A hot-dip galvannealed high-strength steel sheet and a method of manufacturing the same

Abstract

The application discloses a hot-dip galvanizing zinc-aluminum-magnesium high-strength steel plate, which comprises a base plate and a zinc-aluminum-magnesium alloy coating, and the chemical components of the base plate are as follows in percentage by mass: C 0.16-0.20%, Si 0.9-1.2%, Mn 2.0-2.6%, Als 0.02-0.06%, P≤0.025%, S≤0.01%, and the balance of Fe and inevitable impurities; the chemical components of the zinc-aluminum-magnesium alloy coating are as follows in percentage by mass: Al 9.0-26.0%, Mg 5.0-8.0%, Si 0.04-0.8%, and the balance of Zn and inevitable impurities. Through the control of the chemical component design of the base plate and the zinc-aluminum-magnesium alloy coating and the control of key process points such as the final rolling temperature, laminar cooling and coiling temperature in the production process, the hot-dip galvanizing zinc-aluminum-magnesium high-strength steel plate prepared has a yield strength of 460-580 MPa, a tensile strength of 780-900 MPa, an elongation of more than 17% and excellent corrosion resistance, and can meet the material demand of photovoltaic support and other industries under severe environment.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel production in the steel industry, and relates to a hot-dip galvanized aluminum-magnesium high-strength steel and its production method. Background Technology

[0002] Hot-dip galvanized aluminum-magnesium coating is a new type of coating that adds appropriate amounts of Al and Mg to traditional zinc-based coatings, thereby changing the structure of the coating and the properties of corrosion products. Because its corrosion resistance is significantly better than that of traditional zinc-based coatings, hot-dip galvanized aluminum-magnesium coating products have been widely used in construction, photovoltaic brackets and other fields.

[0003] Thin slab continuous casting and rolling technology connects the continuous casting and hot rolling processes in traditional steel production, improving production efficiency and reducing energy consumption. Compared to conventional hot rolling, due to the thinner slab thickness, it can directly roll thin steel plates of 0.8–2.5 mm without subsequent cold rolling. Since the 1980s, thin slab continuous casting and rolling technologies (such as CSP technology and ISP technology) have been widely developed.

[0004] Chinese patent CN115109999B discloses a cold-rolled hot-dip galvanized aluminum-magnesium high-strength steel with a yield strength greater than 400 MPa, using CSP hot-rolled raw material coils. The chemical element composition and its weight percentage are: C: 0.18–0.22%, Si: 0.2–0.3%, Mn: 0.5–1.0%, Als: 0.02–0.05%, P≤0.02%, S≤0.008%, N≤0.008%, with the balance being iron and unavoidable impurities; the zinc-aluminum-magnesium alloy coating... The chemical composition, by weight percentage, includes: Al: 4.0–8.0%, Mg: 2.0–4.0%, Si: 0.0–0.5%, with the balance being Zn and unavoidable impurities. The tensile strength of the coated product is 520–630 MPa, and when the yield strength is greater than 500 MPa, the elongation is less than 12%, making it unsuitable for some processing with large deformations. Therefore, there is room for further improvement in tensile properties. Higher strength is beneficial for achieving "high strength with thinner sheet," thereby saving material consumption. Although the corrosion resistance of the coated product is significantly better than traditional zinc-based coatings, for some more demanding service environments, the corrosion resistance of the coated product needs further improvement. Furthermore, the coated substrate is prepared by CSP hot rolling and cold rolling processes. For steel plates with a thickness of 0.8 mm or more within the specified steel thickness range, direct CSP rolling is possible. Therefore, developing a hot-dip galvanized aluminum-magnesium steel sheet with higher strength and excellent corrosion resistance, which can be directly rolled by CSP, is crucial. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a hot-dip galvanized aluminum-magnesium high-strength steel plate and its production method in order to overcome the shortcomings of the prior art. By using the CSP process to manufacture hot-rolled coils and then hot-dip galvanizing aluminum-magnesium after pickling, the steel plate obtained has high strength and high corrosion resistance.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0007] A hot-dip galvanized aluminum-magnesium high-strength steel sheet, comprising a substrate and a zinc-aluminum-magnesium alloy coating, wherein the chemical composition of the substrate, by mass percentage, is: C 0.16%–0.20%, Si 0.9%–1.2%, Mn 2.0%–2.6%, Al 0.02%–0.06%, P ≤ 0.025%, S ≤ 0.01%, with the balance being Fe and unavoidable impurities; the chemical composition of the zinc-aluminum-magnesium alloy coating, by mass percentage, is: Al 9.0%–26.0%, Mg 5.0%–8.0%, Si 0.04%–0.8%, with the balance being Zn and unavoidable impurities.

