A zinc-aluminum-magnesium-nickel alloy plated steel sheet and a method for manufacturing the same

Abstract

The application relates to a zinc-aluminum-magnesium-nickel alloy plated steel sheet and belongs to the technical field of plating. The technical problem solved by the application is that the zinc-aluminum-magnesium plated steel sheet in the prior art is prone to under-film filamentous corrosion. The technical scheme adopted by the application is that the mass fraction of Mg elements in the plating layer is controlled to be 0.5%-1.5%, the mass fraction of Al elements is controlled to be 1%-3%, and the mass fraction of Ni elements is controlled to be 0.03%-1%. By controlling the Mg, Al and Ni contents in the plating layer, the Mg-Zn compound is facilitated to form fine grains, the dissolution speed of the Mg-Zn compound is delayed, so that the filamentous corrosion occurrence speed is slowed down. In addition, by combining the Ni elements and the Al elements in a proper proportion to form Ni-Al compounds, the grains of the plating layer can be refined, the growth of the Mg-Zn compound is inhibited, so that the Mg-Zn compound is divided into fine grains, the dissolution speed of the Mg-Zn compound is delayed, and the filamentous corrosion occurrence speed is slowed down.

Description

Technical Field

[0001] This application relates to the field of coating technology, and more particularly to a zinc-aluminum-magnesium-nickel alloy coated steel sheet. Background Technology

[0002] Zinc-aluminum-magnesium coated steel sheet is a new type of corrosion-resistant alloy coated steel sheet. This coating was developed based on the traditional pure zinc coating, with the addition of magnesium and aluminum elements, which significantly improves the corrosion resistance of the coating on both the surface and the cut surface. It can be widely used in the manufacture of automobiles, home appliances, building exterior walls, etc.

[0003] However, zinc-aluminum-magnesium coatings can experience filamentous corrosion under organic films under certain conditions. This filamentous corrosion forms corrosion morphologies that extend in a specific direction, affecting the appearance quality of the organic film and, in severe cases, even the corrosion resistance of the coating. Summary of the Invention

[0004] This application provides a zinc-aluminum-magnesium-nickel alloy coated steel sheet to solve the technical problem of underfilm filiform corrosion that easily occurs in zinc-aluminum-magnesium coated steel sheets in the prior art.

[0005] In a first aspect, this application provides a zinc-aluminum-magnesium-nickel alloy coated steel sheet, the steel sheet comprising a steel substrate and a coating covering the surface of the steel substrate, the coating comprising the following chemical composition:

[0006] Mg: 0.5 wt% - 1.5 wt%, Al: 1 wt% - 3 wt%, Ni: 0.03 wt% - 1 wt%, Zn.

[0007] Optionally, the thickness of the surface layer of the coating is 0.05μm-0.5μm.

[0008] Optionally, the ratio of Ni content in the surface layer of the coating to the total Ni content in the coating is ≥80%.

[0009] Optionally, the ratio of the mass fraction of Al element in the coating to the mass fraction of Mg element in the coating is 2-3.

[0010] Optionally, the ratio of the area of ​​the Mg-Zn compound in the surface layer to the total area of ​​the coating is ≤20%.

[0011] Optionally, the ratio of the area of ​​the aluminum-rich phase in the surface layer of the coating to the total area of ​​the coating is ≥10%.

[0012] Secondly, this application provides a method for preparing a zinc-aluminum-magnesium-nickel alloy coated steel sheet to achieve the steel sheet described in any embodiment of the first aspect, the method comprising:

[0013] Heat the steel substrate to the first set temperature;

[0014] The heated steel substrate is placed in a plating solution containing the chemical composition of claim 1, heated to a second set temperature, and then held at that temperature for a first set time to obtain a steel plate.

[0015] The heat-insulated steel plate is cooled to a third set temperature at a first set cooling rate;

[0016] The steel plate, after being cooled to a third set temperature, is then cooled at a second set cooling rate.

[0017] Optionally, the first set temperature is set to 450℃-500℃.

[0018] Optionally, the second set temperature is set to 450℃-500℃, and the first set duration is set to 15 seconds-30 seconds.

