JPS6026836B2 - Manufacturing method of zinc-nickel alloy plated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a zinc-nickel alloy coated steel sheet that improves corrosion resistance and the like by lowering the concentration of impurity elements.

Traditionally, metal plating to improve the corrosion resistance of steel sheets includes:
Galvanizing has been widely practiced.

This plating mainly prevents corrosion of the steel plate by sacrificial corrosion protection of zinc, and the corrosion resistance depends on the amount of zinc deposited. In other words, in order to obtain high corrosion resistance, the amount of zinc deposited must be increased, and in this case, several problems such as increased cost or decreased weldability due to the increased amount of zinc required can be avoided. I can't. In recent years, with the expansion of the application of anti-corrosion galvanized steel sheets to automobile bodies to extend their corrosion-resistant lifespan, various types of plating with good corrosion resistance and a small amount of plating coverage have been reconsidered, and this is one of them. has a zinc-nickel alloy plating.

It is known that this zinc-nickel alloy plating has excellent corrosion resistance in the range of about 10 to 20% nickel content, and exhibits superior corrosion resistance compared to zinc plating with the same basis weight.
Since electrolytic zinc nickel alloy plating can be plated at high current density and the bath has good electrical conductivity, it is usually plated with acidic properties mainly consisting of chlorides or sulfates. When producing industrial zinc-nickel alloy plating using this method, conventional plating conditions such as zinc and nickel concentration, ordinary temperature, high pH, current density, and relative speed between ordinary and strip are used for plating. However, there are problems in that the quality characteristics of the product often vary, resulting in products with poor corrosion resistance, gloss, and uniform appearance.

Therefore, an object of the present invention is to solve this problem and to industrially and stably produce a zinc-nickel alloy plated steel sheet that always has good corrosion resistance and appearance.

According to the present invention, when performing electrolytic zinc-nickel alloy plating on a steel plate using an acid plating method containing zinc and nickel, the Fe concentration in the coating is set to 1.0/or less and Pb, Cd.
The above object can be achieved by setting the total concentration of Cu to 9/20 or less.

According to the research conducted by the present inventors, the corrosion resistance or deterioration of the appearance of zinc-nickel alloy plating has a strong correlation with the concentration of impurity elements, especially Fe, Pb, Cd, and Cu, in the plating layer. The present inventors discovered that an important factor causing variations in quality characteristics in the industrial production of galvanized steel sheets is due to changes in the concentration of these elements, and based on this discovery, the present invention was achieved.

The specific effects, appropriate range, etc. of the method according to the present invention will be explained in detail below. Figure 1 shows the iron ion concentration and basis weight of acidic plating medium mainly composed of zinc sulfate and nickel sulfate.
This figure shows the relationship between the corrosion resistance and the appearance of a plating film when plated with a coating temperature of 0.0 tm. From this figure, it can be seen that when iron ions are present for more than one day, the corrosion resistance deteriorates and the appearance becomes dull. The effect of ferric ions was greater than that of ferrous ions, but the direction was the same. Figure 2 shows the individual and total concentrations of lead, cadmium, and copper in the same acidic plating medium as in Figure 1;
This figure shows the relationship between the corrosion resistance and the appearance of the plating film when the coating weight is 20 mm/elbow plating.

From this figure, it can be seen that there is a proportional relationship with the concentration, and 2
It can be seen that when the ratio exceeds 9/0, both corrosion resistance and appearance deteriorate. From the above, it is extremely important to control the concentration of impurities in the bath for zinc-nickel alloy plating, and in order to industrially stably obtain products with excellent corrosion resistance and appearance, it is necessary to It is clear that it is effective to make the total concentration of lead cadmium and copper less than 9/20.

The deterioration of corrosion resistance due to the increase in iron concentration in Yunaka is due to the fact that the iron concentration is 5.
Since the amount of nickel in the plating layer does not change at temperatures below 1/2, it is unlikely that this is due to an essential change in the plating film. This is probably because the adhesion of iron into the plating layer promotes the battery action in the plating film and accelerates the progress of corrosion. Lead, cadmium, and copper have a negative effect at much lower concentrations than iron, and all have the common characteristic that they all increase the amount of nickel in the plating layer. Therefore, the deterioration in corrosion resistance due to these elements is thought to be caused by the increase in corrosion current due to the formation of a nickel-enriched layer in the plating layer, in addition to the electrodeposition of lead, cadmium, and copper. The contamination of iron into the plating material is mainly due to the melting of the strip.

