Highly corrosion-resistant zinc-aluminum-magnesium coating layer, and preparation method and application thereof

Abstract

This invention discloses a high corrosion-resistant zinc-aluminum-magnesium coating and its preparation method, belonging to the field of hot-dip galvanizing technology. The steps are as follows: 1) Prepare a Ti-containing zinc-aluminum-magnesium hot-dip galvanizing solution in a zinc pot, controlling the temperature of the solution at 460-490℃; wherein, by mass percentage, the Ti content is 0.12-0.15%; 2) First, heat the pretreated substrate in a N2-H2 mixed protective atmosphere, controlling the temperature of the substrate entering the pot at 460-490℃, then immerse the substrate in the zinc pot of step 1), and perform hot-dip galvanizing under pure N2 protection; 3) Cool under pure N2 protection to obtain the high corrosion-resistant zinc-aluminum-magnesium coating. This invention, through the synergistic regulation of Ti element and the temperature of the substrate entering the pot, refines the Al-rich phase grains and optimizes the eutectic structure distribution, resulting in a thick coating with excellent corrosion resistance. It can be applied to fields such as automotive lightweighting, photovoltaic brackets, building steel structures, and marine engineering, showing broad prospects.

Description

Technical Field

[0001] This invention belongs to the field of hot-dip galvanizing technology, specifically relating to a high corrosion-resistant zinc-aluminum-magnesium coating, its preparation method, and its application. Background Technology

[0002] Hot-dip zinc-aluminum-magnesium (ZAM) coatings have gradually replaced traditional hot-dip galvanizing coatings due to their excellent corrosion resistance, processability, and cost-effectiveness. They are widely used in automotive lightweighting, photovoltaic brackets, building steel structures, and marine engineering, among other fields. Their core corrosion resistance mechanism relies on the synergistic effect of zinc, aluminum, and magnesium elements in the coating to form dense corrosion products such as layered double hydroxides and alkaline zinc salts, providing both physical barrier and sacrificial anode protection. However, in special environments, such as marine high-salt spray and industrial humid heat environments with periodic corrosion, traditional ZAM coatings are still prone to problems such as corrosion product peeling and localized pitting corrosion expansion, severely affecting the service life of components.

[0003] To address the aforementioned problems of spalling and pitting corrosion, existing technologies mainly employ three optimization paths, but all have significant drawbacks: First, increasing the content of aluminum and magnesium elements to enhance the stability of corrosion products can improve short-term corrosion resistance, but excessive brittle phases lead to decreased coating ductility, making it prone to crack propagation after mechanical damage. Furthermore, medium-to-high aluminum-magnesium systems significantly deteriorate coating formability and weldability, making them unsuitable for the processing requirements of high-end fields such as automobiles. Second, adding trace elements such as silicon and rare earth elements to regulate the microstructure can improve adhesion by inhibiting excessive growth of the Fe-Al alloy layer, but it reduces the overall corrosion resistance of the coating. Rare earth elements, on the other hand, are costly, sensitive to addition amounts, and prone to causing microstructure segregation, making large-scale stable application impossible. Third, refining grains by optimizing the post-plating cooling process, such as using segmented cooling to promote microstructure homogenization, can only improve the surface microstructure and has limited effect on controlling internal grain boundary defects. In extreme corrosive environments, it is still difficult to prevent corrosive media from penetrating along grain boundaries.

[0004] Microalloying is a key direction for optimizing the performance of zinc-aluminum-magnesium (ZAMg) coatings. Ti can combine with aluminum to form Al3Ti heterogeneous nucleation cores, improving coating density by refining Al-rich phase grains and suppressing MgZn2 phase coarsening, thereby improving corrosion resistance and structural stability. However, its application has significant shortcomings: First, there is a lack of clear optimization standards for the amount of Ti added. If the addition is too low, the number of nucleation cores is insufficient, failing to effectively refine the grains. If the addition is too high, the amount of zinc dross generated will increase significantly, causing surface defects in the coating and reducing the adhesion between the coating and the substrate, resulting in performance fluctuations. Second, Ti's control over the coating phase structure is singular; it can only optimize grain size and cannot improve the uniformity of the distribution of Al-rich and MgZn2 phases. The problem of weak local phase interface bonding still exists, which can easily become corrosion initiation sources under the combined effects of periodic corrosion and mechanical stress. Third, Ti... The introduction of elements will change the electrochemical properties of the coating. Existing technologies have not optimized the composition system for this change, resulting in a decrease in the uniformity of sacrificial anode protection of the coating, and preferential corrosion in local areas, making it difficult to meet the requirements for long-term corrosion resistance.