[0008] In the above scheme, the metallographic matrix of the substrate is bainite, the volume percentage of retained austenite is 3% to 5%, and the volume percentage of ferrite is 0% to 10%.

[0009] In the above scheme, the microstructure of the zinc-aluminum-magnesium alloy coating includes dendritic (Al) phase, blocky MgZn2 phase, blocky (Zn) phase, Mg2Si phase, and multiphase eutectic Al / Zn / MgZn2 microstructure, and each phase is uniformly distributed in the zinc-aluminum-magnesium alloy coating.

[0010] In the above scheme, the yield strength of the high-strength steel plate is 460-580 MPa, the tensile strength is 780-900 MPa, and the elongation is ≥17%.

[0011] In the above scheme, a dense Al-Fe compound layer exists between the substrate and the zinc-aluminum-magnesium alloy coating. Some Si exists in the microstructure of the zinc-aluminum-magnesium alloy coating in the form of Mg2Si and other Si-containing phases, while some Si is enriched and dissolved in the Al-Fe compound.

[0012] The present invention also provides a method for producing the above-mentioned hot-dip galvanized aluminum-magnesium high-strength steel sheet. The method includes forming a substrate using a CSP process, wherein the substrate is pickled and then hot-dip galvanized to form a zinc-aluminum-magnesium alloy coating. The CSP process includes the following steps: smelting, refining, continuous casting of thin slabs, homogenization of the cast slabs, rolling, laminar flow cooling, coiling, and leveling. The chemical composition of the plating solution used in the hot-dip galvanizing process, by mass percentage, is: Al 9.0%–26.0%, Mg 5.0%–8.0%, Si 0.04%–0.8%, with the balance being Zn and unavoidable impurities.

[0013] In the above scheme, in the thin slab continuous casting step, the slab thickness is 65-75mm and the casting speed is 3.5-4.5m / s; in the slab homogenization step, the slab temperature entering the furnace is 800-950℃ and the furnace temperature exiting the furnace is 1150-1200℃; in the rolling step, the descaling process is high-pressure water descaling before entering the rolling mill, and the inlet and outlet descaling water pressure is 320-370bar; the finishing rolling temperature is 850-900℃.

[0014] In the above scheme, the coiling temperature in the coiling step is 400-450℃; the laminar flow cooling step selects direct rapid cooling or slow cooling followed by rapid cooling according to the target performance requirements; direct rapid cooling means that the strip is directly and rapidly cooled to the target coiling temperature after exiting the rolling mill, with a cooling rate ≥60℃ / s; slow cooling followed by rapid cooling means that the strip is not cooled by cooling water after exiting the rolling mill, only air cooling is used, the time does not exceed 4s, and then it is rapidly cooled to the target coiling temperature, with a cooling rate ≥60℃ / s; the rolling force in the leveling step is controlled at 180-220 tons; the pickling is to remove the iron oxide scale from the strip, the acid temperature is controlled at 82-92℃, and the thickness of the strip obtained after pickling is 1.0-3.0mm.

[0015] In the above scheme, the hot-dip galvanizing process involves heating the pickled strip steel to 550–650°C at a heating rate of 5–20°C / s, then cooling the strip steel at a rate greater than 20°C / s to a temperature 15–25°C higher than the galvanizing bath temperature, and then hot-dip galvanizing the strip steel in a zinc pot. After exiting the zinc pot, the strip steel is cooled by first air cooling and then water cooling, with an average cooling rate greater than 20°C / s before solidification. The galvanizing bath temperature is 45–55°C higher than the melting point of the corresponding zinc-aluminum-magnesium alloy.

