A super-thick coated aluminum-zinc-magnesium steel sheet and its preparation method

Abstract

The present invention discloses a super-thick coated aluminum-zinc-magnesium steel sheet and a preparation method thereof. By optimizing the chemical compositions of the substrate and the aluminum-zinc-magnesium coating, the quality of the cold-rolled substrate, and the strip steel process, the purpose of stably controlling the thickness of the zinc layer, stably controlling the surface quality of the zinc layer, and stably controlling the thickness of the alloy layer is achieved without increasing equipment investment. Indirectly, the toughness and adhesion of the zinc layer are improved, the stable, high-quality and high-efficiency production of the super-thick coated aluminum-zinc-magnesium product is realized, the occurrence of defects such as zinc layer peeling, zinc layer cracks and adhesion is reduced, the corrosion resistance of the product is ensured, and the problem that the existing preparation method of the super-thick coated aluminum-zinc-magnesium steel sheet cannot stably control the thickness and surface quality of the zinc layer, resulting in easy zinc layer peeling and affecting its corrosion resistance, is effectively solved.

Description

Technical Field

[0001] The present disclosure relates to the field of cold rolling, and specifically to a production method of aluminized zinc - magnesium steel sheets. Background Art

[0002] Aluminized zinc - magnesium alloy coated products are high - corrosion - resistant coated products. They combine the excellent corrosion resistance of aluminum and the cathodic corrosion protection of zinc. At the same time, by adding a certain amount of Mg element, the problem of poor notch protection of aluminized zinc products is effectively solved. Therefore, aluminized zinc - magnesium steel sheets have excellent atmospheric corrosion resistance, and their corrosion resistance is 8 - 10 times that of hot - dip galvanized steel sheets with the same coating thickness. In addition, aluminized zinc - magnesium coatings also exhibit good painting properties, processing formability, and excellent heat - reflection performance. Due to their good comprehensive properties, the development of aluminized zinc - magnesium products is very rapid and they are widely used in industries such as construction, automobiles, agriculture, and household appliances.

[0003] However, compared with conventional - specification aluminized zinc - magnesium alloy coated products, ultra - thick - coated aluminized zinc - magnesium products are prone to problems such as zinc layer peeling and zinc layer cracking during use, seriously affecting the surface quality and corrosion resistance of the products. At the same time, due to the lower viscosity of aluminized zinc - magnesium zinc solution, the zinc solution has better fluidity compared with hot - dip pure zinc zinc solution, and it is very difficult to control the zinc weight to reach the target value during the production of ultra - thick - coated products. Summary of the Invention

[0004] In view of this, the present disclosure provides a preparation method of ultra - thick - coated aluminized zinc - magnesium steel sheets, which solves the problems that the existing preparation methods of ultra - thick - coated aluminized zinc - magnesium steel sheets cannot stably control the zinc layer thickness and surface quality, resulting in easy zinc layer peeling and affecting its corrosion resistance.

[0005] In addition, the present disclosure also provides an ultra - thick - coated aluminized zinc - magnesium steel sheet prepared by the above method.

[0006] In the first aspect, the preparation method of the ultra - thick - coated aluminized zinc - magnesium steel sheet includes the chemical composition design of the substrate and the aluminized zinc - magnesium coating, the quality control of the cold - rolled substrate, and the strip steel process control. Among them, the method for controlling the quality of the cold - rolled substrate includes:

[0007] Controlling the surface quality of the cold - rolled substrate, controlling the I - value of the cold - rolled substrate, and controlling the wave height of the cold - rolled substrate;

[0008] The control of the surface quality of the cold - rolled substrate includes visually inspecting the surface of the cold - rolled substrate to ensure that there are no visually visible defects, and the surface roughness Ra≥2.0um.

[0009] In the present disclosure and possible embodiments, the control of the I value of the cold-rolled substrate includes: when the steel grade is S0 to S4 and the substrate thickness is ≤ 1.0 mm, the average value of the I value is controlled to be 2.5; when the steel grade is S7 to S8 and the tensile strength is above 780 MPa, the average value of the I value is controlled to be 15.0; when the steel grade is S5 to S6 and others, the average value of the I value is controlled to be 5.0.

