JPH09143792A - Production of galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a film, which is hard and has high melting point as compared with galvanizing or galvannealing layer and is further improved in the peeling strength of a sheet as the object of adhesion, on the surface of a galvanized steel sheet. SOLUTION: A galvanized steel sheet is subjected to cathodic electrolysis at (1 to 150)A/dm<2> current density in an aqueous solution of 30-70 deg.C, having (0.3 to 2.0)mol/l total concentration of nickel sulfate and ferrous sulfate and also having 1-3 pH value, by which an Fe-Ni alloy film is formed on the surface of the plating layer of the galvanized steel sheet. It is desirable that the plating layer is a galvannealing layer of 7-15wt.% Fe content, an electrogalvanizing layer, or a hot dip galvanizing layer. By this method, the galvanized steel sheet, excellent in press formability, spot weldability, and adhesion, can be provided.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to a press formability,
The present invention relates to a method for producing a galvanized steel sheet having excellent spot weldability and adhesiveness.

[0002]

2. Description of the Related Art Galvanized steel sheets are widely used as various kinds of rust-proof steel sheets because they have various excellent characteristics. In order to use this galvanized steel sheet as an anti-corrosion steel sheet for automobiles, in addition to corrosion resistance, paint compatibility, etc., it is required to have excellent press formability, spot weldability and adhesion as the performance required in the body manufacturing process. It is important that

However, zinc-based plated steel sheets generally have a drawback that they are inferior in press formability to cold-rolled steel sheets. This is because the sliding resistance between the zinc-based plated steel sheet and the press die is higher than that in the case of cold-rolled steel sheet.If this sliding resistance is high, near the bead part of the die during pressing. It becomes difficult for the galvanized steel sheet to flow into the press die, and the steel sheet easily breaks.

As a method of improving the press formability of a zinc-based plated steel sheet, a method of applying a high-viscosity lubricating oil is generally widely used. However, in this method, since the lubricating oil has a high viscosity, there are problems such as a coating defect due to poor degreasing in the next coating step, and oil depletion, which causes unstable press performance. There is a high demand for improvement in press formability of galvanized steel sheets.

On the other hand, in a zinc-based plated steel sheet, copper, which is an electrode, reacts with molten zinc during spot welding to easily form a brittle alloy layer, so that the copper electrode is greatly worn and its life is short. There is a problem that continuous hot spotting properties are inferior to cold rolled steel sheets.

Further, in the manufacturing process of an automobile body,
Although various adhesives are used for the purpose of rust prevention and vibration control, it has recently become clear that zinc-based plated steel sheets are inferior in adhesiveness to cold-rolled steel sheets.

As a method for solving the above problem, Japanese Patent Laid-Open No. Sho 5
Japanese Patent Application Laid-Open No. 3-60332 and Japanese Patent Application Laid-Open No. 2-190483 disclose that a surface of a zinc-based plated steel sheet is subjected to electrolytic treatment, dipping treatment, coating oxidation treatment, or heat treatment.
A technique (hereinafter, referred to as "Prior Art 1") for improving weldability or workability by generating an oxide film mainly containing ZnO is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 4-88196 discloses that the surface of a zinc-based plated steel sheet is immersed in an aqueous solution containing 5 to 60 g / l of sodium phosphate and having a pH of 2 to 6, or
By electrolytic treatment and spraying the above aqueous solution, P
A technique (hereinafter referred to as "prior art 2") for improving press moldability and chemical conversion treatability by forming an oxide film mainly containing an oxide is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 3-191093 discloses a technique (hereinafter, referred to as "Prior Art 3") of forming Ni oxide to improve press formability and chemical conversion treatability.

[0010]

The above-mentioned prior art 1 has the following problems. That is, Prior Art 1
In this method, an oxide mainly composed of ZnO is generated on the surface of the plating layer by various treatments, so that the effect of reducing sliding resistance between the press die and the plated steel sheet is small, and the effect of improving press formability is small. Is small. Further, an oxide mainly composed of ZnO deteriorates the adhesiveness.

