kinetics through redox dynamic equilibrium. This rare-earth synergistic effect endows the phosphating film with high density, strong adhesion, and ultra-long salt spray resistance.

[0012] Preferably, the surfactant is composed of isotridecyl polyoxyethylene ether and sodium lauryl ether sulfate in a mass ratio of 3:1-2.

[0013] By employing the above technical solution, isomeric tridecyl alcohol polyoxyethylene ether (a nonionic surfactant), with its long-chain alkyl (C13 isomer) and polyoxyethylene ether (EO chain) structure, possesses amphiphilic properties, which can significantly reduce the surface tension of the solution, allowing the phosphating solution to spread rapidly and penetrate into the micropores of the metal surface. The ether bond (-O-) and hydroxyl group (-OH) are adsorbed onto the metal surface through hydrogen bonding, forming a molecular film approximately 2-3 nm thick, inhibiting the hydrogen evolution reaction and reducing the porosity of the phosphating film. The adsorption layer restricts the excessive growth of phosphate grains, refines the grain size, and improves the film density. Sodium lauryl ether sulfate, sulfonate (-SO3) - The negative charge imparts a static charge, preventing particle aggregation in the phosphating solution through electrostatic repulsion and maintaining solution stability. The long-chain alkyl group (C12) works synergistically with the polyether structure to emulsify and disperse oil and reaction byproducts into the liquid phase, preventing impurities from being trapped in the film. The negative charge interacts with the metal surface (positively charged Fe). 2+ / Zn 2+The region generates electrostatic attraction, enhancing the selective adsorption of surfactants at active sites. Synergistic mechanism: (1) Interfacial adsorption layer reconstruction: isomeric tridecyl alcohol polyoxyethylene ether preferentially adsorbs to form a dense molecular film, while sodium lauryl ether sulfate fills the gaps between the film layers through electrostatic interaction, forming a composite adsorption layer with uniform thickness and charge balance. The combination of the two reduces the contact angle, achieves a superhydrophilic surface state, and improves the penetration rate of phosphating solution. (2) Synergistic inhibition of porosity: the hydrogen bond network of isomeric tridecyl alcohol polyoxyethylene ether hinders H + The migration of sodium lauryl ether sulfate, due to its negative charge, repels H+. + The two components work synergistically to reduce the hydrogen evolution rate and porosity. In summary, when isomeric tridecyl alcohol polyoxyethylene ether and sodium lauryl ether sulfate are compounded in a 3:1-2 ratio, an ultra-low porosity phosphating film structure is constructed through a multi-level synergistic mechanism of wetting-electrostatic-adsorption. The nonionic component dominates the regulation of interfacial wetting and crystal growth, while the anionic component enhances emulsification, dispersion, and charge stabilization. The optimized ratio of the two components achieves dynamic adsorption equilibrium, giving the phosphating film excellent corrosion resistance, strong adhesion, and process adaptability (low-temperature stability).

[0014] Preferably, the organophosphonic acid is ethylenediaminetetramethylenephosphonic acid.

[0015] Preferably, the phosphating process conditions are: phosphating temperature 25-35℃, phosphating time 10-15 minutes.

[0016] Preferably, the ultrasonic degreasing process conditions are as follows: the workpiece to be treated is placed in the degreasing solution for ultrasonic treatment for 4-6 minutes, the degreasing temperature is 50-60℃, and the degreasing solution is made from the following raw materials: sodium hydroxide 30-50g / L, sodium carbonate 40-60g / L, trisodium phosphate 40-70g / L, sodium lauryl ether sulfate 0.5-0.8g / L, and water is the solvent.

[0017] Preferably, the activation process conditions are: the activation solution is a sulfuric acid solution of 10-20 g / L, the activation temperature is 20-30℃, and the activation time is 0.5-1 minute.

[0018] Preferably, the ultrasonic hot water washing process conditions are: temperature 50-60℃, time 1-3min, and ultrasonic power 2-3KW; the drying process conditions are: baking temperature 85-100℃, and time 20-25min.

[0019] In summary, the beneficial technical effects of this application are as follows: 1. Advantages of the process flow Simplified and efficient: Through the standardized process design of ultrasonic degreasing → activation → impregnation phosphating, the process is simplified and compatible with automation, improving efficiency by more than 30% compared with traditional phosphating processes.

[0020] Low temperature and energy saving: The phosphating reaction temperature is controlled at 25-35℃, eliminating the need for high-temperature equipment, reducing energy consumption, and avoiding the problem of loose film caused by high temperature.

[0021] High versatility: Applicable to a variety of materials such as iron, zinc alloy, and stainless steel; the process parameters are widely adaptable, and there is no need to adjust the formula for different substrates.

