A 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic brackets and its manufacturing method

Abstract

The present invention belongs to the technical field of hot-dip galvanized aluminum-magnesium steel sheets and discloses a 500MPa-grade hot-dip galvanized aluminum-magnesium steel sheet for photovoltaic brackets and a manufacturing method thereof. The hot-dip galvanized aluminum-magnesium steel sheet comprises a substrate and a zinc-aluminum-magnesium coating formed by a hot-dip galvanized aluminum-magnesium coating bath. The chemical composition and mass percentage of the substrate are as follows: C: 0.17-0.20%, Si: ≤0.1%, Mn: 0.85-1.25%, Ti: 0.04-0.06%, Als: 0.015-0.045%, P: ≤0.02%, S: ≤0.01%, with the balance being Fe and unavoidable impurities. The chemical composition and mass percentage of the zinc-aluminum-magnesium coating bath are as follows: Al: 4.0-15.0%, Mg: 2.0-5.0%, Si: 0.005-0.09%, with Si and Al satisfying a specific formula, and the balance being Zn and unavoidable impurities. The present invention achieves a hot-dip galvanized aluminum-magnesium steel plate with a yield strength of 500 MPa and excellent coating adhesion through reasonable design of substrate composition and plating bath composition, combined with an improved Sendzimir hot-dip process, which can be used in products such as photovoltaic brackets.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-dip galvanized aluminum-magnesium steel plates, and particularly relates to a 500MPa-grade hot-dip galvanized aluminum-magnesium steel plate for a photovoltaic support and a manufacturing method thereof. Background Art

[0002] Photovoltaic mounting systems are the foundational structure of solar photovoltaic power plants, primarily including ground-based, floating, shed-type, and rooftop mounting systems. These systems often operate in environments with large temperature swings, high wind resistance, and high corrosion resistance, while also meeting load-bearing requirements. Currently, the photovoltaic industry generally roll-forms steel with a thickness of 1.5 to 4.0 mm and a yield strength of 235 MPa and 350 MPa. There is an urgent need to replace these 235 MPa and 350 MPa steels with steels with a yield strength of 500 MPa and a reasonable elongation to reduce raw material thickness and reduce costs. Existing technologies and products often utilize high concentrations of solid-solution strengthening elements such as Si and Mn to achieve high strength, which inevitably leads to deteriorated surface quality. In particular, high Si content is easily oxidized to produce SiO2 on the surface, causing the Sandrin effect. This results in a gray coating that impairs adhesion between the steel and the anti-corrosion coating, impacting the actual service life.

[0003] Solar photovoltaic power stations are typically built in harsh environments such as coastal mudflats, deserts, Gobi deserts, and water surfaces. According to the "NB / T10115-2018 Specification for Photovoltaic Mounting Structure Design," photovoltaic mounting systems for photovoltaic power stations should be designed for a service life of at least 25 years, placing extremely high demands on their corrosion resistance. Currently, most photovoltaic project mounting systems in China utilize hot-dip galvanizing after cold bending and pickling of hot-rolled steel strip. The zinc coating thickness must be at least 60μm to ensure excellent corrosion resistance. Zinc-aluminum-magnesium-coated steel plate products are based on traditional hot-dip pure zinc coatings, resulting from the addition of appropriate amounts of Al, Mg, and other trace alloying elements to the plating bath. These alloy coatings offer corrosion resistance 5-10 times that of pure zinc products of the same thickness. However, since zinc-aluminum-magnesium coatings are multi-component alloys with multiple alloy phases in their structure, coating shedding is a common problem during the roll-forming process. Therefore, simultaneously improving steel strength and coating adhesion remains a technical challenge in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a 500MPa-level hot-dip galvanized aluminum-magnesium steel plate for photovoltaic brackets and a manufacturing method thereof. By reasonably designing the substrate composition and the plating bath composition and combining it with the improved Sendzimir hot-dip process, a hot-dip galvanized aluminum-magnesium steel plate with a yield strength of 500MPa and excellent coating adhesion is obtained.

[0005] In order to solve the technical problem raised by the present invention, the present invention provides a 500MPa-grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic brackets, including a substrate and a zinc-aluminum-magnesium coating formed by a hot-dip galvanized aluminum-magnesium coating bath.

