A zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology, its preparation method and application

Abstract

The present invention discloses a zinc-aluminum-magnesium coated steel sheet based on hot-dip plating and hot-forming technology, and its preparation method and application. The steel sheet is obtained by hot-dip plating and austenitizing and stamping under high-temperature conditions. The dipping solution for hot-dip plating is a Zn-Al-Mg dipping solution, and its composition is located in the zinc-rich corner of the Zn-Al-Mg ternary phase diagram, and the mass percentage meets the following requirements: the Zn content is 85-95 wt.%, the Al content is 4.5-8.5 wt.%, and the Mg content is 1-4.5 wt.%. After hot-dip plating, the steel sheet becomes a zinc-aluminum-magnesium coated steel sheet, which is composed of a steel sheet, a zinc-aluminum-magnesium coating-2, and an intermediate compound layer. Among them, the zinc-aluminum-magnesium coating contains Zn, Al, and MgZn2 phases; the zinc-aluminum-magnesium coating contains a Zn-Al two-phase eutectic and a Zn-Al-MgZn2 three-phase eutectic; the intermediate compound layer is an Fe-Al or Fe-Al-Zn intermetallic compound. After austenitizing, the zinc-aluminum-magnesium coated steel sheet becomes a steel sheet to be stamped, which is composed of a steel sheet and a zinc-aluminum-magnesium coating-3. The zinc-aluminum-magnesium coating-3 contains an α-Fe(Zn,Al) phase. As a corrosion-resistant material, the corrosion current density I corr is (1.20-1.68)×10 ‑5 A / cm 2 ; as a high-temperature mechanical material, the elongation is 38-54%.

Description

Technical Field

[0001] The present invention relates to coated steel for automobiles, and particularly to a zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technologies, and its preparation method and application. Technical Background

[0002] During the hot stamping process of steel sheet hot-dip plating technology, it has the advantages of preventing oxidation and decarburization of the steel sheet surface. The coatings used mainly include Al-Si coatings, pure Zn coatings, Zn-based alloy coatings, etc. Among them, the most widely used at present is the Al-Si coating, which can effectively prevent oxidation and decarburization of the steel sheet surface. However, such coatings have problems of poor corrosion resistance at cut edges and perforations; compared with the Al-Si coating, the Zn-based coating not only has the function of preventing oxidation and decarburization of the steel sheet surface, but also has the function of cathodic protection, that is, excellent perforation corrosion resistance and cut edge corrosion resistance. However, at present, there are technical problems of crack generation and propagation to the substrate during the hot stamping process of the Zn-based coating. This technical problem directly limits the application of the Zn-based coating in the field of automobile manufacturing.

[0003] According to the existing literature 1 (Li Xuetao, Zhang Jie, Jiang Sheming, etc. Crack generation and propagation during the forming process of galvanized hot stamping steel plates [J]. Heat Treatment of Metals, 2019, 44(03): 202-6.), the reason for the crack generation during the deformation of the pure zinc coating hot stamping steel is that there is a large amount of Zn element enrichment in the pure zinc coating. Under the combined action of high temperature and external stress, liquid zinc diffuses along the austenite grain boundary and continuously generates α-Fe(Zn) with the substrate, and the crack continuously propagates along the α-Fe(Zn) and liquid phase interface, resulting in brittle fracture of the substrate.

[0004] Based on the above reasons, a method of adding alloying elements such as Al and Ni to the pure zinc plating solution can be used to generate alloy inhibition layers such as Fe2Al5 at the coating-substrate interface, so as to keep the enriched liquid zinc element away from the substrate and inhibit the diffusion of zinc element to the substrate.

[0005] However, in the existing literature 2 (Cui Qingling, Li Jianping, Li Shiyu, etc. Microstructure evolution and crack formation during heating of Zn-based coatings on 22MnB5 steel [J]. Journal of Iron and Steel Research, 2019, 31(02): 227-32.), during the austenitization process, all the Al elements in the Fe2Al5 alloy inhibition layer of the GI coating plate migrate to the coating surface, and the Fe2Al5 alloy layer disappears, and the inhibition effect fails. A large amount of locally enriched zinc elements in the coating diffuse to the substrate, resulting in brittle fracture of the substrate.

[0006] To solve the above problems, the existing literature 3 (Ultra-high strength zinc-aluminum-magnesium coated steel sheet for hot forming and its manufacturing method, CN107099748B[P].2019) discloses an ultra-high strength zinc-aluminum-magnesium coated steel sheet for hot forming and its manufacturing method. Before hot forming, the coating includes three microstructures: Zn / Al eutectic microstructure, Zn / Al / Zn2Mg ternary eutectic microstructure, and pure Zn particles. However, this technology still has the following problems: it is difficult to control the content of the Zn / Al / Zn2Mg ternary eutectic microstructure in the coating alloy and the enrichment of zinc element, and it is difficult to inhibit the high-temperature reaction between the locally enriched zinc element and the steel substrate, resulting in high-temperature cracking of the hot-dip galvanized steel sheet. Summary of the Invention

[0007] The object of the present invention is to provide a zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technologies and its preparation method. Aiming at the high-temperature cracking problem caused by the uneven micro-distribution of the coating composition mentioned in the background technology, a fully eutectic microstructure is formed by regulating the coating solution composition and the hot-dip plating process to improve the micro-segregation of the coating composition and the local enrichment phenomenon of Zn element; the austenitization process parameters and the hot stamping process parameters are regulated to inhibit the high-temperature cracking of the hot-dip galvanized steel sheet; at the same time, the low-potential phase MgZn2 generated by the reaction of the added Mg element and the Zn element when regulating the coating solution composition can greatly improve the corrosion resistance of the coating.

