A method for preparing a hot-dip galvanized layer of a hot-rolled high-strength steel plate having high corrosion resistance

Abstract

The present application relates to the technical field of metal material surface treatment, in particular to a hot-dip galvanizing layer preparation method of hot-rolled high-strength steel plate with high corrosion resistance. First, the hot-rolled steel plate is formed after smelting, continuous casting and hot rolling; second, the corrosion-resistant hot-rolled high-strength steel plate is put into a heat treatment furnace which can be filled with protective gas for hydrogen reduction after alcohol degreasing; then, the corrosion-resistant hot-rolled high-strength steel plate after hydrogen reduction is immersed in a plating aid for soaking; next, the corrosion-resistant hot-rolled high-strength steel plate soaked in the plating aid is immersed in a Zn-Al-Mg alloy plating solution for hot-dip galvanizing; finally, the hot-dip galvanized hot-rolled high-strength steel plate is taken out of the plating solution in a high-purity Ar protective atmosphere and is placed in a protective cover filled with high-purity Ar protective atmosphere for natural cooling to room temperature. The present application can effectively improve the corrosion resistance of the Zn-Al-Mg alloy plating layer on the surface of the hot-rolled steel plate, and has higher corrosion resistance than other hot-dip galvanizing technologies.

Description

Technical Field

[0001] This invention relates to the field of metal material surface treatment technology, specifically to a method for preparing a hot-dip galvanized layer on hot-rolled high-strength steel sheet with high corrosion resistance, applicable to the application of high-strength steel with tensile strength ≥780MPa in harsh corrosive environments such as automobile chassis and marine engineering. Background Technology

[0002] In the field of advanced steel materials, the processing of advanced ultra-high strength steel plates and their coated plates is a key direction for meeting the requirements of lightweighting and high safety. However, existing hot-rolled high-strength steels (such as those with tensile strength ≥780MPa) often face problems such as poor coating adhesion and insufficient corrosion resistance during hot-dip galvanizing due to the enrichment of base alloying elements and the difficulty in controlling the surface oxidation state. This seriously restricts the application performance and promotion of advanced ultra-high strength steel plates and their coated plates in harsh corrosive environments (such as automotive chassis and construction machinery).

[0003] Hot-rolled high-strength steel faces numerous problems in traditional hot-dip galvanizing processes, such as insufficient adhesion between the coating and the substrate, and poor corrosion resistance. These issues not only affect product lifespan but also limit its application in high-end fields. Currently, various hot-dip galvanizing technologies for advanced ultra-high-strength steel plates have been developed and applied both domestically and internationally, but these technologies still have shortcomings in improving the adhesion between the coating and high-strength steel and its corrosion resistance. In traditional hot-dip galvanizing processes, pickling of high-strength steel is usually required to remove surface oxide scale, but pickling processes suffer from severe environmental pollution, high costs, and a tendency to cause substrate corrosion. Current flux designs primarily use zinc chloride and ammonium chloride, which, while meeting basic galvanizing requirements, have limited effectiveness in improving the adhesion between the coating and the substrate and its corrosion resistance. Regarding the composition of the galvanizing bath, while common Zn-Al-Mg alloy baths offer some corrosion resistance compared to traditional Zn-1Al baths, there is still room for improvement in the adhesion and corrosion resistance to high-strength steel surfaces.

[0004] Patent CN110760773A discloses a hot-dip galvanized high-strength steel sheet with high surface quality and excellent corrosion resistance, and its manufacturing method. It improves coating adhesion through pre-plating a Ni layer and an Fe-Al barrier layer. However, the improved corrosion resistance relies on the electrode potential advantage of the Ni layer, failing to address the fundamental problem caused by the enrichment of alloying elements in the high-strength steel matrix. Furthermore, the pre-plating Ni process increases production costs. Patent CN116790986A discloses a low-cost, high-hole-expansion-performance 780MPa-grade hot-dip galvanized duplex steel and its preparation method. The 780MPa-grade hot-dip galvanized duplex steel improves hole-expansion performance through heating and tempering in the two-phase region. However, the pretreatment relies on pickling, and its corrosion resistance improvement relies solely on the conventional Zn-Al-Mg system, which cannot meet the requirements of harsh corrosive environments. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a hot-dip galvanized layer on hot-rolled high-strength steel sheet with high corrosion resistance. This method can effectively improve the corrosion resistance of the Zn-Al-Mg alloy coating on the surface of hot-rolled steel sheet, and at the same time, it has higher corrosion resistance than other hot-dip galvanizing technologies, thereby improving the quality of hot-rolled high-strength steel hot-dip galvanized sheet.

