Alloyed hot-dip galvanized steel plate having good performance in zirconization pretreatment for coating, and manufacturing method therefor

Abstract

Disclosed in the present invention is an alloyed hot-dip galvanized steel plate having good performance in a zirconization pretreatment for coating. The steel plate comprises a substrate, on a surface of which an alloyed hot-dip galvanized layer is provided, wherein the surface of the alloyed hot-dip galvanized layer is covered with a composite nanostructure treatment layer. The composite nanostructure treatment layer comprises: nanoparticles and irregular nanostructures, wherein a micro-region potential difference formed between the nanoparticles and the alloyed hot-dip galvanized layer is 30-500 mv; and the irregular nanostructures have active groups for deposition and film formation, which active groups are selected from at least one of silane groups, carboxyl groups, amino groups, allyl groups and mercapto groups. Also disclosed in the present invention is a method for manufacturing the steel plate, the method comprising: performing hot dipping, an alloying heat treatment and flattening on a substrate, so as to form an alloyed hot-dip galvanized layer on the surface of the substrate; and performing a surface treatment on the alloyed hot-dip galvanized layer by using a water-based treating agent, so as to obtain a composite nanostructure treatment layer.

Description

Alloyed hot-dip galvanized steel sheet having excellent pretreatment performance for zirconium treatment before painting and method for manufacturing the same TECHNICAL FIELD

[0001] The present invention relates to a steel sheet and a method for manufacturing the same, and more particularly, to a zinc-plated steel sheet and a method for manufacturing the same. BACKGROUND

[0002] A phosphorus-free thin film zirconium treatment process (hereinafter referred to as "zirconium treatment process") realizes phosphorus-free wastewater discharge, energy consumption reduction, and significant environmental performance improvement compared to a conventional phosphating pretreatment process. However, since the zirconium treatment process has a film thickness of about 20-200 nm, which is nearly two orders of magnitude different from the film thickness (3-5 μm) of the conventional phosphating process, it poses new requirements for the surface characteristics of a vehicle body material.

[0003] A plated material for a vehicle body is prone to have problems such as insufficient film thickness, uneven crystallization, poor adhesion, and appearance defects in the process of phosphating or zirconium treatment before painting, and the occurrence of the above problems can significantly adversely affect the appearance and corrosion resistance of the vehicle body after painting.

[0004] In order to solve the above problems, the prior art mainly adjusts the alloyed plated layer composition and heat treatment process, for example:

[0005] A Chinese patent document with the publication number CN103814148A and the publication date of May 21, 2014, entitled "Alloyed hot-dip galvanized steel sheet having excellent corrosion resistance after painting" discloses an alloyed hot-dip galvanized steel sheet having excellent corrosion resistance after painting, which is characterized by having a zinc-plated layer containing Fe: 7-15%, Al: 0.02-0.30%, and the balance consisting of Zn and inevitable impurities on the surface of the steel sheet, and the exposed rate of the metal Zn on the surface of the zinc-plated layer is 20% or more.

[0006] A Chinese patent document with the publication number CN101583734 and the publication date of November 18, 2009, entitled "High-strength alloyed hot-dip galvanized steel sheet having excellent phosphate treatment properties" discloses an alloyed hot-dip galvanized steel sheet stably exhibiting good phosphate treatment properties, which is mainly directed to alloying hot-dip galvanizing of a high-strength substrate, and improves the phosphating performance by optimizing the elements in the plated layer.

[0007] However, the above scheme mainly controls the alloyed plated layer structure and surface composition to optimize the phosphate chemical conversion treatment performance, but does not mention the influence on the zirconium treatment pretreatment performance of the environmental protection zirconium thin film. SUMMARY

[0008] One of the purposes of the present application is to provide an alloyed hot-dip galvanized steel sheet with excellent zincate pre-treatment performance, which has good electrochemical reactivity and surface zincate treatment film forming efficiency, thereby optimizing the pre-treatment performance.

