JPH01230797A - Zn-ni composite electroplated steel sheet having superior corrosion resistance and workability - Google Patents

Abstract

PURPOSE:To improve corrosion resistance and workability by forming a Zn-Ni composite plating layer having a compsn. consisting of specified amts. of Ni, Cr, SiO2, Fe and Zn on a steel sheet by electroplating. CONSTITUTION:This Zn-Ni composite electroplated steel sheet has a plating layer having a compsn. consisting of, by weight, 1-15% Ni, 0.1-10% Cr, 0.1-10% SiO2, 0.01-3% Fe and the balance Zn. The Cr and SiO2 are uniformly deposited in the plating layer to improve the corrosion resistance and the very small amt. of Fe ensures workability.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to Zn-
The present invention relates to a Ni-based composite electroplated steel sheet.

(Prior Art) It is well known that electrogalvanized steel sheets are already widely used as surface-treated steel sheets that can be mass-produced without impairing the corrosion resistance of cold-rolled steel sheets, the corrosion resistance after painting, and workability.

However, in recent years, attempts have been made to use galvanized steel sheets as anti-rust steel sheets for automobiles in response to the salt sprayed on roads in winter to prevent roads from freezing in cold regions, and there is an increasing demand for corrosion resistance in harsh corrosive environments.

In response to these demands for improving the corrosion resistance of galvanized steel sheets, it is known that corrosion resistance can be improved by increasing the amount of zinc plating (adhesion amount). Many have been proposed.

Many of these contain iron group elements such as Fe, Ni, and Co as alloy components, and in particular, Zn-
Ni, Zn-Co alloy plating.

The usefulness of Zn--Fe alloy plating has been recognized and it has been put into practical use.

(Problems to be Solved by the Invention) Recently, various proposals have been made regarding composite plating in which substances other than metals are eutectoid. For example, JP-A-5
No. 4-146228 discloses Zn-5iOz, and JP-A No. 60-141898 discloses a composite plating in which SiO□, TiO□, etc. are contained in a Zn-iron group element alloy plating.

JP-A-60-125395.61-270398 discloses a composite plating in which alumina is contained in the plating layer.

The key to the corrosion resistance of these composite platings is the uniformity of the eutectoids such as alumina and SiO2 within the plating layer, and depending on the plating conditions and changes in composition, the eutectoids may aggregate. It is extremely unstable, as it may eutectoid in lumps or the amount of co-existence itself may become unstable, and the expected effect may not be achieved.

In addition, it is pointed out that the processability is lowered and the corrosion resistance is still insufficient in severe corrosive environments such as in cold regions.

(Object of the Invention) The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and to provide a Zn-Ni composite electroplated steel sheet having excellent performance such as corrosion resistance and workability.

(Means for solving problems) The present invention was made based on the following findings.

(1) As the eutectoid substance, Sin is the most effective in terms of corrosion resistance, and the corrosion resistance is improved to a factor of 11 only when it is uniformly eutectoid in the plating layer in a fine state.

(2) As a eutectoid promoter for SiO
As shown in No. 141898, iron group elements, especially Ni, are effective, but it is difficult to stably eutectoid SiO2 in the plating layer using these alone. As a solution to this problem, the addition of Cr3+ is extremely effective.
When r ions coexist, it is possible to stably and uniformly eutectoid SiO2. Furthermore, since Cr also co-deposit with SLO□, the corrosion resistance is further improved. This point is the first point of the present invention.

This is because Ni ions and Cr ions are adsorbed around SiO□, increasing the repulsive force between the Sin2 particles, and as a result, the aggregation of SiO□ is suppressed, and S
It is presumed that this is because iO2 is stably incorporated into the plating layer.

(3) However, it is difficult to eutectoid Zn metal and chromium metal, and the same <Si particles adsorbed with Ni and Cr are
If it is attempted to be deposited in n metal, the workability will be reduced.

To improve this, it is necessary to further add Fe.

In other words, the effect of Fe is to prevent the Cr ions added for SiO2 precipitation from inhibiting the uniform electrodeposition growth of Zn and Ni, resulting in a plating structure lacking in uniformity and smoothness. At the point. The second point of the present invention lies in the discovery of this effect of adding 176.