[0016] This invention also provides a method for producing the above-mentioned hot-dip galvanized aluminum-magnesium high-strength steel sheet, comprising the following steps: smelting, refining, thin slab continuous casting, billet homogenization, rolling, laminar flow cooling, coiling, leveling, pickling, and hot-dip galvanizing.

[0017] (1) Smelting, refining, and thin slab continuous casting: the slab thickness is 65-75mm, and the casting speed is 3.5-4.5m / s;

[0018] (2) Homogenization of billet: The billet temperature entering the furnace is 800-950℃, and the temperature exiting the furnace is 1150-1200℃;

[0019] (3) Rolling: The finishing rolling temperature is 850-900℃; the descaling process is to use high-pressure water descaling before entering the rolling mill, and the inlet and outlet descaling water pressure is 320-370 bar;

[0020] (4) Laminar flow cooling: Select direct rapid cooling or slow cooling followed by rapid cooling according to the target performance requirements; the direct rapid cooling means that the strip is directly and rapidly cooled to the target coiling temperature after leaving the rolling mill, with a cooling rate of ≥60℃ / s; the slow cooling followed by rapid cooling means that the strip is not cooled with cooling water after leaving the rolling mill, only air cooling is used, the time does not exceed 4s, and then it is rapidly cooled to the target coiling temperature, with a cooling rate of ≥60℃ / s.

[0021] (5) Winding: The winding temperature is 400-450℃;

[0022] (6) Leveling: Rolling force is controlled at 180-220 tons;

[0023] (7) Pickling: The acid temperature is controlled at 82-92℃, and the thickness of the strip obtained after pickling is 1.0-3.0mm;

[0024] (8) Hot-dip galvanizing: The strip steel is heated to 550-650°C at a heating rate of 5-20°C / s, and then cooled to a temperature 15-25°C higher than the temperature of the galvanizing solution at a rate greater than 20°C / s. Then, it is hot-dip galvanized aluminum-magnesium in a zinc pot. After exiting the zinc pot, the cooling method is first air cooling and then water cooling. The average cooling rate before solidification is greater than 20°C / s. The temperature of the galvanizing solution is 45-55°C higher than the melting point of the zinc-aluminum-magnesium alloy of the corresponding composition.

[0025] The composition design of the substrate of this invention is based on: (1) a phase transformation strengthening mechanism, a bainitic matrix, retained austenite, and little or no ferrite. (2) low cost, without introducing elements such as Nb and Ti. The content of the main alloying elements is controlled as follows:

[0026] The role of carbon (C): Solid solution of C increases the strength of the material; C enrichment in retained austenite lowers the martensitic transformation initiation point and increases the amount and stability of retained austenite. This invention controls the C content to 0.16%–0.20%. Excessive C content significantly reduces the material's plasticity, negatively impacting formability and weldability; conversely, too low a C content leads to insufficient strength and prevents the formation of sufficient retained austenite, resulting in a weak transformation-induced plasticity effect.

[0027] The role of Si: Si is a non-carbide-forming element. During cooling, Si can inhibit carbide formation and delay pearlite formation. In the isothermal transformation region of bainite, Si inhibits carbide nucleation, which is beneficial for the formation of carbon-rich austenite. This invention controls the Si content to be between 0.9% and 1.2%. Excessive Si content will reduce the plasticity of the material and increase the defect rate in steelmaking, continuous casting, and hot rolling processes; excessively low Si content will lead to the formation of pearlite during cooling, consuming the carbon used to form stable retained austenite.

[0028] The role of manganese (Mn): Mn can lower the martensitic transformation initiation temperature and improve the stability of retained austenite. Mn plays a solid solution strengthening role in steel, and its adverse effects on plasticity and toughness are relatively small. This invention controls the Mn content at 2.0%–2.6%. Excessively high Mn content is detrimental to weldability; excessively low Mn content leads to low strength and is also unfavorable for the formation of retained austenite.

[0029] The design concept of this invention regarding the chemical composition of the zinc-aluminum-magnesium alloy coating is as follows:

[0030] Al: Increasing Al content helps improve the corrosion resistance of the coating, but when the Al content is too high, the corrosion resistance tends to saturate. In addition, the melting point of the plating solution increases with increasing Al content, and the higher plating solution temperature promotes the formation of zinc ash and zinc dross. Zinc ash and zinc dross adhere to the steel substrate or the coating surface, causing surface defects such as zinc dross, zinc ash, and exposed iron on the coated steel sheet. Therefore, the Al content in the coating of this invention is controlled at 9.0% to 26.0%.