[0009] To achieve the above-mentioned purpose, the present application provides an alloyed hot-dip galvanized steel sheet with excellent zincate pre-treatment performance, which comprises a substrate, and an alloyed hot-dip galvanized layer on the surface of the substrate;

[0010] The surface of the alloyed hot-dip galvanized layer is covered with a composite nanostructure treatment layer; the composite nanostructure treatment layer comprises: nanoparticles and irregular nanostructures;

[0011] The micro-area potential difference between the nanoparticles and the alloyed hot-dip galvanized layer is 30-500 mV;

[0012] The irregular nanostructures have deposition film forming active groups, and the deposition film forming active groups are selected from at least one of silane groups, carboxyl groups, amino groups, allyl groups and mercapto groups.

[0013] The stamping lubrication processing performance of the alloyed hot-dip galvanized steel sheet of the present application comprises a substrate and an alloyed hot-dip galvanized layer on the surface of the substrate.

[0014] In the present application, the initial nucleation efficiency of the zirconiumization reaction is promoted by mainly constructing the electrochemical active sites through the micro-area potential difference between the nanoparticles and the surface of the plated layer, thereby improving the zirconiumization film forming performance. When the micro-area potential difference between the nanoparticles and the alloyed hot-dip galvanized layer is too low, it cannot play a role in promoting the nucleation active sites during the pre-treatment process before phosphating or zirconization, thereby achieving the effect of significantly optimizing the pre-treatment phosphating or zirconization performance before coating. When the micro-area potential difference between the nanoparticles and the alloyed hot-dip galvanized layer is too high, film forming unevenness is prone to occur during the pre-treatment process before phosphating or zirconization.

[0015] In the present application, the deposition film forming active groups are mainly used for the growth after nucleation.

[0016] In some embodiments, the chemical composition of the substrate is as follows: C: ≤0.12%, Si: ≤0.25%, Mn: ≤0.8%, P: ≤0.045%, S: ≤0.045%, Ti: ≤0.3%, and the balance is Fe and inevitable impurities.

[0017] In some embodiments, the chemical composition of the substrate satisfies at least one of the following:

[0018] C: 0.01%-0.12%;

[0019] Si: 0.05% to 0.25%;

[0020] Mn: 0.05% to 0.8%;

[0021] P: 0.005% to 0.045%;

[0022] S: 0.005% to 0.045%;

[0023] Ti: 0.01% to 0.3%.

[0024] In the present application, the galvannealed layer comprises Zn-Fe alloy phase.

[0025] Further, in the galvannealed steel sheet of the present application, the mass percentage of Fe element in the Zn-Fe alloy phase in the galvannealed layer is 7% to 12.5%.

[0026] In the present application, the presence of Fe on the surface of the coating can promote the phosphating or zirconizing reaction, thereby forming a more uniform and dense surface treatment effect. The change of the iron content in the coating will affect the nucleation and growth rate of the phosphating or zirconizing reaction. When the mass percentage of Fe element in the Zn-Fe alloy phase in the galvannealed layer is too low, it will be not conducive to the film forming efficiency of the phosphating and zirconizing reaction; when the mass percentage of Fe element in the Zn-Fe alloy phase in the galvannealed layer is too high, the brittle structure in the coating increases, the hardness rises, and the risk of poor coating adhesion and insufficient corrosion resistance is easy to occur. In some embodiments, the mass percentage of Fe element in the Zn-Fe alloy phase in the galvannealed layer can be further controlled to be 8% to 11%.

[0027] Further, in the galvannealed steel sheet of the present application, the galvannealed layer further contains Al element and at least one of Bi, Cd, Co, Ni, Sn elements.

[0028] Preferably, in the galvannealed steel sheet of the present application, the galvannealed layer further contains Al element and at least one of Bi, Co, Ni, Sn elements.

[0029] Further, in the galvannealed steel sheet of the present application, the mass percentage of Al element in the galvannealed layer is 0.03% to 0.2%.