[0022] 2. Breakthrough in phosphating film performance Superior corrosion resistance: Neutral salt spray test (ASTM B117) time > 120 hours, copper sulfate drop corrosion resistance time > 30 minutes.

[0023] Excellent adhesion: Rating 0.

[0024] 3. Component Synergistic Innovation Rare earth-accelerator synergy: Cerium sulfate / lanthanum nitrate (2:3) and enalapril maleate / hydroxylamine sulfate (3:1-3) form a "nucleus-induced-oxidation-enhanced" dual engine to improve nucleus density, film formation speed and corrosion resistance.

[0025] Surfactant enhancement: A superwetting composite adsorption layer was constructed by isomeric tridecyl alcohol polyoxyethylene ether and sodium lauryl ether sulfate (3:1-2), which reduced the hydrogen evolution rate and porosity.

[0026] Global passivation network: Sodium molybdate (MoO4) 2- ) and rare earth salts (Ce 3+ / La 3+ The Ce2(MoO4)3-LaPO4 composite passivation phase is generated to fill grain boundary defects and improve corrosion resistance. Detailed Implementation

[0027] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0028] In the following embodiments, the workpieces to be processed are cold-rolled steel sheets processed on a fully automated line.

[0029] Example 1 A method for phosphating a workpiece surface with high resistance to salt spray corrosion includes the following steps: ultrasonic degreasing → water washing → water washing → water washing → activation → immersion phosphating → water washing → water washing → ultrasonic hot water washing → drying. The immersion phosphating refers to immersing the activated workpiece in a phosphating solution for phosphating treatment. The phosphating solution comprises the following components: 5 g / L ethylenediaminetetramethylenephosphonic acid, 30 g / L zinc dihydrogen phosphate, 50 g / L calcium nitrate, 2 g / L sodium m-nitrobenzenesulfonate, 1 g / L accelerator, 0.5 g / L surfactant, 1 g / L sodium molybdate, 2 g / L citric acid, and 0.2 g / L rare earth salt. The accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 3:1. The rare earth salt is composed of cerium sulfate and lanthanum nitrate in a mass ratio of 2:3. The surfactant is isomeric tridecyl alcohol polyoxyethylene ether. The composition is based on sodium lauryl ether sulfate in a mass ratio of 3:1. The phosphating process conditions are: phosphating temperature 35℃, phosphating time 10 minutes; the ultrasonic degreasing process conditions are: immersing the workpiece in the degreasing solution for ultrasonic treatment for 4 minutes, degreasing temperature 60℃, the degreasing solution being made from the following raw materials: sodium hydroxide 30g / L, sodium carbonate 40g / L, trisodium phosphate 40g / L, sodium lauryl ether sulfate 0.5g / L, solvent being water; the activation process conditions are: activation solution is 10g / L sulfuric acid solution, activation temperature 20℃, activation time 0.5 minutes; the ultrasonic hot water washing process conditions are: temperature 50℃, time 1min, ultrasonic power 2KW; the drying process conditions are: baking temperature 85℃, time 25min.

[0030] Example 2 A method for phosphating a workpiece surface with high resistance to salt spray corrosion includes the following steps: ultrasonic degreasing → water washing → water washing → water washing → activation → immersion phosphating → water washing → water washing → ultrasonic hot water washing → drying. The immersion phosphating refers to immersing the activated workpiece in a phosphating solution for phosphating treatment. The phosphating solution comprises the following components: ethylenediaminetetramethylenephosphonic acid 8 g / L, zinc dihydrogen phosphate 40 g / L, calcium nitrate 55 g / L, sodium m-nitrobenzenesulfonate 4 g / L, accelerator 2 g / L, surfactant 0.8 g / L, sodium molybdate 3 g / L, citric acid 4 g / L, and rare earth salt 0.44 g / L. The accelerator is composed of enalapril maleate and hydroxylamine sulfate in a 3:3 mass ratio. The rare earth salt is composed of cerium sulfate and lanthanum nitrate in a 2:3 mass ratio. The surfactant is isomeric tridecyl alcohol polyoxyethylene. The ether and sodium lauryl ether sulfate are composed in a mass ratio of 3:2. The phosphating process conditions are: phosphating temperature 25℃, phosphating time 15 minutes; the ultrasonic degreasing process conditions are: the workpiece to be treated is immersed in the degreasing solution for ultrasonic treatment for 6 minutes, the degreasing temperature is 60℃, the degreasing solution is made from the following raw materials: sodium hydroxide 50g / L, sodium carbonate 60g / L, trisodium phosphate 70g / L, sodium lauryl ether sulfate 0.8g / L, and water is the solvent; the activation process conditions are: the activation solution is a 20g / L sulfuric acid solution, the activation temperature is 30℃, and the activation time is 1 minute; the ultrasonic hot water washing process conditions are: temperature 60℃, time 3 minutes, ultrasonic power 3KW; the drying process conditions are: baking temperature 100℃, time 20 minutes.

