Hot-dip galvanized steel sheet of zinc-aluminum-magnesium-calcium alloy and method for producing the same

Abstract

The present invention discloses a hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet including a steel substrate and an alloy plating layer on the surface of the steel substrate. The chemical elements of the alloy plating layer contain Zn and inevitable impurities, and further contain the following chemical elements in the following mass percentage contents: Al: 12-27%, Mg: 2-8%, Ca: 0.02-5%, Si: 0.15-1.0%; provided that the mass percentage contents of Al, Mg, and Ca in the alloy plating layer further satisfy the following relationships: 4% ≤ (Mg + Ca) ≤ 10%, Al / (Mg + Ca) ≥ 2.5. Further, the present invention also discloses a manufacturing method of the above hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet including the following steps. (1) Immerse a steel substrate annealed in a non-oxidizing atmosphere into a zinc-aluminum-magnesium-calcium alloy plating solution; (2) After taking the plated strip out of the plating bath, first spray-cool the plated strip in a cooling spray tank at a cooling rate ≥ 10 °C / s until the temperature of the plated strip is less than 100 °C, and then put the plated strip into a water granulation tank for water cooling.

Description

Technical Field

[0001] Technical Field The present invention relates to steel materials and a method for manufacturing the same, and particularly to a plated steel sheet and a method for manufacturing the same.

Background Art

[0002] Background Art As is well known, the hot-dip plating process is an economical and efficient method for surface treatment of steel, which can be used for the preparation of a new plating layer with higher corrosion resistance and better economy, and has always been a hot spot in the development of steel surfaces.

[0003] In the past 20 years, zinc-aluminum-magnesium plating layers have been one of the research hot spots of high-corrosion-resistant plating layers. This type of plating layer improves the corrosion resistance of the plating layer by adding different contents of Al and Mg elements to the conventional plating layers such as GI (Zn-0.2% Al), GF (Zn-5% Al), GL (55% Al-43.5% Zn-1.5% Si), etc., thereby realizing the upgrade of the corrosion resistance of the original plating layer.

[0004] Since the 21st century, a series of zinc-aluminum-magnesium plating products with different Al contents have gradually been formed internationally and are widely used in fields such as automobiles, household appliances, and construction. Along with the current development trend of steel materials towards being green, low-carbon, and environmentally friendly, it is expected that methods for further enhancing the corrosion resistance of the plating layer of plated steel sheets will be further explored and developed.

[0005] For example, in a Chinese patent document with a publication number of CN1342211A, a publication date of March 27, 2002, and a title of "Plated Steel Material, Plated Steel Sheet, Coated Steel Sheet with Excellent Corrosion Resistance and Manufacturing Method Thereof", a plated steel material with excellent corrosion resistance and its manufacturing method were provided. In the technical solution, the plating layer contains Mg: 1 to 10% by weight, Al: 2 to 19% by weight, Si: 0.01 to 2% by weight, and Mg + Al satisfies Mg(%) + Al(%) ≤ 20%. Additionally, it may contain elements such as In, Bi, Sn, Ca, Be, Ti, etc., and the balance is Zn and inevitable impurities.

[0006] Also, for example, in a Chinese patent document with a publication number of CN1398304A, a publication date of February 19, 2003, and a title of "High-Al-Containing Molten Zn-Al-Mg Alloy Plated Steel Sheet", a high-Al-containing molten Zn-Al-Mg alloy plated steel sheet was provided. In the technical solution, the molten plating layer of the steel sheet contains, in %(mass), Al: 10 to 22%, Mg: 1 to 5%, and Ti: 0.002 to 0.1%, B: 0.001 to 0.045%, Si: 0.005 to 0.5%. The purpose of the technical solution is to determine the upper limits of the Al content and Mg content in an industrially producible Zn-based molten plating layer, and it was considered that good appearance and low corrosion loss could be achieved even when the Al content reached 22% and the Mg content reached 5%. However, in reality, there is still room for improvement in the corrosion resistance of the plating layer through the design of the plating layer composition and the optimization of the plating process.

[0007] Also, it should be noted that in industries such as civil engineering, construction, solar power generation, agriculture, and livestock, in addition to requiring corrosion resistance in the plating layer of the plated steel sheet, high hardness and good scratch resistance are also required in the plating layer of the plated steel sheet. A plated steel sheet having a plating layer with high hardness and excellent scratch resistance brings great convenience to the processing and forming of structural parts, construction, and installation.

[0008] Regarding the zinc-aluminum-magnesium plating layer, although the hardness of the zinc-aluminum-magnesium plating layer is improved compared to the pure zinc plating layer (GI), due to differences in composition design, there is a large variation in hardness for each product. However, in previous patents, little attention has been paid to the hardness of the plating layer. Moreover, in the zinc-aluminum-magnesium plating layer, due to differences in the elongation of each physical phase structure, the plated steel sheet is prone to concentrated large cracks and peeling of the plating layer during use processing, and even simple bending forming. Although the zinc-aluminum-magnesium plating layer has a certain degree of "self-healing" effect, the corrosion resistance of the plating layer deteriorates due to the presence of large cracks and peeling.

[0009] Based on this, in order to solve the drawbacks existing in the prior art, the present invention hopes to obtain a continuously hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet with excellent corrosion resistance, scratch resistance, and formability through reasonable design, so as to better meet the usage needs in the fields of architecture, civil engineering, and household appliances.

Summary of the Invention

Problems to be Solved by the Invention

[0010] Content of the Invention One object of the present invention is to provide a hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet, which has good corrosion resistance, excellent scratch resistance, and formability, brings great convenience to the processing, forming, construction, and installation of structural parts, and can better meet the usage needs in the fields of architecture, civil engineering, and household appliances.

