Black zinc-aluminum-magnesium coated steel plate and manufacturing method thereof

Abstract

The invention relates to a black zinc-aluminum-magnesium coated steel plate and a manufacturing method thereof, the coated steel plate is composed of a steel base material, a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium blackening layer and a black paint film, the thickness of the zinc-aluminum-magnesium coating is 5-30 [mu] m, the thickness of the zinc-aluminum-magnesium blackening layer is 5-30 [mu] m, and the thickness of the black paint film is 5-30 [mu] m; the brightness value of the zinc-aluminum-magnesium blackening layer is Llt; 40). The method has the advantages that the surface of the plating layer blackened by potassium permanganate is clean and is of a compact structure with fine pores, the surface structure can increase the adhesive force of a surface paint film, a degreasing procedure and a surface conditioning procedure in black paint film coating pretreatment can be omitted, a layer of black paint film is directly coated on the plating layer, the technological process is greatly shortened, and the production cost is reduced. The production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of steel plate coating, and in particular relates to a black zinc-aluminum-magnesium coated steel plate and a manufacturing method thereof. Background Art

[0002] In the construction steel, home appliances, automobile and other industries, good surface appearance, excellent corrosion resistance and simple operation procedures are the main factors for material selection. Zinc-aluminum-magnesium coated steel has good corrosion resistance. In a corrosive environment, it can form a corrosion product film with good adhesion and certain fluidity, thereby preventing further erosion by harmful substances. Since the Mg element in the zinc-aluminum-magnesium coating is more active and easily oxidized and blackened, the coating surface can be further blackened in a strong chemical oxidant. This process is called blackening. The Mg content in the coating and the oxidizing environment are the main factors affecting the degree of blackening.

[0003] In the prior art, patent application number CN201280072590.8 discloses a black coated steel plate, which has a Zn coating containing molten Al and Mg, wherein the Zn coating containing molten Al and Mg contains 1.0 to 22.0 mass % of Al and 1.3 to 10.0 mass % of Mg, and black oxide of Zn is distributed in the coating. That is, the Zn coating containing molten Al and Mg is directly plated on the steel plate, and the black color is presented by the black oxide of Zn, which mainly relies on high-temperature treatment with water vapor. The treatment process is unstable, and it is difficult to ensure uniformity, which is not conducive to industrial production. Patent application number CN201680082619.9 discloses a method for manufacturing a black coated steel plate, an apparatus for manufacturing a black coated steel plate, and a system for manufacturing a black coated steel plate, wherein a coated steel plate having a substrate steel plate and a Zn coating containing molten Al and Mg formed on the surface of the substrate steel plate is in contact with water vapor inside a sealed container, thereby manufacturing a black coated steel plate. The manufacturing process is carried out in a sealed container to make the area of ​​the coated steel plate that should be blackened more uniform. This method uses water vapor to react at high temperature to make the steel plate black, which makes it difficult to ensure uniformity, is not conducive to industrial production, and has too high production costs. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a black zinc-aluminum-magnesium coated steel plate and a method for manufacturing the same. The strong chemical oxidizing property of potassium permanganate is used to blacken the surface of the zinc-aluminum-magnesium coating, so as to obtain a black zinc-aluminum-magnesium coated steel plate which is paint-free after stamping and has good corrosion resistance and heat dissipation. The surface of the blackened coating is clean and has a dense structure with fine pores, and the degreasing process and the surface adjustment process can be omitted in the process of coating the black paint film.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A black zinc-aluminum-magnesium coated steel plate, the coated steel plate consists of a steel substrate, a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium blackening layer, and a black paint film. The zinc-aluminum-magnesium coating has a thickness of 5 to 30 μm, the zinc-aluminum-magnesium blackening layer has a thickness of 5 to 30 μm, and the black paint film has a thickness of 5 to 30 μm; the zinc-aluminum-magnesium blackening layer has a lightness value L<40.

