Treatment method for improving corrosion resistance of hot-dip galvanized aluminum magnesium plate strip

Abstract

The invention relates to the technical field of metal surface treatment, and discloses a treatment method for improving the corrosion resistance of a hot-dip zinc-aluminum-magnesium plate strip, which comprises the following steps: S1, selecting Zn, Al, Mg and Si metal simple substances as raw materials, weighing and proportioning according to a certain proportion, and smelting in an electric arc smelting furnace to obtain molten zinc-aluminum-magnesium alloy liquid; s2, the roughness of the surface of the steel base plate is pretreated through abrasive paper; s3, the pretreated steel base plate is subjected to alkali washing; s4, the steel substrate subjected to alkali washing is subjected to annealing treatment; s5, the steel base plate obtained after annealing treatment is immersed in molten zinc-aluminum-magnesium alloy liquid at a certain temperature for a certain time; and S6, after hot dipping is completed, the steel plate is taken out of the zinc-aluminum-magnesium alloy liquid, and after a plating layer is air-cooled for a certain time, the plating layer is cooled at a fixed cooling speed. According to the method, residual stress possibly existing in the steel subjected to cold machining is released, the ductility and formability of the steel are improved, and the coating quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and particularly to a treatment method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium sheet and strip. Background Art

[0002] In the field of metal protection, hot-dip galvanized aluminum-magnesium steel sheets have become one of the most widely used technologies in the field of steel corrosion protection due to the excellent anti-corrosion performance of the zinc-aluminum-magnesium coating alloy, the unique notch self-healing performance, and the good processability.

[0003] At present, there have been many research reports attempting to further improve the corrosion resistance of hot-dip galvanized aluminum-magnesium coatings. Common methods include doping alloy elements, adjusting the hot-dip plating temperature, or performing heat treatment on it to adjust and change the microstructure of the coating, thereby improving its corrosion resistance. For example, Prosek et al. obtained alloy samples with different microstructures by heat-treating Zn-3wt.%Al-2wt.%Mg alloy (Prosek T, J, Persson D, Fuertes N, Lindberg F, O, Taxén C, J, Thierry D. Effect of the microstructure of Zn-Al and Zn-Al-Mg model alloys on corrosion stability. Corrosion Science. 2016 Sep 1; 110: 71-81). Based on the corrosion test results, they found that the formation of fine microstructure in the alloy was beneficial to the improvement of the overall corrosion resistance of the alloy. Wint studied the effect of microstructure refinement by increasing the cooling rate on the micro-corrosion behavior of Zn-2.7wt.%Al-1.5wt.%Mg coatings (Wint N, Cooze N, Searle JR, Sullivan JH, Williams G, McMurray HN, Luckeneder G, Riener C. The effect of microstructural refinement on the localized corrosion of model Zn-Al-Mg alloy coatings on steel. Journal of The Electrochemical Society. 2019 Apr 25; 166(11): C3147). They found that as the cooling rate increased from 5°C / s to 100°C / s, the microstructure of the coating was refined, the lateral growth rate of corrosion on the coating increased, while the corrosion penetration rate decreased. At the same time, it was found that elements such as Sn (Ding C, Ma Z, Liu S, et al. Research on design and microstructure of hot-dip Zn-Al-Mg / Sn alloy[J]. Materials Characterization, 2022, 185: 111746-.) could refine the grains and thus enhance the corrosion resistance of the coating, and at the same time improve the microstructure uniformity and stability of the corrosion products and thus improve the durability of the coating.

