JPS63192900A - Multiply plated steel sheet having superior plating adhesion and corrosion resistance after painting - Google Patents

Abstract

PURPOSE:To obtain a multiply plated steel sheet having superior plating adhesion and superior corrosion resistance after painting by successively forming a layer of a specified metal, a Zn layer contg. dispersed water insoluble hyperfine particles and a layer of a specified Fe alloy on the surface of a steel sheet by plating. CONSTITUTION:A layer of one or more among Fe, Ni, Co, Cu, Sn and Pb is formed as a first layer on the surface of a cold rolled steel sheet as a steel sheet for an automobile by plating by 0.01-2g/m<2>. A Zn or Zn alloy layer contg. dispersed water insoluble hyperfine particles of SiO2, TiO2, Al2O3, ZrO3, MoS2, graphite, Al, Cr, BaCrO4, phenol resin or the like having <=5mum average particle size is formed as a second layer on the first layer by electroplating by >=5g/m<2>. A layer of an Fe alloy contg. >70wt.% Fe such as Fe-Zn-Cr, Fe-Zn or Fe-P is further formed as a third layer on the second layer by plating by >=1g/m<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a multilayer electroplated steel sheet that has excellent tamping adhesion and corrosion resistance and can be used for various purposes, such as steel sheets for automobiles.

(Prior Art and Problems) Application of various plated steel sheets is being studied and promoted to solve the problem of corrosion of automobile bodies due to rock salt sprayed to prevent roads from freezing during the winter in cold regions.

Corrosion on the exterior of the car body occurs when the car is hit by pebbles or scattered rock salt thrown up from the road surface while driving on the road (this phenomenon is called chipping.The speed at which the pebbles or scattered rock salt collide is
Same as the driving speed of a car 50~l 50 x m/h
This is an extremely large impact force. ) The paint on the car body surface peels off, or scratches reach the base steel plate, which is accelerated by the action of water from melting snow and sprayed salt. For example, a Zn-plated steel plate is used as a countermeasure against corrosion on the outer surface of a vehicle body. Due to its strong sacrificial anticorrosion effect, Zn plating has the ability to sufficiently protect steel sheets even if scratches reach the base steel sheet, but when used as a coating on the outside of a car body, the coating film may swell, known as blisters. It has the disadvantage of being prone to rust.

Therefore, recently Zn-Ni, Zn-Fe
.

Zn-Co, Zn-Fe-Cr, Zn-Ni-
Co, Zn-Cr.

Zn-Mn, Zn-Ti, Zn-8n, Z
n-Cu, Zn-Cd.

Electroplating of Zn-based alloys such as Zn-Pb, multi-layered plating of these (that is, stacking of Zn-based alloy plating layers with different components and compositions), and gradient-based plating of concentration (
In other words, steel plates coated with plating whose composition changes in the direction of the thickness of the plating layer have been developed, have been recognized to have good blister resistance, and are beginning to be put into practical use.

In addition, as described in Japanese Patent Publication No. 60-38400 (Japanese Unexamined Patent Publication No. 60-141898),
As shown in No. 1, JP-A No. 61-64899, non-metal fine particles are combined, and JP-A No. 60-96786, corrosion-inhibiting pigment is added. In contrast to conventional simple alloy plating, such as composite plating, insoluble particles having a size larger than a certain level that are difficult to dissolve in an acidic plating bath are added to Zn alone as a matrix plating or in Zn-based alloy plating. New types of dispersion-coated steel sheets (hereinafter referred to as Zn-based dispersion electroplated steel sheets) have been disclosed one after another.These Zn-based dispersion electroplated steel sheets have not yet been put into practical use, but they are similar to conventional Zn-based dispersion electroplated steel sheets. Zn-based alloy electroplated steel sheet: It has superior corrosion resistance compared to Zn-based alloy electroplated steel sheets, and in order to meet the increasingly sophisticated performance requirements, it is necessary to put it into practical use as soon as possible.However, Zn-based dispersed electroplating Coated steel sheets still have many problems to overcome in terms of quality and manufacturing.

One of the major issues in terms of quality is that the adhesion of the dispersion plating layer to the steel plate base is weak.

