JPH09279385A - Electric zinc alloy coated steel sheet having excellent workability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the formability of a steel sheet by subjecting the outermost layer of a Zn-Ni alloy electroplating layer to Zn-Ni plating of a specific current density and coating weight in an acidic Zn-Wi plating bath vessel contg. a specific amt. of Pb. SOLUTION: The outermost layer of the Zn-Ni alloy electroplating layer is subjected to the Zn-Ni plating in the acidic Zn-Ni plating bath vessel contg. 0.01 to 500ppm Pb. The plating conditions are the current density of 10 to 200A/dm<2> and the coating weight is 0.1 to 10g/m<2> . If the coating weight is below 0.1g/m<2> , the press formability is insufficient. If the coating weight exceeds 10g/m<2> , the effective is satd. If the current density is below 10A/dm<2> , non-plating occurs and if the current density exceeds 200A/dm<2> , unequal plating burn occurs. The use of the Zn-Ni alloy coated steel sheet for hardly formable parts of automobiles and household electrical products to which the application of this steel sheet is heretofore difficult is made possible.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric Zn alloy plated steel sheet having excellent press formability and corrosion resistance, which is suitable as a surface-treated steel sheet used for difficult-to-form articles in automobiles and home electric appliances, and a method for producing the same. Is.

[0002]

2. Description of the Related Art A wide variety of surface-treated steel sheets are used as measures against corrosion of automobile bodies by sprayed rock salt for road freezing in winter in cold regions. The simplest surface-treated steel sheet is a Zn-plated steel sheet, but in automobile applications, high corrosion resistance is required, so it is necessary to thicken the plating layer, which causes problems such as weldability and workability at the vehicle body assembly stage. . Therefore, many alloy platings with high corrosion resistance have been developed even if the plating layer is thin. Among them, Fe, C
Z containing an iron group metal such as o or Ni as an alloy component
It is recognized that the n-based alloy plating has good weldability and workability as well as corrosion resistance, and is widely used.

On the other hand, automobiles and home electric appliances are required to have higher and more versatile formability in accordance with the diversification of needs, and various types can be obtained depending on the forming technique of materials making full use of formability and rolling / annealing conditions. A steel sheet having the forming characteristics of is developed. However, in the case of a Zn-based alloy-plated steel sheet, even if the plating film is simply applied on the high formability steel sheet, the physical properties of the steel sheet as the base material and the plating film are significantly different,
The forming characteristics of the steel sheet itself may not be sufficiently exhibited in the actual forming stage.

This is because the surface that actually contacts the press die becomes a plating film, and the effect of its characteristics increases.
When attempting to apply a plated steel sheet to a difficult-to-form product that requires deep drawing or a complicated shape, unexpected forming defects such as cracks and mold galling are likely to occur. To solve such a problem, as described in JP-A-2-274853-6, a technique for improving the formability by previously adjusting the roughness of the steel sheet surface in the alloyed hot dip Zn plated steel sheet, and Kaihei 4-21
As described in Japanese Patent No. 4877, there is a technique for imparting an inorganic compound to the surface of a Zn-plated steel sheet to improve slidability, but none of them has reached a satisfactory level.

[0005]

[Problems to be Solved by the Invention] With a plated steel sheet, it is impossible to follow higher forming even if the material of the steel sheet is increased. Therefore, the plating film itself is reformed into a state excellent in press formability. Requires technology. JP-A-4-
As disclosed in Japanese Patent No. 224877, coating with a different type of film is also one measure, but it is not necessarily a good measure because deterioration of other quality such as weldability and cost increase are assumed.

As described above, Zn-based alloy-plated steel sheets have not been utilized sufficiently because they have excellent corrosion resistance, but their applications are limited in terms of press formability. Especially Z
Since the n-Ni alloy plated steel sheet is thin and has excellent corrosion resistance, there is a great need for expanding applications to automobiles and home appliances.
Improvement of press formability is desired.

An object of the present invention is to provide an electric Zn alloy plated steel sheet which can satisfy a high degree of press formability mainly for automobiles and home appliances, and a method for producing the same.

[0008]

The electric Zn alloy-plated steel sheet of the present invention comprises an outermost Zn-Ni alloy electroplated layer,
Acidic Zn-Ni containing 0.01 to 500 ppm of Pb
An electric Zn alloy-plated steel sheet having excellent workability, which is obtained by performing Zn-Ni plating with a deposition amount of 0.1 to 10 g / m ² at a current density of 10 to 200 A / dm ^{2 in} a plating bath. . Moreover, the manufacturing method of the electrical Zn alloy plated steel sheet of this invention WHEREIN: The acidic Zn which contained 0.01-500 ppm of Pb in the outermost layer of Zn-Ni alloy electroplating layer.
Zn-Ni with an adhesion amount of 0.1 to 10 g / m ^{2 in} a Ni plating bath with a current density of 10 to 200 A / dm ^2.
It is a method for producing an electroplated Zn alloy-plated steel sheet having excellent workability by plating.

The present inventors have studied Zn-Ni alloy plated steel sheet to improve press formability without impairing excellent quality such as corrosion resistance. As a result, Zn-Ni alloy plating is produced. At this time, Zn-from the plating bath in which a trace amount of Pb ions was added to the outermost layer part
It was found that the press formability was significantly improved by Ni plating. The present invention has been made based on this finding.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the results of experiments conducted by the present inventors.

