500MPa-grade Ti micro-alloyed zinc-aluminum-magnesium coating steel belt for low-alloy high-corrosion-resistance photovoltaic bracket and preparation method of 500MPa-grade Ti micro-alloyed zinc-aluminum-magnesium coating steel belt

Abstract

The invention discloses a 500 MPa-level Ti microalloyed zinc-aluminum-magnesium coating steel belt for a low-alloy high-corrosion-resistance photovoltaic support and a preparation method of the 500 MPa-level Ti microalloyed zinc-aluminum-magnesium coating steel belt, and relates to the technical field of metal material preparation. Through the full-process innovation of component design, a smelting process, a rolling system and a coating technology, the contradiction among strength, corrosion resistance, processing performance and cost of the steel belt for the photovoltaic support is solved, and the steel belt is suitable for being used as a supporting structure material for photovoltaic power station construction in complex service environments such as extremely cold plateau, desert gobi, industrial dust and large wind and snow loads. The yield strength of the prepared 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coating steel strip for the low-alloy and high-corrosion-resistance photovoltaic support is larger than or equal to 500MPa, the tensile strength is larger than or equal to 550MPa, the ductility is larger than or equal to 15%, no crack exists when R is equal to 1t in a cold bending test, and the forming requirement of a complex support structure is met; and the red rust resistance time of a salt spray test is not less than 2500 hours, and the service life is more than 30 years.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of metal material preparation, in particular to a 500MPa-grade Ti micro-alloyed zinc-aluminum-magnesium plated steel strip for a low-alloy high-corrosion-resistance photovoltaic support and a preparation method thereof. BACKGROUND

[0002] With the promotion of the global "double carbon" target, photovoltaic energy, as a core component of clean and renewable energy, has shown explosive growth in installed capacity. According to the data of the International Energy Agency (IEA), the global photovoltaic newly installed capacity in 2024 broke through 300GW, and it is expected that the cumulative installed capacity will exceed 3000GW in 2030. Photovoltaic support, as a support system for photovoltaic components, accounts for about 15-20% of the total cost of photovoltaic power stations, and its performance directly affects the safety and service life of the power station.

[0003] The material for photovoltaic support needs to meet the following core requirements: (1) mechanical properties: need to withstand wind load (such as regional > 12 typhoon) and snow load (such as > 1.5kPa accumulated snow in northern regions) under extreme weather, and the steel strip requires yield strength > 500MPa, tensile strength > 600MPa, and elongation after fracture > 20%, to ensure structural stability and anti-deformation ability. (2) Corrosion resistance: the service cycle of photovoltaic support is usually 25-30 years, and it needs to maintain structural integrity in complex environments such as industrial dust, wind and snow load, and with the deepening of national development, energy resources in the northwest are being developed, but the harsh environment of extremely cold highlands, deserts and gobi requires higher corrosion resistance of photovoltaic support; the service life of traditional hot-dip galvanized steel strip in the region is only 8-10 years, which cannot meet the long-term demand. (3) Processing performance: needs to adapt to cold bending forming, welding, punching and other processing technologies, and requires the steel strip to have good plasticity, weldability and surface quality to avoid problems such as cracks and plating peeling during processing. (4) Cost economy: with the promotion of the photovoltaic industry's flat price online, material cost control becomes the key. Traditional high-strength steel relies on high-priced alloy elements such as Nb and V, and the plating process has high energy consumption, resulting in high support cost.

[0004] Currently, there are the following technical problems in manufacturing 500MPa steel strip for high corrosion resistance photovoltaic support: (1) high price alloy element dependence: for example, CN 117127106A discloses a 500MPa hot-dip galvanizing aluminum magnesium steel plate for photovoltaic support, wherein the chemical composition of the substrate (in mass percent) is: 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%, the balance is iron and inevitable impurities; the chemical composition and mass percent of the zinc aluminum magnesium plating bath are: Al: 4.0%-15.0%, Mg: 2.0%-5.0%, Si: 0.005%-0.09%, the balance is Zn and inevitable impurities. The patent involves reasonable substrate composition and plating bath composition, cooperates with improved Sendzimir hot-dip galvanizing process, and obtains a hot-dip galvanizing aluminum magnesium steel plate with yield strength of 500MPa and excellent plating adhesion, which can be used for photovoltaic support and other products. However, the C content in the substrate is as high as 0.17%-0.20%, which will result in general welding performance of the steel plate; the low Si content and high Mn content will result in weak solid solution strengthening and high cost. The upper limit of Mg content in the plating layer is 5.0%, which easily leads to an increase in brittle phase, thereby affecting the bonding force. In addition, during the preparation of the steel strip, the Ti burning loss control and inclusion regulation in smelting are not mentioned, which easily forms angular inclusions, increases surface defects and plating peeling risk. As can be seen from the above, the high C and high Mg design in the above patent sacrifices the comprehensive performance, and short process is not used, so the energy consumption and cost are high. (2) Technical bottleneck of Ti micro-alloying: Ti has strong affinity with N (TiN formation free energy is-333kJ / mol), if N control is not proper during smelting process ([N]>80ppm), coarse TiN inclusions (size>5μm) are easily formed, which becomes a crack source and reduces the plating layer bonding force. (3) Insufficient plating layer composition optimization: in the prior art, the Mg content in the plating layer is mostly 1%-3%, but the influence of Mg content on the plating layer corrosion product film has not been systematically studied. When Mg<1.5%, only loose Zn(OH)2 film is formed on the surface of the plating layer, and the salt spray resistance time is <800h; when Mg>3.0%, the increase of Mg2Zn1 phase increases the brittleness of the plating layer, and the cross-cut test peeling rate is >10%. In addition, although the addition of rare earth elements (RE) can improve the flowability of the plating solution, the RE content in the existing process is mostly >0.3%, which leads to the increase of the viscosity of the plating solution and the uneven thickness of the plating layer (deviation >±3μm). (4) Interface bonding problem between substrate and plating layer: when the thickness of the steel strip surface oxide film (FeO / Fe3O4) is >2μm, it will hinder the formation of Fe-Zn alloy layer, resulting in a decrease in the bonding force. Although the traditional pickling process (hydrochloric acid concentration >15%) can remove the oxide film, excessive corrosion will cause the surface roughness Ra>2.0μm, increasing the plating layer porosity (>5%).(5) The synergy defect of smelting and processing process: the LF refining time in the prior art is too short (<25 min), the [T.O] in the molten steel is >30 ppm, the inclusions are mainly angular Al2O3 (accounting for >40%), the rolling process is easy to scratch the roll and form surface defects. And when Ca treatment, Ca / S ratio <1.0, MnS cannot be completely converted into spherical CaS, resulting in sulfide inclusions along the rolling direction, reducing the transverse toughness (impact energy <20 J).(6) The hot rolling temperature system is unreasonable: when the finish rolling temperature >950℃, the TiC precipitated phase size >200nm, the pinning effect of grain boundary is weakened, and the grain size >10μm; when the finish rolling temperature <800℃, the austenite recrystallization is blocked, the residual stress increases after cold rolling, resulting in edge crack defects (occurrence rate >8%) in the annealing process. SUMMARY

