420MPa-grade steel strip for high-corrosion-resistance photovoltaic bracket based on Ti microalloying and low-aluminum high-magnesium coating synergistic reinforcement and preparation method of 420MPa-grade steel strip

Abstract

The invention discloses a 420MPa-grade steel strip for a high-corrosion-resistance photovoltaic support based on Ti microalloying and low-aluminum high-magnesium coating synergistic reinforcement and a preparation method of the 420MPa-grade steel strip, and relates to the technical field of metal materials. Aiming at the requirements of a distributed photovoltaic bracket, a microalloy component taking a Ti element as a core is designed, and the microalloy component is matched with a low-aluminum high-magnesium micro-titanium coating system to prepare the 420MPa-grade steel belt for the high-corrosion-resistance photovoltaic bracket, which is based on Ti microalloying and low-aluminum high-magnesium coating synergistic reinforcement and has balanced performance and good corrosion resistance. And meanwhile, controlled rolling and controlled cooling and low-temperature annealing are adopted in the preparation process, so that the problem of poor formability of traditional steel is solved, energy consumption is reduced by utilizing a low-temperature rapid plating process, and the production efficiency is improved. While the alloy cost is reduced, balanced optimization of strength-corrosion resistance-forming-welding performance is achieved, and low cost and greenization of a photovoltaic support material are promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a 420 MPa grade steel strip for a highly corrosion-resistant photovoltaic support based on synergistic strengthening of Ti microalloying and a low-aluminum, high-magnesium coating, and a preparation method thereof. Background Art

[0002] With the rapid popularization of photovoltaic power generation systems, the application scenarios of photovoltaic brackets are becoming more and more extensive, and the performance requirements are constantly improving: high load-bearing capacity to meet the wind load (≤60m / s) and snow load (2.4kN / m 2 ) demand; the need for resistance to salt spray corrosion in coastal and island photovoltaic power stations; the need for acid rain and chemical corrosion resistance in industrially polluted areas around chemical plants and mining areas; and the need for high-temperature oxidation resistance in coatings used in deserts and high-temperature environments. These factors are driving demand for support materials characterized by moderate strength (primarily 420MPa), excellent corrosion resistance, good formability, and cost sensitivity. According to statistics, the cost of centralized photovoltaic support brackets accounts for 15%-20% of the total system cost, and steel costs account for 70%-80% of the total support cost. Reducing material costs has become a core demand of the industry.

[0003] Existing photovoltaic bracket materials have the following defects: (1) Excessive alloying costs: Traditional 420MPa grade steel strips are generally micro-alloyed with Nb (0.01-0.05wt%) and V (0.02-0.06wt%), whose unit prices are 10 times and 8 times that of Ti, respectively, resulting in a ton of steel alloy cost of 150-300 yuan, which is difficult to meet the economic requirements of distributed photovoltaics. (2) Insufficient corrosion resistance: Existing hot-dip galvanized coatings (such as Zn-5%Al) have a service life of only 8-12 years in moderately corrosive environments (such as areas with an annual corrosion rate of 0.05-0.1mm / a), while the design life of distributed brackets is required to be 15-20 years. This requires increasing the coating thickness (≥80μm) or applying additional paint, which increases costs. (3) Forming defects: Traditional high-strength steel strips (such as Nb-containing steels) have a high yield strength ratio (≥0.85), which is prone to rebound and cracking during cold bending (bending radius R=2t), with a yield rate of only 85%-90%; and the coating is prone to peeling during the stamping process, affecting subsequent painting. (4) Low welding efficiency: Alloy element segregation causes the hardness of the welding heat-affected zone (HAZ) to increase (≥280HV), and it needs to be preheated to above 150°C to avoid cold cracks, increasing welding energy consumption and time costs. (5) Process energy consumption and environmental protection issues: The traditional hot-dip Zn-Al process needs to maintain a bath temperature of 480-500°C, and dichromate passivation (containing Cr) is required after plating. 6+ ), not only has high energy consumption (1 ton of steel consumes 120-150kWh of electricity), but also has the risk of heavy metal pollution. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of the present invention is to provide a 420MPa grade steel strip for photovoltaic supports with high corrosion resistance based on the synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating and its preparation method. In response to the needs of distributed photovoltaic supports, the present invention designs a microalloying component with Ti element as the core, and combines it with a low aluminum and high magnesium micro-titanium coating system to produce a 420MPa grade steel strip for photovoltaic supports with balanced performance and good corrosion resistance based on the synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating. At the same time, when preparing the 420MPa grade steel strip for photovoltaic supports with high corrosion resistance based on the synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating, controlled rolling and controlled cooling (final cooling temperature 580℃-640℃) and low temperature annealing (730℃-810℃) are adopted to solve the problem of poor formability in traditional steel, and use low temperature and fast plating process to reduce energy consumption and improve production efficiency. While reducing the cost of alloy, the present invention achieves balanced optimization of "strength-corrosion resistance-forming-welding" performance, promoting the low cost and greenness of photovoltaic support materials.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The first aspect of the present invention provides a 420MPa grade steel strip for a photovoltaic support with high corrosion resistance based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating, comprising a substrate and a zinc aluminum magnesium coating; wherein,

[0007] The substrate includes the following chemical components in mass percentage: C 0.07%-0.14%, Si≤0.12%, Mn0.45%-0.8%, P≤0.015%, S≤0.010%, Ti 0.035%-0.070%, Als 0.01%-0.04%, N≤0.006%, O≤0.003%, and the rest is Fe and other inevitable impurities.

