Method for controlling blocky spots on surface of medium aluminum, zinc, aluminum and magnesium

Abstract

The invention discloses a method for controlling blocky spots on the surface of medium aluminum, zinc, aluminum and magnesium, which comprises the following steps of: controlling parameters of a cleaning section: controlling the temperature of a bath solution for chemical cleaning to be 60-80 DEG C, and controlling the conductivity of an alkali solution of the cleaning section to be 50ms / cm-60ms / cm; controlling the atmosphere of the cooling section of the annealing furnace: controlling the dew point of each section of the furnace area behind the slow cooling section to be below-25 DEG C, and controlling the oxygen content to be below 20ppm; adjusting the air tightness of a furnace nose area; adjusting the humidifying parameters of the furnace nose: adjusting the humidifying parameters of the furnace nose aiming at high-strength structural steel with the yield strength of more than 350Mpa, and controlling the humidifying nitrogen flow of the furnace nose to be 1-4Nm < 3 > / h; the flow of the wet nitrogen is controlled to be 4-10 Nm < 3 > / h, and the humidifying temperature is controlled to be 30-50 DEG C; the invention aims to provide a method for controlling blocky spots on the surface of medium aluminum, zinc, aluminum and magnesium. The blocky spots on the surface of a finished product are basically eliminated.

Description

Technical Field

[0001] This invention belongs to the field of zinc-aluminum-magnesium coating technology, and particularly relates to a method for controlling blocky spots on the surface of zinc-aluminum-magnesium coatings. Background Technology

[0002] Zinc-aluminum-magnesium coated steel sheet is a new type of environmentally friendly and highly corrosion-resistant coated steel sheet. Its coating composition is mainly zinc and varying proportions of Al and Mg. Through a continuous hot-dip process, the zinc layer achieves a composite effect, resulting in excellent properties such as corrosion resistance, abrasion resistance, and ease of forming. Compared to pure zinc coatings, zinc-aluminum-magnesium coatings not only significantly improve corrosion resistance, reaching 3-7 times that of pure zinc coatings of the same thickness, but also provide cut protection due to the fluidity of their corrosion products. With the development of zinc-aluminum-magnesium products, zinc-aluminum-magnesium coated steel sheets can currently be classified into three types based on the range of magnesium and aluminum content: low-aluminum-low-magnesium, medium-aluminum-medium-magnesium, and high-aluminum-medium-magnesium. Low-aluminum-low-magnesium zinc-aluminum-magnesium coating: aluminum content ranges from 1-3%, and magnesium content ranges from 1-3%. This coating is formed by adding certain amounts of aluminum, magnesium, and other elements to hot-dip galvanizing. Medium-aluminum-medium-magnesium zinc-aluminum-magnesium coating: aluminum content ranges from 5-13%, and magnesium content ranges from 2-4%. This is equivalent to adding magnesium to a Galfan coating. High-aluminum-medium-magnesium zinc-aluminum-magnesium coating: aluminum content ranges from 47-57%, and magnesium content ranges from 2-4%. This coating is formed by adding certain amounts of magnesium and other elements to a hot-dip aluminum-zinc coating.

[0003] During the production of high-strength structural steel plates (yield strength above 350 MPa) made of aluminum, magnesium, zinc, aluminum, and magnesium, blocky defects frequently appear on the surface. These defects are elliptical or elongated, and in severe cases, they may have a slight tactile feel. Radial diagonal lines are present at the boundary, and the area surrounded by these lines contains numerous irregularly distributed dotted pits on both the upper and lower surfaces. Figure 1 As shown; analysis of its microstructure reveals incomplete coating formation in the defective areas, thinner coating around the point-like defects, and missed coating at the point-like locations. Based on scanning electron microscopy (SEM) morphology observation and energy dispersive spectroscopy (EDS) analysis, the coating formation in the defective areas is incomplete, the coating around the point-like defects is thin, and missed coating exists at the point-like locations, such as... Figure 2 As shown, it can be determined that the blocky spots were formed during the annealing and coating processes. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the purpose of this invention is to provide a method for controlling blocky spots on the surface of aluminum, zinc, aluminum and magnesium, so that the blocky spots on the surface of the finished product are basically eliminated.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium alloys, comprising:

[0007] Cleaning section parameter control:

[0008] Chemical cleaning, physical brushing, and electrolytic cleaning are used to remove residual rolling oil, iron powder, and non-metallic solid particles from the surface of cold-rolled strip steel. After the strip steel exits the cleaning tank, it is squeezed dry by squeeze rollers, then brushed and rinsed with hot water to remove the degreasing solution, and finally dried with hot air. The temperature of the chemical cleaning tank solution is controlled at 60℃-80℃, and the conductivity of the alkaline solution in the cleaning section is reduced to 50ms / cm-60ms / cm.