Means for Solving the Problems

[0011] To achieve the above object, the present invention provides a hot-dip zinc-aluminum-magnesium-calcium alloy-plated steel sheet including a steel substrate and an alloy plating layer on the surface of the steel substrate. The chemical elements of the alloy plating layer contain Zn and inevitable impurities, and further contain the following chemical elements in the following mass percentage contents: Al: 12 - 27%, Mg: 2 - 8%, Ca: 0.02 - 5%, Si: 0.15 - 1.0%; However, the mass percentage contents of Al, Mg, and Ca in the alloy plating layer further satisfy the following relationships: 4% ≤ (Mg + Ca) ≤ 10%, Al / (Mg + Ca) ≥ 2.5.

[0012] Furthermore, in the hot-dip zinc-aluminum-magnesium-calcium alloy-plated steel sheet according to the present invention, the mass percentage content ratios of the respective chemical elements of the alloy plating layer are: Al: 12 - 27%, Mg: 2 - 8%, Ca: 0.02 - 5%, Si: 0.15 - 1.0%, and the balance is Zn and inevitable impurities; However, the mass percentage contents of Al, Mg, and Ca in the alloy plating layer further satisfy the following relationships: 4% ≤ (Mg + Ca) ≤ 10%, Al / (Mg + Ca) ≥ 2.5.

[0013] In one or more embodiments, the mass percentage content of Al in the alloy plating layer is 12%, 12.8%, 13%, 15%, 20%, 20.1%, 21%, 25%, 26.3%, 27%, or within the range between any two of the above numerical values.

[0014] In one or more embodiments, the mass percentage content of Mg in the alloy plating layer is 2%, 2.5%, 4%, 4.3%, 4.8%, 5%, 7%, 7.5%, 7.8%, 8%, or within the range between any two of the above numerical values.

[0015] In one or more embodiments, the mass percentage content of Ca in the alloy plating layer is 0.02%, 0.05%, 0.1%, 1%, 2%, 2.3%, 2.5%, 4%, 4.5%, 5%, or within the range between any two of the above numerical values.

[0016] In one or more embodiments, the mass percentage content of Si in the alloy plating layer is 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or within the range between any two of the above values.

[0017] In one or more embodiments, the mass percentage content of Mg and Ca in the alloy plating layer satisfies the following: (Mg + Ca) is 4%, 5%, 6%, 7%, 8%, 9%, 9.3%, 9.5%, 10%, or within the range between any two of the above values.

[0018] In one or more embodiments, the mass percentage content of Al, Mg, and Ca in the alloy plating layer satisfies the following: Al / (Mg + Ca) is 2.5, 2.7, 3, 3.2, 3.4, 3.6, 3.8, 4, or within the range between any two of the above values.

[0019] In order to achieve the object of the present invention, from the perspective of the balance between corrosion resistance and workability, the inventors optimized the chemical composition of the alloy plating layer and the design of the plating process, and obtained a specific alloy plating layer structure, thereby providing a continuous hot-dip zinc-aluminum-magnesium-calcium alloy-plated steel sheet with excellent corrosion resistance, scratch resistance, and formability, which better meets the usage needs in the fields of architecture, civil engineering, and household appliances.

[0020] In the present invention, by immersing the designed steel substrate in a zinc-aluminum-magnesium-calcium alloy plating bath to form an alloy plating layer on the surface of the steel substrate, the hot-dip zinc-aluminum-magnesium-calcium alloy-plated steel sheet according to the present invention can be obtained. However, it can be understood that the chemical composition in the plating solution is the chemical composition of the alloy plating layer.

[0021] When designing the chemical composition of the zinc-aluminum-magnesium-calcium alloy plating layer, the inventors of the present invention discovered the following through research: with the increase in the Al content, there is still room for further improvement in the Mg content in the alloy plating layer; and the presence of the Ca element has a similar effect to that of the Mg element, and within an appropriate range, it can simultaneously improve the planar corrosion resistance and notch corrosion resistance of the plated steel sheet; for the plating layer containing Mg and Ca elements, its corrosion products are stable and dense, and can further slow down the progress of corrosion; and under appropriate process conditions, the size of the Ca and Mg hard intermetallic compounds is small, which can not only increase the hardness of the plating layer, but also bring excellent scratch resistance to the plating layer, and it is less likely to become the starting point of large cracks during the forming process.

[0022] In the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the design principle of each chemical element in the alloy plating layer is as follows.

[0023] Al: According to early reports, when the Al element content in the plating layer is further increased to 20%, the corrosion resistance of the plating layer will be significantly reduced. On the other hand, the increase in the Al element content in the plating layer also leads to an increase in the plating bath temperature, and the oxidation of the zinc liquid surface becomes severe. Moreover, when the Al content in the plating solution is >8.0%, brittle Fe-Al compounds grow significantly at the interface between the hot-dip plating solution and the steel substrate, and the bonding property between the plating layer and the substrate deteriorates. Therefore, in the conventional zinc-aluminum-magnesium-calcium alloy plating layer, the Al element content is usually controlled at about 10%. Therefore, in the zinc-aluminum-magnesium-calcium alloy plating layer designed by the existing prior art, the added Al content was not high in any case.

[0024] However, in the present invention, the inventors have discovered through research that: on the premise of controlling the oxidation of the plating solution surface so as to avoid the interference of the oxidized slag, controlling the content of Al element in the plating solution to be high contributes to the improvement of the corrosion resistance of the formed plating layer. Moreover, when Mg, Ca and Al added to the plating solution are controlled to meet an appropriate ratio, the oxidation of the plating solution surface can be controlled. However, it should be noted that the content of Al element in the plating solution should not be too high. Considering that if the content of Al element in the plating solution is too high, it will indeed lead to a reduction in the Zn content in the plating layer and a weakening of the sacrificial protection effect of Zn on the Fe substrate, in the present invention, the mass percentage content of Al element in the alloy plating layer is controlled to be 12-27%.