[0019] Optionally, the first set cooling rate is set to 5℃ / s-30℃ / s, and the third set temperature is set to 200℃, and / or

[0020] The second set cooling rate is 1℃ / s-10℃ / s.

[0021] The technical solutions provided in this application have the following advantages compared with the prior art:

[0022] The zinc-aluminum-magnesium-nickel alloy coated steel sheet provided in this application includes a steel sheet and a coating covering the surface of the steel sheet. The coating contains elements such as Mg, Al, and Ni, wherein the mass fraction of Mg is 0.5%-1.5%, the mass fraction of Al is 1%-3%, and the mass fraction of Ni is 0.03%-1%. By controlling the appropriate proportions of Mg, Al, and Ni content, it is beneficial to form fine grains of Mg-Zn compound, which slows down the dissolution rate of Mg-Zn compound, thereby slowing down the occurrence rate of filamentous corrosion. In addition, by combining Ni and Al elements to form Ni-Al compound, the grains of the coating can be refined, inhibiting the growth of Mg-Zn compound, thereby dividing Mg-Zn compound into fine grains, slowing down the dissolution rate of Mg-Zn compound, and thus slowing down the occurrence rate of filamentous corrosion. This effectively solves the technical problem of underfilm filamentous corrosion that easily occurs in zinc-aluminum-magnesium coated steel sheets in the prior art. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Scanning electron microscope image of the zinc-aluminum-magnesium-nickel alloy coated steel plate provided in Embodiment 1 of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0028] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0029] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising" and "including" mean "including but not limited to".

[0030] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0031] The technical solution provided in this application is to solve the above-mentioned technical problems, and the overall approach is as follows:

[0032] In a first aspect, this application provides a zinc-aluminum-magnesium-nickel alloy coated steel sheet, the steel sheet comprising a steel substrate and a coating covering the surface of the steel substrate, the coating comprising the following chemical composition:

[0033] Mg: 0.5 wt% - 1.5 wt%, Al: 1 wt% - 3 wt%, Ni: 0.03 wt% - 1 wt%, Zn.

[0034] In this embodiment, the Mg element in the coating can significantly improve the coating's atmospheric corrosion resistance. The mechanism is that Mg in the coating preferentially dissolves into the water film on the coating surface in the atmosphere. In the water film, it reacts with dissolved carbon dioxide to precipitate a dense protective film. This protective film is stable in neutral and weakly alkaline environments and also promotes the electrolyte solution on the coating surface to become a weakly alkaline solution, thereby improving the coating's corrosion resistance. When the Mg content in the coating exceeds 0.5%, the coating will preferentially corrode the Mg during the corrosion process, allowing Mg to dissolve into the water film on the coating surface and form a dense protective film. However, if the Mg content is too high, it will cause the formation of more coarse Mg-Zn compounds in the coating. These compounds dissolve rapidly in acidic solutions, inducing filamentary corrosion of the coating under the organic film. Therefore, the Mg content in the coating does not exceed 1.5%.

[0035] In this embodiment, the Mg element in the coating mainly exists in the eutectic structure of the coating in the form of Mg-Zn compounds, with a very small amount existing in the zinc-rich phase of the coating in solid solution form. The main reason for the filamentous corrosion of the zinc-aluminum-magnesium coating in the atmosphere is the Mg-Zn compounds in the coating. Under the condition of a humid acidic water film on the coating surface, these compounds easily combine with hydrogen ions and acid radical ions in the water film to form soluble magnesium salts, causing localized rapid corrosion. The rapid corrosion progresses forward under the organic film, further increasing the acidity of the corrosion front, thereby promoting the formation of filamentous corrosion morphology.

[0036] In this embodiment, the Al element in the coating can provide the coating with high-quality atmospheric corrosion resistance. The principle is that during the corrosion process, the Al element can form dense oxides and dense hydroxides on the surface. If there is no Al in the coating, the bonding force between the coating and the steel plate will be very poor, making the coating unusable and reducing corrosion resistance. Therefore, the mass fraction of Al element in the coating is not less than 1%. When the Al element content in the coating exceeds 3%, a large number of dendritic aluminum-rich crystals will appear in the coating, making the coated steel plate prone to surface cracking during deep drawing deformation, such as when manufacturing automotive parts, thus affecting the corrosion resistance of the coating.

