JPH04337099A - High corrosion resistant surface treated steel sheet excellent in impact resistance and adhesion - Google Patents

Abstract

PURPOSE:To improve the impact resistance and adhesion of a steel sheet by successively laminating a Zn-Ni alloy plated thin base layer (A layer) in which fine cracks are present, plural Zn-Ni alloy plated layers (B and C layers) with different Ni content, a chromated layer (D layer) and a protective resin film layer (E layer) on the surface of a steel sheet under specified conditions. CONSTITUTION:At least on one side of a steel sheet, multiple layers of a Zn-Ni alloy plated thin base layer (A layer) in which fine cracks having 0.01 to 0.5mum crack width as well as 10 to 60% crack areal fraction and having no directional properties are present, 10 to 50g/m<2> Zn-Ni alloy plated layer (B layer) having <=13wt.% Ni content, 0.5 to 20g/m<2> Zn-Ni alloy plated layer (C layer) having 10 to 40wt.% Ni content, a D layer having 30 to 300mg/m<2> Cr content and 0.2 to 2.0mu E layer are successively formed. Furthermore, the Ni content in the A layer is regulated to 1.2 to 5 times that in the B layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a highly corrosion-resistant surface-treated steel sheet that has excellent impact adhesion, process adhesion, and corrosion resistance of the plating film, and exhibits excellent performance when applied to, for example, automobile steel sheets. be.

0002

[Prior art and its problems] In recent years, the corrosion resistance of automotive steel sheets (
The requirements for pitting corrosion resistance and external rust resistance have become more sophisticated over the years, and the conventionally used "simple cold-rolled steel sheets" have been replaced by "galvanized steel sheets" and "zinc-based alloy plated steel sheets." ” is becoming more common.

However, in environments where there is a tendency to come into contact with corrosive substances, such as areas where rock salt is sprayed to prevent roads from freezing in the winter, even when plated steel sheets such as those described above are used, the coating may not adhere to the plate. It has been pointed out that sufficient corrosion resistance cannot be obtained unless the amount is excessive. However, when the amount of plating is increased, the plating layer tends to peel off in powder form (powdering) and peel off (flaking) during press processing, resulting in a problem that press workability is significantly hindered. .

[0004] In order to solve these problems, a metal-organic multilayer coated steel sheet has been devised, in which a plated steel sheet is subjected to chromate treatment and anti-rust coating. However, the proposal in the initial process was "rust-proof steel plate with zinc-rich coating" as seen in Japanese Patent Publication No. 45-24230.
However, the level of improvement in corrosion resistance was not yet sufficient, and there was a problem that the Zn powder contained in the coating film peeled off during press processing, making it impossible to improve powdering resistance to the desired level. .

[0005] Subsequently, a multi-layer coated steel sheet was proposed in which two layers of a chromate film and an organic composite silicate film were applied to a zinc-plated steel sheet (Japanese Unexamined Patent Application Publication No. 1983-1999).
108212, JP-A-58-224174, JP-A-60-174879, etc.). However, although these multi-layer coated steel sheets do not contain metal powder such as Zn powder in the coating film, and their powdering resistance is greatly improved, they still do not have the corrosion resistance required for current automotive steel sheets. It wasn't up to the level.

[0006] For these reasons, recently, in addition to research on improving the properties of chromate films and organic films, various studies have been conducted to further improve the properties of the zinc-plated steel sheet itself, which is the bottom layer. It has started to be done from a viewpoint. As a result, for example, the Ni content is 9 to 9.
20% (Hereinafter, percentages representing component ratios are weight percentages)
A surface-treated steel sheet with a chromate treatment layer and a conductive paint layer on Ni-Zn (γ layer) alloy plating (Japanese Patent Laid-Open No. 58
-210192), a surface-treated steel sheet in which a Fe-Zn alloy plating layer with an Fe content of 10 to 40%, a chromate treatment layer, and a conductive pigment layer are layered on a γ-phase Ni-Zn alloy plating layer. (Japanese Unexamined Patent Publication No. 58-210190), a surface-treated steel sheet in which a chromate treatment layer and a polymer coating layer are multilayered on a Ni-Zn alloy plating layer with a Ni content of 1 to 3% (Japanese Unexamined Patent Publication No. 58-210190). No. 61-84381) have been proposed.

Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 63-203778, Si, A, etc. are added during Zn or Zn alloy plating.
A surface treatment that improves the characteristics of the plating film itself by dispersing fine particles of 5 μm or less such as oxides, carbides, and nitrides, and forms a chromate treatment layer and an organic coating on the plating surface. Steel plates have also been proposed.