[0031] Mg: The corrosion resistance of the coating increases with increasing Mg content. Mg mainly forms the brittle compound phase MgZn2 in the coating structure. When the Mg content is greater than 4%, the volume percentage of the MgZn2 phase in the coating exceeds 20%, which is detrimental to the coating's formability. However, the increase in Al content leads to the formation of a large amount of highly ductile (Al) phase during solidification, which can mitigate the adverse effects of the MgZn2 phase. Therefore, to balance the high corrosion resistance and formability of hot-dip galvanized aluminum-magnesium high-strength steel sheets, the Mg content in the coating can be appropriately increased while increasing the Al content. Due to the easy oxidation of Mg, excessively high Mg content leads to excessive slag, which is detrimental to the surface quality of the coated steel sheet. Excessive MgZn2 also hinders the coating's formability. Therefore, the Mg content in the coating of this invention is controlled at 5.0%–8.0%.

[0032] Si: At high temperatures, the reaction between Al in the plating bath and Fe in the substrate is intense. Si promotes the formation of the Fe-Al reaction layer at the interface between the steel substrate and the coating, reducing the corrosion of the steel substrate by the plating bath and providing adhesion between the coating and the steel substrate. In this invention, the Si content in the coating is controlled at 0.04% to 0.8%. This is because excessive Si will produce a large amount of scum, affecting the surface quality of the coated steel sheet; and due to the intense reaction between Al and Fe, excessively low Si content will also fail to suppress the corrosion of the steel substrate by the high Al content of the plating bath.

[0033] The key process design of this invention in the production of hot-dip galvanized aluminum-magnesium high-strength steel sheets is as follows:

[0034] Final rolling temperature: To ensure that the strip microstructure is fully austenitized before cooling, the final rolling temperature is set at 850–900℃ to avoid the formation of excessive ferrite in the two-phase region, which would significantly reduce the material's strength. Excessively high final rolling temperatures require higher furnace exit temperatures from previous processes, but this promotes oxide formation on the slab surface.

[0035] Laminar flow cooling: Different laminar flow cooling processes are employed to address varying strength and elongation requirements of the product. For products aiming for high strength, the strip is directly water-cooled to the target coiling temperature after exiting the rolling mill, with a cooling rate greater than 60°C / s. The microstructure consists of bainite and a small amount of retained austenite, with no ferrite. For products aiming for high plasticity, the strip is first air-cooled to the ferrite-austenite two-phase region and then water-cooled to the bainite formation temperature, with a water cooling rate greater than 60°C / s. The microstructure consists of bainite and a small amount of retained austenite and ferrite. Air cooling should not exceed 4 seconds to introduce a small amount of ferrite to improve the material's plasticity. Excessive air cooling time will lead to the formation of excessive ferrite, significantly reducing the material's strength.

[0036] Winding temperature: The winding temperature should be within the bainite formation temperature range. Too low a winding temperature will result in a martensitic matrix, significantly reducing the material's plasticity; too high a winding temperature will reduce the material's strength. This invention sets the winding temperature to 400–450°C.

[0037] Final microstructure: The matrix of the substrate metallographic structure is bainite, with a retained austenite volume percentage of 3%–5% and a ferrite volume percentage of 0–10%. Bainite mainly provides the strength of the material, while its plasticity is better than that of martensite; the transformation-induced plasticity effect of the retained austenite provides both strength and plasticity during material deformation; depending on the target requirements, a small amount of ferrite can further enhance plasticity.

[0038] Compared with existing technologies, the beneficial effects of this invention are:

[0039] (1) This invention provides a hot-dip galvanized aluminum-magnesium high-strength steel sheet with high strength and excellent corrosion resistance. Its yield strength is 460–580 MPa, tensile strength is 780–900 MPa, and elongation is above 17%. Compared to traditional zinc-aluminum-magnesium coatings with less than 11% Al and less than 3% Mg content, this invention increases the Al and Mg content to achieve superior corrosion resistance in the resulting steel sheet, meeting the material requirements of industries such as construction and photovoltaic brackets in harsh environments.