[0005] In view of the above prior art, the purpose of the present application is to provide a 500MPa grade Ti micro-alloyed zinc-aluminum-magnesium coated steel strip for low-alloy high-corrosion-resistance photovoltaic support and a preparation method thereof. Through the whole process innovation of component design, smelting process, rolling system and coating technology, the present application solves the contradiction between strength, corrosion resistance, processability and cost of the steel strip for photovoltaic support, and is suitable for the support structure material for photovoltaic power station construction in complex service environments such as extremely cold plateau, desert Gobi, industrial dust and heavy snow load.

[0006] To achieve the above purpose, the present application adopts the following technical scheme:

[0007] In the first aspect of the present application, a 500MPa grade Ti micro-alloyed zinc-aluminum-magnesium coated steel strip for low-alloy high-corrosion-resistance photovoltaic support is provided, comprising a substrate and a zinc-aluminum-magnesium coating.

[0008] The chemical composition and weight percentage of the substrate are as follows: C 0.04%-0.08%, Si≤0.15%, Mn 0.55%-0.9%, P≤0.020%, S≤0.010%, Ti 0.05%-0.08%, Als 0.015%-0.050%, Ca 0.008%-0.025%, N≤0.006%, O≤0.0025%, H≤0.006%, As≤0.01%, Sn≤0.05%, Co≤0.10%, the balance being Fe and unavoidable impurities.

[0009] The chemical composition and weight percentage of the zinc-aluminum-magnesium coating are as follows: Zn 92%-95%, Al 3.0%-6.0%, Mg 1.5%-3.0%, RE 0.05%-0.2%, Ti 0.05%-0.2%, impurities≤0.5%, wherein RE includes Ce and La.

[0010] As preferred, the atomic ratio of Ti and C in the substrate is 3.5-4.5.

[0011] The component design principle of the substrate is:

[0012] Ti element: form fine TiC (lattice constant ) and TiN (lattice constant ), diffuse and precipitate (size 50-200 nm) during hot rolling and cooling, pin the grain boundary and inhibit grain growth;

[0013] The Ti / C ratio is controlled at 3.5-4.5 (atomic ratio), which ensures effective C fixation, and the remaining free C forms pearlite to improve the strength of the substrate (e.g., when Ti = 0.05%, the theoretical C fixation amount = 0.05% x 12 / 48 = 0.0125%, and the C content in the present application is 0.04-0.08%, N needs to be fixed by AlN to control [N] ≤ 60ppm).

[0014] Al element: deoxidation to form Al2O3 (melting point 2050℃), as the main component of refining slag, and form AlN (melting point 2200℃) to pin the grain boundary and cooperate with TiC to refine the grain; when the Al2O3 content in the surface oxide layer of the steel strip is ≥ 30%, it can promote the adsorption of Zn 2+ , Mg 2+ in the plating solution and improve the uniformity of the alloy layer growth.

[0015] The component design principle of the zinc-aluminum-magnesium coating is:

[0016] Dual role of Mg: in the early stage of corrosion, Mg preferentially dissolves to form Mg 2+ , Zn 2+ , and generates basic zinc-magnesium carbonate complex (Zn5(OH)8MgCO3·5H2O), covering the surface of the coating and hindering the penetration of Cl - ; and the Mg content affects the corrosion current density, for example, when Mg = 2.0%, the corrosion current density (Icorr) decreases to 1.2 μA / cm 2 , which is 79% lower than that of pure Zn coating (Icorr = 5.8 μA / cm 2 );

[0017] Modification effect of RE: Ce and La form a solid solution with Zn, reducing the surface tension of the plating solution (from 0.78 N / m to 0.72 N / m), promoting the spreading of the plating solution, and reducing the plating defects; RE oxides (CeO2, La2O3) form a nanoscale protective film on the surface of the coating, inhibiting the expansion of local corrosion pits.

