阅读说明：本技术 锌铝镁钢板及有效控制csp工艺热镀锌铝镁钢板表面黑点的制备方法 (Zinc-aluminum-magnesium steel plate and preparation method for effectively controlling black spots on surface of hot-dip galvanized aluminum-magnesium steel plate by CSP (cast steel plate) process ) 是由 杜昕 邹明 李积鹏 高伟民 赵永科 董世文 王瑾 张国堂 孙朝勇 刘海军 于 2019-11-22 设计创作，主要内容包括：本发明涉及冶金防腐技术领域,具体而言,涉及锌铝镁钢板及有效控制CSP工艺热镀锌铝镁钢板表面黑点的制备方法。锌铝镁钢板包括基板和设置在基板上的镀层,按质量百分比,基板的化学成分包括C：0.045-0.070％,Als：0.020-0.050％,Ca：0.0020-0.0050％,其余为Fe和不可避免的杂质；镀层的化学成分包括Al：9-13％,Mg：1-4％,Si：0.01-0.3％和Ni:0.01-0.1％,其余为Zn和不可避免的杂质。通过控制镀层和基板的化学成分以及各个化学成分的用量保证形成的锌铝镁钢板表面质量良好且表面无黑点缺陷,使得锌铝镁钢板具有良好的耐腐蚀性和结合力等。(The invention relates to the technical field of metallurgical corrosion prevention, in particular to a zinc-aluminum-magnesium steel plate and a preparation method for effectively controlling black spots on the surface of a hot-dip galvanized aluminum-magnesium steel plate by a CSP (chip scale plate) process. The zinc-aluminum-magnesium steel plate comprises a substrate and a coating arranged on the substrate, and the chemical components of the substrate comprise C: 0.045-0.070%, Als: 0.020-0.050%, Ca: 0.0020 to 0.0050 percent, and the balance of Fe and inevitable impurities; the chemical composition of the plating layer comprises Al: 9-13%, Mg: 1-4%, Si: 0.01-0.3% and 0.01-0.1% of Ni, the balance being Zn and unavoidable impurities. The chemical components of the coating and the substrate and the use amount of each chemical component are controlled to ensure that the formed zinc-aluminum-magnesium steel plate has good surface quality and no black spot defect on the surface, so that the zinc-aluminum-magnesium steel plate has good corrosion resistance, bonding force and the like.)

1. The zinc-aluminum-magnesium steel plate is characterized by comprising a substrate and a coating arranged on the substrate, wherein the substrate comprises the following chemical components in percentage by mass: 0.045-0.070%, Als: 0.020-0.050%, Ca: 0.0020 to 0.0050%, Mn: 0.60-0.8%, less than or equal to 0.05% of Si, less than or equal to 0.020% of P, less than or equal to 0.010% of S, and the balance of Fe and inevitable impurities;

the chemical composition of the coating comprises Al: 9-13%, Mg: 1-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

2. The zinc-aluminum-magnesium steel plate according to claim 1, characterized in that the base plate further comprises, in mass percent, Nb: 0.015 to 0.045%, Ti: 0.030-0.075% and V: 0.020-0.080% of at least one;

preferably, the chemical composition of the substrate comprises C: 0.054-0.060%, Si: 0.014-0.016%, Mn: 0.675-0.700%, Als: 0.0352-0.0432%, Ca: 0.0032-0.0045%, P: 0.008-0.015% and S: 0.003-0.006% of Fe and inevitable impurities as the rest;

preferably, the chemical composition of the plating layer comprises, by mass percent, Al: 10-12%, Mg: 2-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

3. The zinc-aluminum-magnesium steel plate according to claim 1, wherein a eutectic crystal is formed in the plating layer;

preferably, the co-crystal comprises a binary co-crystal and a ternary co-crystal;

preferably, the binary eutectic comprises Al/MgZn₂And Zn/MgZn₂At least one of;

preferably, the ternary eutectic comprises Al/Zn/MgZn₂And Al/Zn/Mg₂Zn₁₁；

Preferably, Mg is contained in any portion of the zinc-aluminum-magnesium steel sheet₂Zn₁₁Is less than 1%, preferably less than 0.5%.

4. The zinc-aluminum-magnesium steel sheet according to any one of claims 1 to 3, wherein the grain size of the zinc-aluminum-magnesium steel sheet is 8.5 to 12.0; preferably 10.0 to 11.0;

preferably, the zinc-aluminum-magnesium steel plate has the hardness of 150-250 HV.

