Production method for eliminating tooth-like defects on the surface of zinc-aluminum-magnesium coated steel sheets and zinc-aluminum-magnesium coated steel sheets

Abstract

This invention relates to the field of metallic materials, and discloses a production method for eliminating tooth-like defects on the surface of zinc-aluminum-magnesium coated steel sheets, as well as the zinc-aluminum-magnesium coated steel sheets themselves. The production method includes: S1, controlling the temperature of the strip steel entering the zinc pot; S2, controlling the distance between the top of the guide dam inside the furnace nose and the surface of the plating solution to 2-5 mm, and the rotation speed of the zinc slag pump to 80-120 rpm; S3, controlling the ingot feeding speed of zinc-aluminum-magnesium ingots. This invention reduces the generation and flow of zinc slag by controlling the temperature entering the zinc pot, the ingot feeding speed, the distance between the top of the guide dam and the surface of the plating solution, and the rotation speed of the zinc slag pump, thereby eliminating tooth-like defects on the surface of thick-gauge, thick-coated zinc-aluminum-magnesium coated steel sheets.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, specifically to a production method for eliminating tooth-like defects on the surface of zinc-aluminum-magnesium coated steel sheets and zinc-aluminum-magnesium coated steel sheets. Background Technology

[0002] With increasingly stringent requirements for energy conservation, environmental protection, and safety in key components such as automobiles, home appliances, and structural parts, it is essential to ensure that steel materials are not severely corroded during their service life. Adding appropriate amounts of magnesium and aluminum to pure zinc can improve the corrosion resistance of the coating, significantly extending the service life of the coated steel sheet. Furthermore, it can reduce zinc consumption by decreasing the coating weight, thus offering significant social benefits and worthy of widespread application.

[0003] In the field of photovoltaic mounting systems, double-sided 275g / m 2 Zinc-aluminum-magnesium coating products, replacing traditional double-sided 600g / m 2 The above-mentioned batch-galvanized products, despite the reduced coating thickness, do not suffer a reduction in service life, meeting the 25-year service life requirement in the photovoltaic field. Furthermore, using zinc-aluminum-magnesium coated sheets at the user end allows for direct processing into photovoltaic brackets, reducing the pickling, galvanizing, and passivation processes required for batch galvanizing of hot-rolled products at the user end, thus contributing to the green development of the customer base.

[0004] Zinc-aluminum-magnesium (ZAM) coated products, due to the addition of easily oxidized elements such as Al and Mg, generate a significant amount of zinc dross during production, making surface quality control more difficult. When the thickness of the ZAM-coated steel sheet is ≥1.5mm, the double-sided coating weight should be ≥275g / m². 2 At that time, a large number of tooth marks defects are easily generated on the surface of the steel plate. Therefore, there is an urgent need for a method to improve the surface quality of thick-gauge zinc-aluminum-magnesium coated steel plates.

[0005] CN 110438427 A, entitled "A Method for Eliminating Surface Defects in Thick Zinc-Aluminum-Magnesium Coated Steel," discloses a method for eliminating circular black spot defects on the surface of thick zinc-aluminum-magnesium coated steel. The method primarily achieves this by controlling the temperature of the zinc bath at 445-455℃ and controlling the power of the cooling tower fan during post-plating cooling. This solution targets black spot defects but does not specify the zinc bath immersion plating process, air knife parameter control, post-plating cooling temperature, or finishing process.

[0006] CN 108018514A, "A Method for Controlling Surface Defects in Zn-Al-Mg Alloy Coated Sheets and Zn-Al-Mg Alloy Coated Sheets," discloses a method for controlling surface defects in Zn-Al-Mg alloy coated sheets. The plating bath has the following composition by mass percentage: Al 0.15%-6.5%, Mg 0.2%-7%, RE≤0.2%, Sr 0.002%-0.2%, with the balance being Zn and other unavoidable impurities, and the Mg / Al ratio greater than 1.0. The temperature of the plating bath is 360-480℃. The air knife scraping medium used is limited to a gas with an oxygen content of less than 5% by volume. This method mainly achieves the production of high-quality zinc-aluminum-magnesium coated products by limiting the oxygen content of the air knife medium and the Mg / Al ratio to be greater than 1.