[0006] The technical solution of this invention is:

[0007] A method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance includes the following steps:

[0008] The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.02%–0.2%, Si: 0.02%–0.2%, Mn: 0.5%–3.0%, Cr: 0.4%–4.0%, Mo: 0.05%–0.5%, V: 0.001%–0.01%, Ru: 0.1%–0.3%, Lu: 0.01%–0.05%, P: ≤0.05%, S: ≤0.005%, Ti: 0.01%–0.05%, N: 0.002%–0.02%, B: 0.0001%–0.01%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate.

[0009] The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The plate is heated to 500-650°C in a high-purity Ar protective atmosphere with a flow rate of 2-4 L / min and a heating rate of 15-30°C / min. Once the temperature is reached, the plate is replaced with a reducing atmosphere with a flow rate of 2-4 L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 20-40% H2. The plate is held in the reducing atmosphere for 60-120 minutes, then switched to high-purity Ar with a flow rate of 2-4 L / min and allowed to cool naturally to room temperature.

[0010] The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent. The fluxing agent comprises the following components: zinc chloride 90–180 g / L, potassium chloride 10–30 g / L, aluminum chloride 15–40 g / L, sodium titanate 5–40 g / L, triphenyl phosphate 2–10 g / L, surfactant 1–5 g / L, and water as the balance. The fluxing agent temperature is 20–80°C, and the immersion time is 10–120 seconds. After immersion, the surface is dried.

[0011] The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is: Si: 0.1%–0.5%, Re: 0.05%–0.5%, Al: 10%–13%, Mg: 2%–5%, Ti: 0.01%–0.1%, V: 0.01%–0.1%, Ru: 0.05%–0.2%, W: 0.1%–0.5%, Pb: ≤0.003%, Cu: ≤0.002%, Fe: ≤0.05%, Cd: ≤0.002%, with the balance being Zn. The hot-dip galvanizing bath temperature is 460–480℃, and the hot-dip galvanizing time is 5–120 seconds.

[0012] The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

[0013] In the method for preparing the hot-dip galvanized layer of the hot-rolled high-strength steel sheet with high corrosion resistance, preferably, in the first step, Ru is 0.22% and Lu is 0.03%.

[0014] In the method for preparing the hot-dip galvanized layer of the hot-rolled high-strength steel plate with high corrosion resistance, preferably, in the third step, the sodium titanate is 15 g / L, the triphenyl phosphate is 4 g / L, and the surfactant is 2 g / L.

[0015] In the method for preparing the hot-dip galvanized layer of the hot-rolled high-strength steel sheet with high corrosion resistance, preferably, in the third step, the surfactant is ammonium polyphosphate.

[0016] In the third step of the method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance, a flux layer with a thickness of 5 to 20 μm is formed on the surface of the corrosion-resistant hot-rolled high-strength steel sheet.

[0017] In the method for preparing the hot-dip galvanized layer of the hot-rolled high-strength steel sheet with high corrosion resistance, preferably, in the fourth step, Ru is 0.12% and W is 0.3%.

[0018] In the fourth step of the method for preparing a hot-dip galvanized layer of hot-rolled high-strength steel sheet with high corrosion resistance, a hot-dip galvanized layer with a thickness of 80-110 μm is obtained on the surface of the flux.

[0019] The design concept of this invention is:

[0020] In existing hot-dip galvanizing processes for hot-rolled high-strength steel, the formation of a continuous oxide layer due to the enrichment of base alloying elements (Si, Mn, etc.) leads to poor coating adhesion. This invention proposes a method for preparing a hot-dip galvanized coating on hot-rolled high-strength steel sheets with high corrosion resistance. Through innovative chemical composition and process optimization, it solves the problems of insufficient coating adhesion and poor corrosion resistance in traditional hot-dip galvanizing processes for hot-rolled high-strength steel. Ru and Lu elements are added to the high-strength steel to refine the grain and enhance the adhesion between the coating and the substrate. A hydrogen reduction process without acid washing is used to form a reduced iron layer, avoiding acid washing contamination and providing a clean surface. Sodium titanate and triphenyl phosphate are introduced into the flux to enhance coating adhesion and reduce the surface tension of the plating bath. Ru and W elements are added to the Zn-Al-Mg alloy plating bath to further improve the coating hardness and corrosion resistance. Overall, this invention achieves a significant improvement in the quality of hot-dip galvanized high-strength steel sheets while also being environmentally friendly and highly efficient. Therefore, through innovative chemical composition design and process improvement, this invention significantly improves the adhesion and corrosion resistance of the coating to high-strength steel plates.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The innovative hot-rolled high-strength steel composition of this invention incorporates rare earth elements Ru and Lu on the basis of traditional high-strength steel composition. These elements can refine the grains, improve the strength and toughness of the steel, and at the same time form stable compounds during the hot-dip galvanizing process, enhancing the adhesion between the coating and the substrate.

