A method for producing a plated steel sheet, plated steel sheet and plated steel strip

Abstract

The present application belongs to the field of strip steel coating, and particularly relates to a steel plate coating, a coated steel plate and a preparation method of a coated strip steel. The coating comprises the following elements: Al, Si, Mg, Sm and Zn. Through the design of the coating composition, the present application can refine the coating grains, prevent the formation of coarse MgZn2 metal compounds, and improve the corrosion resistance and processability of the coating.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of strip steel coating, and particularly relates to a steel plate coating, a coated steel plate and a method for preparing a coated strip steel. BACKGROUND

[0002] A photovoltaic array is a core component of photovoltaic power generation, which needs to be installed on a photovoltaic support and in an outdoor environment with sufficient sunlight. Since the outdoor environment needs to face the harsh weather of exposure to the sun and rain, and the photovoltaic power station design requires a service life of more than 25 years, the corrosion resistance of the support is extremely high, and the current requirement for the coating of the photovoltaic support is that the red rust time under the neutral salt spray test condition is greater than or equal to 3000 hours. Before the zinc-aluminum-magnesium coating technology, the method for manufacturing the photovoltaic support was to first process the strip steel into parts, and then hot-dip galvanize, with the coating thickness needing to reach 65μ (950g / m 2 ) or more, which is not only high in cost and large in waste, but also not energy-saving and environmentally friendly. Under this background, the zinc-aluminum-magnesium alloy coating technology has been rapidly developed through the progress of the coating technology, and the zinc-aluminum-magnesium coating has excellent corrosion resistance, which is 3-15 times of that of the ordinary pure zinc coating with the same thickness, and the zinc-aluminum-magnesium coating with a thickness of 275g / m 2 ) can have a red rust time of 3000 hours under the NSST, meeting the corrosion resistance requirement of the photovoltaic support, and having the advantages of low carbon, energy saving and environmental protection. However, the zinc-aluminum-magnesium coating, especially the medium aluminum zinc-aluminum-magnesium coating, is prone to coating bending cracks in the processing of the photovoltaic support, which leads to the decrease of the corrosion resistance and thus affects the service life of the photovoltaic power generation; meanwhile, the coating is also prone to zinc powder falling due to friction with the processing groove, which affects the quality and processing efficiency of the parts.

[0003] Some methods for producing zinc-aluminum-magnesium coated strip steel or improving the quality and performance of the aluminum-magnesium-zinc coating are disclosed in the prior art, such as:

[0004] CN106222593A applies for a high-corrosion-resistant hot-dip galvanized zinc-aluminum-magnesium-nickel-rare earth alloy coated strip steel and a production method thereof, and the alloy composition of the coating is (5-25%Al)-(1-5%Mg)-(0.1-0.3%Si)-(0.01-0.1%Ni)-(0.01-0.1Ce)-Zn. The surface oxidation resistance of the strip steel coating is improved, and the blackening resistance and corrosion resistance of the strip steel coating are improved.

[0005] CN105420653B authorizes a hot-dip plated Zn-Al-Mg alloy layer on the surface of a bridge steel wire and a preparation method thereof, and the alloy layer composition is Zn 30-97%, Al 5-60%, Mg 0.02-11% by mass percentage, and the total satisfies 100%. The plated layer has better corrosion resistance than the galvanized and zinc-aluminum alloy plated layers, and the preparation method comprises: oil and rust removal of the bridge steel wire, hot-dip plating of the alloy layer and stabilization treatment.

[0006] CN110760774A discloses a method for preparing zinc-aluminum-magnesium strip steel and effectively controlling black spots on the surface of hot-dip galvanized aluminum-magnesium strip steel using the CSP process. The coating alloy composition is Al: 10-12%, Mg: 2-4%, Si: 0.01-0.3%, Ni: 0.01-0.1%, Ce: 0.01-0.15%, with the remainder being Zn and unavoidable impurities. This method ensures good surface quality of the zinc-aluminum-magnesium strip steel without black spot defects.

