Method for controlling dark spots on surface of medium aluminum zinc aluminum magnesium

Abstract

The invention discloses a method for controlling dark spots on the surface of medium aluminum, zinc, aluminum and magnesium, which is characterized in that a special cooling process route is designed according to the cooling requirement of a medium aluminum, medium magnesium, zinc, aluminum and magnesium coating, and cooling after plating is controlled in four sections; the plating solution comprises the following chemical components in percentage by mass: 5-2% of A < l >, 2-4.0% of Mg, 0.05-0.5% of S and the balance of Zn; the temperature of the plating solution is controlled to be 410-440 DEG C; the thickness of the steel plate is 0.8-2.5 mm, and the weight of the coating is 120-275 g / m < And the hot dipping operation speed is 60-150m / min. The invention provides a method for controlling the dark spots on the surface of medium aluminum, zinc, aluminum and magnesium, and the dark spots are not found on the surface of a finished product by adopting the cooling process after plating for control.

Description

Technical Field

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

[0003] 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.

[0004] During the manufacturing process of Chalco's magnesium-coated steel sheets, due to the ternary alloy coating, the phase structure is relatively complex during the solidification process. After hot-dip galvanizing, dark spot defects are very likely to appear on the surface of the steel sheet during the cooling process. These dark spot defects are about 2-5mm in diameter, and when they appear, they are numerous and irregular. Steel sheets with dark spot defects will become darker in color after being left for a period of time, so customers find it difficult to accept such products.

[0005] This invention patent has obtained a process technology for controlling dark spots on the surface of zinc-aluminum-magnesium coated steel plates with aluminum and magnesium series through research. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium alloys.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for controlling dark spots on the surface of aluminum-zinc-aluminum-magnesium alloy coatings. A special cooling process route is designed to address the cooling requirements of the aluminum-magnesium alloy coating, dividing the post-plating cooling into four stages for control. The first stage involves wind box #1, with the outlet temperature controlled at 370-410℃; the second stage involves wind box #2, with the outlet temperature controlled at 340-380℃; the third stage involves wind boxes #3 and #4, with the outlet temperature controlled at 300-340℃; and the fourth stage involves wind boxes #5 and #6, with the tower top roller pyrometer controlling the temperature at 200-260℃.

[0009] The chemical composition of the plating solution by mass percentage is Al: 5-2%, Mg: 2-4.0%, Si: 0.05-0.5%, with the balance being Zn; the plating solution temperature is controlled at 410-440℃.

[0010] Steel plate thickness 0.8-2.5mm, coating weight 120-275g / ㎡;

[0011] The hot-dip galvanizing operation speed is 60-150 m / min.

[0012] Furthermore, the post-plating cooling device for implementing the aforementioned cooling process route includes:

[0013] The cooling fan consists of 6 sections, each 6-8m long, with a single fan power ranging from 130KW to 260KW.

[0014] The air inlet of the blower is filtered by a filter; the blower and the pipes connected to the air box are all treated with anti-corrosion; the No. 1 and No. 2 air boxes use slit nozzles, and the rest use hole nozzles.

[0015] High-precision infrared pyrometers with a measurement range of 300-1000℃ are installed at the outlets of wind boxes #1, #2, and #4. A pyrometer is also installed at the top roller of the cooling tower after plating. A closed-loop control system is designed between pyrometer #1 and wind box #1, pyrometer #2 and wind box #2, pyrometer #3 and wind boxes #3 and #4, and the tower top pyrometer and wind boxes #5 and #6.

[0016] Furthermore, before producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan filtration system is cleaned.

[0017] Furthermore, during the production of aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan box will be adjusted to a high-temperature gauge closed-loop control mode.

[0018] Furthermore, the appropriate hot-dip galvanizing speed is set according to the steel plate thickness and annealing temperature.

[0019] Furthermore, during the normal production process, the export quality inspectors inspect the surface at a fixed frequency. When the thickness changes, the quality inspectors must inspect the surface and make minor adjustments if dark spots are found within the above-mentioned process range.

[0020] This invention also provides a method for controlling dark spots on the surface of aluminum, zinc, aluminum and magnesium alloys, which is applied to the finished product surface after plating to ensure no dark spots.

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

[0022] When producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets of different thicknesses and coating weights, as shown in Table 2, the above-mentioned post-plating cooling process was used for control, and no dark spots were found 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 This is a schematic diagram of the post-plating cooling device;

[0025] Figure 2 For medium-aluminum and medium-magnesium coated steel plates with dark spot defects;

[0026] Figure 3 The surface of the aluminum-magnesium coated steel plate after the invention is implemented. Detailed Implementation

[0027] A method for controlling dark spots on the surface of Alcoa zinc-aluminum-magnesium alloy coatings is proposed. A special cooling process route is designed to meet the cooling requirements of Alcoa magnesium-aluminum-magnesium alloy coatings. The post-coating cooling is controlled in four stages: the first stage is the No. 1 wind box, with the outlet temperature (No. 1 pyrometer) controlled at 370-410℃; the second stage is the No. 2 wind box, with the outlet temperature (No. 2 pyrometer) controlled at 340-380℃; the third stage is the No. 3 and No. 4 wind boxes, with the outlet temperature (No. 3 pyrometer) controlled at 300-340℃; and the fourth stage is the No. 5 and No. 6 wind boxes, with the tower top roller pyrometer controlling the temperature at 200-260℃.

