A chromium-free passivation and fingerprint-resistant composite treatment method for high-aluminum zinc-aluminum-magnesium steel plate

Abstract

This invention discloses a chromium-free passivation and fingerprint-resistant composite treatment method for high-aluminum-zinc-aluminum-magnesium steel plates, belonging to the field of metal sheet surface protection technology. The specific steps of the method are as follows: A fine-grained high-aluminum-zinc-aluminum-magnesium steel plate is selected as the substrate, and firstly, it undergoes multi-stage cleaning and hot air drying. Next, the dried substrate is immersed in a composite chromium-free passivation solution to form a passivation precursor film. Then, a porous inorganic passivation layer is prepared through low-temperature hot air curing. Subsequently, a modified fingerprint-resistant resin is roller-coated onto its surface to form an organic precursor film. Finally, a constant-temperature curing treatment is performed to produce a chromium-free passivation and fingerprint-resistant composite film. This invention uses multi-stage cleaning and chromium-free passivation processes on the high-aluminum-zinc-aluminum-magnesium steel plate to form a porous inorganic passivation layer, enhancing corrosion resistance. Then, a composite protective film layer is constructed by reverse roller coating of modified fingerprint-resistant resin, achieving functional integration. This process improves the environmental protection and protective properties of the plate, meets the needs of multiple fields, and expands the application scenarios and market scope.

Description

Technical Field

[0001] This invention relates to the field of surface protection treatment technology for metal sheets, specifically a chromium-free passivation and fingerprint-resistant composite treatment method for high-aluminum zinc-aluminum-magnesium steel sheets. Background Technology

[0002] High-alumina-zinc-alumina-magnesium steel sheets, with their excellent corrosion resistance, mechanical strength, and forming and processing characteristics, have become core application materials in industrial fields such as construction, home appliances, and automobiles. Their surface protection treatment directly determines the service life and application effect of the sheets. With the continuous tightening of environmental protection policies and the continuous improvement of market product quality requirements, the surface treatment of metal sheets is gradually developing towards chromium-free and functional composite directions. Traditional chromium-containing passivation processes are no longer suitable for green production standards due to the risk of heavy metal pollution. The widespread application of fine-grained high-alumina-zinc-alumina-magnesium substrates places higher demands on the adaptability of surface treatment processes, film bonding strength, and functional integration. The industry urgently needs surface composite treatment technologies that combine environmental protection attributes, high-efficiency protection, and practical functions to solve the industry pain point of the mismatch between current surface treatment processes and high-end sheet applications, and meet the actual needs of industrial continuous production.