[0007] The coated steel plate comprises, from the inside to the outside, a steel substrate, a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium blackening layer, and a black paint film.

[0008] In the zinc-aluminum-magnesium coating, the Mg content is 1.0% to 4%, the Al content is 1% to 13%, and the rest is Zn and inevitable impurities.

[0009] A method for manufacturing a black zinc-aluminum-magnesium coated steel plate comprises the following steps:

[0010] 1) Preheat the zinc-aluminum-magnesium coated steel plate at a temperature of 20 to 150°C;

[0011] 2) The preheated steel substrate is immersed in a blackening liquid for blackening treatment;

[0012] 3) Drying: After drying, the surface of the steel plate is dry, clean and has a dense structure with tiny pores.

[0013] The immersion described in step 2) is carried out in a blackening system, which includes an immersion tank, a sinking roller, a turning roller, and a squeezing roller. The front and rear sides of the immersion tank are provided with sinking rollers, the turning rollers are arranged outside the front and rear sides of the immersion tank, and the back side of the turning roller arranged at the back side of the immersion tank is provided with a squeezing roller. The steel plate sinks into the blackening tank after being turned by the turning roller, and is subjected to immersion blackening treatment between the sinking rollers in the blackening tank. After immersion, the steel plate rises to the outside of the immersion tank through the turning roller, and then is squeezed out of the excess blackening liquid on the surface of the steel plate by the squeezing roller, and then enters the drying device for drying.

[0014] The blackening solution is a mixed solution of potassium permanganate solution and corrosion inhibitor, the concentration of potassium permanganate is 5% to 25%, and the concentration of corrosion inhibitor is 0.5% to 8%.

[0015] The corrosion inhibitor is one or more of hexamethylenetetramine, ethanolamine, ethylenediamine and thiourea.

[0016] The soaking time in step 2) is 5 to 20 seconds, and the soaking temperature is 5 to 30°C.

[0017] The drying temperature in step 3) is 70-200° C. and the drying time is 5-25 seconds.

[0018] Step 3) The steel plate after drying is coated with a black paint film and dried at a temperature of 210 to 250° C. for 50 to 200 seconds.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention utilizes the clean surface of the coating after blackening with potassium permanganate and has a dense structure with fine pores. This surface structure can not only increase the adhesion of the surface paint film, but also save the degreasing process and surface adjustment process in the pretreatment of the black paint film coating, and directly coat a layer of black paint film thereon, which greatly shortens the process flow and reduces the production cost.

[0021] 2. The black zinc-aluminum-magnesium coated steel plate manufactured by the present invention does not require painting after stamping. The surface of the steel plate is black, and the base color exposed after stamping deformation is also black, which saves the subsequent painting process and saves time cost and re-coating process cost for the stamping plant.

[0022] 3. The zinc-aluminum-magnesium coated steel plate is blackened by an immersion blackening system, and then coated with a black paint film after drying. After blackening, the appearance is gray-black to varying degrees depending on the Mg content and the oxidizing environment. After blackening, a stable oxide layer is formed on the coating, and the coating has stable performance and good corrosion resistance. The blackening treatment uses chemical reagents to achieve a reaction at room temperature, with a fast and uniform reaction speed.

[0023] 4. The black appearance is decorative, corrosion-resistant and has good heat dissipation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of black zinc-aluminum-magnesium coated steel plate.

[0025] Figure 2 It is a structural diagram of the blackening system.