[0018] Ti: control the content of Ti in the coating is 0.05%-0.2%, form Zn-Mg-Ti ternary phase, Ti as a heterogeneous nucleation agent, make the coating grain from the conventional 50-100 μm to 10-25 μm (equiaxed crystal ratio from 20-30% to 60-80%), the total area of grain boundary increases 2-3 times, effectively hinder the penetration of corrosive medium (grain boundary corrosion current density is reduced by 40%), reduce magnesium burning loss and uniform coating.

[0019] The second aspect of the application provides a preparation method of the above-mentioned 500MPa grade Ti micro-alloyed zinc-aluminum-magnesium coating steel strip for low-alloy high-corrosion-resistant photovoltaic support, comprising the following steps:

[0020] The preparation method comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling, cold rolling, continuous annealing and hot galvanizing.

[0021] The converter smelting process comprises end point control, alloying process and argon bottom blowing stirring.

[0022] The LF refining process comprises refining slag system optimization and calcium treatment process.

[0023] The specific operation of the refining slag system optimization is: CaO-Al2O3-SiO2-based slag is used, and the slag is adjusted by aluminum particles, silicon carbide and calcium carbide, the basicity R is 2.5-3.5, the melting point is 1350-1400℃, the viscosity is ≤0.5 Pa·s, and the high-efficiency absorption of Al2O3 and TiO2 inclusions is ensured; at the same time, the aluminum content is increased by feeding the aluminum wire first, and then the titanium wire is fed to increase the titanium content, and the titanium content in the titanium wire is ≥99.5%;

[0024] The aluminum content is increased by feeding the aluminum wire first, and the residual oxygen potential of the molten steel is reduced by using the strong deoxidizing property of Al ([Al] x [T.O] ≤2.5 x 10 -5 ) and then feeding the titanium wire (Ti content ≥99.5%) to increase the titanium content, so as to reduce the oxidation loss of Ti as much as possible (the loss rate is reduced from 20% to less than 10%);

[0025] The specific operation of the calcium treatment is: high calcium wire is added in the later stage of refining, the Ca / S is controlled to be 2.0-3.0, the MnS inclusions are converted into spherical CaS, at the same time, the TiN inclusions are wrapped to form Ca-Ti-Al-O composite inclusions, and the proportion of angular inclusions is reduced from 70% to less than 20%; the refining temperature is controlled to be 1590-1610℃, and the refining time is controlled to be 35-40min.

[0026] Hot rolling process: including heating, rolling and cooling process; in the rolling process, the open rolling temperature is controlled at 1080-1150℃ (in the non-recrystallization region of austenite), multi-pass large reduction is adopted, the single-pass reduction rate is ensured to be ≥15%, the total deformation amount is ensured to be ≥60%, the cast structure is broken and the TiC is precipitated at the austenite grain boundary; the finish rolling temperature is controlled at 840-900℃, which is above the ferrite transformation temperature, so that the structure after hot rolling is uniform austenite, which provides a good foundation for subsequent cold rolling and annealing;

[0027] Continuous annealing process: the annealing temperature is controlled at 760-830℃ to form ferrite + pearlite two-phase region, the holding time is 2-5min, the volume fraction of ferrite is ≥90%, the pearlite is in the form of fine flake and the lamellar spacing is ≤0.5μm; the jet cooling is adopted in the rapid cooling section, the cooling rate is ≥50℃ / s, the interval of 400-500℃ is rapidly passed through, so as to inhibit the precipitation of coarse cementite and ensure that the yield strength fluctuation is ≤±10MPa;

[0028] Hot plating process: including pre-plating treatment, immersion plating and post-plating treatment; the pre-plating treatment includes electrolytic cleaning, activation treatment and plating solution control;

[0029] The specific operation of the activation treatment is: the substrate is immersed in a 5% H2SO4 solution for 10-20s, so that Fe 2+ active sites are formed on the surface of the steel strip, which promotes the reduction reaction of Zn 2+ in the plating solution.

[0030] As preferred, in the converter smelting process, the tapping temperature is controlled at 1620-1660℃ to ensure that the alloy is fully dissolved; the argon blowing operation is performed throughout the converter smelting, the gun position is controlled during the smelting process, the carbon is pulled out once, and the cold material is added completely 3min before the end point, so as to avoid the influence of the incomplete melting of the cold material on the end point temperature and carbon content control, and ensure that the composition and temperature meet the standards at the time of tapping; at the time of tapping, the bottom argon flow is controlled at 200-300L / min, and the duration is 3-5min, which promotes the homogenization of the alloy and avoids the local segregation of Mn element.

[0031] Further, the gun height is adjusted according to the molten pool temperature, carbon content and decarburization requirement, specifically: low gun position (the oxygen lance is closer to the molten pool surface) can enhance the stirring intensity of oxygen and molten pool, accelerate the carbon oxidation reaction (decarburization) and increase the molten pool temperature; high gun position has weak stirring, which is beneficial to reducing the iron loss and stabilizing the decarburization rate. By monitoring the molten pool carbon content and temperature in real time, the gun position is adjusted to achieve the target carbon content (one-time carbon pulling).

[0032] As preferred, in the LF refining process, the refining end point control [S]≤0.010%, [N]≤60ppm (fixed by AlN), [T.O]≤25ppm, to ensure the steel liquid purity to meet the subsequent processing requirements.

