WO2021248765A1 - Hot-dipped zinc-aluminum-magnesium coated steel sheet and manufacturing method therefor - Google Patents

Abstract

Disclosed by content of the present disclosure is a hot-dipped zinc-aluminum-magnesium coated steel sheet having cut corrosion resistance, comprising a steel sheet and a coating; the mass percents of chemical components of the coating are: aluminum, 2-12%, magnesium, 1-4%, and the remainder being zinc and unavoidable impurities; also, the mass percent of the aluminum is 2-3 times the mass percent of the magnesium; and the thickness of the coating is not less than 5% the thickness of the steel sheet. Further disclosed by content of the present disclosure is a preparation method for the coated steel sheet: utilizing the chemical components of the coating and obtaining a coating liquid; preheating the coating liquid and obtaining a preheated coating liquid, the temperature of the preheated coating liquid not being lower than the melting point of the coating liquid and not being higher than 500 ℃; obtaining a steel sheet, dipping the steel sheet into the preheated coating liquid, and obtaining a steel sheet having a coating; and lastly cooling the steel sheet having the coating. The provided preparation method allows for a cut location on a steel sheet to be amply covered by a solution, and a dense hydroxide double layered compound is formed, causing the hot dipped zinc-aluminum-magnesium coated steel sheet to have uniquely superior cut corrosion resistance.

Description

Hot-dip galvanized aluminum-magnesium coated steel sheet and manufacturing method thereof

Cross-references to related applications

This application requires the priority of the Chinese patent application filed on June 8, 2020, with the application number 202010513855.X and the title "A hot-dip galvanized aluminum-magnesium coated steel sheet with excellent cut corrosion resistance and its manufacturing method". Right, the entire disclosure of which is incorporated herein by reference for all purposes.

Technical field

The present disclosure relates to the technical field of steel preparation, in particular to a hot-dip galvanized aluminum-magnesium coated steel sheet and a preparation method thereof.

Background technique

Hot-dip galvanizing is to make the molten zinc and its alloy react with the steel matrix to form a strong metallurgical bonding coating. This kind of hot-dip galvanized steel has the advantages of strong coating bonding force, long service life, simple manufacturing process, low product price, etc., and its demand is increasing in various industries such as the automobile industry, the electrical industry and the construction industry.

The common hot-dip galvanized hot-rolled steel sheet is pure zinc coating. With the improvement of the corrosion resistance requirements of hot-dip galvanized hot-rolled steel sheets, the traditional pure zinc-coated steel sheets can no longer meet the corrosion resistance requirements, so hot-dip galvanizing has been developed Zinc-aluminum-magnesium alloy coating.

Although the zinc-aluminum-magnesium alloy coating has good corrosion resistance, it has been found in use that when the thickness of the steel plate is thick, it is easy to rust at the cut position of the steel plate, which is difficult to meet the needs of use. In addition, in some harsh use environments, the cut position is prone to rust, so a more optimized design of the product is required.

Therefore, how to develop a hot-dip galvanized aluminum-magnesium coated steel sheet with notch corrosion resistance has become a technical problem to be solved urgently.

Summary of the invention

In order to overcome the shortcomings of the prior art, the present disclosure provides a hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance and a preparation method thereof. The preparation method of hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance provided by the present disclosure is beneficial to form a magnesium ion, aluminum ion, and zinc ion solution with good fluidity in the early stage of corrosion, so that the solution can fully cover the steel sheet At the incision position, a dense hydroxide double-layer compound is formed, thereby obtaining a hot-dip galvanized aluminum-magnesium-coated steel sheet with excellent incision corrosion resistance.

In one aspect of the present disclosure, there is provided a hot-dip galvanized aluminum-magnesium-coated steel sheet. The hot-dip galvanized aluminum-magnesium-coated steel sheet may include a steel plate and a coating; the mass fraction of the chemical composition of the coating is: 2% to 2% aluminum. 12%, magnesium 1% to 4%, the rest is zinc and unavoidable impurities; and the mass fraction of aluminum is 2 to 3 times the mass fraction of magnesium; the thickness of the coating is not less than that of the steel sheet 5‰ of thickness.

In some embodiments, the mass fraction of aluminum may be 2.3 times the mass fraction of magnesium.

In some embodiments, the thickness of the steel plate may range from 0.5 mm to 6 mm.

In some embodiments, the mass fraction of magnesium and aluminum in the coating can be controlled according to the thickness of the steel sheet, which specifically includes: when 0.5mm≤the thickness of the steel sheet≤2mm, the mass fraction of the chemical composition of the coating can be: aluminum 2%-12%, magnesium 1%-4%, the rest is zinc and unavoidable impurities; when 2mm<the thickness of the steel plate≤4mm, the mass fraction of the chemical composition of the coating can be: aluminum 3%-12%, Magnesium 1.5%～4%, the rest is zinc and unavoidable impurities; when 4mm<the thickness of the steel plate≤5mm, the mass fraction of the chemical composition of the coating can be: aluminum 4%-12%, magnesium 2%-4% , The rest are zinc and unavoidable impurities; when 5mm<the thickness of the steel sheet≤6mm, the mass fraction of the chemical composition of the coating can be: aluminum 6%-12%, magnesium 3%-4%, and the rest zinc and inevitable Impurities to avoid.