(Hereinafter, the plating that is in direct contact with the steel sheet substrate will be referred to as the adhesion to the steel sheet.) This means that the dispersion plating layer is a discontinuous plating layer consisting of the plating metal as a matrix and insoluble particles. This is due to certain reasons.Also, it is common to apply three coats of cationic electrodeposition coating, intermediate coating, top coating, and painting (1) to a total thickness of approximately 100 μm or more on the external surface of automobiles. During baking, the shrinkage stress of time acts on the plating layer, and the adhesion to the substrate is lower than when unpainted.Furthermore, in cold regions in winter, the temperature is -30 to -40℃.
Temperatures have fallen to 100,000 yen, and the shrinkage of the coating film has progressed, so the stress acting on the plating layer has also increased, and its adhesion to the substrate has become even lower. When subjected to the above-mentioned chipping under such conditions where the adhesion to the substrate is further reduced, the plated layer of the Zn-based dispersion electroplated steel sheet has the disadvantage of peeling.

Conventional Zn-based alloy electroplated steel sheets also have the above-mentioned problems due to their large internal stresses.

Special measures have already been taken to improve the plating adhesion of Zn-based alloy coated steel sheets (hereinafter, the adhesion of the plating to the steel sheet is referred to as plating adhesion, regardless of whether it is in direct contact with the steel sheet base or not). As in JP-A-59-200789 (Cr, Mn, Fe.

C0. Ni, Cu, In, Zn, Cd, S
A method is disclosed in which a coating layer consisting of one or more of Zn, Pb, and Pb is provided between an iZn alloy plating and a base steel plate.

However, this method only confirms the adhesion of Zn-based alloy electroplated steel sheets under mild conditions such as unpainted extrusion molding (51 Erichsen overhang) at room temperature.

(Means for Solving the Problems) In view of the above-mentioned circumstances, the present inventors have determined that Zn-based dispersion-plated steel sheets coated with three coats for automobiles are subject to chipping at low temperatures of about -30 to -40'C. Various experiments were conducted with the aim of obtaining good plating adhesion even when the coating was applied. As a result, Fe, Ni, C0.
Precipitates consisting of one or more of Cu, Sn, and Pb with a rate of 0.01 to 2y/rr? After that, Zn-based dispersion plating is applied as a second layer on the coating layer, and Fe is further applied as a third layer on the coating layer.
It was confirmed that plating adhesion under the intended severe conditions could be obtained by applying Fe-based alloy plating containing 0% by weight or more. In other words, since the surface of a steel sheet has normally gone through heating, rolling, pickling, and annealing processes, a diffusion concentration layer of non-metals such as C and Si and compounds with acids exist on the surface, and this is the reason for the Zn-based alloy plating. This is a factor that completely inhibits adhesion. Zn-based dispersion plating has a structure that is different from Zn plating and Zn-based alloy plating and is a discontinuous plating layer, so it is particularly likely to be promoted.

The present inventors have fully confirmed that in order to improve the plating adhesion of Zn-based dispersion plating, it is necessary to first provide a metal layer with a simple structure between the Zn-based alloy plating and the base steel sheet. Among them, Fe, Ni, Co.

It has been found that Cu, 'Sn, and Pb have good adhesion to the steel plate and that the adhesion of Zn-based dispersion plating is good. However, since this surface treatment alone was still insufficient, we next focused on the fact that in low-temperature chipping, the impact force from chip collision is directly transmitted to the Zn-based dispersion plating, which deteriorates the adhesion of the plating. . In other words, if a treatment is applied to reduce the impact force of chipping before it is transmitted to the Zn-based dispersion plating, the Zn
The adhesion of n-type dispersion plating becomes even better. The present inventors further applied F on the Zn-based dispersed plating as a treatment to reduce the impact force of chipping before it is transmitted to the Zn-based dispersed plating layer.
As a result of various searches, it has been found that Fe-based alloy plating containing 70% by weight or more of e is industrially best. This impact-reducing effect is due not only to the Fe-based alloy plating itself, but also to the quality of the phosphate film applied as a coating base treatment on top of the Fe-based alloy plating.

The phosphate film on the Zn-based alloy plating film has a thickness of 5 to 10μ.
Acicular Hepeite (Zn5(PO4)2H
4H,O), which has some ability to alleviate impact forces.

On the other hand, the phosphate film on the Fe-based alloy plating containing more than 170 F of Fe consists of angular grain-like pho with a diameter of 0.5 to 1 μm.
spophyllite (zn2Fe(po4),
, 4n2o), and because the crystals are fine, the ability to absorb and disperse the impact force of chipping is thick (it was found that the transmission of the impact of chipping to the Zn-based dispersion plating is alleviated.