[0003] Traditional surface treatment processes for high-aluminum-zinc-aluminum-magnesium steel sheets have many intractable drawbacks. Most processes still use chromium-containing passivation, which generates heavy metal pollution during production and use, violating environmental protection production and application standards. Single passivation or fingerprint-resistant treatments cannot simultaneously achieve the dual functions of corrosion prevention and fingerprint resistance, making it difficult to meet the needs of high-end application scenarios. Traditional cleaning processes are imperfect, and impurities and oil stains on the substrate surface are not thoroughly removed, directly reducing the adhesion of subsequent film layers and easily causing quality problems such as film layer delamination and peeling. Unreasonable curing process parameters can lead to uneven surface film structure, significantly reducing protective and wear-resistant properties. Film layer damage is prone to occur during processing, transportation, and use, making it impossible to guarantee the long-term protective effect of the substrate. At the same time, traditional processes have poor compatibility with continuous production lines, resulting in insufficient product quality stability, which seriously restricts the expansion of the application range of high-aluminum-zinc-aluminum-magnesium steel sheets. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a chromium-free passivation and fingerprint-resistant composite treatment method for high-aluminum-zinc-aluminum-magnesium steel sheets. Through a complete process of multi-stage cleaning and drying, chromium-free passivation dip coating and low-temperature curing, and modified fingerprint-resistant resin roller coating and constant-temperature curing, a stable inorganic-organic composite protective film is formed on the substrate surface. This method uses a chromium-free passivation system, abandoning traditional chromium-containing processes, making the entire process green and environmentally friendly. The porous inorganic passivation layer significantly improves the film's adhesion, preventing delamination and peeling. The composite film possesses multiple properties such as long-lasting corrosion resistance, fingerprint resistance, stain resistance, and wear resistance, making it suitable for continuous industrial production. The finished product quality is stable and reliable. This invention effectively solves the environmental defects and performance shortcomings of traditional surface treatments, significantly improves the overall quality of the sheet material, broadens the application range of high-aluminum-zinc-aluminum-magnesium steel sheets, and provides an efficient and feasible technical solution for the green and functional surface treatment of metal sheets.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a chromium-free passivation fingerprint-resistant composite treatment method for high-aluminum zinc-aluminum-magnesium steel plates, the specific steps of which are as follows: S1, Select fine-grained high-alumina-zinc-alumina-magnesium steel plate as the substrate, perform multi-stage cleaning operations on the surface of the substrate, and perform hot air drying treatment on the substrate after cleaning. S2, the dried substrate is immersed in a composite chromium-free passivation solution to perform a dip coating operation, and a passivation precursor film is prepared on the surface of the substrate; S3, a porous inorganic passivation layer is prepared by performing low-temperature hot air curing on a substrate with a passivation precursor film attached to its surface. S4, a roller coating operation is performed on the surface of the porous inorganic passivation layer to coat the modified fingerprint-resistant resin and prepare an organic fingerprint-resistant precursor film. S5, a constant temperature curing treatment is performed on the substrate with an organic fingerprint-resistant precursor film attached to its surface to prepare a chromium-free passivated fingerprint-resistant composite film.

[0006] Further, in step S1, the alloy composition of the fine-grained high-alumina-zinc-aluminum-magnesium steel plate comprises 53% aluminum, 43.4% zinc, 1.6% silicon, and 2% magnesium, and the coating weight of the steel plate is controlled at 150 g / m². 2 Up to 200g / m 2 Between these processes, the steel plate substrate is either DX53D or DX54D. The steel plate is formed by pre-melting pot constant temperature liquid supply and air knife coating. After coating, solidification is completed by large air box cooling and variable diameter pressurized air outlet.

[0007] Furthermore, in step S1, the multi-stage cleaning operation adopts a nine-stage progressive cleaning process, which consists of alkaline rinsing, alkaline brushing, electrolytic cleaning, secondary alkaline brushing, secondary electrolytic cleaning, tertiary alkaline brushing, water brushing, primary water rinsing, and secondary water rinsing. The temperature throughout the nine-stage progressive cleaning process is controlled between 50°C and 60°C.

[0008] Furthermore, in step S1, the nine-stage progressive cleaning process includes two sets of electrolytic cleaning devices, and the current density of the electrolytic cleaning devices is controlled at 9A / dm³. 2 Up to 11A / dm 2 Between; the nine-stage progressive cleaning process is also equipped with three sets of magnetic filtration devices, the magnetic field strength of which is controlled between 1700Gs and 1900Gs.

[0009] Furthermore, in step S1, the temperature of the hot air drying process is controlled between 70°C and 80°C.

[0010] Furthermore, in step S2, the composite chromium-free passivation solution is a titanium zirconium-silicate-molybdate composite system, the pH value of the composite chromium-free passivation solution is controlled between 3.6 and 4.0, the temperature of the dip coating operation is controlled between 28°C and 32°C, and the duration of the dip coating operation is controlled between 18s and 22s.

[0011] Furthermore, in step S2, the composite chromium-free passivation solution comprises ammonium fluorotitanate, ammonium fluorozirconate, tetraethyl orthosilicate, sodium molybdate, and sodium nitrate. The concentration of ammonium fluorotitanate is controlled between 8 g / L and 12 g / L, the concentration of ammonium fluorozirconate is controlled between 6 g / L and 10 g / L, the concentration of tetraethyl orthosilicate is controlled between 3 g / L and 5 g / L, the concentration of sodium molybdate is controlled between 2 g / L and 4 g / L, and the concentration of sodium nitrate is controlled between 1 g / L and 3 g / L.