[0008] The specific technical solution of the present invention is as follows:

[0009] The present invention provides a zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technologies, which is obtained by hot-dip plating and austenitization of the steel sheet under high-temperature conditions;

[0010] The immersion solution for the hot-dip plating is a Zn-Al-Mg immersion solution, and specifically, the mass percentages of the components of the Zn-Al-Mg immersion solution satisfy: the Zn content is 85-95 wt.%, the Al content is 4.5-8.5 wt.%, and the Mg content is 1-4.5 wt.%;

[0011] After the hot-dip plating of the steel sheet, it becomes a zinc-aluminum-magnesium coated steel sheet based on the hot-dip plating technology. The zinc-aluminum-magnesium coated steel sheet based on the hot-dip plating technology is composed of a steel sheet, a zinc-aluminum-magnesium coating-2, and an intermediate compound layer between the steel sheet and the coating. Among them,

[0012] The zinc-aluminum-magnesium coating-2 contains Zn, Al, and MgZn2 phases; the zinc-aluminum-magnesium coating-2 contains Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic;

[0013] In the Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic of the zinc-aluminum-magnesium coating-2, the total eutectic content of the Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic is 50-95%, the Zn element exists in the form of Zn phase and MgZn2 phase, and the lamellar spacing of the eutectic structure is less than 1 micron;

[0014] The intermediate compound layer between the steel plate and the coating, hereinafter referred to as the intermediate compound layer, is a Fe-Al or Fe-Al-Zn intermetallic compound;

[0015] The thickness of the intermediate compound layer is 0.3-3 microns;

[0016] The zinc-aluminum-magnesium coated steel plate based on the hot-dip coating technology becomes a zinc-aluminum-magnesium coated steel plate to be stamped based on the hot-dip coating and high-temperature austenitization technologies after being austenitized at 900-920 °C,

[0017] The zinc-aluminum-magnesium coated steel plate to be stamped based on the hot-dip coating and high-temperature austenitization technologies is composed of a steel plate and a zinc-aluminum-magnesium coating-3. The zinc-aluminum-magnesium coating-3 is composed of a single-layer α-Fe(Zn,Al) structure. In the single-layer α-Fe(Zn,Al) structure, Fe, Zn, Al, and Mg elements are evenly distributed. The Zn element content is 3.5-10.3 wt.%, the Al element content is 0.5-12.2 wt.%, the Mg element is 0-0.2 wt.%, and the O element is 0.5-8.2 wt.%.

[0018] Furthermore, in the above technical solution, the mass percentages of the components of the steel plate are as follows: the C content is 0.31-0.35 wt.%, the Si content is 0.05-0.20 wt.%, the Mn content is 1.40-1.50 wt.%, the P content does not exceed 0.020 wt.%, the S content does not exceed 0.004 wt.%, the Al content is not less than 0.060 wt.%, the Ti content is 0.010-0.025 wt.%, the V content is 0.16-0.20 wt.%, the N content does not exceed 0.0045 wt.%, the B content is 0.0010-0.0030 wt.%, and the rest are Fe and unavoidable impurities;

[0019] Furthermore, in the above technical solution, in the Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic of the zinc-aluminum-magnesium coating-2, the Zn element exists in the form of Zn phase and MgZn2 phase, and the Al element exists in the form of Al phase; the lamellar spacing of the structure is less than 1 micron.

[0020] Furthermore, in the above technical solution, the thickness of the intermediate compound layer is 0.3-3 microns.

[0021] Further, in the above technical solution, the Zn content in the immersion plating solution is 85-95 wt.%; the composition of the Zn-Al-Mg immersion plating solution is located at the zinc-rich corner of the Zn-Al-Mg ternary phase diagram.

[0022] The present invention provides a method for preparing a zinc-aluminum-magnesium coated steel sheet to be stamped based on hot dip plating and high-temperature austenitization techniques, comprising the following steps:

[0023] Step 1, preparation of the steel sheet to be hot dip plated;

[0024] Step 2, hot dip plating of the steel sheet to be hot dip plated. First, prepare the immersion plating solution, and then, under certain conditions, perform hot dip plating on the steel sheet to be hot dip plated obtained in Step 1, thereby obtaining a zinc-aluminum-magnesium coated steel sheet based on the hot dip plating technique, named Sample 1-2;

[0025] In Step 2, the mass percentages of the immersion plating solution are as follows: the Al content is 4.5-8.5 wt.%, the Mg content is 1-4.5 wt.%, and the balance is Zn and inevitable impurities;

[0026] In Step 2, the conditions for hot dip plating are as follows: the dip plating temperature is 440-460 °C, the dip plating time is 3-10 seconds, and the cooling rate after dip plating is greater than 30 °C / s until cooled to room temperature;

[0027] Step 3, austenitization of the zinc-aluminum-magnesium coated steel sheet based on the hot dip plating technique. Austenitize the Sample 1-2 obtained in Step 2 under certain conditions, thereby obtaining a zinc-aluminum-magnesium coated steel sheet to be stamped based on the hot dip plating and high-temperature austenitization techniques, named Sample 1-3;

[0028] In Step 3, the conditions for austenitization are as follows: the austenitization temperature is 900-920 °C, and the holding time is 1-3 min;

[0029] The present invention provides a stamping and forming method for the above zinc-aluminum-magnesium coated steel sheet to be stamped based on the hot dip plating and high-temperature austenitization techniques. After the Sample 1-3 obtained in Step 3 is completed in austenitization, immediately perform stamping and forming and quickly cool to room temperature, thereby obtaining a zinc-aluminum-magnesium coated steel sheet based on the hot dip plating and high-temperature forming techniques.