In another aspect of the present disclosure, there is provided a hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance, including a steel sheet and a coating; the mass fraction of the chemical composition of the coating may be: 2-12% aluminum, Magnesium 1-4%, calcium 0.01%-0.1%, the rest is zinc and unavoidable impurities; and the mass fraction of aluminum can be 2 to 3 times the mass fraction of magnesium; the thickness of the coating can be no less than 5‰ of the thickness of the steel plate.

In some embodiments, when the mass fraction of calcium is 0.01%, the mass fractions of magnesium and aluminum in the coating can be controlled according to the thickness of the steel plate, specifically including: when 0.5mm≤the thickness of the steel plate≤2.5mm, the The mass fraction of the chemical composition of the coating can be: 2% to 12% of aluminum, 1% to 4% of magnesium, and the rest is zinc and inevitable impurities; when 2.5mm<the thickness of the steel plate≤4mm, the quality of the chemical composition of the coating The fraction can be: aluminum 2.5%-12%, magnesium 1.2%-4%, and the rest is zinc and inevitable impurities; when 4mm<the thickness of the steel plate≤5mm, the mass fraction of the chemical composition of the coating can be: aluminum 3.8 %-12%, magnesium 1.8%-4%, the rest is zinc and unavoidable impurities; when 5mm<the thickness of the steel sheet≤6mm, the mass fraction of the chemical composition of the coating can be: aluminum 5%-12%, magnesium 2.5% to 4%, the rest is zinc and unavoidable impurities.

In yet another aspect of the present disclosure, there is provided a method for preparing the hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance. The preparation method may include: adopting the hot dip coating with notch corrosion resistance. The chemical composition of the coating of the zinc-aluminum-magnesium-coated steel plate obtains a plating solution; the plating solution is heated to obtain a preheated plating solution, and the temperature of the preheated plating solution is controlled to be not lower than the melting point of the plating solution, and at the same time Not higher than 500°C; obtain a steel plate, immerse the steel plate in the preheated plating solution to obtain a plated steel plate; cool the plated steel plate to obtain a hot dip galvanizing with cut corrosion resistance Aluminum-magnesium coated steel sheet.

In some embodiments, the cooling the steel plate with the coating layer may include: when the temperature of the steel plate with the coating layer is between the temperature of the coating bath and 360° C., cooling can be performed at a first cooling rate, The first cooling rate can be controlled at: 0<cooling rate≤1°C/s; when the temperature of the coated steel sheet is between 360°C and 300°C, it can be cooled at the second cooling rate. The second cooling rate can be ≥5°C/s.

In some embodiments, cooling the steel plate with a coating layer may include: blowing air or spraying water on the surface of the coating layer of the steel plate with a coating layer for cooling.

In some embodiments, before immersing the steel plate in the plating bath, the steel plate may be preheated to the preheating temperature of the steel plate. The range of the preheating temperature of the steel plate is the temperature of the preheating plating solution ±10°C.

In some embodiments, before immersing the steel plate in the plating bath, the steel plate may be preheated to the steel plate preheating temperature, and the steel plate preheating temperature is controlled according to the thickness of the steel plate. It may include: when 0.5mm≤thickness of the steel plate≤2mm, the temperature of the preheated plating solution≤the temperature of the steel plate preheating≤the temperature of the preheated plating solution+10°C; when 2mm<the thickness of the steel plate≤4mm, The temperature of the preheated plating solution -5°C ≤ the preheating temperature of the steel plate ≤ the temperature of the preheated plating solution; The heating temperature is less than or equal to the temperature of the preheated plating solution -5°C.

In some embodiments, obtaining the steel sheet may include: obtaining a steel sheet with a surface roughness Ra of 1 μm to 2 μm.

According to one or more technical solutions of the embodiments of the present disclosure, there are at least the following technical effects or advantages: The present disclosure provides a hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance and a preparation method thereof, including: (1) In terms of composition, 2%-12% aluminum, 1%-4% magnesium, and the rest are zinc and inevitable impurities; and the mass fraction of aluminum is 2% of the mass fraction of magnesium. ~3 times; the thickness of the plating layer is not less than 5‰ of the thickness of the steel sheet; (2) In terms of method, the temperature of the preheated plating solution is controlled to be not lower than the melting point of the plating solution and not higher than 500 ℃; This is beneficial to the formation of magnesium ion, aluminum ion and zinc ion solution with good fluidity in the early stage of corrosion, so that the solution can fully cover the incision position of the steel plate and form a dense hydroxide double-layer compound, thereby obtaining an excellent incision Corrosion-resistant hot-dip galvanized aluminum-magnesium coated steel sheet.

Description of the drawings

In order to more clearly explain the technical solutions in the embodiments of the present disclosure, the following will briefly introduce the drawings needed in the description of the embodiments. Obviously, the drawings in the following description are some implementations of the present disclosure. For example, for those of ordinary skill in the art, without creative work, other drawings can be obtained from these drawings.