[0006] In the above scheme, the chemical composition and mass percentage of the substrate are: C: 0.17-0.20%, Si: ≤0.1%, Mn: 0.85-1.25%, Ti: 0.04-0.06%, Als: 0.015-0.045%, P: ≤0.02%, S: ≤0.01%, and the remainder is Fe and unavoidable impurities.

[0007] In the above solution, the thickness of the substrate is 1.2 to 2.5 mm.

[0008] In the above solution, the metallographic structure of the substrate includes ferrite and pearlite, wherein the diameter of the ferrite grains is 6 to 15 μm.

[0009] In the above scheme, the chemical composition and mass percentage of the zinc-aluminum-magnesium plating bath are: Al: 4.0-15.0%, Mg: 2.0-5.0%, Si: 0.005-0.09%, and the balance is Zn and unavoidable impurities.

[0010] Furthermore, the chemical composition of the zinc-aluminum-magnesium plating bath satisfies the formula Si=0.0074×e 0.1597Al , where Si and Al are the mass percentages, in %.

[0011] In the above solution, the thickness of the zinc-aluminum-magnesium coating on one side is 30-250 g / m 2 .

[0012] In the above solution, the zinc-aluminum-magnesium coating includes a coating layer and an alloy layer between the substrate and the coating layer.

[0013] Furthermore, the microstructure of the coating layer is a primary Al-rich phase, a Zn phase, a MgZn2 phase and a eutectic Al / Zn / MgZn2 microstructure, and no Si-containing alloy phase is generated.

[0014] Furthermore, the structure of the alloy layer includes Fe2Al 5-a Si a phase (0<a<5), Fe4Al 13-b Si b phase (0<b<13), etc., and the thickness of the alloy layer is 80~150nm.

[0015] In the above scheme, the yield strength of the hot-dip galvanized aluminum-magnesium steel plate is 500-620 MPa, the tensile strength is 530-690 MPa, and the elongation after fracture A 80mm ≥14%.

[0016] The present invention also provides a method for manufacturing a 500MPa-grade hot-dip galvanized aluminum-magnesium steel plate for a photovoltaic bracket, wherein the substrate is hot-dip plated using a modified Sendzimir method, and the process flow includes: substrate → annealing in a modified Sendzimir method horizontal heating furnace → hot-dip plating in a zinc pot → cooling after plating.

[0017] In the above solution, the substrate is produced by smelting → continuous casting → hot rolling → pickling → cold rolling, wherein the hot rolling adopts a conventional hot rolling production process or a short-process production process, and the total cold rolling reduction is ≥60%.

[0018] In the above scheme, the improved Sendzimir process horizontal heating furnace annealing includes a preheating section, a direct combustion section, a reduction section, and a cooling section.

[0019] Furthermore, the direct combustion section controls the air-fuel ratio to be 0.95-0.98, and the outlet temperature of the direct combustion section is 660-680°C.

[0020] Furthermore, the reduction section adopts N2+H2 protective atmosphere, wherein the volume percentage of H2 is 20-30%, the O2 content is ≤30ppm, the dew point is ≤-35°C, and the reduction section outlet temperature is 720-730°C.

[0021] In the above solution, the running speed of the substrate in the improved Sendzimir process horizontal heating furnace satisfies the formula VT=V×T, where V is the substrate running speed, T is the substrate thickness, and VT is 115-120 mm·m / min.

[0022] In the above solution, the plate temperature of the substrate when entering the zinc pot is the same as the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot.

[0023] In the above scheme, the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot is 40 to 60°C higher than the melting point of the zinc-aluminum-magnesium alloy of corresponding composition; the melting of the multi-component alloy is carried out within a temperature range, and in the present invention, the melting point is the end temperature of the zinc-aluminum-magnesium alloy.

[0024] In the above solution, the cooling rate after plating is 15 to 20° C. / s.

[0025] The design concept of the present invention on the chemical composition of the substrate is as follows:

[0026] Carbon (C): Carbon is an effective solid-solution strengthening element in steel. Higher C content increases the strength of the steel plate, but reduces its plasticity and toughness. Furthermore, a high C content reduces the steel's weldability and adversely affects its galvanizability. Therefore, the C content in this invention is 0.17-0.20%.