[0026] In the figure: 1-steel substrate 2-zinc-aluminum-magnesium coating 3-zinc-aluminum-magnesium blackening layer 4-black paint film 5-steel plate 6-water receiving trough 7-turning roller 8-sinking roller 9-immersion tank 10-squeezing roller 11-drying device. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] See Figure 1A black zinc-aluminum-magnesium coated steel plate, the coated steel plate is composed of a steel substrate, a zinc-aluminum-magnesium coating 2, a zinc-aluminum-magnesium blackening layer 3, and a black paint film 4. The coated steel plate is composed of a steel substrate, a zinc-aluminum-magnesium coating 2, a zinc-aluminum-magnesium blackening layer 3, and a black paint film 4 from the inside to the outside or from the bottom to the top. The thickness of the zinc-aluminum-magnesium coating 2 is 5 to 30 μm, the thickness of the zinc-aluminum-magnesium blackening layer 3 is 5 to 30 μm, and the thickness of the black paint film 4 is 5 to 30 μm; the lightness value L of the zinc-aluminum-magnesium blackening layer 3 is less than 40. In the zinc-aluminum-magnesium coating 2 and the zinc-aluminum-magnesium blackening layer 3, the Mg content is 1.0% to 4%, the Al content is 1% to 13%, and the rest is Zn and unavoidable impurities.

[0029] A black zinc-aluminum-magnesium coated steel plate and a manufacturing method thereof, wherein a zinc-aluminum-magnesium coating 2 is coated on a steel substrate 1, and a strong chemical oxidant is used to blacken the surface of the zinc-aluminum-magnesium coating 2 to form a zinc-aluminum-magnesium blackened layer 3, and the preparation method is as follows:

[0030] 1. The coated steel plate 5 provided in the embodiment is a hot-dip zinc-aluminum-magnesium coated steel plate, and the plating solution composition and coating thickness are shown in Table 1; the zinc-aluminum-magnesium coated steel plate 5 is first preheated, and the preheating temperature is 20-150° C. The preheating method can be box furnace baking, induction heating, etc.

[0031] 2. The surface of the zinc-aluminum-magnesium coating 2 was blackened using potassium permanganate solutions of different concentrations. The corrosion inhibitor added in Examples 2, 5 and 7 was ethanolamine, and the corrosion inhibitor added in the remaining examples was hexamethylenetetramine. The blackening immersion process is shown in Table 2.

[0032] See Figure 2 The blackening system includes a soaking tank 9, a sinking roller 8, a steering roller 7, and a squeezing roller 10. Sinking rollers 8 are provided on the front and rear sides of the soaking tank 9. The sinking rollers 8 are arranged at the lower part of the soaking tank 9. The steering rollers 7 are arranged outside the front and rear sides of the soaking tank 9. A squeezing roller 10 is provided on the rear side of the steering roller 7 arranged on the rear side of the soaking tank 9, and a water receiving trough 6 is provided below the squeezing roller 10.

[0033] The galvanized aluminum-magnesium coated steel sheet 5 is adjusted by the steering roller 7 and then sunk into the blackening pool. It is immersed in the blackening pool between the sinking rollers 8. After immersion, the steel sheet 5 rises to the outside of the immersion pool 9 through the steering roller 7, and then the excess blackening liquid on the surface of the steel sheet 5 is squeezed out by the squeezing roller 10, and then enters the drying device 11 for drying, which plays the role of drying the liquid and curing. After drying, the surface of the steel sheet 5 is dry, clean and has a dense structure with fine pores. The blackening drying process and the lightness value after blackening are shown in Table 3;

[0034] 3. A layer of black paint film 4 is coated on the blackened zinc-aluminum-magnesium coated steel plate 5. The black paint film 4 can be a Nippon brand home appliance polyester paint. The coating process is shown in Table 4.

[0035] The bendability and reverse impact adhesion of the black zinc-aluminum-magnesium steel sheet were tested according to test standard 7 and 8 of the Test Methods for Color Coated Steel Sheets and Strips (GB / T13448-2009). The test results are shown in Table 5.