FIG. 1 is a diagram of the protection process of the zinc-aluminum-magnesium coating according to an embodiment of the present disclosure to the cut.

Fig. 2 is a flowchart of a method for preparing a hot-dip galvanized aluminum-magnesium coated steel sheet according to an embodiment of the present disclosure.

detailed description

The following will specifically describe the present disclosure in conjunction with specific implementations and examples, and the advantages and various effects of the present disclosure will be presented more clearly. Those skilled in the art should understand that these specific implementations and examples are used to illustrate the present disclosure, but not to limit the present disclosure.

Throughout the specification, unless otherwise specified, the terms used herein should be understood as the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this disclosure belongs. If there is a conflict, this manual takes precedence.

Unless otherwise specified, the various raw materials, reagents, instruments, and equipment used in the present disclosure can be obtained through market purchase or can be obtained through existing methods.

The embodiments of the present disclosure provide a hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance. The general idea is as follows:

In order to overcome the shortcomings of the prior art, the embodiments of the present disclosure provide a hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance, which may include a steel sheet and a coating; the chemical composition mass percentage ratio of the coating may be: 2% to 12% of aluminum, 1% to 4% of magnesium, and the rest are zinc and inevitable impurities; and the content of the aluminum mass fraction may be 2 to 3 times the content of the magnesium mass fraction; The thickness of the plating layer may not be less than 5‰ of the thickness of the steel sheet.

In some embodiments of the present disclosure, FIG. 1 shows a process diagram of the protection process of the zinc-aluminum-magnesium coating on the cut. At the initial stage of atmospheric corrosion, the water vapor in the atmosphere condenses on the surface of the coating to form a water film; the magnesium element in the coating first undergoes an anode reaction, and the formed magnesium ions are dissolved in the water film; the hydroxide and hydroxide formed by the reaction of magnesium ions with the cathode Carbonate groups combine to form compounds such as magnesium carbonate and basic magnesium carbonate with good fluidity. In addition, aluminum ions and zinc ions in the coating also dissolve anodes to form aluminum ions and zinc ions. These compounds containing magnesium ions and aluminum ions flow with the liquid film to the incision position of the steel plate. Due to the presence of magnesium ions and aluminum ions, the pH value in the liquid film will not exceed 10, so that zinc ions will not form loose and porous zinc oxide, but tend to form basic zinc carbonate, basic zinc chloride, etc. Dense oxide. These compounds in turn will form a dense double-layer hydroxide protective layer with magnesium carbonate and aluminum hydroxide, thereby forming a good protective effect on the incision. However, in order for the incision position of the steel plate to be covered by these protective layers, it is required to form a solution of magnesium ion, aluminum ion and zinc ion with good fluidity in the early stage of corrosion, so that the solution can fully cover the incision position of the steel plate and form a dense hydroxide. Double-layer compound.

In some embodiments of the present disclosure, the reason why the mass fraction of magnesium can be set to 1% to 4% is: firstly, a certain amount of magnesium is required in the coating, and the main function of magnesium is to form good fluidity in the initial stage of corrosion. Aqueous solution. On the one hand, this magnesium ion-containing aqueous solution can accelerate the dissolution of aluminum and zinc to form aluminum ions and zinc ions; on the other hand, it can prevent the aluminum ions and zinc ions in the solution from rapidly precipitating into loose compounds, but allows aluminum ions and zinc The ionic solution reacts slowly with carbon dioxide in the atmosphere to form dense oxides. If the magnesium content in the plating layer is less than 1%, this effect cannot be exhibited. However, if the magnesium content is too high, it is easy to form excessively thick magnesium oxide on the surface, which is not conducive to the dissolution of aluminum and zinc. At the same time, it is easy to form hard particles of Mg-Zn compound, which are embedded in the coating to cause electrochemical corrosion effect and reduce Corrosion resistance of the coating. Therefore, the magnesium content should not exceed 4%.

In some embodiments of the present disclosure, the reason why the mass fraction of aluminum can be set to 2%-12% is: the aluminum content in the coating layer should not be less than 2%, because aluminum is the main skeleton forming the double-layer compound Element is also the main element that fills the voids between loose zinc oxide and zinc hydroxide. If the aluminum content is too high, it will cause serious galvanic corrosion effects, and a corrosion current will be formed between aluminum and zinc, which will reduce the corrosion resistance of the coating. The maximum aluminum content in the coating is 12%.