Having discovered the above-mentioned findings regarding the plating adhesion of Zn-based dispersed plating and the effects of the first and third coating layers, the present invention has been developed. It was done.

The present invention has been made based on the above knowledge, and the gist thereof is to provide at least one side of a steel plate with
Fe as the first layer from the surface of the steel plate.

Ni, C0. A plating layer consisting of one or more of Cu, Sn, and Pb with a thickness of 0.01 to 21/d
A coating layer of 52/door or more is formed as a second layer, and a Zn-based dispersion plating layer consisting of Zn alone or Zn-based alloy plating containing water-insoluble fine particles with an average particle size of 5 μ or less is formed, and further, A multilayer plated steel sheet having excellent plating adhesion and post-painting corrosion resistance, characterized in that a Fe-based alloy plating layer containing 70% by weight or more of Fe is used as the third layer to form a coating layer of 1y≠ or more.

(effect) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows that when the amounts of coating layers of the first layer and the third layer are changed in the present invention, the amount of 2oy/rr applied to the second layer is changed. Zn coating
FIG. 2 is a correlation diagram showing how the plating adhesion changes immediately after the production of system dispersion plating.

In Figure 1, A is a multi-layer plating in which Co is electroplated alone as the first layer and the third layer is 0; B is the first layer.
Co alone is electroplated as a layer, and Zn is applied as a third layer.
Fe-Zn alloy electroplating with 25 wt% residual Fe 0.5
Multi-layer plating with y/-; C is electroplated with Co alone as the first layer, and 25% by weight Zn remaining as the third layer.
e Fe-Zn alloy electroplating 1t/rr? A, B, and C are correlation curves showing how the plating adhesion of Zn-based dispersed plating changes with changes in the amount of the first layer deposited. Plating adhesion was evaluated according to the method shown in Table 1.

Co for all purposes of improving plating adhesion in Zn-based dispersion plating
When a single lower layer coating is applied, the curved line in Figure 1 (= as shown, the amount of Co deposited is 0.01 f/rr? or more to zfl
Up to rd, the plating adhesion of Zn-based dispersion plating also improves as the amount of Co deposited increases. However, the effect of the first layer coating is saturated when the steel sheet surface is completely covered (=2y/l?), so the plating adhesion of the Zn-based dispersed plating is insufficient.

0.5f/Fe-Zn alloy plating as the third layer
Although the curve B obtained by applying rr/ has a better range than the curve A, it is in an unsatisfactory condition as a whole. This is because the third layer cannot completely cover the surface of the second layer, so the crystal structure of the phosphate described above is different from that of Hepeite and phos-phophy.
It is presumed that the cause is that the vi force of chipping cannot be sufficiently buffered due to the eutectic state of lllta.

Curve C, in which Fa-Zn alloy plating was applied as the third layer at 19/rM', is in a better state than the peak value of curve A when the Co adhesion amount c) of the first layer is o1f/m' or more. This is because the crystal structure of the phosphate mentioned above is entirely phoa-phop.
This is because the impact force of chipping can be sufficiently buffered.

In the present invention, the first layer that is directly applied to the surface of the steel plate is made of Fe.
, Ni, C0. 0, 01-2f/rr consisting of one or more of Cu, an, and Pb? Formed with a plating layer. The adhesion amount of the first layer is 0.01~2f
/rrl was selected for the following reason. As shown in Fig. 1, the correlation between the adhesion amount and plating adhesion when the first layer FCO is used alone is 0.01 y/ry? This is because if it is less than 2f/-, the plating adhesion can be improved, but if it exceeds 2f/-, the effect will be saturated and there is a concern that it will have an adverse effect in terms of corrosivity.

The metal used for the first layer is Fa. Ni, Co
.

One or more of Cu, Sn, and Pb can be selected, but among them, Fe and Fe group metals, which are the main components of steel sheets, Ni and Co, have a crystal structure similar to that of Fs. Great effect on improving adhesion. When a mixture of two or more types is used, the content of each is not particularly limited.

Also, these and P, W, B, M.

O may be used alone or in combination with two or more.

The second layer in the present invention is formed of a Zn-based dispersed plating layer of 5+/- or more consisting of Zn alone or Zn-based alloy plating containing water-insoluble fine particles with an average particle size of 5 μm or less. Here, the water-insoluble fine particles contained in the Zn-based dispersed plating layer refer to fine particles that are insoluble or 'l1aIW' in an acidic plating bath, such as a sulfuric acid bath or a chloride bath.