[0028] 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.

[0029] The temperature of the plating solution is controlled at 410-440℃.

[0030] Specifications and speed control for Chalco's magnesium-zinc-aluminum-magnesium steel plates: Steel plate thickness 0.8-2.5mm, coating weight 120-275g / ㎡. Hot-dip galvanizing speed 60-150m / min.

[0031] Before producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan filtration system is cleaned.

[0032] When producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan box is adjusted to a high-temperature gauge closed-loop control mode.

[0033] The appropriate hot-dip galvanizing speed is set according to the steel plate thickness and annealing temperature.

[0034] The strip temperature is controlled in a closed-loop manner according to the four-stage cooling process requirements, as shown in Table 1:

[0035] Table 1 Temperature control range for each stage of post-plating cooling

[0036] Serial Number bellows range Temperature control range First paragraph #1 bellows 370-410℃ Second paragraph #2 bellows 340-380℃ Third paragraph 3# / 4# bellows 300-340℃ Third paragraph 5# / 6# bellows 200-260℃

[0037] During the normal production process, the export quality inspectors check the surface at a fixed frequency. When the thickness changes, the quality inspectors must check the surface and make minor adjustments within the above-mentioned process range if dark spots are found.

[0038] Example

[0039] When producing medium-aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets of different thicknesses and coating weights, as shown in Table 2, no dark spots were found on the finished product surface when the above-mentioned post-plating cooling process was used for control. The dark spot defect situation before and after using the above-mentioned control process is as follows: Figure 2 , Figure 3 As shown.

[0040] Table 2 Examples of steel sheets with medium aluminum, medium magnesium, zinc, aluminum and magnesium coatings of different thicknesses

[0041] Serial Number Steel plate thickness (mm) Coating weight (g / ㎡) Speed ​​(m / min) 1 0.6 275 120 2 0.7 120 120 3 0.8 220 120 4 1 275 120 5 1.5 275 90 6 1.8 275 85 7 1.9 275 80 8 2 275 78 9 2.2 275 75 10 2.5 275 68

[0042] 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 dark spots on the surface of aluminum, zinc, aluminum, and magnesium alloys, characterized in that: To address the cooling requirements of the magnesium-zinc-aluminum-magnesium coating at Chalco, a special cooling process route was designed, dividing the post-plating cooling into four controlled stages. The first stage is the No. 1 wind box, with the outlet temperature controlled at 370-410℃; the second stage is the No. 2 wind box, with the outlet temperature controlled at 340-380℃; the third stage consists of No. 3 and No. 4 wind boxes, with the outlet temperature controlled at 300-340℃; and the fourth stage consists of No. 5 and No. 6 wind boxes, with the tower top roller pyrometer controlling the temperature at 200-260℃. The chemical composition of the plating solution by mass percentage is Al: 5-2%, Mg: 2-4.0%, Si: 0.05-0.5%, with the balance being Zn; the plating solution temperature is controlled at 410-440℃. Steel plate thickness 0.8-2.5mm, coating weight 120-275g / ㎡; The hot-dip galvanizing operation speed is 60-150 m / min.

2. The method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: The post-plating cooling device for implementing the aforementioned cooling process route includes: The cooling fan consists of 6 sections, each 6-8m long, with a single fan power ranging from 130KW to 260KW. The air inlet of the blower is filtered by a filter; the blower and the pipes connected to the air box are all treated with anti-corrosion; the No. 1 and No. 2 air boxes use slit nozzles, and the rest use hole nozzles. High-precision infrared pyrometers with a measurement range of 300-1000℃ are installed at the outlets of wind boxes #1, #2, and #4. A pyrometer is also installed at the top roller of the cooling tower after plating. A closed-loop control system is designed between pyrometer #1 and wind box #1, pyrometer #2 and wind box #2, pyrometer #3 and wind boxes #3 and #4, and the tower top pyrometer and wind boxes #5 and #6.

3. The method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: Before producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan filtration system is cleaned.

4. The method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: When producing aluminum-magnesium-zinc-aluminum-magnesium coated steel sheets, the post-coating cooling fan box is adjusted to a high-temperature gauge closed-loop control mode.

5. The method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: The appropriate hot-dip galvanizing speed is set according to the steel plate thickness and annealing temperature.

6. The method for controlling dark spots on the surface of aluminum, zinc, aluminum, and magnesium as described in claim 1, characterized in that: During the normal production process, the export quality inspectors check the surface at a fixed frequency. When the thickness changes, the quality inspectors must check the surface and make minor adjustments within the above-mentioned process range if dark spots are found.

7. The method for controlling dark spots on the surface of aluminum, zinc, aluminum and magnesium as described in claim 1 is applied to the surface of the finished product after plating to eliminate dark spots.

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