In some embodiments of the present disclosure, the content of the mass fraction of aluminum may be 2 to 3 times the content of the mass fraction of magnesium because: in the initial stage of atmospheric corrosion, the water vapor in the atmosphere condenses on A water film is formed on the surface of the coating. The magnesium element in the coating first undergoes an anode reaction to form magnesium ions and dissolve in the water film. The hydroxide and carbonate formed by the reaction of magnesium ions with the cathode combine to produce basic magnesium carbonate Mg(OH) ₂ ·MgCO ₃ and magnesium hydroxide Mg(OH) ₂ . Due to the presence of magnesium ions and aluminum ions, the pH value in the water film will not exceed 10, so that zinc ions will not form loose and porous zinc oxide, but tend to form basic zinc carbonate, basic zinc chloride, etc. Dense oxide. These compounds in turn will form a dense double-layer hydroxide protective layer with magnesium carbonate and aluminum hydroxide, which provides a good protective effect on the incision. This double-layer hydroxide protective layer (LDH) includes MgAl-LDH and ZnAl-LDH, wherein the number of Mg and Al atoms in the molecule of the former is 6 and 2, respectively, and the number of Al atoms in the molecule of the latter is 2. In terms of stability, the stability of ZnAl-LDH is more than 5 times that of MgAl-LDH, so it is mainly that the double-layer hydroxide forming ZnAl-LDH protects the coating and cuts, thereby improving the corrosion resistance. When the total amount of ZnAl-LDH is 5 times that of MgAl-LDH, the total Al content in the double-layer hydroxide is twice that of Mg, so the Al in the coating is at least twice that of Mg. However, if there are too many aluminum ions in the plating layer, too much Al(OH) ₄ ^- compound precipitation is likely to occur in the initial stage, and on the contrary, a dense double-layer hydroxide cannot be formed. In some embodiments of the present disclosure, the aluminum content in the plating layer is preferably 2.3 times the magnesium content, which can more significantly inhibit the oxidation of magnesium.

In some embodiments of the present disclosure, the thickness of the plating layer may not be less than 5‰ of the thickness of the steel plate. The reason is that if the thickness of the plating layer is less than 5‰ of the thickness of the steel plate, the double-layer compound protective layer cannot cover The cut side of the steel plate also cannot protect the cut of the steel plate.

In some embodiments of the present disclosure, the mass fraction of the chemical composition of the coating may be: 2%-12% of aluminum, 1%-4% of magnesium, the rest being zinc and inevitable impurities; and the quality of the aluminum The content of the fraction can be 2 to 3 times the content of the mass fraction of the magnesium; the thickness of the coating layer can be no less than 5‰ of the thickness of the steel sheet, which together make the coating layer form magnesium ions with good fluidity in the early stage of corrosion , Aluminum ion and zinc ion solution, which is conducive to the solution to fully cover the incision position of the steel plate, forming a dense hydroxide double-layer compound, so as to obtain a hot-dip galvanized aluminum-magnesium coated steel plate with excellent incision corrosion resistance.

In some embodiments of the present disclosure, the thickness of the steel plate may range from 0.5 mm to 6 mm. In the case of relying on the zinc-aluminum-magnesium coating to protect the cut of the steel plate, there are certain requirements for the thickness of the steel plate. If the steel plate is too thick, it will not be able to achieve excellent cut corrosion resistance, usually should not exceed 6mm. If the steel plate is too thin, there is also a certain application risk, because the incision that is too thin will form extremely sharp edges and pits from a microscopic point of view. The radius of curvature of these positions is often smaller than the smallest radius of curvature that can be infiltrated by the surface tension of the aqueous solution. It is covered by a solution containing aluminum ions and magnesium ions, so that a protective layer cannot be formed. In some embodiments of the present disclosure, it is required that the thickness of the steel plate is not less than 0.5 mm.

The applicant found through research that the thicker the steel plate, the higher the content of aluminum and magnesium required to achieve better notch corrosion resistance, specifically: when the thickness of the steel plate does not exceed 2 mm, the magnesium in the coating When the content reaches 1% and the aluminum content reaches 2%, a good cut protection effect can be achieved. Of course, the premise is to meet the manufacturing process requirements of the present disclosure. However, as the thickness of the steel plate increases, the required lower limits of aluminum content and magnesium content increase. Generally speaking, when the thickness of the steel plate reaches 4mm, the magnesium content in the coating should not be less than 1.5%, and the aluminum content should not be less than 3%; when the thickness of the steel plate reaches 5mm, the magnesium content in the coating should not be low When the thickness of the steel plate reaches 6mm, the magnesium content in the coating should not be less than 3%, and the aluminum content should not be less than 6%.

The applicant’s research further found that adding a certain amount of Ca element to the coating can inhibit the formation of large particles of Mg-Zn compound on the surface, prevent the premature reaction of aluminum and hydroxide to form a precipitate, and improve the mobility of aluminum ions, thereby making magnesium Ions and aluminum ions can more fully cover the incision position. Therefore, adding a certain amount of Ca element to the plating layer can improve the corrosion resistance of the notch. In some embodiments of the present disclosure, the addition amount of Ca element may exceed 0.01%. At this time, the formed Mg-Zn compound transforms from polygonal particles to blunt round particles, and the particle size can be further reduced from 50 microns to 20 microns. the following. If the addition of Ca element exceeds 0.1%, it is easy to cause zinc dross defects during production and form galvanic corrosion, thereby reducing the corrosion resistance of the coating. In some embodiments of the present disclosure, the addition amount of calcium element may be 0.01% to 0.1%, and at the same time, it must also meet: aluminum 2-12%, magnesium 1-4%, and the rest is zinc and unavoidable impurities; and The content of the mass fraction of aluminum may be 2 to 3 times the content of the mass fraction of magnesium; the thickness of the coating layer may not be less than 5‰ of the thickness of the steel sheet.