[0004] The disadvantages of these conventional methods are that on the one hand, they will increase the production process steps and production time, thereby leading to an increase in production costs. At the same time, they often lead to a decrease in the mechanical properties such as the hardness and wear resistance of the steel plate coating, thus reducing the durability of the coating. Related research has found that the surface roughness of the substrate is another important factor that affects the coating microstructure and properties. For example, Guo et al. studied the effect of substrate roughness on the corrosion resistance of thermal barrier coatings and found that reducing the substrate roughness helps to improve the corrosion resistance of thermal barrier coatings (Guo L, Li G, Gan Z. Effects of surface roughness on CMAS corrosion behavior for thermal barrier coating applications. Journal of Advanced Ceramics. 2021 Jun; 10: 472-81). Yi studied the effects of substrate grain size and surface roughness on the microstructure and magnetic properties of Ni79Fe21 deposition films and found that the roughness and uniformity of the substrate surface have a great influence on the electroplated film and its properties (Yi JB, Li XP, Ding J, Seet HL. Study of the grain size, particle size and roughness of substrate in relation to the magnetic properties of electroplated permalloy. Journal of alloys and compounds. 2007 Jan 31; 428(1-2): 230-6). Amiriafshar et al. first studied the effect of substrate surface roughness on superhydrophobic coatings. The research results showed that when the substrate surface roughness was 4.62±0.15μm, the uniformity and adhesion durability of the coating on the substrate were significantly improved (Amiriafshar M, Rafieazad M, Duan X, Nasiri A. Fabrication and coating adhesion study of superhydrophobic stainless steel surfaces: The effect of substrate surface roughness. Surfaces and Interfaces. 2020 Sep 1; 20: 100526). Theoretically speaking, the surface roughness of the steel substrate will also affect the microstructure of the zinc-aluminum-magnesium coating, thereby affecting the corrosion resistance of the coating.However, there has been no attempt or report on how to effectively improve the corrosion resistance of the zinc-aluminum-magnesium coating by adjusting the roughness of the steel substrate and the mechanism by which the corrosion resistance is improved. To this end, this application proposes a method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip by adjusting the roughness of the steel substrate. Summary of the invention

[0005] The object of the present invention is to provide a treatment method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a treatment method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip, comprising the following steps:

[0007] Step S1, selecting Zn, Al, Mg, and Si metal single substances with a purity of 99.95-99.99% as raw materials, weighing and proportioning them according to the mass percentage of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn, placing them in an arc melting furnace for melting, and repeating the melting process for not less than 5 times to obtain a molten zinc-aluminum-magnesium alloy liquid;

[0008] Step S2, using sandpaper with a mesh size of 500 to 5000 to pre-treat the roughness of the surface of the steel substrate to obtain a steel substrate with different surface roughness;

[0009] Step S3, alkali washing the pretreated steel substrate;

[0010] Step S4, annealing the steel substrate after alkali washing;

[0011] Step S5, immersing the annealed steel substrate in a molten zinc-aluminum-magnesium alloy liquid at a certain temperature and maintaining it for a certain period of time;

[0012] Step S6: After the hot dip coating is completed, the steel plate is taken out from the zinc-aluminum-magnesium alloy liquid, and after the coating is air-cooled for a certain period of time, the coating is cooled at a fixed cooling rate.

[0013] Preferably, the hot-dip alloy composition in step S1 is weighed and proportioned according to the mass percentage of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn.

[0014] Preferably, the mesh number of the sandpaper used in step S2 is 500 to 5000. The surface of the steel substrate is polished with the sandpaper. Before each replacement of the sandpaper during the polishing process, the surface of the sample needs to be wiped with alcohol to remove the surface impurities. When replacing the sandpaper, the polishing direction needs to be adjusted to rotate 90° clockwise or 90° counterclockwise. After pretreatment, the surface roughness of the steel substrate ranges from 3.00±0.05μm to 0.5±0.05μm.

[0015] Preferably, in step S3, the caustic cleaning solution is a sodium hydroxide (NaOH) solution with a solution concentration of 20%.

[0016] Preferably, in step S3, the caustic cleaning time is 60s. After the caustic cleaning, the steel substrate is rinsed clean with deionized water and then dried in an oven at 50°C for 20min to ensure that the surface moisture is completely volatilized.

[0017] Preferably, in step S4, the steel substrate is annealed. The annealing temperature is set at 550°C to 650°C, and the duration is 1 to 3h. During the annealing process, a mixed atmosphere of hydrogen (H2) and carbon monoxide (CO) with a volume ratio of 1:1 is used for protection.

[0018] Preferably, in step S5, the hot-dip plating temperature is 400°C to 500°C, and the hot-dip plating time is 10s to 30s.