[0007] CN 113584346A, "A Zinc Alloy Coating with Excellent Corrosion Resistance," discloses a zinc alloy coating with excellent corrosion resistance. It includes a substrate and a coating plated on the surface of the substrate. The coating contains the following chemical composition by weight percentage: Al 0.5%–6%; Mg 0.1%–3%; Si 0.05%–0.1%; Re 0.05%–0.1%; total impurities less than 0.01%; and the balance being Zn. This method, by controlling the coating elements and their content, can significantly reduce the coating thickness, while simultaneously mitigating oxidation of the plating bath surface, reducing surface defects, and improving the corrosion resistance of hot-dip galvanized aluminum-magnesium alloy steel sheets; thus ensuring the surface quality of the steel sheet.

[0008] CN 110760774 A, "Preparation Method of Zinc-Aluminum-Magnesium Steel Plate and Effective Control of Black Spots on the Surface of Hot-Dip Galvanized Aluminum-Magnesium Steel Plate Using CSP Process," discloses a method for preparing zinc-aluminum-magnesium steel plates and effectively controlling black spots on the surface of hot-dip galvanized aluminum-magnesium steel plates using the CSP process. This method ensures good surface quality and the absence of black spot defects in the resulting zinc-aluminum-magnesium steel plate by controlling the chemical composition of the coating and the substrate, as well as the amount of each chemical component. This results in good corrosion resistance and adhesion of the zinc-aluminum-magnesium steel plate. Furthermore, the combination of the CSP process and the continuous hot-dip galvanizing process guarantees the good surface quality and absence of black spot defects in the prepared zinc-aluminum-magnesium steel plate, thereby ensuring its corrosion resistance, strength, and oxidation resistance.

[0009] CN 108642493 A, "A Method for Improving Color Difference Defects on the Surface of Zinc-Aluminum-Magnesium Alloy Coatings," discloses a method for improving color difference defects on the surface of zinc-aluminum-magnesium alloy coatings. By adding other alloying elements (any one or more of the following alloying elements: boron, silicon, copper, nickel, manganese) to the zinc-aluminum-magnesium alloy coating, the stability of the coating in the atmospheric environment is improved, overcoming the color difference defect on the coating surface and achieving the effect of improving the appearance quality of the zinc-aluminum-magnesium coating.

[0010] CN104060209A, "A Hot-Dip Galvanized Aluminum-Magnesium Steel Sheet and its Manufacturing Method," discloses a method for producing a zinc-aluminum-magnesium (ZAM) composition. The plating bath composition is Al: 1.9%-3.9%, Mg: 1.9%-3.9%, with the balance being Zn and unavoidable impurities. This method has a relatively high Mg content, resulting in more slag and poor surface quality. The main purpose of improving corrosion resistance is to extend the immersion time, leading to poor resistance to blackening.

[0011] CN 103966537 A, "A Method for Controlling Zinc Flow Marks in Thick-Film, Thick-Coated Hot-Dip Galvanized Products," discloses a method for controlling zinc flow marks in thick-film, thick-coated hot-dip galvanized products. The method involves adjusting the temperature of the blowing medium to improve its cooling capacity on the strip steel, while simultaneously optimizing the air knife process parameters. Specific parameter selections are as follows: 1) Controlling the temperature in the blower chamber within the range of 0–10℃ before production; 2) Optimizing air knife parameters: the distance between the blade lip and the liquid surface is 600–1000 mm; the distance between the blade lip and the strip steel is 15–30 mm; and the air knife pressure is set between 100–300 mbar depending on the unit speed and coating thickness.