[0023] (2) The present invention introduces a pickling-free hydrogen reduction process to pre-treat hot-rolled high-strength steel. A reduced iron layer is formed on the surface of the high-strength steel through the hydrogen reduction process, which avoids the environmental pollution and substrate corrosion problems caused by the traditional pickling process, and provides a cleaner surface for subsequent galvanizing.

[0024] (3) The innovative flux formulation of this invention adds sodium titanate and triphenyl phosphate to the flux. Sodium titanate can form a dense titanium oxide film on the surface of high-strength steel, which enhances the bonding force between the coating and the substrate. At the same time, it innovatively proposes to use ammonium polyphosphate as a surfactant, which can improve the dispersibility and stability of the plating solution, and further improve the uniformity and adhesion of the coating.

[0025] (4) The innovation of the alloy plating solution composition in this invention is the addition of Ru and W elements to the Zn-Al-Mg alloy plating solution. These elements can form stable compounds with zinc, aluminum, and magnesium, further improving the hardness and corrosion resistance of the coating, while enhancing the adhesion between the coating and the high-strength steel plate.

[0026] In summary, this invention, through innovative chemical composition design and process improvement, significantly enhances the adhesion and corrosion resistance of the coating to high-strength steel plates, overcomes the shortcomings of existing technologies, and provides an efficient, environmentally friendly, and high-quality solution for the hot-dip galvanizing of hot-rolled high-strength steel plates.

[0027] The advantages and beneficial effects of this invention are:

[0028] 1. This invention innovatively incorporates rare earth elements Ru and Lu into the traditional high-strength steel composition. These elements can refine the grain size, improve the strength and toughness of the steel, and simultaneously form stable compounds during the hot-dip galvanizing process, enhancing the adhesion between the coating and the substrate.

[0029] 2. In this invention, Ru and W elements are added to the Zn-Al-Mg alloy plating bath. These elements can form stable compounds with zinc, aluminum and magnesium, further improving the hardness and corrosion resistance of the coating, while enhancing the adhesion between the coating and the high-strength steel plate.

[0030] 3. This invention forms a reduced iron layer on the surface of high-strength steel through a hydrogen reduction process, avoiding the environmental pollution and substrate corrosion problems caused by traditional pickling processes, while providing a cleaner surface for subsequent galvanizing.

[0031] 4. The hot-dip galvanized layer preparation method for hot-rolled high-strength steel plates with high corrosion resistance described in this invention significantly improves the bonding force and corrosion resistance between the coating and the high-strength steel plate through innovative chemical composition design and process improvement, overcoming the shortcomings of the prior art and providing an efficient, environmentally friendly and high-quality solution for the hot-dip galvanizing preparation of hot-rolled high-strength steel plates.

[0032] 5. The performance indicators of the hot-rolled high-strength steel galvanized sheet obtained after preparing the Zn-Al-Mg hot-dip galvanized layer using the present invention are as follows: the corrosion potential is -1.10 to -1.40 V and the corrosion current density is 9.0 × 10⁻⁶ V, as determined by electrochemical workstation testing. -7 ~9.5×10 -7 A / cm 2 The polarization resistance is 10000~10300Ω·cm 2 The coating bonding strength is 730-750 MPa. Attached Figure Description

[0033] Figure 1 The image shows the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 1.

[0034] Figure 2 The image shows the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 2.

[0035] Figure 3 The image shows the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 3.

[0036] Figure 4 The image shows the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 4. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1:

[0039] In this embodiment, a method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance includes the following steps:

[0040] The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.02%, Si: 0.2%, Mn: 3.0%, Cr: 2.6%, Mo: 0.05%, V: 0.005%, Ru: 0.3%, Lu: 0.01%, P: 0.04%, S: 0.005%, Ti: 0.05%, N: 0.012%, B: 0.01%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate.