[0019] Preferably, in step S6, the air-cooling time is 10s, and the cooling rate of the hot-dip plating process is 5°C / s to 25°C / s. During the cooling process, nitrogen (N2) must be introduced as the protective gas.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) By annealing the steel substrate used in the present invention, the residual stress that may exist inside the steel after cold working is released, its ductility and formability are increased, and the coating quality is improved;

[0022] (2) The hot-dip plating temperature is 400°C - 500°C. At this temperature range, the zinc liquid has appropriate fluidity, which can promote the full mixing of Zn with Al and Mg elements. At the same time, this temperature range can avoid excessive oxidation of the substrate and ensure good bonding between the coating and the substrate;

[0023] (3) The hot-dip plating time is 10s to 30s, which can effectively promote the diffusion reaction of alloy elements, form a dense and uniform microstructure, and improve the corrosion resistance of the coating;

[0024] (4) By changing the surface roughness of the steel substrate, the ternary eutectic structure in the coating is effectively increased, and the grain orientation on the coating surface is changed, so that the corrosion resistance of the coating is improved.

[0025] (5) The corrosion resistance of the alloy coating produced by the method of the present invention is stably improved, and the method of the present invention is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flowchart of the method of the present invention;

[0027] Figure 2 is the Tafel polarization curve of the comparative example in 3.5 wt% NaCl solution;

[0028] Figure 3 is the Tafel polarization curve of Examples 1 to 3 in 3.5 wt% NaCl solution;

[0029] Figure 4 is the atomic force microscope (AFM) photograph of the steel substrate: (a) comparative example; (b) Example 1; (c) Example 2; (d) Example 3;

[0030] Figure 5 is the XRD diffraction pattern of the alloy of the hot-dip galvanized strip coating;

[0031] Figure 6 is the SEM image of the hot-dip galvanized strip coating: (a)-(c) are the cross-sectional microstructures of the ZAM1, ZAM2, and ZAM3 coatings respectively, and (d)-(f) are the cross-sectional microstructures of the ZAM1, ZAM2, and ZAM3 coatings respectively;

[0032] Figure 7 is the EDS-area scan image of the coating surface: (a) ZAM1; (b) ZAM2; (c) ZAM3;

[0033] Figure 8 is the EBSD map of the steel substrate surface and the coating surface: (a) is the EBSD-IPF map of the steel substrate surface of the unpolished sample, (b) is the EBSD-IPF map of the steel substrate surface of the polished sample, (c) is the EBSD-phase distribution map of the ZAM1 coating surface, (d) is the EBSD-phase distribution map of the ZAM2 coating surface; (e) is the EBSD-IPF map of the ZAM3 coating surface, (f) is the EBSD-IPF map of the ZAM1 coating surface;

[0034] Figure 9 is the EBSD-ODF map of the coating surface: (a)-(c) are the ODF maps of each structure of the ZAM1 coating; (d)-(f) are the ODF maps of each structure of the ZAM2 coating; (g)-(i) are the ODF maps of each structure of the ZAM3 coating.

[0035] (Note: In the drawings, ZAM1, ZAM2, and ZAM3 correspond to Examples 1, 2, and 3 respectively) Specific Embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] Please refer to Figure 1 , a method for treating a hot-dip galvanized aluminum-magnesium sheet to improve its corrosion resistance, including the following steps:

[0038] Step S1: Select Zn, Al, Mg, and Si metal elements with a purity of 99.95-99.99% as raw materials, weigh and mix them according to the mass percentages of Al 5.0-19.0 wt.%, Mg 1.0-5.0 wt.%, Si 0.02-0.3 wt.%, and the balance being Zn, and place them in an electric arc melting furnace for melting. To ensure the uniformity of the composition, the melting process is repeated no less than 5 times to obtain a molten zinc-aluminum-magnesium alloy liquid;

[0039] Step S2: Pretreat the surface roughness of the steel substrate by using sandpaper with a mesh number of 500 to 5000 to obtain steel substrates with different surface roughnesses;

[0040] Step S3: Alkaline wash the pretreated steel substrate to remove impurities such as residual grease and cutting fluid on the surface of the steel substrate;

[0041] Step S4: Anneal the alkaline-washed steel substrate to release the residual stress that may exist inside the steel after cold working, and increase its ductility and formability to improve the coating quality;

[0042] Step S5: Immerse the annealed steel substrate in the molten zinc-aluminum-magnesium alloy liquid at a certain temperature and maintain it for a certain time;

[0043] Step S6: After hot-dip plating is completed, take out the steel plate from the zinc-aluminum-magnesium alloy liquid. After the coating is air-cooled for a certain time, cool the coating at a fixed cooling rate.