[0009] Atmosphere control in the cooling section of the annealing furnace:

[0010] After cleaning, the cold-rolled strip steel enters the continuous annealing furnace of the full radiant tube for annealing. The annealing furnace is divided into a preheating section, a heating section, a slow cooling section, a fast cooling section, an equalization section, and a furnace nose. The atmosphere inside the furnace is a nitrogen-hydrogen mixture. The dew point of each section of the furnace area after the slow cooling section is controlled below -25℃, and the oxygen content is controlled below 20ppm.

[0011] Adjustment of airtightness in the burner nose area:

[0012] Before producing aluminum-magnesium high-strength structural steel, the airtightness of the furnace nose needs to be tested. The focus should be on measuring the expansion joint of the furnace nose, the flange connection at the end of the furnace nose, and other locations with flanges and welds. A handheld hydrogen content detector or spraying soapy water can be used to test the airtightness. Any leaks found must be dealt with before production.

[0013] Adjusting the humidification parameters of the furnace nose:

[0014] For high-strength structural steel with a yield strength of over 350 MPa, the humidification parameters of the furnace nose are adjusted, and the flow rate of wet nitrogen gas for humidification at the furnace nose is controlled at 1-4 Nm. 3 / h; wet nitrogen flow rate controlled at 4-10Nm 3 / h, humidification temperature controlled at 30-50℃.

[0015] Furthermore, the plating solution composition is Al: 5-2%, Mg: 2-4.0%, Si: 0.05-0.5%, with the balance being Zn.

[0016] Furthermore, the steel plate thickness is 0.8-2.5mm, and the coating weight is 80-450g / ㎡.

[0017] Furthermore, the hot-dip galvanizing speed is 60-150 m / min.

[0018] Furthermore, the temperature of the aluminum-magnesium plating bath is 410-440℃.

[0019] Furthermore, it is suitable for producing high-strength structural steel with a yield strength of 350 MPa or higher.

[0020] This invention also provides a method for controlling blocky stains on the surface of aluminum-zinc-aluminum-magnesium coated steel sheets, which can be used to eliminate blocky stains on aluminum-magnesium coated steel sheets during the production process.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0022] When producing high-strength structural steel with a yield strength of over 350 MPa using a medium-aluminum-magnesium-zinc-aluminum-magnesium coating, as shown in Table 1, the above-mentioned control methods can basically eliminate blocky spots on the surface of the finished product. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 The surface morphology of blocky stains on aluminum, magnesium, zinc, aluminum and magnesium alloys;

[0025] Figure 2 For scanning electron microscopy morphology observation and energy dispersive spectroscopy detection of coatings in defective areas;

[0026] Figure 3 Medium-aluminum and medium-magnesium coated steel plates with patchy stains

[0027] Figure 4 Therefore, the surface of the aluminum-magnesium coated steel plate after the implementation of this invention. Detailed Implementation

[0028] A process control method for controlling blocky spots on the surface of zinc-aluminum-magnesium coated steel sheets with a mid-aluminum alloy includes:

[0029] Cleaning section parameter control

[0030] Chemical cleaning, physical brushing, and electrolytic cleaning are used to remove residual rolling oil, iron powder, and non-metallic solid particles from the surface of cold-rolled strip steel. After the strip steel exits the cleaning tank, it is squeezed dry by squeeze rollers, then brushed and rinsed with hot water to remove the degreasing solution, and finally dried with hot air. The temperature of the chemical cleaning tank solution is controlled at 60℃-80℃, and the conductivity of the alkaline solution in the cleaning section is reduced to 50ms / cm-60ms / cm.

[0031] Atmosphere control of the cooling section of the annealing furnace

[0032] After cleaning, the cold-rolled strip steel enters a continuous annealing furnace with full radiant tubes for annealing. The annealing furnace is divided into a preheating section, a heating section, a slow cooling section, a rapid cooling section, an equalization section, and a furnace nose. The atmosphere inside the furnace is a nitrogen-hydrogen mixture. Because the chemical composition of high-strength structural steel has a high content of oxygen-loving elements such as Mn and Si, if the dew point or oxygen content is controlled too high during the annealing process, oxides of Mn and Si will form on the surface of the strip steel. As a result, during the galvanizing process, the areas with oxides on the surface will have poor adhesion, resulting in incomplete coating formation or missed coating. Therefore, it is necessary to control the dew point of each section of the furnace area after the slow cooling section to below -25°C and the oxygen content to below 20 ppm.

[0033] Adjustment of airtightness in the furnace nose area

[0034] The furnace nose area is the crucial passage connecting the annealing furnace and the zinc pot. Its airtightness directly affects the adhesion and surface quality of the coating. Therefore, the airtightness of the furnace nose needs to be tested before producing aluminum-magnesium high-strength structural steel. The focus should be on measuring the expansion joint of the furnace nose, the flange connection at the end of the furnace nose, and other locations with flanges and welds. A handheld hydrogen content detector or spraying soapy water can be used to test the airtightness. Any leaks found must be dealt with before production.