For example, stow l 'rt0. , u, 0. ,
zr0. , oxides such as Fe2O3; S1c, TI
Carbide such as C; Nitride such as stN, BN; Mo32
Sulfides such as; graphite; corrosion inhibiting pigments.

Hardly soluble substances such as SrCrO4, BaCrO4, PbCrO4; Ni, Cr.

It refers to a releasable metal powder such as stainless steel; a metal powder such as M or Zn that has been rendered insoluble by chromate treatment; and organic particles such as a phenol resin or an epoxy resin, and these can be used alone or in combination.

Moreover, from the viewpoint of corrosion resistance, 810. , Tie
,.

AM-201, ZrO2, MoO2, graphite, BaCr
Particularly effective are O4, PbCrO4°Cr powder, M powder, phenol resin, and epoxy resin.

It is necessary that the average particle size of these fine particles is 5μ or less, and in a dispersed plating layer containing fine particles with a size exceeding 5μ, even if a multilayer structure as in the present invention is formed, the plating adhesion will be poor. It is difficult to secure. Corrosion resistance, workability,
Considering overall quality such as weldability, finer particles of 1 μm or less are preferred.

Note that the average particle size means the particle size that has the largest distribution among all particles.

The content of fine particles is preferably 0.01 wt.s or more to improve corrosion resistance, and 30 wt.s or less to ensure plating adhesion.

The second layer matrix plating is Zn alone or Zn-based alloy plating. Here, Zn-based alloy plating includes Zn-Ni, Zn-Fe, Zn-Co
, Zn-re-Cr, Zn-Ni-Co, Z
a-Cr, Zn-Mn, Zn-Ti.

Zn-an, Zn-Cu, Zn-Cd, Z
Refers to n-Pb etc.

Note that Zn-based alloy plating is more effective in improving corrosion resistance. What is the adhesion amount of the second layer Zn-based dispersion plating St/v? The reason for the above is that if it is less than 52/-, no anticorrosive effect on the steel plate can be obtained.

The third layer of the present invention contains 1 containing 70% by weight or more of Fe.
It is formed of an Fe-based alloy plating layer of y/rd or more.

The reason why the content of Fe is set to 70% by weight or more is that the above-mentioned phosphate film due to phosphophylLlte is formed within this range. Is the amount of Fe-based alloy plating 1g/W? The reason for this is that, as explained by comparing curves B and C in Figure 1, below 1t/rr/ the third layer cannot completely cover the surface of the second layer. The crystal structure of Hapeite and phos
Eutectic state of phophyllite: Because it is two-dimensional.

This is because the impact force of chipping cannot be sufficiently buffered.

In addition, Fe-based alloy plating is
．． Fe-7,a-Cr alloy plating of 1 to 1.0 weight IkeIb ■Re-Zn alloy plating of 3 to 30 weight 1kts of Zn ■Fe-P alloy plating of P 0゜01 to 30 weight The one I met was Tsukito.

A small amount of Zn, Cr, and P become the formation nucleus for phosphate treatment and Fe
This is because it has been found that finer phosphate crystals can be obtained than by single plating, and that it has the effect of softening the impact force of chipping.

Zn-based dispersion plating can be obtained from a dispersion plating bath in which water-insoluble fine particles are added to Zo alone or a Zn-based alloy plating bath. The water-insoluble fine particles may be in the form of a colloid, a sol, or a powder.

In the case of organic particles, it is necessary to add a small amount of surfactant to improve dispersibility in the plating bath. The manufacturing conditions may be according to normal conditions, for example, pH 0.5-5, bath temperature 30-5.
It can be manufactured under the conditions of 70°C, current density of 5 to 3 ooA/am'', and line speed of 10 to 300 m/mxn.

The structure of the plating layer can be applied either vertically or horizontally. In addition, the power source for plating is not limited to direct current, but may also be a pulse power source with a high cathode electrolysis ratio or a direct current alternating current heavy power source without any particular problem.

The multi-layer plated steel sheet of the present invention is prepared by: (1) normal degreasing (strong alkali,
Degreasing agents such as weak alkalis and solvents, and degreasing methods such as immersion, spray, counterflow, and electrolysis). Fa, pretreated steel plate
Ni, C0. Cu.