[0044] Example 1

[0045] (1) Select Zn, Al, Mg, and Si metal elements with a purity of 99.95 - 99.99% as raw materials. Weigh and proportion them according to the mass percentage: Al 5.0 - 19.0 wt.%, Mg 1.0 - 5.0 wt.%, Si 0.02 - 0.3 wt.%, and the balance is Zn. Then place them in an arc melting furnace for melting. To ensure the uniformity of the composition, the melting process is repeated no less than 5 times to obtain a molten zinc-aluminum-magnesium alloy liquid;

[0046] (2) Use sandpapers with mesh numbers of 2000 and 3000 to polish the surface of the steel substrate. During the polishing process, first use the 2000-mesh sandpaper, and then replace it with the 3000-mesh sandpaper. Before each replacement of the sandpaper during the polishing process, wipe the surface of the steel plate with alcohol. When replacing the sandpaper, adjust the polishing direction, generally rotating 90° clockwise or 90° counterclockwise. After the treatment, the surface roughness of the obtained steel substrate is measured to be 1.579 ± 0.05 μm (the corresponding result corresponds to Figure 4 (b) as shown);

[0047] (3) Use a 20% sodium hydroxide (NaOH) solution to alkali-wash the steel substrate. The alkali-washing time is 60 s. After the alkali-washing is completed, rinse the steel substrate thoroughly with deionized water, and then dry it in an oven at 50°C for 20 min to ensure that the surface moisture is completely volatilized;

[0048] (4) Carry out a holding annealing treatment on the alkali-washed steel substrate at a temperature of 560°C. The annealing time is 2.5 h. During the annealing process, use a mixed atmosphere of hydrogen and carbon monoxide with a volume ratio of 1:1 for protection to prevent oxidation of the steel surface;

[0049] (5) Immerse the annealed steel substrate into the 490°C zinc-aluminum-magnesium molten alloy liquid and stay in the alloy liquid for 10 s;

[0050] (6) After hot-dip plating is completed, take out the steel plate from the zinc-aluminum-magnesium molten alloy liquid, air-cool for 10 s, and then cool the coating at a cooling rate of 5°C / s - 25°C / s to obtain a hot-dip galvanized aluminum-magnesium coated steel plate;

[0051] (7) Carry out electrical discharge cutting on the coated steel plate to obtain 10×10 mm sheet specimens, and test their Tafel polarization curves in a 3.5 wt% NaCl solution through an electrochemical workstation (the corresponding results are shown in Appendix Figure 3 -ZAM1), and obtain the self-corrosion potential of the specimen as -1.3673 A / cm 2 , and the self-corrosion current as 1.6212×10 -6 A / cm 2 .

[0052] Example 2

[0053] (1) Selecting Zn, Al, Mg, and Si metal elements with a purity of 99.95-99.99% as raw materials, weighing and proportioning them according to the mass percentage of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn, placing them in an arc melting furnace for melting, and repeating the melting process for no less than 5 times to ensure the uniformity of the composition, to obtain a molten zinc-aluminum-magnesium alloy liquid;

[0054] (2) The surface of the steel substrate was polished using sandpaper with mesh numbers of 1000 and 2000. During the polishing process, 1000-mesh sandpaper was used first, and then replaced with 2000-mesh sandpaper. Before each replacement of sandpaper during the polishing process, the surface of the steel plate was wiped with alcohol. When replacing the sandpaper, the polishing direction was adjusted, generally rotating 90° clockwise or 90° counterclockwise. After the treatment, the surface roughness of the steel substrate obtained was tested to be 2.072±0.05μm (the corresponding result corresponds to Figure 4 (c));

[0055] (3) using a 20% sodium hydroxide (NaOH) solution to alkaline wash the steel substrate for 60 seconds, rinsing the steel substrate with deionized water after the alkaline washing, and then drying it in an oven at 50° C. for 20 minutes to ensure that the surface moisture is completely volatilized;

[0056] (4) The alkali-washed steel substrate was subjected to heat preservation annealing at 580°C for 2 hours. During the annealing process, a mixed atmosphere of hydrogen and carbon monoxide with a volume ratio of 1:1 was used for protection to prevent oxidation of the steel surface;