[0033] As preferred, in the continuous casting process, the mold parameters are: using low-moderate basicity low-carbon steel protective slag with melting temperature of 1080-1150℃, balancing the flowability, quickly forming liquid slag layer, and inhibiting Ti oxidation; controlling the liquid surface fluctuation in the mold ≤±6mm to avoid slag entrapment; the water temperature in the front section of the secondary cooling zone is 25-45℃, and the water temperature in the rear section is 45-60℃; controlling the water quantity to be 80-120m 3 / h to control the uniformity of the primary shell thickness (deviation ≤5%); the mold can be used with asymmetric sinusoidal vibration, the frequency is 200-300 times / min, the amplitude is 3-5mm, the negative slip time is 0.2-0.3s, and the vibration mark depth is reduced from 0.3mm to 0.15mm;

[0034] Further, gradient water temperature design can be used to control the cooling water temperature in the mold.

[0035] For example, the water temperature in the upper section of the mold is 30-33℃, and the water temperature in the lower section is 33-36℃, to enhance the cooling intensity in the meniscus region, optimize the shell thickness, and reduce the standard deviation from 0.5mm to 0.25mm.

[0036] As preferred, in the continuous casting process, the weak cooling process is used in the secondary cooling zone process, the specific water quantity is 0.4-0.8L / kg, the water temperature in the front section (0-2m) of the secondary cooling zone is controlled to be 35-45℃, and the water temperature in the rear section (2-4m) is controlled to be 50-60℃, so that the surface temperature of the casting blank ≥1000℃ enters the straightening zone, reducing the risk of cracks; after the casting blank is discharged, it is slowly cooled to below 600℃ at a cooling rate of ≤5℃ / min, to avoid the coarse precipitation of TiC (size >200nm) in the high temperature zone, and to ensure the full dissolution of TiC during subsequent hot rolling.

[0037] As preferred, in the hot rolling process, the furnace temperature is controlled in three sections: preheating section 800-950℃, heating section 950-1150℃, and soaking section 1150-1190℃ (lower than 1200℃ of Nb steel), total heating time ≥90min, to ensure complete dissolution of TiC (dissolution temperature ≥1150℃), while avoiding excessive dissolution of AlN (AlN dissolution temperature ≥1250℃).

[0038] The preheating section can gradually increase the temperature of the billet and reduce thermal stress; the heating section can quickly increase the temperature of the billet to close to the austenitizing temperature; and the soaking section can make the temperature of the billet uniform and ensure complete dissolution of TiC. The total heating time refers to the total heating time of the billet in the heating furnace, i.e. the cumulative time of the preheating section, the heating section and the soaking section, to ensure sufficient heating and uniformization of the structure of the billet.

[0039] As preferred, in the cooling process in the hot rolling process, the billet is air-cooled at a cooling rate of 5-15℃ / s to 540℃-620℃ after rolling, to promote the dispersion of TiC (peak precipitation temperature 550℃), the size of the precipitated phase is 50nm-200nm, and the distribution density is ≥1×10 16 3 .

[0040] As preferred, in the cold rolling process, a six-high reversible rolling mill is used, the total reduction is 50%-70%, and 3-7 passes of rolling are performed, the pass reduction is gradually decreased, the first pass is 25%-30%, and the last pass is 10%-15%, and the surface roughness Ra≤1.5μm.

[0041] As preferred, in the electrolytic cleaning process, a hydrochloric acid with a volume fraction of 5%-10% is used, the current density is 10-15A / dm 2 , and the time is 30s-60s; in the activation treatment, a H2SO4 solution with a volume fraction of 5% is used to remove the surface oxide film (thickness from 3μm to 0.5μm), and at the same time, a micro-rough surface (Ra=0.8-1.2μm) is formed to increase the adhesion area of the coating.

[0042] As preferred, the plating bath control parameters are: temperature 450℃-475℃, to avoid excessive evaporation of Mg, the boiling point of Mg is 1090℃, the loss rate of Mg in the plating bath is ≤5%, the pH value is 4.5-5.5, the density is 7.2-7.5g / cm 3 , and the Zn-Al-Mg alloy ingot (purity ≥99.5%) is regularly supplemented;

[0043] As preferred, the immersion plating time is 2.0s-8.0s.

[0044] Further, the immersion plating time is adjusted according to the thickness of the steel strip to ensure uniform thickness of the coating (deviation ≤±2μm), and the specific adjustments are as follows:

[0045] When the thickness of the steel strip is 1.0mm-2.0mm, the immersion plating time is 3.0s-5.0s;

[0046] When the thickness of the steel strip is 2.0mm-4.0mm, the immersion plating time is 5.0s-8.0s.

[0047] ​As preferred, the specific operation of the post-plating treatment is: air cooling to room temperature at a cooling rate of ≤10℃ / s to avoid rapid cooling to increase the internal stress of the plating layer; then performing a finishing treatment with a reduction rate of 1%-2% to improve the surface flatness and eliminate the micro-cracks on the surface of the plating layer.

[0048] The beneficial effects of the present application are:

[0049] The present application solves the contradiction between strength, corrosion resistance, processability and cost of the steel strip for photovoltaic support through the whole-process innovation of component design, smelting process, rolling system and plating technology, and is suitable for the support structure material for the construction of photovoltaic power station under complex service environments such as extremely cold plateau, desert Gobi, industrial dust and heavy snow load. The yield strength of the 500MPa-grade Ti micro-alloyed zinc-aluminum-magnesium plating layer steel strip for photovoltaic support with high corrosion resistance prepared by the present application is ≥500MPa, the tensile strength is ≥550MPa, the elongation is ≥15%, the cold bending test R=1t is free of cracks, and the forming requirement of the complex support structure is met; the red rust resistance time of the salt spray test is ≥2500 hours, which is 1.5-2.5 times of that of the traditional zinc plating layer, the product can be used in C5-M high corrosive marine environment in coastal areas, C5-I industrial high corrosive environment near coal-fired power plants, and has a service life of more than 30 years, which is twice of that of conventional products.