5. A preparation method for effectively controlling black spots on the surface of a hot-dip galvanized aluminum-magnesium steel plate by a CSP process is characterized by being used for preparing the zinc-aluminum-magnesium steel plate as claimed in any one of claims 1 to 4, and the preparation method comprises the steps of forming a substrate by the CSP process and then forming a coating on the substrate by a continuous hot-dip process.

6. The production method according to claim 5, wherein the continuous hot-dipping process comprises: before the molten liquid of the coating on the substrate is cooled to a freezing point, accurately controlling the cooling rate;

preferably, the cooling rate is from 5 to 35 ℃/S, preferably from 10 to 25 ℃/S;

preferably, the cooling width is 5-20mm wider than the width of the substrate when cooling;

preferably, the molten liquid is naturally cooled in air after being solidified;

preferably, the temperature of the zinc-aluminum-magnesium steel plate after air cooling is 5-20 ℃;

preferably, the cooling medium is an inert gas, more preferably argon or nitrogen;

preferably, the purity of the gas is greater than or equal to 96%, preferably greater than or equal to 99%;

preferably, the pressure of the inert gas is 0.3 to 1.0MPa, preferably 0.4 to 0.8 MPa.

7. The production method according to claim 6, wherein the continuous hot dipping process further comprises: cleaning the substrate before forming the melt on the substrate,

preferably, the cleaning comprises cleaning the substrate with a lye;

more optionally, the temperature of the alkali liquor is 50-70 ℃, and the mass concentration of the alkali liquor is 0.6-3.0%;

preferably, the continuous hot dipping process further comprises: carrying out heat treatment on the cleaned substrate;

preferably, the heat treatment comprises heating and cooling in sequence;

preferably, the heating comprises heating at 650-;

preferably, the cooling comprises heating at 600-720 ℃ for 0.5-3 minutes, then at 450-540 ℃ for 0.5-3 minutes, and finally at 460-550 ℃ for 0.5-3 minutes;

preferably, the continuous hot dipping process further comprises: reacting the heat-treated substrate with the melt;

preferably, the continuous hot dipping process further comprises: before the substrate acts with the molten liquid, controlling the temperature of the substrate to be 5-25 ℃ lower than that of the molten liquid;

preferably, the conditions of the continuous hot-dip process are: the dew point temperature is-35 to-15 ℃, the whole hot-dip coating process keeps a reducing atmosphere to prevent surface oxidation, the belt speed is 40 to 150m/min, and the temperature of the molten liquid in the process of the action of the substrate and the molten liquid is +/-1 ℃ of the temperature of the zinc pot.

8. The production method according to any one of claims 5 to 7, wherein the substrate is cold-rolled before being subjected to the continuous hot-dipping process;

preferably, the cold rolling is a PLTCM cold rolling process;

preferably, the process conditions of the PLTCM cold rolling process are: the pickling temperature is 55-85 ℃, and the mass concentration of the emulsion is 1.5-3.0%; the cold rolling relative reduction rate is more than or equal to 55 percent;

preferably, the surface reflectivity of the substrate after cold rolling is more than or equal to 70%.

9. The manufacturing method according to claim 8, wherein the CSP process includes a CSP continuous casting process and a CSP hot rolling process;

preferably, the CSP continuous casting process has the following process conditions: the temperature of the tundish is 1540-0 ℃, the pulling speed is 4.5-4.9m/min, and the heat flow ratio is controlled at 75-95%;

preferably, the fluctuation of the liquid level in the CSP continuous casting process is controlled within +/-3 mm;

preferably, the CSP continuous casting process adopts full-process protection casting;

preferably, the CSP hot rolling process has the process conditions: the tapping temperature is 1160 +/-20 ℃, the finishing temperature is 890 +/-20 ℃, and the coiling temperature is 550 +/-20 ℃;

preferably, the CSP hot rolling process comprises two times of finish rolling, and the reduction rates of the two finish rolling are respectively more than 45% and 43%;

preferably, the thickness of the scale on the surface of the substrate formed by the CSP hot rolling process is less than or equal to 40 um.