[0005] Therefore, it is urgent to fully leverage the performance optimization effect of Ti on zinc-aluminum-magnesium coatings to achieve long-term high corrosion resistance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a high corrosion-resistant zinc-aluminum-magnesium coating, its preparation method, and its application. The aim is to solve the problems of incomplete plating / accumulation defects, uneven structure, and insufficient corrosion resistance in traditional coatings, and to achieve high corrosion resistance with refined microstructure, excellent surface quality, and no red rust after 632 hours of cyclic salt spray.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a highly corrosion-resistant zinc-aluminum-magnesium coating is provided, comprising the following steps: 1) Prepare a zinc-aluminum-magnesium hot-dip galvanizing bath containing Ti in a zinc pot, with the bath temperature controlled at 460-490℃; wherein, by mass percentage, the Ti content is 0.12-0.15%; 2) First, heat the pretreated substrate in a N2-H2 mixed protective atmosphere and control the temperature of the substrate entering the pot to 460-490℃. Then, immerse the substrate in the zinc pot of step 1) and perform hot-dip plating under pure N2 protection. 3) Cooling is carried out under pure N2 protection to ensure uniform solidification of the coating and avoid stress defects during the cooling process, thus obtaining a high corrosion-resistant zinc-aluminum-magnesium coating.

[0008] According to the above scheme, in step 1), the hot-dip galvanizing solution composition, by mass percentage, includes 5-11% Al, 1.8-3.0% Mg, 0.15-0.2% Si and 0.12-0.15% Ti, with the balance being Zn and unavoidable impurities.

[0009] According to the above scheme, in step 1), the temperature of the hot-dip galvanizing solution is controlled at 475-485℃; in step 2), the temperature of the plate entering the pot is 475-485℃.

[0010] According to the above scheme, in step 1), the preparation of the hot-dip galvanizing solution in the zinc pot is specifically as follows: Zn, Al, Mg and Si metal ingots are added to the zinc pot in proportion and heated to 460-490℃ to melt; after the alloy is completely melted, Ti ingots (purity 99.9%) are added, and the mixture is stirred to ensure that the Ti element is evenly dispersed, and the temperature of the zinc pot is maintained at 460-490℃.

[0011] Preferably, the stirring time is 20-40 minutes.

[0012] According to the above scheme, in step 2), SPHC hot-rolled pickled plate is used as the substrate.

[0013] According to the above scheme, in step 2), the pretreatment method is: to remove oil stains and machining coolant from the substrate surface by alkaline washing process to complete the pretreatment.

[0014] Preferably, the alkaline washing process uses a NaOH solution with a mass fraction of 2-5%, the alkaline washing temperature is 55-65℃, and the alkaline washing time is 6-10 minutes.

[0015] According to the above scheme, in step 2), heating is carried out in a N2-H2 mixed protective atmosphere to prevent the substrate from oxidizing; wherein the volume ratio of N2 to H2 is 4-5:1.

[0016] According to the above scheme, in step 2), the hot-dip plating time is 2-3 seconds.

[0017] According to the above scheme, in step 3), nitrogen gas knife cooling is used.

[0018] According to the above scheme, in step 3), the cooling rate is 10-15℃ / s.

[0019] According to the above scheme, in step 3), the thickness of the obtained high corrosion-resistant zinc-aluminum-magnesium coating is 35-45μm.

[0020] A highly corrosion-resistant zinc-aluminum-magnesium coating prepared by the above preparation method is provided.

[0021] According to the above scheme, the phase composition of the coating includes Al-rich phase, MgZn2 phase, Zn / MgZn2 binary eutectic phase, Zn / MgZn2 / Al ternary eutectic phase and Mg2Si phase.

[0022] According to the above scheme, the coating did not produce red rust after 632 hours of continuous cyclic salt spray test.

[0023] This invention provides an application of the aforementioned high corrosion-resistant zinc-aluminum-magnesium coating in automotive lightweighting, photovoltaic brackets, building steel structures, or marine engineering.