[0050] The specific operation is as follows:

[0051] (1) Low-cost strengthening mechanism of Ti micro-alloying: 500MPa-grade strength is realized by taking Ti as a single micro-alloying element (0.05-0.08%), and the precipitation strengthening (contribution of about 60-100MPa) and grain refinement (average grain size of 6-10μm, Hall-Petch coefficient k=0.12MPa·mm 1 / 2 ) of TiC / TiN are realized to replace Nb and V alloys, and the raw material cost is reduced by 15-20%. Compared with the steel containing 0.05% Nb, the Ti element cost of the steel of the present application is only 1 / 3 of that of the former, and the strength fluctuation is smaller (standard deviation ≤20MPa). And the welding performance is improved by designing low C (≤0.08%) to reduce the carbon equivalent (CE ≤0.35%).

[0052] (2) Precise control of Mg content in the plating layer and optimization of corrosion resistance: a quantitative relationship between Mg content and corrosion resistance of the plating layer is established: when Mg=1.5-3.0%, the Mg(OH)2 content in the corrosion product film increases from 10% to 25%, the film porosity decreases from 15% to less than 5%, and the red rust resistance time of the salt spray test is ≥2500h.

[0053] (3) Calcium aluminate modification of inclusions in LF refining: Through high basicity slag (R = 2.5-3.5) and calcium treatment (Ca / S≥1.5), brittle inclusions such as Al2O3, TiN are converted into spherical CaO-Al2O3-TiO2 composite inclusions, the average diameter of inclusions is reduced from 10 μm to less than 5 μm, the proportion of angular inclusions is reduced from 60% to 15%, and the surface defect rate of steel strip is reduced from 5% to 0.8%.

[0054] (4) Synergistic grain refinement of hot rolling finishing temperature and deformation: finishing at 840-900 °C and controlling total deformation≥60%, using the grain crushing effect of unrecrystallized austenite, the density of TiC precipitated phase is increased by 30%, the number of grain boundary pinning points is significantly increased. The ferrite grain size is refined from 20 μm to 6-10 μm, the grain boundary area is increased by 20%, and the grain boundary strengthening contribution is increased by 10-20 MPa.

[0055] (5) Annealing temperature and microstructure matching of strength and toughness: annealing at 760-830 °C to form ferrite (≥88%) + pearlite (12%) microstructure, the dislocation density in ferrite is controlled at 1×10 14 m -2 , and the pearlite interlamellar spacing is≤0.3 μm. This microstructure makes the steel strip yield strength≥500 MPa, elongation≥20%, and impact energy at -20 °C≥30 J, solving the contradiction between high strength and low toughness, especially suitable for photovoltaic support applications in complex regions such as extremely cold, coastal, plateau, and windy areas.

[0056] (6) Energy consumption optimization of full-flow and short-flow processes: canceling RH vacuum treatment and multi-step annealing, directly controlling steel liquid purity through converter-LF refining, replacing forced water cooling with hot rolling air cooling, and precisely controlling plating liquid temperature (fluctuation ±5 °C), so that the energy consumption per ton of steel is reduced from 650 kWh to 550 kWh, meeting the requirements of green manufacturing.

[0057] (7) Coordinated optimization of coating and substrate: through surface activation treatment (hydrochloric acid concentration 5-10%) before plating to control the thickness of the oxide film <1 μm, combined with the interface reaction of Mg (1.5-3.0%) in the coating and Al (0.015-0.050%) in the substrate, a dense Fe-Zn-Al-Mg alloy coating (thickness 3-5 μm) is formed, which improves the adhesion and corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 : optical microstructure of hot rolled steel strip in Example 1, scale is 50 μm;

[0059] by Figure 1It can be seen that the hot-rolled steel strip in Example 1 has a ferrite + pearlite two-phase structure, with a ferrite volume fraction ≥90%, and the pearlite is distributed in fine lamellar form with a lamellar spacing ≤0.5μm. The grain size is uniformly distributed and there are no obvious coarse grains. This is due to the reasonable control of hot rolling process parameters, which ensures the good mechanical properties of the steel strip.

[0060] Figure 2 Metallographic structure of cold-rolled annealed steel strip in Example 1 at a scale of 10μm;

[0061] Figure 3 : SEM image of hot-rolled steel strip in Comparative Example 1 at a scale of 10 μm;

[0062] Depend on Figure 3 It can be seen that the size of MnS is about 5μm and the size of TiN is about 8μm, which leads to their poor performance;

[0063] Figure 4 : Figure 3 Composition energy spectrum of MnS inclusions in the sample;

[0064] Figure 5 : Figure 3 The compositional energy spectrum of TiN inclusions in the sample. Detailed Implementation

[0065] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0066] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0067] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0068] Examples 1-3 and Comparative Examples 1-2:

[0069] 1. Composition:

[0070] The 500MPa grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets includes a substrate and a zinc-aluminum-magnesium coating, wherein:

[0071] The chemical composition of the substrate is shown in Table 1.

[0072] Table 1. Chemical composition (by mass percentage) of the substrate in the steel strips prepared in Examples 1-3 and Comparative Examples 1-2.

[0073]

[0074] The chemical composition of the zinc-aluminum-magnesium plating layer is shown in Table 2.