10. The method of manufacturing according to claim 9, comprising, prior to performing the CSP process: smelting the raw materials for forming the substrate;

preferably, the smelting comprises: decarbonizing and deoxidizing;

preferably, the decarburization comprises controlling dissolved oxygen in the molten steel at the end of the decarburization;

preferably, the dissolved oxygen in the end point molten steel is 500-650 ppm;

preferably, after decarburization, the carbon content in the molten steel is less than or equal to 0.045%;

preferably, the smelting comprises: tapping after the decarburization and before the deoxidation, and adding synthetic slag and lime to the tapped molten steel when tapping 1/3;

preferably, the synthetic slag is added to the steel at 4-5Kg/t, and the lime added to the steel at 1.5-2 Kg/t;

preferably, the deoxidation comprises performing aluminium deoxidation;

preferably, when aluminum deoxidation is performed, a raw material containing at least one element of Nb, Ti, and V is added to the molten steel so that the substrate contains Nb: 0.015 to 0.025%, Ti: 0.030-0.075% and V: 0.020-0.080% of at least one;

preferably, smelting further comprises: performing calcium treatment after deoxidation;

preferably, before the calcium treatment, the deoxidized molten steel is kept stand for 5-8 minutes;

preferably, the weak blowing is not less than 8min after the calcium treatment;

preferably, the steel sheet has a T.O.ltoreq.30 ppm.

Technical Field

The invention relates to the technical field of metallurgical corrosion prevention, in particular to a zinc-aluminum-magnesium steel plate and a preparation method for effectively controlling black spots on the surface of a hot-dip galvanized aluminum-magnesium steel plate by a CSP (chip scale plate) process.

Background

With the development of the steel industry, the construction, highway, household electrical industry, automobile machinery manufacturing industry and other industries are rapidly developed. Due to different use environments, the corrosion resistance of steel part products is provided with high challenge, products such as zinc, aluminum zinc, zinc-iron alloy and the like coated on the surface are widely used due to good corrosion resistance, formability, weldability and coating property, the corrosion resistance of the existing zinc-coated products cannot meet the requirements with continuous improvement of use requirements, and the corrosion resistance of the zinc-aluminum-magnesium coated steel plate developed in China in recent years is 5-20 times that of the zinc-aluminum-magnesium coated steel plate, so that the use requirements of severe conditions are greatly met. However, the surface structure of the aluminum magnesium zinc plating layer in the prior art has certain defects, such as color difference, oxidation resistance, black spots and the like, and particularly, the existence of the black spots on the surface of the zinc aluminum magnesium plating layer not only affects the appearance of the zinc aluminum magnesium steel plate, but also reduces the corrosion resistance and the bonding force between the plating layer and the substrate, thereby further reducing the service life of the zinc aluminum magnesium steel plate.

Disclosure of Invention

The invention aims to provide a zinc-aluminum-magnesium steel plate and a preparation method for effectively controlling black spots on the surface of the zinc-aluminum-magnesium steel plate by a CSP process. The zinc-aluminum-magnesium steel plate has no black spots, the corrosion resistance of the zinc-aluminum-magnesium steel plate is good, and the binding force between a plating layer and a substrate in the zinc-aluminum-magnesium steel plate is strong.

The invention is realized by the following steps:

in a first aspect, an embodiment of the present invention provides a zinc-aluminum-magnesium steel plate, which includes a substrate and a plating layer disposed on the substrate, where the substrate includes, by mass: 0.045-0.070%, Als: 0.020-0.050%, Ca: 0.0020 to 0.0050%, Mn: 0.60-0.8%, less than or equal to 0.05% of Si, less than or equal to 0.020% of P, less than or equal to 0.010% of S, and the balance of Fe and inevitable impurities;

the chemical composition of the coating comprises Al: 9-13%, Mg: 1-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

In an alternative embodiment, the substrate further includes Nb: 0.015 to 0.045%, Ti: 0.030-0.075% and V: 0.020-0.080% of at least one;

preferably, the chemical composition of the substrate comprises C: 0.054-0.060%, Si: 0.014-0.016%, Mn: 0.675-0.701%, Als: 0.0352-0.0432%, Ca: 0.00: 32-0.0045%, P: 0.008-0.015% and S0.003-0.006%, the rest is Fe and inevitable impurities;

preferably, the chemical composition of the plating layer comprises, by mass percent, Al: 10-12%, Mg: 2-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

In an alternative embodiment, a eutectic is formed within the plating;

preferably, the co-crystal comprises a binary co-crystal and a ternary co-crystal;

preferably, the binary eutectic comprises Al/MgZn₂And Zn/MgZn₂At least one of;

preferably, the ternary eutectic comprises Al/Zn/MgZn₂And Al/Zn/Mg₂Zn₁₁；

Preferably, Mg is contained in any portion of the zinc-aluminum-magnesium steel sheet₂Zn₁₁Less than 1%, preferably less than 0.5%;

in an alternative embodiment, the zinc-aluminum-magnesium steel sheet has a grain size of 8.5 to 12.0; preferably 10.0 to 11.0;

preferably, the zinc-aluminum-magnesium steel plate has the hardness of 150-250 HV.