[0010] In the present disclosure and possible embodiments, the control of the wave height of the cold-rolled substrate includes:

[0011] When the nominal width is ≤ 1100 mm, if the nominal thickness < 0.70 mm, the wave height is controlled to be ≤ 5 mm / m; when the nominal thickness is 0.70 - 1.20 mm, the wave height is controlled to be ≤ 4 mm / m; when the nominal thickness ≥ 1.20 mm, the wave height is controlled to be ≤ 3 mm / m;

[0012] When the nominal width is 1100 - 1250 mm, if the nominal thickness < 0.70 mm, the wave height is controlled to be ≤ 6 mm / m; when the nominal thickness is 0.70 - 1.20 mm, the wave height is controlled to be ≤ 5 mm / m; when the nominal thickness ≥ 1.20 mm, the wave height is controlled to be ≤ 4 mm / m;

[0013] When the nominal width is 1250 - 1550 mm, if the nominal thickness < 0.70 mm, the wave height is controlled to be ≤ 8 mm / m; when the nominal thickness is 0.70 - 1.20 mm, the wave height is controlled to be ≤ 7 mm / m; when the nominal thickness ≥ 1.20 mm, the wave height is controlled to be ≤ 5 mm / m.

[0014] In the present disclosure and possible embodiments, the strip process control includes:

[0015] Determine the zinc pot inlet temperature, zinc liquid temperature and unit speed according to the strip thickness and zinc coating thickness;

[0016] When the strip thickness ≤ 0.6 mm and the double-sided zinc coating thickness is 150 - 300 g / m2, the zinc pot inlet temperature is 580 - 590 °C, the zinc liquid temperature is 590 - 595 °C, and the unit speed is 140 m / min;

[0017] When the strip thickness is 0.61 - 1.00 mm and the double-sided zinc coating thickness is 150 - 300 g / m2, the zinc pot inlet temperature is 575 - 580 °C, the zinc liquid temperature is 585 - 590 °C, and the unit speed is 130 m / min;

[0018] When the strip thickness is 1.01 - 1.40 mm and the double-sided zinc coating thickness is 150 - 300 g / m2, the zinc pot inlet temperature is 570 - 575 °C, the zinc liquid temperature is 580 - 585 °C, and the unit speed is 100 m / min;

[0019] When the strip thickness is 1.41-1.80 mm and the double-sided thickness of the zinc layer is 150-300 g / m2, the zinc pot temperature is 565-570°C, the zinc liquid temperature is 575-580°C, and the unit speed is 80 m / min;

[0020] When the strip thickness is 1.81-2.00 mm and the double-sided thickness of the zinc layer is 150-300 g / m2, the zinc pot temperature is 555-565°C, the zinc liquid temperature is 570-585°C, and the unit speed is 70 m / min;

[0021] When the thickness of the steel strip is 2.01-2.30 mm and the double-sided thickness of the zinc layer is 150-300 g / m2, the temperature of the zinc pot is 550-560°C, the temperature of the zinc liquid is 565-570°C, and the unit speed is 60 m / min.

[0022] In the present disclosure and possible embodiments, the chemical composition of the substrate is calculated by mass percentage as follows:

[0023] C: 0.001% ~ 0.80%, Si: 0.001% ~ 2.2%, Mn: 0.06% ~ 10.50%, P ≤ 0.04%, S ≤ 0.04%, Al: 0.02% ~ 3.00%, Ti ≤ 0.20%, B ≤ 0.005%, Cr: 0.03% ~ 0.70%; Mo: 0.01% ~ 1.60%, Cu ≤ 0.70%, Ni: 0.15% ~ 1.2%, Nb ≤ 0.08%; the rest is Fe and unavoidable impurities.

[0024] The chemical composition of the aluminum-zinc-magnesium coating is as follows by mass percentage: Al: 55%-65%, Si: 1.2%-15%, Mg: 1.0%-2.0%, Ti: 0.03%-0.50%, Re: 0.01%-0.20%, Li: 0.05%-3%, Cu: 0.1%-5.0%, Fe: 0.03%-1.0%, Mn: 0.5%-3.0%, Ni: 0.5%-4.0%, V: 0.01%-0.5%, Zr: 0.5%-1.0%, Cr: 0.1%-1.0%; the rest is Zn and unavoidable impurities.

[0025] In the second aspect, the ultra-thick coated aluminum-zinc-magnesium steel plate is prepared by the method described in the first aspect.