[0030] In the present application, the Al element in the alloyed hot-dip galvanizing layer can improve the uniformity of the coating, and ensure the appearance quality of the product. When the mass percentage of Al element in the alloyed hot-dip galvanizing layer is too low, unevenness is prone to occur, which directly affects the consistency of the surface activity in the pre-treatment process before coating; when the mass percentage of Al element in the alloyed hot-dip galvanizing layer is too high, the surface brittleness of the alloyed hot-dip galvanizing layer will increase, and zinc powder peeling is prone to occur, thereby causing the risk of poor coating adhesion and insufficient corrosion resistance. In some embodiments, the mass percentage of Al element in the alloyed hot-dip galvanizing layer can be further controlled to be 0.08%-0.15%.

[0031] Further, in the alloyed hot-dip galvanizing steel plate described in the present application, the total mass percentage of Bi, Cd, Co, Ni, and Sn elements in the alloyed hot-dip galvanizing layer is not more than 0.1% (i.e. ≤0.1%).

[0032] Preferably, in the alloyed hot-dip galvanizing steel plate described in the present application, the total mass percentage of Bi, Co, Ni, and Sn elements in the alloyed hot-dip galvanizing layer is not more than 0.1% (i.e. ≤0.1%).

[0033] In the present application, Bi, Cd, Co, Ni, and Sn elements in the alloyed hot-dip galvanizing layer can be combined with the manufacturing process requirements to further optimize the hardness and uniformity of the coating.

[0034] Further, in the alloyed hot-dip galvanizing steel plate described in the present application, the surface of the alloyed hot-dip galvanizing layer has a zinc-iron alloy crystallization region and a randomly distributed platform region, and the area ratio of the zinc-iron alloy crystallization region in the unit area is 15%-85%.

[0035] In the present application, the platform region is formed by using a flattening roller to process the surface of the alloyed hot-dip galvanizing steel plate in the flattening step in the manufacturing method of the alloyed hot-dip galvanizing steel plate.

[0036] In the present application, the zinc-iron alloy crystallization region has a certain crystallinity and grain size, has good corrosion resistance, and provides more active sites through physical structure, which is helpful for the adsorption and reaction of the zirconiumizing agent. When the area ratio of the zinc-iron alloy crystallization region is too low, it is not conducive to the adhesion and stability of the zirconiumizing film, and there is a risk of reduced corrosion resistance of coating. When the area ratio of the zinc-iron alloy crystallization region is too high, when the area ratio of the zinc-iron alloy crystallization region is greater than 85%, the surface roughness of the zinc-iron alloy coating is high, which further affects the appearance quality of the coating.

[0037] Further, in the alloyed hot-dip galvanizing steel plate described in the present application, the equivalent spherical radius of the nanoparticles is 10-150 nm.

[0038] In the present application, when the equivalent spherical radius of the nanoparticles is too low, it is easy to cause uneven distribution of the particles on the surface, resulting in excessive zirconization or non-zirconization in some local areas, thereby reducing the uniformity of the zirconization layer. When the equivalent spherical radius of the nanoparticles is too high, it will cause the zirconizing agent to be unable to penetrate into the deep layer or small recesses of the metal surface, resulting in the inability to form a zirconization layer in the local area of the metal surface, thereby reducing the zirconization effect of the metal. In some embodiments, the equivalent spherical radius of the nanoparticles can be further controlled between 30-100 nm.

[0039] Further, in the galvannealed steel sheet according to the present application, the nanoparticles are randomly distributed on the surface of the galvannealing layer in a spherical form.

[0040] In the present application, the nanoparticles are distributed on the surface of the galvannealing layer. In some embodiments, the nanoparticles are randomly distributed on the surface of the galvannealing layer.

[0041] In the present application, at least a portion of the nanoparticles are in a spherical form.

[0042] The spherical nanoparticles can provide more effective reaction surface, thereby further increasing the contact area between the metal surface and the zirconizing agent, and being more conducive to the progress of the zirconization reaction.