[0012] CN 110684929 A, "An Ultra-Thick Coated Hot-Dip Galvanized Steel Strip for Corrugated Pipes in Underground Utility Tunnels and Its Production Method," discloses an ultra-thick coated hot-dip galvanized steel strip for corrugated pipes in underground utility tunnels and its production method. By reducing the air knife height, increasing the distance between the blade lip and the strip steel, and implementing segmented control of the blade lip opening, the generation of zinc flow marks and edge thickness defects is suppressed. The thickness is 1.3–2.0 mm, the width is 1000–1480 mm, the process speed is 90–130 m / min, the annealing temperature is 690–710℃, the holding time is 2–4 min, the zinc bath temperature is 457–463℃, the entry temperature is 420–450℃, the air knife height is 150–180 mm, the distance between the blade lip and the strip steel is 50–56 mm, and the air knife pressure is 100–120 mbar. In this scheme, the temperature difference between the inlet temperature and the zinc bath temperature is large, which easily causes large fluctuations in the bath temperature, high power operation of the induction heater, and a lot of zinc dross agitation in the bath; the distance between the blade lip and the strip is large, resulting in poor uniformity of the coating when blown by the air knife, which easily leads to defects such as excessively thick coating at the edges of the strip.

[0013] Currently, there are many technical solutions for zinc-aluminum-magnesium alloy coatings. Existing solutions mainly focus on the composition and surface treatment of zinc-aluminum-magnesium alloy coatings, but do not address the control of tooth-like defects on the surface of thick-gauge zinc-aluminum-magnesium products. Summary of the Invention

[0014] The purpose of this invention is to overcome the problem of difficulty in controlling the surface quality of thick-gauge, thick-coated zinc-aluminum-magnesium products in the prior art, and to provide a production method and zinc-aluminum-magnesium coated steel plate with tooth-like defects on the surface. This solution uses methods such as controlling the temperature of the zinc pot, the ingot feeding speed, the distance between the top of the guide dam and the surface of the plating solution, and the speed of the zinc slag pump to reduce the generation and flow of zinc slag, thereby eliminating tooth-like defects on the surface of thick-gauge, thick-coated zinc-aluminum-magnesium coated steel plates.

[0015] To achieve the above objectives, the present invention provides a production method for eliminating tooth-like defects on the surface of zinc-aluminum-magnesium coated steel sheets, the production method comprising:

[0016] S1. Control the temperature of the strip entering the zinc pot according to formula (1):

[0017] T2=T1-0.01v-0.005s (1)

[0018] In formula (1), T2 represents the temperature of the strip entering the zinc pot, in °C; T1 represents the temperature of the zinc pot, in °C; v represents the speed of the steel plate moving in the zinc pot, in m / min; and s represents the cross-sectional area of ​​the strip, in mm. 2 The present invention controls the temperature T2 of the strip entering the zinc pot, and relies on the heat of the strip to ensure the stability of the zinc pot temperature, thereby maintaining the stable operating power of the zinc pot induction heater and preventing the zinc dross from being stirred up due to high power operation, which would affect the quality of the strip plate.

[0019] S2. The distance between the top of the guide dam inside the furnace nose and the surface of the plating solution is controlled to be 2-5mm, and the speed of the zinc slag pump is 80-120 rpm.

[0020] S3. Control the ingot feeding rate of zinc-aluminum-magnesium ingots according to formula (2):

[0021] v1 = 100 × (2 × c) 2 ×t 2 ×w) / (v×8.47×10 8 (2)

[0022] In formula (2), v1 represents the ingot feeding rate of zinc-aluminum-magnesium ingots, in cm / min. That is, in this invention, the ingot feeding rate of zinc-aluminum-magnesium ingots refers to the descent speed of zinc-aluminum-magnesium ingots relative to the surface of the plating solution; t represents the thickness of the finished zinc-aluminum-magnesium coated steel plate, in mm; c represents the width of the finished zinc-aluminum-magnesium coated steel plate, in mm; and w represents the double-sided coating weight of the finished zinc-aluminum-magnesium coated steel plate, in g / m². 2 .

[0023] The main process flow for preparing zinc-aluminum-magnesium coated steel sheets according to the present invention includes: annealing the strip steel in an annealing furnace, cooling it to the temperature for entering the zinc pot, and sending it into the zinc pot for hot-dip galvanizing (the plating solution will be consumed during the hot-dip galvanizing process, and zinc-aluminum-magnesium ingots need to be added for replenishment. During the melting of zinc-aluminum-magnesium ingots, the zinc pot induction heater provides the temperature), and then adjusting the air knife parameters to control the weight of the double-sided coating.