[0025] Correspondingly, by adding a predetermined amount of Si, the Fe-Al reaction is suppressed. Preferably, in order to further avoid the influence of adverse factors, the surface of the plating bath pot is protected in an inert atmosphere.

[0026] Si: In the present invention, when designing a zinc-aluminum-magnesium-calcium alloy plating solution, the Fe-Al reaction is suppressed by controllably adding a predetermined amount of Si. As explained by the above design principle of the Al element in the present invention, when the content of Al element in the plating solution is high (according to actual research, when the Al content > 8.0%), brittle Fe-Al compounds grow significantly at the interface between the plating solution and the substrate. At this time, if a small amount of Si element is added to the plating solution, the growth of the Fe-Al compounds can be effectively suppressed, which can contribute to the improvement of the bonding property between the alloy plating layer and the steel substrate.

[0027] In addition, it is necessary to explain that by adding a small amount of Si element, the blackening of the alloy plating layer can be further suppressed. However, if the content of Si element is too high, it is disadvantageous to the occurrence of Fe-Al reaction on the steel substrate and generates a large amount of scum in the zinc pot. Therefore, the content of Si element added to the zinc-aluminum-magnesium-calcium alloy plating solution should not be too high. Therefore, in the present invention, the mass percentage content of Si element in the generated alloy plating layer is controlled to be 0.15-1.0%, and the addition principle is Si≒Al×3%.

[0028] Correspondingly, in the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, when designing the zinc-aluminum-magnesium-calcium alloy plating solution, in addition to controlling the above Al and Si elements, the inventors further controllably add Ca and Mg elements to the plating solution. Moreover, the inventors control the mass percentage content of a single chemical element and at the same time further control the mass percentage content of Al, Mg, and Ca in the alloy plating layer to satisfy 4%≦(Mg+Ca)≦10% and Al / (Mg+Ca)≧2.5.

[0029] As is well known, the zinc-aluminum-magnesium plating layer has good corrosion resistance because Mg in the plating layer can uniformly form stable and dense corrosion products with a certain degree of fluidity, and the existence of the corrosion products brings a "self-healing" mechanism to the processing cut of the steel sheet.

[0030] And in the present invention, the inventors have discovered through research that by adding Ca to the plating solution, a corrosion product stabilization effect similar to that of Mg element can be achieved. In the solidification process of the plating solution, the Al phase forms dendrites earliest, and the intermetallic compounds containing Ca and Mg are introduced into the Zn phase. In a corrosive environment, the Zn phase is corroded first, and at the same time, Ca and Mg elements are released, and the corrosion products can be more effectively stabilized in the initial stage of corrosion.

[0031] In addition, through research, the inventors of the present invention further discovered the following: Granular intermetallic compounds such as MgZn2, Mg2Si, Al2Ca, Al4Ca, and Al2CaSi2 formed by Mg and Ca elements can improve the hardness of the plating layer and, consequently, the scratch resistance of the plating layer if appropriately controlled.

[0032] Therefore, while designing the further addition of Ca and Mg elements, considering that if the Mg and Ca contents are too high, it is disadvantageous to the surface quality of the plating layer, in the present invention, the mass percentage content of Ca element is controlled to be 0.02 - 5%, the mass percentage content of Si element is controlled to be 0.15 - 1.0%, and 4% ≤ (Mg + Ca) ≤ 10%.

[0033] Correspondingly, when the content of Al is 2.5 times or more that of (Mg + Ca), the surface oxidation of the plating bath pot and the plating layer can be better controlled, so Al / (Mg + Ca) ≥ 2.5 is controlled.

[0034] Furthermore, in the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the alloy plating layer may further contain one or two of Ti: 0.01 - 0.1% and B: 0 - 0.05%.

[0035] In one or more embodiments, the mass percentage content of Ti in the alloy plating layer is 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or within the range between any two of the above numerical values.

[0036] In one or more embodiments, the mass percentage content of B in the alloy plating layer is 0, 0.001%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or within the range between any two of the above numerical values.

[0037] In this hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet designed according to the present invention, when the steel substrate is immersed in a zinc-aluminum-magnesium-calcium alloy plating bath, Ti and B elements may be further added to the plating solution. When the plating solution contains Ti and B elements, the structure of the plating layer can be further refined. The two elements may exist independently or in combination in the plating solution.

[0038] However, if the contents of Ti and B are too high, Ti-Al, Al-B, and Ti-B based precipitates will be formed in the plating layer, and fine particles will be formed on the plating layer, causing appearance defects in the plated steel sheet. Therefore, it is necessary to pay attention that the contents of Ti and B elements in the plating solution should not be too high. Therefore, in the present invention, by controlling the alloy components in the plating solution, the alloy plating layer can be controlled to contain one or two of Ti: 0.01 to 0.1% and B: 0 to 0.05%.

[0039] Furthermore, in the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the microstructure of the alloy plating layer includes an Al-rich phase, an MgZn2 phase, a Zn-rich phase, an Mg2Si phase, and Mg- and Ca-element rich granular intermetallic compounds.

[0040] Furthermore, in the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the granular intermetallic compound contains at least one of MgZn2, Mg2Si, Al2Ca, Al4Ca, Al2CaSi2, and Ca3Zn.

[0041] Furthermore, in the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the hardness of the alloy plating layer is 140 to 240 Hv, for example, 160 Hv, 180 Hv, 200 Hv, or 220 Hv.