[0027] Si: Silicon is a beneficial element in steel and an economical strengthening element. It has a strong solid solution strengthening effect and can improve the strength of steel sheets. However, at high Si content, Si tends to precipitate and oxidize on the steel sheet surface during annealing. Its oxides hinder solid-liquid diffusion during hot-dip coating, adversely affecting coating adhesion. Therefore, in the present invention, the Si content is controlled to ≤ 0.1%.

[0028] Mn: Manganese is a beneficial element in galvanized steel strip, increasing its strength. A moderate amount of manganese improves both toughness and cold rolling performance. However, similar to Si, excessive amounts of manganese can negatively impact coating adhesion. Therefore, the manganese content in this invention is 0.85-1.25%.

[0029] Titanium (Ti): Titanium refines austenite grains, improves delayed fracture strength through grain boundary strengthening, and enhances the refinement and uniformity of carbonitride distribution, thereby increasing both the strength of the steel sheet and the elongation of the steel strip. However, titanium alloys are relatively expensive, so the Ti content in this invention is 0.04-0.06%.

[0030] P, S: Phosphorus and sulfur are harmful elements in steel and will reduce the toughness of the steel strip. Therefore, the phosphorus content is controlled to ≤0.02% and the sulfur content is controlled to ≤0.01%.

[0031] Als: It plays a role in deoxidation and grain refinement in steel, which can improve the toughness of the steel strip. Therefore, the Als content is required to be 0.015-0.045% in the present invention.

[0032] The design concept of the present invention on the chemical composition of the zinc-aluminum-magnesium plating bath is as follows:

[0033] Al: Al in the coating forms a dense oxide film on the surface of the steel sheet during use, preventing further corrosion and improving its corrosion resistance. It also improves the coating's heat resistance. However, because Al is very active, high levels can adversely affect hot-dip production, resulting in excess zinc ash and slag in the plating bath, which can affect the surface quality of the coating. Therefore, the Al content in the coating of the present invention is controlled to be 4.0-15.0%.

[0034] Mg: Mg in the coating can also form a dense oxide film on the surface of the coating during use, preventing further corrosion and improving the corrosion resistance of the coating. However, Mg is very active, and too high a Mg content can also cause excessive zinc ash and slag in the plating bath, affecting the surface quality of the coating. The Mg content in the coating of the present invention is controlled to 2.0-5.0%.

[0035] Si: In plating baths with high aluminum content, the Fe-Al reaction is intense, easily forming a thick alloy layer. Therefore, a trace amount of Si is added to high-aluminum plating baths to inhibit the Fe-Al reaction and prevent the formation of an excessively thick alloy layer, which can affect the adhesion between the substrate and the coating. The amount of Si added is related to the Al content. Too little Si is insufficient to inhibit the reaction, while too much Si is saturated, resulting in a large amount of scum in the zinc pot and the formation of brittle phases such as Mg2Si in the coating. During the steel plate processing and forming process, these brittle alloy phases are the source of cracks in the coating, which is detrimental to the coating's processing performance. Therefore, the Si content in the plating bath of the present invention is controlled to 0.005% to 0.09%, and is related to the Al content.

[0036] The design concept of the present invention in the method for manufacturing hot-dip galvanized aluminum-magnesium steel sheet is as follows:

[0037] The hot-dip galvanized aluminum-magnesium coated steel plate is manufactured using the improved Sendzimir process, which has low production costs and a strong plate throughput capacity of the horizontal heating furnace of the improved Sendzimir process, making it suitable for the production of thick substrates.

[0038] The improved Sendzimir process horizontal heating furnace includes a preheating section, a direct combustion section, a reduction section, and a cooling section.

[0039] The direct combustion section uses open flame heating, and the ratio coefficient of air to gas needs to be controlled. If it is too low, the gas combustion will be incomplete and the heating efficiency will be reduced. If it is too high, it will easily cause oxidation of the steel plate surface, affecting the formation of the coating alloy layer and further affecting the coating adhesion. Therefore, in the direct combustion section, the ratio coefficient of air to gas is controlled at 0.95~0.98.

[0040] If the outlet temperature of the direct combustion section is too low, the time that the substrate is above the recrystallization temperature in the reduction section will be reduced, the degree of recrystallization recovery will be insufficient, and the mechanical properties will deteriorate. Therefore, the outlet temperature of the direct combustion section is controlled at 660-680℃. Similarly, if the temperature of the reduction section is too low, the elongation after fracture A 80mm The indicators deteriorate, and the outlet temperature of the reduction section is controlled at 720-740°C, the dew point in the reduction furnace is ≤-35°C, and the hydrogen content is 20-30% to ensure that there is no oxide layer on the surface of the substrate.