[0012] Furthermore, in step S3, the temperature of the low-temperature hot air curing treatment is controlled between 85°C and 95°C, the hot air velocity is controlled between 3m / s and 5m / s, the curing time is controlled between 10s and 15s, the thickness of the porous inorganic passivation layer is controlled between 0.3μm and 0.5μm, and the porosity of the porous inorganic passivation layer is controlled between 15% and 20%.

[0013] Furthermore, in step S4, the modified fingerprint-resistant resin is a nano-SiO2-aminosilane modified waterborne polyurethane-fluorocarbon blend resin. The roll coating operation adopts a reverse roll coating method, the ratio of the coating roller speed to the steel plate running speed is controlled between 1.07 and 1.09, and the wet film thickness of the roll coating operation is controlled between 1.4μm and 1.6μm.

[0014] Furthermore, in step S5, the temperature of the isothermal curing process is controlled between 108°C and 112°C, the curing time is controlled between 22s and 24s, the total thickness of the chromium-free passivation fingerprint-resistant composite film is controlled between 1.0μm and 1.6μm, the thickness of the porous inorganic passivation layer in the composite film is controlled between 0.3μm and 0.5μm, and the thickness of the organic fingerprint-resistant layer is controlled between 0.7μm and 1.1μm.

[0015] Compared with existing technologies, the chromium-free passivation fingerprint-resistant composite treatment method for high-aluminum zinc-aluminum-magnesium steel plates has the following advantages: I. This invention thoroughly removes impurities and oil stains from the surface of high-aluminum-zinc-aluminum-magnesium steel plates through multi-stage progressive cleaning and precise hot air drying, creating a clean base for film adhesion. It employs a chromium-free composite passivation system to replace traditional chromium-containing treatment processes, avoiding the risk of heavy metal pollution at the source. This aligns with green production and environmentally friendly application standards. The dip-coating process, combined with low-temperature hot air curing, forms a uniformly structured porous inorganic passivation layer on the substrate surface. This porous structure significantly enhances the bonding strength with subsequent organic layers, preventing film delamination, peeling, and detachment, and improving the overall stability of the film. This passivation layer effectively blocks external moisture and corrosive media from contacting the substrate, greatly enhancing the corrosion resistance of the plate and extending its service life. The entire process is compatible with continuous production, with precise control at each stage, eliminating uneven surface treatment defects, ensuring stable finished product quality, and simultaneously improving the environmental friendliness, protective properties, and production adaptability of the plate.

[0016] II. This invention utilizes a reverse roller coating process to apply modified fingerprint-resistant resin to the surface of a porous inorganic passivation layer, combined with constant temperature curing, to construct a composite protective film layer that integrates inorganic and organic functions. This achieves a unified passivation protection and fingerprint resistance function. The modified resin layer and the porous inorganic layer form a tightly interlocked structure, significantly improving the film layer's wear resistance and impact resistance, and making it resistant to physical losses during subsequent processing and transportation. The composite film layer combines the long-lasting anti-corrosion advantages of the inorganic layer with the fingerprint resistance and easy-to-clean properties of the organic layer, preventing fingerprint residue from affecting the appearance during use. It also enhances the board's stain resistance. Combined with the excellent material properties of the high-aluminum-zinc-aluminum-magnesium substrate, the overall performance of the board is comprehensively optimized, meeting the environmental protection, durability, and aesthetic requirements of various fields, effectively expanding the application scenarios and market adaptability of the board.

[0017] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0019] Figure 1 A flowchart of a chromium-free passivation fingerprint-resistant composite treatment method for high-aluminum zinc-aluminum-magnesium steel plates; Figure 2 Schematic diagram of the surface microstructure of high-aluminum zinc-aluminum-magnesium coating; A—aluminum-rich phase; B—zinc-rich interdendritic phase; C—MgZn2; D—Mg2Si; Figure 3 Schematic diagram of corrosion product morphology at the cut edge of aluminum-zinc coating and zinc-aluminum-magnesium coating after cyclic corrosion test; (a) Morphology of corrosion products of aluminum-zinc coating (b) Morphology of corrosion products of zinc-aluminum-magnesium coating; Figure 4 The diagram shows the microscopic corrosion morphology of aluminum-zinc and zinc-aluminum-magnesium coatings after cyclic corrosion tests; a: aluminum-zinc coating 4 cycles; b: aluminum-zinc coating 30 cycles; c: zinc-aluminum-magnesium coating 30 cycles; d: zinc-aluminum-magnesium coating 150 cycles. Detailed Implementation

[0020] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below. Example 1:

[0021] Chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum-zinc-aluminum-magnesium steel sheets, the specific steps are as follows: Figure 1 As shown.