[0042] In the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the single-sided plating amount of the alloy plating layer is 120 to 300 g / m2 It may be, for example, 130 g / m 2 , 140 g / m 2 , 150 g / m 2 , 160 g / m 2 , 200 g / m 2 , 300 g / m 2 .

[0043] Correspondingly, another object of the present invention is to provide a method for manufacturing the above-mentioned hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet. According to the manufacturing method, a continuous hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet excellent in both corrosion resistance, scratch resistance, and formability can be obtained.

[0044] To achieve the above object, the method for manufacturing the above-mentioned hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet provided by the present invention includes the following steps: (1) Immerse a steel substrate annealed in a non-oxidizing atmosphere in a zinc-aluminum-magnesium-calcium alloy plating solution; (2) After taking the plated strip out of the plating bath, first spray-cool the plated strip in a cooling spray tank at a cooling rate ≥ 10 °C / s until the temperature of the plated strip is less than 100 °C, and then put the plated strip into a granulation tank for water cooling.

[0045] In one or more embodiments, in the step (2), the cooling rate is 10 °C / s, 15 °C / s, 20 °C / s, 25 °C / s, 30 °C / s, 35 °C / s, 40 °C / s, or within the range between any two of the above numerical values.

[0046] In the manufacturing method according to the present invention, first, the composition and process of the steel substrate applied to the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention are not particularly limited, but the operator can arbitrarily select the required cold-rolled or hot-rolled substrate according to the target use of the product.

[0047] Correspondingly, during actual production, an operator needs to dip a steel substrate annealed in a non-oxidizing atmosphere into a designed zinc-aluminum-magnesium-calcium alloy plating solution in a plating bath pot to obtain an alloy plating layer solidified on the surface of the steel substrate. However, to ensure the quality of the plating layer, when dipping the steel plate into the plating solution, the relationship between the steel plate temperature (T Fe ) and the plating solution temperature (T Zn ) may be further optimized and controlled to satisfy (T Zn - 5°C) ≤ T Fe ≤ (T Zn + 20°C).

[0048] It should be noted that to ensure the quality of plating, it is preferable to cover the surface of the plating bath pot with a sealed cover and protect the surface of the plating bath pot with an inert atmosphere. The internal atmosphere of the sealed cover may be controlled to an inert gas and O2 with a volume content ≤ 3%.

[0049] After taking the plated strip out of the plating bath pot, it is necessary to quickly cool the surface of the plating layer to avoid oxidation of Mg and Ca on the surface of the plating layer. In the present invention, specifically, the plated strip is spray-cooled at a cooling rate ≥ 10°C / s with a slightly stepped cooling spray tank until the temperature of the plated strip is less than 100°C. Moreover, a fast cooling rate also contributes to the formation of a uniform plating layer structure, and the cracks formed by deformation are more uniform and finer compared to slow-cooled sample plates. The cooling spray tank may be installed from a position 2 - 4 m away from the liquid level of the alloy plating solution to the position of the top roll, and during this period, it may be divided into three to eight steps as needed, for example, three steps, four steps, five steps, six steps, seven steps, eight steps.

[0050] Furthermore, in the manufacturing method according to the present invention, in the step (1), the temperature of the zinc-aluminum-magnesium-calcium alloy plating solution is 460 - 560°C, for example, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C.

[0051] In the above technical solution of the present invention, the plating solution temperature of the plating bath using the zinc-aluminum-magnesium-calcium alloy plating solution can be adjusted according to different plating solution compositions. Specifically, it is controlled at 460 to 560 °C.

[0052] In the present invention, it is necessary to immerse a cold-rolled or hot-rolled substrate (i.e., a steel substrate) in the designed zinc-aluminum-magnesium-calcium alloy plating solution. Since the difference in the composition of the zinc-aluminum-magnesium-calcium plating layer leads to the difference in the actual freezing point, the principle for setting the plating solution temperature is that it is 40 to 50 °C higher than the freezing point of the plating layer. Therefore, according to the change in the plating solution composition (= plating layer composition), the plating solution temperature is set at 460 to 560 °C. If the plating solution temperature is too low, a good Fe-Al reaction layer cannot be formed, which affects the bonding strength between the plating layer and the substrate. However, if the plating solution temperature is too high, the Fe-Al reaction is too strong, the alloy plating layer is too thick, and a good bond between the plating layer and the substrate cannot be obtained.

[0053] Furthermore, in the manufacturing method according to the present invention, in the step (1), when the steel substrate is immersed in the zinc-aluminum-magnesium-calcium plating solution, the temperature T Fe of the steel substrate and the temperature T Zn of the zinc-aluminum-magnesium-calcium plating solution are controlled to satisfy the relationship of (T Zn - 5 °C) ≤ T Fe ≤ (T Zn + 20 °C).

[0054] In the manufacturing method according to the present invention, in the step (1), the immersion time of the steel substrate in the zinc-aluminum-magnesium-calcium plating solution may be 1 to 5 seconds, for example, 2 seconds, 3 seconds, or 4 seconds.

[0055] Furthermore, in the manufacturing method according to the present invention, before the strip temperature is cooled to 340 °C, all the cooling gases sprayed by the cooling spray tank are normally compressed N2 and O2 with a volume content ≤ 3%.

[0056] In the above technical solution of the present invention, before the plated strip is cooled to 340°C, a sealed tank is installed on the strip between the cooling spray tank and the plating bath pot and is also protected with an inert gas. The internal atmosphere of the sealed tank may be controlled to be an inert gas and O2 with a volume content ≤ 3%. Without protection by an inert gas, although the surface quality of the plating layer deteriorates and minor appearance defects such as "horizontal streaks" and "punctiform particles" are likely to occur, the minor defects do not affect the corrosion resistance, scratch resistance, and formability of the plating layer, and do not hinder the practical application of the high-corrosion-resistant plating layer in the construction and civil engineering fields.