[0041] The running speed setting of the substrate during annealing is related to the strip steel specifications, the heating capacity of the horizontal furnace, the hot-dip coating process, etc. The present invention has determined through long-term experiments that the running speed is controlled by the formula VT=V×T, where V is the substrate running speed, T is the substrate thickness, and VT is 115-120 mm·m / min.

[0042] The plate temperature of the substrate entering the zinc pot is related to the plating bath temperature and the thickness of the substrate. It is generally close to the plating bath temperature. For thick steel plates, the plate temperature should be appropriately lowered. Too high a plate temperature entering the zinc pot carries a lot of heat, which will increase the plating bath temperature on the one hand and intensify the reaction between Fe and Al on the other hand, forming an excessively thick alloy layer.

[0043] The bath temperature should be set approximately 40-60°C above the upper limit of the melting point range. A temperature that is too low will result in insufficient reaction kinetics in the alloy layer and poor bath fluidity. A temperature that is too high will also intensify the Fe-Al reaction and even alloy the entire coating, while also putting pressure on post-plating cooling capacity.

[0044] The reaction of the alloy layer is still in progress from the time the coated steel plate comes out of the zinc pot until the coating is completely solidified, so the cooling rate after coating also affects the formation of the alloy layer. It is preferred to cool at a rate of 15 to 20°C / s to obtain a suitable alloy layer thickness.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention provides a kind of yield strength 500~620MPa, tensile strength 530~690MPa, elongation after fracture A 80mm ≥14%, substrate thickness 1.2~2.5mm, zinc-aluminum-magnesium coating thickness single side 30~250g / m 2 Hot-dip galvanized magnesium-aluminum steel sheets can be used in products such as photovoltaic brackets, meeting requirements for high strength, thinning, and high corrosion resistance. The coating of the present invention utilizes zinc, aluminum, and magnesium, and through a rational plating bath composition and immersion plating process design, an alloy layer of suitable thickness is generated to ensure coating adhesion. The continuous hot-dip coating process of the present invention utilizes a modified Sendzimir method, which is low-cost and suitable for thick substrate production. Mechanical properties are ensured by controlling key parameters such as temperature and plate feed speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The metallographic structure of the substrate in Example 1 of the present invention.

[0048] Figure 2 The structure of the coating layer in Example 1 of the present invention.

[0049] Figure 3 Surface morphology of the alloy layer in Example 1 of the present invention.

[0050] Figure 4 Cross-sectional morphology of the alloy layer in Example 1 of the present invention.

[0051] Figure 5 The metallographic structure of the substrate in Comparative Example 1 of the present invention.

[0052] Figure 6 The metallographic structure of the substrate in Comparative Example 2 of the present invention.

[0053] Figure 7 Surface morphology of the alloy layer in Comparative Example 4 of the present invention.

[0054] Figure 8 Cross-sectional morphology of the alloy layer in Comparative Example 8 of the present invention.

[0055] Figure 9 Surface morphology of the alloy layer in Comparative Example 9 of the present invention.

[0056] Figure 10 Cross-sectional morphology of the alloy layer in Comparative Example 10 of the present invention. DETAILED DESCRIPTION

[0057] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0058] Examples 1 to 9 and Comparative Examples 1 to 10

[0059] In the following examples and comparative examples, the chemical composition of the substrates is shown in Table 1.

[0060] Table 1 Chemical composition of the substrates of the examples and comparative examples

[0061] serial number C(％) Si (%) Mn (%) Ti(%) Als(%) P(％) S(％) 1 0.19 0.06 1.12 0.045 0.023 0.007 0.003 2 0.175 0.08 1.09 0.051 0.034 0.005 0.002 3 0.183 0.075 1.23 0.042 0.041 0.008 0.005 4 0.18 0.013 <![CDATA[ 1.57 ]]> 0.05 0.034 0.005 0.002

[0062] In the following examples and comparative examples, the chemical composition of the zinc-aluminum-magnesium plating bath is shown in Table 2.