In some embodiments of the present disclosure, when 0.01% Ca is added, when the thickness of the steel sheet does not exceed 2.5 mm, the magnesium content in the coating can reach 1%, and the aluminum content can reach 2%, which can achieve good results. The cut protection effect. In some embodiments of the present disclosure, when the thickness of the steel sheet reaches 4mm, the magnesium content in the coating should not be less than 1.2%, and the aluminum content should not be less than 2.5%; and when the thickness of the steel sheet reaches 5mm, the content of magnesium in the coating The magnesium content should not be less than 1.8%, and the aluminum content should not be less than 3.8%; when the thickness of the steel plate reaches 6mm, the magnesium content in the coating should not be less than 2.5%, and the aluminum content should not be less than 5%.

The present disclosure also provides a method for preparing the hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance, which may include: using the hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance. The chemical composition of the plating layer obtains a plating solution; heats the plating solution to obtain a preheated plating solution, and the temperature of the preheated plating solution is controlled to be not lower than the melting point of the plating solution and at the same time not higher than 500°C; to obtain a steel plate Immersing the steel sheet in the preheated plating solution to obtain a steel sheet with a coating; cooling the steel sheet with the coating to obtain a hot-dip galvanized aluminum-magnesium coated steel sheet with notch corrosion resistance.

In some embodiments of the present disclosure, the temperature of the preheated plating solution can be controlled to be not lower than the melting point of the plating solution and not higher than 500° C. The reason is: if the temperature of the preheating plating solution is If it is too high, the oxidation reaction of the plating bath will be violent, and the alloy elements on the surface of the plating bath will be easily oxidized and evaporated, which will make the alloying elements in the plating bath unevenly distributed. There are few elements on the surface and many elements inside, so that the resulting plating layer The element distribution cannot be uniform, which greatly deteriorates the corrosion resistance of the coating. In some embodiments of the present disclosure, the temperature of the preheated plating solution cannot exceed 500°C. If the temperature of the preheated plating solution is lower than the melting point of the plating solution, the plating solution will solidify.

In some embodiments of the present disclosure, the surface roughness Ra of the obtained steel sheet may be 1 μm to 2 μm. The rough morphology of the steel sheet surface is beneficial to improve the adhesion between the coating and the steel sheet, and to improve the corrosion resistance of the coating during the corrosion process, and it is not easy to peel off the coating. If the surface of the steel sheet is too rough, the following adverse effects will occur: the local coating will be significantly thinned, and the corrosion resistance of the coating will decrease; the rough peaks of the steel plate during hot-dip coating will react quickly to form an excessively thick Fe-Al-Zn compound The layer will consume aluminum in the plating solution, causing the corrosion resistance of the plating layer to decrease due to insufficient aluminum in the plating layer. Therefore, in some embodiments of the present disclosure, the surface roughness Ra of the obtained steel sheet may be limited to not more than 2.0 μm and not less than 1.0 μm.

In some embodiments of the present disclosure, before immersing the steel plate in the plating bath, the steel plate may be preheated to the steel plate preheating temperature, and the steel plate preheating temperature is based on the thickness of the steel plate. The control may specifically include: when 0.5mm≤the thickness of the steel plate≤2mm, the temperature of the preheated plating solution≤the preheating temperature of the steel plate≤the temperature of the preheated plating solution+10℃; when 2mm<the thickness of the steel plate When ≤4mm, the temperature of the preheated plating solution -5°C ≤ the steel plate preheating temperature ≤ the temperature of the preheated plating solution; when 4mm <the thickness of the steel plate ≤ 6mm, the temperature of the preheated plating solution -10 ℃ ≤ steel plate preheating temperature ≤ temperature of the preheated plating solution -5℃.

In some embodiments of the present disclosure, when 0.5mm≤the thickness of the steel plate≤2mm, the preheating temperature of the steel plate may be from the temperature of the preheating bath to a temperature higher than the temperature of the preheating bath before the hot dip coating. A temperature higher than 10°C (the temperature of the preheated plating solution ≤ the temperature of the steel plate preheating ≤ the temperature of the preheated plating solution + 10°C). This is to ensure that a stable Fe-Al-Zn compound is formed between the steel sheet and the plating solution, and to improve the adhesion of the coating, so that the coating is not easily peeled off. However, if the temperature is too high, the compound will be too thick, resulting in loss of corrosion resistance due to the reduction of aluminum in the coating. If the thickness of the steel plate exceeds 2mm, during the reaction process between the steel plate and the plating solution, the temperature inside the steel plate cannot be reduced in time, and the heat cannot be conducted in time; and if the temperature of the steel plate is too high, the internal heat of the steel plate will continue to follow. External conduction makes the Fe-Al-Zn compound layer formed between the steel plate and the plating solution too thick, which consumes the aluminum in the plating solution, resulting in the loss of corrosion resistance due to the reduction of aluminum in the plating layer. Therefore, in some embodiments of the present disclosure, when the thickness of the steel sheet exceeds 2 mm but not more than 4 mm, the preheating temperature of the steel sheet may range from a temperature 5° C. lower than the temperature of the preheated plating solution to a temperature lower than that of the preheated plating solution. Temperature (temperature of the preheated plating solution -5°C ≤ steel plate preheating temperature ≤ temperature of the preheated plating solution); in some embodiments of the present disclosure, when the thickness of the steel plate exceeds 4 mm and does not exceed 6 mm, the steel plate The preheating temperature can range from a temperature 10°C lower than the temperature of the preheating bath to a temperature 5°C lower than the temperature of the preheating bath (the temperature of the preheating bath -10°C≤steel plate preheating temperature≤said Preheat the bath temperature -5°C).