In a second aspect, embodiments of the present invention provide a preparation method for effectively controlling black spots on a surface of a zinc-aluminum-magnesium hot-dipped steel sheet in a CSP process, the preparation method being used for preparing the zinc-aluminum-magnesium steel sheet according to any one of the preceding embodiments, and the preparation method including forming a substrate by using the CSP process and then forming a plating layer on the substrate by using a continuous hot-dipping process.

In an alternative embodiment, the continuous hot dip process comprises: before the molten liquid of the coating on the substrate is cooled to a freezing point, accurately controlling the cooling rate;

preferably, the cooling rate is from 5 to 35 ℃/S, preferably from 10 to 25 ℃/S;

preferably, the cooling width is 5-10mm wider than the width of the substrate when cooling;

preferably, the molten liquid is naturally air-cooled after being solidified, and the temperature of the zinc-aluminum-magnesium steel plate after air cooling is 5-20 ℃;

preferably, the cooling medium is an inert gas, more preferably argon or nitrogen;

preferably, the purity of the gas is greater than or equal to 96%, preferably greater than or equal to 99%;

preferably, the pressure of the inert gas is 0.3 to 1.0MPa, preferably 0.4 to 0.8 MPa.

In an alternative embodiment, the continuous hot dip process further comprises: cleaning the substrate before forming the melt on the substrate,

preferably, the cleaning comprises cleaning the substrate with a lye;

more optionally, the temperature of the alkali liquor is 50-70 ℃, and the mass concentration of the alkali liquor is 0.6-3.0%;

preferably, the continuous hot dipping process further comprises: carrying out heat treatment on the cleaned substrate;

preferably, the heat treatment comprises heating and cooling in sequence;

preferably, the heating comprises heating at 650-;

preferably, the cooling comprises heating at 600-720 ℃ for 0.5-3 minutes, then at 450-540 ℃ for 0.5-3 minutes, and finally at 460-550 ℃ for 0.5-3 minutes;

preferably, the continuous hot dipping process further comprises: reacting the heat-treated substrate with the melt;

preferably, the continuous hot dipping process further comprises: before the substrate acts with the molten liquid, controlling the temperature of the substrate to be 5-25 ℃ lower than that of the molten liquid;

preferably, the conditions of the continuous hot-dip process are: the dew point temperature is-35 to-15 ℃, the belt speed is 40 to 150m/min, and the temperature fluctuation value of the molten liquid in the process of the action of the substrate and the molten liquid is +/-1 ℃ of the temperature of the zinc pot.

In an alternative embodiment, the substrate is cold rolled prior to the continuous hot dip process;

preferably, the cold rolling is a PLTCM cold rolling process;

preferably, the process conditions of the PLTCM cold rolling process are: the pickling temperature is 55-85 ℃, and the mass concentration of the emulsion is 1.5-3.0%; the cold rolling relative reduction rate is more than or equal to 55 percent;

preferably, the surface reflectivity of the substrate after cold rolling is more than or equal to 70%.

In an alternative embodiment, the CSP process includes a CSP continuous casting process and a CSP hot rolling process;

preferably, the CSP continuous casting process has the following process conditions: the temperature of the middle ladle is 1540 and 1560 ℃, the pulling speed is 4.5-4.9m/min, and the heat flow ratio is controlled at 75-95 percent, wherein the heat flow ratio represents the ratio of the heat flow density of the narrow surface of the crystallizer to the heat flow density of the wide surface of the crystallizer;

preferably, the fluctuation of the liquid level in the CSP continuous casting process is controlled within +/-3 mm;

preferably, the CSP continuous casting process adopts full-process protection casting;

preferably, the CSP hot rolling process has the process conditions: the tapping temperature is 1160 +/-20 ℃, the finishing temperature is 890 +/-20 ℃, and the coiling temperature is 550 +/-20 ℃;

preferably, the CSP hot rolling process comprises performing two finishing rolls with reduction ratios of greater than 45% and 43%, respectively.

In an alternative embodiment, prior to performing the CSP process, comprising: smelting the raw materials for forming the substrate;

preferably, the smelting comprises: decarbonizing and deoxidizing;

preferably, the decarburization comprises controlling dissolved oxygen in the molten steel at the end of the decarburization;

preferably, the dissolved oxygen in the end point molten steel is 500-650 ppm;

preferably, after decarburization, the carbon content in the molten steel is less than or equal to 0.045%;

preferably, the smelting comprises: tapping after the decarburization and before the deoxidation, and adding synthetic slag and lime to the tapped molten steel when tapping 1/3;

preferably, the synthetic slag is added to the steel at 4-5Kg/t, and the lime added to the steel at 1.5-2 Kg/t;

preferably, the deoxidation comprises performing aluminium deoxidation;

preferably, when aluminum deoxidation is performed, a raw material containing at least one element of Nb, Ti, and V is added to the molten steel so that the substrate contains Nb: 0.015 to 0.025%, Ti: 0.030-0.075% and V: 0.020-0.080% of at least one;

preferably, smelting further comprises: performing calcium treatment after deoxidation;

preferably, before the calcium treatment, the deoxidized molten steel is kept stand for 5-8 minutes;

preferably, the weak blow is not less than 8min after the calcium treatment.

