JPH06116779A - Production of zn-ni alloy electroplated steel sheet excellent in workability - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and press workability of a steel sheet by plating it at prescribed current density in a Zn-Ni alloy electroplating bath contg. a trace of a phthalic ester compound and controlling the form of the crystals of the plating. CONSTITUTION:A Zn-Ni alloy plating bath contg. 10 to 30ppm phthalic ester compound (such as dibutyl phthalate, didecyl phthalate, decyl isooctyl phthalate or the like) is prepd. In this plating bath, the steel sheet is applied with electroplating at 10 to 150A/dm<2> current density to obtain bar-form plating crystals, e.g. having 0.2 to 1mu minor axis and 2 to 5mu major axis. The Zn-Ni alloy plating constituted of the same crystals is good in lubricating oil properties at the time of press working and is excellent in press workability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Zn-Ni alloy electroplated steel sheet having excellent workability and suitable for automobiles and home appliances.

[0002]

2. Description of the Related Art It is well known that electrogalvanized steel sheets are widely used as surface-treated steel sheets which improve the corrosion resistance of cold-rolled steel sheets and the corrosion resistance after coating and can be mass-produced without impairing workability. In recent years, the use of galvanized steel sheets has been tried as a rust preventive measure for automobiles against scattered rock salt for preventing road freezing in winter in cold regions, and high corrosion resistance in severe corrosive environments is required. In order to meet the demand for improving the corrosion resistance of galvanized steel sheets, there is a means of increasing the zinc coating amount (adhesion amount), but this has many problems in terms of weldability and workability.
Therefore, many alloy platings have been proposed as a method of suppressing the dissolution of zinc itself and extending the life of zinc plating. Most of these are Zn alloy plating containing an iron group metal such as Fe, Co and Ni as an alloy component.

Of these, Zn-Ni alloy plated steel sheets are
In particular, it has excellent unpainted corrosion resistance and good post-painting performance, workability, and weldability, and is therefore widely used, starting with rust-preventive steel sheets for automobiles. However, it does not sufficiently satisfy all the required qualities, and therefore, for example, Japanese Patent Laid-Open No. 2-70
No. 089 discloses a method for producing a Zn-based alloy plating having excellent chemical conversion treatability, and JP-A No. 2-70091 discloses a Zn-Ni alloy-plated steel sheet excellent in impact adhesion, and various other methods for improving specific performance. Is disclosed. As a recent trend, high press workability is being demanded mainly for automobiles and home electric appliances, and Zn, which has more excellent workability, is being demanded.
-Ni-based alloy plated steel sheets are desired. In order to cope with this, a study has been made on a lubricating oil that can withstand a high degree of press working as well as a steel plate material.
Since it is not possible to improve the workability of the system alloy plating itself, the essential solution has not been reached.

[0004]

In order to satisfy the requirements for high press workability of Zn-Ni alloy plated steel sheet, not only the study of the steel sheet material and the lubricating oil used for press workability but also the Zn-Ni system It is necessary to add a function of improving press workability to the alloy plating itself. It is known that Zn-Ni alloy plating exhibits a high degree of corrosion resistance at a Ni content rate at which a γ phase, which is an alloy phase of Zn-Ni, is formed. However, the crystal morphology of the plating in the Ni content range where high corrosion resistance is expressed is dense and has a low roughness, and the lubricating oil holding power at the time of press working is poor, so that it is not suitable for press working. Therefore, the present inventors have found that Zn-Ni
It was presumed that the press workability would be improved if the crystal of the alloy-based alloy plating could be controlled to a form having a high lubricating oil holding force, and the present invention was reached as a result of extensive studies on a method of controlling the crystal form.

[0005]

The gist of the present invention is Zn-
When manufacturing a Ni-based alloy electroplated steel sheet, Zn-Ni
10-3 phthalate compound in base alloy plating bath
The present invention is a method for producing a Zn-Ni-based alloy electroplated steel sheet having excellent workability, which is characterized in that the steel sheet is electroplated at a current density of 10 to 150 A / dm ² by containing 00 ppm.