[0037] In this embodiment, Ni can combine with Al in the coating to form Ni-Al compounds, refining the grain size of the coating, especially inhibiting the growth of Mg-Zn compounds by dividing them into fine grains and slowing down their dissolution rate. This reduces the rate of filamentary corrosion. Therefore, the Ni content in the coating is required to be no less than 0.03%. However, if the Ni content is too high, it will lead to the formation of coarse Ni-Al compounds in the coating, resulting in decreased coating toughness. This makes the coated steel sheet prone to surface cracking during deep drawing deformation, such as in the manufacture of automotive parts, thus affecting the corrosion resistance of the coating. Therefore, the Ni content in the coating does not exceed 1%.

[0038] In some embodiments, the thickness of the surface layer of the coating is 0.05 μm to 0.5 μm.

[0039] In this embodiment, if the surface layer is too thin, it will quickly lose its effectiveness in an acidic water film; if the surface layer is too thick, it will cause the coating to lose its corrosion resistance in the atmosphere.

[0040] In some embodiments, the ratio of Ni content in the surface layer of the coating to the total Ni content in the coating is ≥80%.

[0041] In this embodiment, when the surface layer of the coating contains a large amount of Ni, it can separate the Mg-Zn compounds on the surface of the coating, making it difficult for the dissolution and corrosion sites of the Mg-Zn compounds to develop rapidly, thereby inhibiting filamentous corrosion.

[0042] In some embodiments, the ratio of the mass fraction of Al in the coating to the mass fraction of Mg in the coating is 2-3.

[0043] In this embodiment, to suppress the adverse effects of Mg, the ratio of Al to Mg in the coating can be increased. A higher Al content in the coating promotes the formation of fine grains in the Mg-Zn compound, slowing its dissolution rate and thus reducing the rate of filamentary corrosion. Therefore, the mass fraction of Al in the coating should be at least twice the mass fraction of Mg. However, if the Al to Mg ratio is too high, it will make it difficult for the coating to deposit a dense protective film in the atmosphere, reducing its corrosion resistance; therefore, the ratio should not exceed three times.

[0044] In some embodiments, the ratio of the area of ​​the Mg-Zn compound in the surface layer to the total area of ​​the coating is ≤20%.

[0045] In this embodiment, the area ratio of Mg-Zn compound on the coating surface does not exceed 20%. This ensures that Ni, Ni-Al compounds, Al elements, and aluminum-rich phases in the coating can function effectively, breaking down the Mg-Zn compound into small grains. If the ratio exceeds 20%, it becomes difficult to achieve the desired effect, leading to a severe tendency for filamentous corrosion.

[0046] In some embodiments, the ratio of the area of ​​the aluminum-rich phase in the surface layer of the coating to the total area of ​​the coating is ≥10%.

[0047] In this embodiment, the area ratio of the aluminum-rich phase on the coating surface is not less than 10%. The aluminum-rich phase can divide the Mg-Zn compound into fine grains. The aluminum-rich phase itself is relatively stable in the acidic water film and will not cause local corrosion, thereby slowing down the dissolution rate of the Mg-Zn compound and thus slowing down the rate of filamentous corrosion.

[0048] Secondly, this application provides a method for preparing a zinc-aluminum-magnesium-nickel alloy coated steel sheet to achieve the steel sheet described in any embodiment of the first aspect, the method comprising:

[0049] Heat the steel substrate to the first set temperature;

[0050] The heated steel substrate is placed in a plating solution containing the chemical composition of claim 1, heated to a second set temperature, and then held at that temperature for a first set time to obtain a steel plate.

[0051] The heat-insulated steel plate is cooled to a third set temperature at a first set cooling rate;

[0052] The steel plate, after being cooled to a third set temperature, is then cooled at a second set cooling rate.