(1) Electric Zn-Ni plating Zn ²⁺ (0.3 to 2 mol / l) -Ni ²⁺ (0.3 to 2 mol / l) -pH (0.5 to 6) base plating After applying Zn-Ni plating in a bath (bath temperature 40 to 70 ° C),
Pb acetate was added to a Zn-Ni plating bath having the same composition, and the outermost layer Zn-Ni plating was applied from the plating bath in which the Pb concentration in the plating bath was changed to 0.01 to 500 ppm. The adhesion amount of the outermost layer plating was set to 0.1 to 10 g / m ² . When it is 0.1 g / m ² or less, press formability is insufficient as will be shown later. Further, even if it exceeds 10 g / m ² , the effect is saturated, so the upper limit is defined as 10 g / m ² .

The current density was set in the range of 10 to 200 A / dm ² for both the lower layer plating and the outermost layer plating. 10 A / dm
^If it is less than ² , non-plating may occur, and 200
If it exceeds A / dm ² , uneven plating burn may occur.

In the present invention, the coating amount of the lower layer plating obtained from the Pb-free plating bath is not particularly limited, but from the viewpoint of corrosion resistance and manufacturing cost, it is practically 10 to 60 g / m ^2. It is a typical range.

(2) Workability evaluation The test conditions for workability evaluation are as follows.

A Ti-added ultra-low carbon steel is used as a plating base plate, and under the plating conditions shown in (1), lower layer plating is 20 or 30 g / m ² , and outermost layer plating is 0.1 to 1.
It was applied at 0 g / m ^{2 and} subjected to a press molding test. As a press molding test, 10 cylindrical press moldings were carried out by applying low viscosity oil under the conditions of punch diameter 50mm and drawing ratio 2.2, cracking number, punch load, and powdering by side wall taping of the pressed product. It was evaluated by. The evaluation points are as shown in Table 1.

[0016]

[Table 1] 5: No cracks, punch load is almost at original plate level, powdering is slight 4: No cracks, punch load is slightly higher than the original plate, powdering is minor 3: Number of cracks is 1 to 3, punch load is Higher than the original plate,
Minor powdering 2: 4 or more cracks, or many powdering 1: 4 or more cracks, or considerably powdering

Table 2 shows the results of evaluation of press formability. When the outermost layer is plated, the Pb concentration in the plating bath is 0.01 to 500 ppm, and the outermost layer plating amount is 0.1 to
Within the range of 10 g / m ² , the evaluation point was 4 or more, and extremely stable press formability was exhibited.

(3) Pb supply method As a Pb supply method, a chemical such as Pb acetate is generally added directly to the plating bath. In addition, P on the plating electrode
A method of using a b-type insoluble electrode and slightly dissolving Pb in the plating bath can also be adopted.

[0019]

EXAMPLE When Zn-Ni plating is performed on a Ti-added ultra-low carbon steel sheet, Zn-Ni alloy plating is applied to the outermost layer from Zn-Ni plating baths with various Pb concentrations, and then press formability and corrosion resistance are obtained. Was evaluated. The press formability was evaluated by the above-mentioned test, and the corrosion resistance was evaluated by the salt spray test (JIS
(According to Z2371). The evaluation criteria for corrosion resistance are: ○: equivalent to Zn-Ni plating without outermost layer plating,
X: Decreased as compared with Zn-Ni plating without outermost layer plating.

Table 2 shows the contents of the test materials and the evaluation results.

[0021]

[Table 2]

Comparative Examples 1 and 2 contain Pb in the outermost layer plating bath.
The press formability of the plated steel sheet was insufficient due to the absence or a small amount. In Comparative Examples 4 and 5, the press formability was insufficient because there was no or little outermost layer plating. In Comparative Example 3, the corrosion resistance was deteriorated because the Pb concentration in the plating bath was too high.

In the examples of the present invention, the press formability could be improved without impairing the corrosion resistance.

[0024]

INDUSTRIAL APPLICABILITY The present invention makes it possible to obtain an electric Zn alloy-plated steel sheet having excellent press formability, and Zn-Ni alloy plating is applied to difficult-to-form parts in automobiles and home appliances that have been difficult to apply in the past. It is extremely effective in expanding the applications of steel sheets.

Claims (2)

[Claims] 1. An acidic Zn-containing Pb in an amount of 0.01 to 500 ppm in the outermost layer of the Zn-Ni alloy electroplating layer.
An electric Zn having excellent workability obtained by applying Zn-Ni plating with a deposition amount of 0.1 to 10 g / m ^{2 in} a Ni plating bath at a current density of 10 to 200 A / dm ^2.
Alloy plated steel sheet. 2. An acidic Zn-containing 0.01 to 500 ppm Pb layer in the outermost layer of the Zn-Ni alloy electroplating layer.
A method for producing an electric Zn alloy-plated steel sheet having excellent workability, which comprises applying Zn-Ni plating with a deposition amount of 0.1 to 10 g / m ^{2 in} a Ni plating bath at a current density of 10 to 200 A / dm ² .