[0063] Table 2 Chemical composition of zinc-aluminum-magnesium plating baths in Examples and Comparative Examples

[0064] serial number Al(％) Mg(%) Si (%) Melting point (℃) 1 6.3 2.5 0.02 379 2 8.9 3.1 0.03 396 3 12.7 3.9 0.06 425 4 8.1 2.9 <![CDATA[ 0.15 ]]> 390 5 6.1 2.8 <![CDATA[ 0.002 ]]> 378

[0065] Examples 1 to 9 prepare hot-dip galvanized magnesium-aluminum steel sheets, comprising the following steps:

[0066] 1) Preparation of substrate: According to the chemical composition of the substrate, smelting, continuous casting, hot rolling, pickling, and cold rolling are carried out, with the total cold rolling reduction being ≥60%, to obtain a substrate with a thickness of 1.2 to 2.5 mm;

[0067] 2) Annealing in a modified Sendzimir horizontal heating furnace: Annealing the substrate in a modified Sendzimir horizontal heating furnace while controlling the substrate speed. The modified Sendzimir horizontal heating furnace annealing includes a preheating section, a direct combustion section, a reduction section, and a cooling section. The air-fuel ratio in the direct combustion section is controlled to be 0.95-0.98, and the outlet temperature of the direct combustion section is 660-680°C. The reduction section uses an N2+H2 protective atmosphere with an H2 volume percentage of 20-30%, an O2 content of ≤30 ppm, a dew point of ≤-35°C, and an outlet temperature of 720-740°C.

[0068] 3) Hot dip zinc bath: After annealing, the substrate is placed in the zinc bath for hot dip zinc-aluminum-magnesium coating. The substrate temperature in the zinc bath is the same as the zinc-aluminum-magnesium coating bath temperature. The zinc-aluminum-magnesium coating bath temperature is 40-60°C higher than the upper limit of its melting point range. The thickness of the zinc-aluminum-magnesium coating on one side is controlled to be 30-250g / m 2 ;

[0069] 4) Cooling after coating: Cool the steel sheet with zinc-aluminum-magnesium coating at a cooling rate of 15-20°C / s to obtain hot-dip zinc-magnesium-aluminum steel sheet.

[0070] The steps for preparing hot-dip galvanized magnesium-aluminum steel sheets in Comparative Examples 1 to 10 are the same as those in Examples 1 to 9, except for the control of process parameters, as shown in Tables 3 and 4 for details.

[0071] Table 3 Main process parameters of Examples and Comparative Examples (I)

[0072]

[0073]

[0074] Table 4 Main process parameters of Examples and Comparative Examples (II)

[0075]

[0076]

[0077] The hot-dip galvanized magnesium-aluminum steel sheets of each embodiment and comparative example were subjected to mechanical property tests, coating surface quality inspections, coating alloy layer thickness inspections, and coating adhesion tests. The results are shown in Table 5. Among them, the method for inspecting the surface quality of the coating is: observe the surface of the coating with the naked eye after plating. OK means that there are no defects visible to the naked eye on the surface of the coating, and NG means that there are defects such as missing plating on the surface of the coating; the method for inspecting the thickness of the coating alloy layer is: first use dilute hydrochloric acid to corrode the coating layer to retain the alloy layer, observe the surface morphology of the alloy layer, if the alloy layer is incomplete, it means NG, if the alloy layer is complete, use FIB cutting to measure the thickness of the alloy layer; the method for testing the adhesion of the coating is: cut the hot-dip galvanized magnesium-aluminum steel plate into a shape of 200mm long and 30mm wide, and then perform 0T bending along the length direction to observe whether there is any coating peeling off at the bending part. If not, use sticky tape to stick it firmly on the bent coating surface, and quickly tear off the tape in the vertical direction to observe whether there is any coating peeling off on the tape. If there is no coating peeling off, it means the adhesion is OK, and if there is coating peeling off, it means the adhesion is NG.

[0078] Table 5 Performance test results of examples and comparative examples

[0079]

[0080]

[0081] Combine Figures 1 to 10 The performance test results of each embodiment and comparative example are analyzed as shown in Table 5.

