A decorative yellowing aluminum-zinc-magnesium coated steel plate and a manufacturing method thereof

Abstract

The invention discloses a decorative yellowing aluminum-zinc-magnesium coated steel plate and a preparation method thereof, wherein the steel plate is composed of a three-layer structure of a steel substrate (1), a hot-dip aluminum-zinc-magnesium coating (2), and a passivation film (3), wherein the film weight of the passivation film is 1.2 to 2.0 g / m 2 The thickness of the hot-dip aluminum-zinc-magnesium coating is 5 to 25 μm; the surface chromaticity of the steel plate is: lightness value L>70, yellow-blue value B>15, red-green value-2.0≤A≤-1.0, color difference value ΔE>10; the yellowing grade is: 6≤ΔYi≤15; the problem that the existing aluminum-zinc-magnesium coated steel plate is prone to oxidation reaction after being placed for a long time, causing the plate surface to darken and blacken, resulting in failure to meet the decorative function requirements of enterprises.

Description

Technical Field

[0001] The invention relates to the field of hot-dip galvanizing, in particular to an aluminum-zinc-magnesium coated steel plate. Background Art

[0002] Aluminum-zinc-magnesium coating is a product that adds a small amount of magnesium to the original hot-dip aluminum-zinc coating product. This can significantly improve the corrosion resistance of the plate during use, especially for the problem of poor corrosion resistance of the aluminum-zinc coating cut edges. The addition of magnesium causes a large amount of eutectic Zn-Al-Mg multi-element alloy and Mg-Zn intermetallic compound to form in the dendrite gap. When the cut edge is invaded by the corrosive atmosphere, a corrosion product film with good adhesion and certain fluidity can be formed, thereby preventing further erosion by harmful substances.

[0003] Since the melting point of magnesium metal is low, the melting point of the eutectic phase formed is significantly lower than that of aluminum alloys. Various magnesium-containing phases are often enriched on the outer surface of the aluminum-zinc-magnesium coating. Therefore, the addition of magnesium brings an adverse effect, that is, the magnesium-containing phase is very easy to be oxidized and blackened first, and will lose its luster earlier than the previous aluminum-zinc coating products, which will seriously affect the appearance of the product. For this reason, most aluminum-zinc-magnesium commercial plates are usually protected by passivation. A passivation liquid with protective function is coated on the aluminum-zinc-magnesium coating, and it can only be used after drying. However, the passivation film is mostly a porous organic resin film, which has a certain oxidizing property. After being placed for a long time, air can still penetrate the pores and react with the coating substrate to cause the plate surface to darken and blacken.

[0004] At present, in addition to the extensive use of the metal color of the coating itself, more and more companies require the production of panels of various colors, so many color passivators have been extended. However, most color passivators will reduce the corrosion resistance of the passivation film itself when dyes are added.

[0005] As mentioned above, although the aluminum-zinc-magnesium coating is prone to oxidation reaction after being placed for a long time, causing the plate surface to darken and blacken, the aluminum-zinc-magnesium coated steel plate has excellent corrosion resistance after all, and its snowflake-shaped appearance has also been favored by the decorative materials industry. Therefore, if the above defects can be overcome and aluminum-zinc-magnesium coated steel plates with good corrosion resistance and decorative effects can be developed, it will inevitably meet the needs of enterprises to a greater extent. Summary of the invention

[0006] In view of this, the present invention provides a decorative yellowing aluminum-zinc-magnesium coated steel plate to solve the problem that the existing aluminum-zinc-magnesium coated steel plate is prone to oxidation reaction after being placed for a long time, causing the plate surface to become dark and black, resulting in failure to meet the decorative function requirements of enterprises.

[0007] In addition, the present invention also provides a method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet.

[0008] In a first aspect, the decorative yellowing aluminum-zinc-magnesium coated steel sheet is composed of a three-layer structure of a steel substrate (1), a hot-dip aluminum-zinc-magnesium coating (2), and a passivation film (3), wherein:

[0009] The film weight of the passivation film is 1.2 to 2.0 g / m 2 The thickness of the hot-dip aluminum-zinc-magnesium coating is 5 to 25 μm;

[0010] The surface chromaticity of the steel plate is: lightness value L>70, yellow-blue value B>15, red-green value -2.0≤A≤-1.0, color difference value ΔE>10; the yellowing grade is: 6≤ΔYi≤15.