[0030] Further, in the above technical solution, in Step (1), after heating the steel to be treated into molten iron, through molten iron pretreatment, converter smelting, secondary refining, and continuous casting, a steel billet is obtained. Then, heat the steel billet, roll it, control cooling, coil it, pickling, cold rolling, thereby obtaining a steel sheet. Finally, perform continuous annealing on the steel sheet under the conditions of an annealing temperature of 800 ± 5 °C and a dew point of -50 ± 10 °C, thereby obtaining the steel sheet to be hot dip plated.

[0031] The present invention provides an application of the above zinc-aluminum-magnesium coated steel sheet based on hot-dip plating technology as a corrosion-resistant material. In a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density I corr is (1.20 - 1.68)×10 -5 A / cm 2 .

[0032] The present invention provides an application of the above zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology as a high-temperature mechanical material. The elongation at 920 °C for 1 - 3 min is 38 - 54%.

[0033] The technical effects of the present invention are tested as follows:

[0034] The cross-section SEM and EDS tests of the above zinc-aluminum-magnesium coated steel sheet based on hot-dip plating technology show that the coating contains Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic; the total eutectic content of Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic is 50 - 95%, Zn element exists in the form of Zn phase and MgZn2 phase, and the lamellar spacing of the structure is less than 1 micron. The intermediate compound layer between the steel sheet and the coating contains Fe-Al or Fe-Al-Zn intermetallic compounds, and the thickness is 0.3 - 3 microns.

[0035] The corrosion resistance test of the above zinc-aluminum-magnesium coated steel sheet based on hot-dip plating technology shows that in a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density (I corr ) is (1.20 - 1.68)×10 -5 A / cm 2 .

[0036] The cross-section SEM and EDS tests of the above zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology show that the coating contains α-Fe(Zn,Al), and the elements Fe, Zn, Al, and Mg are evenly distributed in the α-Fe(Zn,Al) single-layer structure.

[0037] The high-temperature tensile mechanical property test of the above zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology shows that under the conditions of a temperature of 920 °C and a holding time of 1 - 3 min, the elongation is 38 - 54%.

[0038] Therefore, it can be seen from the above experimental tests that the present invention has the following advantages:

[0039] 1. Compared with the prior art, the zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology of the present invention has higher high-temperature tensile mechanical properties, that is, at a temperature of 920 °C and a holding time of 1 - 3 min, the tensile strength is 77.2 MPa and the elongation is 46.6%. Compared with the coated plate with pure zinc plating solution in Comparative Ratio 1, under the same temperature and holding time, the elongation increases by 7.4%;

[0040] 2. Compared with the prior art, the zinc-aluminum-magnesium coated steel sheet based on hot-dip plating technology of the present invention has higher corrosion resistance, that is, in a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density (I corr ) is 1.35×10 -5 A / cm 2 . Compared with the coated plate with pure zinc plating solution in Comparative Ratio 1, in the same temperature and test solution, the corrosion current density decreases by 0.5×10 -5 A / cm 2 .

[0041] 3. The zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technology designed and prepared by the present invention does not use rare earth elements, which reduces the raw material cost compared with the existing rare earth-containing coating technology and is easy to be commercially promoted. Description of the Drawings

[0042] Figure 1 It is for calculating the distribution of the plating solution components in the liquid phase projection diagram of the Zn-Al-Mg alloy of the present invention. Among them, Figure 1 a is the distribution position of the Zn-4.5Al-3.0Mg alloy in the phase diagram in Example 1 and Comparative Ratio 2; Figure 1 b is the distribution position of pure Zn in the phase diagram in Comparative Ratio 1; Figure 1 c is the distribution position of the Zn-4.5Al-1.1Mg alloy in the phase diagram in Example 2; Figure 1 d is the distribution position of the Zn-6.0Al-3.6Mg alloy in the phase diagram in Example 3; Figure 1 e is the distribution position of the Zn-8.5Al-4.2Mg alloy in the phase diagram in Example 4;

[0043] Figure 2 It is the cross-sectional SEM images of the samples 1-2, 0-2, 2-2, 3-2, 4-2 prepared in Example 1, Comparative Ratio 2, Comparative Ratio 1, Example 2 - 4 of the present invention;

[0044] Figure 3 It is the potentiodynamic polarization curve images of the samples 1-2, 0-2, 2-2, 3-2, 4-2 prepared in Example 1, Comparative Ratio 2, Comparative Ratio 1, Example 2 - 4 of the present invention in a 3.5 wt.% NaCl solution at 25 °C;

[0045] Figure 4 These are the cross-sectional SEM images of Samples 1-3, 0-3, 0-3', 2-3, 3-3, and 4-3 prepared in Example 1, Comparative Ratio 1-2, and Example 2-4 of the present invention.

[0046] Figure 5 These are the stress-strain curve images of Samples 1-3, 0-3, 2-3, 3-3, and 4-3 prepared in Example 1, Comparative Ratio 1, and Example 2-4 of the present invention under the conditions of a temperature of 920°C and a holding time of 1-3 minutes. Detailed implementation manners

[0047] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it is not a limitation of the present invention.

[0048] By experimentally determining the primary phases and phase contents of alloys with different compositions, a liquidus projection plane diagram of the Zn-Al-Mg system was constructed. Based on the phase compositions, the phase equilibrium relationship of the Zn-Al-Mg system was established, and some relevant data in the liquidus projection phase diagram database of the Zn-Al-Mg system were disclosed in this invention to obtain the phase types and volume fractions in the Zn-Al-Mg alloy.