The invention has the following beneficial effects: the invention ensures that the formed zinc-aluminum-magnesium steel plate has good surface quality and no black spot defect on the surface by controlling the chemical components of the coating and the substrate and the dosage of each chemical component, so that the zinc-aluminum-magnesium steel plate has good corrosion resistance, bonding force and the like. Meanwhile, the combination of the CSP process and the continuous hot-dip coating process ensures that the prepared zinc-aluminum-magnesium steel plate has good surface quality and no black spot defect on the surface, thereby ensuring the corrosion resistance, the strength, the oxidation resistance and the like of the zinc-aluminum-magnesium steel plate.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a SEM test result chart of the surface of a zinc-aluminum-magnesium steel sheet provided in example 4;

FIG. 2 is a SEM test result chart of the side surface of the zinc-aluminum-magnesium steel sheet provided in example 4;

FIG. 3 is a SEM measurement result chart of the surface of a zinc-aluminum-magnesium steel sheet provided in example 9;

fig. 4 is a side SEM examination result chart of the zinc-aluminum-magnesium steel sheet provided in example 9.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The features and properties of the present invention are described in further detail below with reference to examples.

The embodiment of the invention provides a zinc-aluminum-magnesium steel plate which comprises a substrate and a plating layer arranged on the substrate, wherein the substrate comprises the following chemical components in percentage by mass: 0.045-0.070%, Als: 0.020-0.050%, Ca: 0.0020 to 0.0050%, Mn: 0.60-0.8%, less than or equal to 0.05% of Si, less than or equal to 0.020% of P, less than or equal to 0.010% of S, and the balance of Fe and inevitable impurities;

the chemical composition of the coating comprises Al: 9-13%, Mg: 1-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

Preferably, the chemical composition of the substrate comprises C: 0.054-0.060%, Si: 0.014-0.016%, Mn: 0.675-0.701%, Als: 0.0352-0.0432%, Ca: 0.00: 32-0.0045%, P: 0.008-0.015% and S: 0.003-0.006% of Fe and inevitable impurities as the rest;

preferably, the chemical composition of the plating layer comprises, by mass percent, Al: 10-12%, Mg: 2-4%, Si: 0.01-0.3%, Ni 0.01-0.1%, Ce: 0.01-0.15%, and the balance of Zn and inevitable impurities.

According to the invention, through controlling the chemical components in the substrate and the coating and the proportion of each chemical component, black spots on the surface of the coating are reduced, even no black spots are formed on the surface of the coating, and then the corrosion resistance, strength, binding force between the coating and the substrate, oxidation resistance and the like of the zinc-aluminum-magnesium steel plate can be improved.

Further, according to the mass percentage, the substrate further comprises Nb: 0.015 to 0.045%, Ti: 0.030-0.075% and V: at least one of 0.020-0.080%, and the addition of the chemical components into the substrate can further improve the performance of the zinc-aluminum-magnesium steel plate and prolong the service life of the zinc-aluminum-magnesium steel plate. The substrate further comprises at least one of the raw materials, the raw materials are added according to the proportion, and after any one raw material is added according to the proportion, the residual raw material in the substrate is Fe and inevitable impurities.

Further, eutectic crystals are formed in the plating layer; eutectic crystals are formed in the plating layer, so that the corrosion resistance of the zinc-aluminum-magnesium steel plate, the binding force between the plating layer and the substrate and other performances can be further improved.

Preferably, the co-crystal comprises a binary co-crystal and a ternary co-crystal;

preferably, the binary eutectic comprises Al/MgZn₂And Zn/MgZn₂At least one of;

preferably, the ternary eutectic comprises Al/Zn/MgZn₂And Al/Zn/Mg₂Zn₁₁The eutectic can further improve the corrosion resistance, hardness, strength and oxidation resistance of the zinc-aluminum-magnesium steel plate.

