Ultrahigh-corrosion-resistance zinc-aluminum-magnesium steel strip and manufacturing method thereof

Abstract

The invention provides an ultrahigh corrosion-resistant zinc-aluminum-magnesium steel strip which comprises a cold-rolled or hot-rolled acid flat substrate and a plating layer plated on the substrate, the plating layer takes zinc (Zn) as the balance and comprises the following chemical components in percentage by mass: 17-23% of aluminum (Al), 5-9% of magnesium (Mg), 0.23 + / -0.05% of silicon (Si), 0.04 + / -0.02% of titanium (Ti), 0.3 + / -0.2% of cerium (Ce), 0.14 + / -0.2% of calcium (Ca) and 0.17 + / -0.2% of tin (Sn); the coating is controlled to form a compact network-shaped structure which takes Fe2Al5 as a crystal nucleus, Al crystal dendrites and MgZn2 secondary crystal dendrites grow in a staggered manner and is connected by Mg2Si, and the compact network-shaped structure is finally wrapped by a Zn phase, so that uniform distribution of a magnesium element in the coating is ensured, and a material basis is provided for a dual protection and self-repairing mechanism.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for metal materials, and in particular to an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip and its manufacturing method. Background Technology

[0002] Metal corrosion is one of the main causes of failure in steel materials, leading to huge economic losses and safety hazards. While traditional hot-dip pure zinc (GI) coatings offer some sacrificial anodic protection, their corrosion resistance is limited, typically with a service life of only 3-5 years. Corrosion easily spreads at damaged areas such as cuts and scratches. To improve corrosion resistance, coatings such as zinc-5% aluminum (GF) and 55% aluminum-zinc alloy (GL) have been developed. However, their improvement in planar corrosion resistance is limited (GL is approximately 3-5 times that of GI), and their protection of cuts is generally poor. They remain insufficient in harsh environments such as marine, high-humidity and heat, and chemical environments.

[0003] In recent years, zinc-aluminum-magnesium (ZAM) coatings have attracted widespread attention due to their excellent comprehensive performance. It is known that ZAM coatings (e.g., Al content 3-11%, Mg content 1-3%) exhibit significantly improved corrosion resistance compared to traditional galvanizing (e.g., a formulation with 11% Al and 3% Mg content shows approximately 5-8 times the salt spray resistance of GI, with a lifespan of 15-25 years). However, existing technologies still have the following limitations:

[0004] There is still room for improvement in corrosion resistance, especially in extreme corrosive environments (such as marine atmospheres, high ammonia environments in livestock and poultry houses, etc.), where its service life and resistance are difficult to meet the long-term requirements of more than 50 years.

[0005] Although some formulations (such as Zn-Al-Mg-Si) show certain self-healing capabilities, their mechanisms are unclear and their effects are unstable. In particular, their "self-healing" protective capabilities at cut and scratch sites need to be strengthened.

[0006] Certain zinc-aluminum-magnesium coatings with specific compositions are prone to surface defects such as black spots during solidification, affecting their appearance quality. Complex subsequent processes (such as special heating and cooling cycles) are required to suppress specific harmful phases (such as Mg2Zn). 11 The generation of phase.

[0007] High aluminum and high magnesium alloying may lead to increased coating brittleness and poor machinability. It is necessary to balance corrosion resistance and machinability through precise addition of trace elements and process control. To this end, an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip and its manufacturing method are proposed. Summary of the Invention

[0008] In view of this, embodiments of the present invention provide an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip and its manufacturing method, so as to solve or alleviate the technical problems existing in the prior art, and at least provide a beneficial option.

[0009] The technical solution of this invention is implemented as follows: an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip, comprising a cold-rolled or hot-rolled acid-coated substrate and a coating plated on the substrate, wherein the coating has zinc (Zn) as the balance and contains the following chemical composition by mass percentage: Aluminum (Al) is 17-23%, magnesium (Mg) is 5-9%, silicon (Si) is 0.23±0.05%, titanium (Ti) is 0.04±0.02%, cerium (Ce) is 0.3±0.2%, calcium (Ca) is 0.14±0.2%, and tin (Sn) is 0.17±0.2%.

[0010] In some embodiments, the microstructure of the coating includes Fe2Al5 as the crystal nucleus, Al growing from the Fe2Al5 crystal nucleus to form Al dendrites, MgZn2 growing from the Al dendrites as branches to form secondary dendrites, Mg2Si uniformly distributed between the dendrites, and Mg2Si connecting adjacent secondary dendrites together, and Zn encapsulating the Al and MgZn2 dendrites to form a compact zinc-rich phase structure.