[0008] It is true that these technologies have made it possible to secure steel sheets that exhibit even better corrosion resistance, but the "corrosion resistance" improved by the above-mentioned technologies does not primarily mean "porosity resistance." According to studies conducted by the present inventors, it has become clear that each of the surface-treated steel sheets described above does not necessarily have sufficient performance as a steel sheet for automobiles in terms of "external surface rust resistance." Here, "external rust resistance" refers to the performance that indicates the "resistance of the paint film to blistering, etc." that occurs when the paint film on the outer surface of an automobile is damaged by stone chips, scratches, etc. Needless to say.

[0009] Of course, various proposals have been made for plated steel sheets that aim at external rust resistance, but even in such cases, it is important to have both external rust resistance and hole resistance, and in addition to these, press processing. At present, a surface-treated steel sheet that fully satisfies the properties has not yet been found.

[0010] For this reason, the purpose of the present invention is, of course, to exhibit sufficient "porosity resistance";
It also has excellent "external rust resistance" including resistance to plating peeling off due to stone chips, etc. (low temperature chipping resistance: impact resistance adhesion).
Furthermore, the objective was to realize a highly corrosion-resistant surface-treated steel sheet that has good "press workability" and is fully satisfactory as a steel sheet for automobiles.

[0011]

[Means for Solving the Problems] The present invention has been completed based on the research results of the present inventors through repeated numerous experiments in order to achieve the above object.
As shown in Fig. 1, A) Zn has non-directional "microcracks" with a crack width of 0.01 to 0.5 μm and a crack density of 10 to 60% as a crack area fraction on at least one side of the steel plate. - Ni-based alloy plated thin base layer, B) Zn-N with Ni content of 13% by weight or less
Plated layer of i-based alloy: 10-50 g/m2, C) Plated layer of Zn-Ni-based alloy with Ni content of 10-40% by weight: 0.5-20 g/m2, D) Chromate treated layer: Cr amount is 30-300mg/
m2, E) Protective resin film layer: 0.2-2.0μ
The major feature is that a surface-treated steel sheet with excellent external rust resistance including impact resistance adhesion, hole resistance, and press workability has been realized by providing multiple layers of m, in this order. In addition, ``As shown in Figure 2, on at least one side of the steel plate,
Non-directional with a crack width of 0.01 to 0.5 μm and a crack density of 10 to 60% in terms of crack area fraction.
A thin base layer of Zn-Ni alloy plating in which "microcracks" exist, and on one side of the steel plate a) a plating layer of Zn-Ni alloy with a Ni content of 13% by weight or less: 10 to 50 g; /m2, b) Plating layer of Zn-Ni alloy with a Ni content of 10 to 40% by weight: 0.5 to 20 g/m2, multi-layered in this order, and then sufficiently coated. A) Plating layer of Zn-Ni alloy with Ni content of 13% by weight or less: 10 to 50 g/m2, b) Ni content of 10 to 40% by weight on the other surface excluding one intended surface Plating layer of Zn-Ni alloy: 0.5 to 20 g/m2, c) Chromate treatment layer: Cr amount of 30 to 300 mg/m2
m2, d) Protective resin film layer: 0.2 to 2.0μ
Another feature is that we have created a surface-treated steel sheet with excellent external rust resistance, including impact resistance and adhesion, hole resistance, and press workability by providing multiple layers of m, in this order. There is.

[0012] Here, the above-mentioned "Zn-Ni alloy (those forming a thin base layer with microcracks, those forming a plating layer with a Ni content of 13% or less, and those forming a plating layer with a Ni content of 10 to 40%) The term ``all three of those constituting the plating layer'' means not only the Zn-Ni alloy, but also those containing Co, a well-known corrosion resistance improving element, in a range of 0.3% or less, and `` Zn-Ni with Ni content of 13% or less
Z alloy with substantially zero Ni content
This also includes n metals.

Further, the above-mentioned "chromate treatment layer" may be formed by any of the known electrolytic chromate treatment, coating type chromate treatment, or immersion type chromate treatment.

The resin composition of the "protective resin film layer" may be epoxy resin, polyester resin, melamine resin, vinyl resin, styrene resin, acrylic resin, polyurethane resin, phthalic acid resin, etc. alone or modified. Known pigments containing anticorrosive pigments such as BaCrO4, coloring pigments such as Fe2O3, or pigments such as SiO2 may be used.