[0053] In this embodiment, the coated steel sheet is prepared using hot-dip galvanizing technology, and the composition of the plating solution used in hot-dip galvanizing is the same as the composition range of the coating.

[0054] In some embodiments, the first set temperature is 450℃-500℃.

[0055] In this embodiment, the steel substrate needs to be heated before hot-dip galvanizing. If the temperature of the steel substrate is too low, the adhesion between the coating and the steel substrate will be too poor, and the coating will peel off during the part forming process, making it unable to protect the steel plate. However, if the temperature of the steel substrate is too high, it will cause the formation of coarse Mg-Zn compounds in the coating, especially on the coating surface, which will worsen the filamentous corrosion of the coating. Therefore, the heating temperature range of the steel substrate is 450℃-500℃.

[0056] In some embodiments, the second set temperature is 450℃-500℃, and the first set duration is 15 seconds-30 seconds.

[0057] In this embodiment, after hot-dip galvanizing, the strip steel needs to undergo further heat treatment. The purpose of this heat treatment is to allow the Ni and Al elements in the coating to form Ni-Al compounds and fully diffuse into the surface layer. If the heat treatment temperature is too low or the time is too short, Ni will not diffuse sufficiently. If the heat treatment temperature is too high or the time is too long, the surface layer will be too thick, and the Mg element in the coating will be oxidized to MgO, weakening the coating's corrosion resistance. Therefore, the strip steel is heated to 450℃-500℃ and held for 15-30 seconds.

[0058] In some embodiments, the first set cooling rate is 5°C / s-30°C / s, the third set temperature is 200°C, and / or

[0059] The second set cooling rate is 1℃ / s-10℃ / s.

[0060] In this embodiment, the strip steel after heat treatment needs to be cooled to room temperature. During the cooling process, it is first necessary to cool to 200°C at a relatively fast rate to ensure that a large amount of Mg-Zn compound phase does not appear on the coating surface. This is because Mg-Zn compound phases typically form within the range of 360°C ± 30°C, and secondary precipitation also occurs within the range of 240°C ± 40°C. This temperature is lower than the solidification temperature of the zinc-rich phase. Therefore, if the cooling rate is too slow within this temperature range, it will promote the growth of Mg-Zn compounds and their enrichment on the coating surface. Thus, a relatively fast cooling rate to 200°C is required. However, if the cooling rate is too fast, it will result in too little aluminum-rich phase on the surface, causing the aluminum-rich phase to concentrate in the middle of the coating. Therefore, a cooling rate of 5-30°C / s is required to cool to 200°C.

[0061] In this embodiment, the cooling rate can be slowed down when the temperature drops below 200°C, at which point the aluminum-rich phase and Mg-Zn compounds have completely solidified and precipitated. However, if the cooling rate is too slow, the Ni element on the coating surface will react slowly with oxygen in the air to form an oxide layer, losing its effect of inhibiting filamentous corrosion. If the cooling rate is too fast, excessively high temperature stress will accumulate on the coating surface at this stage and cannot be released, leading to cracks in the coating at room temperature and reducing its corrosion resistance. Therefore, a cooling rate of 1°C / s to 10°C / s is required to cool to room temperature.

[0062] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0063] Relevant experimental and effect data:

[0064] Figure 1 This is a scanning electron microscope image of Example 1.

[0065] Examples 1-13 and Comparative Examples 1-5 were prepared according to the preparation process parameters shown in Table 2. The preparation methods included:

[0066] S1. Heat the steel substrate to the first set temperature;

[0067] S2. The heated steel substrate is placed in the plating solution, heated to the second set temperature, and then held at the temperature for the first set time to obtain a steel plate;

[0068] S3. Cool the heat-insulated steel plate to a third set temperature at a first set cooling rate;

[0069] S4. The steel plate, after being cooled to the third set temperature, is cooled at the second set cooling rate.

[0070] The coating characteristics of Examples 1-13 and Comparative Examples 1-5 are shown in Table 1.

[0071] Table 1

[0072]

[0073] Table 2

[0074]

[0075]

[0076] Corrosion evaluation was performed on the zinc-aluminum-magnesium coated steel sheets prepared according to the process parameters in the above embodiments and comparative examples.