In some embodiments of the present disclosure, the cooling of the steel plate with a coating layer may include: blowing air or spraying water on the surface of the coating layer of the steel plate with a coating layer for cooling.

In some embodiments of the present disclosure, the cooling may be performed in two stages, specifically: when the temperature of the coated steel sheet is between the plating bath temperature and 360° C., the first cooling rate may be used. For cooling, the first cooling rate can be controlled at: 0<cooling rate≤1°C/s; when the temperature of the coated steel sheet is between 360°C and 300°C, it can be cooled at the second cooling rate , The second cooling rate may be ≥5°C/s. The inventor found that when the plating layer begins to solidify, the plating solution and the substrate rapidly react to form an aluminum-rich compound, and at the same time, large pieces of aluminum-rich crystals that precipitate first are formed. If the cooling rate is appropriate, it is beneficial to form a large number of dendrites rich in aluminum and magnesium. Such dendrites rich in aluminum and magnesium are difficult to react with the medium in the subsequent corrosion process, and have good corrosion resistance. The inventor also found that when the temperature of the coating is lowered below 360° C., all the crystals precipitated first have been precipitated, and the eutectic reaction process has begun. During the eutectic reaction, a mixture structure containing one or more of Al/Zn/Mg-Zn, Al/Mg-Zn or Zn/Mg-Zn will be formed. The structure of the mixture is out of phase and more dense. In subsequent use, this dense mixture can quickly react with carbon dioxide and water in the air to form an aqueous solution containing zinc, aluminum, and magnesium, which can cover and protect the incision. Therefore, in some embodiments of the present disclosure, in order to form a large number of dendrites rich in aluminum and magnesium, when the temperature of the coated steel sheet is between the plating bath temperature and 360°C, the first The cooling rate is used for cooling, and the first cooling rate can be controlled at: 0<cooling rate≤1°C/s. In some embodiments of the present disclosure, in order to promote the formation of a fine eutectic structure on the surface of the coating (a mixture containing one or more of Al/Zn/Mg-Zn, Al/Mg-Zn or Zn/Mg-Zn Structure), when the temperature of the coated steel sheet is between 360°C and 300°C, it can be cooled at a second cooling rate, and the second cooling rate may be ≥5°C/s.

According to one or more technical solutions of the embodiments of the present disclosure, it is advantageous to form a magnesium ion, aluminum ion, and zinc ion solution with good fluidity in the early stage of corrosion, so that the solution can fully cover the incision position of the steel plate and form dense hydroxide. It is a double-layer compound, so that the obtained hot-dip galvanized aluminum-magnesium-coated steel sheet has excellent notch corrosion resistance. The content of the mass fraction The content of the mass fraction

Hereinafter, a hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance and its preparation method will be described in detail in combination with experimental data. A hot-rolled steel sheet is used as the substrate, and the material of the hot-rolled steel sheet is CQ grade.

According to one or more technical solutions of the embodiments of the present disclosure, test groups 1-17 are established. In addition, set up comparison groups 1-12. Among them, the test group 1-6 and the comparison group 1-6 use cold-rolled steel plate as the base plate, and the steel plate material is CQ grade; the test group 7-17 and the comparative group 7-12 use hot-rolled steel plate as the base plate, and the steel plate material is CQ level. In the test group 1-17 and the comparative group 1-12, the coated steel plate was prepared according to the relevant steps in the preparation method of the hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance provided in the present disclosure; the difference is different The point is that the chemical composition of the plating solution in the experimental group 1-17 and the comparative group 1-12 is shown in Table 1, and the specific preparation process and parameters are shown in Table 2.