By the way, the highly corrosion-resistant surface-treated steel sheet according to the present invention can be manufactured as follows. That is,
As shown in FIG. 3, first, a Zn-Ni alloy (preferably Ni content of 13
% Zn-Ni alloy) plating 0.1~5g/m
2, and then electroless immersion in an acid solution such as a Zn-Ni alloy plating solution or anodic electrolysis in an electrolytic solution to preferentially dissolve the Zn in the plating film. By doing so, microcracks without directionality are generated in the extremely thin plating film, resulting in a plating base treatment layer with a relatively high Ni content. Next, the first and second layers are electroplated using the same electrolytic treatment operations as in the production of ordinary Zn-Ni alloy plated steel sheets, followed by the usual chromate treatment and application of a protective resin film. implement.

[0016]Next, the reason why the composition of the plating layer, the plating weight, etc. in the highly corrosion-resistant surface-treated steel sheet of the present invention is numerically limited as described above will be explained in detail, together with the effect thereof.

[Function] (a) Zn-Ni alloy plating base layer Zn-
The Ni-based alloy plating thin base layer is applied to improve the adhesion of the plating and to improve the impact resistance and processing adhesion of the plating film. These microcracks in the thin base layer play an extremely important role in improving plating adhesion through the anchor effect, but the width of the microcracks is 0.0
If the thickness is less than 1 μm, even if an upper layer of Zn-Ni alloy is plated thereon, the plating will not reach inside the crack, making it impossible to obtain good plating adhesion. On the other hand, if the width of the microcracks exceeds 0.5 μm, the above-mentioned effect as an underlayer cannot be obtained, and no improvement in plating adhesion can be expected. Therefore, the width of the micro crack in the underlying layer is 0.01
~0.5 μm.

[0017] The width of micro cracks can be easily adjusted by adjusting the time of immersion in an acid solution (plating solution, etc.) or the time of anodic electrolysis treatment in an acid solution after initial thin plating. .

FIG. 4 is a graph showing the relationship between the width of microcracks existing in the base layer and the impact resistant adhesion of the two-layer Zn-Ni alloy plating applied thereon. It can also be seen that the impact resistance adhesion decreases rapidly even when the width of the microcracks is less than 0.01 μm and exceeds 0.5 μm.

Furthermore, the density of microcracks in the underlayer has a great influence on the improvement of plating adhesion, but if the density is less than 10% in terms of area fraction, the Zn formed on the underlayer will
- Since the area in which the Ni-based alloy plating penetrates between the cracks is small, a sufficient anchoring effect cannot be obtained, and the desired impact-resistant adhesion improvement effect cannot be obtained. On the other hand, when the density of microcracks exceeds 60% in terms of area fraction, the effect of surface treatment cannot be obtained and no contribution is made to improving adhesion. Therefore, the density of microcracks is 1
It was set as 0 to 60%.

[0020] This micro-crack density also increases as the time of immersion in an acid solution (plating solution, etc.) or the time of anodic electrolytic treatment in an acid solution increases after the initial thin plating. %, it is sufficient to adjust the amount of dissolution during immersion of the initial plating film in acid solution or during anodic electrolysis treatment in acid solution.

FIG. 5 is a graph showing the relationship between the density of microcracks existing in the base layer and the impact resistance adhesion of the two-layer Zn-Ni alloy plating applied thereon.
It can also be seen from the above that the impact resistant adhesion rapidly decreases when the density of the microcracks is less than 10% or more than 60% in terms of the area fraction of the cracks.

[0022] In order to ensure better plating adhesion, the length of the microcracks can be reduced to 10 μm by adjusting the processing conditions such as the melting time of the initial plating.
It is preferable to regulate it as follows (However, since cracks are generally branched, "crack length" here means "the length along the crack between the crack branching points") ).

Furthermore, the width and density of the microcracks in the underlayer are closely related to the "amount of Zn dissolved by non-current immersion", in other words, the "Ni content of the film after non-current immersion", so they can be directly determined. By controlling the Ni content of the thin underlayer, the impact-resistant adhesion can be improved as a result, even if the crack situation is not controlled.

[0024]The Ni content of this thin base layer is also related to the "Ni content of the plating layer immediately above it" and affects the plating adhesion, so it is important to note that from the perspective of ensuring better adhesion, It can be said that it is preferable that the "Ni content of the base layer" is 1.2 to 5 times the "Ni content of the plating layer directly above it."