[0049] Then, based on the constructed thermodynamic phase diagram database of the Zn-Al-Mg system, the alloys corresponding to Examples 1-4 and Comparative Ratio 1-2 as shown in Figure 1 were obtained by thermodynamic calculation, and the results are shown in Table 1.

[0050] Table 1 Composition table of Zn-Al-Mg coating alloys

[0051]

[0052] For the convenience of description, the naming principle of the samples in the embodiments of the present invention is described. The specific naming principle is: Sample a-b, where a represents the serial number of the example, and b represents the product of the specific step in each example. If it is the product obtained in Step 2 of Example 1, it is named: Sample 1-2; if it is the product obtained in Step 3 of Example 2, it is named Sample 2-3.

[0053] Example 1:

[0054] A method for preparing a zinc-aluminum-magnesium coated steel sheet to be stamped based on hot-dip plating and high-temperature austenitization technologies, that is, a method for preparing a zinc-aluminum-magnesium coated steel sheet with a plating solution composition of Zn-4.5Al-3.0Mg, specifically including the following steps:

[0055] Step 1, Preparation of the steel sheet to be hot-dip galvanized: After heating the steel to be processed into molten iron, through molten iron pretreatment, converter smelting, secondary refining, and continuous casting, a steel billet is obtained. Then, the steel billet is heated, rolled, controlled cooled, coiled, pickled, and cold rolled to obtain a steel sheet. Finally, the steel sheet is continuously annealed under the conditions of an annealing temperature of 800 ± 5 °C and a dew point of -50 ± 10 °C to obtain the steel sheet to be hot-dip galvanized;

[0056] To confirm the composition of the steel sheet to be hot-dip galvanized, ICP testing was carried out. The test results show that the mass percentages of the steel sheet composition are as follows: the C content is 0.33 wt.%, the Si content is 0.10 wt.%, the Mn content is 1.45 wt.%, the P content does not exceed 0.020 wt.%, the S content does not exceed 0.004 wt.%, the Al content is 0.080 wt.%, the Ti content is 0.02 wt.%, the V content is 0.18 wt.%, the N content does not exceed 0.0040 wt.%, the B content is 0.0020 wt.%, and the rest are Fe and inevitable impurities.

[0057] Step 2, Hot-dip galvanizing of the steel sheet to be hot-dip galvanized: First, prepare the galvanizing solution with a mass percentage of: Al content of 4.5 wt.%, Mg content of 3.0 wt.%, and the rest being Zn and inevitable impurities. Then, under the conditions of a dipping temperature of 440 - 460 °C, a dipping time of 3 - 10 seconds, and a cooling rate after dipping greater than 30 °C / s to room temperature, the steel sheet to be hot-dip galvanized obtained in Step 1 is hot-dip galvanized to obtain a zinc-aluminum-magnesium coated steel sheet based on hot-dip galvanizing technology, named Sample 1-2;

[0058] To prove the phase types and microstructures of the zinc-aluminum-magnesium coating in Sample 1-2 obtained in Step 2, SEM testing and EDS testing were carried out on the cross-section of Sample 1-2. The test results are as Figure 2 shown. Sample 1-2 consists of a steel sheet, a zinc-aluminum-magnesium coating-2, and an intermediate compound layer between the steel sheet and the coating; among them,

[0059] The zinc-aluminum-magnesium coating-2 is composed of a Zn-Al two-phase eutectic and a Zn-Al-MgZn2 three-phase eutectic; the total eutectic content of the Zn-Al two-phase eutectic and the Zn-Al-MgZn2 three-phase eutectic is 95%. The Zn element exists in the forms of Zn phase and MgZn2 phase, and the lamellar spacing of the structure is less than 1 micron;

[0060] The intermediate compound layer is a Fe-Al or Fe-Al-Zn intermetallic compound with a thickness of 0.3 - 1 micron.

[0061] The test results show that the structure in the coating of Sample 1-2 is uniform and there is no local zinc enrichment phenomenon.

[0062] To prove the corrosion resistance of Sample 1-2, a corrosion resistance test was conducted. The test results are as Figure 3 shown. In a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density (I corr ) is 1.35×10 -5 A / cm 2 . The test results show that through the hot dip plating in Step 2, the formed Zn-Al-MgZn2 three-phase eutectic can improve the corrosion resistance of the zinc-aluminum-magnesium coated steel sheet.

[0063] Step 3: Preparation of the zinc-aluminum-magnesium coated steel sheet to be stamped based on hot dip plating and high-temperature austenitization technology. The sample 1-2 obtained in Step 2 was austenitized at an austenitization temperature of 920 °C for a holding time of 3 min, and thus the zinc-aluminum-magnesium coated steel sheet to be stamped based on hot dip plating and high-temperature austenitization technology was obtained, named Sample 1-3;

[0064] To prove the phase types and microstructural morphologies of the zinc-aluminum-magnesium coating in Sample 1-3 obtained in Step 3, SEM test and EDS test were carried out on the cross-section of Sample 1-3. The test results are as Figure 4 shown. Sample 1-3 consists of a steel sheet and a zinc-aluminum-magnesium coating-3. Among them, the intermediate compound layer between the steel sheet and the zinc-aluminum-magnesium coating-2 disappears; the zinc-aluminum-magnesium coating-3 is composed of a single-layer α-Fe(Zn,Al) structure, and the elements Fe, Zn, Al, and Mg are evenly distributed in the single-layer α-Fe(Zn,Al) structure. The content of Zn element is 4.6 - 8.1 wt.%, the content of Al element is 0.7 - 1.2 wt.%, Mg is 0 - 0.1 wt.%, and O is 0.9 - 8.2 wt.%. The test results show that through the austenitization in Step 3, the coating structure changes from a Zn-Al two-phase eutectic and a Zn-Al-MgZn2 three-phase eutectic to α-Fe(Zn,Al).