[0008] The zinc-aluminum-magnesium coating includes the following chemical components in mass percentage: Zn 92%-97%, Al 1.5%-5.0%, Mg 1.5%-5.0%, Ti 0.04%-0.25%, RE 0.01%-0.03%, and the total amount of impurities is ≤0.5%, wherein RE includes Ce and La.

[0009] The composition design principle of the substrate is:

[0010] C: C combines with Ti to form TiC particles ≤200nm, which exert a fine-grain strengthening effect. Excessive pearlite precipitation and reduced plasticity due to excessive C content will not occur. When the C content is 0.07%, the uniform distribution of TiC maintains strength. When the C content reaches 0.14%, combined with controlled rolling and controlled cooling processes, pearlite coarsening can be avoided, ensuring an elongation of ≥16%.

[0011] Ti: It preferentially combines with N to form TiN (lattice constant close to Fe, mismatch <5%), pinning grain boundaries to inhibit grain growth (average grain size ≤ 8μm), replacing the grain boundary strengthening function of traditional Nb. At 0.035%, Ti can preferentially combine with N to form TiN (mismatch <5%), effectively pinning grain boundaries to inhibit grain growth (average grain size ≤ 10μm). At 0.070%, TiN particle aggregation can be avoided by controlling the rolling temperature, still replacing the traditional Nb grain boundary strengthening function without significantly increasing the alloy cost.

[0012] The mechanism of action of Ti element in each process stage:

[0013] (1) Smelting stage

[0014] During converter / electric furnace steelmaking and LF refining, Ti preferentially combines with nitrogen in the molten steel to form TiN particles (lattice constant close to that of Fe). When the Ti content is 0.035%-0.070%, the TiN particles can be controlled to a size of 50nm-200nm, evenly distributed in the molten steel. This "pinning effect" inhibits grain growth during subsequent rolling. Furthermore, Ti fixes free nitrogen in the steel (to keep [N] ≤ 0.006%), preventing the formation of the brittle Fe4N phase during welding and reducing the hardness of the weld heat-affected zone (≤ 250HV).

[0015] (2) Rolling stage

[0016] During the temperature-controlled hot rolling process, the heating temperature (1100℃-1180℃) causes 60%-70% of the TiN particles to dissolve, and the undissolved particles serve as precipitation cores during subsequent cooling. During the finishing rolling stage (final rolling temperature 850℃-900℃), TiC particles disperse and precipitate at the austenite grain boundaries, hindering the coarsening of austenite grains (austenite recrystallization grain size 8μm-15μm). During the controlled cooling process (cooling rate 1.0-6.0℃ / s), the Ti element promotes the preferential precipitation of ferrite at the austenite grain boundaries, forming a uniform "ferrite + pearlite" dual-phase structure, of which ferrite accounts for 80%-92%, ensuring that the steel strip has good formability (cold bending R=1t without cracks).

[0017] (3) Annealing stage

[0018] During low-temperature annealing (730°C-810°C), the Ti element inhibits abnormal ferrite grain growth, stabilizing the grain size at 10μm-15μm. Simultaneously, the precipitation strengthening effect of TiC particles synergizes with the plasticity of ferrite to control the yield strength ratio to 0.75-0.83, addressing the poor formability of conventional high-strength steel strip.

[0019] Low P and S: Reduce the brittle phase at the grain boundary and cooperate with the solid solution strengthening of Mn. The Mn content is 0.45%-0.8%, avoiding the decrease in toughness caused by excessive Mn content and achieving a balance between strength and plasticity and toughness.

[0020] The composition design principle of zinc-aluminum-magnesium coating is:

[0021] Main components: Compared with traditional high-aluminum coatings, the Al content is reduced by 20%-80% and the Mg content is increased by 0-60%;

[0022] Trace elements include Ti: 0.04%-0.25% (forming Zn-Mg-Ti ternary phase), RE (La+Ce) 0.01-0.03%; Ti acts as a heterogeneous nucleating agent, which refines the coating grains from the conventional 50μm-100μm to 10μm-25μm (the equiaxed grain ratio increases from 20%-30% to 60%-80%), increases the total grain boundary area by 2-3 times, and effectively hinders the penetration of corrosive media (the corrosion current density at the grain boundary is reduced by 40%).