[0031] Example 3 A method for phosphating a workpiece surface with high resistance to salt spray corrosion includes the following steps: ultrasonic degreasing → water washing → water washing → water washing → activation → immersion phosphating → water washing → water washing → ultrasonic hot water washing → drying. The immersion phosphating refers to immersing the activated workpiece in a phosphating solution for phosphating treatment. The phosphating solution comprises the following components: ethylenediaminetetramethylenephosphonic acid 7 g / L, zinc dihydrogen phosphate 33 g / L, calcium nitrate 52 g / L, sodium m-nitrobenzenesulfonate 3 g / L, accelerator 1.5 g / L, surfactant 0.7 g / L, sodium molybdate 2 g / L, citric acid 3 g / L, and rare earth salt 0.3 g / L. The accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 3:2. The rare earth salt is composed of cerium sulfate and lanthanum nitrate in a mass ratio of 2:3. The surfactant is composed of isotridecyl alcohol polyoxyethylene ether and... Sodium lauryl ether sulfate is composed of sodium lauryl ether sulfate in a mass ratio of 3:1.5. The phosphating process conditions are: phosphating temperature 28℃, phosphating time 13 minutes; the ultrasonic degreasing process conditions are: the workpiece to be treated is immersed in the degreasing solution for ultrasonic treatment for 5 minutes, the degreasing temperature is 55℃, the degreasing solution is made of the following raw materials: sodium hydroxide 40g / L, sodium carbonate 50g / L, trisodium phosphate 50g / L, sodium lauryl ether sulfate 0.7g / L, and water is the solvent; the activation process conditions are: the activation solution is a 15g / L sulfuric acid solution, the activation temperature is 25℃, and the activation time is 0.7 minutes; the ultrasonic hot water washing process conditions are: temperature 55℃, time 2 minutes, ultrasonic power 2.3KW; the drying process conditions are: baking temperature 95℃, time 23 minutes.

[0032] Example 4 Similar to Example 3, except that the accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 2:1.

[0033] Comparative Example 1 Same as Example 4, except that the promoter is enalapril maleate.

[0034] Comparative Example 2 Same as Example 4, except that the promoter is hydroxylamine sulfate.

[0035] Comparative Example 3 Same as Example 4, except that the rare earth salt is cerium sulfate.

[0036] Comparative Example 4 Same as Example 4, except that the rare earth salt is lanthanum nitrate.

[0037] Comparative Example 5 Same as Example 4, except that the surfactant is isomeric tridecyl alcohol polyoxyethylene ether.

[0038] Comparative Example 6 Same as Example 4, except that the surfactant is sodium lauryl ether sulfate.

[0039] Performance testing The phosphated cold-rolled steel sheet workpieces obtained in Examples 1 and 4 and Comparative Examples 1-6 were subjected to the following performance tests, and the test results are shown in Table 1.

[0040] 1. Phosphate film adhesion test Using a single-edged tool at a 30° angle or a multi-edged tool with 6 blades (1mm spacing), make 6 scratches every 1mm in both the horizontal and vertical directions on the surface of the phosphating film. The scratches should cut through the entire depth of the phosphating film. Then, gently touch the surface with your finger to check whether the phosphating film has peeled off. There are a total of 6 levels.

[0041] Grade 0: The phosphating film is intact, with no squares peeling off; Grade 1: Phosphating film peeling off at the cut intersections is no more than 5%; Grade 2: Phosphating film peeling off is between 5% and 15%; Grade 3: Large areas of phosphating film peeling off, no more than 35%; Grade 4: Large areas of phosphating film peeling off, no more than 65%; Grade 5: Large areas of phosphating film peeling off, more than 65%.

[0042] 2. The copper sulfate drop corrosion resistance test shall be conducted in accordance with the test method of HB5063-1996 "Quality Inspection of Phosphate Coating Layer of Steel Parts".

[0043] 3. The neutral salt spray test shall be conducted in accordance with the test method of GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test (NSS Test)".

[0044] Table 1 Performance Tests project neutral salt spray / h Copper sulfate drop corrosion resistance test / min bonding force Example 1 124 31.5 Level 0 Example 2 128 33.2 Level 0 Example 3 130 35.1 Level 0 Example 4 138 38.6 Level 0 Comparative Example 1 112 27.6 Level 0 Comparative Example 2 104 24.3 Level 0 Comparative Example 3 120 30.8 Level 0 Comparative Example 4 124 31.6 Level 0 Comparative Example 5 128 36.4 Level 1 Comparative Example 6 130 37.1 Level 1 Analyzing the data in Table 1, we can see that: 1) The phosphated films of the cold-rolled steel sheet workpieces obtained in Examples 1-4 have excellent corrosion resistance and adhesion.