[0011] A method for manufacturing an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip includes the following steps: S1. Clean the cold-rolled or hot-rolled acid-coated substrate; S2. The cleaned substrate is continuously annealed and hot-dip galvanized. The temperature of the strip entering the zinc pot during hot-dip galvanizing is controlled at 520±5℃. S3. Use an air knife to control the hot-dip galvanized strip to adjust the coating thickness; S4. The strip steel after the air knife is sequentially cooled by air jet cooling, air cooling, and water quenching tank cooling, wherein: After jet cooling, the strip temperature is controlled at 450±10℃, and the cooling rate is 18-22℃ / s. Then it is cooled to 390±10℃ by fixed air cooling at No. 1, with a cooling rate of 25-30℃ / s; Then, it is cooled to 355±5℃ by fixed air cooling in unit #2; The inlet temperature of the air-cooled tower top steering roller is ≤290℃; When the strip steel finally enters the water quenching tank, the inlet temperature is controlled at ≤100℃; S5. Perform finishing and tension leveling on the cooled strip.

[0012] In some embodiments, in S3, the air knife control dynamically adjusts the air knife height, pressure, and angle according to the target coating weight: When the weight of the zinc layer produced is less than 120g / ㎡, the air knife height should be 250±30mm from the zinc liquid surface, and the pressure should be 15-20KPa. The front air knife angle is controlled within -0.5 to -1.0°, and the rear air knife angle is controlled within -0.5 to -2.0°, with the difference between the two controlled within 1.0°; When the weight of the zinc layer produced is 120-180g / ㎡, the height of the air knife is 200±50mm from the zinc liquid surface, and the pressure is 12-18KPa. The front air knife angle is controlled within ±0.2-1.5°, and the rear air knife angle is controlled within ±0.5-2.0°, with the difference between the two controlled within 2.0°; When the weight of the zinc layer produced is 180-450g / ㎡, the air knife height is 200±50mm from the zinc liquid surface, and the pressure is 4-10KPa. The front air knife angle is controlled within ±0.2-1.5°, and the rear air knife angle is controlled within ±0.5-2.0°, with the difference between the two controlled within 2.0°.

[0013] In some embodiments, in S4, the temperature of the strip entering the water quenching tank is controlled at ≤100°C to prevent aluminum from reacting with water vapor at temperatures above 100°C to form [Al(OH)4]. - .

[0014] In some embodiments, in S4, the water temperature in the water quenching tank is ≤40℃, and the water quality is desalinated water (conductivity <30μs / cm).

[0015] In some embodiments, in S1, the cleaning adopts a combined cleaning mode of alkaline rinsing, alkaline brushing, electrolytic cleaning and hot water rinsing.

[0016] In some embodiments, a hot tension chamber and a furnace nose are provided between the continuous annealing and hot-dip plating in S2, wherein the temperature of the hot tension chamber is controlled at 520-540°C.

[0017] In some embodiments, an oxygen-free sealing cover is used during the cooling process of S4. The temperature of the oxygen-free sealing cover is controlled at 450°C, and the pressure is 0.04-0.06 MPa. The number of opening sections of the oxygen-free sealing cover is automatically controlled according to the production line speed. When the production line speed is ≤50m / min, the first section will automatically open, and the second, third, and fourth sections will automatically close. When the production line speed is 50-80m / min, the first and second sections open automatically, and the third and fourth sections close automatically. When the production line speed is 80-120m / min, the first, second and third sections open automatically, and the fourth section closes automatically. When the production line speed is ≥120m / min, all four sections will open automatically.

[0018] Application of an ultra-corrosion resistant zinc-aluminum-magnesium steel strip in photovoltaic brackets, marine facilities, highway guardrails, automobile chassis parts, agricultural and livestock facilities, building materials, or conveying and protective equipment.

[0019] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention controls the formation of a coating with Fe2Al5 as the crystal nucleus, Al dendrites and MgZn2 secondary dendrites growing interlaced and connected by Mg2Si, which is ultimately encapsulated by the Zn phase. This ensures the uniform distribution of magnesium in the coating and provides a material basis for the "dual protection + self-repair" mechanism.