[0023] Microstructure formation mechanism of low aluminum and high magnesium micro-titanium coating:

[0024] (1) Thermodynamic process

[0025] When the zinc-aluminum-magnesium coating is hot-dip coated at 400-490°C, the free energy change of the system drives the element diffusion and phase separation:

[0026] The Al element tends to diffuse to the substrate interface to form a Zn-Al alloy layer (thickness 2μm-5μm), which has high thermodynamic stability (low formation enthalpy) and can enhance the bonding strength between the coating and the substrate;

[0027] Mg element diffuses to the surface of the coating to form a Zn-Mg enriched layer (thickness 15μm-25μm). Since the standard electrode potential of Mg is lower than that of Zn, it corrodes first and forms a Mg(OH)2 protective film (solubility product constant Ksp=1.8×10 -11 ), significantly improving corrosion resistance.

[0028] (2) Kinetic process

[0029] Ti element acts as a heterogeneous nucleating agent, reducing the critical nucleation energy of coating crystallization and increasing the nucleation rate by 2-3 times:

[0030] In the initial stage of hot-dip plating (1.5s-5.0s), Ti forms tiny particles (size 5nm-10nm) in the plating solution, providing attachment sites for Zn, Al, and Mg atoms;

[0031] During the crystallization process, Ti atoms are adsorbed on the grain boundaries, hindering the growth of grains, refining the grain size of the coating from the conventional 50-100μm to 20μm-30μm, and increasing the total area of ​​the grain boundaries by 2-3 times, effectively blocking the penetration path of corrosive media (such as Cl-) (the corrosion current density at the grain boundaries is reduced by more than 40%).

[0032] The dense eutectic structure (Zn-Mg phase + Zn-Al phase) formed by the coating has a high hardness (120-150HV), which improves the scratch resistance and improves the fluidity of the molten pool during welding, ensuring that the strength matching of the welded joint is ≥95%.

[0033] Preferably, the metallographic structure of the substrate in the 420MPa grade steel strip used for manufacturing the photovoltaic bracket is ferrite + pearlite.

[0034] Furthermore, ferrite accounts for 80%-92% and pearlite accounts for 8%-20%.

[0035] Preferably, the zinc-aluminum-magnesium coating consists of a Zn-Mg enriched layer and a Zn-Al alloy layer, wherein the side away from the substrate is the Zn-Mg enriched layer, and the side close to the substrate is the Zn-Al alloy layer.

[0036] Furthermore, the thickness of the Zn-Mg enriched layer is 15 μm-25 μm, and the thickness of the Zn-Al alloy layer is 2 μm-5 μm.

[0037] A second aspect of the present invention provides a method for preparing the above-mentioned 420 MPa grade steel strip for high corrosion-resistant photovoltaic supports based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating, comprising the following steps:

[0038] Smelting and continuous casting, temperature-controlled hot rolling, cold rolling annealing, pre-plating treatment, low-temperature hot-dip coating and green passivation post-treatment; among them,

[0039] The smelting and continuous casting process includes converter / electric furnace steelmaking, LF refining and continuous casting;

[0040] The temperature-controlled hot rolling process includes heating, rough rolling, finishing rolling and controlled cooling. During the controlled cooling process, a weak cooling process is adopted, and the cooling rate is controlled at 1.0-6.0℃ / s, which can ensure the preferential precipitation of ferrite at the austenite grain boundaries and the uniformity of the dual-phase structure. In actual production, it can be flexibly adapted according to the thickness of the steel strip (1.2mm-3.0mm). When the thickness is larger, a lower cooling rate (1.0-3.0℃ / s) is adopted, and when the thickness is smaller, a higher cooling rate (3.0-6.0℃ / s) is adopted, both of which can achieve the uniformity of the dual-phase structure. The final cooling temperature is 580℃-640℃, so that ferrite is preferentially precipitated at the austenite grain boundaries to form a uniform dual-phase structure.

[0041] The cold rolling and annealing process includes cold rolling and annealing. During the annealing process, the annealing temperature is controlled at 730℃-810℃ to ensure appropriate ferrite grain growth and a yield ratio that meets the standard. The holding time is 2-3 minutes, and nitrogen protection is used at a dew point of ≤-40℃, which allows the ferrite grains to grow to 10μm-15μm and reduces the yield ratio to 0.75-0.83.

[0042] Pre-plating treatment includes acid electrolytic etching and magnetron sputtering deposition of TiC transition layer;

[0043] The low-temperature hot-dip process includes hot-dip and bath recovery. During the hot-dip process, sodium lauryl sulfate and nano-SiO2 are added to the zinc-aluminum-magnesium base solution as the bath. The bath temperature is controlled at 400-490°C, the immersion time is 1.5s-5.0s, and the post-plating air knife pressure is 0.2MPa-0.4MPa. The coating thickness uniformity deviation can be controlled to ≤5%.