[0065] To prove the mechanical properties of Sample 1-3 under high-temperature conditions, a high-temperature tensile mechanical property test was conducted. The test results are as Figure 5 shown. Under the conditions of a temperature of 920 °C and a holding time of 3 min, the tensile strength of Sample 1-3 is 77.2 MPa, and the elongation is 46.6%. The test results show that through the austenitization in Step 3, the high-temperature mechanical properties of the zinc-aluminum-magnesium coated steel sheet to be stamped based on hot dip plating and high-temperature austenitization technology are improved.

[0066] Step 4: Stamping forming of the zinc-aluminum-magnesium coated steel sheet to be stamped based on hot dip plating and high-temperature austenitization technology. After the sample 1-3 obtained in Step 3 was austenitized, it was immediately stamped and rapidly cooled to room temperature, and thus the zinc-aluminum-magnesium coated steel sheet based on hot dip plating and high-temperature forming technology was obtained.

[0067] In order to prove the influence of Al element and Mg element in the immersion plating solution on the properties of the coated plate, Comparative Ratio 1 is provided. The immersion plating solution of the coated plate is pure zinc, that is, the case where no aluminum element and magnesium element are added to the immersion plating solution.

[0068] Comparative Ratio 1

[0069] A coated plate with an immersion plating solution of pure zinc, the steps not specifically described are the same as those in Example 1, except that: the immersion plating solution in Step 2 is pure zinc, without adding Al and Mg elements; the product obtained in Step 2 is named Sample 0-2, and the product obtained in Step 3 is named Sample 0-3.

[0070] The SEM test and EDS test results of Sample 0-2 are as Figure 2 shown. Sample 0-2 is composed of a steel plate, a coating layer, and an intermediate compound layer between the steel plate and the coating layer; among them,

[0071] the coating layer is composed of a pure Zn phase;

[0072] the intermediate compound layer is a Fe-Zn intermetallic compound with a thickness of 10 microns, and there are many microcracks in the intermediate compound layer.

[0073] The test results show that due to the absence of aluminum element and magnesium element in the immersion plating solution, there is no eutectic structure in the coating layer of Sample 0-2. Compared with Example 1, Example 1 obtains a Zn-Al two-phase eutectic and a Zn-Al-MgZn2 three-phase eutectic through its immersion plating solution.

[0074] The corrosion resistance test results of Sample 0-2 are as Figure 3 shown. In a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density (I corr ) is 1.85×10 -5 A / cm 2 . The test results show that the Zn-Al two-phase eutectic and Zn-Al-MgZn2 three-phase eutectic obtained by Example 1 through its immersion plating solution improve its corrosion resistance.

[0075] The SEM test and EDS test results of Sample 0-3 are as Figure 4 shown. In Sample 0-3, the intermediate compound layer between the steel plate and the coating layer disappears and is composed of a steel plate and a coating layer; among them,

[0076] the coating layer is composed of a single-layer α-Fe(Zn) structure, and there is an enrichment phenomenon of Zn element at the contact with the steel plate in the single-layer α-Fe(Zn) structure.

[0077] The test results show that through the austenitization in Step 3, the coating layer structure changes from a pure Zn phase to α-Fe(Zn). Compared with Example 1, liquid zinc contacts the steel plate during the austenitization process.

[0078] The test results of the high-temperature tensile mechanical properties of Samples 0-3 are as follows Figure 5 shown. The tensile strength at 920 °C for 3 min is 86.9 MPa, and the elongation is 39.2%. The test results show that, compared with Example 1, during the austenitization process in Example 1, the liquid zinc did not come into contact with the steel plate, thus obtaining a higher elongation of the coated plate.

[0079] To prove the influence of the austenitization temperature on the microscopic distribution uniformity of the coating composition, Comparative Example 2 is provided. The immersion plating solution is the coated plate of Zn-4.5Al-3.0Mg in Example 1, but its austenitization temperature is 850 °C.

[0080] Comparative Example 2

[0081] A coated plate with an immersion plating solution of Zn-4.5Al-3.0Mg, the steps not specifically described are the same as those in Example 1, except that: the product obtained in Step 2 is named Sample 0-2'; the austenitization temperature in Step 3 is 850 °C, and the product obtained in Step 3 is named Sample 0-3'.

[0082] The SEM test, EDS test and corrosion resistance test results and conclusions of Sample 0-2' are the same as those in Example 1.

[0083] The SEM test and EDS test results of Sample 0-3' are as follows Figure 4 shown. In Sample 0-3', the thinner intermediate compound layer between the steel plate and the coating disappeared, and it is composed of the steel plate and the coating; among them,

[0084] the lower layer of the coating is composed of a single-layer structure of α-Fe(Zn), and there is an enrichment phenomenon of Zn element at the contact with the steel plate in the single-layer structure of α-Fe(Zn); the upper layer of the coating is composed of a single-layer structure of α-Fe(Zn,Al), and there is an enrichment phenomenon of Zn and Al elements.

[0085] The test results show that through the austenitization in Step 3, the coating structure is stratified, and the eutectic transformation from the Zn-Al-MgZn2 three-phase eutectic to the structure composed of α-Fe(Zn) in the lower layer and α-Fe(Zn,Al) in the upper layer occurs. Compared with Example 1, the coating structure shows non-uniformity during the austenitization process.