[0007] CN103507324A discloses an alloyed zinc-aluminum-magnesium coated steel strip and its production method. The alloy composition of the coating is: Al: 1.0wt%–11wt%, Mg: 0.5wt%–5wt%, mixed rare earth content: 0.01wt%–0.10wt%, with the remainder being Zn and unavoidable impurities. The alloying temperature is 450–650℃, the alloying time is 3–20s, and the Fe content in the alloyed coating does not exceed 5%, ensuring that the coating does not peel off during complex forming processes. This allows the zinc-aluminum-magnesium coating to exhibit excellent corrosion resistance and extend the service life of components.

[0008] CN110777290A discloses a method for preparing hot-dip galvanized aluminum-magnesium high-strength steel. The coating alloy composition is: Al: 9.0-13.0%, Mg: 2.0-4.0%, Si: 0.02-0.1%, Ni: 0.01-0.05%, RE: 0.01-0.2%, with the balance being Zn and unavoidable impurity elements. Through a process scheme and core production technology control of smelting, hot rolling, cold rolling, and annealing, hot-dip galvanized aluminum-magnesium high-strength steel with a yield strength greater than 550MPa and an elongation greater than 17% is produced.

[0009] The coated steel strips obtained by the aforementioned patents have improved surface quality, coating corrosion resistance, coating adhesion, and steel base strength, but they have failed to solve the problems of coating cracks and friction zinc powder in the processing of zinc-aluminum-magnesium coated steel strips, especially those made of Alcoa zinc-aluminum-magnesium coated steel. This results in a decrease in corrosion resistance and processability, and thus cannot meet the high requirements of corrosion resistance and processability of photovoltaic brackets.

[0010] In view of this, the present invention is hereby proposed. Summary of the Invention

[0011] To address the technical problems existing in the prior art, this invention provides a method for preparing steel plate coatings, coated steel plates, and coated strips. This invention, through the design of the coating composition, achieves the goal of refining the coating grains, preventing the formation of coarse MgZn2 metal compounds, and improving the corrosion resistance and processability of the coating. Sm, with its active chemical properties, readily combines with Si, preferentially forming crystal nuclei during plating solution solidification, fully utilizing the heterogeneous crystallization process to refine the coating microstructure and further improve corrosion resistance and processability. Simultaneously, Sm has a density comparable to Zn solution, facilitating uniform distribution in the plating solution, reducing slag formation and improving product surface quality and uniformity. Furthermore, the Zn / Mg ratio in the plating solution is designed to hinder the growth of the MgZn2 phase, preventing the formation of coarse MgZn2 phases that could negatively impact coating performance. The post-plating cooling employs a "controlled cooling + rapid cooling + slow cooling" mode, which not only solves the black spot problem but also refines the coating microstructure and MgZn2 phase, effectively improving the corrosion resistance and processability of the coating.

[0012] This invention includes the following technical solutions:

[0013] The first aspect of the present invention provides a steel plate coating comprising the following elements: Al, Si, Mg, Sm and Zn.

[0014] Further, the coating comprises the following components by weight percentage: Al: 11.1-18.0%, Si: 0.30-0.65%, Mg: 2.0-3.0%, Sm: 0.1-0.3% and Zn: 78.10-86.20%.

[0015] A second aspect of the present invention provides a coated steel sheet comprising the coating described above.

[0016] A third aspect of the present invention provides a method for preparing a coated steel sheet, comprising the following steps:

[0017] Clean the steel strip;

[0018] The cleaned strip steel is then annealed.

[0019] The annealed strip steel is hot-dip galvanized, and the galvanizing solution is the steel plate coating described above.

[0020] Cooling the hot-dip galvanized steel strip yields coated steel strip.

[0021] The coated steel strip undergoes finishing and corrosion-resistant coating treatment.

[0022] Furthermore, a corrosion-resistant coating is applied to the coated steel strip, the corrosion-resistant coating comprising: silane, water-based resin, corrosion inhibitor and special lubricant; preferably, the coated steel strip is subjected to a finishing treatment before applying the corrosion-resistant coating.