[0044] Green passivation post-treatment process: immerse the hot-dip galvanized steel strip in a tannic acid-phytic acid composite passivation solution, control the temperature at 40°C-50°C, and treat for 30s-60s. After passivation, dry it with hot air at 80°C-100°C for 1min-2min to form a uniform passivation film. The tannic acid-phytic acid composite passivation solution has a pH of 4-5, a total concentration of tannic acid and phytic acid of 3-5g / L, and a mass ratio of tannic acid to phytic acid of 1:1.

[0045] Preferably, in the plating solution, the mass fraction of sodium lauryl sulfate is 0.02% and the mass fraction of nano-SiO2 is 0.1%; the sodium lauryl sulfate in the plating solution can reduce the surface tension to 40mN / m, and the nano-SiO2 can improve the stability of the plating solution.

[0046] Preferably, during the LF refining process, the S content in the molten steel is controlled to be ≤ 0.010%, the P content is ≤ 0.015%, the inclusion rating is ≤ 1.0, and the gas content [N] is ≤ 60 ppm, and [O] is ≤ 30 ppm.

[0047] Preferably, during the continuous casting process, dynamic soft reduction technology is used at the end of the solidification phase of the slab. Dynamically adjustable reduction (0.5-3 mm / m (reduction per meter of slab)) is applied by the continuous casting rollers to compensate for solidification shrinkage and improve internal quality. The reduction rate is matched with the drawing speed and solidification speed to avoid surface cracks or internal tears in the slab and reduce shrinkage, porosity, and segregation in the center of the slab (the center segregation index can be reduced by 10%-20%). This reduces the cropping rate during subsequent rolling and improves the yield rate by 1-3%. Electromagnetic stirring is also used, with a controlled current of 200A-300A, to reduce TiN particle aggregation. The resulting slab has a thickness of 175mm-200mm and a drawing speed of 1.0-1.5m / min.

[0048] As a preferred embodiment, the parameter control at each stage in the temperature-controlled hot rolling process is as follows:

[0049] Heating stage: 1100-1180℃ for 1.5 hours. This temperature is lower than the 1200℃ of niobium-containing steel, which can ensure that the TiN ions are partially dissolved, dissolving up to 60%-70%, and retaining undissolved particles as precipitation cores during subsequent cooling;

[0050] Rough rolling stage: control the starting rolling temperature ≥1050℃ and the cumulative reduction rate ≥40% to break the as-cast structure;

[0051] Finishing rolling stage: Control the final rolling temperature to 850℃-900℃ to control the austenite recrystallized grain size to 8-15μm.

[0052] Preferably, during the cold rolling process, the total reduction rate is 40%-60%, the thickness after rolling is 1.2mm-3.0mm, and the surface roughness Ra is ≤0.8μm.

[0053] As a preferred embodiment, during the acid electrolytic etching process, the electrolyte is a mixture of sulfuric acid and sodium chloride, the mass fraction of sulfuric acid in the electrolyte is 10%, the mass fraction of sodium chloride is 0.5%, and the current density is 1.5-5.0A / dm 2 The processing time is 30-60s, and a network groove with a depth of 1.5μm-5.0μm is formed on the surface of the steel strip.

[0054] Preferably, the thickness of the TiC transition layer is 50 nm-100 nm to improve the chemical compatibility between the substrate and the coating, and the contact angle between the substrate and the coating is ≤30°.

[0055] Preferably, ceramic filtration + vacuum distillation technology is used to recover the plating solution, with a plating solution utilization rate of ≥98% and a Zn recovery rate in the slag of ≥95%.

[0056] Beneficial effects of the present invention:

[0057] 1. Aiming at the needs of distributed photovoltaic supports, the present invention designs a microalloy component with Ti as the core, and combines it with a low-aluminum, high-magnesium micro-titanium coating system to produce a 420MPa grade steel strip for high-corrosion-resistant photovoltaic supports with balanced performance and good corrosion resistance, which is based on the synergistic strengthening of Ti microalloying and low-aluminum, high-magnesium coating. At the same time, when preparing the 420MPa grade steel strip for high-corrosion-resistant photovoltaic supports based on the synergistic strengthening of Ti microalloying and low-aluminum, high-magnesium coating, controlled rolling and controlled cooling (final cooling temperature 580℃-640℃) and low-temperature annealing (730℃-810℃) are adopted to solve the problem of poor formability in traditional steel, and the low-temperature rapid plating process is used to reduce energy consumption and improve production efficiency. While reducing the cost of the alloy, the present invention achieves balanced optimization of the "strength-corrosion resistance-forming-welding" performance, promoting the low cost and greenness of photovoltaic support materials.