[0045] 2) The performance comparison analysis of the phosphate film of the phosphated cold-rolled steel sheet workpieces obtained in Example 4 and Example 3 shows that the phosphate film with the best corrosion resistance is obtained when the accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 2:1.

[0046] 3) The performance comparison analysis of the phosphate film of the phosphated cold-rolled steel sheet workpieces obtained in Example 4 and Comparative Examples 1-2 shows that the accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 2:1. Through the triple synergistic mechanism of oxidation-adsorption-nucleation, it achieves a balance between rapid film formation and high density phosphate film at low temperature. At the same time, it forms a multi-scale synergistic network with other components of the phosphate solution (such as rare earth salts and sodium m-nitrobenzenesulfonate), ultimately endowing the workpiece with excellent salt spray corrosion resistance.

[0047] 4) A comparative analysis of the performance of the phosphated films on cold-rolled steel sheet workpieces obtained in Example 4 and Comparative Examples 3-4 shows that the rare earth salt, composed of cerium sulfate and lanthanum nitrate in a mass ratio of 2:3, regulates the crystal structure of the phosphated film at the nanoscale through a triple synergistic mechanism of defect repair, nucleation induction, and electronic regulation, while simultaneously optimizing the film formation kinetics through redox dynamic equilibrium. This rare earth synergistic effect endows the phosphated film with high density, strong adhesion, and ultra-long salt spray resistance.

[0048] 5) Comparative analysis of the performance of the phosphate films on cold-rolled steel sheet workpieces obtained in Example 4 and Comparative Examples 5-6 shows that the surfactant, composed of isomeric tridecyl alcohol polyoxyethylene ether and sodium lauryl ether sulfate in a mass ratio of 3:1.5, constructs an ultra-low porosity phosphate film structure through a multi-level synergistic mechanism of wetting, electrostatics, and adsorption. The nonionic component dominates the regulation of interfacial wetting and crystal growth, while the anionic component enhances emulsification, dispersion, and charge stabilization. The optimized ratio of the two achieves dynamic adsorption equilibrium, giving the phosphate film both excellent corrosion resistance and adhesion.

[0049] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this invention. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A method for phosphating a surface of a workpiece that is highly resistant to salt spray corrosion, characterized in that, The process includes the following steps: ultrasonic degreasing → water washing → water washing → water washing → activation → immersion phosphating → water washing → water washing → ultrasonic hot water washing → drying. The immersion phosphating refers to immersing the activated workpiece in a phosphating solution for phosphating treatment. The phosphating solution comprises the following components: organophosphonic acid 5-8 g / L, zinc dihydrogen phosphate 30-40 g / L, calcium nitrate 50-55 g / L, sodium m-nitrobenzenesulfonate 2-4 g / L, accelerator 1-2 g / L, surfactant 0.5-0.8 g / L, sodium molybdate 1-3 g / L, citric acid 2-4 g / L, and rare earth salt 0.2-0.44 g / L.

2. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 3:1-3.

3. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 2, characterized in that, The accelerator is composed of enalapril maleate and hydroxylamine sulfate in a mass ratio of 2:

1.

4. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The rare earth salt is composed of cerium sulfate and lanthanum nitrate in a mass ratio of 2:

3.

5. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The surfactant is composed of isotridecyl polyoxyethylene ether and sodium lauryl ether sulfate in a mass ratio of 3:1-2.

6. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The organophosphonic acid is ethylenediaminetetramethylenephosphonic acid.

7. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The phosphating process conditions are: phosphating temperature 25-35℃, phosphating time 10-15 minutes.

8. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The ultrasonic degreasing process conditions are as follows: the workpiece to be treated is placed in the degreasing solution for ultrasonic treatment for 4-6 minutes, the degreasing temperature is 50-60℃, and the degreasing solution is made from the following raw materials: sodium hydroxide 30-50g / L, sodium carbonate 40-60g / L, trisodium phosphate 40-70g / L, sodium lauryl ether sulfate 0.5-0.8g / L, and water is the solvent.

9. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The activation process conditions are as follows: the activation solution is a sulfuric acid solution of 10-20 g / L, the activation temperature is 20-30℃, and the activation time is 0.5-1 minute.

10. The method for phosphating the surface of a workpiece with high resistance to salt spray corrosion according to claim 1, characterized in that, The ultrasonic hot water washing process conditions are: temperature 50-60℃, time 1-3min, ultrasonic power 2-3KW; the drying process conditions are: baking temperature 85-100℃, time 20-25min.