[0024] The beneficial effects of this invention are as follows: This invention provides a method for preparing a high corrosion-resistant zinc-aluminum-magnesium coating. By establishing a precise synergistic matching relationship between Ti element and the temperature of the plate entering the pot, the method fully leverages the grain-optimizing effect of Ti element, enabling Ti to preferentially form Al3Ti heterogeneous nucleation cores with Al, refining Al-rich phase grains and optimizing the eutectic structure distribution. This achieves full-dimensional optimization of the coating's microstructure, which is beneficial for obtaining a thicker coating. No red rust was generated during a 632-hour cyclic salt spray test, demonstrating excellent corrosion resistance. The coating can be directly applied to fields such as automotive lightweighting, photovoltaic brackets, building steel structures, and marine engineering, with broad application prospects. Attached Figure Description

[0025] Figure 1 Equilibrium phase diagram of the Zn-11Al-2.8Mg-0.2Si-0.14Ti alloy calculated by Thermo-Cale.

[0026] Figure 2 The coating surface morphology of the hot-rolled pickled plates obtained in Example 1 and Comparative Examples 1-3 is shown below; where: (a) is without Ti at 480℃ in Comparative Example 1; (b) is with Ti at 440℃ in Comparative Example 2; (c) is with Ti at 480℃ in Example 1; and (d) is with Ti at 520℃ in Comparative Example 3.

[0027] Figure 3 The coating surface morphology (Mg2Si phase) of the hot-rolled pickled plate with Ti element added at a plate temperature of 480℃ in Example 1 is shown.

[0028] Figure 4 The coating surface morphology (Al3Ti phase) of the hot-rolled pickled plate with Ti element added at a plate temperature of 480℃ in Example 1 is shown.

[0029] Figure 5 The images show the surface morphology of the hot-rolled pickled plates obtained in Example 1 and Comparative Examples 1-3; where: (a) is the plate without Ti at 480℃ in Comparative Example 1; (b) is the plate with Ti at 440℃ in Comparative Example 2; (c) is the plate with Ti at 480℃ in Example 1; and (d) is the plate with Ti at 520℃ in Comparative Example 3.

[0030] Figure 6The coating cross-sectional morphology of the hot-rolled pickled plates obtained in Example 1 and Comparative Examples 1-3 is shown below; (a) is without Ti at 480℃ in Comparative Example 1; (b) with Ti at 440℃ in Comparative Example 2; (c) with Ti at 480℃ in Example 1; and (d) with Ti at 520℃ in Comparative Example 3.

[0031] Figure 7 Salt spray test results for the coatings obtained in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1 A method for preparing a highly corrosion-resistant zinc-aluminum-magnesium coating is provided, comprising the following steps: Substrate pretreatment: Take an SPHC hot-rolled pickled plate (220mm×110mm×2.3mm), wash it with 5% NaOH solution (60℃) for 10 minutes to remove surface oil, rinse with water and dry.

[0034] Plating solution preparation: Add Zn, Al, Mg and Si metal ingots into the zinc pot in the ratio of Zn-11%Al-2.8%Mg-0.2%Si, and heat to 480℃ to melt; after the alloy is completely melted, add Ti ingots (purity 99.9%) accounting for 0.14% of the plating solution mass, stir for 30 minutes to ensure uniform dispersion of Ti element, and maintain the zinc pot temperature at 480℃.

[0035] Hot-dip galvanizing: The pretreated substrate is placed in a continuous hot-dip galvanizing simulation test machine (CAG-2010 type). During the heating stage, a N2-H2 (4:1) mixed gas is introduced. After the temperature is raised to 480℃, it is sent into the zinc pot for immersion galvanizing for 3 seconds. During the immersion galvanizing and cooling process (using nitrogen gas knife cooling), pure N2 protection is introduced, and the cooling rate is controlled at 10℃ / s.

[0036] The coated samples were machined to sizes of 5mm × 10mm (metallographic analysis) and 30mm × 20mm (salt spray test). The metallographic samples were polished with 2000-grit sandpaper and diamond polished, then etched with 2% nitric acid alcohol for 5 seconds, cleaned with alcohol, and dried. Performance testing was performed, and the results are as follows: Microstructure: Observed with a Gemini SEM500, the coating cross section contains granular Al-rich phase and lamellar eutectic phase, the alloy layer thickness is <1μm, and the Al-rich phase is uniformly distributed.

[0037] Coating thickness: The coating thickness reaches 42.38μm, and the coating weight reaches 0.0237g / cm³. 2The thick and heavy coating obtained in this embodiment indicates that the plating solution adheres more easily to the steel plate and the interface wetting is better. The increased thickness but no cracking or peeling during 0T bending indicates better metallurgical bonding, lower internal stress, and better toughness.