Table 1

Table 2

Group	Preheat bath temperature	Preheat the temperature of the steel plate	Steel plate roughness	First cooling rate	Second cooling rate
To	°C	°C	Micron	℃/s	℃/s
Test group 1	420	420	1	0.5	10
Test group 2	440	440	1.2	0.1	12
Test group 3	430	430	1.3	0.4	12
Test group 4	450	445	1.5	0.2	10
Test group 5	500	495	1.9	0.8	5
Test group 6	410	408	2	1	8
Test group 7	440	430	2	0.1	10
Test group 8	450	445	1.2	0.2	12
Test group 9	490	487	1.9	0.9	12
Test group 10	500	496	1.9	0.3	10
Test group 11	400	390	1	0.9	5
Test group 12	400	393	2	0.9	8
Test group 13	450	445	1.3	0.1	12
Test group 14	430	420	1.2	0.2	5
Test group 15	430	420	1.8	0.2	11
Test group 16	450	440	1.9	0.8	10

Test group 17	450	440	2	0.03	8
Comparison group 1	460	460	0.8	1.2	3
Comparison group 2	470	480	0.8	0.3	8
Comparison group 3	430	450	1.2	3	10
Comparison group 4	510	510	1.2	0.4	12
Comparison group 5	520	500	1.5	0.8	12
Comparison group 6	430	440	2.1	0.2	2
Comparison group 7	500	460	2.3	0.2	12
Comparison group 8	550	500	4.3	5	9
Comparison group 9	590	500	2.1	5	3
Comparison group 10	450	450	2.9	0.2	12
Comparison group 11	430	450	1.2	0.8	12
Comparison group 12	470	460	1.9	0.2	2

The cut corrosion resistance of the zinc-aluminum-magnesium coated steel sheets obtained in the above test groups 1-17 and the comparative groups 1-12 was evaluated for 480 hours by a neutral salt spray test, and the red rust area ratio at the cut position was observed. Using the bending method, the zinc-aluminum-magnesium-coated steel plates obtained in the above test groups 1-17 and the comparative groups 1-12 were respectively bent at 90°, and then the ratio of peeling of the coating was observed. The experimental evaluation results are shown in Table 3.

table 3

Group	Proportion of red rust area (%)	Plating peeling ratio (%)
Test group 1	1	0
Test group 2	3	0
Test group 3	2	0
Test group 4	0	0
Test group 5	0	0
Test group 6	0	0

Test group 7	1	0
Test group 8	3	0
Test group 9	2	0
Test group 10	2	0
Test group 11	2	0
Test group 12	0	0
Test group 13	0	0
Test group 14	0	0
Test group 15	0	0
Test group 16	0	0
Test group 17	0	0
Comparison group 1	12	2
Comparison group 2	17	2
Comparison group 3	15	0
Comparison group 4	10	0
Comparison group 5	18	0
Comparison group 6	20	4
Comparison group 7	14	5
Comparison group 8	20	10
Comparison group 9	twenty one	10
Comparison group 10	20	0
Comparison group 11	34	0
Comparison group 12	twenty three	0

It can be seen from Table 3 that in the hot-dip galvanized aluminum-magnesium coated steel sheets with cut corrosion resistance obtained in test groups 1-17, the proportion of red rust area is in the range of 0-3%; and the proportion of coating peeling is all 0% . In the hot-dip galvanized aluminum-magnesium-coated steel sheets with cut corrosion resistance obtained in Comparative Groups 1-12, the proportion of red rust area is in the range of 12-34%; and the proportion of coating peeling is 2-10%. Obviously, the red rust area ratio and the coating peeling ratio of the hot-dip galvanized aluminum-magnesium-coated steel plates with cut corrosion resistance obtained according to the test groups 1-17 of the examples of the present disclosure are significantly lower.

In the comparative group 1-12, the coatings did not satisfy the requirements of aluminum 2%-12%, magnesium 1%-4%, the rest being zinc and unavoidable impurities; and the content of the aluminum mass fraction was the above The content of the mass fraction of magnesium is 2 to 3 times; so that the thickness of the obtained coating is not less than 5‰ of the thickness of the steel sheet, resulting in poor cut corrosion resistance.

In summary, the present disclosure provides a method for preparing a hot-dip galvanized aluminum-magnesium coating with cut corrosion resistance, which is conducive to the formation of a magnesium ion, aluminum ion, and zinc ion solution with good fluidity in the early stage of corrosion, so that The solution can fully cover the incision position of the steel sheet to form a dense hydroxide double-layer compound, thereby obtaining a hot-dip galvanized aluminum-magnesium coated steel sheet with excellent incision corrosion resistance.

Finally, it should be noted that the terms "include", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also It also includes other elements that are not explicitly listed, or elements inherent to the process, method, article, or equipment.

Although the preferred embodiments of the present disclosure have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present disclosure.

Obviously, those skilled in the art can make various changes and modifications to the present disclosure without departing from the spirit and scope of the present disclosure. In this way, if these modifications and variations of the present disclosure fall within the scope of the claims of the present disclosure and equivalent technologies, the present disclosure is also intended to include these modifications and variations.