[0043] Further, in the galvannealed steel sheet according to the present application, the spherical nanoparticles contain a metal-based compound, and the metal in the metal-based compound is selected from at least one of Fe, Cu, Sr, Ba, Mn, V, Ti, and Sn.

[0044] In the present application, Cu, Sr, Ba, Mn, V, Ti, and Sn mainly come from the water-based treatment agent, and Fe mainly comes from the steel sheet.

[0045] In the present application, the nanoparticles are also composed of non-metallic elements, which include one or more of Si, O, C, N, and H elements.

[0046] Further, in the galvannealed steel sheet according to the present application, the proportion of the spherical nanoparticles to the total number of nanoparticles in a unit area of the surface is 30%-80%.

[0047] In the present application, the needle-like particles and the spherical particles form a suitable number ratio, which can more fully play their physical riveting function. When the number ratio of the spherical nanoparticles to the total nanoparticles is too low, the needle-like particles are too much, and the uniformity of the coverage of the zirconization layer is prone to be non-uniform and the compactness is prone to be reduced, thereby affecting the adhesion of the electrophoretic paint film and the corrosion resistance of the coating; when the number ratio of the spherical nanoparticles to the total nanoparticles is too high, due to the relatively small surface area and the relatively high volume of the spherical particles, the phenomenon that the zirconization reaction rate promoting effect is not obvious in the zirconization reaction is likely to occur.

[0048] Further, in the galvannealed steel sheet described in the present application, the micro-area potential difference formed between the nanoparticles and the galvannealing layer is 80-400 mV.

[0049] Further, in the galvannealed steel sheet described in the present application, the mass percentage of the nanoparticles in the composite nanostructure treatment layer is 30%-70%.

[0050] In the present application, when the mass percentage of the nanoparticles in the composite nanostructure treatment layer is too low, the electrochemical reaction activity optimization is not significant, and the phosphating or zirconization film forming efficiency before coating is affected; when the mass percentage of the nanoparticles in the composite nanostructure treatment layer is too high, the electrochemical reaction activity is too high, which increases the risk of non-uniform phosphating or zirconization film forming before coating.

[0051] Further, in the galvannealed steel sheet described in the present application, the mass percentage of the deposition film forming active group (referred to as active group) in the irregular nanostructure is 10%-75%.

[0052] In the present application, when the mass percentage of the active group in the irregular nanostructure is too high, too many active groups are prone to cause the phosphating or zirconization film forming rate before coating to be too fast or non-uniform, thereby affecting the quality and stability of the zirconization film; when the mass percentage of the active group in the irregular nanostructure is too low, too few active groups cannot achieve the effect of promoting the film forming reaction rate, resulting in insufficient film forming efficiency and incomplete film forming, thereby affecting the adhesion and corrosion resistance of the coating film.

[0053] Another object of the present application is to provide a manufacturing method of a galvannealed steel sheet, which conveniently and economically obtains a galvannealed steel sheet with excellent zirconization pretreatment performance for coating by performing hot dipping, galvannealing heat treatment and leveling on a substrate and performing surface treatment.

[0054] In order to achieve the above object, the present application provides a manufacturing method of a galvannealed steel sheet, which comprises the steps of:

[0055] hot-dip plating, alloying heat treatment and leveling are performed on the substrate to form the alloyed hot-dip galvanizing layer on the surface of the substrate;

[0056] The alloyed hot-dip galvanizing layer is surface treated by using a water-based treatment agent to obtain the composite nano-structure treatment layer.

[0057] Further, in the manufacturing method, the water-based treatment agent comprises a first substance providing a metal-based compound and a second substance providing a deposition film-forming active group, and the mass ratio of the first substance to the second substance is 2:1 to 1:8.

[0058] Further, in the manufacturing method, the mass content of the first substance in the water-based treatment agent can be 0.5% to 10%, and the mass content of the second substance in the water-based treatment agent can be 2% to 10%.

[0059] Further, in the manufacturing method, the first substance is selected from at least one of manganese nitrate, silver nitrate, sodium fluorotitanate, ammonium fluorotitanate, potassium fluorotitanate, copper nitrate, strontium nitrate, barium nitrate, vanadyl oxalate, ammonium vanadate, vanadium acetate, stannous chloride, tin nitrate, tin citrate, and tin acetate.