[0038] Corrosion resistance: In the CK-901S salt spray chamber, a cyclic salt spray test was conducted (NaCl concentration 100±5g / L, pH 4.5-6.7, 45℃ salt spray / 65℃ drying, cycle 23h (15h spray + 8h drying)). After 632h, the sample showed no red rust, and only a small amount of uniform white rust on the surface.

[0039] Comparative Example 1 (without Ti element, 480℃ for pot plate temperature) Except for the absence of Ti element in the plating solution, the other steps are the same as in Example 1.

[0040] Test results: The coating thickness is 35.78μm, and there are scattered small pits on the surface; red rust appeared after 537 hours of salt spray test, and the red rust area accounted for more than 50%.

[0041] Comparative Example 2 (Ti element added, 440℃ for pot plate temperature) Except for adjusting the temperature of the pot plate to 440°C, the other steps are the same as in Example 1.

[0042] Test results: The coating thickness is 39.05μm, and there are obvious areas of uncoated and decoated areas on the surface; white rust appears after 395h of salt spray test and red rust appears after 500h.

[0043] Comparative Example 3 (Ti element added, 520℃ for pot plate temperature) Except for adjusting the temperature of the pot plate to 520°C, the other steps are the same as in Example 1.

[0044] Test results: The coating thickness is 39.69 μm, and local accumulation and flow marks appear on the surface; red rust appears after 450 hours of salt spray testing, and the red rust is concentrated at the accumulation defects.

[0045] Figure 1 The equilibrium phase diagram of the Zn-11Al-2.8Mg-0.2Si-0.1Ti alloy calculated by Thermo-Cale; the figure shows: through Figure 1According to Thermo-Calc thermodynamic calculations, the liquidus temperature of Zn-11%Al-2.8%Mg-0.2%Si-0.14%Ti is 424℃, and the solidus temperature is 345.5℃. When the temperature is below the liquidus, a metastable β-Al-rich phase precipitates first, followed by the formation of magnesium-silicon compounds through a binary eutectic reaction, forming a β-Al / Mg2Si binary eutectic structure. Subsequently, a ternary eutectic reaction continues to occur, forming a mixed structure of β-Al-rich, Mg2Si, and MgZn2 phases (C14_Laves). The formation temperature of Ti-Zn compounds is higher than that of some low-melting-point phases in the alloy (such as the Zn / MgZn2 eutectic phase), and a small amount of Ti-Zn phase precipitates in the later stages of solidification.

[0046] At room temperature, the equilibrium solidification microstructure of this alloy consists of Al-rich phase, Zn-rich phase, and Mg2Zn. 11 Phase, small amount of β-Al / Mg2Zn 11 Phase, Zn / Mg2Zn 11 Binary eutectic structure and Zn / Al / Mg2Zn 11 The ternary eutectic structure, due to the rapid cooling rate during hot-dip galvanizing, results in non-equilibrium solidification of the alloy, making it difficult for Al and Mg elements to accumulate in large quantities, leading to Mg2Zn. 11 The relevant structures are difficult to form, and instead a relatively stable MgZn2 phase is generated; the final room temperature structure is an Al-rich phase, a Zn-rich phase, a Zn / MgZn2 binary eutectic structure, and a Zn / Al / MgZn2 ternary eutectic structure, and a Mg2Si phase will appear under a certain cooling rate.

[0047] Figure 2 The figures show the surface morphology of the coatings on the hot-rolled pickled plates obtained in Example 1 and Comparative Examples 1-3; where: (a) is the coating at 480℃ without Ti in Comparative Example 1; (b) is the coating at 440℃ with Ti in Comparative Example 2; (c) is the coating at 480℃ with Ti in Example 1; (d) is the coating at 520℃ with Ti in Comparative Example 3; the figures show that the Zn-Al-Mg coating contains typical dendritic, rod-shaped, and blocky Al-rich phases, as well as MgZn2 phases surrounding the Al-rich phases. Binary eutectic phases Zn / MgZn2 and ternary eutectic phases Al / Zn / MgZn2 also exist in some regions of the MgZn2 phase. (Comparison) Figure 2 As shown in (a) and (c), the addition of Ti promotes the precipitation of Al3Ti, thus refining the Al-rich phase grains to a certain extent and further optimizing the growth morphology of the Al-rich phase. The presence of the Al3Ti alloy is also confirmed by energy dispersive spectroscopy (EDS) surface scanning analysis. The addition of Ti also promotes the refinement of the eutectic structure. Figure 2 As shown in Figures b, c, and d, when Ti is added to all of them, it can be observed by changing the temperature of the inlet plate that as the temperature increases, the Al-rich dendrites gradually coarsen and the proportion of the eutectic phase gradually decreases.