[0011] In a second aspect, a method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet according to the first aspect comprises:

[0012] Passivation treatment step: the passivation solution used when the passivation treatment is performed on the surface of the coating has the following composition and content:

[0013] Zinc dihydrogen phosphate 1.5-4.0g / kg, ammonium fluorotitanate 0.5-3.0g / kg, tartaric acid 0.1-0.5g / kg, polyurethane 30-40g / kg, coupling agent 0.5-1.0g / kg, 40% palm wax emulsion 1.8-3.0g / kg, nano silicon dioxide 0.5-1.5g / kg, ammonium metavanadate 0.5-2.5g / kg, the balance is water;

[0014] In the roller coating process of the passivation process, based on the plate and strip speed v0, the coating roller speed is 1.4-1.6v0, the feed roller speed is 0.7-0.95v0, the relative insertion amount between the coating roller and the feed roller is 0.5-2.5mm, and the relative insertion amount between the coating roller and the strip is 10-20mm;

[0015] In the curing process of the passivation process, the curing time of the aluminum-zinc-magnesium coated steel plate is 0.5 to 2 minutes and the curing temperature is 75 to 95° C.;

[0016] In the yellowing process after the passivation treatment, the aluminum-zinc-magnesium coated steel plate is heated in a baking furnace after it comes off the line for yellowing treatment, and the humidity in the baking furnace is controlled to be 10-25%, the baking temperature is 200-260°C, and the baking time is 30-120 minutes.

[0017] In the present disclosure and possible embodiments, the polyurethane is a water-based polyether polyurethane, and the coupling agent is a titanate coupling agent.

[0018] In the present disclosure and possible embodiments, the composition and content of the plating solution used in hot-dip aluminum-zinc-magnesium plating are as follows:

[0019] Mg is 0.5-1.6wt%, Al is 50-56wt%, Si is 1.0-2.0wt%, rare earth elements are 0.05-0.15wt%, and the balance is Zn and unavoidable impurities.

[0020] In the present disclosure and possible embodiments, the rare earth element is La or Ce.

[0021] The present invention has the following beneficial effects:

[0022] The decorative yellowing aluminum-zinc-magnesium coated steel sheet of the present invention has a yellow-blue value B>15 and a yellowing grade of 6≤ΔYi≤15; the B value indicates the degree of yellowing, the larger the B value, the more obvious the yellowing, and the B value is generally greater than 15 and has an obvious yellow color; the yellowing grade ΔYi indicates the degree of yellowing of the material, if ΔYi≤6, the yellowing degree cannot achieve the decorative effect, if ΔYi≥15, the passivation film will affect its corrosion resistance due to excessive baking; the passivation solution used in the preparation of the present invention contains ammonium metavanadate The addition of is beneficial to the enhancement of corrosion resistance and the increase of yellowing grade; in the salt spray resistance test, the steel plate has a white rust resistance improved by more than 300h compared with the non-yellowing zinc-magnesium coated steel plate, the surface lightness L value exceeds 70, is relatively bright, and the yellowness value B exceeds 15. Therefore, the decorative yellowing aluminum-zinc-magnesium coated steel plate of the present invention not only has good corrosion resistance, but also has a good decorative effect, can be directly used for decorative materials, and provides technical guarantee for the performance improvement of the current aluminum-zinc-magnesium coated steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0024] Figure 1 Schematic diagram of the structure of a decorative yellowing aluminum-zinc-magnesium steel plate according to an embodiment of the present invention;

[0025] Figure 2 Schematic diagram of color difference according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0027] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present disclosure, and the drawings are not actually drawn to scale.