[0023] Furthermore, the plating solution comprises the following components by weight percentage: Al: 11.1–18.0%, Si: 0.30–0.65%, Mg: 2.0–3.0%, Sm: 0.1–0.3%, and Zn: 78.10–86.20%, with a Zn / Mg ratio satisfying 35 ± 4.

[0024] Furthermore, the hot-dip galvanizing process is as follows: the temperature of the strip steel entering the zinc pot is 490-510℃, and the temperature of the galvanizing solution is 480-500℃.

[0025] Furthermore, the cleaning process is as follows: the strip steel is sequentially cleaned twice, through a degreasing cleaning tank and a rinsing tank, and then dried; preferably, the temperature of the bath solution in the degreasing cleaning tank is 60-80℃, and the free alkalinity of the alkali solution is 75±10Pt; the free alkalinity of the rinsing tank is ≤15Pt; and the drying temperature is ≥120℃.

[0026] Furthermore, the annealing process is as follows: annealing temperature 690-780℃; the furnace uses a nitrogen-hydrogen protective gas with an H2 content of 5-10%.

[0027] Furthermore, the hot-dip galvanized strip steel is subjected to a three-stage cooling method; preferably, the three-stage cooling includes a first cooling section (which can move vertically and horizontally), a second cooling section (which can move horizontally), and a third cooling section (a fixed cooling section). The first cooling section moves vertically to a position of 500-800mm in the air knife height direction, and the cooling rate is controlled at 8-12℃ / s; the second cooling section has a cooling rate ≥15℃ / s, and the temperature of the strip steel when it exits the second cooling section is ≤330℃; the third cooling section has a cooling rate ≥5℃ / s, and the high-span cooling temperature is ≤260℃.

[0028] By adopting the above technical solution, the present invention has the following advantages:

[0029] 1. This invention, through the design of the coating composition, aims to refine the coating grains and improve the coating's corrosion resistance and processability. Sm, being chemically reactive, readily combines with Si, preferentially forming crystal nuclei during plating solution solidification. This fully leverages the heterogeneous crystallization process, refining the coating structure and further enhancing its corrosion resistance and processability. Simultaneously, Sm has a density comparable to Zn solution, facilitating uniform distribution in the plating solution, reducing slag formation and improving product surface quality and uniformity.

[0030] 2. In this invention, the Zn / Mg ratio satisfies 35±4. If the Zn / Mg ratio is lower than the lower limit, the probability of MgZn2 phase formation and growth will increase, resulting in coarse MgZn2 phases with a size exceeding 20μm, which is detrimental to the corrosion resistance and processability of the coating. If the Zn / Mg ratio is higher than the upper limit, the proportion of fine ternary eutectic structure in the coating decreases, and undesirable Mg2Zn structure is formed. 11An increased probability of the MgZn2 phase is detrimental to the corrosion resistance of the coating. By constraining the Zn / Mg ratio, the size of the MgZn2 phase can be controlled within 10 μm, ensuring a fine ternary eutectic structure and improving the corrosion resistance of the coating.

[0031] 3. This invention employs a three-stage cooling system, namely, post-plating cooling using a "controlled cooling + rapid cooling + slow cooling" mode. If the controlled cooling is too rapid, the large airflow will quickly oxidize the plating layer, resulting in black spot defects. If the cooling is too slow, it will form undesirable Mg2Zn microstructure. 11 After controlled cooling, rapid cooling is used to quickly cool the plating solution below the eutectic point, refining the coating grains and MgZn2 phase to improve the coating's corrosion resistance and processability. Finally, slow cooling is applied to meet the final process requirements.

[0032] 4. The coated steel strip of the present invention can meet the high requirements of corrosion resistance and processability of photovoltaic brackets.

[0033] 5. The present invention controls the content of coating components to prevent the formation of coarse MgZn2 phase in binary eutectic and to control the formation of MgZn2 condensation phase in ternary eutectic structure, which has the advantages of refining grains and improving the corrosion resistance and processability of coating. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a diagram of the coating microstructure when the Zn / Mg ratio is 35.