[0026] The present invention has the following beneficial effects:

[0027] The preparation method of the ultra-thick coated aluminum-zinc-magnesium steel sheet of the present invention optimizes the chemical compositions of the substrate and the aluminum-zinc-magnesium coating, the quality of the cold-rolled substrate and the strip steel process. First, to effectively avoid the influence of the surface defects of the cold-rolled substrate on the surface morphology of the coating or the adhesion between the coating and the substrate, it is controlled that there are no visually visible defects on the cold-rolled substrate. At the same time, to reduce the production difficulty during the coating process of the thick coating, the surface roughness Ra of the cold-rolled substrate is controlled to be ≥2.0 um. Then, because the shape fluctuation after rolling has a great influence on the coating thickness control of the ultra-thick coated aluminum-zinc-magnesium steel sheet, and the viscosity of the aluminum-zinc-magnesium coating itself is relatively low, and its thickness fluctuation has an obvious influence on the shape of the substrate, so the corresponding average value of I is specified for each steel grade in the method of the present invention. In addition, on the one hand, the wave shape after rolling is prone to collide with the rack during the subsequent annealing process to generate scratch defects, which affects the surface quality of the thick-coated aluminum-zinc-magnesium product and the zinc layer thickness control. On the other hand, the wave shape brings different forces on the liquid coating at different positions, which affects the overall coating uniformity and thickness control. Therefore, the method of the present invention stipulates the corresponding wave height standard for the cold-rolled substrate shape of thick-coated aluminum-zinc-magnesium products of different specifications. Moreover, on the one hand, the wave shape after rolling is prone to collide with the rack during the subsequent annealing process to generate scratch defects, which affects the surface quality of the thick-coated aluminum-zinc-magnesium product and the zinc layer thickness control. On the other hand, the wave shape brings different forces on the liquid coating at different positions, which affects the overall coating uniformity and thickness control. The method of the present invention sets the wave height standard for the cold-rolled substrate shape of thick-coated aluminum-zinc-magnesium products of different specifications. By adopting the above optimization measures, the method of the present invention achieves the purpose of stably controlling the zinc layer thickness, stably controlling the surface quality of the zinc layer and stably controlling the alloy layer thickness without increasing equipment investment, and indirectly improves the toughness and adhesion of the zinc layer, realizes the stable, high-quality and high-efficiency production of ultra-thick coated aluminum-zinc-magnesium products, ensures the stable operation of the unit and the product quality meets the requirements, and effectively solves the problem that the existing preparation method of ultra-thick coated aluminum-zinc-magnesium steel sheet cannot stably control the zinc layer thickness and surface quality, resulting in easy zinc layer peeling and affecting its corrosion resistance. Detailed implementation manners

[0028] The following describes the present disclosure based on embodiments. However, it is worth noting that the present disclosure is not limited to these embodiments. In the following detailed description of the present disclosure, some specific details are described in detail. However, for the parts not described in detail, those skilled in the art can also fully understand the present disclosure.

[0029] At the same time, unless the context clearly requires otherwise, the words such as "including" and "comprising" in the whole specification and claims should be interpreted as the meaning of including rather than exclusive or exhaustive meaning; that is, the meaning of "including but not limited to".

[0030] The present disclosure elaborates on the method of the present invention through examples to help further understand the technical solution of the present invention and the inventive effect of the present application. The methods adopted in each example are as follows:

[0031] I. Chemical composition design of the substrate and the aluminum-zinc-magnesium coating:

[0032] 1. The chemical composition of the substrate is by mass percentage: C: 0.001% - 0.80%, Si: 0.001% - 2.2%, Mn: 0.06% - 10.50%, P ≤ 0.04%, S ≤ 0.04%, Al: 0.02% - 3.00%, Ti ≤ 0.20%, B ≤ 0.005%, Cr: 0.03% - 0.70%; Mo: 0.01% - 1.60%, Cu ≤ 0.70%, Ni: 0.15% - 1.2%, Nb ≤ 0.08%; the balance is Fe and unavoidable impurities.

[0033] 2. The chemical composition of the aluminum-zinc-magnesium coating is by mass percentage: Al: 55% - 65%, Si: 1.2% - 15%, Mg: 1.0% - 2.0%; Ti: 0.03% - 0.50%, Re: 0.01% - 0.20%, Li: 0.05% - 3%, Cu: 0.1% - 5.0%, Fe: 0.03% - 1.0%, Mn: 0.5% - 3.0%, Ni: 0.5% - 4.0%, V: 0.01% - 0.5%, Zr: 0.5% - 1.0%, Cr: 0.1% - 1.0%; the balance is Zn and unavoidable impurities.