[0020] Second, the salt spray resistance of the coating is 15-20 times that of traditional hot-dip galvanizing, and the service life is as long as 30-50 years. The coating also exhibits excellent resistance to various corrosive media. Its ammonia resistance and alkali resistance are about 2-3 times that of conventional zinc-aluminum-magnesium coatings and are superior to 300 series stainless steel. It is particularly suitable for extreme environments such as livestock and poultry houses, chemical plants, and marine environments.

[0021] Third, this invention benefits from the uniformly distributed magnesium element and unique ternary eutectic structure in the coating. When the coating is damaged by cuts, scratches, etc., it can quickly achieve "self-healing" through the migration and deposition of corrosion products (such as dense zinc hydroxide, basic zinc carbonate, magnesium hydroxide, etc.), effectively preventing the spread of red rust. The protection performance is rated as "super strong".

[0022] Fourth, by adding rare earth elements such as Si, Ti and Ce, and using an optimized cooling process, this invention effectively suppresses the brittleness of the coating and the formation of zinc ash and zinc slag, refines the grains, and makes the coating have high density, good hardness and ductility. It is not easy to crack or powder during processing, and the surface quality is stable without black spots or other appearance defects.

[0023] The above overview is for illustrative purposes only and is not intended to be limiting in any way. Detailed Implementation

[0024] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention.

[0025] It is important to note that terms such as "first," "second," "symmetric," "array," "set in," and "set with" are used only to distinguish between descriptive and positional descriptions and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified with terms such as "first" or "symmetric" may explicitly or implicitly include one or more of that feature; similarly, when the quantity of certain features is not limited by words such as "two" or "three," it should be noted that such features also explicitly or implicitly include one or more features.

[0026] In this invention, unless otherwise explicitly specified and limited, terms such as “installation,” “connection,” and “fixation” should be interpreted broadly; for example, they can be fixed connections, detachable connections, or integral moldings; they can be mechanical connections, direct connections, welding, or indirect connections through an intermediate medium; they can be internal connections between two components or the interaction between two components.

[0027] Example 1 This invention provides an ultra-high corrosion resistant zinc-aluminum-magnesium steel strip, comprising a cold-rolled or hot-rolled acid-coated substrate and a coating plated on the substrate. The coating has zinc (Zn) as the balance and contains the following chemical composition by mass percentage: Aluminum (Al) is 17-23%, magnesium (Mg) is 5-9%, silicon (Si) is 0.23±0.05%, titanium (Ti) is 0.04±0.02%, cerium (Ce) is 0.3±0.2%, calcium (Ca) is 0.14±0.2%, and tin (Sn) is 0.17±0.2%.

[0028] In this embodiment, specifically, the microstructure of the coating includes Fe2Al5 as the crystal nucleus, Al growing from the Fe2Al5 crystal nucleus to form Al dendrites, MgZn2 growing from the Al dendrites as branches to form secondary dendrites, Mg2Si uniformly distributed between the dendrites, and Mg2Si connecting adjacent secondary dendrites together, and Zn encapsulating the Al and MgZn2 dendrites to form a compact zinc-rich phase structure.

[0029] In this embodiment, specifically, Fe2Al5 crystal nuclei (the foundation of the core framework): During the hot-dip galvanizing process, aluminum (Al) in the coating reacts with iron (Fe) in the steel substrate at the interface to form a layer of Fe2Al5 intermetallic compound. This compound layer serves as a heterogeneous nucleation site, becoming the "crystal nucleus" for the subsequent growth of the coating structure.

[0030] It not only enhances the bonding force between the coating and the substrate, but also provides a structural basis for the directional growth of crystals inside the coating, making the coating structure more orderly and stable.

[0031] Al dendrites (primary dendritic framework): Based on Fe2Al5 crystal nuclei, aluminum elements grow outward to form a primary dendritic structure.

[0032] Al dendrites form the skeletal network of the coating, providing support for the growth of subsequent phases. The presence of aluminum helps to form a dense physical barrier, preventing the intrusion of corrosive media.

[0033] MgZn2 secondary dendrites (filler and active source): Magnesium-zinc compound (MgZn2) grows attached to the branches of Al dendrites, forming secondary dendrites, and fills the gaps between Al dendrites, refining the grains, filling the gaps between Al dendrites, and greatly improving the density of the coating.

[0034] This unique growth process allows magnesium to be distributed highly uniformly within the coating in the form of MgZn2. This uniform magnesium distribution forms the basis for the subsequent "self-healing" reaction and the formation of dense corrosion products.

[0035] Mg2Si (connecting phase): The Mg2Si phase formed by the reaction of silicon and magnesium is uniformly distributed between the dendrites.