[0057] (5) Immerse the annealed steel substrate in a molten zinc-aluminum-magnesium alloy at 460°C and keep it in the alloy for 20 seconds;

[0058] (6) After the hot-dip coating is completed, the steel plate is taken out from the zinc-aluminum-magnesium molten alloy liquid, air-cooled for 10 seconds, and then the coating is cooled at a cooling rate of 5°C / s to 25°C / s to obtain a hot-dip zinc-aluminum-magnesium coated steel plate;

[0059] (7) The coated steel plate was electrospark cut to obtain a 10×10 mm sheet sample, and its Tafel polarization curve in 3.5 wt % NaCl solution was tested by an electrochemical workstation (the corresponding results are shown in the attached Figure 3 -ZAM2), the self-corrosion potential of the sample was -1.3494A / cm 2 , self-corrosion current 1.5254×10 -6 A / cm 2 .

[0060] Implementation 3

[0061] (1) Selecting Zn, Al, Mg, and Si metal elements with a purity of 99.95-99.99% as raw materials, weighing and proportioning them according to the mass percentage of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn, placing them in an arc melting furnace for melting, and repeating the melting process for no less than 5 times to ensure the uniformity of the composition, to obtain a molten zinc-aluminum-magnesium alloy liquid;

[0062] (2) The surface of the steel substrate was polished using sandpaper with mesh numbers of 500 and 1000. During the polishing process, 500-mesh sandpaper was used first, and then replaced with 1000-mesh sandpaper. Before each replacement of sandpaper during the polishing process, the surface of the steel plate was wiped with alcohol. When replacing sandpaper, the polishing direction was adjusted, generally rotating 90° clockwise or 90° counterclockwise. After the treatment, the surface roughness of the steel substrate obtained was tested to be 2.772±0.05μm (the corresponding result corresponds to Figure 4 (d));

[0063] (3) using a 20% sodium hydroxide (NaOH) solution to alkaline wash the steel substrate for 60 seconds, rinsing the steel substrate with deionized water after the alkaline washing, and then drying it in an oven at 50° C. for 20 minutes to ensure that the surface moisture is completely volatilized;

[0064] (4) The alkali-washed steel substrate was subjected to heat preservation annealing at 620° C. for 1.5 h. During the annealing process, a mixed atmosphere of hydrogen and carbon monoxide with a volume ratio of 1:1 was used for protection to prevent oxidation of the steel surface;

[0065] (5) Immerse the annealed steel substrate in a molten zinc-aluminum-magnesium alloy at 430°C and keep it in the alloy for 30 seconds;

[0066] (6) After the hot-dip coating is completed, the steel plate is taken out from the zinc-aluminum-magnesium molten alloy liquid, air-cooled for 10 seconds, and then the coating is cooled at a cooling rate of 5°C / s to 25°C / s to obtain a hot-dip zinc-aluminum-magnesium coated steel plate;

[0067] (7) The coated steel plate was electrospark cut to obtain a 10×10 mm sheet sample, and its Tafel polarization curve in 3.5 wt % NaCl solution was tested by an electrochemical workstation (the corresponding results are shown in the attached Figure 3 -ZAM3), the self-corrosion potential of the sample was -1.3830A / cm 2 , self-corrosion current 1.2746×10 -6 A / cm 2 .

[0068] Comparative Example 1

[0069] (1) Select Zn, Al, Mg, and Si metal elements with a purity of 99.95 - 99.99% as raw materials. Weigh and proportion them according to the mass percentages: Al 5.0 - 19.0 wt.%, Mg 1.0 - 5.0 wt.%, Si 0.02 - 0.3 wt.%, and the balance is Zn. Then place them in an arc melting furnace for melting. To ensure the uniformity of the composition, the melting process is repeated no less than 5 times to obtain a molten zinc-aluminum-magnesium alloy liquid.

[0070] (2) Conduct AFM testing on the original steel substrate without sandpaper polishing treatment, and measure the roughness of the steel substrate to be 1.054 ± 0.05 μm (as shown in the corresponding steel substrate roughness result Figure 4 (a)).

[0071] (3) Use a 20% sodium hydroxide (NaOH) solution to alkali-wash the steel substrate for 60 s. After the alkali-washing is completed, rinse the steel substrate with deionized water, and then dry it in an oven at 50 °C for 20 min to ensure that the surface moisture is completely volatilized.