[0075] Table 2 Chemical composition of zinc-aluminum-magnesium plating layer in steel strips prepared in Examples 1-3 and Comparative Examples 1-2 (in mass percent)

[0076] Element Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Zn 94 93 92.5 95 92 Al 4.0 5.0 4.5 2.0 6.0 Mg 2.0 2.5 2.2 1.0 4.0 RE (Ce + La) 0.1 0.15 0.12 0.03 0.3 Ti 0.1 0.12 0.15 0.03 0.25 Impurities 0.3 0.25 0.3 0.6 0.45

[0077] 2. Preparation process:

[0078] The process comprises converter smelting, LF refining, continuous casting, hot rolling, cold rolling, continuous annealing, and hot plating; wherein,

[0079] (1) Converter smelting process:

[0080] After pretreatment, the molten iron is subjected to converter smelting, and the tapping temperature is controlled to ensure full dissolution of the alloy; argon is blown at the bottom to stir during tapping, and the argon flow rate and time are controlled to promote alloy homogenization and avoid local segregation of Mn elements. Argon is blown throughout the converter smelting process, and appropriate gun position and charging timing are controlled during the smelting process to ensure one-time carbon pulling, and cold material is added completely 3 minutes before the end point to ensure the tapping temperature.

[0081] The above converter smelting process can achieve efficient utilization of Ti elements and initial inclusion control. The specific parameters in the converter smelting process are shown in Table 3.

[0082] Table 3 Parameters in the converter smelting process

[0083] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Tapping temperature (°C) 1625 1635 1640 1610 1670 Bottom argon blowing flow rate (L / min) 250 280 230 180 320 Bottom argon blowing time (min) 4 3.5 4.5 2 5.5

[0084] (2) LF refining process:

[0085] Refining slag optimization: CaO-Al2O3-SiO2-based slag is used, and aluminum particles, silicon carbide, and calcium carbide are used for slag conditioning to control the slag basicity R and melting point, and to ensure efficient absorption of Al2O3 and TiO2 inclusions. Aluminum wire is fed first to increase aluminum content, and then titanium wire (Ti content ≥ 99.5%) is fed to increase titanium content.

[0086] Calcium treatment process: high calcium wire is added in the late refining stage to control the Ca / S ratio, convert MnS inclusions into spherical CaS, and wrap TiN inclusions to form Ca-Ti-Al-O composite inclusions, reducing the proportion of angular inclusions from 70% to below 20%.

[0087] The refining time and temperature are controlled, and the refining end point is controlled: [S] ≤ 0.010%, [N] ≤ 60 ppm (fixed by AlN), [T.O] ≤ 25 ppm, to ensure that the steel liquid purity meets the subsequent processing requirements.

[0088] The above LF refining can realize the control of inclusion morphology and the improvement of molten steel purity. The specific parameters in the LF refining process are shown in Table 4.

[0089] Table 4 Parameters in the LF refining process

[0090] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Slag basicity R 2.5 2.7 2.6 2.0 4.0 Melting point (°C) 1380 1370 1390 1300 1450 Refining temperature (°C) 1600 1590 1610 1570 1630 Refining time (min) 35 38 37 30 45 Inclusion rating 1.0 grade 1.0 grade 0.5 grade 2.0 grade 1.5 grade Ca / S ratio 2.5 2.8 2.6 1.5 3.5

[0091] (3) Continuous casting process:

[0092] The mold parameters: low-moderate basicity low-carbon steel protection slag is used to balance the fluidity, quickly form a liquid slag layer, and inhibit Ti oxidation. The liquid level fluctuation is controlled to avoid slag entrapment, and the mold cooling water temperature and the casting speed are controlled. The secondary cooling zone process: weak cooling process is used to control the water temperature of the front and rear ends of the secondary cooling zone, so that the surface temperature of the casting blank is ≥1000℃ entering the straightening zone, reducing the risk of cracks. The thickness of the casting blank is 175mm, and after the casting blank is offline, it is slowly cooled at a cooling rate of ≤5℃ / min, and the slow cooling temperature is controlled, so that the center segregation of the macrostructure is ≤1.5 level.

[0093] The above continuous casting process can improve the casting blank quality and the uniformity control of the microstructure, and the specific parameters of the continuous casting process are shown in Table 5.

[0094] Table 5 Parameters of the continuous casting process

[0095] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Liquid surface fluctuation (mm) 5 4 6 8 7 Mould water temperature (°C) 35 33 35 28 42 Drawing speed (m / min) 1.15 1.20 1.25 1.0 1.35 Front section water of secondary cooling zone (°C) 40 38 42 30 50 Rear section water of secondary cooling zone (°C) 55 53 57 45 65 Tempering temperature (°C) 595 600 592 620 580

[0096] (4) Hot rolling process:

[0097] The preheating section temperature, soaking section temperature and heating time of the heating furnace are controlled to ensure that TiC is completely dissolved, while avoiding excessive dissolution of AlN. The opening rolling temperature is controlled, and multi-pass large reduction is used, and the total deformation is ≥60%, which breaks the as-cast structure and promotes the precipitation of TiC at the austenite grain boundary. The finish rolling temperature is controlled, and the microstructure after heat preservation rolling is uniform austenite, which provides a good foundation for subsequent cold rolling and annealing. The air cooling temperature after rolling is controlled to promote the dispersion precipitation of TiC.

[0098] The above hot rolling process can refine the grains and control the precipitated phase. The specific parameters of the hot rolling process are shown in Table 6.