[0035] Adjusting the humidification parameters of the furnace nose

[0036] For high-strength structural steel with a yield strength of over 350 MPa, the humidification parameters of the furnace nose are adjusted, and the flow rate of wet nitrogen gas for humidification at the furnace nose is controlled at 1-4 Nm. 3 / h. The flow rate of wet nitrogen should be controlled at 4-10 Nm. 3 / h, humidification temperature controlled at 30-50℃.

[0037] Plating solution composition control

[0038] The composition of the magnesium-based plating solution of China Aluminum is Al: 5-2%, Mg: 2-4.0%, Si: 0.05-0.5%, and the balance is Zn.

[0039] Specifications and speed control of China Aluminum, China Magnesium, Zinc, Aluminum and Magnesium Steel Plates

[0040] The steel plate thickness is 0.8-2.5mm, and the coating weight is 80-450g / ㎡.

[0041] High-strength structural steel with a yield strength of 350 MPa or higher.

[0042] Hot-dip galvanizing speed: 60-150 m / min.

[0043] Zinc-aluminum-magnesium plating bath temperature control

[0044] The temperature of the zinc-aluminum-magnesium plating bath is controlled at 410-440℃.

[0045] Before producing aluminum-magnesium high-strength structural steel plates, the airtightness of the furnace nose is tested and treated according to method 2.3 to ensure good airtightness in the furnace nose area.

[0046] The appropriate hot-dip galvanizing speed is set according to the steel plate thickness and annealing temperature.

[0047] During production, the cleaning parameters are adjusted according to 2.1 to ensure that the cleaning quality reaches the optimal state.

[0048] During production, the dew point of each section of the furnace area after the slow cooling section is controlled below -25℃, and the oxygen content is controlled below 20ppm.

[0049] Control the flow rate of humidified nitrogen at the furnace nose to 1-4 Nm. 3 / h. The flow rate of wet nitrogen should be controlled at 4-10 Nm. 3 / h, humidification temperature controlled at 30-50℃.

[0050] Case

[0051] When producing high-strength structural steel with a yield strength of over 350 MPa and aluminum-magnesium-zinc-aluminum-magnesium coatings, as shown in Table 1, the above control methods effectively eliminated blocky blemishes on the finished product surface. The blemish conditions before and after applying the above control methods are shown in Table 1. Figure 3 , Figure 4 As shown.

[0052] Table 1 Examples of steel sheets with medium aluminum, medium magnesium, zinc, aluminum and magnesium coatings of different thicknesses

[0053]

[0054]

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium alloys, characterized in that: include: Cleaning section parameter control: Chemical cleaning, physical brushing, and electrolytic cleaning are used to remove residual rolling oil, iron powder, and non-metallic solid particles from the surface of cold-rolled strip steel. After the strip steel exits the cleaning tank, it is squeezed dry by squeeze rollers, then brushed and rinsed with hot water to remove the degreasing solution, and finally dried with hot air. The temperature of the chemical cleaning tank solution is controlled at 60℃-80℃, and the conductivity of the alkaline solution in the cleaning section is reduced to 50ms / cm-60ms / cm. Atmosphere control in the cooling section of the annealing furnace: After cleaning, the cold-rolled strip steel enters the continuous annealing furnace of the full radiant tube for annealing. The annealing furnace is divided into a preheating section, a heating section, a slow cooling section, a fast cooling section, an equalization section, and a furnace nose. The atmosphere inside the furnace is a nitrogen-hydrogen mixture. The dew point of each section of the furnace area after the slow cooling section is controlled below -25℃, and the oxygen content is controlled below 20ppm. Adjustment of airtightness in the burner nose area: Before producing aluminum-magnesium high-strength structural steel, the airtightness of the furnace nose needs to be tested. The focus should be on measuring the expansion joint of the furnace nose, the flange connection at the end of the furnace nose, and other locations with flanges and welds. A handheld hydrogen content detector or spraying soapy water can be used to test the airtightness. Any leaks found must be dealt with before production. Adjusting the humidification parameters of the furnace nose: For high-strength structural steel with a yield strength of over 350 MPa, the humidification parameters of the furnace nose are adjusted, and the flow rate of wet nitrogen gas for humidification at the furnace nose is controlled at 1-4 Nm. 3 / h; wet nitrogen flow rate controlled at 4-10Nm 3 / h, humidification temperature controlled at 30-50℃.

2. The method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: The plating solution composition is Al: 5-2%, Mg: 2-4.0%, Si: 0.05-0.5%, with the balance being Zn.

3. The method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: The steel plate thickness is 0.8-2.5mm, and the coating weight is 80-450g / ㎡.

4. The method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: Hot-dip galvanizing speed: 60-150 m / min.

5. The method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: The temperature of the aluminum-magnesium plating bath is 410-440℃.

6. The method for controlling blocky stains on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: It is suitable for producing high-strength structural steel with a yield strength of 350 MPa or higher.

7. The method for controlling blocky spots on the surface of aluminum-zinc-aluminum-magnesium alloys according to claim 1 can be applied to the production process of aluminum-magnesium alloy coated steel sheets to eliminate blocky spots.

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