[0086] To prove the influence of the eutectic structure in the coating on the performance of the coated plate, that is, to prove the role of the Zn-Al-Mg system thermodynamic phase diagram in the technical solution at the same time, Examples 2, 3 and 4 are provided, where

[0087] The plating solution composition of Example 2 was determined according to the Zn-Al two-phase eutectic line in the phase diagram. The mass percentages of the specific immersion plating solution composition were as follows: the Zn content was 94.4 wt.%, the Al content was 4.5 wt.%, and the Mg content was 1.1 wt.%. The immersion plating solution was simply referred to as plating solution A;

[0088] The plating solution composition of Example 3 was determined according to the Al-MgZn2 two-phase eutectic line in the phase diagram. The mass percentages of the specific immersion plating solution composition were as follows: the Zn content was 90.4 wt.%, the Al content was 6.0 wt.%, and the Mg content was 3.6 wt.%. The immersion plating solution was simply referred to as plating solution B;

[0089] The plating solution composition of Example 4 was determined according to the Al-MgZn2 two-phase eutectic line in the phase diagram. The mass percentages of the specific immersion plating solution composition were as follows: the Zn content was 87.3 wt.%, the Al content was 8.5 wt.%, and the Mg content was 4.2 wt.%. The immersion plating solution was simply referred to as plating solution C.

[0090] Example 2

[0091] A zinc-aluminum-magnesium coated steel sheet with plating solution A as the immersion plating solution. The steps not specifically described were the same as those in Example 1, except that: the immersion plating solution in step 2 was plating solution A; the product obtained in step 2 was named sample 2-2, and the product obtained in step 3 was named sample 2-3.

[0092] The SEM test and EDS test results of sample 2-2 were as Figure 2 shown. Sample 2-2 consisted of a steel sheet, a coating layer, and an intermediate compound layer between the steel sheet and the coating layer; among them,

[0093] the coating layer was composed of a pure Zn phase and a Zn-Al two-phase eutectic, and the content of the Zn-Al two-phase eutectic was 50%;

[0094] the intermediate compound layer was an Fe-Al or Fe-Al-Zn intermetallic compound with a thickness of 0.3 - 1 micron.

[0095] The test results showed that due to the change in the composition of the immersion plating solution, the content of the Zn-Al two-phase eutectic structure in the coating layer of sample 2-2 was relatively high. Compared with Example 1, Example 2 contained more Zn-Al two-phase eutectics.

[0096] The corrosion resistance test results of sample 2-2 were as Figure 3 shown. In a 3.5 wt.% NaCl solution at 25°C, the corrosion current density (I corr ) was 1.20×10 -5 A / cm 2 . The test results showed that due to the change in the composition of the immersion plating solution, Example 2 contained more Zn-Al two-phase eutectics, resulting in higher corrosion resistance.

[0097] The SEM test and EDS test results of Sample 2-3 are as follows Figure 4 shown. In Sample 2-3, the intermediate compound layer between the steel plate and the coating layer disappears, and it is composed of the steel plate and the coating layer. Among them,

[0098] the coating layer is composed of a single-layer structure of α-Fe(Zn,Al). In the single-layer structure of α-Fe(Zn,Al), the elements Fe, Zn, and Al are evenly distributed. The content of Zn element is 3.5-7.5 wt.%, the content of Al element is 0.5-1.7 wt.%, the content of Mg is 0-0.1 wt.%, and the content of O is 0.5-10.0 wt.%.

[0099] The test results show that through the austenitization in Step 3, the coating layer structure changes from a pure Zn phase and a Zn-Al two-phase eutectic to α-Fe(Zn,Al), and its structure composition is similar to that of Example 1.

[0100] The high-temperature tensile mechanical property test results of Sample 2-3 are as follows Figure 5 shown. The tensile strength at 900°C for 1 min is 75.8 MPa, and the elongation is 46.0%. The test results show that through the austenitization in Step 3, its elongation decreases.

[0101] By comparing Example 1 and Example 2, it can be seen that the increase in the content of the Zn-Al two-phase eutectic improves the corrosion resistance, but decreases the elongation.

[0102] Example 3

[0103] A zinc-aluminum-magnesium coated steel plate with plating solution B as the immersion plating solution. The steps not specifically described are the same as those in Example 1, except that: the immersion plating solution in Step 2 is plating solution B; the product obtained in Step 2 is named Sample 3-2, and the product obtained in Step 3 is named Sample 3-3.

[0104] The SEM test and EDS test results of Sample 3-2 are as follows Figure 2 shown. Sample 3-2 is composed of a steel plate, a coating layer, and an intermediate compound layer between the steel plate and the coating layer. Among them,

[0105] the coating layer is composed of a Zn-Al two-phase eutectic and an Al-MgZn2 two-phase eutectic. The content of the Al-MgZn2 two-phase eutectic is 80%. The lamellar spacing of the Al-MgZn2 two-phase eutectic structure is less than 1 micron. In the Al-MgZn2 two-phase eutectic, the Zn element exists in the form of MgZn2;

[0106] the intermediate compound layer is a Fe-Al or Fe-Al-Zn intermetallic compound, and its thickness is 1-2 microns.

[0107] The test results show that due to the change in the composition of the immersion plating solution, the content of the Al-MgZn2 two-phase eutectic structure in the coating of Sample 3-2 is relatively high. Compared with Example 1, Example 3 contains more Al-MgZn2 two-phase eutectic.

[0108] The corrosion resistance test results of Sample 3-2 are as Figure 3 shown. In a 3.5 wt.% NaCl solution at 25 °C, the corrosion current density (I corr ) is 1.52×10 -5 A / cm 2 . The test results show that due to the change in the composition of the immersion plating solution, Example 3 contains more Al-MgZn2 two-phase eutectic, resulting in a decrease in its corrosion resistance.