S0. After applying Pb alone, electroplating, or electroplating consisting of these for 2 seconds or more, through a water washing process,
After applying Zn-based dispersion electroplating and washing process with Fe
Obtained by electroplating the alloy.

The plating structure of the present invention does not necessarily have to be used on both sides of a steel plate; depending on the application, only one side may be plated, and the other side may be plated as the steel plate surface, or may be coated with Zn plating, Zn-based alloy plating, or Zn-based plating. Dispersion plating may also be applied.

The base steel plate to which the present invention is applied is usually a mild steel plate that has been subjected to dull finish rolling, but it may also be a mild steel plate that has been subjected to prite finish rolling, a high-strength steel plate that contains a large amount of Mn, Ill, P, etc. as steel components, Cr, Cu, Ni, etc. It is also possible to apply this method to highly corrosion-resistant steel plates that contain a large amount of P, etc. and have a low corrosion rate.

Examples below? The effects of the present invention will now be explained in more detail.

(Example) We mainly conducted plating adhesion evaluation tests and blister resistance evaluations in low-temperature chipping after 3-coat automotive coating on multi-layer plated steel sheets according to the present invention and plated steel sheets other than the present invention. A corrosion resistance test was conducted after painting.

Table 1 shows coating conditions, test conditions, and evaluation criteria. Tables 2 (1) to (3) summarize the plating layer composition and evaluation test results.

Samples 1-27.35-61.69-95 are examples of the present invention,
Moreover, samples Ugly 28-34.62-68.96-102 are comparative examples. To explain the comparative example, N1 of the comparative example
2B, 62.96 does not have the first and third layers of the present invention, and Comparative Example 29.63,9F has the amount of the first layer deposited below the range of the present invention. Comparative examples 30, 64.
98, the size of the fine particles contained in the second layer exceeds the range of the present invention, so Comparative Examples 32, 66.100
Because the Fa content of the layer is below the range of the present invention.

Comparative Examples 33 and 67.101 do not have the third layer of the present invention, and Comparative Examples 34.68 and 102 have a Zn-based dispersion because the amount of the third layer deposited is below the range of the present invention. The adhesion of the plating was poor or insufficient, and the corrosion resistance after chipping was also inevitably poor or insufficient.

In Comparative Example 31, 65.99, since the amount of the second layer deposited was below the range of the present invention, the adhesion of the Zn-based dispersed plating was good, but the corrosion resistance after coating was poor.

In contrast, the plating adhesion and post-coating corrosion resistance of the multilayer plated steel sheet of the present invention are clearly good regardless of the structure of the second fake Zn-based dispersed plating layer.

(Effects of the Invention) As described above, the multilayer plated steel sheet of the present invention is a high-performance steel sheet with excellent plating adhesion and post-painting corrosion resistance.
Its practical value is truly great.

[Brief explanation of the drawing]

Figure 1 shows the amounts of coating layers of the first and third layers in the present invention. When changed, the zo9/lr applied to the second layer? It is a correlation diagram showing how the plating adhesion of Zn-based dispersion electroplating of the coating changes. Procedural amendment May λ2, 1986

Claims (4)

[Claims] (1) On at least one side of the steel plate, from the surface of the steel plate, a plating layer consisting of one or more of Fe, Ni, Co, Cu, Sn, and Pb of 0.01 to 2 g/
m^2 coating layer is formed, and the second layer is a Zn-based dispersion plating layer consisting of Zn alone or Zn-based alloy plating containing water-insoluble fine particles with an average particle size of 5 μ or less, and 5 g/m^2
The above coating layer was formed, and 70% Fe was added as a third layer.
1g/m^2 for Fe-based alloy plating layer containing more than % by weight
A multilayer plated steel sheet with excellent plating adhesion and post-painting corrosion resistance, characterized by forming the above-mentioned coating layer. (2) The third layer contains 3 to 29% by weight of Zn and 0.1 to 1% of Cr.
．． A multilayer plated steel sheet having excellent plating adhesion and post-painting corrosion resistance according to claim 1, which is plated with a Fe-Zn-Cr alloy containing 0% by weight. (3) The third layer is Fe- containing 3 to 30% by weight of Zn.
A multi-layer plated steel sheet having excellent plating adhesion and post-painting corrosion resistance according to claim 1, which is Zn alloy plated. (4) The third layer contains F containing 0.01 to 30% by weight of P.
A multi-layer plated steel sheet having excellent plating adhesion and post-painting corrosion resistance as claimed in claim 1, which is plated with an e-P alloy.