[0036] Figure 2 This is a diagram of the coating microstructure when the Zn / Mg ratio is 27.

[0037] Figure 3 The relationship between the size of the MgZn2 phase and the Zn / Mg ratio in the coating;

[0038] Figure 4 The relationship between the ternary eutectic and the Zn / Mg ratio in the coating;

[0039] In the attached diagram: 1-Al-rich phase, 2-ternary eutectic, 3-Al-rich phase, 4-MgZn2. Detailed Implementation

[0040] The following description provides many different embodiments or examples for implementing various features of the invention. The elements and arrangements described in the specific examples below are only for concise expression of the invention and are merely examples, not intended to limit the invention.

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] This embodiment provides a steel plate coating, which includes the following elements: Al, Si, Mg, Sm and Zn.

[0043] Further, the coating comprises the following components by weight percentage: Al: 11.1-18.0%, Si: 0.30-0.65%, Mg: 2.0-3.0%, Sm: 0.1-0.3%, Zn: 78.10-86.20%.

[0044] The present invention controls the content of the coating components to prevent the formation of coarse MgZn2 phase, such as... Figures 1-3 And increase the proportion of ternary eutectic, such as Figure 4 At the same time, it prevents the formation of undesirable Mg2Zn. 11 Phase formation has the advantages of refining grains and improving the corrosion resistance and processability of the coating.

[0045] This embodiment also provides a coated steel sheet, including the coating described above.

[0046] This embodiment also provides a method for preparing coated steel sheet, including the following steps:

[0047] Clean the steel strip;

[0048] The cleaned strip steel is then annealed.

[0049] The annealed strip steel is then hot-dip galvanized; the galvanizing solution is the steel plate coating described above.

[0050] Cooling the hot-dip galvanized steel strip yields coated steel strip.

[0051] Further, a corrosion-resistant coating is applied to the coated steel strip; preferably, the coated steel strip is subjected to a finishing treatment before applying the corrosion-resistant coating.

[0052] The finishing rolling force is ≥200T to ensure good surface roughness, which helps to improve the adhesion and uniformity of the environmentally friendly coating.

[0053] Furthermore, the corrosion-resistant coating comprises: silane, water-based resin, corrosion inhibitor, and special lubricant. The specially selected water-based resin and corrosion inhibitor further enhance corrosion resistance, while the water-based resin and lubricant facilitate processing lubrication and reduce zinc powder shedding.

[0054] Furthermore, the cleaning process is as follows: the strip steel is sequentially cleaned twice, through a degreasing cleaning tank and a rinsing tank, and then dried; preferably, the temperature of the bath solution in the degreasing cleaning tank is 60-80℃, and the free alkalinity of the alkali solution is 75±10Pt; the free alkalinity of the rinsing tank is ≤15Pt; and the drying temperature is ≥120℃.

[0055] Furthermore, the annealing process is as follows: annealing temperature 690–780℃; the furnace uses a nitrogen-hydrogen protective gas with an H2 content of 5–10%. This reduces the surface of the strip steel to spongy pure iron, improving coating adhesion and eliminating defects such as incomplete coating and poor coating adhesion.

[0056] Furthermore, the strip enters the zinc pot at a temperature of 490–510°C. Through the core heat of the strip, it helps to retain heat after exiting the zinc pot and improves the fluidity of the plating solution, thereby improving the coating quality.

[0057] Further, the plating bath comprises the following components by weight percentage: Al: 11.1–18.0%, Si: 0.30–0.65%, Mg: 2.0–3.0%, Sm: 0.1–0.3%, and Zn: 78.10–86.20%, wherein the Zn / Mg ratio satisfies 35 ± 4. Sm in the plating bath can refine the coating structure and reduce slag formation during burning, further improving the coating's corrosion resistance, processability, and surface quality. By constraining the Zn / Mg ratio within the range of 35 ± 4, coarse MgZn2 phase is prevented, thus improving the coating's corrosion resistance.