[0060] Further, in the manufacturing method, the second substance is selected from at least one of 3,4,5-trihydroxybenzoic acid, ethylenediaminetetraacetic acid, citric acid, oxalic acid, salicylic acid, tartaric acid, tannic acid, cysteine, mercaptoacetic acid, mercaptomethanol, mercaptoethanol, polyethyleneimine, glycine, aspartic acid, ammonia, ethanolamine, propanolamine, isopropanolamine, ethylsilanol, and propenylsilanol.

[0061] In some embodiments, in the manufacturing method, the chemical composition of the zinc liquid used for hot-dip plating satisfies that the mass percentage of Al is 0.02% to 0.3%, the mass percentage of Bi is 0 to 0.03%, the mass percentage of Co is 0 to 0.03%, the mass percentage of Ni is 0 to 0.08%, the mass percentage of Sn is 0 to 0.08%, and the rest is Zn and inevitable impurities.

[0062] Further, in the manufacturing method, the temperature of the alloying heat treatment is 470 to 570℃.

[0063] Further, in the manufacturing method, the water-based treatment agent is coated on the alloyed hot-dip galvanizing layer in a manner of roll coating, spraying or dip coating to perform surface treatment, and then dried by blowing or drying.

[0064] The alloyed hot-dip galvanizing steel plate with excellent pretreatment performance before zirconium coating and the manufacturing method thereof have the following characteristics and beneficial effects:

[0065] The alloyed hot-dip galvanized steel sheet with excellent pre-treatment performance for coating zirconium treatment described in this invention has good electrochemical reactivity and high efficiency in surface zirconium treatment film formation, thereby optimizing the pre-treatment performance for coating.

[0066] The surface treatment layer of the alloyed hot-dip galvanized steel sheet with excellent pretreatment performance before coating zirconium coating described in this invention is environmentally friendly and phosphorus-free, avoiding the negative environmental impact of phosphorus-containing surface chemical treatments and exhibiting higher environmental friendliness.

[0067] The manufacturing method of the alloyed hot-dip galvanized steel sheet with excellent pretreatment performance for coating zirconium coating described in this invention is convenient and economical, and can reduce production costs. Detailed Implementation

[0068] The following will further explain and illustrate the alloyed hot-dip galvanized steel sheet with excellent pretreatment performance for coating zirconium coating and its manufacturing method according to the present invention, with reference to specific embodiments. However, this explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0069] Examples 1-7 and Comparative Examples 1-3

[0070] The alloyed hot-dip galvanized steel sheets of Examples 1-7 of this invention were all prepared by the following method:

[0071] (1) Obtaining the substrate: The substrate used in Examples 1-7 and Comparative Examples 1-3 of this invention is DC53D+ZF (Baosteel) with a thickness of 0.7 μm.

[0072] Table 1 lists the chemical composition ratios of the substrates used in Examples 1-7 and Comparative Examples 1-3 of the present invention.

[0073] Table 1. (The balance is Fe and other unavoidable impurities)

[0074] (2) The substrate is subjected to hot-dip galvanizing, alloying heat treatment and flattening to form an alloyed hot-dip zinc plating layer on the substrate surface.

[0075] Cold-rolled strip steel is hot-dip galvanized by immersing it in molten zinc in a hot-dip galvanizing pot, with a coating thickness of 45 g / m. 2 Then, the steel plate is heated to 470-570℃ in a vertical heat treatment furnace for alloying heat treatment, and then held for 2-8 seconds to allow the steel plate substrate to react and diffuse with liquid zinc, transforming into Fe-Zn intermetallic compounds, thereby forming an alloyed hot-dip galvanized layer on the substrate surface; then, a leveling process is performed using leveling rollers.

[0076] Table 2-1 lists the chemical composition of the zinc solutions in Examples 1-7 and Comparative Examples 1-3 of the present invention.