[0041] The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The plate is heated to 650°C at a rate of 15°C / min in a protective atmosphere of high-purity Ar (volume purity 99.999%) with a flow rate of 4L / min. Once the temperature is reached, the atmosphere is changed to a reducing atmosphere with a flow rate of 3L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 20% H2. The plate is held at the reducing atmosphere for 120 minutes, then switched to high-purity Ar with a flow rate of 4L / min and allowed to cool naturally to room temperature.

[0042] The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent. The fluxing agent comprises the following components: zinc chloride 90 g / L, potassium chloride 20 g / L, aluminum chloride 15 g / L, sodium titanate 35 g / L, triphenyl phosphate 2 g / L, ammonium polyphosphate 2 g / L, and water as the balance. The fluxing agent temperature is 20°C, and the immersion time is 80 seconds. After immersion, the surface is dried, forming a fluxing agent layer with a thickness of 10 μm on the surface of the corrosion-resistant hot-rolled high-strength steel sheet.

[0043] The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is: Si: 0.1%, Re: 0.25%, Al: 11.8%, Mg: 5%, Ti: 0.1%, V: 0.06%, Ru: 0.2%, W: 0.5%, Pb: 0.003%, Cu: 0.002%, Fe: 0.05%, Cd: 0.002%, with the balance being Zn. The hot-dip galvanizing bath temperature is 480℃, and the hot-dip galvanizing time is 120s, resulting in a 110μm thick hot-dip zinc layer on the flux surface.

[0044] The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

[0045] like Figure 1 As shown in the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 1, the coating cross-section exhibits a clear multi-layer structure. The bottom layer is a high-strength steel substrate, providing a good foundation for mechanical properties. Above this is a reduced iron layer, which is a continuous reduced iron layer formed after the reduction of the original iron oxide layer on the high-strength steel surface. After fluxing and galvanizing, it is eroded, resulting in a discontinuous state. The surface of the reduced iron layer contains compound deposits formed by the reaction of the flux, constituting a flux layer. This layer is not continuous, and this structure facilitates the adhesion of the subsequent galvanized layer. The top layer is a zinc-aluminum-magnesium hot-dip galvanized layer approximately 110 μm thick, with uniform and dense thickness, exhibiting excellent corrosion resistance. The overall multi-layer structure design, progressing layer by layer from the bottom to the surface, effectively improves the comprehensive protective performance of the sample, significantly enhancing its service life and reliability in complex environments.

[0046] In this embodiment, the performance indicators of the hot-rolled high-strength steel galvanized sheet are as follows: the corrosion potential is -1.35V and the corrosion current density is 9.462×10⁻⁶ in the electrochemical workstation test results. -7 A / cm 2 The polarization resistance is 10244.7 Ω·cm. 2 The coating bonding strength is 745 MPa.

[0047] Example 2:

[0048] In this embodiment, a method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance includes the following steps:

[0049] The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.2%, Si: 0.08%, Mn: 2.0%, Cr: 0.4%, Mo: 0.5%, V: 0.01%, Ru: 0.1%, Lu: 0.03%, P: 0.05%, S: 0.003%, Ti: 0.03%, N: 0.002%, B: 0.0001%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate.

[0050] The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The plate is heated to 600°C at a rate of 30°C / min in a high-purity Ar (volume purity 99.999%) protective atmosphere with a flow rate of 3L / min. Once the temperature is reached, the atmosphere is changed to a reducing atmosphere with a flow rate of 2L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 25% H2. The plate is held at the reducing atmosphere for 90 minutes, then switched to high-purity Ar with a flow rate of 3L / min and allowed to cool naturally to room temperature.

[0051] The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent, which comprises the following components: 180 g / L zinc chloride, 10 g / L potassium chloride, 40 g / L aluminum chloride, 5 g / L sodium titanate, 10 g / L triphenyl phosphate, 4 g / L ammonium polyphosphate, and water as the balance. The fluxing agent temperature is 80°C, and the immersion time is 10 seconds. After immersion, the surface is dried, forming a fluxing agent layer with a thickness of 15 μm on the surface of the corrosion-resistant hot-rolled high-strength steel sheet.