[0058] In this invention, the Zn / Mg ratio of the plating solution meets the requirement of 35±4. If the Zn / Mg ratio is lower than the lower limit, a MgZn2 phase will be generated before the ternary eutectic, increasing the probability of abnormal growth of the MgZn2 phase. Figure 2 This leads to the formation of coarse MgZn2 phases with a size greater than 20 μm, deteriorating the corrosion resistance and processability of the coating. If the Zn / Mg ratio exceeds the upper limit, undesirable Mg2Zn microstructures will form in the coating. 11 The increased probability of phase formation and reduced proportion of fine ternary eutectic crystals are detrimental to the corrosion resistance of the coating. This can be addressed by controlling the Zn / Mg ratio of the plating solution, such as... Figure 1 The coating structure is mainly composed of Al-rich phase and ternary eutectic. The MgZn2 phase is mainly present in the fine ternary eutectic, or precipitates with a size of less than 10 μm, which improves the corrosion resistance of the coating.

[0059] Furthermore, the hot-dip plating process involves a plating bath temperature of 480–500°C. This aims to improve the fluidity of the plating bath and enhance the quality of the plating layer.

[0060] Furthermore, a nitrogen gas knife is used to blow on the hot-dip coated steel strip to achieve a coating weight of 275–350 g / m². The nitrogen gas knife improves the fluidity of the plating solution and the surface quality of the steel strip.

[0061] Furthermore, the hot-dip galvanized strip steel is cooled using a three-stage cooling method: controlled cooling + rapid cooling + slow cooling. Preferably, the three-stage cooling includes a first cooling section (movable vertically and horizontally), a second cooling section (movable horizontally), and a third cooling section (fixed cooling section). The first cooling section is moved vertically to a position 500–800 mm above the air knife, with a cooling rate controlled at 8–12 °C / s. The second cooling section has a cooling rate ≥15 °C / s, and the strip steel temperature upon exiting the second cooling section is ≤330 °C. The third cooling section has a cooling rate ≥5 °C / s, and the high-span cooling temperature is ≤260 °C. Through three-stage cooling, the formation of phases during the solidification process of the plating solution is controlled, black spot defects are avoided, the coating grains and MgZn2 phase are refined, and the corrosion resistance, processability, and surface quality of the coating are improved.

[0062] Example 1

[0063] This invention discloses a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 71℃, the free alkalinity of the alkaline solution in the degreasing tank is 66Pt, the free alkalinity in the rinsing tank is 10Pt, and the hot air drying temperature of the strip is 120℃. The strip annealing temperature is 692℃, the nitrogen-hydrogen protective gas H2 content is 6.2%, the strip enters the zinc pot at 490℃, and the composition of the plating solution in the zinc pot is 11.32% Al, 0.35% Si, 2.73% Mg, 0.24% Sm, 85.22% Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 31.2. The plating solution temperature is 480℃, the first cooling section maintains a 500mm distance from the air knife, the cooling rate is 8℃ / s, the second cooling section has a cooling rate of 18℃ / s, the strip exits the second cooling section at 320℃, and the final cooling temperature is 280℃. The coating weight is 275g / m2, the finishing rolling force is 220T, and the surface is treated with a corrosion-resistant coating.

[0064] Testing revealed that the coating composition of the obtained coated steel sheet was 11.72% Al, 0.31% Si, 2.86% Mg, 0.27% Sm, and 84.67% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0065] Example 2

[0066] The present invention describes a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 62℃, the free alkalinity of the alkaline solution in the degreasing tank is 83Pt, the free alkalinity in the rinsing tank is 15Pt, and the hot air drying temperature of the strip is 130℃. The strip annealing temperature is 775℃, the nitrogen-hydrogen protective gas H2 content is 9.5%, the strip entering the zinc pot temperature is 510℃, and the plating solution composition is 17.38%Al, 0.60%Si, 2.25%Mg, 0.20%Sm, 79.42%Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 35.3. The plating solution temperature is 498℃, the first cooling section maintains a distance of 780mm from the air knife, the cooling rate is 12℃ / s, the second cooling section has a cooling rate of 16℃ / s, the strip exiting the second cooling section has a temperature of 330℃, and the highest cooling temperature is 255℃. The coating weight is 350g / m2, the finishing rolling force is 240T, and the surface is treated with a corrosion-resistant coating.