[0006]

A feature of the present invention is that electroplating is performed by adding a trace amount of a phthalate compound to a Zn-Ni alloy plating bath. The corrosion resistance of the Zn-Ni alloy-plated steel sheet is controlled by the Ni content, the γZn-Ni phase is formed, the αNi phase is not formed, that is, the Ni content is 5 to 20%, and high corrosion resistance is exhibited. Particularly excellent corrosion resistance is exhibited in the γ single phase region of%. Since the γ-phase plated crystal is dense and has a low roughness, it is not possible to sufficiently retain the lubricating oil during press working, which is a factor that impedes severe press workability. However, by adding a small amount of a phthalate compound to the Zn-Ni alloy plating bath and performing electrolysis under appropriate conditions, the minor axis is 0.2 to 1 μm,
A rod-shaped plated crystal having a major axis of 2 to 5 µ is obtained.

Zn-Ni composed of such rod-shaped plating crystals
Since the alloy-based alloy plating has good lubricating oil characteristics at the time of press working, the press-workability is remarkably excellent as compared with the conventional Zn-Ni-based alloy plating which is dense and has low roughness. For example, the pressing load at the time of drawing can be reduced by 10 to 30%.
Although there is a concern that the corrosion resistance may deteriorate due to such a change in crystal morphology, if the Ni content is controlled in the good corrosion resistance region, the deterioration of the corrosion resistance is at a negligible level. The addition amount of the phthalate compound is 10 to 3
00 ppm is suitable, and if it is less than 10 ppm, the effect on the crystal form is not remarkable, and if it exceeds 300 ppm, deterioration of corrosion resistance cannot be ignored, which is not preferable. The more preferable addition amount range of the phthalate compound is 50 to 200 pp.
m.

The phthalate compound is a monoester shown below,

[0009]

[Chemical 1]

Particularly, phthalic acid diesters are effective. Among the phthalic acid diesters, dibutyl phthalate where R = R ′ = C ₄ H ₉ , diisooctyl phthalate where R = R ′ = C ₈ H ₁₇ , or dioctyl phthalate R = R ′ = C ₁₀ H ₂₁ Diisodecyl phthalate, or didecyl phthalate, R = R '= C ₁₂ H ₂₅ , diralyl phthalate, R = C ₈ H ₁₇ , R' = C ₁₀ H ₂₁ , decylisooctyl phthalate are particularly effective. .

In order to obtain the above Zn-Ni alloy plating from the plating bath containing the phthalate compound, it is necessary to further increase the current density to 10 to 150 A / dm ² . It is presumed that the phthalate compound is adsorbed on the surface of the steel plate that is the cathode during electrolysis to affect Zn-Ni electrodeposition, but since it is a trace amount and a polymer, it becomes diffusion-controlled at high current densities. -It becomes impossible to follow the electrodeposition of Ni, and therefore the action on the crystal morphology is reduced. For this reason, the upper limit of the current density is 150 A / dm ² . In addition, a low current density of 10 A / dm ² or less is not preferable from the viewpoint of production efficiency.

The Zn-Ni alloy plating to be used in the present invention is a Zn plating mainly containing Ni, specifically Zn-Ni, Zn-Ni-Co, Zn.
-Ni-Fe, Zn-Ni-Cr, Zn-Ni-Fe-
This refers to Zn-Ni containing other metal components such as Cr. The Ni content is preferably 5 to 20% by weight. 5% by weight
If it is less than 20% by weight, the corrosion resistance is insufficient, and if it exceeds 20% by weight, the workability is deteriorated, which is not preferable. More preferable range is 10
~ 15% by weight. The total amount of metal components other than Ni is 5
It is preferably less than 5% by weight, and not more than 5% by weight because the effect of Ni is diminished. About the adhesion amount is 10
50 g / m ² is preferred.