[0024] In this invention, the annealing temperature of the strip steel is controlled at 550-700℃ during annealing. Controlling the annealing temperature within this range can reduce the core heat carried inside the steel plate and prevent excessive zinc dross caused by high temperature when the strip steel enters the zinc pot. This is because when there is a lot of zinc dross, some of it will adhere to the surface of the strip steel along with the plating solution during the immersion plating process. Then, when the coating weight is controlled by air knife blowing, some of the zinc dross will fall off under the action of airflow and gravity, and the location of the fall-off will form tooth mark defects. Therefore, it is necessary to prevent the occurrence of excessive zinc dross.

[0025] In step S1 of this invention, the zinc pot contains the following components by weight percentage: Al content of 1-13 wt%, Mg content of 1-6 wt%, and the remainder being Zn and unavoidable impurities such as Fe.

[0026] In a preferred embodiment, in step S1, the temperature is controlled to be 420℃≤T1≤460℃. Controlling the zinc pot temperature T1 within this range can effectively reduce the core heat carried inside the steel plate. When T1 is high, more zinc dross is produced, and when T1 is low, the fluidity of the plating solution will be poor. Therefore, it is more appropriate to control T1 within the above range.

[0027] In step S1 of this invention, the speed of the steel plate running in the zinc pot is controlled to be 65m / min≤v≤75m / min. The speed v is increased to this range. The greater the linear speed, the faster the plating solution flows, the faster the zinc dross carried by the plating solution floats to the surface, and the less likely the zinc dross will adhere to the surface of the steel strip.

[0028] In this invention, it is necessary to keep the induction heater of the zinc pot in a low-power operation state during production, with an operating power of 10-30KW, to prevent disturbance of the plating solution flow field when the induction heater is operating at high power, which would stir up the zinc dross.

[0029] In this invention, the cross-sectional area s of the strip is equal to the product of the strip width and the strip thickness.

[0030] Since the coating does not change the width of the finished zinc-aluminum-magnesium coated steel sheet, it will affect the thickness of the finished zinc-aluminum-magnesium coated steel sheet. However, the change in thickness is at the micrometer level and can be ignored. Therefore, in this invention, the width of the finished zinc-aluminum-magnesium coated steel sheet is equal to the width of the strip, and the thickness of the finished zinc-aluminum-magnesium coated steel sheet is equal to the thickness of the strip.

[0031] In the production method described in this invention, controlling the position of the guide dam inside the zinc boiler nose and the rotation speed of the zinc slag pump to maintain the overflow of the plating solution inside the guide dam can discharge the zinc slag inside the boiler nose to the outside of the boiler nose, thereby reducing contact with the strip steel. Therefore, it is more appropriate to control the distance between the top of the guide dam and the surface of the plating solution and the rotation speed of the zinc slag pump within the range described in step S2.

[0032] As the plating solution in the zinc pot is gradually consumed during the hot-dip galvanizing process, zinc, aluminum and magnesium ingots need to be added to replenish the plating solution. The composition of the zinc, aluminum and magnesium ingots used is basically the same as that of the zinc pot. That is, the added zinc, aluminum and magnesium ingots contain the following weight percentage components: Al content of 1-13wt%, Mg content of 1-6wt%, and the remainder being Zn and unavoidable impurities such as Fe.

[0033] Furthermore, the added zinc, aluminum, and magnesium ingots are rectangular in shape. When adding zinc, aluminum, and magnesium ingots to the zinc pot, it is preferable to add them to the plating solution along the length of the ingots. This can minimize the cross-sectional area when the zinc, aluminum, and magnesium ingots are in contact with the plating solution, and can minimize the disturbance to the plating solution in the zinc pot when adding zinc, aluminum, and magnesium ingots. The amount of zinc, aluminum, and magnesium ingots added is only required to ensure that the content requirements of each component in the plating solution are met.

[0034] In one specific embodiment of the present invention, the dimensions of the added zinc-magnesium-aluminum ingot are: length × width × height = 1180mm × 600mm × 200mm.

[0035] Furthermore, when adding zinc, magnesium and aluminum ingots, it is also necessary to control the ingot adding speed at the same time. The ingot adding speed is controlled according to formula (2) in step S3, so that the ingot adding method is slow addition, to prevent the amount of zinc, magnesium and aluminum ingots added at one time from being too much, causing the temperature of the zinc liquid near the zinc, magnesium and aluminum ingots to drop sharply, causing disturbance of the zinc pot flow field, stirring up zinc dross, and adhering to the surface of the strip steel.