[0077] Table 2-1 (wt%, the balance being Zn and unavoidable impurities)

[0078] Table 2-2 lists the chemical composition contents in the galvannealed layers of the galvannealed steel sheets of Examples 1-7 and Comparative Examples 1-3 of the present application and the process parameters.

[0079] Table 2-2. Note: (1) In Table 2, the mass percentage content of Fe element in the Zn-Fe alloy phase was measured by X-ray fluorescence spectroscopy; (2) In Table 2, the mass percentage contents of Al, Bi, Co, Ni and Sn elements in the galvannealed layer were measured by inductively coupled plasma optical emission spectrometry / mass spectrometry (ICP-OES / MS); (3) In Table 2, the area ratio of the zinc-iron alloy crystallization region was obtained by randomly selecting 1 cm2of the region in the photograph, identifying the platform region by an image processing program and calculating the area ratio. 2

[0080] (3) The galvannealed layer was surface treated by using a water-based treatment agent to obtain a composite nano-structured treatment layer.

[0081] The water-based treatment agent comprises a first substance providing a metal-based compound and a second substance providing a deposition film-forming active group.

[0082] The first substance providing a metal element is selected from at least one of manganese nitrate, silver nitrate, sodium fluorotitanate, ammonium fluorotitanate, potassium fluorotitanate, copper nitrate, strontium nitrate, barium nitrate, vanadyl oxalate, ammonium vanadate, vanadium acetate, stannous chloride, tin nitrate, tin citrate, and tin acetate.

[0083] The second substance providing a deposition film-forming active group is selected from at least one of 3,4,5-trihydroxybenzoic acid, ethylenediaminetetraacetic acid, citric acid, oxalic acid, salicylic acid, tartaric acid, tannic acid, cysteine, mercaptoacetic acid, mercaptomethanol, mercaptoethanol, polyethyleneimine, glycine, aspartic acid, ammonia, ethanolamine, propanolamine, isopropanolamine, ethylsilanol, and propenylsilanol.

[0084] The water-based treatment agent is composed of the first substance, the second substance, and water.

[0085] The water-based treatment agent is applied to the steel strip by roll coating, spraying, or dip coating, and then dried by blowing or baking to form a film.

[0086] Comparative Examples 1 and 2 also used the above steps, but the specific parameters did not meet the present application. Comparative Example 3 also used the same substrate as the examples of the present application and performed steps (1) and (2), but did not perform step (3). ​

[0087] Table 3 lists the ingredient composition of the water-based treatment agent for the galvannealed steel sheet of Examples 1-7 and Comparative Examples 1-3 of the present application and the coating process, and the values in the brackets after the ingredients are the mass percentage of the ingredient in the water-based treatment agent.

[0088] Table 3.

[0089] Table 4 lists the characteristics of the composite nanostructure treatment layer of the galvannealed steel sheet of Examples 1-7 and Comparative Examples 1-3 of the present application.

[0090] Table 4. Note: (1) The equivalent spherical radius of the nanoparticles is observed and measured by high-resolution scanning electron microscopy; (2) The metal type of the metal-based compound is detected by energy dispersive spectroscopy (EDS); (3) The proportion of spherical nanoparticles in the total number of nanoparticles is evaluated by the proportion of the number of particles per unit area (e.g., 1 mm 2 ) to the total number of particles; (4) The micro-area potential difference between the nanoparticles and the galvannealing layer is measured by scanning electrochemical microscopy (SECM); (5) The mass percentage of the nanoparticles in the composite nanostructure treatment layer is calculated by combining the composition and volume percentage of the nanoparticles and the thin film, which are determined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic absorption spectroscopy (AAS), respectively, and the density of the composition and volume percentage; (6) The type of active group and the mass percentage of the active group in the irregular nanostructure are measured by weighing the surface composite nanostructure film before and after applying the water-based treatment agent, detecting the content of the two active groups, i.e., the N element in the amino group and the characteristic chemical bond in the carboxyl group, by X-ray photoelectron spectroscopy (XPS), and calculating the mass percentage of the active group by the following formula: (amino group mass + carboxyl group mass) / composite nanostructure layer mass * 100%.