Prior art 2 is a method of forming an oxide film mainly composed of P oxide on the surface of a zinc-plated steel sheet, so that it has a great effect of improving press formability and chemical conversion treatability, but it does not have spot weldability and There is a problem that the adhesiveness deteriorates. Here, the spot weldability refers to the continuous spotting property in the spot welding of thin steel sheets, and in general, the continuous spotting property is the number of times spot welding can be performed continuously without having to care for or replace the electrode tip of the welding. It is shown and is consistent with continuous usable electrode life (same in this application).

Since the prior art 3 is a Ni oxide single-phase film, it has a problem that the press formability is improved but the adhesiveness is deteriorated.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a method for producing a zinc-based plated steel sheet having excellent press formability, spot weldability and adhesiveness.

[0014]

As a result of intensive studies to solve the above problems, the present inventors formed an appropriate Fe-Ni alloy film on the surface of the plating layer of a zinc-based plated steel sheet. It has been found that the press formability, spot weldability, and adhesiveness can be greatly improved.

Here, the proper Fe-Ni alloy film is
And the following: The amount of adhesion of this film is in the range of 10 to 2000 mg / m ² , and the Fe content in this film is 5 to 80 wt. %, Preferably 10 to 50 wt. It was found that it was within the range of%, and that it satisfied.

The press formability of the zinc-based plated steel sheet is inferior to that of the cold-rolled steel sheet because the sliding resistance is low because zinc having a low melting point and the die cause an adhesion phenomenon under high surface pressure. The cause is the increase. In order to prevent this, it is effective to form a film that is harder and has a higher melting point than the zinc or zinc alloy plating layer on the surface of the plating layer of the zinc-based plated steel sheet. The sliding resistance between the die and the die decreases, the zinc-based plated steel sheet easily slips into the press die, and the press formability improves.

The continuous spotting property in spot welding of a zinc-based plated steel sheet is inferior to that of a cold-rolled steel sheet because the molten zinc and the copper of the electrode come into contact with each other during welding to form a brittle alloy layer. In addition, the deterioration of the electrode becomes severe. Therefore, as a method for improving the continuous spotting property of a zinc-based plated steel sheet, it is considered effective to form a high melting point film on the plated surface. The present inventors have studied various coatings in order to improve the spot weldability of zinc-based plated steel sheets, and have found that Ni metal is particularly effective. Although the details of this reason are not clear, it is considered that Ni metal has a high melting point and high electric conductivity.

It was known that the adhesion of the zinc-based plated steel sheet was inferior to that of the cold-rolled steel sheet, but the cause was not clear. However, it has been found that the adhesiveness is improved by forming a Fe-Ni alloy film in which Fe is alloyed.

The present invention has been made based on the above findings, and by appropriately forming a Fe-Ni alloy film on the surface of the plating layer of a zinc-based plated steel sheet,
It is a method for producing a zinc-based plated steel sheet excellent in press formability, spot weldability and adhesiveness, and is as follows. In the method for producing a zinc-based plated steel sheet of the present invention, the total concentration of nickel sulfate and ferrous sulfate is 0.3 to 2.
An aqueous solution having a pH in the range of 0 mol / l and a pH in the range of 1 to 3 is prepared, and then the aqueous solution is used as a plating solution, and the temperature of the plating solution is 30 using a zinc-based plated steel sheet as a cathode. Characteristic for forming a Fe-Ni alloy film on the surface of the electrode by cathodic electrolysis in the range of ~ 70 ° C and in the range of current density of 1 to 150 A / dm ² (hereinafter, " The first invention ").

A desirable method for producing a zinc-based plated steel sheet according to the present invention is that in the method according to the first aspect of the present invention, the zinc-based plated steel sheet before plating by cathodic electrolysis has an Fe content of 7 to 15 wt. The alloy is characterized by being an alloyed hot-dip galvanized steel sheet within the range of%.

Another preferable method for producing a zinc-based plated steel sheet according to the present invention is the production method according to the first aspect, wherein the zinc-based plated steel sheet before plating by cathodic electrolysis is an electrogalvanized steel sheet or a hot-dip galvanized steel sheet. It is characterized by being present.