[0058] 2. Alloy cost advantage: Ti (0.035%-0.070wt%) is used to replace more than 80% of Nb and V elements. The Ti content is only half of that of traditional niobium-containing steel. By utilizing the grain boundary pinning effect of TiC particles (average particle size 30-200nm), while maintaining a strength of 420MPa, the alloy cost is reduced by 20%, and the cost per ton of steel is reduced by 50-100 yuan.

[0059] 3. This invention designs a low-aluminum, high-magnesium micro-titanium coating formulation, specifically comprising: 92%-97% Zn, 1.5-5.0% Al, 1.5-5.0% Mg, 0.04%-0.25% Ti, and 0.01-0.03% RE. The Mg content is 1-2 times higher than that of conventional processes, forming a denser Mg(OH)2 corrosion product layer. The coating withstands a neutral salt spray test according to GB / T 10125 for ≥2600 hours, improving corrosion resistance by 50% at the same thickness. Ti acts as a heterogeneous nucleation core in the Zn solution, significantly refining the coating's grain size from the conventional 50-100 μm to 20-30 μm. This results in a dense eutectic structure, increasing the coating's hardness (120-150 HV) and scratch resistance, while also improving formability and weldability.

[0060] 4. Performance balance: Yield strength 440-490MPa, tensile strength 480-580MPa, elongation ≥16%, cold bending R=1t without cracks, meeting the forming requirements of complex bracket structures; neutral salt spray test according to GB / T 10125, salt spray resistance time ≥2600 hours, equivalent to 1.5-2.5 times that of traditional galvanized layer, suitable for medium and high corrosion environments.

[0061] 5. High plasticity structure design: Through controlled rolling and controlled cooling (final cooling temperature 580℃-640℃) and low-temperature annealing (730℃-810℃), a "ferrite (80-92%) + pearlite (8-20%)" dual-phase structure is formed, with an elongation after fracture ≥16%, and cold bending performance R=1t without cracks, solving the problem of poor formability of traditional steel grades.

[0062] 6. Advanced Process: The bath temperature is lowered to 440-490°C, 40-80°C lower than conventional processes. Adding 0.02-0.05% surfactant (such as sodium lauryl sulfate) to the bath shortens the plating time to 1.5-5.0 seconds, neutralizing the energy consumption caused by the reduced fluidity of the zinc bath due to the lower temperature. This reduces energy consumption by 30% and increases production efficiency by 20%. Furthermore, the hot-dip temperature is reduced by 40-80°C, reducing energy consumption per ton of steel to 60-100 kWh, and shortening the production cycle by 15%.

[0063] 7. Weld-friendly composition control: This invention strictly controls the S content in the substrate to ≤ 0.010wt% and the P content to ≤ 0.015wt%. Ti is used to stabilize nitrogen atoms in the steel ([N] ≤ 0.006wt%), preventing the formation of a brittle, hard Fe4N phase during welding. The hardness of the weld heat-affected zone is ≤ 250HV, enabling preheat-free welding at ambient temperatures ≥ 0°C. Furthermore, the weld joint strength match is ≥ 95%, enabling automated robotic welding (increasing welding speed by 20%) and significantly improving stent processing efficiency.

[0064] 8. Green passivation process: Use tannic acid-phytic acid composite passivation (concentration 3-5g / L, pH=4-5) to replace chromium-containing passivation, and the Cr in the passivation film 6+ The content is less than 0.1ppm, and the total phosphorus discharge in wastewater is reduced by 60%, which complies with the GB / T39286 "Green Product Evaluation of Steel Products" standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 : Metallographic structure diagram of the base material hot-rolled steel strip of Example 1 at a scale of 20 μm;

[0066] Figure 2 : Metallographic structure diagram of the cold-rolled annealed steel strip in Example 1 at a scale of 10 μm;

[0067] Figure 3 : Scanning electron microscope morphology of the 420 MPa grade steel strip for high corrosion-resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating in Example 1;

[0068] Figure 4 : Composition energy spectrum corresponding to the scanning electron microscope morphology image of the 420MPa grade steel strip for high corrosion-resistant photovoltaic support based on the synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating in Example 1. DETAILED DESCRIPTION

[0069] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0070] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0071] The experimental materials used in the examples of the present invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0072] Examples 1-3 and Comparative Examples 1-2:

[0073] 1. The 420MPa grade steel strip for photovoltaic brackets includes a substrate and a zinc-aluminum-magnesium coating. The chemical compositions of the substrate and the zinc-aluminum-magnesium coating are shown in Table 1 and Table 2:

[0074] Table 1 Chemical composition of substrate (in weight percentage)

[0075] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 C 0.10 0.09 0.08 0.05 0.06 Si 0.11 0.10 0.09 0.22 0.25 Mn 0.66 0.70 0.75 1.05 1.12 P 0.09 0.012 0.011 0.010 0.009 S 0.010 0.009 0.007 0.008 0.011 Ti 0.055 0.050 0.047 0.020 0.020 Nb - - - 0.050 0.045 Als 0.037 0.030 0.040 0.035 0.038 N 0.0056 0.0043 0.0045 0.0139 0.0087 O 0.0028 0.0030 0.0020 0.0089 0.0077

[0076] Table 2 Chemical composition of zinc-aluminum-magnesium coating (in weight percentage)

[0077]

[0078] Note: The coating composition of Comparative Example 1 is: Zn 99.5%, impurities ≤ 0.5%; and that of Comparative Example 2 is: Zn 95.5%, Al 4.5%, impurities ≤ 0.5%.