[0067] Testing revealed that the coating composition of the obtained coated steel sheet was 17.67% Al, 0.56% Si, 2.43% Mg, 0.22% Sm, and 78.94% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0068] Example 3

[0069] The present invention discloses a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 80℃, the free alkalinity of the alkaline solution in the degreasing tank is 75Pt, the free alkalinity in the rinsing tank is 8Pt, and the hot air drying temperature of the strip is 135℃. The strip annealing temperature is 740℃, the nitrogen-hydrogen protective gas H2 content is 8.0%, the strip entering the zinc pot temperature is 500℃, and the plating solution composition is 13.72% Al, 0.44% Si, 2.57% Mg, 0.18% Sm, 82.95% Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 32.3. The plating solution temperature is 490℃, the first cooling section maintains a distance of 600mm from the air knife, the cooling rate is 10℃ / s, the second cooling section has a cooling rate of 19℃ / s, the strip exits the second cooling section at 325℃, and the final cooling temperature is 245℃. The coating weight is 320g / m2, the finishing rolling force is 220T, and the surface is treated with an environmentally friendly coating.

[0070] Testing revealed that the coating composition of the obtained coated steel sheet was 14.01% Al, 0.42% Si, 2.64% Mg, 0.18% Sm, and 82.53% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0071] Example 4

[0072] The present invention describes a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 68℃, the free alkalinity of the alkaline solution in the degreasing tank is 80Pt, the free alkalinity in the rinsing tank is 12Pt, and the hot air drying temperature of the strip is 122℃. The strip annealing temperature is 710℃, the nitrogen-hydrogen protective gas H2 content is 5.0%, the strip entering the zinc pot temperature is 492℃, and the plating solution composition is 15.25%Al, 0.52%Si, 2.18%Mg, 0.12%Sm, 81.75%Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 37.5. The plating solution temperature is 495℃, the first cooling section of the high-span is maintained at a distance of 700mm from the air knife, the cooling rate is 10℃ / s, the second cooling section has a cooling rate of 21℃ / s, the strip exiting the second cooling section has a temperature of 315℃, and the high-span temperature is 235℃. The coating weight is 285g / m2, the finishing rolling force is 260T, and the surface is treated with an environmentally friendly coating.

[0073] Testing revealed that the coating composition of the obtained coated steel sheet was 14.85% Al, 0.52% Si, 2.13% Mg, 0.14% Sm, and 82.11% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0074] Example 5

[0075] The present invention discloses a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 75℃, the free alkalinity of the alkaline solution in the degreasing tank is 70Pt, the free alkalinity in the rinsing tank is 7Pt, and the hot air drying temperature of the strip is 125℃. The strip annealing temperature is 735℃, the nitrogen-hydrogen protective gas H2 content is 6.0%, the strip entering the zinc pot temperature is 508℃, and the plating solution composition is 12.31%Al, 0.32%Si, 2.37%Mg, 0.16%Sm, 84.53%Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 35.6. The plating solution temperature is 480℃, the first cooling section in the high span is maintained at a distance of 600mm from the air knife, the cooling rate is 12℃ / s, the cooling rate in the second cooling section is 20℃ / s, the strip exiting the second cooling section is 325℃, and the high span temperature is 250℃. The coating weight is 300g / m2, the finishing rolling force is 260T, and the surface is treated with an environmentally friendly coating.