[0072] (4) Conduct a heat preservation annealing treatment on the alkali-washed steel substrate at a temperature of 560 °C for 2.5 h. During the annealing process, use a mixed atmosphere of hydrogen and carbon monoxide with a volume ratio of 1:1 for protection to prevent oxidation of the steel surface.

[0073] (5) Immerse the annealed steel substrate into the 490 °C zinc-aluminum-magnesium molten alloy liquid and stay in the alloy liquid for 10 s.

[0074] (6) After hot-dip plating is completed, take out the steel plate from the zinc-aluminum-magnesium molten alloy liquid. After air-cooling for 10 s, cool the coating at a cooling rate of 5 °C / s - 25 °C / s to obtain a hot-dip galvanized zinc-aluminum-magnesium coated steel plate.

[0075] (7) Conduct electrical discharge machining on the coated steel plate to obtain 10×10 mm sheet specimens, and test their Tafel polarization curves in a 3.5 wt% NaCl solution through an electrochemical workstation (the corresponding results are shown in the appendix Figure 2 ), and obtain the self-corrosion potential of the specimen as -1.4030 A / cm 2 , and the self-corrosion current as 2.0212×10 -6 A / cm 2，

[0076] Table 1 Corrosion resistance of hot-dip plated strip in Comparative Example 1 and Examples 1 - 3

[0077]

[0078] The roughness, self-corrosion potential, and self-corrosion current of the steel substrates in Comparative Example 1 and Examples 1-3 are shown in Table 1. For Comparative Example 1 without sandpaper polishing, the self-corrosion potential and self-corrosion current of the coating are -1.4030 A / cm 2 and 2.0212×10 -6 A / cm 2 . For Examples 1, 2, and 3, as the roughness increases, the self-corrosion potential is higher than that of Comparative Example 1, and the self-corrosion current is smaller than that of Comparative Example 1, indicating that the corrosion resistance of the three examples is better than that of Comparative Example 1. It can be seen that after being treated by the method proposed in the present invention, the corrosion resistance of the hot-dip galvanized aluminum-magnesium coating is improved.

[0079] The reason for the improvement of the corrosion resistance of the hot-dip galvanized aluminum-magnesium coating in the present invention is explained as follows: It can be seen that although the roughness of the steel substrate is different, the phase composition of the obtained coating alloy is the same and does not change with the roughness of the steel plate substrate, hot-dip plating time, and temperature. However, through Figure 5 it can be seen that as the roughness of the steel substrate and the hot-dip plating time increase, and the hot-dip plating temperature decreases, the size of the Al-rich dendrites on the coating surface decreases, the area fraction of the Al dendrites gradually decreases, and the area fraction of the eutectic structure gradually increases. From Figure 6 and Figure 6 it can be further seen that when the roughness of the steel substrate surface is increased, there are more Al-rich dendrites on the contact surface between the steel substrate and the coating, indicating that the larger roughness of the steel substrate surface provides a more favorable environment for the growth of the coating structure. Increasing the hot-dip plating time can promote the formation of the intermetallic compound layer, and the lower hot-dip plating temperature can prevent the grains of the Al-rich phase dendrites from being too large. From the EBSD-IPF diagrams of the steel substrate surface and the coating surface shown in Figure 7 , it can be seen that as the roughness of the steel substrate surface and the hot-dip plating time increase, and the hot-dip plating temperature decreases, the grains of the Al-rich phase dendrites on the coating surface gradually decrease, and the phase area fraction gradually decreases; the phase area fraction of the eutectic structure gradually increases; the phase area fraction of the MgZn2 phase gradually increases. From Figure 8 it can be seen that as the roughness of the steel substrate surface and the hot-dip plating time increase, and the hot-dip plating temperature decreases, the grains of the Al-rich phase dendrites on the coating surface gradually decrease, the phase area fraction gradually decreases; the phase area fraction of the eutectic structure gradually increases; the phase area fraction of the MgZn2 phase gradually increases. From Figure 9The EBSD-ODF images of the shown coating structure further show that the Al-rich phase dendrites in the coating exhibit a typical Cube{001}<100> texture, and the eutectic structure exhibits a typical {10-10}<11-20> texture. By comparison, it can be found that with different roughnesses of the steel substrate, there are obvious differences in the texture distributions of the pole figures and ODF maps. The greater the roughness of the steel substrate, the more heterogeneous the grain orientations on the coating surface, showing anisotropy. The above results indicate that the surface roughness of the steel substrate, the hot-dip coating time, and the hot-dip coating temperature have a great influence on the microstructure of the hot-dip galvanized aluminum-magnesium coating. For the coating microstructures obtained after hot-dip coating with different hot-dip coating parameters, the greater the roughness, the longer the hot-dip coating time, and the lower the hot-dip coating temperature, the smaller the size and area fraction of the Al-rich phase dendrites on the coating surface, and the greater the area fraction of the eutectic structure. This shows that by increasing the surface roughness of the steel substrate and decreasing the hot-dip coating temperature, the grains and content of the Al-rich phase dendrites in the coating can be reduced, and there are more ternary eutectic structures. At the same time, the grain orientations of the phases in the coating show higher anisotropy. In addition, with the increase of the hot-dip coating time, the elements such as Al and Mg in the coating diffuse sufficiently, preventing the segregation of elements and causing pitting corrosion. These factors improve the corrosion resistance of the hot-dip galvanized aluminum-magnesium coating.