[0079] 2. Preparation process:

[0080] Smelting and continuous casting, temperature-controlled hot rolling, cold rolling annealing, pre-plating treatment, low-temperature hot-dip coating and green passivation post-treatment;

[0081] (1) Smelting and continuous casting process: including converter / electric furnace steelmaking, LF refining and continuous casting.

[0082] During the LF refining process, arc heating is used to precisely control the molten steel temperature to meet continuous casting temperature requirements (fluctuation ±10°C). Argon agitation promotes the floating of inclusions, improving the purity of the molten steel. Harmful elements (S) are controlled to ≤ 0.010%, P to ≤ 0.015%, inclusion rating to ≤ Grade 1.0, and gas content (N) to ≤ 60 ppm and (O) to ≤ 30 ppm.

[0083] During the continuous casting process, dynamic soft reduction technology is used at the end of the solidification phase (the mushy zone) of the strand. Dynamically adjustable reduction is applied by the caster rollers to compensate for solidification shrinkage and improve internal quality. Electromagnetic stirring is also used during continuous casting to reduce TiN particle aggregation. Specific parameters are shown in Table 3.

[0084] Table 3 Specific parameters during continuous casting

[0085] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Current (A) 250 280 260 220 240 Casting speed (m / min) 1.3 1.4 1.2 1.5 1.3 Thickness of casting billet (mm) 180 190 175 200 195

[0086] (2) Temperature-controlled hot rolling process: including heating, rough rolling, finishing rolling and controlled cooling.

[0087] Heating stage: heating to 1100-1180℃ and holding for 1.5h to ensure partial dissolution of TiN particles, retaining undissolved particles as precipitation cores during subsequent cooling;

[0088] Rough rolling: Control the starting rolling temperature and cumulative reduction rate to break up the cast structure;

[0089] Finish rolling: Control the final rolling temperature to control the austenite recrystallized grain size;

[0090] Controlled cooling: Use weak cooling process to control the cooling rate and final cooling temperature so that ferrite precipitates preferentially at the austenite grain boundary to form a uniform dual-phase structure.

[0091] The specific parameters of the temperature-controlled hot rolling process are shown in Table 4.

[0092] Table 4 Process parameters of temperature-controlled hot rolling process

[0093] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Heating temperature (℃) 1150 1160 1140 1200 1190 Rolling temperature (℃) 1080 1070 1060 1090 1080 Cumulative reduction rate (%) 45 48 42 50 47 Finish rolling temperature (℃) 880 870 890 910 900 Cooling rate (℃ / s) 3.0 2.5 4.0 5.5 6.0 Final cooling temperature (℃) 610 620 600 650 660

[0094] (3) Cold rolling annealing process:

[0095] Cold rolling: control the total reduction rate, rolled thickness and surface roughness;

[0096] Annealing: Control the annealing temperature for insulation, use nitrogen protection process, dew point ≤ -40℃, so that the ferrite grains grow moderately and the yield ratio is reduced.

[0097] The specific parameters of the cold rolling annealing process are shown in Table 5.

[0098] Table 5 Process parameters in cold rolling annealing process

[0099]

[0100] (4) Pre-plating treatment process: including acid electrolytic etching and magnetron sputtering nano-TiC coating.

[0101] Acid electrolytic etching: The electrolyte is prepared from sulfuric acid and sodium chloride, wherein the mass fraction of sulfuric acid is 10% and the mass fraction of sodium chloride is 0.5%. The current density is controlled to form a network of grooves on the surface of the steel strip;

[0102] Magnetron sputtering nano-TiC coating: Magnetron sputtering technology is used to deposit TiC coating to improve the chemical compatibility between the substrate and the coating.

[0103] The specific parameters of the pre-plating treatment process are shown in Table 6.

[0104] Table 6 Process parameters of pre-plating treatment process

[0105]

[0106]

[0107] (5) Low-temperature hot-dip plating process: including hot-dip plating and plating solution recovery.