[0028] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0029] Figure 1 Schematic diagram of the structure of a decorative yellowing aluminum-zinc-magnesium steel plate according to an embodiment of the present invention; Figure 1 As shown: the decorative yellowing aluminum-zinc-magnesium steel sheet is prepared by hot-dip coating an aluminum-zinc-magnesium coating 2 on a steel substrate 1 and then performing a passivation treatment on the surface of the aluminum-zinc-magnesium coating 2 to obtain a passivation film 3.

[0030] On the basis of the existing aluminum-zinc-magnesium coated steel sheet and its preparation method, under the premise of maintaining the corrosion resistance, in order to obtain a yellowing aluminum-zinc-magnesium steel sheet with decorative effect, the applicant has found through extensive research that the following phenomena and laws will affect the corrosion resistance and decorative yellowing performance of the patented steel sheet, and accordingly set the indicators of the patented steel sheet and the corresponding preparation method, specifically:

[0031] like Figure 2 As shown, L value indicates brightness, the larger the value, the better the decorative effect, L should not be less than 70; B value indicates yellowness, the larger the value, the more obvious the yellowness, after baking, B value is generally greater than 15, it will have obvious yellow color; A value indicates red-green color, in order to prevent color abnormality, the passivation liquid is adjusted to control the A value after baking to be in the range of -2.0 to -1.0; color difference value ΔE = [(L1-L2) ∧ 2+(A1-A2) ∧ 2+(B1-B2) ∧ 2] ∧ 1 / 2; Yellowing grade ΔYi indicates the degree of yellowing of the material. If ΔYi≤6, the yellowing degree cannot achieve the decorative effect. If ΔYi≥15, the passivation film will affect its corrosion resistance due to over-baking.

[0032] During the curing process, the oven should be kept dry as much as possible, otherwise water vapor will easily penetrate into the passivation film layer, causing oxidation and blackening of the board surface and a decrease in brightness (L value); generally, the higher the baking temperature, the more obvious the yellowing, but too high a temperature will easily lead to blackening and oxidation, and the low melting point eutectic phase of aluminum, zinc and magnesium is prone to transformation. For this reason, this patent sets the baking temperature at 200-260°C; if the baking time is too short, the yellowing is not obvious, but if the baking time is too long, it will easily lead to oxidation and blackening in the coating and reduce the brightness.

[0033] The thicker the passivation film of the aluminum-zinc-magnesium coated steel sheet, the better the corrosion resistance and the greater the yellowing degree. However, it is difficult to produce a production line with too thick a thickness. Therefore, this patent sets the film weight of the passivation film to 1.2-2.0 g / m 2 .

[0034] In the roller coating process of the passivation process, the faster the relative speed of the feed roller is, the more passivation liquid is carried along. For this reason, this patent adopts the method of increasing the feed roller speed as much as possible to increase the thickness of the passivation film; the smaller the insertion amount between the coating roller and the feed roller, and between the coating roller and the strip, the greater the coating film thickness, but the coating quality must be taken into account at the same time, especially the edges of the strip. This patent comprehensively considers the above factors and designs a reasonable applicable range: based on the strip speed v0, the coating roller speed is 1.4~1.6v0, the feed roller speed is 0.7~0.95v0, the relative insertion amount between the coating roller and the feed roller is 0.5~2.5mm, and the relative insertion amount between the coating roller and the strip is 10~20mm.

[0035] Based on the above rules, the passivation film weight of the decorative yellowing aluminum-zinc-magnesium coated steel sheet of this patent is 1.2-2.0g / m 2 The thickness of the hot-dip aluminum-zinc-magnesium coating is 5 to 25 μm; the surface color of the steel plate is: lightness value L>70, yellow-blue value B>15, red-green value -2.0≤A≤-1.0; the yellowing grade is: 6≤ΔYi≤15.