In this application and in the context of the present invention, a Fe-Ni alloy film as an upper layer formed on the surface of the plating layer of a zinc-based plated steel sheet is referred to as a "film", while When referring to zinc or zinc-based plating layer as the lower layer, it is called "plating layer" and "coating"
I decided not to say.

[0023]

Next, the reason for limiting the manufacturing conditions of the present invention as described above will be described. In the present invention, nickel sulfate and ferrous sulfate are used as components of the plating solution used for forming the Fe-Ni alloy film on the surface of the plating layer of the zinc-based plated steel sheet.
-By electrolyzing a zinc-based plated steel sheet on which a Ni alloy film is to be formed as a cathode, Fe-Ni can be efficiently formed in the film.
This is because it is suitable for forming an alloy film.

The total concentration of nickel sulfate and ferrous sulfate is 0.3 to 2.0 mol / l for the following reason. If the total concentration is less than 0.3 mol / l, the electrolysis voltage is high because the conductivity of the plating bath is low, and if the current density is high, plating burn occurs and Ni and Fe are generated.
Of the above-mentioned hydroxide is involved, and the weldability of the zinc-plated steel sheet is likely to deteriorate. On the other hand, the total concentration is 2.0 mol /
Above 1, the nickel sulphate and / or ferrous sulphate reach the solubility limit and precipitate at lower temperatures.

The electrolytic solution contains Z contained in the plating layer of the zinc-based plated steel sheet used in the present invention.
n, Co, Mn, Mo, Al, Ti, Sn, W, Si,
It may inevitably contain cations such as Pb, Nb, and Ta, hydroxides and oxides, and anions other than sulfate ions.

The reason why the electrolytic solution whose pH is in the range of 1 to 3 is used is as follows. PH of electrolyte
When the value is less than 1, the generation of hydrogen during electrolysis becomes the main component of the cathode reaction, and the current efficiency is greatly reduced. On the other hand, p of the electrolyte
When H exceeds 3, ferric hydroxide is precipitated.

The reason why the temperature of the plating bath is required to be within the range of 30 to 70 ° C. is as follows. If the temperature of the plating bath is lower than 30 ° C., the conductivity of the plating bath is low and the electrolysis voltage is high. If the current density is high, the plating burn occurs and the hydroxides of Ni and Fe are entrained. The weldability of system-plated steel sheets is likely to deteriorate. On the other hand, when this temperature exceeds 70 ° C., the amount of evaporation of the electrolytic solution increases, and it becomes difficult to control the nickel and iron ion concentrations. Therefore, the temperature of the plating bath is 30 to 70.
It is desirably in the range of ° C.

The current density during plating is 1 to 150 A /
The reason why it should be within the range of dm ² is as follows. When the current density is less than 1 A / dm ² , hydrogen generation becomes the main component of the cathode reaction, and the current efficiency is greatly reduced. On the other hand, if the current density exceeds 150 A / dm ² , burning of the plating occurs, the hydroxides of Ni and Fe are entangled in the coating, and the weldability decreases.

In the present invention, as the zinc-based plated steel sheet used for forming the Fe-Ni alloy coating on the surface, the plated layer on the surface is an alloyed hot-dip galvanized layer having an iron content of 7 to 15 wt.%. It is desirable to use the above-mentioned material, an electrogalvanized layer, or a hot dip galvanized layer. The reason is that the zinc-based plated steel sheet having these plated layers is inferior to the cold rolled steel sheet and the zinc-nickel alloy plated steel sheet in workability, particularly press formability, and weldability. This is because forming the Ni alloy film on the surface of the plating layer has a great effect of improving press formability and spot weldability.

Fe- used in the present invention
The zinc-based plated steel sheet before forming the Ni alloy film may be a steel sheet having a zinc-based plated layer formed on the surface of the steel sheet by a hot dipping method, an electroplating method, a vapor phase plating method or the like. The composition of this zinc-based plating layer is pure zinc or F
e, Ni, Co, Mn, Cr, Al, Mo, Ti, S
Metals such as i, W, Sn, Pb, Nb and Ta (however,
Si is also treated as a metal) or oxide, or a single-layer or multi-layer plating layer containing one or more organic substances. Further, the plating layer may contain fine particles such as SiO ₂ and Al ₂ O ₃ . Further, as the zinc-based plated steel sheet, a multi-layer plated steel sheet having a different composition of a plating layer and a functionally graded plated steel sheet can be used.