By the way, the "impact adhesion" shown in FIGS. 4 and 5 was evaluated as follows. That is,
First, in accordance with the impact adhesion test specified in ASTM D-3170-74, a 150 mm x 100 mm steel plate test piece was coated with 3 coats for automobiles (total film thickness: 100 mm).
A gravel chipping test was carried out on the plated material (μm) at a low temperature of -20°C, and the results were 4...Good, no plating peeled off, 3...Plating peeling area rate less than 0.2%, 2...Plating peeling area rate. was 0.2% or more and less than 1%, 1...The rate of peeled area of plating was 1% or more.

(b) Lower layer (first layer) plating layer The first layer of the multilayer surface-treated steel sheet according to the present invention has a Ni content in order to ensure sufficient external rust resistance and pitting resistance. Zn-Ni alloy plating containing 13% or less (including pure Zn plating) or alloy plating containing 0.3% or less Co is applied, but if the Ni content of the Zn-Ni alloy is 13
If it exceeds %, the external rust resistance will be poor, and the corrosion of the base steel plate will be accelerated due to the local battery action of Ni residue generated as corrosion progresses.

Furthermore, if the basis weight of the first layer Zn-Ni alloy plating is less than 10 g/m2, the effect of improving the external rust resistance and pitting resistance is not sufficient;
If it exceeds m2, it will not be possible to secure an improvement effect commensurate with the cost increase. Therefore, the basis weight of the first layer Zn--Ni alloy plating was limited to 10 to 50 g/m2.

(c) Upper layer (second layer) plating layer In the multilayer surface-treated steel sheet according to the present invention, the Ni content is 10 to 40% in order to ensure the desired hole resistance and press sliding properties.
Zn-Ni alloy plating" or alloy plating containing 0.3% or less of Co is applied as the second layer. In this case, the Ni content of the Zn-Ni alloy that is the second layer is 10 If it is less than %, the press slidability will deteriorate, and if there is no resin coating, problems of cracking and galling of the steel plate will occur, and sufficient hole resistance cannot be ensured.On the other hand, the Ni If the content exceeds 40%, the external rust resistance will become poor, and as corrosion progresses, the corrosion of the base steel plate will be accelerated, and the perforation resistance will deteriorate further. No improvement will be seen.

[0029] Also, when the basis weight of the second layer Zn-Ni alloy plating is less than 0.5 g/m2, sufficient hole resistance and press sliding properties cannot be ensured; If it exceeds 20 g/m2, it will not be possible to secure an improvement effect commensurate with the cost increase, so the second layer Zn-N
The basis weight of the i-based alloy plating was limited to 0.5 to 20 g/m2.

(d) Chromate treatment layer If the amount of the chromate treatment layer formed is less than 30 mg/m2 based on the amount of Cr, the desired porosity resistance cannot be secured; If it exceeds 300 mg/m2, electrodeposition coating properties and spot weldability will deteriorate, so the amount of chromate treatment layer to be formed should be 30 to 300 mg/m2 in terms of Cr content.
It was limited to m2.

(e) Protective resin film layer As mentioned above, resin coatings for the protective film include epoxy resin, polyester resin, melamine resin, vinyl resin,
BaCrO4 is added to styrene resin, acrylic resin, polyurethane resin, phthalic acid resin, etc. alone or in modified form.
Rust-preventive pigments such as, colored pigments such as Fe2O3, or S
A known material containing a pigment such as iO2 if necessary is applied, but if the thickness of this protective resin film layer is 0.2μ
If it is less than m, sufficient perforation resistance cannot be ensured;
If the thickness exceeds 2.0 μm, electrodeposition coating properties and spot weldability deteriorate, so the thickness of the protective resin film layer was limited to 0.2 to 2.0 μm.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

[Example] A steel plate having a thickness of 0.8 mm was prepared and treated according to the steps shown in FIG. 3 to obtain a multilayer surface-treated steel plate. That is, after first performing alkaline degreasing and pickling of the steel plate, Table 1
Initial plating was performed using the sulfuric acid bath shown in Figure 2, and then immersion was performed without electricity in the same plating solution as used for the initial plating to form a base treatment layer in which cracks of a predetermined width were present at a predetermined density.

[0033]

[0034] Next, using the same plating solution, Z
By applying n-Ni alloy plating (first layer plating) and controlling the concentrations of Zn2+ and Ni2+ in the plating solution, a second layer Zn with a predetermined Ni content and a predetermined thickness is formed.
-Ni-based alloy plating was applied. In addition, Ni in the plating film
The content can be adjusted by controlling the concentration of Zn2+ and Ni2+.
The plating weight was adjusted by controlling the amount of electricity.