Further, the inventors found out the area Mg where black spots appear after creative work₂Zn₁₁Is more than 1 percent, namely a certain area of the zinc-aluminum-magnesium steel plate is Mg₂Zn₁₁When the content of (b) is more than 1%, the region appears as a black dot. That is, if Mg is present at any position in the Zn-Al-Mg steel sheet₂Zn₁₁If the mass content of the zinc-aluminum-magnesium alloy is less than 1 percent, no black spots can be generated, and the corrosion resistance, the hardness, the strength and the oxidation resistance of the zinc-aluminum-magnesium steel plate can be further ensured.

In particular, Mg at any part of the Zn-Al-Mg steel sheet₂Zn₁₁The mass content of the zinc-aluminum-magnesium alloy is less than 0.5%, so that black spots can be further prevented from forming, and the performance of the zinc-aluminum-magnesium steel plate is ensured.

Meanwhile, the proportion of the chemical components of the substrate and the coating can be controlled to ensure that Mg at any position in the zinc-aluminum-magnesium steel plate₂Zn₁₁Is less than 0.5 percent, and then the formation of black spots is reduced or even inhibited.

Further, the inventors found that MgZn is present at any portion of the zinc-aluminum-magnesium steel sheet₂Is more than 13 percent, preferably more than 15 percent, and the zinc-aluminum-magnesium steel plate has excellent performances of corrosion resistance, bonding strength, oxidation resistance and the like.

Furthermore, the grain size of the zinc-aluminum-magnesium steel plate is 8.5-12.0; preferably 10.0 to 11.0;

preferably, the zinc-aluminum-magnesium steel plate has the hardness of 150-250 HV.

The embodiment of the invention also provides a preparation method for effectively controlling the black spots on the surface of the CSP process hot-dip galvanized aluminum-magnesium steel plate, which is used for preparing the zinc-aluminum-magnesium steel plate. The zinc-aluminum-magnesium steel plate is produced by combining the CSP process and the continuous hot-dip coating process, so that the zinc-aluminum-magnesium steel plate has good surface quality, the formation of black spots is reduced or even inhibited, the attractiveness of the zinc-aluminum-magnesium steel plate is improved, and the performances of corrosion resistance, binding force, strength, oxidation resistance and the like of the zinc-aluminum-magnesium steel plate are also improved.

Specifically, S1, smelting;

smelting the raw materials for forming the substrate, and further smelting comprises: decarburization and deoxidation. The decarburization comprises the step of controlling the dissolved oxygen in the molten steel at the decarburization end point to be 500-650ppm, and the dissolved oxygen in the molten steel at the decarburization end point is controlled, so that the cleanliness is favorably controlled, the influence of impurities mixed in the molten steel on the surface of the substrate is reduced, the bonding force of a coating and the substrate is improved, and the formation of black spots can be reduced.

After decarburization, the carbon content in the molten steel is less than or equal to 0.045%, and the final carbon content after finishing smelting is less than or equal to 0.045%, the carbon content is controlled, the performance of the base plate can be further ensured, and then the performance of the zinc-aluminum-magnesium steel plate is ensured.

And (3) tapping after decarburization, strictly controlling slag discharge during tapping, adding 4-5Kg/t of synthetic slag into the tapped molten steel during tapping 1/3, adding 1.5-2Kg/t of lime into the steel, and carrying out ladle slag washing. The synthetic slag and lime are added, so that slag removal is facilitated, the performance of the substrate is guaranteed, subsequent deoxidation is facilitated, the formation of subsequent eutectic is facilitated, and the performances of corrosion resistance, oxidation resistance, strength and the like of the zinc-aluminum-magnesium steel plate are further improved. And the adopted synthetic slag is calcium-aluminum synthetic slag in the prior art.

Further, deoxidation is carried out after decarburization, wherein the deoxidation comprises aluminum deoxidation; when aluminum deoxidation is performed, a raw material containing at least one element of Nb, Ti and V is added to molten steel so that the substrate contains Nb: 0.015 to 0.025%, Ti: 0.030-0.075% and V: 0.020-0.080% of at least one; at this time, the raw material containing the chemical components is added to ensure the performance of the substrate.

Further, calcium treatment is carried out after deoxidation; the calcium treatment is to remove aluminum added during deoxidation, reduce the formation of impurities, ensure the flatness and cleanliness of the surface of the substrate, and then reduce the formation of subsequent black spots.

Preferably, before the calcium treatment, the deoxidized molten steel is kept stand for 5-8 minutes;

preferably, the weak blow is not less than 8min after the calcium treatment.

By adopting the calcium treatment method, the aluminum removal effect can be ensured, and the performance of the substrate can be further ensured.

Meanwhile, T.O is less than or equal to 30ppm in the whole smelting process, so that the influence of the endogenous non-metallic inclusions on the surface quality of the substrate is reduced, and the formation of subsequent black spots is reduced.