The Fe-Ni alloy film formed on the surface of the plating layer of the zinc-based plated steel sheet under the above-mentioned limiting conditions eliminates the phenomenon of adhesion between the steel sheet and the mold during press forming, which reduces sliding resistance. , The slipping into the mold is improved, the formation of a brittle alloy layer with the electrode copper during spot welding is suppressed, and continuous spotting property is improved.
The effect of the alloy film containing e has the effect of improving the adhesiveness.

[0032]

Next, the present invention will be further described with reference to examples. As the galvanized steel sheet before the electrolytic treatment according to the method of the present invention and the comparative method, a galvanized steel sheet formed with any one of the following GA, GI and EG was used. GA: 10 wt. An alloyed hot-dip galvanized layer consisting of% Fe and the balance Zn is formed, and the adhesion amount is 60 g / m ² on both surfaces. GI: A hot-dip galvanized layer is formed, and the adhesion amount is 90 g / m ² on both sides. EG: An electrogalvanized layer was formed, and the adhesion amount was 40 g / m ² on both sides.

Using the above zinc-based plated steel sheet as a cathode, electrolytic treatment was carried out in a mixed solution of nickel sulfate and ferrous sulfate having a predetermined concentration to form an Fe-Ni alloy film on the surface of the galvanized steel sheet. However, some were not subjected to electrolytic treatment. Table 1 shows the electrolytic treatment conditions of Examples 1 to 12 in which the electrolytic treatment was performed under the conditions within the scope of the present invention, and Comparative Examples 2 to 9 in which at least one of the conditions was outside the scope of the present invention. Further, Comparative Examples 1, 10 and 11 which were not subjected to the electrolytic treatment are also shown. In the same table, the plating species of the steel sheet before electrolytic treatment, the component composition of the electrolytic solution, pH, temperature, current density and energization time are shown. Each specimen was prepared from the examples and comparative examples.

[0034]

[Table 1]

With respect to the Fe-Ni alloy film formed on each of the specimens electrolytically treated as described above, the amount of the film deposited and the Fe content (wt.%) In the film were measured as follows.

[Measurement of Coating Amount and Fe Content in Coating] For specimens with plating species of GI and EG, Fe--Ni alloy coating was used as a lower plating layer (Zn-based plating layer, The same amount as the surface layer) was removed by dissolution with dilute hydrochloric acid, and Fe and Ni were quantitatively analyzed by the ICP method to measure the adhered amount and composition of the Fe—Ni alloy film. Then, the Fe content in the film was calculated. In the case of the GA test sample, the lower plating layer contains the constituent elements (Ni and Fe) in the Fe-Ni alloy film, so that in the ICP method, the upper Fe-Ni alloy film constituent elements and the lower layer It is difficult to completely separate the constituent elements in the plating layer. Therefore, only the component elements of the Fe-Ni alloy film which are not contained in the lower plated layer were quantitatively analyzed by the ICP method. Further, after Ar ion sputtering, measurement of each component element in the Fe—Ni alloy coating was repeated from the coating surface by XPS method to measure the composition distribution of each component element with respect to the depth of the plating layer.
In this measuring method, the distance between the depth at which the constituent element of the Fe-Ni alloy film not contained in the lower plating layer is the maximum concentration and the position at half the depth at which the element is no longer detected, The thickness of the Fe-Ni alloy film was used. Then, from the results of the ICP method and the XPS method, Fe-N
The amount and composition of the i alloy coating were calculated. Then, the Fe content in the film was calculated.

Tables 2 and 3 show the Fe-Ni of each of the specimens obtained in Examples 1-12 and Comparative Examples 1-11.
The measurement results of the amount of the alloy film deposited and the Fe content in the film are shown.

[0038]

[Table 2]

[0039]

[Table 3]

Next, for each specimen, press formability,
In order to evaluate the spot weldability and the adhesiveness, the friction coefficient measurement, the continuous spotting test in the spot welding and the adhesiveness test were performed by the methods described below.