[0077] The corrosion evaluation method involves placing the galvanized steel sheet in a cyclic corrosion test chamber and conducting 18 cycles of cyclic corrosion testing. The cyclic corrosion test must meet the requirements of Annex A of ISO 1 1997-1:2017. Then, the mass loss of the coating before and after the test is measured, and the corrosion resistance of the coating is evaluated by the amount of mass loss per unit area. The less the mass loss, the better the corrosion resistance.

[0078] Evaluation of resistance to filamentous corrosion of zinc-aluminum-magnesium coating: A 20-micron-thick PVB organic film was coated on the surface of the zinc-aluminum-magnesium coating. Then, scratches were made on the surface of the organic film, with a scratch width of 1 mm and a scratch depth reaching the steel substrate. 5 μL of acetic acid solution with a concentration of 1 mol / dm³ was injected into the scratched areas. 3 The samples were then placed in a constant temperature and humidity environment (22℃, 86% RH) and stored for 4 weeks. The growth length of filamentary corrosion on the sample surface was then evaluated according to GB / T 30789.9. Longer corrosion filaments indicate a greater susceptibility to filamentary corrosion.

[0079] Table 3

[0080]

[0081]

[0082] In summary, the zinc-aluminum-magnesium-nickel alloy coated steel sheet prepared through the embodiments of this application, by adding appropriate amounts of Mg, Al, and Ni to the coating, facilitates the formation of fine grains of the Mg-Zn compound, slows down the dissolution rate of the Mg-Zn compound, and thus slows down the rate of filamentous corrosion. In addition, by combining Ni and Al elements in an appropriate ratio to form Ni-Al compounds, the grains of the coating are refined, the growth of the Mg-Zn compound is inhibited, thereby dividing the Mg-Zn compound into fine grains, slowing down the dissolution rate of the Mg-Zn compound, and thus slowing down the rate of filamentous corrosion.

[0083] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0084] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to."

[0085] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0086] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A zinc-aluminum-magnesium-nickel alloy coated steel sheet, characterized in that, The steel plate comprises a steel substrate and a coating covering the surface of the steel substrate, the coating being composed of the following chemical components: Mg: 0.5 wt%-1.5 wt%, Al: 1 wt%-3 wt%, Ni: 0.05 wt%-1 wt%, balance Zn; The ratio of Ni content in the surface layer of the coating to the total Ni content in the coating is ≥80%. The ratio of the area of ​​the Mg-Zn compound on the surface layer to the total area of ​​the coating is ≤20%.

2. The steel plate according to claim 1, characterized in that, The thickness of the surface layer of the coating is 0.05μm-0.5μm.

3. The steel plate according to claim 1 or 2, characterized in that, The ratio of the mass fraction of Al to the mass fraction of Mg in the coating is 2-3.

4. The steel plate according to claim 1, characterized in that, The ratio of the area of ​​the aluminum-rich phase in the surface layer of the coating to the total area of ​​the coating is ≥10%.

5. A method for preparing a zinc-aluminum-magnesium-nickel alloy coated steel sheet, characterized in that, The method for preparing the steel plate according to any one of claims 1-4 comprises: Heat the steel substrate to the first set temperature; The heated steel substrate is placed in a plating solution containing the chemical composition of claim 1, heated to a second set temperature, and then held at that temperature for a first set time to obtain a steel plate. The heat-insulated steel plate is cooled to a third set temperature at a first set cooling rate; The steel plate, after being cooled to a third set temperature, is then cooled at a second set cooling rate.

6. The method according to claim 5, characterized in that, The first set temperature is between 450℃ and 500℃.

7. The method according to claim 5, characterized in that, The second set temperature is set between 450℃ and 500℃, and the first set duration is set between 15 seconds and 30 seconds.

8. The method according to claim 5, characterized in that, The first set cooling rate is set to 5℃ / s-30℃ / s, and the third set temperature is set to 200℃, and / or The second set cooling rate is 1℃ / s-10℃ / s.

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