S2, CSP process;

and performing a CSP process after the smelting is finished, wherein the CSP process comprises a CSP continuous casting process and a CSP hot rolling process.

Specifically, the CSP continuous casting process has the following process conditions: the tundish temperature is 1540-; the slag inclusion caused by slag entrapment of the crystallizer can be reduced by controlling the process conditions, so that the influence of exogenous nonmetallic inclusion on the surface quality of the substrate is reduced, the possibility of black spot formation is reduced, and the binding force of the substrate and the coating is also ensured. Meanwhile, the stability and the heat flow ratio are controlled, the formation of cracks on the surface of the substrate can be prevented, and the performances of corrosion resistance, oxidation resistance, strength and the like of the zinc-aluminum-magnesium steel plate are further ensured.

Furthermore, the CSP continuous casting process adopts whole-process protection casting to prevent the secondary oxidation of molten steel, thereby ensuring the performance of the formed zinc-aluminum-magnesium steel plate.

The CSP hot rolling process is carried out after the CSP continuous casting process, and specifically, the process conditions of the CSP hot rolling process are as follows: the tapping temperature is 1160 +/-20 ℃, the finishing temperature is 890 +/-20 ℃, and the coiling temperature is 550 +/-20 ℃; two times of finish rolling are carried out in the CSP hot rolling process, and the reduction rates of the two times of finish rolling are respectively more than 45 percent and 43 percent; the thickness of the iron oxide is ensured to be less than or equal to 8um by controlling the CSP hot rolling process so as to reduce the pickling pressure, ensure the performance of the substrate, further reduce and inhibit the formation of black spots, and further ensure the performances of corrosion resistance, strength, oxidation resistance, aging resistance and the like of the zinc-aluminum-magnesium steel plate.

It should be noted that the number of finish rolling in the CSP hot rolling process is not limited to two, and may be 3, 4, 5, 6, etc., and it is only necessary to ensure that the reduction ratio of the finish rolling of the first two is within the above-mentioned required range, and then to ensure that the formed substrate has good properties, and further to ensure various properties of the zinc-aluminum-magnesium steel sheet. Meanwhile, the operations of the CSP continuous casting process and the CSP hot rolling process are conventionally known operations, and the present invention will not be described in detail.

S3, cold rolling;

the substrate formed by the CSP process is subjected to cold rolling, specifically, the cold rolling is a PLTCM cold rolling process, and the technological conditions of the PLTCM cold rolling process are as follows: the pickling temperature is 55-85 ℃, and the concentration of the emulsion is 1.5-3.0%; the cold rolling relative reduction rate is more than or equal to 55 percent.

By adopting the process conditions, the surface reflectivity of the cold-rolled substrate can be ensured to be more than or equal to 70%, the influence of residual oil and residual iron on the surface of the substrate on the adhesiveness of the coating can be effectively reduced, the binding force between the substrate and the coating is improved, the defects on the surface of the coating are reduced, and the formation of black spots can be reduced.

It should be noted that the CSP process may be followed by cold rolling, but it is within the scope of the present invention to perform the continuous hot-dip process directly without cold rolling.

S4, carrying out a continuous hot-dip process;

firstly, cleaning a cold-rolled substrate, specifically, cleaning the substrate by using alkali liquor; wherein the temperature of the alkali liquor is 50-70 ℃, and the mass concentration of the alkali liquor is 0.6-3.0%; the alkaline solution used is an aqueous solution of an alkali which is conventional in the prior art, such as an aqueous solution of sodium hydroxide, aqueous ammonia, aqueous potassium hydroxide, and the like.

The substrate is cleaned by the above conditions, so that the cleanness of the surface of the substrate before the coating is formed is ensured, the acting force between the coating and the substrate is further ensured, the surface performance of the zinc-aluminum-magnesium steel plate is also ensured, and the formation of black spots is reduced.

Carrying out heat treatment on the cleaned substrate; specifically, the heat treatment includes heating and cooling in this order; the substrate is directly heated to a proper temperature without heating and cooling, and the substrate is subjected to thermal treatment by heating and cooling in the embodiment of the invention, so that the substrate undergoes the processes of thermal expansion and cold contraction, the performance of the substrate is further improved, and the performance of the zinc-aluminum-magnesium steel plate is further improved.

Specifically, the heating comprises heating for 1-4 minutes at 650-750 ℃, so as to heat the substrate, reduce the temperature difference between the substrate and the molten liquid of the coating, ensure the binding force between the substrate and the coating, and improve the oxidation resistance, corrosion resistance, weather resistance and other properties of the zinc-aluminum-magnesium steel plate.