[0099] Table 6 Parameters of the hot rolling process

[0100] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Preheating section temperature (°C) 850 880 830 780 980 Heating section temperature (°C) 1050 1080 1030 1000 1180 Soaking section temperature (°C) 1150 1160 1155 1120 1190 Heating time (min) 95 100 92 85 110 Opening rolling temperature (°C) 1100 1120 1090 1050 1180 Finishing rolling temperature (°C) 870 883 890 820 920 Air cooling temperature (°C) 580 600 590 550 630

[0101] (5) Cold rolling process:

[0102] A six-high reversible mill is used to control the total reduction rate and rolling pass. Through the cold rolling process, the hardness and surface roughness of the cold rolled steel strip can be controlled, thereby optimizing the processing performance. The specific parameters of the cold rolling and annealing process are shown in Table 7.

[0103] Table 7 Parameters of cold rolling process

[0104] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Total reduction rate (%) 65 62 63 55 75 Rolling passes 3 5 5 2 8 Hardness (HV) 182 175 180 170 190 Surface roughness (μm) 1.5 1.2 1.3 2.0 1.0

[0105] (6) Continuous annealing process:

[0106] The annealing temperature and holding time are controlled so that the ferrite volume fraction is ≥ 90% and the pearlite is distributed in the form of fine flakes. Air jet cooling is used in the fast cooling section. The substrate is obtained after the continuous annealing process, and the annealing process can make the steel strip structure more uniform and control the strength. The specific parameters of the annealing process are shown in Table 8.

[0107] Table 8 Parameters of annealing process

[0108] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Annealing temperature (°C) 780 790 800 750 850 Soaking time (min) 3.5 3.0 2.5 2.0 6.0

[0109] (7) Hot plating process:

[0110] It includes pre-plating treatment, immersion plating and post-plating treatment, wherein the pre-plating treatment includes electrolytic cleaning, activation treatment and plating solution control;

[0111] During the electrolytic cleaning process, hydrochloric acid is used to remove the surface oxide film and form a micro-rough surface at the same time, increasing the plating layer adhesion area. Then the steel strip is immersed in a 5% sulfuric acid solution for activation treatment, so that the surface of the steel strip forms Fe 2+ active sites, promoting the reduction reaction of Zn 2+ in the plating solution. The plating solution temperature is controlled, the steel strip is immersed for plating treatment, and then air-cooled to room temperature for finishing treatment to improve the surface flatness and eliminate the micro-cracks on the surface of the plating layer.

[0112] Through the above hot plating process, the interface bonding can be improved and the plating layer quality can be controlled. The specific parameters of the hot plating process are shown in Table 9.

[0113] Table 9 Parameters of hot plating process

[0114] Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Hydrochloric acid concentration (%) 7 8 8 5 12 Current density (A / dm 2 )]]> 12 13 11 8 16 Electrolytic cleaning time (s) 45 50 40 25 70 Immersion time (s) 15 18 12 8 25 Plating solution temperature (°C) 470 465 455 440 490 Immersion plating time (s) 4.0 4.0 6.0 3.0 7.0

[0115] 3. Performance

[0116] (1) Mechanical properties:

[0117] The mechanical properties of the steel strips prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 10.

[0118] Table 10 Mechanical properties of steel strips prepared in Examples 1-3 and Comparative Examples 1-2

[0119] Group Thickness mm Yield strength (MPa) Tensile strength (MPa) Elongation after fracture (%) Impact energy at -20 °C (J) Example 1 2.0 531 634 22 45 Example 2 1.8 553 657 20.5 46 Example 3 3.0 548 629 21 38 Comparative Example 1 3.0 568 663 12.5 17 Comparative Example 2 2.5 557 649 11.8 21

[0120] As shown in Table 10, the yield strength of the steel strips prepared in Examples 1-3 is all ≥500 MPa, the elongation after fracture is ≥20%, and the impact energy is ≥30 J, meeting the requirements of high strength and high toughness of photovoltaic support. The plasticity and toughness of Comparative Examples 1 and 2 are lower.

[0121] (2) Corrosion resistance and bonding force:

[0122] The corrosion resistance and bonding force of the steel strips prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 11.

[0123] Table 11 Corrosion resistance and bonding force of the steel strips prepared in Examples 1-3 and Comparative Examples 1-2

[0124]

[0125] As shown in Table 11, the salt spray resistance time of the steel strips prepared in Examples 1-3 is all ≥2500 h, the bonding force is 0 level, and there is no peeling; Comparative Example 1 uses the traditional hot galvanizing process, and the corrosion resistance of the coating is poor; Comparative Example 2 has high brittleness of the coating due to the Mg content of 4.0% in the coating, and the peeling rate increases.

[0126] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A 500 MPa grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy high-corrosion-resistant photovoltaic racks, characterized in that, The substrate and a zinc-aluminum-magnesium coating layer are included; wherein, The chemical composition of the substrate and the percentage by weight are as follows: C 0.04%-0.08%, Si≤0.15%, Mn 0.55%-0.9%, P≤0.020%, S≤0.010%, Ti 0.05%-0.08%, Als 0.015%-0.050%, Ca 0.008%-0.025%, N≤0.006%, O≤0.0025%, H≤0.006%, As≤0.01%, Sn≤0.05%, Co≤0.10%, the balance being Fe and inevitable impurities, and the atomic ratio of Ti and C in the substrate is 3.5-4.5; The chemical composition of the zinc-aluminum-magnesium coating layer and the percentage by mass are as follows: Zn 92%-95%, Al 3.0%-6.0%, Mg 1.5%-3.0%, RE 0.05%-0.2%, Ti 0.05%-0.2%, impurities≤0.5%, wherein RE includes Ce and La.