[0052] The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is: Si: 0.5%, Re: 0.05%, Al: 12.2%, Mg: 2%, Ti: 0.05%, V: 0.01%, Ru: 0.12%, W: 0.1%, Pb: 0.001%, Cu: 0.0015%, Fe: 0.01%, Cd: 0.001%, with the balance being Zn. The hot-dip galvanizing bath temperature is 460℃, and the hot-dip galvanizing time is 5s, resulting in a 105μm thick hot-dip zinc layer on the flux surface.

[0053] The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

[0054] like Figure 2As shown in the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 2, the coating cross-section exhibits a clear multi-layer structure. The bottom layer is the high-strength steel sheet substrate, providing a good foundation for mechanical properties. Above this is a reduced iron layer, which is a continuous reduced iron layer formed after the reduction of the original iron oxide layer on the high-strength steel surface. After fluxing and galvanizing, it is eroded, resulting in a discontinuous state. The surface of the reduced iron layer contains compound deposits formed by the reaction of the flux, constituting a flux layer. This layer is not continuous; this structure facilitates the adhesion of the subsequent galvanized layer. The top layer is a zinc-aluminum-magnesium hot-dip galvanized layer approximately 105 μm thick, with uniform and dense thickness, exhibiting excellent corrosion resistance. The overall multi-layer structure design, progressing layer by layer from the bottom to the surface, effectively improves the comprehensive protective performance of the sample, significantly enhancing its service life and reliability in complex environments.

[0055] In this embodiment, the performance indicators of the hot-rolled high-strength steel galvanized sheet are as follows: the corrosion potential is -1.32V and the corrosion current density is 9.138×10⁻⁶ in the electrochemical workstation test results. -7 A / cm 2 The polarization resistance is 10 × 10⁶.3 Ω·cm. 2 The coating bonding strength is 737 MPa.

[0056] Example 3:

[0057] In this embodiment, a method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance includes the following steps:

[0058] The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.1%, Si: 0.05%, Mn: 0.5%, Cr: 1.5%, Mo: 0.35%, V: 0.001%, Ru: 0.22%, Lu: 0.04%, P: 0.03%, S: 0.004%, Ti: 0.01%, N: 0.02%, B: 0.0015%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate.

[0059] The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The temperature is raised to 500°C at a rate of 25°C / min in a protective atmosphere of high-purity Ar (volume purity 99.999%) with a flow rate of 2L / min. Once the temperature is reached, the temperature is changed to a reducing atmosphere with a flow rate of 4L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 30% H2. The temperature is maintained in the reducing atmosphere for 60 minutes, then the flow rate is changed to high-purity Ar with a flow rate of 2.5L / min, and the plate is allowed to cool naturally to room temperature.

[0060] The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent, which comprises the following components: 150 g / L zinc chloride, 25 g / L potassium chloride, 30 g / L aluminum chloride, 40 g / L sodium titanate, 4 g / L triphenyl phosphate, 1 g / L ammonium polyphosphate, and water as the balance. The fluxing agent temperature is 60°C, and the immersion time is 120 seconds. After immersion, the surface is dried, forming a 20 μm thick fluxing agent layer on the surface of the corrosion-resistant hot-rolled high-strength steel sheet.

[0061] The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is: Si: 0.3%, Re: 0.35%, Al: 10%, Mg: 3.5%, Ti: 0.01%, V: 0.1%, Ru: 0.08%, W: 0.15%, Pb: 0.002%, Cu: 0.0005%, Fe: 0.03%, Cd: 0.0015%, with the balance being Zn. The hot-dip galvanizing bath temperature is 470℃, and the hot-dip galvanizing time is 60s, resulting in a 100μm thick hot-dip zinc layer on the flux surface.

[0062] The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

[0063] like Figure 3 As shown in the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 3, the coating cross-section exhibits a clear multi-layer structure. The bottom layer is a high-strength steel substrate, providing a good foundation for mechanical properties. Above this is a reduced iron layer, which is a continuous reduced iron layer formed after the reduction of the original iron oxide layer on the high-strength steel surface. After fluxing and galvanizing, it is eroded, resulting in a discontinuous state. The surface of the reduced iron layer contains compound deposits formed by the reaction of the flux, constituting a flux layer. This layer is not continuous; this structure facilitates the adhesion of the subsequent galvanized layer. The top layer is a zinc-aluminum-magnesium hot-dip galvanized layer approximately 100 μm thick, with uniform and dense thickness, exhibiting excellent corrosion resistance. The overall multi-layer structure design, progressing layer by layer from the bottom to the surface, effectively improves the comprehensive protective performance of the sample, significantly enhancing its service life and reliability in complex environments.

