JPS58130299A - Production of zn-ni alloy electroplated steel plate having high corrosion resistance in worked part - Google Patents

Abstract

PURPOSE:To produce a titled steel plate easily and inexpensively with the same plating soln. in the stage of electroplating a Zn-Ni alloy, by applying lower layer plating thinly at specific current density and quantity of electricity then applying upper layer plating at the higher current density. CONSTITUTION:Two layers of plating are applied on a steel plate, by using the same Zn-Ni plating soln. and in order to make the content of Ni in the under layer higher than the upper layer, the current density is regulated as follows: The under layer plating is applied at 2-<20A/dm<2> current density and 1-300 coulomb quantity of electricity. Then, the upper layer plating is applied at >=20A/dm<2> current density. The content of Ni in the lower layer plating is increased and is made electrochemically nobler than the upper layer by providing a step to the current density in the above-mentioned way. The layer of the under layer plating is made thin and is made difficult to crack in the stage of working by limiting the quantity of electricity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a Zn--Ni alloy electroplated steel sheet that exhibits excellent corrosion resistance even if cracks occur in the plating layer due to processing.

In recent years, the use of electrogalvanized steel sheets has been expanded to include use K, which requires a high degree of corrosion resistance, and a plating layer that has a higher degree of corrosion resistance than the conventional single zinc coating is required. For this reason, various zinc alloy plated steel sheets have been developed, one of which is a KZn-Ni alloy electroplated steel sheet. This conventional steel sheet was manufactured by plating a Zn-Ni alloy on a ``'C steel sheet using a Zn-Ni plating solution under the same conditions from beginning to end.The Ni distribution in the plating layer was uniform, and the unplated surface was It exhibited excellent corrosion resistance in the processed state.

However, compared to pure zinc, the Zn-Ni alloy of the mating layer is hard (inferior to workability and inferior in sacrificial corrosion resistance. Therefore, when bending is performed, cracks that reach the steel base may occur). If such a rack occurs, red rust will occur in a short period of time.Therefore, conventional Zm
-When using processed Ni alloy electroplated steel sheet,
There was a problem in that red rust developed from the cracks in a short period of time, and this progressed throughout the alloy, resulting in corrosion throughout the Zn--Ni alloy without exerting its inherent corrosion resistance5.

In order to obtain a Zr*-Ni alloy electroplated steel sheet without such problems, strike plating such as nickel strike is applied before Za-Ni alloy plating to create a two-layer structure, and the strike plating layer removes cracks from the steel base. Research is being carried out on ways to prevent corrosion of steel substrates and corrosion of steel substrates.

In the case of the Shiha-Shiko method, the plating is two-layer plating with different components, so the plating baths for each layer must be independent from each other, and measures must be taken to prevent contamination due to strike plating solution being taken out. It is necessary to Therefore, the plating work becomes complicated and is not necessarily a preferable method.

The present invention provides a two-layer Zn-
The present invention provides a method for manufacturing Ni alloy electroplated steel sheets by plating them with the same plating solution.

That is, the present invention uses the same -Zn-Ni plating solution to
As a step, a thin lower layer plating with a high Ni content is applied, and as a second step, an upper layer plating with a lower Ni content than the lower layer is applied, so that the upper layer is electrochemically less noble than the lower layer, and the same plating solution is applied. Zn-N has excellent corrosion resistance in processed parts.
It manufactures i-alloy electroplated steel sheets.

In the present invention, the N1 content of the lower layer is made higher than that of the upper layer using the same plating solution, and this is done by the difference in current density 1. That is, as a first step, 2 Vdr+/ or more,
-F layer plating is performed at a current density of less than 20 A/dPF/, and then, as a second step, upper layer plating is performed at a current density of 20 Adds' or more to increase the Ni content in the lower layer. In this case, the lower layer may be electrochemically stronger or less base than the steel base, but if it is base, a sacrificial corrosion protection effect can be obtained between the steel base and the lower layer plating, and the corrosion resistance will be further improved. Therefore, it is preferable that the corrosion potential of the lower layer plating is more base than the base layer and higher than that of the upper layer, and the plating current density is 4 A/d- or more, 2
0 A/di is in the unconcentrated range. In addition, at less than 4V-, the lower layer becomes more susceptible to corrosion than the steel base, but 2A, 'dm' shows remarkable corrosion resistance compared to a single layer of Zn-Ni alloy plating.
The above is 0 and less than 1. Further, in order to reduce the plating thickness of the lower layer plating, the amount of electricity is limited to 300 coulombs per 1 dm' or less. If an amount of electricity of 300 coulombs or more is applied, the plating layer becomes too thick and cracks are likely to occur during processing. However, if the amount of electricity flowing is small, uniform plating cannot be achieved, so it is necessary to flow 1 coulomb or more.

On the other hand, the amount of electricity used in upper layer plating is not limited in the case of the present invention, so it may be adjusted depending on the desired plating thickness.

The present invention will be specifically explained below using Examples.

After degreasing and pickling a cold heron steel plate with a thickness of 15 m and a size of 100 squares using a conventional method, the lower and upper layers were plated according to the method of the present invention under the conditions of Fitting 1 using a plating solution with the following composition. went.

Plating solution composition NiSO4・6H20270fP/1jZnS04-7
Hz0 120%Na2SO4-10H20
160fyljPH2 Thereafter, the obtained spliced steel plate was subjected to 21 bending processes, and the processed part was subjected to a salt spray test according to JIS-Z 2371 to investigate the time required for red rust to occur.

On the other hand, as a comparative material, single-layer plating was carried out by the conventional method using a plating solution with the above composition, and the red rust occurrence time of the steel plate was investigated in the above manner.Table 1
It is shown in correspondence to the condition of the mating.

In two of the above Examples 1 to 4, the lower layer is more electrochemically active than the JH element, and in the others it is less noble. However, even if the lower layer is made of steel, it has better corrosion resistance than the comparative example.

As mentioned above, the present invention uses the same plating solution to increase the current density V
Since a lower layer having a higher Ni content than the upper layer is formed by changing the , the equipment is inexpensive and the plating work is easy.

In addition, since the lower layer is formed with a thinner thickness, workability is good (,
Cracks are prevented from reaching the steel base, and as a result, it exhibits better corrosion resistance than conventional materials, regardless of whether the underlying layer is resistant or base to the steel base. Furthermore, since the upper layer is less noble than the lower layer, the lower layer is protected by the sacrificial anticorrosion effect of the upper layer, and corrosion does not progress further than the lower layer.

In addition, since the lower and upper layers are similar in composition, their adhesion to each other is good, and there is no smudging compared to between the layers.

Claims (1)

[Claims] When electroplating a steel plate surface K Zn-Ni alloy with a Zn-Ni plating solution, the first step is 1 per 1 at a current density of 2 A/d- or more and less than 20 A/d- in the same plating solution. ~300 coulombs of electricity is applied to apply the lower layer plating, followed by a second step of 20 A.
1. A method for producing a Zn--Ni alloy electroplated steel sheet with excellent corrosion resistance in processed parts, characterized in that upper layer plating is applied at a current density of /d- or more.