[0091] The galvannealed steel sheets of Examples 1-7 and Comparative Examples 1-3 were processed into a size of 75*150 mm.

[0092] To verify the implementation effect of the examples of the present application, the galvannealed steel sheets of Examples 1-7 and Comparative Examples 1-3 were subjected to the processes of degreasing, water washing, zirconization, water washing, and electrophoresis according to the zirconization pretreatment process of the coating film, and the selected degreasing agent was Pakase FC2011, the zirconization treatment agent was Pakase 2000 series product, and the electrophoretic paint was electrophoretic paint Basf series product.

[0093] Table 5 lists the specific process parameters of the zirconization pretreatment process of the coating film of Examples 1-7 and Comparative Examples 1-3 of the present application.

[0094] Table 5.

[0095] Then, the hot-dip galvannealed steel sheet of Examples 1-7 and Comparative Examples 1-3 was subjected to a coating film zirconization pretreatment performance evaluation before painting, and the evaluation results are listed in Table 6. Among them:

[0096] Zirconization film thickness evaluation: The film thickness test was performed by surface element detection using an X-ray fluorescence spectrometer (XRF), and the relationship curve between the peak strength of the characteristic element and the film weight was established by a physical weighing method. The detection results were converted into weight data (unit: mg / m 2 ).

[0097] Electrophoresis after surface paint film adhesion performance evaluation: The specific method refers to standard ISO 2409, and the paint film adhesion (percentage) is evaluated by a cross-hatch test.

[0098] Table 6 lists the performance evaluation results of Examples 1-7 and Comparative Examples 1-3 according to the present application.

[0099] Table 6.

[0100] The symbols in the zirconization film thickness evaluation in Table 6 are explained as follows:

[0101] ◎: 60≤zirconization treatment film weight

[0102] O: 40≤zirconization treatment film weight<60

[0103] Δ: 20≤zirconization treatment film weight<40

[0104] X: zirconization treatment film weight<20

[0105] The symbols in the zirconization film thickness evaluation in Table 6 are explained as follows:

[0106] ◎: paint film adhesion ratio = 100%

[0107] O: 90%≤paint film adhesion ratio<100%

[0108] Δ: 80%≤paint film adhesion ratio<90%

[0109] X: paint film adhesion ratio<80%

[0110] From the above Table 6, it can be seen that the zirconization film performance of the hot-dip galvannealed steel sheet of Examples 1-7 is good in terms of zirconization film thickness and surface paint film adhesion performance after electrophoresis.

[0111] From the comparative example 1, it can be seen that the micro-area potential difference between the electrochemically reactive nanoparticles and the plating layer in the composite nanostructure treatment layer is too high, and the zirconium film thickness is insufficient and uneven, and the adhesion of the electrophoretic paint film is deteriorated.

[0112] From the comparative example 2, it can be seen that the micro-area potential difference between the electrochemically reactive nanoparticles and the plating layer in the composite nanostructure treatment layer is too low, and the zirconium film thickness is too thin, and the adhesion of the surface paint film after electrophoresis is deteriorated.

[0113] From the comparative example 3, it can be seen that since it does not have a composite nanostructure, the zirconium film thickness and the adhesion of the surface paint film after electrophoresis are both insufficient.

[0114] It should be noted that the above listed examples are only specific embodiments of the present application. Obviously, the present application is not limited to the above examples, and similar changes or modifications made in accordance with the disclosure of the present application are directly derived or easily conceived by those skilled in the art, and should all belong to the protection scope of the present application.