[0034] II. Controlling the quality of the cold-rolled substrate:

[0035] 1. Control of the surface quality of the cold-rolled substrate: Surface defects of the cold-rolled substrate are important factors affecting the surface quality of the coating. To effectively avoid the influence of surface defects of the cold-rolled substrate on the surface morphology of the coating or the adhesion between the coating and the substrate, it is required that the cold-hardened substrate has no quality defects such as visible color difference, wide and narrow marks, roll marks, rust, and emulsion residue. At the same time, to reduce the production difficulty during the coating process of thick coatings, it is required that the surface roughness Ra of the cold-hardened substrate ≥ 2.0 um.

[0036] 2. Control of the I value of the cold-hardened substrate: The shape fluctuation after rolling has a great influence on the coating thickness control of thick-coated aluminum-zinc-magnesium products. Since the viscosity of the aluminum-zinc-magnesium coating itself is relatively low, the thickness fluctuation has a more obvious effect on the shape of the substrate. The specific control requirements are shown in Table 1:

[0037] Table 1 Requirements for the average value of the I value of each steel grade

[0038] Steel grade Average value of I value Materials with thickness of S0 - S4 ≤ 1.0mm 2.5 Grade above 780 of (S7 - S8) 15.0 Others of S5 - S6 5.0

[0039] 3. Chilled roll base plate wave height control: On the one hand, the wave shape after rolling is prone to collide with the rack during the subsequent annealing process, resulting in scratch defects, which affect the surface quality of the thick-coated aluminum-zinc-magnesium products and the control of the zinc layer thickness. On the other hand, the wave shape causes different forces on the liquid coating at different positions, affecting the overall coating uniformity and thickness control. The wave height standards for the shape inspection of the chilled roll base plate of thick-coated aluminum-zinc-magnesium products of different specifications are shown in Table 2 as follows:

[0040] Table 2 Inspection standards for the actual shape of the strip after rolling

[0041]

[0042] III. Strip process control:

[0043] On the one hand, the wave shape after rolling is prone to collide with the rack during the subsequent annealing process, resulting in scratch defects, which affect the surface quality of the thick-coated aluminum-zinc-magnesium products and the control of the zinc layer thickness. On the other hand, the wave shape causes different forces on the liquid coating at different positions, affecting the overall coating uniformity and thickness control. The wave height standards for the shape inspection of the chilled roll base plate of thick-coated aluminum-zinc-magnesium products of different specifications are shown in Table 3:

[0044] Table 3 Requirements for the strip temperature entering the zinc pot, zinc liquid temperature and process speed

[0045]

[0046] Examples

[0047] I. The chemical compositions of the base plates and aluminum-zinc-magnesium coatings in Examples 1 to 5 of the present disclosure are shown in Table 4:

[0048] Table 4 Chemical compositions and contents (wt%)

[0049] Composition C Si Mn Cr Mo W Ni Al Mg Example 1 0.21 0.27 0.81 1.07 0.21 0.10 0.09 0.028 0.0042 Example 2 0.20 0.23 0.76 1.05 0.21 0.11 0.08 0.035 0.0054 Example 3 0.21 0.26 0.77 1.07 0.23 0.13 0.08 0.036 0.0043 Example 4 0.23 0.28 0.68 0.97 0.18 0.13 0.07 0.034 0.0063 Comparative example 0.20 0.20 0.82 1.03 0.23 － － － －

[0050] II. The quality of the cold-rolled base plates, strip processes and product production effects in Examples 1 to 5 of the present disclosure are shown in Table 5:

[0051] Table 5 Quality of cold-rolled base plates, strip processes and product production effects

[0052]

[0053] Note: The strip specifications in Table 5 refer to the strip thickness and nominal width.

[0054] As can be seen from Table 5, the coating thicknesses in Examples 1 to 5 are 180 g / m 2The above belongs to an extra-thick coating. Judging from the comprehensive zinc weight qualification rate and rejection rate, the methods of Embodiments 1 to 5 have the effect of stably controlling the zinc layer thickness. The rejection rate is stably controlled below 0.5%, indicating that the methods of Embodiments 1 to 5 have the inventive effect of stably controlling the surface quality of the zinc layer. The alloy layer thickness is between 2 and 3 μm, proving that the methods of Embodiments 1 to 5 have the inventive effect of stably controlling the alloy layer thickness. Therefore, through the implementation of this patent, without increasing equipment investment, the stable, high-quality and high-efficiency production of aluminum-zinc-magnesium products with extra-thick coatings is achieved, reducing the occurrence of defects such as zinc layer peeling, zinc layer cracks and adhesion, and ensuring the corrosion resistance of the products.