[0109] The SEM test and EDS test results of Sample 3-3 are as Figure 4 shown. In Sample 3-3, the intermediate compound layer between the steel plate and the coating disappears, and it is composed of the steel plate and the coating; among them,

[0110] the coating is composed of a single-layer α-Fe(Zn,Al) structure. In the single-layer α-Fe(Zn,Al) structure, the elements Fe, Zn, and Al are evenly distributed. The content of Zn element is 7.2 - 10.3 wt.%, the content of Al element is 7.8 - 12.2 wt.%, the content of Mg is 0 - 0.2 wt.%, and the content of O is 0.9 - 5.6 wt.%.

[0111] The test results show that through the austenitization in Step 3, the coating structure changes from a Zn-Al two-phase eutectic and an Al-MgZn2 two-phase eutectic to α-Fe(Zn,Al), and its tissue composition is similar to that of Example 1.

[0112] The high-temperature tensile mechanical property test results of Sample 3-3 are as Figure 5 shown. The tensile strength at 900 °C for 3 min is 77.1 MPa, and the elongation is 53.2%. The test results show that through the austenitization in Step 3, compared with Example 1, the elongation has increased.

[0113] By comparing Example 1 and Example 3, it can be seen that the increase in the content of the Al-MgZn2 two-phase eutectic reduces the corrosion resistance to some extent, but increases the elongation.

[0114] Example 4

[0115] A zinc-aluminum-magnesium coated steel sheet with immersion plating solution C as the plating solution. The steps not specifically described are the same as those in Example 1, except that: the immersion plating solution in Step 2 is plating solution C; the product obtained in Step 2 is named Sample 4-2, and the product obtained in Step 3 is named Sample 4-3.

[0116] The SEM test and EDS test results of Sample 4-2 are as follows Figure 2 shown. Sample 4-2 consists of a steel plate, a coating layer, and an intermediate compound layer between the steel plate and the coating layer. Among them,

[0117] the coating layer is composed of a Zn-Al two-phase eutectic and an Al-MgZn2 two-phase eutectic. The content of the Al-MgZn2 two-phase eutectic is 80%. The lamellar spacing of the Al-MgZn2 two-phase eutectic structure is less than 1 micron. In the Al-MgZn2 two-phase eutectic, the Zn element exists in the form of MgZn2;

[0118] the intermediate compound layer is a Fe-Al or Fe-Al-Zn intermetallic compound with a thickness of 2-3 microns.

[0119] The test results show that, compared with Example 1, the tissue uniformity in the coating layer is poor.

[0120] The corrosion resistance test results of Sample 4-2 are as follows Figure 3 shown. In a 3.5 wt.% NaCl solution at 25°C, the corrosion current density (I corr ) is 1.68×10 -5 A / cm 2 . The test results show that due to the change in the composition of the immersion plating solution, Example 4 contains more Al-MgZn2 two-phase eutectic, resulting in a decrease in its corrosion resistance.

[0121] The SEM test and EDS test results of Sample 4-3 are as follows Figure 4 shown. In Sample 4-3, the intermediate compound layer between the steel plate and the coating layer disappears and is composed of a steel plate and a coating layer. Among them,

[0122] the coating layer is composed of a single-layer α-Fe(Zn,Al) structure, and the Zn element is enriched at the contact with the steel plate in the single-layer α-Fe(Zn,Al) structure.

[0123] The test results show that through the austenitization in Step 3, the coating layer structure changes from a Zn-Al two-phase eutectic and an Al-MgZn2 two-phase eutectic to α-Fe(Zn,Al). Compared with Example 1, liquid zinc comes into contact with the steel plate during the austenitization process.

[0124] The high-temperature tensile mechanical property test results of Sample 4-3 are as follows Figure 5 shown. The tensile strength at 920°C for 1 min is 82.6 MPa, and the elongation is 38.0%. The test results show that through the austenitization in Step 3, compared with Example 1, its elongation decreases significantly.

[0125] By comparing and analyzing Examples 1-4 and Comparative Examples 1-2, the following conclusions can be obtained:

[0126] 1. The corrosion resistance of the hot-dip galvanized zinc-aluminum-magnesium coated steel plate based on hot-dip galvanizing technology increases with the increase in the content of the Zn-Al two-phase eutectic in the coating structure and decreases with the increase in the content of the Al-MgZn2 two-phase eutectic;

[0127] 2. The elongation of the zinc-aluminum-magnesium coated steel plate to be stamped based on hot-dip galvanizing and high-temperature austenitization technologies decreases with the increase in the content of the Zn-Al two-phase eutectic in the coating structure and increases with the increase in the content of the Al-MgZn2 two-phase eutectic;

[0128] Therefore, according to the above analysis, it can be seen that only by calculating the phase diagram and adopting the method of austenitization to prepare the zinc-aluminum-magnesium coated steel plate can the significant technical effect of the present invention be improved.

[0129] In summary, the method for preparing a zinc-aluminum-magnesium coated steel plate to be stamped based on hot-dip galvanizing and high-temperature austenitization technologies in the above embodiments of the present invention uses phase diagram calculation to guide the composition design. The preparation materials are prepared according to the mass percentage of the dip coating solution components as follows: the Zn content is 85-95 wt.%, the Al content is 4.5-8.5 wt.%, and the Mg content is 1-4.5 wt.%. After hot-dip galvanizing and austenitization, a zinc-aluminum-magnesium coated steel plate based on hot-dip galvanizing and high-temperature forming technologies is obtained. For the zinc-aluminum-magnesium coated steel plate prepared by the present invention, a Zn-Al-MgZn2 three-phase eutectic is formed in the coating structure after hot-dip galvanizing. When the Zn element content is 92.5 wt.%, the Al element content is 4.5 wt.%, and the Mg element content is 3.0 wt.%, the corrosion current density (I corr ) is 1.35×10 -5 A / cm 2 at the same time, under the conditions of 900-920 °C and holding for 1-3 minutes, the elongation is 46.6%.