[0040] (2) The present invention provides a production method for hot-dip galvanized aluminum-magnesium high-strength steel plate. The production process adopts CSP process to manufacture hot-rolled coils and pickled hot-dip galvanized aluminum-magnesium. The CSP process is simple and efficient and can directly roll thin steel plates without cold rolling. This production method introduces a small amount of ferrite by controlling laminar flow cooling, thereby adjusting the strength and elongation of the steel plate material to meet different material requirements. Attached Figure Description

[0041] Figure 1 This is a photograph of the surface microstructure of the coating on the steel sample obtained in Example 1.

[0042] Figure 2 Photographs and energy dispersive spectroscopy analysis of the Al-Fe reaction layer between the coating and the substrate of the steel sample obtained in Example 1.

[0043] Figure 3 This is a photograph of the Si-containing granular phase on the Al-Fe reaction layer between the coating and the substrate of the steel sample obtained in Example 1. Detailed Implementation

[0044] The technical solution of the present invention will be described in full and clear below with reference to the embodiments. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0045] A hot-dip galvanized aluminum-magnesium high-strength steel sheet, comprising a substrate and a zinc-aluminum-magnesium alloy coating, wherein the chemical composition of the substrate, by mass percentage, is: C 0.16%–0.20%, Si 0.9%–1.2%, Mn 2.0%–2.6%, Al 0.02%–0.06%, P ≤ 0.025%, S ≤ 0.01%, with the balance being Fe and unavoidable impurities; and the chemical composition of the zinc-aluminum-magnesium alloy coating, by mass percentage, is: Al 9.0%–26.0%, Mg 5.0%–8.0%, Si 0.04%–0.8%, with the balance being Zn and unavoidable impurities.

[0046] The above-mentioned production method of hot-dip galvanized aluminum-magnesium high-strength steel sheet includes the following steps: smelting, refining, continuous casting of thin slabs, homogenization of cast slabs, rolling, laminar flow cooling, coiling, leveling, pickling, and hot-dip galvanizing.

[0047] (1) Smelting, refining, and thin slab continuous casting: the slab thickness is 65-75mm, and the casting speed is 3.5-4.5m / s;

[0048] (2) Homogenization of billet: The billet temperature entering the furnace is 800-950℃, and the temperature exiting the furnace is 1150-1200℃;

[0049] (3) Rolling: The descaling process is to use high-pressure water descaling before entering the rolling mill. The inlet and outlet descaling water pressure is 320-370 bar; the finishing rolling temperature is 850-900℃.

[0050] (4) Laminar flow cooling: Select direct rapid cooling or slow cooling followed by rapid cooling according to the target performance requirements; direct rapid cooling means that the strip is directly and rapidly cooled to the target coiling temperature after leaving the rolling mill, with a cooling rate of ≥60℃ / s; slow cooling followed by rapid cooling means that the strip is not cooled by cooling water after leaving the rolling mill, only air cooling is used, the time does not exceed 4s, and then it is rapidly cooled to the target coiling temperature, with a cooling rate of ≥60℃ / s;

[0051] (5) Winding: The winding temperature is 400-450℃;

[0052] (6) Leveling: Rolling force is controlled at 180-220 tons;

[0053] (7) Pickling: The acid temperature is controlled at 82-92℃, and the thickness of the strip obtained after pickling is 1.0-3.0mm;

[0054] (8) Hot-dip galvanizing: The strip steel is heated in the furnace at a temperature of 550-650℃ and the heating rate is 5-20℃ / s. Then the strip steel is cooled to a temperature 15-25℃ higher than the galvanizing solution temperature at a rate greater than 20℃ / s. Then it is hot-dip galvanized aluminum-magnesium alloy in a zinc pot. After exiting the zinc pot, the cooling method is first air cooling and then water cooling. The average cooling rate before solidification is greater than 20℃ / s. The galvanizing solution temperature is 45-55℃ higher than the melting point of the corresponding zinc-aluminum-magnesium alloy.