[0108] Hot dip plating: Sodium lauryl sulfate and nano-SiO2 were added to a zinc-aluminum-magnesium base solution to prepare a plating solution. The mass fraction of sodium lauryl sulfate in the plating solution was 0.02%, and the mass fraction of nano-SiO2 was 0.1%. The plating solution containing sodium lauryl sulfate and nano-SiO2 was used in the embodiments, while the zinc-aluminum-magnesium base solution (not containing sodium lauryl sulfate and nano-SiO2) was used in the comparative example. The plating solution temperature was controlled, and immersion plating was performed. The air knife pressure after plating was controlled to control the uniformity deviation of the coating thickness to ≤5%;

[0109] Plating solution recovery: ceramic filtration + vacuum distillation technology is used to recover the plating solution.

[0110] The specific parameters of the low-temperature hot-dip process are shown in Table 7.

[0111] Table 7 Process parameters of low temperature hot-dip coating process

[0112]

[0113] (6) Green passivation post-processing process:

[0114] Preparation of passivation solution: Use tannic acid-phytic acid composite passivation solution, in which the total concentration of tannic acid and phytic acid (passivation solution concentration) is 3-5g / L (the mass ratio of tannic acid to phytic acid is 1:1), and adjust the pH to 4-5 with dilute sulfuric acid or ammonia water.

[0115] Passivation treatment: Immerse the hot-dip steel strip in the passivation solution, control the temperature at 40-50℃, and the treatment time is 30-60s.

[0116] Drying: After passivation, use hot air drying at a temperature of 80-100°C for 1-2 minutes to form a uniform passivation film.

[0117] The specific parameters of the green passivation post-treatment process are shown in Table 8, and the effects are shown in Table 9.

[0118] Table 8 Process parameters of green passivation post-treatment process

[0119]

[0120]

[0121] Table 9 Effect of green passivation post-treatment process

[0122]

[0123] Remark:

[0124] Concentration of passivation solution: The embodiment adopts 3.5-4.5 g / L of tannic acid-phytic acid composite passivation solution, which is lower than 5-5.5 g / L of the comparative example, thereby reducing the consumption of reagents while ensuring the passivation effect.

[0125] Passivation temperature and time: The embodiment is controlled at 42-48°C and 40-50s, while the comparative example has a higher temperature (52-55°C) and a longer time (60-65s). The embodiment process is more energy-efficient and efficient.

[0126] Drying parameters: The drying temperature of the embodiment is 85-95° C. and the drying time is 1.3-1.7 min, which are lower than 105-110° C. and 2.2-2.5 min of the comparative example, further reducing energy consumption.

[0127] Effect difference: Example passivation film thickness 1.1-1.3μm, Cr 6+ Content is less than 0.1ppm, and the salt spray resistance is improved by 38-45%; the comparison example uses traditional chromium passivation, Cr 6+ The content reaches 4.8-5.2ppm, the salt spray resistance is only improved by 18-20%, and there is a risk of heavy metal pollution.

[0128] 3. The photovoltaic brackets prepared in Examples 1-3 and Comparative Examples 1-2 were tested for mechanical properties, corrosion resistance and processing properties at 420 MPa level. The results are shown in Table 10.

[0129] Table 10 Mechanical properties, corrosion resistance and processing properties of 420MPa grade photovoltaic brackets prepared in Examples 1-3 and Comparative Examples 1-2

[0130]

[0131]

[0132] Note: The examples all achieved welding without preheating above 0°C, while the comparative examples required preheating to above 150°C.

[0133] Result analysis:

[0134] Organization and strengthening mechanism: The microstructure of the steel strip in the example is mainly ferrite, with a small amount of pearlite distributed at the grain boundaries. TiN particles are dispersed, effectively hindering dislocation movement and achieving "low-cost strengthening";

[0135] Reason for improved corrosion resistance: High Mg coating forms a double-layer protective film in the salt spray test - the inner layer is a dense Al2O3 layer, and the outer layer is a loose Mg(OH)2 layer. The former prevents the medium from penetrating, and the latter absorbs Cl - ions, reducing the corrosion rate to below 0.02mm / a;

[0136] Forming and welding advantages: Low yield ratio (0.75-0.83) reduces cold bending springback, TiC transition layer enhances coating adhesion, and no preheating welding technology meets on-site construction requirements, especially suitable for the rapid installation of distributed photovoltaics.

[0137] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A 420MPa grade steel strip for photovoltaic supports with high corrosion resistance based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating, characterized in that: It includes a substrate and a zinc-aluminum-magnesium coating; wherein, The substrate includes the following chemical compositions in mass percentage: C 0.07%-0.14%, Si≤0.12%, Mn 0.45%-0.8%, P≤0.015%, S≤0.010%, Ti 0.035%-0.070%, Als 0.01%-0.04%, N≤0.006%, O≤0.003%, and the remainder is Fe and other inevitable impurities; The zinc-aluminum-magnesium coating includes the following chemical components in mass percentage: Zn 92%-97%, Al 1.5%-5.0%, Mg 1.5%-5.0%, Ti 0.04%-0.25%, RE 0.01%-0.03%, and the total amount of impurities is ≤0.5%, wherein RE includes Ce and La.