[0064] In this embodiment, the performance indicators of the hot-rolled high-strength steel galvanized sheet are as follows: the corrosion potential is -1.21V and the corrosion current density is 9.184×10⁻⁶ in the electrochemical workstation test results. -7 A / cm 2 The polarization resistance is 10183.5 Ω·cm. 2 The coating bonding strength is 741 MPa.

[0065] Example 4:

[0066] In this embodiment, a method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance includes the following steps:

[0067] The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.12%, Si: 0.02%, Mn: 2.5%, Cr: 4.0%, Mo: 0.15%, V: 0.002%, Ru: 0.25%, Lu: 0.05%, P: 0.02%, S: 0.001%, Ti: 0.02%, N: 0.005%, B: 0.0065%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate.

[0068] The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The plate is heated to 550°C at a rate of 20°C / min in a high-purity Ar (volume purity 99.999%) protective atmosphere with a flow rate of 2.5 L / min. Once the temperature is reached, the atmosphere is changed to a reducing atmosphere with a flow rate of 3.5 L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 40% H2. The plate is held at the reducing atmosphere for 100 min and then switched to high-purity Ar with a flow rate of 2 L / min. The plate is then allowed to cool naturally to room temperature.

[0069] The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent, which comprises the following components: zinc chloride 120 g / L, potassium chloride 30 g / L, aluminum chloride 20 g / L, sodium titanate 15 g / L, triphenyl phosphate 6 g / L, ammonium polyphosphate 5 g / L, and water as the balance. The fluxing agent temperature is 40°C, and the immersion time is 30 seconds. After immersion, the surface is dried, forming a fluxing agent layer with a thickness of 5 μm on the surface of the corrosion-resistant hot-rolled high-strength steel sheet.

[0070] The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is: Si: 0.35%, Re: 0.5%, Al: 13%, Mg: 2.5%, Ti: 0.06%, V: 0.04%, Ru: 0.05%, W: 0.3%, Pb: 0.0005%, Cu: 0.001%, Fe: 0.02%, Cd: 0.0005%, with the balance being Zn. The hot-dip galvanizing bath temperature is 465℃, and the hot-dip galvanizing time is 30s, resulting in a hot-dip zinc layer with a thickness of 80μm on the flux surface.

[0071] The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

[0072] like Figure 4 As shown in the morphology of the cross-section of the hot-rolled high-strength steel galvanized sheet in Example 4, the coating cross-section exhibits a clear multi-layer structure. The bottom layer is the high-strength steel substrate, providing a good foundation for mechanical properties. Above this is a reduced iron layer, which is a continuous reduced iron layer formed after the reduction of the original iron oxide layer on the high-strength steel surface. After fluxing and galvanizing, it is eroded, resulting in a discontinuous state. The surface of the reduced iron layer contains compound deposits formed by the reaction of the flux, constituting a flux layer. This layer is not continuous; this structure facilitates the adhesion of the subsequent galvanized layer. The top layer is a zinc-aluminum-magnesium hot-dip galvanized layer approximately 80 μm thick, with uniform and dense thickness, exhibiting excellent corrosion resistance. The overall multi-layer structure design, progressing layer by layer from the bottom to the surface, effectively improves the comprehensive protective performance of the sample, significantly enhancing its service life and reliability in complex environments.

[0073] In this embodiment, the performance indicators of the hot-rolled high-strength steel galvanized sheet are as follows: the corrosion potential is -1.13V and the corrosion current density is 9.095×10⁻⁶ in the electrochemical workstation test results. -7 A / cm 2 The polarization resistance is 10029.6 Ω·cm. 2 The coating bonding strength is 731 MPa.