Claims

1. A galvannealed steel sheet having excellent pretreatment performance for painting before zirconium coating, comprising a base plate having a galvannealed layer on the surface thereof; characterized in that: the surface of the galvannealed layer is covered with a composite nanostructure treatment layer; the composite nanostructure treatment layer comprises: nanoparticles and irregular nanostructures; wherein the micro-area potential difference between the nanoparticles and the galvannealed layer is 30-500 mV; wherein the irregular nanostructures have deposition film-forming active groups selected from at least one of silane groups, carboxyl groups, amino groups, allyl groups, and mercapto groups. The galvannealed layer comprises Zn-Fe alloy phases, and the mass percentage of Fe in the Zn-Fe alloy phases in the galvannealed layer is 7%-12.5%. The galvannealed layer further contains Al and at least one of Bi, Co, Ni, and Sn. Preferably, the mass percentage of Al in the galvannealed layer is 0.03%-0.2%.

2. The galvannealed steel sheet according to claim 1, characterized in that, Preferably, the total mass percentage of Bi, Co, Ni, and Sn in the galvannealed layer is not more than 0.1%.

3. The galvannealed steel sheet according to claim 2, characterized in that, The surface of the galvannealed layer has zinc-iron alloy crystalline regions and randomly distributed platform regions, and the area ratio of the zinc-iron alloy crystalline regions in unit area is 15%-85%. The equivalent spherical radius of the nanoparticles is 10-150 nm. The nanoparticles are randomly distributed on the surface of the galvannealed layer in at least a spherical form.

4. The galvannealed steel sheet according to claim 1, characterized in that, The spherical nanoparticles contain metal-based compounds, and the metal in the metal-based compounds is selected from at least one of Fe, Cu, Sr, Ba, Mn, V, Ti, and Sn.

5. The galvannealed steel sheet according to claim 1, characterized in that, In unit area of the surface, the number ratio of the spherical nanoparticles to the total number of nanoparticles is 30%-80%.

6. The galvannealed steel sheet according to claim 1, characterized in that, The micro-area potential difference between the nanoparticles and the galvannealed layer is 80-400 mV.

7. The galvannealed steel sheet according to claim 6, characterized in that, The mass percentage of the nanoparticles in the composite nanostructure treatment layer is 30%-70%.

8. The galvannealed steel sheet according to claim 6, characterized in that, The mass percentage of the active groups in the irregular nanostructures is 10%-75%.

9. The galvannealed steel sheet according to claim 1, characterized in that, The method comprises the steps of: hot-dip plating, galvannealing heat treatment, and leveling on the base plate to form the galvannealed layer on the surface of the base plate; and surface treatment of the galvannealed layer with a water-based treatment agent to obtain the composite nanostructure treatment layer.

10. The galvannealed steel sheet according to claim 1, characterized in that, The water-based treatment agent comprises a first substance providing metal-based compounds and a second substance providing deposition film-forming active groups, and the mass ratio of the first substance to the second substance is 2:1 to 1:

8.

11. The galvannealed steel sheet according to claim 1, characterized in that, Preferably, the first substance is selected from at least one of manganese nitrate, silver nitrate, sodium fluorotitanate, ammonium fluorotitanate, potassium fluorotitanate, copper nitrate, strontium nitrate, barium nitrate, vanadyl oxalate, ammonium vanadate, vanadium acetate, stannous chloride, tin nitrate, tin citrate, and tin acetate.

12. The method of producing a galvannealed steel sheet according to claim 1, characterized by, ​ ​ ​ 13. The production method according to claim 12, wherein ​ ​ Preferably, the second substance is selected from at least one of 3,4,5-trihydroxybenzoic acid, ethylenediaminetetraacetic acid, citric acid, oxalic acid, salicylic acid, tartaric acid, tannic acid, cysteine, mercaptoacetic acid, mercaptomethanol, mercaptoethanol, polyethyleneimine, glycine, aspartic acid, ammonia, ethanolamine, propanolamine, isopropanolamine, ethylsilanol, propenylsilanol.

14. The production method according to claim 12, wherein The temperature of the alloying heat treatment is 470-570°C.

15. The production method according to claim 12, wherein The water-based treatment agent is applied to the galvannealed layer by roll coating, spraying or dip coating, and then dried by blowing or baking to form a film.

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