[0022] Fine-grained high-alumina-zinc-alumina-magnesium steel sheet was selected as the substrate. The alloy composition of the substrate included 53% aluminum, 43.4% zinc, 1.6% silicon, and 2% magnesium. The coating weight of the steel sheet was controlled at 150 g / m². 2 The plating solution is supplied using a pre-melting pot with constant temperature, and the coating is prepared using an air knife coating process. After plating, a large air box is used for cooling and variable-diameter pressurized air outlet to solidify the coating, ensuring that the substrate coating is uniform and dense. Figure 2 As shown.

[0023] The substrate surface is subjected to a multi-stage cleaning process using a nine-stage progressive cleaning procedure. This process involves continuous operation in the following order: alkaline rinsing, alkaline brushing, electrolytic cleaning, secondary alkaline brushing, secondary electrolytic cleaning, tertiary alkaline brushing, water brushing, primary water rinsing, and secondary water rinsing. The cleaning temperature is maintained at 50℃ throughout the process. Two sets of electrolytic cleaning devices are operated during the cleaning process, with the current density stably controlled at 8A / dm³. 2 The electrolysis generates bubbles to peel off iron powder and oil stains from the substrate surface. At the same time, three sets of magnetic filtration devices are turned on to stabilize the magnetic field strength at 1500Gs and adsorb the iron powder impurities that fall off during the cleaning process.

[0024] Immediately after cleaning, the substrate is dried with hot air at a temperature of 70°C until there is no moisture residue on the surface of the substrate. The surface remains dry and clean, providing stable surface conditions for subsequent passivation treatment.

[0025] The dried substrate was uniformly immersed in a composite chromium-free passivation solution to complete the dip-coating operation. The composite chromium-free passivation solution adopted a titanium zirconium-silicate-molybdate composite system. The pH value of the passivation solution was adjusted to 3.5. The temperature was maintained at 25℃ during the dip-coating process, and the dip-coating was carried out continuously for 15 seconds to allow the passivation solution to fully react with the substrate surface and form a uniform and continuous passivation precursor film on the substrate surface. The composite chromium-free passivation solution was prepared with deionized water, with the following concentrations: ammonium fluorotitanate concentration 8 g / L, ammonium fluorozirconate concentration 6 g / L, tetraethyl orthosilicate concentration 3 g / L, sodium molybdate concentration 2 g / L, and sodium nitrate concentration 1 g / L. After preparation, the solution was stirred evenly and allowed to stand for 30 minutes before use.

[0026] The substrate with the passivation precursor film attached to its surface is subjected to low-temperature hot air curing treatment. The curing temperature is controlled at 85℃, the hot air velocity is kept stable at 3m / s, and the curing is continued for 10s, so that the passivation precursor film is rapidly formed to form a porous inorganic passivation layer with a thickness of 0.3μm, a porosity of 15%, and uniform pore distribution and good connectivity.

[0027] A roller coating operation is performed on the surface of the porous inorganic passivation layer using a reverse roller coating method. The ratio of the coating roller speed to the running speed of the steel plate is adjusted to 1.05. Nano-silica-aminosilane modified waterborne polyurethane-fluorocarbon blend resin is coated, and the wet film thickness of the roller coating is controlled to be 1.2μm, so that the resin is evenly covered on the surface of the porous inorganic passivation layer to form a complete organic fingerprint-resistant precursor film.

