JPH01309993A - Production of zn-ni alloy plated steel sheet having superior chipping resistance at low temperature - Google Patents

Abstract

PURPOSE:To easily obtain the subject plated steel sheet having superior adhesion of the plating and superior pitting resistance without lowering productivity by plating a steel sheet with a Zn-Ni alloy plating bath under specified conditions to form a lower layer and by further plating the steel sheet with the same bath to form an upper layer. CONSTITUTION:A steel sheet is plated with a Zn-Ni alloy plating bath under the conditions of 1-50 msec current supply time, 5-50% duty cycle and 10-100A/dm<2> average current density to form a lower layer by 0.1-5.0g/m<2>. The steel sheet is further plated with the same plating both to form an upper layer. A plated steel sheet having superior adhesion and pitting resistance can be obtd. with the conventional Zn-Ni alloy plating bath without lowering productivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a Zn-Ni alloy coated steel sheet with excellent low-temperature chipping properties, and more particularly, the present invention relates to a method for manufacturing a Zn-Ni alloy coated steel sheet with excellent low-temperature chipping properties, and more particularly, it relates to a method for manufacturing a Zn-Ni alloy coated steel sheet having excellent low-temperature chipping properties. The present invention relates to a method for producing a Zn-Ni alloy plated steel sheet with excellent low-temperature chipping.

[Prior art] In order to improve the rust prevention effect of automobiles, Zn-
Ni-based alloy plated steel sheets are now being used in large quantities, and therefore, countermeasures against appearance rust have been studied by applying Zn--Ni based alloy plating to the outer surface of automobiles.

The Zn-Ni alloy plating layer applied to the exterior of the car has a hardness of 200 to 400 Hv), and the stress during plating is large, so it is sprayed in cold regions (rock salt + pebbles). This causes an important problem of so-called low-temperature depping, in which not only the paint applied to the outer surface of the automobile but also the plating layer peels off, and a solution to this problem is desired.

In order to meet the demand for solving this problem, we improved the low-temperature depping properties of the Zn-Ni alloy plating layer.
7. After depositing 3 g/m2 of adhesion m, immersing it in a plating bath without applying electricity. n-Ni alloy plating layer is provided (+filtration method (JP-A-63-007973)), and Zn-Ni with a higher Ni content than normal Zn-Ni alloy plating is used as the base plating layer. 005 alloy plating
08 μm in thickness, and then a Zn-Ni alloy plating layer (Japanese Patent Publication No. 61-000439), and furthermore, as a base plating layer, Cr, Fe5CoSN
i, CuS In.

A precipitate containing one or more of Zn, Cd, Sn, and Pb is dispersed and deposited in an amount of 1 to 1QO mg/m, and then
Techniques such as a method of performing Zn-based alloy or composite electroplating (Japanese Unexamined Patent Publication No. 59-200789) have been developed.

However, in JP-A-61-007973, a normal plating bath is used and there is no need to change the equipment;
After applying a small amount of n-Ni alloy plating, it is necessary to pass through the next plating bath without applying electricity, which reduces the number of effective plating baths and causes a decrease in productivity. be.

In addition, Japanese Patent Publication No. 61-000439 and Japanese Unexamined Patent Publication No. 5
In the publication No. 9-200789, in any case, a predetermined Zn
-Before performing Ni-based alloy plating, it is necessary to perform plating using baths with different bath compositions, and there is a concern that problems with the quality of the plating product may occur due to the mixing of plating baths. Not only does this require a separate new plating bath and work equipment, but when plating in a pond where pre-plating is not required, it takes a lot of time to change out the plating bath, which leads to a decrease in productivity. be.

[Problem to be solved by the invention] The present invention solves the above-mentioned Z
In view of various problems when performing n-Ni alloy plating, the present inventor has conducted extensive research and has found that a normal Zn-Ni alloy plating solution can be used without reducing productivity. By using Zn--Ni alloy plated steel sheets as they are, they have developed a method for producing Zn--Ni alloy-plated steel sheets with excellent low-temperature depping properties, which are particularly suitable as rust-proof steel sheets for automobiles.

[Means for Solving the Problems] The method for manufacturing a Zn-Ni alloy coated steel sheet with excellent low-temperature chipping properties according to the present invention is characterized by: A steel plate is energized in a Zn-Ni alloy plating bath for a period of 1 −
50m5ec, I) Uty Cycle5-50%,
Under conditions of an average current density of 10 to 1.00 A/dm,
After plating the lower layer at a rate of 0.1 to 5.0 g/mt, the upper layer is further plated using the same Zn-Ni alloy plating bath used for the underwear.

The method for producing a Zn-Ni alloy plated steel sheet with excellent low-temperature chipping properties according to the present invention will be described in detail below.

That is, Zn-N with excellent low-temperature chipping properties according to the present invention
The manufacturing method for I-based alloy-plated steel sheets is as follows: In a line that continuously manufactures normal Zn-Ni-based alloy-plated steel sheets, first, in a first plating bath, the current is applied for 1 to 50 m5 ec.
, Duty Cycle 5-50 g/m", average current density 10-100 A/dm" pulse plating 01-5
．． After applying 0 g/m', normal Zn-Ni alloy plating (continuous Ti) is applied to the second and subsequent plating layers to the remaining required amount.