[0036] According to 26.5.1 of GB / T13448-2009 test standard, a periodic aging test was performed (12 hours as a cycle, 8 hours of aster light, blackboard temperature of 60℃±3℃, 4 hours of condensation, blackboard temperature of 50℃±3℃, light source type of UVA-340, irradiation intensity of 0.89W / (m 2 ·nm), wavelength is 340nm. ), after 100 cycles, the gloss loss rate and color difference of eight groups of test samples before and after aging, as well as the chalking level after aging were evaluated according to GB / T1766-2008. The test results are shown in Table 6.

[0037] Table 1 Plating solution composition

[0038]

[0039] Table 2 Blackening soaking process

[0040]

[0041] Table 3 Drying process after blackening and brightness value after blackening

[0042]

[0043]

[0044] Table 4 Coating process

[0045]

[0046] Table 5 Paint film properties

[0047]

[0048] Table 6 Paint film aging test results

[0049]

[0050] The present invention utilizes the clean surface of the coating after blackening with potassium permanganate and a dense structure with tiny pores. This surface structure can not only increase the adhesion of the surface paint film, but also save the degreasing process and surface adjustment process in the pretreatment of the black paint film coating, and directly coat a layer of black paint film thereon, which greatly shortens the process flow and reduces the production cost.

Claims

1. A black zinc-aluminum-magnesium coated steel plate, characterized in that: The coated steel plate consists of a steel substrate, a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium blackening layer, and a black paint film. The zinc-aluminum-magnesium coating has a thickness of 5 to 30 μm, the zinc-aluminum-magnesium blackening layer has a thickness of 5 to 30 μm, and the black paint film has a thickness of 5 to 30 μm. The lightness value of the zinc-aluminum-magnesium blackening layer is L<40.

2. The black zinc-aluminum-magnesium coated steel sheet according to claim 1, characterized in that: The coated steel plate comprises, from the inside to the outside, a steel substrate, a zinc-aluminum-magnesium coating, a zinc-aluminum-magnesium blackening layer, and a black paint film.

3. The black zinc-aluminum-magnesium coated steel sheet according to claim 1, characterized in that: In the zinc-aluminum-magnesium coating, the Mg content is 1.0% to 4%, the Al content is 1% to 13%, and the rest is Zn and inevitable impurities.

4. A method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Preheat the zinc-aluminum-magnesium coated steel plate at a temperature of 20 to 150°C; 2) The preheated steel substrate is immersed in a blackening liquid for blackening treatment; 3) Drying: After drying, the surface of the steel plate is dry, clean and has a dense structure with tiny pores.

5. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that: The immersion described in step 2) is carried out in a blackening system, which includes a immersion tank, a sinking roller, a turning roller, and a squeezing roller. The front and rear sides of the immersion tank are provided with sinking rollers, the turning rollers are arranged outside the front and rear sides of the immersion tank, and the back side of the turning roller arranged at the back side of the immersion tank is provided with a squeezing roller. The steel plate sinks into the blackening tank after being turned by the turning roller, and is subjected to immersion blackening treatment between the sinking rollers in the blackening tank. After immersion, the steel plate rises to the outside of the immersion tank through the turning roller, and then is squeezed out of the excess blackening liquid on the surface of the steel plate by the squeezing roller, and then enters the drying device for drying.

6. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that: The blackening solution is a mixed solution of potassium permanganate solution and corrosion inhibitor, the concentration of potassium permanganate is 5% to 25%, and the concentration of corrosion inhibitor is 0.5% to 8%.

7. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 6, characterized in that: The corrosion inhibitor is one or more of hexamethylenetetramine, ethanolamine, ethylenediamine and thiourea.

8. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that: The soaking time in step 2) is 5 to 20 seconds, and the soaking temperature is 5 to 30°C.

9. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that: The drying temperature in step 3) is 70-200° C. and the drying time is 5-25 seconds.

10. The method for manufacturing a black zinc-aluminum-magnesium coated steel sheet according to claim 4, characterized in that: Step 3) The steel plate after drying is coated with a black paint film and dried at a temperature of 210 to 250° C. for 50 to 200 seconds.

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