[0028] The substrate with the organic fingerprint-resistant precursor film attached to its surface is subjected to constant temperature curing treatment. The curing temperature is controlled at 105℃ and the curing is continued for 20 seconds to allow the modified fingerprint-resistant resin to be completely cross-linked and cured. Finally, a chromium-free passivated fingerprint-resistant composite film is formed on the surface of the substrate. The total thickness of the composite film is 1.0μm, of which the thickness of the porous inorganic passivation layer is 0.3μm and the thickness of the organic fingerprint-resistant layer is 0.7μm. The two film layers are tightly bonded without delamination. Example 2:

[0029] Structural characterization and basic performance testing of chromium-free passivated fingerprint-resistant composite film.

[0030] The surface and cross-sectional morphology of the chromium-free passivation fingerprint-resistant composite film were observed using a scanning electron microscope. Before observation, the sample was sputtered with gold, and the accelerating voltage was set to 15kV. The observation results showed that the surface of the composite film was smooth and flat, without defects such as pinholes, cracks, exposed substrate, and pitting. The cross-sectional structure was clear, the pores inside the porous inorganic passivation layer were evenly distributed, the organic fingerprint-resistant layer completely covered the inorganic passivation layer, and there were no gaps or peeling between the two layers, indicating a good interface bonding state.

[0031] The elemental distribution of the composite membrane was detected using an energy dispersive spectroscopy (EDS) analyzer, with the detection area covering the entire composite membrane layer. The results showed that titanium, zirconium, silicon, molybdenum, aluminum, zinc, and magnesium were uniformly distributed in the composite membrane. There was no local aggregation or segregation of any element in the membrane layer. The elemental distribution was completely consistent with the elemental composition of the titanium zirconium-silicate-molybdate composite passivation system and the modified fingerprint-resistant resin.

[0032] The composite film thickness was measured at multiple points using a magnetic film thickness gauge. Ten measurement points were selected on the sample surface, and the arithmetic mean was taken. The total thickness of the composite film was stable at 1.0 μm, the thickness of the porous inorganic passivation layer was stable at 0.3 μm, and the thickness of the organic fingerprint-resistant layer was stable at 0.7 μm. The thickness deviation at each measurement point did not exceed 0.05 μm, indicating excellent film thickness uniformity.

[0033] The porosity of the porous inorganic passivation layer was determined by mercury intrusion porosimetry. The sample was vacuum dried before testing. The results showed that the porosity of the porous inorganic passivation layer was 15%, and the pore size was concentrated between 50 nm and 100 nm. The pore size distribution was uniform, providing sufficient binding sites for the wetting and penetration of organic fingerprint-resistant resin.

[0034] The adhesion between the composite film and the substrate was tested using the cross-cut test. A 1mm × 1mm grid was drawn on the surface of the film using a cross-cut tester. There was no corner chipping or peeling throughout the process. After the adhesive tape was quickly peeled off, the film layer did not peel off, and the adhesion performance reached the optimal level.

[0035] The flexibility of the composite film was tested by a 180-degree bending test. After bending, the film layer was observed with a magnifying glass. The composite film showed no cracking, no peeling, and no blackening or discoloration. The film layer and the substrate deformed synchronously, and the flexibility fully met the requirements for subsequent processing and use.

[0036] The fingerprint resistance performance was tested by manually pressing the film surface. After pressing the film surface evenly with a finger and letting it stand for 1 minute, it was wiped off. There was no obvious fingerprint residue on the surface, and the appearance maintained the original metallic texture, demonstrating stable fingerprint resistance. Example 3:

[0037] Nine-stage progressive cleaning process parameters optimization.

[0038] All subsequent process parameters, such as substrate treatment, passivation dip coating, curing film formation, and resin coating, were fixed. Only the core parameters of the nine-stage progressive cleaning process were adjusted. Three different sets of cleaning temperatures, electrolytic cleaning current densities, and magnetic filtration magnetic field strengths were set. The core test indicators were the amount of iron powder residue on the substrate surface, the oil removal rate, and the cleanliness of the board surface. The cleaning process parameters were optimized and tested.