[0036] Based on the above description, the preparation method of the decorative yellowing aluminum-zinc-magnesium coated steel sheet of the present invention is described by the following examples, and the performance of the steel sheets prepared in each example is tested to prove the inventive effect of the steel sheet of the present invention; the specific steps of the preparation method are as follows:

[0037] 1. The coated steel sheet used in the following embodiments of the present invention is a hot-dip aluminum-zinc-magnesium coated steel sheet, and the plating solution composition and coating thickness used for the hot-dip aluminum-zinc-magnesium coated steel sheet are shown in Table 1:

[0038] Table 1 Plating solution composition

[0039]

[0040] 2. Passivation treatment is performed on the aluminum-zinc-magnesium coated steel plate in step 1. Embodiments 1 to 8 of the present invention adopt conventional technical means in the art to perform the passivation treatment. The difference is that the passivation solution composition and ratio used in the passivation treatment are shown in Table 2:

[0041] Table 2 Passivation liquid composition ratio

[0042]

[0043] 1 Note: The waterborne polyurethane in Table 2 above uses waterborne polyether polyurethane produced by Shanghai Sisheng Polymer Materials Co., Ltd.; 40% palm wax emulsion represents a solid content of 40%; the titanate coupling agent uses FT-PI2 produced by Nanjing Feiteng New Materials Technology Co., Ltd.

[0044] The components in the passivation solution used in the present invention function as follows:

[0045] (1) Water: dissolves inorganic salts;

[0046] (2) Zinc dihydrogen phosphate Zn(H2PO4)2·2H2O: corrosion resistance;

[0047] (3) Ammonium fluorotitanate (NH4)2Ti / ZrF6: corrosion resistance;

[0048] (4) Tartaric acid: prevents hydrolysis; can react with aluminum-zinc-magnesium coatings and combine with organic chromium to form dense deposits;

[0049] (5) Polyurethane: as a connecting carrier, it is the main film-forming material;

[0050] (6) Palm wax emulsion: It is an emulsified wax that has lubrication properties and makes the board surface shiny;

[0051] (7) Ammonium metavanadate: It is beneficial to enhance corrosion resistance and increase yellowing grade.

[0052] 3. In Examples 1 to 8 of the present invention, the roll coating process and the passivation film thickness used in the passivation process are shown in Table 3:

[0053] Table 3 Roller coating process

[0054]

[0055] 4. After the roller coating process is completed, the steel plates of Examples 1 to 8 are cured. The curing process is shown in Table 4:

[0056] Table 4 Curing process

[0057]

[0058]

[0059] 5. After the passivation treatment, the steel plates of Examples 1 to 8 were subjected to yellowing treatment, and the yellowing process is shown in Table 5:

[0060] Table 5 Yellowing process

[0061] Humidity in furnace (%) Baking temperature (℃) Baking time (min) Embodiment 1 10 200 50 Embodiment 2 10 220 50 Embodiment 3 15 220 30 Embodiment 4 15 240 60 Embodiment 5 20 240 100 Embodiment 6 20 250 120 Embodiment 7 20 260 80 Embodiment 8 25 260 100

[0062] After the passivation treatment, the steel plates of Examples 1 to 8 were tested to show that the aluminum-zinc-magnesium coating prepared by the above-mentioned baking system can both yellow and improve its corrosion resistance.

[0063] 6. In Examples 1 to 8 of the present invention, color difference and yellowing detection were performed on the aluminum-zinc-magnesium passivated coated steel plate prepared after the yellowing treatment in step 5 according to GB / T13448-2019. The results are shown in Table 6, where L1, B1 and A1 are test values ​​before baking, and L2, B2 and A2 are test values ​​after baking.

[0064] Table 6 Color difference and yellowing test results

[0065] L1 B1 A1 L2 B2 A2 ΔE ΔYi Embodiment 1 75.27 -2.39 -1.18 74.12 10.25 -1.18 12.69 6.3 Embodiment 2 75.16 -2.45 -1.2 74.06 12.77 -1.2 15.26 7.2 Embodiment 3 75.03 -2.62 -1.31 74.31 13.57 -1.21 16.21 9.7 Embodiment 4 74.61 -2.42 -1.46 73.29 14.12 -1.26 16.59 11.8 Embodiment 5 74.38 -2.39 -1.62 73.22 15.81 -1.22 18.24 13.4 Embodiment 6 74.29 -2.54 -1.77 71.53 16.41 -1.27 19.16 14.2 Embodiment 7 73.83 -2.67 -1.72 71.02 17.53 -1.22 20.40 14.7 Embodiment 8 74.4 -2.41 -1.53 72.87 14.12 -1.23 16.60 12.8

[0066] It can be seen from Table 6 that the aluminum-zinc-magnesium passivated plated steel sheets prepared in Examples 1 to 8 have a yellowing grade within the range of 6≤ΔYi≤15, a lightness value L>70, which ensures that the steel sheets have a certain brightness, a red-green value of -2.0≤A≤-1.0, which ensures that the red-green color difference of the steel sheets is small, and a yellow-blue value B>15, which ensures that the steel sheets have obvious yellowing.