[0036] Furthermore, in step S3 of the present invention, the parameters are controlled as follows: 1.5mm ≤ t ≤ 2.5mm, 275g / m³. 2 ≤w≤450g / m 2 .

[0037] In this invention, the gas source for the air knife is an inert gas with a purity greater than 99.9%, and the gas source for the air knife is nitrogen.

[0038] In a preferred embodiment of the present invention, the air knife lip gap is controlled to be 1-1.3 mm, the distance between the lip and the strip is 14-25 mm, the air knife height is 180-250 mm, and the air knife pressure is 110-150 mbar.

[0039] A second aspect of the present invention provides a zinc-aluminum-magnesium coated steel sheet produced by the above-described production method.

[0040] The solution of this invention is mainly for steel plates with a thickness of 1.5-2.5mm and a double-sided coating weight of 275-450g / m². 2 By controlling the temperature of the zinc pot, the ingot feeding speed, the distance between the top of the guide dam and the surface of the plating solution, and the speed of the zinc slag pump, the generation and flow of zinc slag are reduced, and the tooth-like defects on the surface of thick-gauge zinc-aluminum-magnesium coated steel sheets are eliminated. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the zinc-aluminum-magnesium ingots added in this invention;

[0042] Figure 2 This is a surface quality diagram of the zinc-aluminum-magnesium coated steel sheet produced in Example 1;

[0043] Figure 3 This is a surface quality diagram of the zinc-aluminum-magnesium coated steel sheet produced in Comparative Example 1. Detailed Implementation

[0044] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0045] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In the following examples and comparative examples, the composition of the zinc pot is as follows: Al content is 5.8 wt%, Mg content is 2.5 wt%, and the remainder is Zn and unavoidable impurities such as Fe; the composition of the added zinc, magnesium and aluminum ingots is the same as that of the zinc pot.

[0047] Example 1

[0048] A production method for eliminating tooth-like defects on the surface of zinc-aluminum-magnesium coated steel sheets, the production method comprising:

[0049] S1. Control the annealing temperature of the strip steel to 650℃, and control the temperature of the strip steel entering the zinc pot according to formula (1):

[0050] T2=T1-0.01v-0.005s (1)

[0051] In formula (1), the zinc pot temperature T1 is 460℃; the running speed v of the steel plate in the zinc pot is 75m / min; and the cross-sectional area s of the strip steel is 1875mm². 2(product of t and c); the calculated temperature T2 of the strip entering the zinc pot is 450℃; and the operating power of the induction heater of the zinc pot is controlled to be 15KW;

[0052] S2. The distance between the top of the guide dam inside the furnace nose and the surface of the plating solution is controlled to be 2mm, and the speed of the zinc slag pump is 120 rpm.

[0053] S3. Control the ingot feeding rate of zinc-aluminum-magnesium ingots according to formula (2):

[0054] v1 = 100 × (2 × c) 2 ×t 2 ×w) / (v×8.47×10 8 (2)

[0055] In formula (2), the thickness t of the finished zinc-aluminum-magnesium coated steel sheet is 1.5 mm; the width c of the finished zinc-aluminum-magnesium coated steel sheet is 1250 mm; and the double-sided coating weight w of the finished zinc-aluminum-magnesium coated steel sheet is 350 g / m². 2 The calculated ingot feeding rate v1 for zinc-aluminum-magnesium ingots is 3.87 cm / min; the added zinc-aluminum-magnesium ingots are rectangular prisms with dimensions of 1180 mm × 600 mm × 200 mm (length × width × height). Figure 1 As shown, the zinc, aluminum and magnesium ingots are added to the plating solution along the length of the zinc, aluminum and magnesium ingots, and the composition of the zinc, aluminum and magnesium ingots is consistent with the composition of the zinc pot.

[0056] The air knife uses nitrogen as its gas source, with a purity greater than 99.9%. The air knife lip gap is controlled at 1.0 mm, the distance between the lip and the strip is 14 mm, the air knife height is 220 mm, and the air knife pressure is 110 mbar.