[0076] Testing revealed that the coating composition of the obtained coated steel sheet was 11.58% Al, 0.38% Si, 2.40% Mg, 0.15% Sm, and 85.18% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0077] Example 6

[0078] The present invention describes a method for preparing coated steel sheet: the degreasing and cleaning tank temperature is 73℃, the free alkalinity of the alkaline solution in the degreasing tank is 85Pt, the free alkalinity in the rinsing tank is 13Pt, and the hot air drying temperature of the strip is 120℃. The strip annealing temperature is 780℃, the nitrogen-hydrogen protective gas H2 content is 7.0%, the strip entering the zinc pot temperature is 495℃, and the plating solution composition is 13.10% Al, 0.42% Si, 2.60% Mg, 0.12% Sm, 83.46% Zn, with the remainder being unavoidable impurities, and the Zn / Mg ratio is 32.1. The plating solution temperature is 490℃, the first cooling section in the high span maintains a distance of 630mm from the air knife, the cooling rate is 10℃ / s, the second cooling section has a cooling rate of 18℃ / s, the strip exiting the second cooling section has a temperature of 330℃, and the high span temperature is 245℃. The coating weight is 300g / m2, the finishing rolling force is 260T, and the surface is treated with an environmentally friendly coating.

[0079] Testing revealed that the coating composition of the obtained coated steel sheet was 13.42% Al, 0.38% Si, 2.55% Mg, 0.15% Sm, and 83.32% Zn, with the remainder being unavoidable impurities. The MgZn2 phase in the coating was uniform and fine. Under neutral salt spray testing conditions, the coated steel sheet exhibited good corrosion resistance, and no coating cracks or indentations caused by zinc powder polymerization occurred during photovoltaic bracket processing. The product demonstrated excellent surface quality, corrosion resistance, and processability, meeting the requirements for photovoltaic bracket applications.

[0080] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing coated steel sheet, characterized in that, The preparation method includes the following steps: Clean the steel strip; The cleaned strip steel is then annealed. The annealed strip steel is then hot-dip galvanized. Cooling the hot-dip galvanized steel strip yields coated steel strip. The coated steel strip undergoes finishing and corrosion-resistant coating treatment; The coating of the coated steel strip includes the following elements: Al, Si, Mg, Sm and Zn; the hot-dip galvanizing solution includes the following components by weight percentage: Al: 11.1-18.0%, Si: 0.30-0.65%, Mg: 2.0-3.0%, Sm: 0.1-0.3%, Zn: 78.10-86.20%, and other unavoidable impurities, with a Zn / Mg ratio of 35±4.

2. The method for preparing a coated steel sheet as described in claim 1, characterized in that, The hot-dip galvanizing process is as follows: the strip steel is placed in the zinc pot at a temperature of 490-510°C, and the galvanizing solution temperature is 480-500°C.

3. The method for preparing a coated steel sheet as described in claim 1, characterized in that, The cleaning process is as follows: the strip steel is sequentially cleaned twice, through a degreasing cleaning tank and a rinsing tank, and then dried; the temperature of the bath solution in the degreasing cleaning tank is 60-80℃, and the free alkalinity of the alkali solution is 75±10Pt; the free alkalinity of the rinsing tank is ≤15Pt; and the drying temperature is ≥120℃.

4. The method for preparing a coated steel sheet as described in claim 1, characterized in that, The annealing process is as follows: annealing temperature 690-780℃; the furnace uses a nitrogen-hydrogen protective gas with an H2 content of 5-10%.

5. The method for preparing a coated steel sheet as described in claim 1, characterized in that, The hot-dip galvanized strip steel is cooled using a three-stage cooling method. The three-stage cooling includes a first cooling section that can move vertically and horizontally, a second cooling section that can move horizontally, and a fixed third cooling section. The first cooling section moves vertically to a position of 500-800 mm in the air knife height direction, and the cooling rate is controlled at 8-12℃ / s. The second cooling section has a cooling rate of ≥15℃ / s, and the temperature of the strip steel when it exits the second cooling section is ≤330℃. The third cooling section has a cooling rate of ≥5℃ / s, and the high-span cooling temperature is ≤260℃.

6. A coated steel sheet, characterized in that, Obtained by the preparation method according to any one of claims 1-5.

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