Regarding the plating bath, the metal ion concentration, p
There are no particular restrictions on H, bath temperature, etc., for example Z
Total concentration of n ²⁺ and Ni ²⁺ ions is 0.5 to 2.5 mol /
1, pH 0.5 to 6, sulfuric acid bath with a bath temperature of 40 to 70 ° C.,
Alternatively, a chloride bath can be used, but the use of a sulfuric acid bath which can use an insoluble electrode is advantageous.
In the plating bath, if necessary, Fe ²⁺ , Co ²⁺ , Cr ³⁺
A small amount of ions and the like may be contained, and irrelevant salts such as Na ⁺ , NH ₄ ⁺ , K ⁺ and Mg ²⁺ ions may be added in order to increase the electric conductivity. The liquid flow rate is preferably 10 to 200 m / min in order to uniformly exert the effect of the phthalate ester compound on the steel sheet.

[0014]

Example A cold-rolled steel sheet (low-carbon steel sheet for deep drawing) having a thickness of 0.8 mm was degreased with alkali, pickled with a 5% sulfuric acid aqueous solution, and then coated with Zn having an adhesion amount of 30 g / m ² under various plating conditions. -N
i-based alloy plating was performed. A sulfuric acid acidic bath was used as a plating bath, and a phthalic acid ester compound was added thereto.
The Zn-Ni alloy-plated steel sheet thus obtained was analyzed for plating composition, and press workability and corrosion resistance were evaluated. These are summarized in Table 1. The phthalate compound in Table 1 is as follows. A: dibutyl phthalate B: dioctyl phthalate C: didecyl phthalate D: dilauryl phthalate E: decyl isooctyl phthalate Further, the evaluation methods of press workability and corrosion resistance are shown below. (1) Press workability Cylindrical deep drawing test (drawing ratio 2.0, wrinkle holding 0.5ton)
The maximum punch load when the drawing speed was 25 mm / min) was evaluated. As a lubricating oil, Z- manufactured by Idemitsu Kosan Co., Ltd.
3 was applied to the surface of the Zn-Ni alloy plated steel sheet at 1 g / m ² . Maximum punch load less than 4 tons: ◎ 4 to 4.5 tons: ○ More than 4.5 tons: × (2) Corrosion resistance As-plated salt spray test (JIS Z2371) 3
It was evaluated by the area where red rust occurred after 36 hours. Red rust generation area less than 1%: ⊚ 1 to 5%: o more than 5%: × In Table 1, the invention examples 1 and 2 are compared with the comparative example 1. Inventive Examples 1 and 2 have better press workability and comparable corrosion resistance than Comparative Example 1 in which the phthalate compound is not added to the plating bath. Invention Example 3 to
7 is compared with Comparative Examples 2-5. Inventive Examples 3 to 7 have better press workability than Comparative Example 2 in which the phthalic acid ester compound is not added to the plating bath or Comparative Example 3 in which the addition amount of the phthalic acid ester compound is too small. The corrosion resistance is also the same.

However, if the amount of the phthalate ester compound in the plating bath is too large as in Comparative Example 4, the corrosion resistance deteriorates. Further, as in Comparative Example 5, even if an appropriate amount of the phthalate compound is added to the plating bath, if the current density is too high, the press workability is not effective. Small amount of Co, F
Other invention examples of the invention examples 14 to 16 containing e and Cr,
The effect of improving the press workability by adding the phthalate compound is clear, and no deterioration in corrosion resistance is observed.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

EFFECTS OF THE INVENTION According to the method for producing a Zn—Ni alloy electroplated steel sheet of the present invention, it is possible to improve the press workability while maintaining the high corrosion resistance inherent to Zn—Ni alloy plating. It is possible to provide a Zn-Ni-based alloy electroplated steel sheet suitable for automobiles and home appliances that require a high degree of press workability.

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[Procedure amendment]

[Submission date] May 30, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

[Table 2]

Claims (1)

[Claims] 1. A Zn-Ni alloy electroplated steel sheet is manufactured by adding a phthalate ester compound in an amount of 10 to 300 ppm in a Zn-Ni alloy plating bath to obtain a current density of 1.
A method for producing a Zn-Ni alloy electroplated steel sheet having excellent workability, which comprises electroplating a steel sheet at 0 to 150 A / dm ² .