2. The process for the production of a low alloy high corrosion resistant photovoltaic racking 500 MPa grade Ti microalloyed zinc-aluminum-magnesium coated steel strip according to claim 1, characterized in that, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The converter smelting process comprises end point control, alloying process and bottom argon blowing stirring. The LF refining process comprises refining slag system optimization and calcium treatment process; the specific operation of the refining slag system optimization is as follows: CaO-Al2O3-SiO2-based slag is used, and the slag is adjusted by using aluminum particles, silicon carbide and calcium carbide; the basicity R is 2.5-3.5, the melting point is 1350-1400℃, and the viscosity is≤0.5Pa·s; at the same time, the aluminum content is increased by feeding aluminum wire first, and then the titanium content is increased by feeding titanium wire, and the titanium content in the titanium wire is≥99.5%; the specific operation of the calcium treatment is as follows: high calcium wire is added in the later stage of refining, and the Ca / S is controlled to be 2.0-3.0; the refining temperature is controlled to be 1590-1610℃, and the refining time is controlled to be 35-40min; The hot rolling process comprises heating, rolling and cooling processes; in the rolling process, the opening rolling temperature is controlled to be 1080-1150℃, multi-pass large reduction is adopted, the single-pass reduction rate is ensured to be≥15%, and the total deformation amount is ensured to be≥60%; and the finish rolling temperature is controlled to be 840-900℃; The continuous annealing process controls the annealing temperature to be 760-830℃, and the holding time to be 2-5min; the jet cooling is adopted in the rapid cooling section; 3. The process for producing 500 MPa grade Ti micro alloyed zinc-aluminum-magnesium coated steel strip for high corrosion resistant photovoltaic racking of claim 2, characterized in that, The hot plating process comprises pre-plating treatment, immersion plating and post-plating treatment; the pre-plating treatment comprises electrolytic cleaning, activation treatment and plating solution control; the specific operation of the activation treatment is as follows: the substrate is immersed in a 5% H2SO4 solution for 10-20s.

4. The method for preparing 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets as described in claim 2, characterized in that, In the converter smelting process, the tapping temperature is controlled to be 1620-1660℃; when tapping, the bottom argon blowing flow is controlled to be 200-300L / min, and the blowing lasts for 3-5min; during smelting, the gun position is controlled to adapt the stirring intensity of the molten pool to the decarburization requirement, and the cold charge is added completely 3min before the end point. In the LF refining process, the refining end point control is as follows: [S]≤0.010%, [N]≤60ppm, and [T.O]≤25ppm.

5. The method for preparing 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets as described in claim 2, characterized in that, In the continuous casting process, the parameters of the crystallizer are set as follows: low-moderate basicity low-carbon steel protective slag with a melting temperature of 1080-1150°C is used, the liquid level fluctuation in the crystallizer is controlled to be ≤±6mm, the water temperature in the front section of the secondary cooling zone is 25-45°C, and the water temperature in the rear section is 45-60°C; the water quantity is controlled to be 80-120m 3 / h; weak cooling process is used in the secondary cooling zone, the specific water quantity is 0.4-0.8L / kg, the water temperature in the front section of the secondary cooling zone is controlled to be 35-45°C, and the water temperature in the rear section is controlled to be 50-60°C, and after the casting blank is discharged, it is slowly cooled to below 600°C at a cooling rate of ≤5°C / min.

6. The method for preparing 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets as described in claim 2, characterized in that, In the hot rolling process, the heating furnace temperature is controlled in three stages, respectively: preheating section 800-950℃, heating section 950-1150℃, soaking section 1150-1190℃, total heating time≥90min; after rolling, air cooling to 540-620℃ at a cooling rate of 5-15℃ / s.

7. The method for preparing 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets as described in claim 2, characterized in that, In the cold rolling process, the pass reduction rate decreases successively, the first pass 25-30%, the last pass 10-15%, the total reduction rate 50-70%, 3-7 passes are rolled, and the surface roughness of the steel strip is controlled to be Ra≤1.5μm.

8. The process for producing 500 MPa grade Ti micro alloyed zinc-aluminum-magnesium coated steel strip for high corrosion resistant PV racking of claim 2, wherein the process is characterized by, In the electrolytic cleaning process, 5-10% hydrochloric acid by volume is used, the current density is 10-15 A / dm 2 , the time is 30-60 s; in the activation process, 5% H2SO4 solution by volume is used; the plating bath control parameters are: temperature 450-475°C, pH value 4.5-5.5, density 7.2-7.5 g / cm 3 ; the immersion plating time is 2.0-8.0 s.

9. The process for producing a 500 MPa grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for high corrosion resistant photovoltaic racking of claim 8, characterized in that, The immersion time is adjusted according to the thickness of the steel strip, specifically as follows: When the thickness of the steel strip is 1.0-2.0mm, the immersion time is 3.0-5.0s; When the thickness of the steel strip is 2.0-4.0mm, the immersion time is 5.0-8.0s.

10. The method for preparing 500MPa-grade Ti microalloyed zinc-aluminum-magnesium coated steel strip for low-alloy, high-corrosion-resistant photovoltaic brackets as described in claim 2, characterized in that, The specific operation of post-plating treatment is: air cooling to room temperature at a cooling rate of≤10℃ / s, followed by light finishing treatment, reduction rate 1-2%.

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