[0055] A batch of steel plates was prepared according to the above-mentioned design and production method for the substrate, zinc-aluminum-magnesium coating, and other components of a hot-dip galvanized aluminum-magnesium high-strength steel plate. All steel plate samples were subjected to relevant performance tests. The specific chemical composition of the substrate is shown in Table 1, the specific chemical composition of the zinc-aluminum-magnesium plating solution is shown in Table 2, some key parameters of the production method are shown in Table 3, and the relevant performance data of the obtained steel plates are shown in Table 4. The coating weight of the experimental sample was 120 g / m² on one side. 2The neutral salt spray test for surface red rust resistance follows standard ASTM B117, using a 5% NaCl solution at a temperature of 35±2℃ until red rust appears. The time from the start of the test to the appearance of red rust is defined as the surface red rust resistance time. The CCT cyclic corrosion test follows standard JASO M609-91, with the following test conditions: one cycle is 8 hours, including 2 hours of salt spray using a 5% NaCl solution at 35℃; followed by 4 hours of drying at 60℃ with a relative humidity of 20%–30%; and then 2 hours of wetting at 50℃ with a relative humidity of 95%. This cycle is repeated until red rust appears, and the time from the start of the test to the appearance of red rust is defined as the CCT surface red rust resistance cycle.

[0056] Table 1. Chemical composition (wt.%) of substrates used in the examples and comparative examples

[0057] serial number category C Si Mn Als P S A Example 0.18 1.2 2.2 0.025 0.008 0.005 B Example 0.16 1.0 2.0 0.024 0.010 0.007 C Example 0.20 0.9 2.6 0.034 0.015 0.007 D Comparative Example <![CDATA[ 0.10 ]]> 1.1 2.3 0.027 0.009 0.009

[0058] Table 2 Chemical composition (wt.%) of coatings in the examples and comparative examples

[0059]

[0060] Table 3. Process parameters of the production methods in the examples and comparative examples.

[0061]

[0062] Table 4 Performance data of steel plates obtained in the examples and comparative examples

[0063]

[0064] Note: √: Good surface finish after plating; ×: Poor surface finish after plating, with obvious exposed iron, zinc dross, zinc ash, or other defects; / : Not tested.

[0065] Figure 1 This is a photograph of the surface microstructure of the coating on the steel sample obtained in Example 1. From... Figure 1 It can be seen that the coating structure includes dendritic (Al) phase, blocky MgZn2 phase, blocky (Zn) phase, acicular Mg2Si phase, and multiphase eutectic Al / Zn / MgZn2 structure, which are uniformly distributed in the coating structure. Figure 2 This is a photograph of the Al-Fe reaction layer microstructure between the coating and the substrate of the steel sample obtained in Example 1. From... Figure 2 It can be seen that a reaction layer is formed between the coating and the substrate, and there is adhesion between the coating and the substrate, making the coating difficult to peel off during processing. The energy dispersive spectroscopy (EDS) composition surface analysis results are Al: 31.19%, Fe: 61.46%, Si: 1.23%, Zn: 6.12%, indicating that an Al-Fe reaction layer is formed between the coating and the substrate, and the Si content is much higher than that of the plating solution, with some Si elements enriched at the interface. Figure 3This is a photograph of the Si-containing granular phase on the Al-Fe reaction layer between the coating and the substrate of the steel sample obtained in Example 1. Figure 1-3 It can be seen that Si elements form needle-like Mg2Si phases, are enriched and dissolved in the Al-Fe phase at the coating and interface, and form Si-containing particulate phases on the Al-Fe reaction layer.

[0066] Based on Tables 1-4, comparing Examples 1-8 and Comparative Examples 6 and 7, it can be seen that when the C content in the substrate is too low, the solid solution strengthening effect is insufficient and residual austenite cannot be generated. The yield strength and tensile strength of the sample decrease, that is, the performance of the steel plate material is reduced.

[0067] Comparing Example 1 and Comparative Example 9, it can be seen that when the coiling temperature drops below 400°C, the supercooled austenite forms a structure with martensite as the matrix, the yield strength and tensile strength of the sample increase, but the elongation decreases significantly, and the plasticity of the steel plate material deteriorates.

[0068] Comparing Example 4 and Comparative Example 8, it can be seen that when the air cooling time is 6s, the air cooling time is too long, and excessive ferrite is generated during the cooling process. The yield strength of the sample drops to below 450 MPa and the tensile strength drops to below 780 MPa.