[0057] Furthermore, in the manufacturing method according to the present invention, in step (2), the temperature when the plated strip reaches the top roll is controlled to ≤ 250°C, for example, 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C.

[0058] Furthermore, in the manufacturing method according to the present invention, the installation height of the first-stage cooling spray tank is 2 - 4 m away from the liquid level of the zinc-aluminum-magnesium-calcium alloy plating solution in the plating bath pot, for example, 2.5 m, 3 m, 3.5 m away.

[0059] Furthermore, in the manufacturing method according to the present invention, the surface of the plating bath pot is covered with a sealed cover, and the internal atmosphere of the sealed cover is an inert gas and O2 with a volume content ≤ 3%.

[0060] Furthermore, in the manufacturing method according to the present invention, the plated strip between the first-stage cooling spray tank and the plating bath pot is protected with a sealed tank.

[0061] The molten zinc-aluminum-magnesium-calcium alloy plated steel sheet and its manufacturing method according to the present invention have the following advantages and beneficial effects compared with the prior art: In the present invention, from the perspective of the balance between corrosion resistance and workability, the inventors optimized the chemical composition of the alloy plating layer and the design of the plating process to obtain a specific alloy plating layer structure, thereby providing a continuously hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet that is excellent in both corrosion resistance, scratch resistance, and formability. This brings great convenience to the processing, forming, construction, and installation of structural parts, and better meets the usage needs in the fields of architecture, civil engineering, and household appliances.

[0062] In the present invention, the excellent performance of the manufactured hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet is manifested based on the optimized and designed alloy plating layer. The surface quality of the alloy plating layer is excellent, and the alloy plating layer and the substrate are well bonded; under the condition of the same plating amount, in the cycle accelerated corrosion test of ISO 14993-2018, the alloy plating layer of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention can reach 10 to 20 times that of the hot-dip zinc plated steel sheet GI in terms of the time corresponding to 5% red rust generation at the plane, cut, and T-bending sites; at the same time, the hardness of the alloy plating layer is also as high as 140 to 240 Hv, which is 2 to 4 times that of the hot-dip zinc plated steel sheet GI, showing good application prospects.

Brief Description of the Drawings

[0063]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0064] Specific Embodiments Hereinafter, based on specific examples and drawings, the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention and its manufacturing method will be further interpreted and described. However, such interpretation and description do not unduly limit the technical solution of the present invention.

[0065] Examples 1 to 10 and Comparative Examples 1 to 10 Regarding the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to the present invention, the inventors have not particularly limited the composition and process of the steel substrate, and those skilled in the art can arbitrarily select the required cold-rolled or hot-rolled substrate according to the target use of the product.

[0066] The hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 and the comparative steel sheets according to Comparative Examples 1 to 10 were all manufactured in the following steps: (1) A cold-rolled low-carbon Al-killed steel sheet with a substrate thickness of 0.8 mm was used as the steel substrate; the steel substrate annealed in a non-oxidizing atmosphere was put into the plating bath pot and immersed in a zinc-aluminum-magnesium-calcium alloy plating solution having different composition formulations shown in Table 1. The plating solution temperature of the zinc-aluminum-magnesium-calcium alloy plating solution was controlled at 460 to 560 °C. When the steel substrate was immersed in the zinc-aluminum-magnesium-calcium alloy plating solution, the steel substrate temperature T Fe and the zinc-aluminum-magnesium-calcium alloy plating solution temperature T Zn and the relationship between them was (T Zn - 5 °C) ≤ T Fe ≤ (T ZnIt was controlled to satisfy (+20°C), and after the steel substrate was immersed in the plating solution for 3 seconds, it was lifted; however, a sealing cover was installed to cover the surface of the plating bath pot, and the internal atmosphere of the sealing cover was controlled to an inert gas and O2 with a volume content ≤ 3%.

[0067] (2) After the plated strip steel was taken out of the plating bath pot, first, the plated strip steel was spray-cooled in a cooling spray tank at a cooling rate ≥ 10°C / s until the temperature of the plated strip steel was less than 100°C. The installation height of the first-stage cooling spray tank was controlled to be 2 - 4 m away from the liquid level of the zinc-aluminum-magnesium-calcium alloy plating solution in the plating bath pot, and the plated strip steel between the first-stage cooling spray tank and the plating bath pot was protected by a sealed tank. The temperature when the plated strip steel reached the top roll was controlled to ≤ 250°C. Then, the plated strip steel was put into a water granulation tank and water-cooled to obtain a plated strip steel with a single-sided plating amount of 140 g / m 2 was obtained; However, before the temperature of the plated strip steel was cooled to 340°C, the cooling gas was normally temperature-compressed N2, and the volume content of O2 in it was controlled to ≤ 3%. After the temperature of the plated strip steel was cooled to 340°C, the above special control was not performed, and the cooling gas sprayed in other cooling spray tanks was all normally temperature-compressed air.

[0068] In the present invention, the inventors prepared hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets having the same plating amount (i.e., the single-sided plating amount is 140 g / m 2 ) but obtained by using plating bath solutions with different composition formulations, and evaluated the influence of the composition of the plating layer on the corrosion resistance of the steel sheet.

[0069] It should be noted that in the present invention, the chemical composition of the alloy plating layer used for the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 - 10 and the related processes implemented all satisfied the requirements of the design specifications of the present invention.

[0070] However, there are some that do not meet the requirements of the present invention in the design of the chemical composition of the alloy plating layer and / or the design of the process parameters of the comparative steel plates according to Comparative Examples 1 to 10. However, Comparative Example 10 listed is the GI reference group.