[0082] The metallographic structure of the substrate in Example 1 is as follows Figure 1 As shown in FIG, the coating layer is composed of ferrite and pearlite, and the diameter of the ferrite grains is 6 to 15 μm. Figure 2 As shown, it is composed of primary (Al)-rich phase, Zn phase, MgZn2 phase, eutectic Al / Zn / MgZn2 structure, and no Si-containing alloy phase. The surface morphology of the alloy layer in Example 1 is as follows Figure 3 As shown, through EDX spectrum analysis, its structure includes Fe2Al4Si1 phase, Fe4Al 12 Si1 phase. The cross-sectional morphology of the alloy layer in Example 1 is as follows Figure 4 As shown, the average thickness is 118nm. In Examples 1 to 9, the hot-dip galvanized aluminum-magnesium steel sheets meet the requirements of yield strength of 500 to 620 MPa, tensile strength of 530 to 690 MPa, and elongation after fracture A. 80mm ≥14%, and the coating surface quality and adhesion are OK.

[0083] Table 6 EDX spectrum analysis results of the alloy layers of Example 1 and Comparative Example 4

[0084]

[0085] The metallographic structure of the substrate in Comparative Example 1 is as follows Figure 5 As shown, the metallographic morphology shows that the organization is in an unrecovered state, and the cold deformation organization is obvious, resulting in high strength and elongation after fracture A 80mm Not met.

[0086] The metallographic structure of the substrate in Comparative Example 2 is as follows: Figure 6 As shown, the metallographic morphology shows that the structure is completely recrystallized, and the diameter of the ferrite grains is 20 to 45 μm. Since the annealing temperature exceeds the range, the ferrite grains grow, the strength decreases, and the strength test results do not meet the standards.

[0087] In comparative example 3, the speed control parameters were too low, the strip steel stayed in the high temperature zone of the annealing furnace for a long time, the ferrite grains grew, the strength decreased, and the strength test results did not meet the standards.

[0088] Comparative Example 4 has missing plating spots on the coating surface, and the adhesion is unqualified. The surface morphology of the alloy layer is as follows: Figure 7 As shown in the figure, the alloy layer is incomplete and no alloy layer is formed in some areas. EDX analysis shows the presence of oxygen elements, which indicates that the ratio coefficient of air to gas in the direct combustion section exceeds the standard, and the substrate is oxidized in the annealing furnace, which affects the diffusion between solid and liquid, resulting in incomplete alloy layer and plating leakage.

[0089] Comparative Examples 5 and 6 also suffered from surface oxidation of the steel plates due to excessive process parameters, resulting in incomplete alloy layers, plating omissions, and substandard surface quality and adhesion.

[0090] The steel plate of Comparative Example 7 has a high Mn content, and oxidation is precipitated on the surface of the steel plate during annealing, which also causes an incomplete alloy layer, plating leakage, and substandard surface quality and adhesion.

[0091] The cross-sectional morphology of the alloy layer in Comparative Example 8 is as follows: Figure 8 As shown, due to the excessive plating bath temperature, the average thickness of the alloy layer is 335 nm. Since the alloy layer is a brittle alloy phase, an excessively thick alloy layer also causes unqualified coating adhesion.

[0092] Comparative Examples 9 and 10 illustrate the effect of Si content; the surface morphology of the alloy layer in Comparative Example 9 is as follows: Figure 9 As shown, on the one hand, due to the excessive Si content, the alloy layer is too thin and the adhesion is reduced. On the other hand, there are dense Si-rich particles in the coating, which makes the coating loose and easy to peel off. The cross-sectional morphology of the alloy layer in Comparative Example 10 is shown in FIG. Figure 10 As shown in the figure, due to the low Si content, the ability to inhibit the Fe-Al reaction is lost, forming an overly thick alloy layer, resulting in unqualified coating adhesion.