[0055] The above embodiments are only for expressing the implementation modes of the present disclosure, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the scope of the patent of the present disclosure. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several deformations, equivalent substitutions, improvements, etc. can be made, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A preparation method of an ultra-thick coated Al-Zn-Mg steel plate, including the chemical composition design of a substrate and an Al-Zn-Mg coating, the quality control of a cold-rolled substrate, and the strip process control, characterized in that, The control method for the quality of the cold-rolled substrate includes: Controlling the surface quality of the cold-rolled substrate, controlling the I value of the cold-rolled substrate, and controlling the wave height of the cold-rolled substrate; The control of the surface quality of the cold-rolled substrate includes visually inspecting the surface of the cold-rolled substrate to ensure that there are no visually visible defects, and the surface roughness Ra ≥ 2.0um; The strip steel process control includes: Determining the temperature of entering the zinc pot, the temperature of the zinc liquid, and the speed of the unit according to the strip steel thickness and the zinc layer thickness; The strip thickness is ≤ 0.6 mm and the double-sided thickness of the zinc coating is 150 - 300 g / m 2 When this is the case, the temperature of entering the zinc pot is 580 - 590 °C, the temperature of the zinc liquid is 590 - 595 °C, and the speed of the unit is 140 m / min; When the strip steel thickness is 0.61 - 1.00mm and the double-sided thickness of the zinc layer is 150 - 300g / m2, the temperature of entering the zinc pot is 575 - 580°C, the temperature of the zinc liquid is 585 - 590°C, and the speed of the unit is 130m / min; The strip thickness is 1.01 - 1.40 mm and the double-sided thickness of the zinc coating is 150 - 300 g / m 2 When the temperature of the strip entering the zinc pot is 570 - 575 °C, the temperature of the zinc bath is 580 - 585 °C, and the line speed is 100 m / min; The strip thickness is 1.41 - 1.80 mm and the double-sided thickness of the zinc coating is 150 - 300 g / m 2 When the temperature of the strip entering the zinc pot is 565 - 570 °C, the temperature of the zinc bath is 575 - 580 °C, and the line speed is 80 m / min; The strip thickness is 1.81 - 2.00 mm and the double-sided thickness of the zinc coating is 150 - 300 g / m 2 When the temperature of the strip entering the zinc pot is 555 - 565 °C, the temperature of the zinc bath is 570 - 585 °C, and the line speed is 70 m / min; When the strip thickness is 2.01 - 2.30 mm and the double-sided thickness of the zinc coating is 150 - 300 g / m 2 , the temperature of entering the zinc pot is 550 - 560 °C, the temperature of the zinc bath is 565 - 570 °C, and the speed of the unit is 60 m / min.

2. The preparation method of the ultra-thick coating aluminum-zinc-magnesium steel sheet according to claim 1, characterized in that : The control of the I value of the cold-rolled substrate includes: when the steel grade is S0 - S4 and the substrate thickness ≤ 1.0mm, controlling the average value of the I value to be 2.5; when the steel grade is S7 - S8 and the tensile strength is above 780MPa, controlling the average value of the I value to be 15.0; when the steel grade is S5 - S6 and others, controlling the average value of the I value to be 5.

0.

3. The preparation method of the ultra-thick coating aluminum-zinc-magnesium steel sheet according to any one of claims 1-2, characterized in that, The chemical composition of the substrate is by mass percentage: C: 0.001% - 0.80%, Si: 0.001% - 2.2%, Mn: 0.06% - 10.50%, P ≤ 0.04%, S ≤ 0.04%, Al: 0.02% - 3.00%, Ti ≤ 0.20%, B ≤ 0.005%, Cr: 0.03% - 0.70%; Mo: 0.01% - 1.60%, Cu ≤ 0.70%, Ni: 0.15% - 1.2%, Nb ≤ 0.08%; the rest are Fe and unavoidable impurities, The chemical composition of the aluminum-zinc-magnesium coating is by mass percentage: Al: 55% - 65%, Si: 1.2% - 15%, Mg: 1.0% - 2.0%; Ti: 0.03% - 0.50%, Re: 0.01% - 0.20%, Li: 0.05% - 3%, Cu: 0.1% - 5.0%, Fe: 0.03% - 1.0%, Mn: 0.5% - 3.0%, Ni: 0.5% - 4.0%, V: 0.01% - 0.5%, Zr: 0.5% - 1.0%, Cr: 0.1% - 1.0%; the rest are Zn and unavoidable impurities.

4. An aluminum-zinc-magnesium steel plate with an ultra-thick coating, characterized in that: It is prepared by using the method according to any one of claims 1 - 3.

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