Next, the obtained plated steel plate was washed with water and dried, and then coated with a coating type chromate treatment solution and baked and dried. In addition, when applying the chromate treatment liquid, use a roll coating.
The amount of chromate treatment layer formed (Cr adhesion amount) was determined by changing the peripheral speed ratio and touch pressure of the pick-up roll and applicator roll, and also by changing the concentration of the chromate treatment solution.
adjusted.

Next, in order to form a protective resin film on the surface of the steel sheet after the chromate treatment, a clear paint was applied by a roll coater method. The thickness of the protective resin film was controlled by adjusting the amount of solvent in the resin and the peripheral speed ratio of the applicator roll and pickup roll.

[0037] The multilayer surface-treated steel sheets produced in this manner were investigated for impact resistance, adhesion, external rust resistance, perforation resistance, press sliding properties, electrodeposition coating properties, and spot weldability. carried out. These results are shown in Tables 2 to 4, and are organized into graphs and shown in FIGS. 6 to 18. In addition, among FIGS. 6 to 18, FIGS. 6 to 10 show the perforation resistance, FIGS. 11 to 13 show the external rust resistance, FIG. 14 shows the electrodeposition coating properties, and FIGS. 15 to 16 show the press resistance. Sliding properties and Figure 1
7 to 18 compare the spot weldability, and the letters (letters) in the figures correspond to the type symbols of the test materials (comparative examples) in Table 4.

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041] Each of the above investigations was conducted in the following manner. Evaluation procedure for external rust resistance (A) Preparation of painted plate test pieces. Zinc phosphate treatment {PBL-3020 (product name of Nippon Parkerizing Co., Ltd.)}→Cationic electrodeposition coating {U-600 (product name of Nippon Paint Co., Ltd.): 20 μm}→Middle and top coats: 35 μm each of melamine alkyd resin. (B) Make a cross cut as shown in Figure 19 on the painted plate test piece. (C) Outdoor exposure test (conducted for 1 year with twice weekly 5% NaCl spraying). (D) External rust resistance was evaluated by measuring the blistering width of the paint film (maximum creep width on one side from the crosscut shown in Figure 19).

Evaluation of pitting resistance: After alkaline degreasing, the back side and edges of the unpainted test piece were sealed with polyester tape and subjected to the following cycle of "accelerated pitting corrosion test (1 cycle: 24 hr)". 20
The maximum erosion depth of the corroded part after 0 cycles was measured and evaluated using a point micrometer. Salt water spray (6 hours) → Dry (2 hours at 50°C) → Wet (95%, 16 hours at 50°C).

Evaluation of press slidability To investigate the slidability between the plated surface and the tool surface, the "improved Bauden test method", which is an improved Bauden test as shown in FIG. 20, is used.
A method was adopted to determine the friction coefficient of the plated surface, and the sliding characteristics were evaluated using this method.

Evaluation of Electrodeposition Coating Properties Even on the inside of equipment such as the trunk lid or bonnet of a car, the finish quality of the coating is visible to the public when the device is opened, and this leads to evaluation of the product. The multilayer surface of the surface-treated steel sheet of the present invention, which is often coated by electrodeposition, is also required to have good electrocoatability. Therefore, the finish condition of the electrodeposition coating was visually observed and graded into 5 grades (◎...excellent, ○).
Evaluation was made as follows: good, △, fair, ×, poor, ××, poor).

Spot weldability evaluation Spot weldability was tested using a CF type electrode (made of Cu-Cr alloy), pressure: 200 kg-f, squeeze time: 20 cycles, energization time: 10 cycles, holding time:
A continuous dotting test was conducted under conditions of 15 cycles and a welding current of 11 kA, a pitch of 20 dots per minute at 1 point/1 second, and the nugget diameter was 4√t (= 3.6 mm, where t is the plate thickness. The life of continuous dots was defined as the point in time when the distance was 0.8 mm or less.

Impact resistance adhesion evaluation: After applying 3 automotive coats (total film thickness 100 μm) to a 70 mm x 150 mm test piece, it was tested with ASTM D- by using a gravel meter at a low temperature of -20°C. 3170-74
A chipping test was carried out as specified in 1. The chipping test was conducted and the plating peeled off area ratio at that time was evaluated according to the following criteria. 4...No plating peeling off, 3...Plating peeling area ratio is less than 0.2%, 2...Plating peeling area ratio is 0.2% or more and less than 1%, 1...Plating peeling area ratio is 1% or more.