[0080] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0081] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip, characterized in that: The steps include: Step S1, selecting Zn, Al, Mg, and Si metal single substances with a purity of 99.95-99.99% as raw materials, weighing and proportioning them according to the mass percentage of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn, placing them in an arc melting furnace for melting, and repeating the melting process for not less than 5 times to obtain a molten zinc-aluminum-magnesium alloy liquid; Step S2, using sandpaper with a mesh size of 500 to 5000 to pre-treat the roughness of the surface of the steel substrate to obtain a steel substrate with different surface roughness; Step S3, alkali washing the pretreated steel substrate; Step S4, annealing the steel substrate after alkali washing; Step S5, immersing the annealed steel substrate in a molten zinc-aluminum-magnesium alloy liquid at a certain temperature and maintaining it for a certain period of time; Step S6: After the hot-dip coating is completed, the steel plate is taken out from the zinc-aluminum-magnesium alloy liquid, and after the coating is air-cooled for a certain period of time, the coating is cooled at a fixed cooling rate.

2. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 1, characterized in that: The hot-dip alloy components in step S1 are weighed and proportioned according to the mass percentages of Al 5.0-19.0wt.%, Mg 1.0-5.0wt.%, Si 0.02-0.3wt.%, and the balance Zn.

3. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 2, characterized in that: In step S2, the mesh number of the sandpaper used is 500 to 5000, and the surface of the steel substrate is polished with the sandpaper. Before each replacement of the sandpaper during the polishing process, the surface of the sample needs to be wiped with alcohol to remove surface impurities. When replacing the sandpaper, the polishing direction needs to be adjusted to rotate 90° clockwise or 90° counterclockwise. The surface roughness of the steel substrate after pretreatment ranges from 3.00±0.05μm to 0.5±0.05μm.

4. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 3, characterized in that: The alkaline washing solution in step S3 is a sodium hydroxide (NaOH) solution, and the concentration of the solution is 20%.

5. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 4, characterized in that: The alkali washing time in step S3 is 60 seconds. After the alkali washing, the steel substrate is rinsed with deionized water and then dried in an oven at 50° C. for 20 minutes to ensure that the surface moisture is completely volatilized.

6. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 5, characterized in that: In the step S4, the steel substrate is annealed, the annealing temperature is set at 550°C to 650°C, the duration is 1 to 3 hours, and a mixed atmosphere of hydrogen (H2) and carbon monoxide (CO) with a volume ratio of 1:1 is used for protection during the annealing process.

7. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 6, characterized in that: The hot-dip coating temperature in step S5 is 400° C. to 500° C., and the hot-dip coating time is 10 s to 30 s.

8. A method for improving the corrosion resistance of hot-dip galvanized aluminum-magnesium strip according to claim 7, characterized in that: The air cooling time in step S6 is 10 seconds, and the cooling rate of the hot dip coating process is 5°C / s to 25°C / s. Nitrogen (N2) must be introduced as a protective gas during the cooling process.

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