[0057] The specific process parameters of Examples 1-3 are shown in Tables 1 and 2 (the gas source for the air knife is nitrogen, and the gas purity is greater than 99.9%). Comparative Examples 1-3 are all implemented according to the production method of Example 1, but the process parameters are different from those of Example 1. The specific process parameters are shown in Tables 1 and 2 (the annealing temperature of the strip steel in Examples 2-3 and Comparative Examples 1-3 is 650℃).

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] Using the above production method, the zinc-aluminum-magnesium coated steel sheet produced in Example 1 has excellent surface quality, with no tooth-like defects, such as... Figure 2As shown; the zinc-aluminum-magnesium coated steel sheets produced in Examples 2-3 are similar to those in Example 1, with excellent surface quality and no tooth-like defects; the zinc-aluminum-magnesium coated steel sheet produced in Comparative Example 1 has obvious tooth-like defects on its surface, such as... Figure 3 As shown in the figure; the zinc-aluminum-magnesium coated steel plates produced in Comparative Examples 2-3 also all have obvious tooth-like defects on their surfaces.

[0063] Therefore, it can be seen that by controlling the process conditions, the present invention can reduce the generation and flow of zinc dross, and effectively eliminate tooth-like defects on the surface of thick-gauge zinc-aluminum-magnesium coated steel plates.

[0064] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0065] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A production method for eliminating the surface dent mark defects of a zinc-aluminum-magnesium plated steel sheet, characterized by, The production method comprises: S1, controlling the temperature of the strip steel entering the zinc pot according to formula (1): T2 = T1 - 0.01v - 0.005s (1) In formula (1), T2 represents the temperature of the strip steel entering the zinc pot, in °C; T1 represents the temperature of the zinc pot, in °C; v represents the running speed of the steel plate in the zinc pot, in m / min; s represents the cross-sectional area of the strip steel, in mm2 2 ; S2, controlling the distance between the dam top of the flow guide dam in the furnace nose and the plating solution surface to be 2-5mm, and the rotation speed of the zinc residue pump to be 80-120r / min; S3, controlling the ingot adding speed of the zinc-aluminum-magnesium ingot according to formula (2): v1 = 100 x (2 x c 2 x t 2 x w) / (v x 8.47 x 10 8 ) (2) In formula (2), v1 represents a speed of adding the ingot of zinc-aluminum-magnesium, in cm / min; t represents a thickness of the finished product of the zinc-aluminum-magnesium plated steel sheet, in mm; c represents a width of the finished product of the zinc-aluminum-magnesium plated steel sheet, in mm; and w represents a double-sided plated layer weight of the finished product of the zinc-aluminum-magnesium plated steel sheet, in g / m 2 ​ The calculation process of the above formula (1) and formula (2) only brings in numerical calculation.

2. The production method according to claim 1, characterized by, The annealing temperature of the strip steel is controlled to be 550-700℃.

3. The production method according to claim 1, characterized by, In step S1, 420℃≤T1≤460℃.

4. The production method according to claim 1 or 3, characterized by, In step S1, the zinc pot contains the following components by weight percentage: the Al content is 1-13wt%, the Mg content is 1-6wt%, and the rest is Zn and inevitable impurities.

5. The production method according to claim 1, characterized by, In step S1, 65m / min≤v≤75m / min.

6. The production method according to claim 1, characterized by, In step S1, the operation power of the zinc pot is 10-30KW.

7. The production method according to claim 1, characterized by, In step S3, 1.5 mm < t < 2.5 mm, 275 g / m 2 ≤ w < 450 g / m 2 .

8. The production method according to claim 1, characterized by, The gas source of the air knife is an inert gas.

9. The production method according to claim 1 or 8, characterized by, The gap between the air knife lip and the strip steel is controlled to be 1-1.3mm, the distance between the air knife lip and the strip steel is controlled to be 14-25mm, the height of the air knife is controlled to be 180-250mm, and the pressure of the air knife is controlled to be 110-150mbar.

10. The zinc-aluminum-magnesium plated steel plate produced by the production method in any one of claims 1-9.

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