[Measurement of Friction Coefficient] FIG. 1 is a schematic front view showing a friction coefficient measuring device. As shown in the figure, a friction coefficient measuring sample 1 taken from a specimen is fixed to a sample table 2, and the sample table 2 is a slide table 3 that can move horizontally.
It is fixed to the upper surface of. On the lower surface of the slide table 3, there is provided a vertically movable slide table support 5 having a roller 4 in contact with the slide table 3, and by pushing up the slide table support 5, a sample for measuring a friction coefficient by a bead 6 is provided. A first load cell 7 for measuring the pressing load N on the 1 is attached to the slide table support 5. With the pressing force applied, a second end for measuring the sliding resistance F for moving the slide table 3 in the horizontal direction is provided at one end of the slide table 3 in the horizontal movement direction. A load cell 8 is attached to one end of the slide table 3.

The coefficient of friction μ between the specimen and the bead is
Formula: Calculated by μ = F / N. However, pressing load N: 400
kgf, sample withdrawing speed (horizontal moving speed of slide table 3): 100 cm / min. The beads used had the following two sizes and shapes. Here, the reason why the second type bead is used is to more clearly evaluate the significant difference in the friction coefficient value between the test pieces by performing the press formability evaluation under more severe conditions.

FIG. 2 is a schematic perspective view showing the shape and dimensions of the first type bead used (hereinafter referred to as "bead type A"). The lower surface of the bead 6 slides while being pressed against the surface of the sample 1. Its bottom surface has a width of 10 m
1/4 of a cylindrical surface having a flat surface with a length of 3 mm in the sliding direction and a width of 10 mm on each of its front and rear surfaces and 4.5 mmR on each line.
The cylinder surfaces are in contact as shown in the figure.

FIG. 3 is a schematic perspective view showing the shape and dimensions of the second type bead used (hereinafter referred to as "bead type B"). In the bead type B, the length of the sliding surface of the bead type A in the sliding direction is increased from 3 mm to 60 mm, and the other parts are the same as the bead type A.
In both of the bead type A and the bead type B, as a lubricating oil, Knox Thrust 550HN manufactured by Japan Percalizing Co., Ltd. was used on the upper surface of the friction coefficient measurement sample 1.
Was applied and tested.

[Continuous RBI Test] Two specimens with the same No.
Resistance welding (spot welding) in which a sheet was stacked and sandwiched from both sides by a pair of electrode tips of a spot welding machine and a current was concentrated by applying pressure was continuously carried out under the following welding conditions.・ Electrode tip: dome type with a tip diameter of 6 mm ・ Pressure force: 250 kgf ・ Welding time: 12 cycles (60 Hz) ・ Welding current: 11.0 KA ・ Welding speed: 1 point / sec. As the evaluation of continuous spotting property, during spot welding, the diameter of the melted and solidified metal part (shape: go-stone, hereafter referred to as nugget) generated at the joint of two welded base materials (specimen) was 4 The number of spots continuously welded until it became less than × t ^1/2 (t: plate thickness of one sheet) was used. The number of hit points is hereinafter referred to as electrode life.

[Adhesion Test] The following test specimens for adhesion test were prepared from the respective test specimens. FIG. 4 is a schematic perspective view illustrating the assembly process. As shown in FIG.
Specimen 13 in which two test pieces 10 having a length of m and a length of 200 mm are stacked and adhered so that the thickness of the adhesive 12 is 0.15 mm with a spacer 11 having a diameter of 0.15 mm therebetween.
And baking at 150 ° C. × 10 min. The test body prepared in this manner was bent into a T-shape as shown in FIG.
A tensile test was performed at a speed of m / min to measure the average peel strength (n = 3 times) when the test body peeled. The peel strength is
The average load was determined from the load chart of the tensile load curve at the time of peeling and expressed in units: kgf / 25 mm. In FIG. 5, P
Indicates tensile load. The adhesive used was a PVC-based hemming adhesive.

In Tables 2 and 3, the results of the coefficient of friction, the number of continuous spots and the peel strength obtained in the above test are shown together. From the results shown in the table, the following matters are clear.