The reason for this is not clear, but when Cr ions adsorbed on Sun are deposited, only through Fe.
It is expected that a stable structure will be formed in the Zn-Ni plating layer. As a result, it is estimated that Cr and SiO□ are incorporated without hindering the uniform growth of the Zn-Ni plating layer, resulting in a structure with excellent workability.

(4) Furthermore, if the upper layer is thinly plated with Zn or Zn-based alloy, the corrosion resistance of the coating machine will be particularly improved.

The present invention was achieved based on the above knowledge and further detailed studies. That is, the gist of the present invention is that Ni: 1 to 15% by weight, Cr: 0.1 to
10% by weight, 5io2: 0.1~IO% by weight, Fe
: Zn-N consisting of 0.01 to 3% by weight, the balance being Zn
A Zn-Ni composite electroplated steel sheet with excellent corrosion resistance and workability formed by forming an i-based composite electroplating layer, and further formed by forming a Zn or Zn-based alloy electroplating layer on the upper layer of the composite electroplating layer. Zn- with excellent corrosion resistance and workability
This is a Ni-based composite electroplated steel sheet.

(for production) The present invention will be explained in more detail below.

The Ni content of the Zn-Ni composite electroplated layer of the present invention was set at 1 to 15%, but this is because Ni is adsorbed to SiO□ together with Cr in a plating bath, and SiO2 is uniformly distributed in the plating layer. The main focus is on conditions that make it easy to disperse and eutectoid, and N
This is because the alloy effect of i is taken into consideration. If the Ni content is less than 1% by weight, the corrosion resistance of the uncoated product will be insufficient, and if it exceeds 15% by weight, the processability will be significantly reduced.
Undesirable.

Although the Cr content was set at 0.1 to 10% by weight, such a large amount of Cr precipitation is possible due to the coexistence of Fe and 5i02. The amount of Cr precipitated is determined in relation to the SiO□ content and Fe content, but if it is less than 0.1% by weight, no corrosion resistance improvement effect is observed, and if it exceeds 10% by weight, the effect is saturated, and Processability decreases.

The content of Sin was set at 0.1 to 10% by weight, but in order to stably and uniformly eutectoid it in the plating layer, N
i. In addition to Fe, Cr3+ must be present in the plating bath. SiO2 contributes to improving corrosion resistance, but
This is thought to be because it has a buffering capacity against the atmospheric pH and because it prevents the diffusion of corrosion products. If SiO2 is less than 0.1% by weight, there is no effect of improving corrosion resistance, and if it exceeds 10% by weight, processability and plating adhesion deteriorate, which is not preferable.

The Fe content was determined to be 0.01 to 3% by weight, and the role of Fe in the composite plated steel sheet is mainly to assist in bonding between Cr and Zn, which is the main component of the coating layer. The point is to improve workability. In this sense, if it is less than 0.01% by weight, there will be no above effect, and if it is less than 3% by weight.
If it is too high, not only the above effect will be saturated, but also the corrosion resistance of the unpainted product will deteriorate. The amount of plating deposited is 10~
At 50 g/m2, sufficient corrosion resistance can be ensured.

The composite electroplated steel sheet formed in this way may be left as a single layer, or the upper layer may be coated with Zn, Zn-Ni, or Zn-F.
A small current may be used for Zn-based alloy plating such as e.

When the upper layer is plated with Zn or a Zn-based alloy, it is preferably 1 to 5 g/m, and by doing so, stable and good paint removal and corrosion properties can be obtained. It is also advantageous in preventing coating film defects during cationic electrodeposition coating.

As for the amount of plating deposited, corrosion resistance can be sufficiently ensured with a coating weight of 10 to 50 g/m.
In addition to Fe, Co, Pb, Sn, Ag,
In, Bi, Cu, Sb, As.

Even if AQ, Ti, Na, P, O, C, etc. inevitably eutectoid in small amounts, the effects of the present invention essentially remain unchanged.