The cooling comprises heating at 600-720 ℃ for 0.5-3 min, then at 450-540 ℃ for 0.5-3 min, and finally at 460-550 ℃ for 0.5-3 min; by adopting the cooling mode, the temperature of the substrate can be gradually reduced, the substrate is ensured not to generate bubbling and other phenomena, the surface of the substrate is ensured to be smooth, the binding force of the substrate and the coating is further improved, and the performance of the zinc-aluminum-magnesium steel plate is favorably improved.

The heat treatment process is carried out in a vertical full radiant tube continuous annealing furnace.

Meanwhile, the raw materials for forming the coating are melted in a zinc pot to form molten liquid.

And then, reacting the substrate after the heat treatment with the molten liquid, wherein the temperature of the substrate is controlled before the substrate reacts with the molten liquid, so that the temperature of the substrate is 5-25 ℃ lower than that of the molten liquid, and the temperature difference between the substrate and the molten liquid is controlled, thereby avoiding the influence of the overlarge temperature difference on the coating.

The conditions of the continuous hot-dip plating process are as follows: the dew point temperature is-35 to-15 ℃, the reduction atmosphere is maintained, the belt speed is 40 to 150m/min, and the temperature fluctuation value of the molten liquid is +/-1 ℃ of the temperature of the zinc pot in the process of the action of the substrate and the molten liquid. The dew point is controlled, the reducing atmosphere is kept, the zinc ash is effectively controlled, and the zinc ash is prevented from being adhered to the surface of the substrate and oxidized on the surface.

The substrate is put into a zinc pot and reacts with the molten liquid in the continuous hot-dip coating process, and the specific operation is a conventional operation known in the art, and the inventor does not need to describe the operation in detail.

Substrate and fuseAfter the action of the molten liquid, the molten liquid is attached to the surface of the substrate, then the substrate is taken out and cooled, then the molten liquid is solidified and cooled, and then a coating is formed on the substrate, so that the zinc-aluminum-magnesium steel plate is obtained. However, the inventors have found that the cooling of the melt is effective on Mg₂Zn₁₁And MgZn₂Has a significant influence, in particular on the formation of Mg in the eutectic₂Zn₁₁And MgZn₂Has an important influence on the formation of small black spots.

By adopting the cooling mode provided by the embodiment of the invention for cooling, Mg can be effectively reduced₂Zn₁₁Can effectively control MgZn in binary or ternary eutectic structure₂The formation of the zinc-aluminum-magnesium steel plate can avoid Mg in binary or ternary eutectic structures in any area₂Zn₁₁Too high, in turn, can effectively reduce or inhibit the formation of black spots.

Specifically, the cooling process includes precisely controlling the cooling rate before the melt of the plating layer on the substrate is cooled to the freezing point.

Preferably, the cooling rate is from 5 to 35 ℃/S, preferably from 10 to 25 ℃/S;

when cooling, the cooling width is 5-20mm wider than the width of the substrate.

Preferably, the molten liquid is naturally cooled in air after being solidified;

preferably, the temperature of the zinc-aluminum-magnesium steel plate after air cooling is 5-20 ℃;

by adopting the mode for cooling, Mg can be effectively reduced₂Zn₁₁Reducing Mg in any region of the Zn-Al-Mg steel sheet₂Zn₁₁In turn, reduces or inhibits the formation of small black spots. Meanwhile, by adopting the cooling mode, Mg can be controlled₂Si is formed to improve the adhesion between the substrate and the zinc-aluminum-magnesium plating layer.

Further, the cooling medium is an inert gas, more preferably argon or nitrogen;

preferably, the purity of the gas is greater than or equal to 96%, preferably greater than or equal to 99%;

preferably, the pressure of the inert gas is 0.3 to 1.0MPa, preferably 0.4 to 0.8 MPa.

The cooling medium can prevent the problem of oxidation after plating caused by air or water vapor, so that the performance of a plating layer is ensured, and the performance of the zinc-aluminum-magnesium steel plate is ensured.

Meanwhile, by adopting the CSP process and the continuous hot coating process, Si in the substrate can be effectively controlled to be less than or equal to 0.05 percent, and the adhesiveness of the substrate and the zinc-aluminum-magnesium coating is further improved.

It should be noted that the invention only provides the key parameters in the preparation process, and when alloy raw materials are added to adjust the element content of the molten liquid, so that the methods of the finished product, such as the content of the substrate and the coating meeting the requirements, are the existing adding methods and time periods, and the invention is not detailed.