2. The 420 MPa grade steel strip for high corrosion resistance photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 1, characterized in that: The metallographic structure of the substrate is ferrite+pearlite; the ferrite accounts for 80%-92% and the pearlite accounts for 8%-20%.

3. The 420 MPa grade steel strip for high corrosion resistance photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 1, characterized in that: The zinc-aluminum-magnesium coating consists of a Zn-Mg enriched layer and a Zn-Al alloy layer, wherein the side away from the substrate is the Zn-Mg enriched layer, and the side close to the substrate is the Zn-Al alloy layer; the thickness of the Zn-Mg enriched layer is 15μm-25μm, and the thickness of the Zn-Al alloy layer is 2μm-5μm.

4. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: Smelting and continuous casting, temperature-controlled hot rolling, cold rolling annealing, pre-plating treatment, low-temperature hot-dip coating and green passivation post-treatment; among them, The smelting and continuous casting process includes converter / electric furnace steelmaking, LF refining and continuous casting; The temperature-controlled hot rolling process includes heating, rough rolling, finishing rolling and controlled cooling. During the controlled cooling process, a weak cooling process is adopted, the cooling rate is controlled at 1.0-6.0℃ / s, and the final cooling temperature is 580℃-640℃. The cold rolling and annealing process includes cold rolling and annealing. During the annealing process, the annealing temperature is controlled at 730-810°C, the holding time is 2-3 minutes, and nitrogen protection is used at a dew point of ≤-40°C, so that the ferrite grains grow to 10μm-15μm and the yield ratio is reduced to 0.75-0.

83. Pre-plating treatment includes acid electrolytic etching and magnetron sputtering deposition of TiC transition layer; The low-temperature hot-dip process includes hot-dip and bath recovery. During the hot-dip process, sodium lauryl sulfate and nano-SiO2 are added to a zinc-aluminum-magnesium base solution as a bath. The bath temperature is controlled at 400°C-490°C, the immersion time is 1.5s-5.0s, and the post-plating air knife pressure is 0.2MPa-0.4MPa. The mass fraction of sodium lauryl sulfate in the bath is 0.02%, and the mass fraction of nano-SiO2 is 0.1%. Green passivation post-treatment process: immerse the hot-dip galvanized steel strip in a tannic acid-phytic acid composite passivation solution, control the temperature at 40°C-50°C, and treat for 30s-60s. After passivation, dry it with hot air at 80°C-100°C for 1min-2min to form a uniform passivation film. The pH of the tannic acid-phytic acid composite passivation solution is 4-5, the total concentration of tannic acid and phytic acid is 3-5g / L, and the mass ratio of tannic acid to phytic acid is 1:

1.

5. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: During the LF refining process, the S in the molten steel is controlled to be ≤ 0.010%, P ≤ 0.015%, the inclusion rating is ≤ 1.0, and the gas content [N] ≤ 60ppm, [O] ≤ 30ppm.

6. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: During the continuous casting process, dynamic soft reduction technology is used at the end of the solidification of the ingot, and electromagnetic stirring is used at the same time. The current is controlled at 200A-300A to reduce the segregation of TiN particles. The resulting ingot thickness is 175mm-200mm and the pulling speed is 1.0-1.5m / min.

7. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: The parameter control at each stage in the temperature-controlled hot rolling process is as follows: Heating stage: 1100-1180℃ for 1.5 hours, which is lower than the 1200℃ for niobium-containing steel; Rough rolling stage: control the starting rolling temperature ≥1050℃ and the cumulative reduction rate ≥40%; Finishing rolling stage: The final rolling temperature is controlled at 850℃-900℃ to control the austenite recrystallized grain size to 8-15μm.

8. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: During the cold rolling process, the total reduction rate is 40%-60%, the thickness after rolling is 1.2mm-3.0mm, and the surface roughness Ra≤0.8μm.

9. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: During the acid electrolytic etching process, the electrolyte is prepared from sulfuric acid and sodium chloride, with a mass fraction of sulfuric acid of 10% and a mass fraction of sodium chloride of 0.5%, and a current density of 1.5-5.0A / dm 2 The processing time is 30s-60s, and a network groove with a depth of 1.5μm-5.0μm is formed on the surface of the steel strip; the thickness of the TiC transition layer is 50nm-100nm.

10. The method for preparing a 420 MPa grade steel strip for a high corrosion resistant photovoltaic support based on synergistic strengthening of Ti microalloying and low aluminum and high magnesium coating according to claim 4, characterized in that: The plating solution is recovered by using ceramic filtration + vacuum distillation technology, with a plating solution utilization rate of ≥98% and a Zn recovery rate in the slag of ≥95%.

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