[0048] Figure 3 The figure shows the surface morphology (Mg2Si phase) of the coating of the hot-rolled pickled plate with Ti element added at a plate temperature of 480℃ in Example 1. The figure shows that the Mg phase and Si phase are highly overlapping, and the Mg2Si phase can be clearly seen to be attached to the Al-rich phase in an irregular blocky form.

[0049] Figure 4 The figure shows the surface morphology (Al3Ti phase) of the coating on a hot-rolled pickled plate with Ti added at a plate temperature of 480℃ in Example 1; the figure shows the surface morphology after energy dispersive spectroscopy (EDS) surface scanning analysis. Figure 4 This also confirms the existence of the Al3Ti alloy.

[0050] Figure 5 The images show the surface morphology of hot-rolled pickled plates from Examples 1-3 with an initial plate temperature of 480℃ and without Ti, and hot-rolled pickled plates with Ti added at different initial plate temperatures ranging from 440℃ to 520℃. (a) No Ti added at 480℃; (b) Ti added at 440℃; (c) Ti added at 480℃; (d) Ti added at 520℃. The figures show the surface morphology from... Figure 5 It is clearly evident that when Ti is not added and the loading temperature is 480℃, the coating, while possessing a metallic luster, exhibits minor defects such as scattered small pits. With the addition of Ti, at a loading temperature of 440℃, surface defects are more pronounced, with obvious areas of incomplete plating and deplating, resulting in poor coating continuity. At a loading temperature of 480℃, surface defects are significantly reduced, and the uniformity and continuity of the coating are greatly improved, with good overall flatness. When the loading temperature rises to 520℃, localized accumulation and flow marks appear in the coating, edge defects increase, and uniformity decreases. Overall, with the addition of Ti, the coating surface morphology at a loading temperature of 480℃ is the most ideal. When the loading temperature is too high (520℃) or too low (440℃), the surface defects after adding Ti increase relatively, and the coating without Ti (480℃) is not as uniform and complete as the coating with Ti added at the same temperature.

[0051] Figure 6The figures show the cross-sectional morphology of the coatings on the hot-rolled pickled plates obtained in Example 1 and Comparative Examples 1-3; where: (a) Comparative Example 1 without Ti at 480℃; (b) Comparative Example 2 with Ti at 440℃; (c) Example 1 with Ti at 480℃; (d) Comparative Example 3 with Ti at 520℃; The figures show that: as shown in Figures a and c, when Ti is not added and the plate temperature is 480℃, the distribution morphology and spacing of the aluminum-rich phase in the microstructure are similar to those when Ti is added and the plate temperature is 480℃. The volume fraction ratio of the eutectic phase and the aluminum-rich phase is moderate, and the overall structure is relatively uniform. After adding Ti to the coating, Al3Ti acts as a heterogeneous nucleation core during solidification, which increases the nucleation rate of the Al-rich phase, inhibits its dendrite development, and reduces the grain size of the Al-rich phase (grain size reduction of 30%-50%), making the Al-rich phase dendrite size suitable (5-15μm) and continuously distributed. Meanwhile, the addition of Ti promotes the refinement and homogenization of the ternary eutectic (Zn / Al / MgZn2) and binary eutectic (Zn / MgZn2) structures, with the interlayer spacing of the eutectic layers being less than 1 μm, thereby indirectly optimizing the uniformity of the Al-rich phase distribution.