When the plating type is GA (alloyed hot-dip galvanized steel sheet), Examples 1 to 6 have better press formability, spot weldability and adhesion than Comparative Example 1 in which the Fe-Ni alloy coating is not formed. Both sexes have improved significantly. On the other hand, Comparative Examples 2 to 9 in which the Fe-Ni alloy film was formed under the conditions outside the scope of the present invention were inferior to the Examples in any of press formability, spot weldability and adhesiveness. That is, Comparative Example 2 in which the current density is outside the range of the present invention is inferior in terms of press formability, spot weldability and adhesiveness, while Comparative Example 3 in which the current density is outside the range of the present invention is large. Are inferior in spot weldability. Comparative Examples 4 to 6 in which the pH of the electrolytic solution is outside the range of the present invention are inferior in all of press moldability, spot weldability and adhesiveness. Further, Comparative Examples 7 to 9 in which the total concentration of nickel sulfate and ferrous sulfate in the electrolytic solution is low outside the range of the present invention are inferior in spot weldability. On the other hand, Examples 1 to 6 have good characteristics.

Even when the plating species are GI (hot dip galvanized steel sheet) and EG (electrogalvanized steel sheet), comparing the characteristic values of Examples and Comparative Examples within the same plating species, Examples 7 to 12 show that Compared to Comparative Example 10 or 11 in which the Fe-Ni alloy film was not formed, press formability,
Both spot weldability and adhesiveness have been greatly improved.

[0050]

The present invention is configured as described above.
Fe- formed on the surface of the plating layer of zinc-based plated steel sheet
Since the Ni alloy coating is harder and has a higher melting point than the zinc or alloyed zinc plating layer, the appropriate amount of Ni alloy coating causes the sliding resistance between the plating layer surface and the press die during press molding. And the zinc-based plated steel sheet easily slips into the press die. Further, the presence of the high melting point Fe—Ni alloy coating improves the continuous spotting property in spot welding. Furthermore, the presence of Fe in the Fe-Ni alloy coating improves the peel strength of the adhesive plate. Therefore, according to the present invention, it is possible to provide a zinc-based plated steel sheet having excellent press formability, spot weldability, and adhesiveness, which brings about an extremely useful effect industrially.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a friction coefficient measuring device.

FIG. 2 is a first type bead in FIG. 1 (bead type A).
It is a schematic perspective view showing the shape and dimensions of.

FIG. 3 is a second type bead in FIG. 1 (bead type B).
It is a schematic perspective view showing the shape and dimensions of.

FIG. 4 is a schematic perspective view illustrating an assembling process of an adhesiveness test specimen.

FIG. 5 is a schematic perspective view illustrating a load of a tensile load when measuring peel strength in an adhesion test.

[Explanation of symbols]

 1 sample for friction coefficient measurement, 2 sample stage, 3 slide table, 4 roller, 5 slide table support, 6 beads, 7 first load cell, 8 second load cell, 9 rail 10 specimens, 11 spacers, 12 adhesives, 13 adhesion test specimens, P tensile load, F sliding resistance, N pressing load.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Inagaki 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masaaki Yamashita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. Forming a film on the surface of a plating layer of a zinc-based plated steel sheet by electrolyzing with a zinc-based plated steel sheet as a cathode in a plating solution consisting of an aqueous solution containing nickel sulfate and ferrous sulfate. In the method for producing a zinc-based plated steel sheet, the total concentration of the nickel sulfate and the ferrous sulfate in the plating solution is 0.3 to 2.
Within the range of 0 mol / l, the pH is within the range of 1 to 3, the temperature of the plating solution is within the range of 30 to 70 ° C., and the current density is within the range of 1 to 150 A / dm ² . A method for manufacturing a zinc-based plated steel sheet, comprising forming an Fe-Ni alloy film by performing the electrolysis under the conditions described in 1. 2. The method for producing a zinc-based plated steel sheet according to claim 1, wherein the plated layer of the zinc-based plated steel sheet is an alloyed hot-dip galvanized layer having an iron content of 7 to 15 wt.%. 3. The method for producing a zinc-based plated steel sheet according to claim 1, wherein the plated layer of the zinc-based plated steel sheet is an electrogalvanized layer or a hot-dip galvanized layer.