[0036] Mg2Si acts as a "bridge" or "weld point," networking the dispersed MgZn2 secondary dendrites. This connection structure further enhances the overall strength and toughness of the coating, prevents brittle spalling, and promotes the synergistic effect of the alloying elements.

[0037] Zn Encapsulation and Zinc-Rich Phase Structure (Ultimate Physical Barrier): The complex three-dimensional network composed of Fe2Al5, Al dendrites, MgZn2 secondary dendrites, and Mg2Si is ultimately completely encapsulated by the zinc matrix.

[0038] A dense zinc-rich phase structure is formed, with zinc serving as the main sacrificial anode material. Its continuous encapsulation ensures the continuity of electrochemical protection. At the same time, the dense structure greatly reduces porosity, forming a solid physical defense.

[0039] By employing a mechanism of "nucleus-guided growth, dendritic interleaving and filling, network reinforcement by connecting phases, and matrix encapsulation and densification," the problems of loose structure and uneven distribution of active elements in traditional coatings are solved. This unique structure enables the coating to possess both extremely high density to block corrosive media and a uniform distribution of active elements (Mg, Al, Zn) to provide long-lasting cathodic protection and self-healing capabilities, thereby achieving the core objective of this invention—ultra-high corrosion resistance.

[0040] In this embodiment, specifically, a method for manufacturing an ultra-high corrosion-resistant zinc-aluminum-magnesium steel strip includes the following steps: S1. Select a 2.0mm thick cold-rolled steel plate as the substrate and use a combination of alkaline rinsing + alkaline brushing + electrolytic cleaning + hot water rinsing to thoroughly remove oil and iron oxide scale from the substrate surface. S2. After cleaning, the substrate enters a continuous annealing furnace. The temperature of the hot tension chamber is controlled at 540℃, the temperature of the furnace nose is 500℃, and the temperature of the strip entering the zinc pot is controlled at 527℃. The composition of the zinc pot is: Al 19.0%, Mg 6.0%, Si 0.23%, Ti 0.04%, Ce 0.30%, Ca 0.14%, and Sn 0.17%, with the balance being Zn and unavoidable impurities. The temperature of the zinc pot is precisely controlled at 520±5℃. S3. The target coating weight is 275g / m². Adjust the air knife parameters: air knife height is 210mm from the zinc liquid surface, pressure is 10KPa; front air knife angle is +1.0°, rear air knife angle is -1.0°, and the difference between the two is 2.0°. S4. After being cooled by mobile air, the strip steel reaches a temperature of 450℃, with a cooling rate of approximately 20℃ / s. It was then cooled to 390℃ by fixed air cooling at No. 1, with a cooling rate of approximately 28℃ / s; Then, it is cooled to 355℃ by fixed air cooling in unit #2; Then air-cooled until the inlet temperature of the top guide roller reaches 290℃; Finally, the strip steel is cooled in a water quenching tank at a temperature of 95°C (the water temperature is controlled at 35°C and the water quality is demineralized water). During the cooling process, the production line speed is 70m / min, and the first and second sections of the oxygen-free sealing cover (450℃, 0.05MPa) open automatically; S5. After cooling, the strip is finished and tensioned to obtain the final product.

[0041] Example 2 Similar to Example 1, the difference is that the target coating weight is 350g / m², and the air knife parameters are adjusted accordingly: height 200mm, pressure 6KPa; front air knife angle -0.8°, rear air knife angle +1.2°, difference 2.0°, production line speed 70m / min, and the first and second sections of the oxygen-free sealing cover open automatically.

[0042] In this embodiment, the specific performance testing and comparison steps are as follows: The performance of the zinc-aluminum-magnesium coated steel strips prepared in Examples 1 and 2 was tested and compared with that of conventional hot-dip galvanizing (GI) and common zinc-aluminum-magnesium coatings (Mg content 3%-Al content 11%). The results are shown in the table below: As can be seen from the table above, the performance indicators of the products in the embodiments of the present invention are significantly better than those of the prior art, especially the planar corrosion resistance and cut protection performance, which have achieved a qualitative leap.

[0043] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high corrosion-resistant zinc-aluminum-magnesium steel strip, comprising a cold-rolled or hot-rolled acid-coated substrate and a coating applied to the substrate, characterized in that: The coating is zinc (Zn) as the balance and contains the following chemical components by mass percentage: Aluminum (Al) is 17-23%, magnesium (Mg) is 5-9%, silicon (Si) is 0.23±0.05%, titanium (Ti) is 0.04±0.02%, cerium (Ce) is 0.30±0.2%, calcium (Ca) is 0.14±0.2%, and tin (Sn) is 0.17±0.2%.