[0039] Three parallel samples were prepared for each set of parameters. After cleaning, the amount of iron powder residue was detected by atomic absorption spectrometry, the oil removal rate was detected by weighing method, and the cleanliness of the plate surface was evaluated by visual inspection combined with magnification. The test results are shown in the table below.

[0040] Table 1. Test results of parameter optimization for the nine-stage progressive cleaning process: Optimization analysis of cleaning process parameters: Test group 2 used a cleaning temperature of 55℃ and an A / dm² temperature. 2 With an electrolytic current density and a magnetic field strength of 1800 Gs, the residual iron powder content in this group of samples was only 0.3 mg / m³. 2 The oil removal rate reached 99.8%, and the board surface cleanliness was rated as excellent, representing the best combination among the three parameter groups. In Test Group 1, the cleaning temperature, electrolytic current density, and magnetic filter magnetic field strength were all at their lower limits, resulting in insufficient cleaning force and an inability to thoroughly remove iron powder and oil from the substrate surface. This led to higher iron powder residue and a lower oil removal rate, with the board surface cleanliness only reaching a good level. In Test Group 3, all parameters were at their upper limits. Excessively high cleaning temperature and current density could cause slight etching on the substrate surface, and excessively high magnetic filter magnetic field strength could easily adsorb too many impurities, causing secondary pollution. The iron powder residue and oil removal rate were lower than in Test Group 2, resulting in a good level of board surface cleanliness. Based on the comprehensive test results, a cleaning temperature of 55℃ and an electrolytic current density of 10A / dm² were optimal. 2 Electrolysis current density and 1800Gs magnetic field strength for magnetic filtration are the optimal process parameters for the nine-stage progressive cleaning. Example 4:

[0041] Optimization of composite chromium-free passivation solution formulation and dip coating process.

[0042] All process parameters, including substrate cleaning, hot air drying, low-temperature curing, and resin coating, were fixed. Only the pH value, dipping temperature, and dipping time of the composite chromium-free passivation solution were adjusted. Three different sets of process parameters were set, with the adhesion of the porous inorganic passivation layer, salt spray resistance, and film uniformity as the core test indicators. The passivation solution formulation and dipping process were optimized and tested.

[0043] The passivation solution was prepared on-site using deionized water, with a uniform stirring time of 30 minutes. During the dip coating process, the substrate was immersed and removed at a uniform speed. Three parallel samples were prepared for each set of parameters. After curing, the performance was tested uniformly, and the test results are shown in the table below.

[0044] Table 2. Test results of composite chromium-free passivation solution formulation and dip coating process optimization: Analysis of Composite Chromium-Free Passivation Solution Formulation and Dip Coating Process Optimization: Test group 2 used a passivation solution with a pH of 3.8, a dipping temperature of 30℃, and a dipping time of 20s. The samples in this group maintained the best adhesion of the porous inorganic passivation layer, achieved a salt spray resistance of 1008 hours, and received an excellent rating for film uniformity, demonstrating the best overall performance. Test group 1 had a passivation solution with a low pH, insufficient dipping temperature and time, resulting in incomplete reaction between the passivation solution and the substrate surface. This led to a thinner passivation film with poor salt spray resistance, reaching only 480 hours, and a good rating for film uniformity. Test group 3 had a passivation solution with a high pH, ​​which easily caused component precipitation. Excessive dipping temperature and time resulted in an overly thick and locally rough film, with a salt spray resistance of only 720 hours and a good rating for film uniformity. Based on the comprehensive test results, a passivation solution pH of 3.8, a dipping temperature of 30℃, and a dipping time of 20s represent the optimal parameters for the composite chromium-free passivation solution and dipping process. Example 5:

[0045] Optimization of the coating and curing process of modified fingerprint-resistant resin.

[0046] All process parameters, including substrate cleaning, passivation dip coating, and low-temperature curing, were fixed. Only the roller speed ratio, wet film thickness, constant temperature curing temperature, and curing time of the modified fingerprint-resistant resin roller coating were adjusted. Three different sets of process parameters were set, and the fingerprint resistance, flexibility, and curing integrity of the organic fingerprint-resistant layer were used as the core test indicators to carry out coating and curing process optimization tests.