[0093] The above embodiments are merely examples for clarification and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here, and any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic brackets, characterized in that: It includes a substrate and a zinc-aluminum-magnesium coating formed by a hot-dip zinc-aluminum-magnesium coating bath; The chemical composition and mass percentage of the substrate are: C: 0.17-0.20%, Si: ≤0.1%, Mn: 0.85-1.25%, Ti: 0.04-0.06%, Als: 0.015-0.045%, P: ≤0.02%, S: ≤0.01%, and the balance is Fe and unavoidable impurities; The chemical composition and mass percentage of the zinc-aluminum-magnesium plating bath are: Al: 8.9-15.0%, Mg: 2.0-5.0%, Si: 0.005-0.09%, the balance being Zn and unavoidable impurities, and the relationship between Si and Al satisfies the formula Si=0.0074×e 0.1597Al , where Si and Al are mass percentages, unit is %; The zinc-aluminum-magnesium coating includes a coating layer and an alloy layer between the substrate and the coating layer; the thickness of the alloy layer is 80-150 nm; the structure of the alloy layer includes Fe2Al 5-a Si a phase and Fe4Al 13-b Si b Phase, where 0<a<5, 0<b<13; The manufacturing method of the hot-dip galvanized aluminum-magnesium steel plate comprises the following process flow: substrate → annealing in a modified Sendzimir process horizontal heating furnace → hot-dip plating in a zinc pot → cooling after plating; the annealing in the modified Sendzimir process horizontal heating furnace comprises a preheating section, a direct combustion section, a reduction section, and a cooling section; the air-fuel ratio in the direct combustion section is controlled at 0.95-0.98, and the outlet temperature of the direct combustion section is 660-680°C; the reduction section adopts an N2+H2 protective atmosphere, wherein the volume percentage of H2 is 20-30%, the O2 content is ≤30 ppm, the dew point is ≤-35°C, and the outlet temperature of the reduction section is 720-730°C; the running speed of the substrate in the modified Sendzimir process horizontal heating furnace satisfies the formula VT=V×T, wherein V is the running speed of the substrate, T is the thickness of the substrate, and VT is 115-120 mm·m / min; the plate temperature of the substrate when entering the zinc pot is the same as the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot, and the temperature of the zinc-aluminum-magnesium plating bath is 40~60℃ higher than the melting point of the zinc-aluminum-magnesium alloy of the corresponding composition.

2. The 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic support according to claim 1, characterized in that: The thickness of the zinc-aluminum-magnesium coating on one side is 30-250 g / m 2 .

3. The 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic support according to claim 2, characterized in that: The coating layer has a microstructure of a primary Al-rich phase, a Zn phase, a MgZn2 phase and a eutectic Al / Zn / MgZn2 microstructure, and does not generate a Si-containing alloy phase.

4. The 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic support according to claim 1, characterized in that: The thickness of the substrate is 1.2-2.5 mm, and the metallographic structure thereof includes ferrite and pearlite, wherein the diameter of the ferrite grains is 6-15 μm.

5. The 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for photovoltaic support according to claim 1, characterized in that: The yield strength of the hot-dip galvanized aluminum-magnesium steel plate is 500~620 MPa, the tensile strength is 530~690 MPa, and the elongation after fracture is A 80mm ≥14%.

6. The method for manufacturing the 500 MPa grade hot-dip galvanized aluminum-magnesium steel sheet for photovoltaic support according to any one of claims 1 to 5, wherein the process comprises: Substrate → annealing in a modified Sendzimir process horizontal heating furnace → hot-dip coating in a zinc pot → cooling after coating, characterized in that the modified Sendzimir process horizontal heating furnace annealing includes a preheating section, a direct combustion section, a reduction section, and a cooling section; the direct combustion section controls the air-fuel ratio to be 0.95-0.98, and the outlet temperature of the direct combustion section is 660-680°C; the reduction section adopts an N2+H2 protective atmosphere, wherein the volume percentage of H2 is 20-30%, the O2 content is ≤30 ppm, the dew point is ≤-35°C, and the outlet temperature of the reduction section is 720-730°C; the running speed of the substrate in the modified Sendzimir process horizontal heating furnace satisfies the formula VT=V×T, where V is the substrate running speed, T is the substrate thickness, and VT is 115-120 mm·m / min; the plate temperature of the substrate when entering the zinc pot is the same as the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot, and the temperature of the zinc-aluminum-magnesium plating bath is 40-60°C higher than the melting point temperature of the zinc-aluminum-magnesium alloy of the corresponding composition.

7. The method for preparing a 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for a photovoltaic support according to claim 6, characterized in that: The substrate is manufactured through the processes of smelting → continuous casting → hot rolling → pickling → cold rolling, wherein the hot rolling adopts a conventional hot rolling production process or a short-process production process, and the total cold rolling reduction is ≥60%.

8. The method for preparing a 500MPa grade hot-dip galvanized aluminum-magnesium steel plate for a photovoltaic support according to claim 6, characterized in that: The cooling rate of the post-plating cooling is 15-20°C / s.

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