[0069] Examples 1-11 and Comparative Examples 1-5 used different plating solution compositions. It was found that when the Al and Mg content in the plating solution increased, the neutral salt spray surface red rust resistance time and the CCT surface red rust resistance cycle of the samples increased, indicating improved corrosion resistance of the steel plate material. However, when the Al content in the plating solution was too high, the surface quality of the samples deteriorated, as shown in Comparative Example 1; when the Mg content in the plating solution was too high, the surface quality of the samples deteriorated, as shown in Comparative Example 2; and as shown in Examples 10, 11 and Comparative Examples 1, 2, when the Al and Mg content was too high, the decrease in the surface quality of the material also led to a decrease in corrosion resistance; when the Mg and Al content in the plating solution was too low, the corrosion resistance of the samples was low, as shown in Comparative Examples 3-5.

[0070] Compared with Example 1 and Comparative Example 10, when the descaling water pressure is too low, the iron oxide scale on the strip surface cannot be effectively removed, resulting in surface defects such as exposed iron during the galvanizing process, which leads to a decrease in corrosion resistance.

[0071] Compared with Example 1 and Comparative Example 11, when the pickling temperature is too low, the dissolution efficiency of iron oxide scale on the surface of the strip steel is low, and residual iron oxide scale on the surface of the strip steel will produce surface defects such as exposed iron during the galvanizing process, resulting in a decrease in corrosion resistance.

[0072] Compared with Example 1 and Comparative Example 12, when the furnace heating temperature is too high, the high temperature will cause Si and Mn to accumulate on the surface of the strip steel to form oxides, and surface defects such as exposed iron will be formed during the galvanizing process, resulting in a decrease in corrosion resistance.

[0073] Compared with Example 1 and Comparative Example 13, when the plating bath temperature is too high, too much zinc dross and zinc ash will be generated, causing surface defects such as zinc ash and zinc dross on the strip steel surface, resulting in a decrease in corrosion resistance.

[0074] Compared with Example 1 and Comparative Example 14, when the cooling rate after plating is too low, the structure of the coating is uneven, which reduces the formability and corrosion resistance of the material.

[0075] In summary, the present invention provides a hot-dip galvanized aluminum-magnesium high-strength steel sheet. This steel sheet has high strength, with a yield strength of 460-580 MPa, a tensile strength of 780-900 MPa, an elongation of over 17%, and excellent corrosion resistance.

[0076] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing hot-dip galvanized aluminum-magnesium high-strength steel sheet, characterized in that, The process includes forming a substrate using CSP (Chemical Solid Proofing) technology, followed by pickling and then hot-dip galvanizing to form a zinc-aluminum-magnesium alloy coating. The hot-dip galvanizing process involves heating the pickled strip to 550–650°C at a rate of 5–20°C / s, then cooling the strip at a rate greater than 20°C / s to a temperature 15–25°C higher than the bath temperature. The strip is then immersed in a zinc bath for hot-dip zinc-aluminum-magnesium galvanizing. After exiting the zinc bath, the strip is cooled first by air and then by water, with an average cooling rate greater than 20°C / s before solidification. The bath temperature is 45–55°C higher than the melting point of the corresponding zinc-aluminum-magnesium alloy. The chemical composition of the substrate, by mass percentage, is: C 0.16%–0.20%, Si 0.9%–1.2%, Mn 2.0%–2.6%, Al 0.02%–0.06%, P ≤ 0.025%, S ≤ 0.01%, with the balance being Fe and unavoidable impurities; the chemical composition of the zinc-aluminum-magnesium alloy coating, by mass percentage, is: Al 9.0%–14.1%, Mg 5.0%–8.0%, Si 0.04%–0.1%, with the balance being Zn and unavoidable impurities. An Al-Fe compound layer exists between the substrate and the zinc-aluminum-magnesium alloy coating; The coating structure includes dendritic Al phase, blocky MgZn2 phase, blocky Zn phase, acicular Mg2Si phase, and multiphase eutectic Al / Zn / MgZn2 structure, which are uniformly distributed in the coating structure. Si elements form needle-like Mg2Si phases, which are enriched and dissolved in the Al-Fe phase at the coating and interface, as well as forming Si-containing particulate phases on the Al-Fe reaction layer.