[0074] The results show that after preparing the Zn-Al-Mg hot-dip galvanized layer, the performance indicators of the hot-rolled high-strength steel galvanized sheet obtained in the examples are as follows: the corrosion potential in the electrochemical workstation test results is -1.13 to -1.35 V, and the corrosion current density is 9.095 × 10⁻⁶. -7 ~9.462×10 -7 A / cm 2 The polarization resistance is 10029.6~10244.7Ω·cm. 2 The coating adhesion strength is 731–745 MPa. This invention incorporates Ru and Lu into the substrate to refine grains and inhibit the segregation of alloying elements. The addition of Ru and W to the plating bath forms stable compounds, enhancing the coating's hardness and corrosion resistance. The grain boundary strengthening effect of Ru and Lu in the substrate synergistically with the alloying effect of Ru and W in the plating bath, significantly improving coating adhesion and corrosion resistance, thus resolving the long-standing contradiction between adhesion and corrosion resistance in high-strength steel zinc plating. The flux incorporates a combination of sodium titanate (forming a dense oxide film) and triphenyl phosphate (reducing surface tension), addressing the insufficient adhesion of traditional fluxes. Ammonium polyphosphate acts as a surfactant, improving wettability. Furthermore, the acid-free hydrogen reduction process eliminates environmental pollution, avoids acid corrosion, and reduces the iron layer, improving the wettability of the zinc bath.

Claims

1. A method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance, characterized in that, Includes the following steps: The first step, by mass percentage, is to determine the chemical composition of the corrosion-resistant hot-rolled high-strength steel plate as follows: C: 0.02%–0.2%, Si: 0.02%–0.2%, Mn: 0.5%–3.0%, Cr: 0.4%–4.0%, Mo: 0.05%–0.5%, V: 0.001%–0.01%, Ru: 0.1%–0.3%, Lu: 0.01%–0.05%, P: ≤0.05%, S: ≤0.005%, Ti: 0.01%–0.05%, N: 0.002%–0.02%, B: 0.0001%–0.01%, with the balance being Fe. The corrosion-resistant hot-rolled high-strength steel plate is then smelted, continuously cast, and hot-rolled to form a hot-rolled steel plate. The second step involves degreasing the corrosion-resistant hot-rolled high-strength steel plate with alcohol and then placing it in a heat treatment furnace that can be purged with a protective gas. The plate is heated to 500-650°C in a high-purity Ar protective atmosphere with a flow rate of 2-4 L / min and a heating rate of 15-30°C / min. Once the temperature is reached, the plate is replaced with a reducing atmosphere with a flow rate of 2-4 L / min. The reducing atmosphere is a hydrogen-nitrogen mixture with a volume fraction of 20-40% H2. The plate is held in the reducing atmosphere for 60-120 minutes, then switched to high-purity Ar with a flow rate of 2-4 L / min and allowed to cool naturally to room temperature. The third step involves immersing the hydrogen-reduced corrosion-resistant hot-rolled high-strength steel sheet in a fluxing agent. The fluxing agent comprises the following components: zinc chloride 90–180 g / L, potassium chloride 10–30 g / L, aluminum chloride 15–40 g / L, sodium titanate 5–40 g / L, triphenyl phosphate 2–10 g / L, surfactant 1–5 g / L, and water as the balance. The surfactant is ammonium polyphosphate. The fluxing agent temperature is 20–80°C, and the immersion time is 10–120 seconds. After immersion, the surface is dried. The fourth step involves immersing the corrosion-resistant hot-rolled high-strength steel sheet, which has been soaked in flux, into a Zn-Al-Mg alloy plating bath for hot-dip galvanizing. The chemical composition of the Zn-Al-Mg alloy plating bath, by mass percentage, is as follows: Si: 0.1%–0.5%, Re: 0.05%–0.5%, Al: 10%–13%; Mg: 2%–5%, Ti: 0.01%–0.1%, V: 0.01%–0.1%, Ru: 0.05%–0.2%, W: 0.1%–0.5%, Pb: ≤0.003%, Cu: ≤0.002%, Fe: ≤0.05%, Cd: ≤0.002%, with the balance being Zn. The hot-dip galvanizing bath temperature is 460–480℃, and the hot-dip galvanizing time is 5–120 seconds. The fifth step is to remove the hot-dip galvanized high-strength steel sheet from the plating bath in a high-purity Ar protective atmosphere and place it in a protective cover filled with a high-purity Ar protective atmosphere to cool naturally to room temperature.

2. The method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance according to claim 1, characterized in that, In the third step, a flux layer with a thickness of 5 to 20 μm is formed on the surface of the corrosion-resistant hot-rolled high-strength steel plate.

3. The method for preparing a hot-dip galvanized layer on a hot-rolled high-strength steel sheet with high corrosion resistance according to claim 1, characterized in that, In the fourth step, a hot-dip galvanized layer with a thickness of 80–110 μm is obtained on the surface of the flux.

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