[0047] During the roll coating process, the running speed of the steel plate was kept stable, the reverse roll coating pressure was uniform, and hot air circulation heating was used during the curing process to ensure uniform temperature. Three parallel samples were prepared for each set of parameters. After curing, the performance was tested uniformly, and the test results are shown in the table below.

[0048] Table 3. Test results of the optimized coating and curing process of the modified fingerprint-resistant resin: Optimization analysis of modified fingerprint-resistant resin coating and curing process: Test group 2 used a roller speed ratio of 1.08, a wet film thickness of 1.5 μm, a curing temperature of 110℃, and a curing time of 23 s. The samples in this group achieved excellent fingerprint resistance and flexibility in their organic fingerprint-resistant layers. The resin cured completely without stickiness or cracking, demonstrating the best curing integrity. Test group 1 had a low roller speed ratio, a thin wet film thickness, and insufficient curing temperature and time. The thin film resulted in only excellent and good grades in fingerprint resistance and flexibility. Test group 3 had a high roller speed ratio, a thick wet film thickness, excessively high curing temperature, and an excessively long curing time. The thick film was prone to sagging, reduced flexibility, and only achieved an excellent grade in fingerprint resistance. Based on the comprehensive test results, a roller speed ratio of 1.08, a wet film thickness of 1.5 μm, a curing temperature of 110℃, and a curing time of 23 s are the optimal process parameters for coating and curing modified fingerprint-resistant resin. Example 6:

[0049] Comprehensive performance testing of chromium-free passivated fingerprint-resistant composite treated steel plates.

[0050] High-alumina-zinc-alumina-magnesium chromium-free passivated fingerprint-resistant composite steel plates prepared with all optimal processes were selected as test samples, while high-alumina-zinc-alumina-magnesium steel plates treated with conventional processes were selected as control samples. The two groups of samples were tested for five core performance aspects: neutral salt spray, fingerprint resistance, adhesion, bending, and surface condition. All tests were performed according to a unified standard, and the test results are shown in the table below.

[0051] Table 4. Comparison Test Results of Comprehensive Performance of Composite-Treated Steel Plates: Comprehensive performance testing and analysis of composite-treated steel plates: The optimal process for treating steel plates achieved a neutral salt spray test duration of 2016 hours, four times that of conventionally treated steel plates. Its fingerprint resistance was rated as excellent, and the film layer showed no cracking or peeling after a 180-degree bend. No mold or rust was observed on the surface during the test period, and the overall condition remained intact. Conventionally treated steel plates, due to incomplete cleaning, insufficient passivation film corrosion resistance, and a weak fingerprint-resistant layer, only achieved a neutral salt spray test duration of 504 hours. After bending, the film layer showed slight cracking, and a small amount of white rust appeared on the surface. Its overall performance was far inferior to that of the optimally treated steel plates. The optimal process, through precise control of cleaning, passivation, coating, and curing parameters, forms a composite film layer on the steel plate surface that combines inorganic passivation with organic fingerprint resistance. This achieves both chromium-free environmental protection requirements and significantly improves the steel plate's corrosion resistance, fingerprint resistance, and processing adaptability, fully meeting the needs of high-end applications. Figure 3 , Figure 4 As shown.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A chromium-free passivation and fingerprint-resistant composite treatment method for high-aluminum-zinc-aluminum-magnesium steel plates, characterized in that, The specific steps of this method are as follows: S1, Select fine-grained high-alumina-zinc-alumina-magnesium steel plate as the substrate, perform multi-stage cleaning operations on the surface of the substrate, and perform hot air drying treatment on the substrate after cleaning. S2, the dried substrate is immersed in a composite chromium-free passivation solution to perform a dip coating operation, and a passivation precursor film is prepared on the surface of the substrate; S3, a porous inorganic passivation layer is prepared by performing low-temperature hot air curing on a substrate with a passivation precursor film attached to its surface. S4, a roller coating operation is performed on the surface of the porous inorganic passivation layer to coat the modified fingerprint-resistant resin and prepare an organic fingerprint-resistant precursor film. S5, a constant temperature curing treatment is performed on the substrate with an organic fingerprint-resistant precursor film attached to its surface to prepare a chromium-free passivated fingerprint-resistant composite film.

2. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S1, the alloy components of the fine-grained high-aluminum zinc-aluminum magnesium steel sheet include 53% aluminum, 43.4% zinc, 1.6% silicon, and 2% magnesium, the coating weight of the steel sheet is controlled to be 150 g / m 2 to 200 g / m 2 , the steel sheet substrate model is DX53D or DX54D, the steel sheet is formed by using a pre-melting pot constant-temperature liquid supply and an air knife plating, and solidification is completed by using a large air box cooling and a variable-diameter pressurized air outlet after plating.

3. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S1, the multi-stage cleaning operation adopts a nine-stage progressive cleaning process, which consists of alkaline rinsing, alkaline brushing, electrolytic cleaning, secondary alkaline brushing, secondary electrolytic cleaning, tertiary alkaline brushing, water brushing, primary water rinsing, and secondary water rinsing. The temperature throughout the nine-stage progressive cleaning process is controlled between 50°C and 60°C.

4. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum zinc-aluminum-magnesium steel plate according to claim 3, characterized in that, In step S1, the nine-stage progressive cleaning process includes two sets of electrolytic cleaning devices, and the current density of the electrolytic cleaning devices is controlled at 9A / dm³. 2 Up to 11A / dm 2 Between; the nine-stage progressive cleaning process is also equipped with three sets of magnetic filtration devices, the magnetic field strength of which is controlled between 1700Gs and 1900Gs.

5. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum-zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S1, the temperature of the hot air drying process is controlled between 70°C and 80°C.

6. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S2, the composite chromium-free passivation solution is a titanium zirconium-silicate-molybdate composite system, the pH value of the composite chromium-free passivation solution is controlled between 3.6 and 4.0, the temperature of the dip coating operation is controlled between 28°C and 32°C, and the duration of the dip coating operation is controlled between 18s and 22s.

7. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum-zinc-aluminum-magnesium steel plate according to claim 6, characterized in that, In step S2, the composite chromium-free passivation solution comprises ammonium fluorotitanate, ammonium fluorozirconate, tetraethyl orthosilicate, sodium molybdate, and sodium nitrate. The concentration of ammonium fluorotitanate is controlled between 8 g / L and 12 g / L, the concentration of ammonium fluorozirconate is controlled between 6 g / L and 10 g / L, the concentration of tetraethyl orthosilicate is controlled between 3 g / L and 5 g / L, the concentration of sodium molybdate is controlled between 2 g / L and 4 g / L, and the concentration of sodium nitrate is controlled between 1 g / L and 3 g / L.

8. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum-zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S3, the temperature of the low-temperature hot air curing treatment is controlled between 85°C and 95°C, the hot air velocity is controlled between 3m / s and 5m / s, the curing time is controlled between 10s and 15s, the thickness of the porous inorganic passivation layer is controlled between 0.3μm and 0.5μm, and the porosity of the porous inorganic passivation layer is controlled between 15% and 20%.

9. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum-zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S4, the modified fingerprint-resistant resin is a nano-SiO2-aminosilane modified waterborne polyurethane-fluorocarbon blend resin. The roller coating operation adopts a reverse roller coating method, the ratio of the coating roller speed to the steel plate running speed is controlled between 1.07 and 1.09, and the wet film thickness of the roller coating operation is controlled between 1.4μm and 1.6μm.

10. The method for chromium-free passivation and fingerprint-resistant composite treatment of high-aluminum zinc-aluminum-magnesium steel plate according to claim 1, characterized in that, In step S5, the temperature of the isothermal curing process is controlled between 108°C and 112°C, the curing time is controlled between 22s and 24s, the total thickness of the chromium-free passivation fingerprint-resistant composite film is controlled between 1.0μm and 1.6μm, the thickness of the porous inorganic passivation layer in the composite film is controlled between 0.3μm and 0.5μm, and the thickness of the organic fingerprint-resistant layer is controlled between 0.7μm and 1.1μm.

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