In the method for producing a Zn-Ni alloy coated steel sheet with excellent low-temperature chipping properties according to the present invention, the current application time is 1 m5.
If the duty cycle is less than 5%, the effect of improving low-temperature depping property is small, and if the duty cycle exceeds 50m5ec, the effect will not improve much. Even if it exceeds %, no further effect can be obtained.

Furthermore, when the average current density is less than 10Δ/dm', Zr+
-Ni content in Ni-based alloy plating is 95 to 14.0w
If the Ni content in the plating exceeds the 1/2 range and the Ni content in the plating layer obtained by continuous energization cannot be obtained.
content, which causes problems with properties other than low-temperature chipping properties, such as corrosion resistance.

In addition, the coating weight of Zn-Ni alloy plating was set to 0.1 to 5.
0g/m" is because low temperature chipping was not observed at O, 1g/m2/'+1, and 5.0g/m2.
/m'' and performing pulse plating on all plating layers is also effective, but it is necessary to perform pulse plating not only in the first plating tank but also in the second and subsequent plating tanks. There is a problem in that the amount of capital investment is large.

The reason why low-temperature chipping properties are improved by pulse plating is not clear, but it is thought to be as explained below.

■ Short-time energization (on-t), which is a feature of pulse plating
ime), no diffusion layer is generated on the surface and interface of the plating solution, or if it is generated, it is extremely thin compared to normal DC electrolysis, so the metal ions in the plating solution can easily move to the surface. Therefore, crystal grain formation occurs on all surfaces, making the crystal grains smaller. Also, since crystal growth occurs easily, it is thought that the plating stress becomes smaller.

■Also, on the plated surface during DC high current density electrolysis, 1'(
It is thought that with the generation of hydroxide, the l)H at the interface increases and some hydroxide is taken into the plating layer.
In pulse plating, since the current application time is short, it is difficult for compounds other than metals to be incorporated. Therefore, it is thought that the adhesion of the plating layer is improved.

(2) Furthermore, it is conceivable that the plating stress is further reduced because a small portion of the plating layer is dissolved by the plating solution during the off-time.

In this way, by performing pulse plating on the steel plate and then plating the plate by continuous energization, it is possible to significantly improve low-temperature depping properties, and at the same time, the appearance is beautiful. It fully satisfies the excellent performance as an automobile protection material such as paintability and corrosion resistance.

[Example] An example of the method for manufacturing a Zn-Ni alloy plated steel sheet having excellent low-temperature chipping properties according to the present invention will be described.

Example A cold-rolled steel plate (aluminum killed M) with a thickness of 0.7 mm was used, and after electrolytic degreasing, water washing, pickling, and water washing, Zn-Ni alloy was prepared under various conditions shown in Table 1. Plating was performed.

Low-temperature chipping property evaluation was performed after plating with automotive phosphate treatment, SD-2500 (manufactured by Nippon Paint Co., Ltd.), and electrodeposition coating (PT-[52, manufactured by Nippon Paint Co., Ltd., 15 μm,
165°C x 20 minutes baking), intermediate coating (OTO-481
5, Nippon Paint Co., Ltd., 36μm, +4-0℃×
After applying three coats (OTO-630, manufactured by Nippon Paint Co., Ltd., 35 μm, 140°C x 20 minutes baking), the sample was frozen at -20°C, and the next coating was applied using a gravelometer. Chipping is performed under certain conditions, and the paint film peels off (
10 pieces with large diameters (including peeling of plating) were measured.

[Graphero condition distance @ 350mm air pressure
4.0kg/cm” sample temperature
-20°C stone (granite, 7.9~11.1mm)
φ) In the 100g table, total adhesion M20~30g/
In the example of the method for producing a Zn-Ni alloy coated steel sheet that has achieved low-temperature chipping properties according to the present invention, the maximum amount of peeling of the coating film and plating was 4. , 0m+n or less, whereas in the Zn-Ni alloy plating in the comparative example,
It has a large diameter exceeding 5.0 mm, indicating that the Example of the method for manufacturing a Zn-Ni alloy plated steel sheet with excellent low-temperature depositing properties according to the present invention is extremely effective.

[Effects of the Invention] As explained above, the method for producing a Zn-Ni alloy coated steel sheet with excellent low-temperature chipping properties according to the present invention has a two-pronged structure, so it can be used without changing the plating solution. , it is possible to easily perform Zn-Ni alloy plating with extremely excellent plating adhesion without hindering productivity, and a multilayer plating plate with excellent depping resistance can be obtained. This has the effect of increasing industrial significance.

Claims (1)

[Claims] The steel plate was energized for 1 time using a Zn-Ni alloy plating bath.
~50msec, DuLyCycle 5~50%, average current density 10~100A/dm^2, 0.
Zn with excellent low-temperature chipping properties characterized by plating a lower layer of 1 to 5.0 g/m^2 and then plating an upper layer using the same Zn-Ni alloy plating bath as the lower layer. - A method for producing a Ni-based alloy plated steel sheet.