[0052] Compared to the initial plate temperature of 480℃, the lower temperature inhibits grain growth, resulting in finer grains. As shown in Figure b, at an initial plate temperature of 440℃, the size of the Al-rich phase in the sample microstructure decreased, and its morphology became more irregular. Although the proportion of the eutectic phase increased, its uniformity was poor. As the initial plate temperature continued to rise to 520℃, as shown in Figure d, the relevant spectra showed a certain degree of "coarsening" of the Al-rich phase, which disrupted the originally harmonious distribution between the Al-rich phase and the eutectic phase. This morphology also led to a decrease in the proportion of the ternary eutectic phase. Since the MgZn2 phase protects the coating through its preferential corrosion, a higher proportion of the ternary eutectic phase results in faster corrosion product formation, which is more conducive to the rapid formation of a protective film. These rapidly formed dense corrosion product films quickly block corrosion channels and isolate the corrosive media (water, oxygen, Cl). - The contact between the eutectic phase and the substrate significantly reduces the subsequent corrosion rate of the coating. Furthermore, the smaller the difference in the spacing between eutectic layers, the higher the volume fraction of the eutectic phase in the microstructure, and the better the corrosion resistance.

[0053] Figure 7For the salt spray test results of the coatings obtained in Example 1 and Comparative Examples 1-3 after approximately 632 hours, the figure shows that during the test, white rust appeared on the surface of the samples without added zinc (TI) and those with added TI and plate temperatures of 440℃ and 520℃, respectively, after 395 hours. The white rust is an initial corrosion product of the coating itself, mainly zinc hydroxide and basic carbonates. Furthermore, the sample without added TI showed red rust after 537 hours, with the red rust covering more than half of the surface. The red rust is a corrosion product of the base iron, mainly iron oxides and hydroxides. During the salt spray test, the location of the red rust exhibited two patterns: firstly, it was mostly concentrated at the edges of the sample, and corrosion spread from the edges to the center; secondly, it appeared in areas where the white rust was unevenly distributed on the sample surface. In addition, previous studies have shown that the presence of white rust has an inhibitory effect on the formation of red rust. Figure 7 The final state of each sample after the salt spray test is shown. Based on the preliminary judgment of the red rust area, the sample with added Ti element and plate temperature of 480℃ in Example 1 has relatively better corrosion resistance.

[0054] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a highly corrosion-resistant zinc-aluminum-magnesium coating, characterized in that, Includes the following steps: 1) Prepare a zinc-aluminum-magnesium hot-dip galvanizing bath containing Ti in a zinc pot, with the bath temperature controlled at 460-490℃; wherein, by mass percentage, the Ti content is 0.12-0.15%; 2) First, heat the pretreated substrate in a N2-H2 mixed protective atmosphere and control the temperature of the substrate entering the pot to 460-490℃. Then, immerse the substrate in the zinc pot of step 1) and perform hot-dip plating under pure N2 protection. 3) Finally, cooling is performed under pure N2 protection to obtain a highly corrosion-resistant zinc-aluminum-magnesium coating.

2. The preparation method according to claim 1, characterized in that, In step 1), the hot-dip galvanizing solution comprises, by mass percentage, 5-11% Al, 1.8-3.0% Mg, 0.15-0.2% Si and 0.12-0.15% Ti, with the balance being Zn and unavoidable impurities.

3. The preparation method according to claim 1, characterized in that, In step 1), the temperature of the hot-dip galvanizing solution is controlled at 475-485℃; in step 2), the temperature of the plate entering the pot is 475-485℃.

4. The preparation method according to claim 1, characterized in that, In step 1), the preparation of the hot-dip galvanizing solution in the zinc pot is specifically as follows: Zn, Al, Mg and Si metal ingots are added to the zinc pot in proportion and heated to 460-490℃ to melt; after the alloy is completely melted, Ti ingots are added and stirred to ensure that the Ti element is evenly dispersed, and the temperature of the zinc pot is maintained at 460-490℃.

5. The preparation method according to claim 1, characterized in that, In step 2), the pretreatment method is as follows: the substrate surface oil and machining coolant are removed by alkaline washing process to complete the pretreatment; the substrate is heated in a N2-H2 mixed protective atmosphere to prevent oxidation; wherein the volume ratio of N2 to H2 is 4-5:

1.

6. The preparation method according to claim 1, characterized in that, In step 2), the hot-dip plating time is 2-3 seconds.

7. The preparation method according to claim 1, characterized in that, In step 3), the cooling rate is 10-15℃ / s.

8. The preparation method according to claim 1, characterized in that, In step 3), the thickness of the obtained high corrosion-resistant zinc-aluminum-magnesium coating is 35-45 μm.

9. A highly corrosion-resistant zinc-aluminum-magnesium coating prepared by the preparation method according to any one of claims 1-8.

10. The application of the high corrosion-resistant zinc-aluminum-magnesium coating of claim 9 in automotive lightweighting, photovoltaic brackets, building steel structures, or marine engineering.

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