[0071] The mass percentage ratios of the respective chemical elements in the zinc-aluminum-magnesium-calcium alloy plating solution used for the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel plates according to Examples 1 to 10 and the comparative steel plates according to Comparative Examples 1 to 10 are shown in Table 1.

[0072]

Table 1

[0073] In the present invention, when the steel substrate is immersed in a zinc-aluminum-magnesium-calcium alloy plating solution for plating, an alloy plating layer is formed on the surface of the steel substrate. Therefore, it can be understood that the chemical composition of the zinc-aluminum-magnesium-calcium alloy plating solution in Table 1 above corresponds to the chemical composition of the alloy plating layer formed in each example and comparative example.

[0074] The specific process parameters in the above process steps of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel plates according to Examples 1 to 10 and the comparative steel plates according to Comparative Examples 1 to 10 are shown in Table 2.

[0075]

Table 2

[0076] To verify the implementation effects of this application and prove the technical effects superior to the prior art of this application, in this application, analysis and measurement were performed on the alloy plating layers obtained from the molten zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 and the comparative steel sheets according to Comparative Examples 1 to 10, and the results of the analysis and measurement of the alloy plating layers of each example and comparative example are shown in Table 3.

[0077] The relevant analysis and measurement means were as follows: (1) By visually observing the number of defects such as "horizontal streaks", "zinc ash", and "zinc slag" on the surface of the alloy plating layer of each example and comparative example, the surface quality of the alloy plating layer was evaluated, and the evaluation criteria were as follows: Evaluation ◎: There are no obvious defects; Evaluation ○: The number of defects is ≤ 4 pieces / 100 m; Evaluation △: The number of defects is 5 - 10 pieces / 100 m; Evaluation ×: The number of defects is > 10 pieces / 100 m.

[0078] In summary, when the surface quality of the plating layer is evaluated as "◎" and "○", it is considered that the requirements for the surface quality control of the present invention can be met.

[0079] (2) Based on the obtained plated steel sheets according to Examples 1 to 10 and Comparative Examples 1 to 10, sample plates of examples and comparative examples with a size of 120 × 200 mm were taken respectively, subjected to 180° 0T bending, and adhered and peeled off with an adhesive tape to visually observe the dezincification situation and evaluate the bonding strength between the plating layer and the substrate. The evaluation criteria were as follows: Evaluation ◎: The plating layer does not peel off at all; Evaluation ○: 1 - 2 peeling points can be visually seen on the adhesive tape; Evaluation △: 3 - 10 peeling points can be visually seen on the adhesive tape; Evaluation ×: The number of peeling points > 10, or the plating layer peels off in flakes.

[0080] In summary, when evaluated as "◎" and "○" by T-bending adhesion, it is considered that the requirements for the bonding strength of the plating layer of the present invention can be met.

[0081] (3) For the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 manufactured under different compositions and process conditions and the comparative steel sheets according to Comparative Examples 1 to 10, the plated steel sheets according to each example and comparative example were sheared into sample plates with a size of 150×70 mm; In accordance with the accelerated test standard specified in ISO 14993-2018, which exposes metals and alloys to salt spray, drying, and wetting conditions and repeats them, corrosion resistance tests were conducted on the sample plates of each example and comparative example at the flat surface, cut edge, and T-bend site, and the cycle numbers corresponding to the occurrence of 5% red rust on the surface, cut edge, and T-bend site of the plating layer under different conditions were recorded. For the GI plating layer (pure zinc plating layer) with a single-sided plating amount of 140 g / m 2 of Comparative Example 10 as the reference group, the relative corrosion resistance improvement multiples of the alloy plating layers of the steel sheets according to Examples 1 to 10 and Comparative Examples 1 to 9 with respect to the GI plating layer (pure zinc plating layer) according to Comparative Example 10 were calculated.

[0082] Accordingly, the plating layer hardness of the alloy plating layers of the plated steel sheets according to each example and comparative example was further measured. According to the method specified in GB / T9790-2021 "Metallic materials - Vickers and Knoop microhardness tests for metallic and other inorganic coating layers", using a load of 100 gf, the hardness H v100g of the plating layers of each example and comparative example was measured.

[0083] The analysis and measurement results of the alloy plating layers of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 and the comparative steel sheets according to Comparative Examples 1 to 10 are shown in Table 3.

[0084]

Table 3

[0085] As can be seen from Table 3 above, in the present invention, for the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10, the alloy plating layers obtained all had very excellent surface quality, and the bonding between the plating layer and the substrate was good. The evaluation results of the surface quality of the plating layer and the evaluation results of T-bend adhesion were both "◎" and "○", meeting the requirements of the present invention.

[0086] Also, as can be seen from the control test of the corrosion resistance of Examples 1 to 10 and the GI reference group (Comparative Example 10), the alloy plating layers of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 of the present invention showed longer cycle numbers and more excellent corrosion resistance in the corrosion resistance tests at the flat surface, cut edge, and T-bend sites. The cycle number corresponding to 5% red rust generation at the flat surface site was 10.5 to 16 times that of the GI reference group, the cycle number corresponding to 5% red rust generation at the cut edge site was 13.3 to 20 times that of the GI reference group, and the cycle number corresponding to 5% red rust generation at the 0T-bend site was 12 to 20.7 times that of the GI reference group.

[0087] In addition, the alloy plating layers of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheets according to Examples 1 to 10 further had a higher plating layer hardness, and the plating layer hardness was 2.2 to 3.7 times that of the GI reference group, having very excellent scratch resistance.