Claims

1. A zinc-aluminum-magnesium coated steel sheet based on hot-dip plating and high-temperature forming technology, characterized in that: The steel plate is obtained by hot dip plating and austenitization under high temperature conditions; The dipping solution for the hot dip plating is a Zn-Al-Mg dipping solution. The percentage composition of the Zn-Al-Mg dipping solution is: the Al content is 4.5 wt.%, the Mg content is 3.0 wt.%, and the rest is Zn and inevitable impurities; After the hot dip plating, the steel plate becomes a zinc-aluminum-magnesium coated steel plate based on the hot dip plating technology. The zinc-aluminum-magnesium coated steel plate based on the hot dip plating technology is composed of a steel plate, a zinc-aluminum-magnesium coating-2, and an intermediate compound layer between the steel plate and the coating. Among them, The mass percentage of the components of the zinc-aluminum-magnesium coated steel plate to be stamped based on the hot dip plating and high temperature austenitization technology is: the C content is 0.33 wt.%, the Si content is 0.10 wt.%, the Mn content is 1.45 wt.%, the P content does not exceed 0.020 wt.%, the S content does not exceed 0.004 wt.%, the Al content is 0.080 wt.%, the Ti content is 0.02 wt.%, the V content is 0.18 wt.%, the N content does not exceed 0.0040 wt.%, the B content is 0.0020 wt.%, and the rest is Fe and inevitable impurities; The zinc-aluminum-magnesium coating contains Zn, Al, and MgZn2 phases; the zinc-aluminum-magnesium coating-2 contains a Zn-Al two-phase eutectic and a Zn-Al-MgZn2 three-phase eutectic. The total eutectic content of the Zn-Al two-phase eutectic and the Zn-Al-MgZn2 three-phase eutectic is 95%. The Zn element exists in the forms of Zn phase and MgZn2 phase, and the Al element exists in the form of Al phase. The eutectic structure spacing is less than 1 micron; The intermediate compound layer between the steel plate and the coating, abbreviated as the intermediate compound layer, is a Fe-Al or Fe-Al-Zn intermetallic compound; The zinc-aluminum-magnesium coated steel plate based on the hot dip plating technology becomes a zinc-aluminum-magnesium coated steel plate to be stamped based on the hot dip plating and high temperature austenitization technology after austenitization at a temperature of 920 °C for a holding time of 3 min; The zinc-aluminum-magnesium coated steel plate to be stamped based on the hot dip plating and high temperature austenitization technology is composed of a steel plate and a zinc-aluminum-magnesium coating-3. The zinc-aluminum-magnesium coating-3 is composed of a single-layer α-Fe(Zn,Al) structure. In the single-layer α-Fe(Zn,Al) structure, the Fe, Zn, Al, and Mg elements are evenly distributed. The Zn element content is 4.6 - 8.1 wt.%, the Al element content is 0.7 - 1.2 wt.%, the Mg is 0 - 0.1 wt.%, and the O is 0.9 - 8.2 wt.%; Under the conditions of a temperature of 920 °C and a holding time of 3 min, the tensile strength of the zinc-aluminum-magnesium coated steel plate to be stamped based on the hot dip plating and high temperature austenitization technology is 77.2 MPa, and the elongation is 46.6%; The corrosion current density (Icorr) of zinc-aluminum-magnesium coated steel sheet based on hot-dip coating technology in 3.5wt.% NaCl solution at 25°C is 1.35×10 -5 A / cm 2 .

2. The hot-dip aluminized and zinc-magnesium coated steel sheet based on hot-dip plating and hot forming technology according to claim 1, wherein: The thickness of the intermediate compound layer is 0.3 - 1 micron.

3. The preparation method of the zinc-aluminum-magnesium coated steel sheet based on hot-dip plating and hot forming technology according to claim 1, characterized in that Including the following steps: Step 1: Preparation of the steel sheet to be hot-dip galvanized. After heating the steel to be processed into molten iron, through molten iron pretreatment, converter smelting, secondary refining, and continuous casting, a steel billet is obtained. Then, the steel billet is heated, rolled, controlled cooled, coiled, pickled, and cold rolled to obtain a steel sheet. Finally, the steel sheet is continuously annealed under the conditions of an annealing temperature of 800 ± 5 °C and a dew point of -50 ± 10 °C to obtain the steel sheet to be hot-dip galvanized; Step 2: Hot-dip galvanizing of the steel sheet to be hot-dip galvanized. First, prepare the galvanizing solution. The mass percentage of the galvanizing solution is that the Al content is 4.5 wt.%, the Mg content is 3.0 wt.%, and the rest is Zn and inevitable impurities. Then, under the conditions of a galvanizing temperature of 440 - 460 °C, a galvanizing time of 3 - 10 seconds, and a cooling rate after galvanizing of greater than 30 °C / s to room temperature, the steel sheet to be hot-dip galvanized obtained in Step 1 is hot-dip galvanized to obtain a zinc-aluminum-magnesium coated steel sheet based on the hot-dip galvanizing technology, named Sample 1-2; Step 3: Austenitization of the zinc-aluminum-magnesium coated steel sheet based on the hot-dip galvanizing technology. The Sample 1-2 obtained in Step 2 is austenitized under the conditions of an austenitization temperature of 920 °C and an insulation time of 3 minutes to obtain a zinc-aluminum-magnesium coated steel sheet to be stamped based on the hot-dip galvanizing and high-temperature austenitization technologies, named Sample 1-3.

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