2. The ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 1, characterized in that: The microstructure of the coating includes Fe2Al5 as the crystal nucleus, Al growing from the Fe2Al5 crystal nucleus to form Al dendrites, MgZn2 growing from the Al dendrites as branches to form secondary dendrites, Mg2Si uniformly distributed between the dendrites, and Mg2Si connecting adjacent secondary dendrites together, and Zn encapsulating the Al and MgZn2 dendrites to form a compact zinc-rich phase structure.

3. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 1, characterized in that, Includes the following steps: S1. Clean the cold-rolled or hot-rolled acid-coated substrate; S2. The cleaned substrate is continuously annealed and hot-dip galvanized. The temperature of the strip entering the zinc pot during hot-dip galvanizing is controlled at 520±5℃. S3. Use an air knife to control the hot-dip galvanized strip to adjust the coating thickness; S4. The strip steel after the air knife is sequentially cooled by air jet cooling, air cooling, and water quenching tank cooling, wherein: After jet cooling, the strip temperature is controlled at 450±10℃, and the cooling rate is 18-22℃ / s. Then it is cooled to 390±10℃ by fixed air cooling at No. 1, with a cooling rate of 25-30℃ / s; Then, it is cooled to 355±5℃ by fixed air cooling in unit #2; The inlet temperature of the air-cooled tower top steering roller is ≤290℃; When the strip steel finally enters the water quenching tank, the inlet temperature is controlled at ≤100℃; S5. Perform finishing and tension leveling on the cooled strip.

4. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: In S3, the air knife control dynamically adjusts the air knife height, pressure, and angle according to the target coating weight: When the weight of the zinc layer produced is less than 120g / ㎡, the air knife height should be 250±30mm from the zinc liquid surface, and the pressure should be 15-20KPa. The front air knife angle is controlled within -0.5 to -1.0°, and the rear air knife angle is controlled within -0.5 to -2.0°, with the difference between the two controlled within 1.0°; When the weight of the zinc layer produced is 120-180g / ㎡, the height of the air knife is 200±50mm from the zinc liquid surface, and the pressure is 12-18KPa. The front air knife angle is controlled within ±0.2-1.5°, and the rear air knife angle is controlled within ±0.5-2.0°, with the difference between the two controlled within 2.0°; When the weight of the zinc layer produced is 180-450g / ㎡, the air knife height is 200±50mm from the zinc liquid surface, and the pressure is 4-10KPa. The front air knife angle is controlled within ±0.2-1.5°, and the rear air knife angle is controlled within ±0.5-2.0°, with the difference between the two controlled within 2.0°.

5. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: In S4, the temperature of the strip entering the water quenching tank is controlled at ≤100℃ to prevent aluminum from reacting with water vapor at temperatures above 100℃ to form [Al(OH)4]. - .

6. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: In S4, the water temperature in the water quenching tank is ≤40℃, and the water quality is desalinated water (conductivity <30μs / cm).

7. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: In S1, the cleaning process employs a combination of alkaline rinsing, alkaline brushing, electrolytic cleaning, and hot water rinsing.

8. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: Between the continuous annealing and hot-dip plating of S2, a hot tension chamber and a furnace nose are also provided, wherein the temperature of the hot tension chamber is controlled at 520-540℃.

9. The method for manufacturing ultra-high corrosion resistant zinc-aluminum-magnesium steel strip according to claim 3, characterized in that: An oxygen-free sealing cover is used during the cooling process of S4. The temperature of the oxygen-free sealing cover is controlled at 450℃, and the pressure is 0.04-0.06MPa. The number of opening sections of the oxygen-free sealing cover is automatically controlled according to the production line speed. When the production line speed is ≤50m / min, the first section will automatically open, and the second, third, and fourth sections will automatically close. When the production line speed is 50-80m / min, the first and second sections open automatically, and the third and fourth sections close automatically. When the production line speed is 80-120m / min, the first, second and third sections open automatically, and the fourth section closes automatically. When the production line speed is ≥120m / min, all four sections will open automatically.

10. The application of the ultra-high corrosion resistant zinc-aluminum-magnesium steel strip as described in claim 1 in photovoltaic brackets, marine facilities, highway guardrails, automobile chassis parts, agricultural and livestock facilities, building materials, or conveying and protective facilities and equipment.

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