[0088] In Comparative Example 1 designed according to the present invention, when the Al element content in the plating layer decreased (6.3%), the flat surface corrosion resistance of the plating layer was only 6.5 times that of the GI reference group, and the value of Al / (Mg + Ca) also decreased, resulting in poor surface quality of the plating layer. In contrast, in Example 1, although the content of (Mg + Ca) did not change compared with Comparative Example 1, when the Al element content in the plating layer increased to 12.8%, the flat surface corrosion resistance of the plating layer was as high as 10.5 times that of the GI reference group, and the corrosion resistance at the cut edge and 0T-bend sites both improved, and the surface quality was also good.

[0089] In Example 2, when the Al element content in the plating layer increases to 20.1%, the upper limit value of the (Mg + Ca) content in the plating solution correspondingly increases, which can improve the corrosion resistance of the plating layer, obtain good surface quality of the plating layer, and the hardness and scratch resistance of the plating layer also improve with the increase of intermetallic compound-forming elements such as Mg and Ca. However, in Comparative Example 9, the Al element content in the plating layer was too high. When the Al element content further increased to 38.5%, the planar corrosion resistance of the finally obtained plating layer was still good, but the notch corrosion resistance of the plating layer decreased sharply, and the number of notch rust cycles of the plating layer was only 5.3 times that of the GI reference group.

[0090] As can be seen from Comparative Example 2, although the Al content in the plating layer is 12.8%, when the total amount of (Mg + Ca) is as low as 1.55%, it also affects the corrosion resistance of the plating layer. In particular, the corrosion resistance at the notch and bending sites is, overall, inferior to that of the plating layer in Comparative Example 1. In Example 1, the total amount of (Mg + Ca) in the plating layer reached 5%, and the corrosion resistance of the plating layer was significantly improved. However, as can also be seen from Comparative Example 8, when the (Mg + Ca) content in the plating layer exceeds the range limited by the present invention, it becomes difficult to obtain perfect surface quality of the plating layer. On the premise of being protected by the atmosphere, the corrosion resistance of the plating layer was fair, but the surface defects of the plating layer had already increased; on the other hand, in Comparative Example 7, under the same manufacturing conditions and without being protected by N2, the surface quality of the plating layer decreased severely, and the corrosion resistance of the plating layer, especially the corrosion resistance at the T-bending processed site, decreased severely due to the influence of extensive cracks and peeling caused by defects. Comparing Example 5 with Example 4, it can be seen that without being protected by the atmosphere, compared with the condition of being protected by an inert atmosphere, the surface quality of the plating layer decreases, and the "horizontal streaks" on the surface of the plating layer increase, but it has no significant impact on other performances.

[0091] As can be seen from Comparative Example 3, when designing the plating layer, even without adding Mg element, adding Ca alone could also contribute well to the improvement of corrosion resistance. However, when adding Ca element alone, the improvement effect on the hardness of the plating layer was limited, and the hardness of the plating layer was only 105 Hv, which still had a significant gap from the desirable scratch resistance of the present invention. On the other hand, in Example 3, when there was no significant difference in the total amount of (Mg + Ca) in the plating layer, further adding Mg element to the plating layer could contribute more greatly to the improvement of the hardness of the plating layer.

[0092] Example 4 is obtained by further adding 0.03% of B to the basis of Example 3, but it did not significantly affect either the surface quality or the corrosion resistance of the plating layer. However, in Comparative Example 4, since the B element was added in excess, the surface defects of the plating layer also increased, affecting the corrosion resistance. The effect of the Ti element was the same. Compared with Example 7, in Comparative Example 5, since Ti was added in excess, a large number of defects occurred on the surface of the plating layer, affecting the aesthetic appearance and at the same time, the corrosion resistance also decreased to a certain extent. Therefore, both of them have a certain effect of refining the microstructure, but the addition amount should be carefully selected to fall within the range specified in the present invention.

[0093] Moreover, as can be seen from Comparative Example 6, the temperature of the zinc - aluminum - magnesium - calcium alloy plating solution in Comparative Example 6 did not meet the design requirements of the present invention. When the temperature of the zinc - aluminum - magnesium - calcium alloy plating solution was too high, the Fe - Al inhibition layer became significantly thicker. Coupled with the fact that it was not protected by the atmosphere after plating, it severely affected the surface quality of the plating layer. Although these surface defects did not significantly affect the planar corrosion resistance of the plating layer, under 0T bending, the cracking and peeling of the plating layer became severe, and the corrosion resistance of the deformed parts deteriorated severely.

[0094] Figure 1 is a surface electron micrograph of the alloy plating layer of the hot - dip zinc - aluminum - magnesium - calcium alloy plated steel sheet according to Example 1.

[0095] In the present invention, the surface state of the alloy plating layer obtained on the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Example 1 is shown in FIG. 1. In this embodiment, the Ca element added to the surface of the alloy plating layer forms white "star"-shaped Al2Ca and Al4Ca intermetallic compound particles, and the Mg element also forms black Mg2Si particles.

[0096] FIG. 2 is a cross-sectional electron micrograph of the alloy plating layer obtained by rapid cooling of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Example 3.

[0097] FIG. 3 is a cross-sectional electron micrograph of the alloy plating layer obtained by slow cooling of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Example 4.

[0098] FIG. 4 conceptually shows the 0T bending crack photograph of Example 3. FIG. 5 conceptually shows the 0T bending crack photograph of Example 4.

[0099] Comparing FIG. 2 and FIG. 3, as can be seen from the difference in the cross-sectional state of the plating layers of Example 3 and Example 4 (FIG. 2, FIG. 3), after the plated strip is taken out of the plating bath pot, the influence of the cooling rate of the rapid cooling carried out on the tissue state is more significant than the addition of the tissue refinement element. The difference in the microstructure state did not have a great influence on the corrosion resistance, but the T-bending cracks on the surface of the plating layer with a high cooling rate were relatively fine (as shown in FIGS. 4 and 5).