As is clear from the results shown in Tables 2 to 4 and FIGS. 6 to 18, the surface-treated steel sheet according to the present invention has shown excellent results in all property investigations, and has It can be seen that the comparative steel sheets that do not meet the conditions specified in the present invention do not have sufficient properties, while the steel sheets fully satisfy the strict requirements for automotive rust-proof steel sheets.

[0048]

[Summary of Effects] As explained above, according to the present invention, not only corrosion resistance such as hole resistance and external rust resistance, but also press workability, spot weldability, electrodeposition coating property, and impact resistant adhesion are achieved. It is possible to provide surface-treated steel sheets with excellent properties such as durability, and can be applied to rust-preventing steel sheets for automobiles and home appliances to further improve their performance. Useful effects are produced.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an example of a surface-treated steel sheet according to the present invention.

FIG. 2 is a schematic diagram of another example of the surface-treated steel sheet according to the present invention.

FIG. 3 is a schematic explanatory diagram of an example of a process for manufacturing a surface-treated steel sheet according to the present invention.

FIG. 4 is a graph showing the relationship between the width of microcracks present in the base layer and the impact-resistant adhesion of the Zn-Ni alloy two-layer plating applied thereon.

FIG. 5 is a graph showing the relationship between the density of microcracks present in the base layer and the impact resistant adhesion of the Zn-Ni alloy two-layer plating applied thereon.

FIG. 6 is a graph arranging and comparing test results in Examples.

FIG. 7 is a graph arranging and comparing test results in Examples.

FIG. 8 is a graph arranging and comparing test results in Examples.

FIG. 9 is a graph arranging and comparing test results in Examples.

FIG. 10 is a graph arranging and comparing test results in Examples.

FIG. 11 is a graph arranging and comparing test results in Examples.

FIG. 12 is a graph arranging and comparing test results in Examples.

FIG. 13 is a graph arranging and comparing test results in Examples.

FIG. 14 is a graph arranging and comparing test results in Examples.

FIG. 15 is a graph arranging and comparing test results in Examples.

FIG. 16 is a graph arranging and comparing test results in Examples.

FIG. 17 is a graph arranging and comparing test results in Examples.

FIG. 18 is a graph arranging and comparing test results in Examples.

FIG. 19 is an explanatory diagram of a method for evaluating external rust resistance.

FIG. 20 is a schematic explanatory diagram of the improved Bauden test method.

Claims (3)

[Claims] Claim 1: A) Zn- in which "microcracks" with no directionality exist on at least one side of the steel plate, with a crack width of 0.01 to 0.5 μm and a crack density of 10 to 60% in terms of crack area fraction; Ni-based alloy plating thin base layer,
B) Plating layer of Zn-Ni alloy with Ni content of 13% by weight or less: 10-50 g/m2, C) Plating layer of Zn-Ni-based alloy with Ni content of 10-40% by weight: 0. 5 to 20 g/m2, D) Chromate treatment layer: 30 to 300 mg/m of Cr
m2, E) Protective resin film layer: 0.2-2.0μ
A highly corrosion-resistant surface-treated steel sheet with excellent impact-resistant adhesion, characterized by comprising multiple layers of m, in this order. [Claim 2] Zn-Ni in which non-directional "microcracks" with a crack width of 0.01 to 0.5 μm and a crack density of 10 to 60% in terms of crack area fraction are present on at least one side of the steel plate. The steel plate has a thin underlayer of alloy plating, and on one side of the steel plate a) a plating layer of a Zn-Ni alloy with a Ni content of 13% by weight or less: 10 to 50 g/m2, b) a Ni content of 10 to 50 g/m2; A plating layer of 10-40% by weight of Zn-Ni alloy: 0.5-20g/m2, in this order, and on the other side a) Zn with a Ni content of 13% by weight or less. -Ni alloy plating layer: 10 to 50 g/m2, b) Zn-Ni alloy plating layer with Ni content of 10 to 40 wt%: 0.5 to 20 g/m2, c) Chromate treatment layer :Cr amount 30-300mg/
m2, d) Protective resin film layer: 0.2 to 2.0μ
characterized by comprising multiple layers of m, in this order,
Highly corrosion-resistant surface-treated steel sheet with excellent impact resistance and adhesion. 3. The method according to claim 1 or 2, wherein the "Ni content of the Zn-Ni alloy plating thin base layer" is 1.2 to 5 times the "Ni content of the plating layer directly above it". Highly corrosion-resistant surface-treated steel sheet with excellent impact resistance and adhesion.