2. The method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to claim 1, characterized in that, The substrate has a bainite matrix, a retained austenite volume percentage of 3% to 5%, and a ferrite volume percentage of 0% to 10%.

3. The method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to claim 1, characterized in that, The high-strength steel plate has a yield strength of 460–580 MPa, a tensile strength of 780–900 MPa, and an elongation of ≥17%.

4. The method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to claim 1, characterized in that, The CSP process includes the following steps: smelting, refining, thin slab continuous casting, billet homogenization, rolling, laminar flow cooling, coiling, and leveling; the chemical composition of the plating solution used in the hot-dip galvanizing process, by mass percentage, is: Al 9.0%~14.1%, Mg 5.0%~8.0%, Si 0.04%~0.1%, with the balance being Zn and unavoidable impurities.

5. The method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to claim 4, characterized in that, In the thin slab continuous casting step, the slab thickness is 65-75 mm and the casting speed is 3.5-4.5 m / s; in the slab homogenization step, the slab temperature entering the furnace is 800-950℃ and the temperature exiting the furnace is 1150-1200℃; in the rolling step, the descaling process is high-pressure water descaling before entering the rolling mill, the inlet and outlet descaling water pressure is 320-370 bar, and the finishing rolling temperature is 850-900℃.

6. The method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to claim 4, characterized in that, In the coiling step, the coiling temperature is 400–450℃; in the laminar flow cooling step, direct rapid cooling or slow cooling followed by rapid cooling is selected according to the target performance requirements; among them, direct rapid cooling means that the strip is directly and rapidly cooled to the target coiling temperature after leaving the rolling mill, with a cooling rate ≥60℃ / s; slow cooling followed by rapid cooling means that the strip is not cooled by cooling water after leaving the rolling mill, only air cooling is used, the time does not exceed 4s, and then it is rapidly cooled to the target coiling temperature, with a cooling rate ≥60℃ / s; in the leveling step, the rolling force is controlled at 180–220 tons; in the pickling step, the acid temperature is controlled at 82–92℃, and the thickness of the strip obtained after pickling is 1.0–3.0 mm.

7. A method for producing a hot-dip galvanized aluminum-magnesium high-strength steel sheet according to any one of claims 1 to 6, comprising the steps of smelting, refining, continuous casting of thin slabs, homogenization of cast slabs, rolling, laminar flow cooling, coiling, leveling, pickling, and hot-dip galvanizing, characterized in that: (1) Smelting, refining, and thin slab continuous casting: the slab thickness is 65-75 mm, and the casting speed is 3.5-4.5 m / s; (2) Homogenization of billet: The billet temperature entering the furnace is 800-950℃, and the temperature exiting the furnace is 1150-1200℃; (3) Rolling: The finishing rolling temperature is 850-900℃; the descaling process is to use high-pressure water descaling before entering the rolling mill, and the inlet and outlet descaling water pressure is 320-370 bar; (4) Laminar flow cooling: direct rapid cooling or slow cooling followed by rapid cooling; the direct rapid cooling means that the strip is directly and rapidly cooled to the target coiling temperature after leaving the rolling mill, with a cooling rate of ≥60℃ / s; the slow cooling followed by rapid cooling means that the strip is not cooled by cooling water after leaving the rolling mill, only air cooling is used, the time is not more than 4s, and then it is rapidly cooled to the target coiling temperature, with a cooling rate of ≥60℃ / s. (5) Winding: The winding temperature is 400-450℃; (6) Leveling: Rolling force is controlled at 180~220 tons; (7) Pickling: The acid temperature is controlled at 82-92℃, and the thickness of the strip obtained after pickling is 1.0-3.0mm; (8) Hot-dip galvanizing: The strip steel is heated to 550-650°C at a heating rate of 5-20°C / s, and then cooled to a temperature 15-25°C higher than the temperature of the galvanizing solution at a rate greater than 20°C / s. Then it is hot-dip galvanized aluminum-magnesium in a zinc pot. After exiting the zinc pot, the cooling method is first air cooling and then water cooling. The average cooling rate before solidification is greater than 20°C / s. The temperature of the galvanizing solution is 45-55°C higher than the melting point of the zinc-aluminum-magnesium alloy of the corresponding composition.

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