Regarding the manufacturing method, Zn2+ is 30 to 60
g/Q, 1 to 30 g/Q of Cr34 in an acidic electroplating bath containing 5 to 60 g/11 of Ni"+,
Sin□ 5-50g/Q, Fe”+ 0.1-10
g/Q coexist, pH 1-3, bath temperature 40-70
℃, electroplating may be performed at a current density of 50 to 300 A/dm2. In addition, suitable conductive aids such as salts such as Na", K" and NH4+, and pH buffers such as halonic acid may be contained. As a Cr source, sulfuric acid C is used in a sulfuric acid acid bath.
r is good. Any of water-dispersed sol, colloidal silica, dry silica, and fume silica may be used as SiO□, but fine ones with a primary particle size of 1 to 100 mμ are preferable.

The structure of the present invention does not necessarily have to be applied to both sides of a steel plate, but can be applied to only one side depending on the application.

The other surface may be a steel plate surface, or may be a plating layer coated with another plating layer or an organic film.

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 bright finish rolled, a high tensile strength steel plate that contains a large amount of Mn, S, P, etc. as steel components, Cr, Cu, Ni. It can also be applied to highly corrosion-resistant steel plates that contain a large amount of P, etc. and have a low corrosion rate.

(Example) After degreasing a cold rolled steel plate with alkali and pickling with 5% sulfuric acid,
After washing with water, electroplating was performed under the following conditions. Liquid flow rate 90+++/min by pump stirring, distance between poles 1
A sulfuric acid acid bath with a bath temperature of 60° C. and a pH of 2 was used. The SiO□ added to the plating bath has an average particle size of 10
~20 mμ colloidal silica and average particle size 30-50
mμ dry silica was used. N contained in the plating layer
The contents of i, Cr, SiO2, and Fe are controlled by the amount of each added in the plating bath and the current density, and the basis weight is 20 g/rr? For one part, Zn or Zn-based alloy plating was applied to the upper layer at a rate of 3 g/piece.

Table 1 shows the composition, corrosion resistance, and workability evaluation results of the plated steel sheets. The corrosion resistance and workability evaluation methods are as follows.

(1) Corrosion resistance evaluation method - Unpainted corrosion-resistant plated material was subjected to 30 cycles of the following cyclic corrosion test with the bare plated material, and the amount of reduction in plate thickness was evaluated.

0~0.1mm ◎0.1-0.
2mm Oo, 2~0.3ml! l
Δ0.3mm～
×■ After coating, perform edible dip-type phosphate treatment and cationic electrodeposition coating (20μ), make a cross cut that reaches the base steel, perform 50 cycles of the following cycle corrosion test, and test the bulge width of the cross cut part. It was evaluated by

0~1mm ◎ 1~3mn+ 0 3~5mm Δ 5mm or more × ■Cycle corrosion test (2) Workability evaluation method After cylindrical press molding of 50φX251.

The tape was peeled off and the weight loss was evaluated.

0-2mg ◎ 2-5mg.

5 to 8 mg Δ 8 mg or more × The examples that are examples of the present invention clearly have better corrosion resistance and workability than the comparative examples.

(Effect of the invention) The present invention uses Zn-Ni alloy plating as a base, and Cr
By uniformly eutectoiding and SiO□ inside the plating layer, corrosion resistance is greatly improved.

In addition, workability was also ensured by containing a small amount of Fe. Therefore, it can be fully expected to be applied to automobiles, home appliances, etc.

Procedural amendment June 1986 Noro day

Claims (2)

[Claims] (1) On the surface of the steel plate, Ni: 1 to 15% by weight, Cr: 0
．． 1 to 10% by weight, SiO_2: 0.1 to 10% by weight,
Fe: 0.01 to 3% by weight, the balance being Zn-
A Zn-Ni composite electroplated steel sheet with excellent corrosion resistance and workability, characterized by forming a Ni composite electroplating layer. (2) On the surface of the steel plate, Ni: 1 to 15% by weight, Cr: 0
．． 1 to 10% by weight, SiO_2: 0.1 to 10% by weight,
Fe: 0.01 to 3% by weight, the balance being Zn-
A Zn-Ni composite electroplated steel sheet having excellent corrosion resistance and workability, comprising a Ni composite electroplating layer and a Zn or Zn alloy electroplating layer formed on the composite electroplating layer.