[0067] 7. In Examples 1 to 8 of the present invention, the salt spray performance of the prepared aluminum-zinc-magnesium passivated plated steel sheets before and after baking was tested respectively. The time for white rust to appear on the surface of the steel sheets is shown in Table 7:

[0068] Table 7 Salt spray test results

[0069]

[0070] As shown in Table 7, it can be seen that the salt spray resistance of the aluminum-zinc-magnesium passivated plated steel plate after yellowing is significantly improved, indicating that the corrosion resistance of the decorative yellowing steel plate of the present invention has not decreased but increased, fully meeting the customer's requirements for the corrosion resistance of the steel plate.

[0071] It can be seen from the test results of the above embodiments of the present invention that the yellowing aluminum-zinc-magnesium passivated coated steel sheet of the present invention has greatly improved performance in both corrosion resistance and decorative performance compared with the existing aluminum-zinc-magnesium passivated coated steel sheet.

[0072] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A decorative yellowing aluminum-zinc-magnesium coated steel sheet, comprising a steel substrate (1), a hot-dip aluminum-zinc-magnesium coating (2), and a passivation film (3). Features: The thickness of the passivation film is 1.2 to 2.0 mg / m 2 The thickness of the hot-dip aluminum-zinc-magnesium coating is 5 to 25 μm; The surface chromaticity of the steel plate is: lightness value L>70, yellow-blue value B>15, red-green value -2.0≤A≤-1.0, color difference value ΔE>10; the yellowing grade is: 6≤ΔYi≤15.

2. The method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet according to claim 1, It is characterized in that include: Passivation treatment step: the passivation solution used when the passivation treatment is performed on the surface of the coating has the following composition and content: Zinc dihydrogen phosphate 1.5-4.0g / kg, ammonium fluorotitanate 0.5-3.0g / kg, tartaric acid 0.1-0.5g / kg, polyurethane 30-40g / kg, coupling agent 0.5-1.0g / kg, 40% palm wax emulsion 1.8-3.0g / kg, nano silicon dioxide 0.5-1.5g / kg, ammonium metavanadate 0.5-2.5g / kg, the balance is water; In the roll coating process of the passivation process, the strip speed v 0 As a benchmark, the paint roller speed is 1.4~1.6v 0 , the speed of the lifting roller is 0.7~0.95v 0 , the relative insertion amount between the coating roller and the material lifting roller is 0.5-2.5mm, and the relative insertion amount between the coating roller and the strip steel is 10-20mm; In the curing process of the passivation process, the curing time of the aluminum-zinc-magnesium coated steel plate is 0.5 to 2 minutes and the curing temperature is 75 to 95° C.; In the yellowing process after the passivation treatment, the aluminum-zinc-magnesium coated steel plate is heated in a baking furnace after it comes off the line for yellowing treatment, and the humidity in the baking furnace is controlled to be 10-25%, the baking temperature is 200-260°C, and the baking time is 30-120 minutes.

3. The method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet according to claim 2, Features: The polyurethane is water-based polyether polyurethane, and the coupling agent is a titanate coupling agent.

4. The method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet according to claim 2 or 3, It is characterized in that The composition and content of the plating solution used in hot-dip aluminum-zinc-magnesium plating are as follows: Mg is 0.5-1.6wt%, Al is 50-56wt%, Si is 1.0-2.0wt%, rare earth elements are 0.05-0.15wt%, and the balance is Zn and unavoidable impurities.

5. The method for preparing the decorative yellowing aluminum-zinc-magnesium coated steel sheet according to claim 4, Features: The rare earth element is La or Ce.

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