[0100] However, whether the slow cooling shown in Example 4 (cooling rate of 10 ° C / s) is adopted or the rapid cooling shown in Example 3 (cooling rate of 30 ° C / s) is adopted, the interior of the finally obtained alloy plating layer is composed of an Al-rich phase, an MgZn2 phase, a Zn-rich phase, and an Mg2Si phase. In its cross section, no obvious intermetallic compound particles other than Mg2Si were observed, and the Ca-containing particulate intermetallic compound tended to be unevenly distributed on the surface layer of the plating layer.

[0101] The prior art part within the scope of protection of the present invention is not limited to the embodiments described in the application documents of this application. It should be explained that all prior arts (including but not limited to prior patent documents, prior published publications, prior public uses, etc.) that do not conflict with the solution of the present invention are incorporated into the scope of protection of the present invention.

[0102] In addition, the combination of each technical feature in this application is not limited to the combination described in the claims of this application or the combination described in the specific embodiments. As long as they do not conflict with each other, all the technical features described in this application can be freely combined or joined in any form.

[0103] Furthermore, it should also be noted that the above-mentioned embodiments are only specific embodiments of the present invention. The present invention is not limited to the above embodiments, and it is obvious that any similar changes or modifications that can be directly derived from or easily conceived by those skilled in the art from the disclosure content of the present invention are included in the scope of protection of the present invention.

Claims

1. A hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet including a steel substrate and an alloy plating layer on the surface of the steel substrate, wherein the chemical elements of the alloy plating layer contain Zn and inevitable impurities, and further contain the following chemical elements in the following mass percentage contents: Al: 12 - 27%, Mg: 2 - 8%, Ca: 0.02 - 5%, Si: 0.15 - 1.0%; However, the mass percentage contents of Al, Mg, and Ca in the alloy plating layer further satisfy the following relationships: 4% ≤ (Mg + Ca) ≤ 10%, Al / (Mg + Ca) ≥ 2.5 A hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet, characterized by the above.

2. The mass percentage content ratios of the respective chemical elements of the alloy plating layer are: Al: 12 - 27%, Mg: 2 - 8%, Ca: 0.02 - 5%, Si: 0.15 - 1.0%, and the balance is Zn and inevitable impurities; However, the mass percentage contents of Al, Mg, and Ca in the alloy plating layer further satisfy the following relationships: 4% ≤ (Mg + Ca) ≤ 10%, Al / (Mg + Ca) ≥ 2.5 The hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Claim 1, characterized by the above.

3. The alloy plating layer of the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Claim 1 or 2, characterized by further containing one or two of Ti: 0.01 - 0.1% and B: 0 - 0.05%.

4. The microstructure of the alloy plating layer contains an Al-rich phase, MgZn ２ phase, a Zn-rich phase, Mg ２ Si phase, and Mg and Ca element-rich granular intermetallic compounds, and is characterized in that it is a hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to claim 1 or 2.

5. The granular intermetallic compound is MgZn ２ , Mg ２ Si, Al ２ Ca, Al ４ Ca, Al ２ CaSi ２ , Ca ３ Zn, and the hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to claim 4 is characterized by containing at least one of them.

6. The hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to Claim 1 or 2, characterized in that the hardness of the alloy plating layer is 140 - 240 Hv.

7. The one-sided plating amount of the alloy plating layer is 120 to 300 g / m ２ The hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to claim 1 or 2, characterized in that it is so.

8. A method for manufacturing a hot-dip zinc-aluminum-magnesium-calcium alloy plated steel sheet according to any one of Claims 1 to 7, characterized by including the following steps. (1) Immerse a steel substrate annealed in a non-oxidizing atmosphere in a zinc-aluminum-magnesium-calcium alloy plating solution; however, the temperature of the zinc-aluminum-magnesium-calcium alloy plating solution is 460 - 560°C; (2) After taking the plated strip out of the plating bath, first spray-cool the plated strip in a cooling spray tank at a cooling rate ≥ 10°C / s until the temperature of the plated strip is less than 100°C, and then put the plated strip into a water granulation tank for water cooling.

9. In the step (1), when the steel substrate is immersed in the zinc-aluminum-magnesium-calcium plating solution, the temperature T of the steel substrate Ｆｅ and the temperature T of the zinc-aluminum-magnesium-calcium plating solution Ｚｎ are controlled so as to satisfy the relationship: (T Ｚｎ - 5°C) ≤ T Ｆｅ ≤ (T Ｚｎ + 20°C). The manufacturing method according to claim 8, characterized in that

10. In the step (2), before the plating strip temperature is cooled to 340°C, all of the cooling gases sprayed by the cooling spray tank are N compressed at normal temperature ２ and O with a volume content ≤ 3% ２ The manufacturing method according to claim 8, characterized in that it is as described above.

11. The manufacturing method according to claim 8, wherein in step (2), the temperature when the plated strip reaches the top roll is controlled to be ≤ 250°C.

12. The manufacturing method according to claim 8, wherein the installation height of the first-stage cooling spray tank is 2 to 4 m away from the liquid level of the zinc-aluminum-magnesium-calcium alloy plating solution in the plating bath pot.

13. The surface of the plating bath pot is covered with a sealed cover, and the internal atmosphere of the sealed cover is an inert gas and O with a volume content of ≤ 3%. ２ The manufacturing method according to claim 8, characterized in that it is as described above.

14. The manufacturing method according to claim 8, wherein the plated strip between the first-stage cooling spray tank and the plating bath pot is protected by a sealed tank.

15. The manufacturing method according to claim 8, wherein before the temperature of the plated strip is cooled to 340°C, a sealed tank is installed on the strip between the cooling spray tank and the plating bath pot and is protected with an inert gas.

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