Claims (10)

1. A hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance, including a steel sheet and a coating;

   The mass fraction of the chemical composition of the coating is: 2%-12% of aluminum, 1%-4% of magnesium, and the rest is zinc and inevitable impurities; and the mass fraction of aluminum is 2~12% of the mass fraction of magnesium. 3 times;

   The thickness of the coating layer is not less than 5‰ of the thickness of the steel plate.
2. The hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance according to claim 1, wherein the thickness of the steel sheet is in the range of 0.5mm-6mm.
3. The hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance according to claim 1 or 2, wherein the mass fraction of magnesium and aluminum in the coating is controlled according to the thickness of the steel sheet, which specifically includes:

   When 0.5mm≤the thickness of the steel plate≤2mm, the mass fraction of the chemical composition of the coating is: aluminum 2%-12%, magnesium 1%-4%, and the rest is zinc and inevitable impurities;

   When 2mm<thickness of steel sheet≤4mm, the mass fraction of the chemical composition of the coating is: aluminum 3%-12%, magnesium 1.5%-4%, and the rest is zinc and inevitable impurities;

   When 4mm<thickness of steel plate≤5mm, the mass fraction of the chemical composition of the coating is: aluminum 4%-12%, magnesium 2%-4%, and the rest is zinc and inevitable impurities;

   When 5mm<thickness of the steel sheet≤6mm, the mass fraction of the chemical composition of the coating is: aluminum 6%-12%, magnesium 3%-4%, and the rest is zinc and inevitable impurities.
4. The hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance according to claim 1, wherein the mass fraction of the chemical composition of the coating is: aluminum 2-12%, magnesium 1-4%, calcium 0.01%-0.1 %, the rest is zinc and unavoidable impurities; and the mass fraction of aluminum is 2 to 3 times the mass fraction of magnesium; the thickness of the coating layer is not less than 5‰ of the thickness of the steel sheet.
5. The hot-dip galvanized aluminum-magnesium coated steel sheet with notch corrosion resistance according to claim 4, wherein when the mass fraction of calcium is 0.01%, the mass fraction of magnesium and aluminum in the coating is controlled according to the thickness of the steel sheet, specifically include:

   When 0.5mm≤the thickness of the steel plate≤2.5mm, the mass fraction of the chemical composition of the coating is: aluminum 2%-12%, magnesium 1%-4%, and the rest is zinc and inevitable impurities;

   When 2.5mm<thickness of the steel sheet≤4mm, the mass fraction of the chemical composition of the coating is: aluminum 2.5%-12%, magnesium 1.2%-4%, and the rest is zinc and inevitable impurities;

   When 4mm<thickness of the steel sheet≤5mm, the mass fraction of the chemical composition of the coating is: aluminum 3.8%-12%, magnesium 1.8%-4%, and the rest are zinc and inevitable impurities;

   When 5mm<thickness of the steel sheet≤6mm, the mass fraction of the chemical composition of the coating is: aluminum 5%-12%, magnesium 2.5%-4%, and the rest is zinc and inevitable impurities.
6. The method for preparing the hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance according to any one of claims 1 to 5, comprising:

   The chemical composition of the coating of the hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance according to any one of claims 1 to 5 is used to obtain a plating solution;

   Heating the plating solution to obtain a preheated plating solution, the temperature of the preheated plating solution is controlled to be not lower than the melting point of the plating solution, and at the same time not higher than 500°C;

   Obtaining a steel plate, immersing the steel plate in the preheated plating solution to obtain a plated steel plate; and

   The coated steel sheet is cooled to obtain a hot-dip galvanized aluminum-magnesium coated steel sheet with cut corrosion resistance.
7. The method for preparing a hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance according to claim 6, wherein said cooling the coated steel sheet comprises:

   When the temperature of the coated steel sheet is between the temperature of the coating bath and 360°C, cooling is performed at a first cooling rate, and the first cooling rate is controlled to be: 0<cooling rate≤1°C/s;

   When the temperature of the coated steel sheet is between 360°C and 300°C, cooling is performed at a second cooling rate, and the second cooling rate is greater than or equal to 5°C/s.
8. The method for preparing a hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance according to claim 6, wherein the steel sheet is preheated before immersing the steel sheet in the plating bath. To the preheating temperature of the steel plate, the range of the preheating temperature of the steel plate is the temperature of the preheating plating solution ±10°C.
9. The method for preparing a hot-dip galvanized aluminum-magnesium-coated steel sheet with cut corrosion resistance according to claim 6, wherein the steel sheet is preheated before immersing the steel sheet in the plating bath. To the preheating temperature of the steel plate, the preheating temperature of the steel plate is controlled according to the thickness of the steel plate, which specifically includes:

   When 0.5mm≤the thickness of the steel plate≤2mm, the temperature of the preheated plating solution≤the preheating temperature of the steel plate≤the temperature of the preheated plating solution+10°C;

   When 2mm<thickness of the steel plate≤4mm, the temperature of the preheated plating solution -5°C ≤ the preheating temperature of the steel plate ≤ the temperature of the preheated plating solution;

   When 4mm<thickness of the steel plate≤6mm, the temperature of the preheated plating solution is -10°C ≤ the temperature of the steel plate preheating ≤ the temperature of the preheated plating solution -5°C.
10. The method for preparing a hot-dip galvanized aluminum-magnesium-coated steel sheet with notch corrosion resistance according to claim 6, wherein said obtaining the steel sheet comprises: obtaining a steel sheet with a surface roughness Ra of 1 μm-2 μm.

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