The concentration of lead increases by dissolving the lead or lead-based aqueous anodes when used, or from impurities in the electrode when using soluble zinc anodes, or by being supplied from the lead electrode bed. increases. Cadmium is mainly introduced into the plating layer from impurities in the electrode, and copper is mixed into the plating layer due to impurities in the electrode and melting of the electrical wiring system around the plating hole. In the case of iron, these harmful components are removed by a method using a chelate resin having a selective adsorption chamber, a precipitation method, or a method of dumping out a part of the plating layer.

In addition, lead, cadmium (copper) can be removed by displacing and depositing zinc powder or zinc grains in addition to a portion of the copper plating solution, or in the case of a sulfate bath, strontium There is a method in which Fe, Pb, Cd, and Cu are usually added as impurities in the plating bath. In many cases, they coexist, but the effect of coexistence is almost an additive level of the effect of each individual concentration.Accordingly, in actual management of metal rating, taking this point into consideration, the Fe concentration should be set to 1 Tanok or less. It is important to maintain a low total concentration of Pb, Cd, and Cu within the range of 20 mg/〆 or less in order to obtain a good product. p containing zinc and nickel
It has an acidic character with an H of about 1.5 to 3.8 degrees.

These are commonly used because they provide a high current density and have good electrical conductivity in plating.
In zinc-nickel alloy plating, the composition of the deposited layer varies depending on the plating conditions such as the plating composition, solution, current density with respect to the strip, and the relative speed of the plate. The goal is to stably produce zinc-nickel alloy plating with excellent corrosion resistance and appearance by reducing the concentrations of lead, cadmium, and copper below a certain level as described above. There is no need to specifically limit the conditions. Hereinafter, the present invention will be explained by giving preferred examples and comparative examples.

[Example 1] A rolled steel strip was plated with zinc-nickel alloy under the following conditions using a horizontal continuous strip plating device.

'1' Eyes bath NiS04/spot 20 300/s, ZnS04/7 ratio 015M/s, Fe0.1/s, Pd 2 9/s,
Cdlm9/evening, Cul place/evening, town 2.0 ordinary temperature 50q
O■ Current density: 6M/d〆'3} Strip speed: 18h/min {4} Amount of plating deposit: 20 evenings/After plating, a corrosion resistance test was conducted using a salt water mist test, and the surface appearance was visually observed. .

The results are shown in Table 1 along with other examples. [Example 2] The same rolled steel strip as in Example 1 was plated with zinc-nickel alloy under the following conditions using the same plating equipment.

'1' Metsuki case NjS04, thin 20300 evening/so, Z
nS04/7 ratio 01502/so, Fe0.6 evening/so, P
b6's 9/so, Cd2's p/even, Cu 2 female/Z, bait
2. u rating temperature 5000 [21 Current density, stripping speed, plating amount...same as Example 1 [Example m] Zinc-nickel was applied to the same cold rolled steel strip using the same plating equipment as Example 1 under the following conditions. Alloy plating was applied.

'11 Metsukiyoku NiC Evening 2 Group 20240 Evening/So, Z
nC Ku2 140 Yu/So, Fe0.3 Tanok, Pb
6 female/even, Cd3 o/ku, Cul p/so, pH 3
．． 0, bath temperature 50 qO {2) Current density, stripping speed, plating coating amount...same as Example 1 [Comparative Example 1] Zinc- Nickel alloy plating applied.

○1 Metsuki case NiS04・Hoso 20 300 evening/so, Z
nS04・7401509noso, Fel. 6th evening/So, P
b8's 9th evening, Cd3's p/so, Cu2's 9/so, bait
2. Rerating temperature 50q○■ Current density, stripping speed, plating coating amount...same as Example 1 [Comparative Example 0] Zinc-nickel was applied to the same cold rolled steel strip using the same plating equipment as Example 1 under the following conditions. Alloy plating was applied.

'1' Metsuki case NiC So2・Thin 20240 Yu/So, Zn
C evening 2 140 Tanok, Fe○-7 evening/so, Pb26
Copycat, Cd5 o/Z, Cu 2 female/Z, pH 3.
0, rating temperature 5 pi○ [21 Current density, stripping speed, plating amount... According to Table 1, which summarizes these results as in Example 1, the concentration of impurities such as iron and lead is It can be seen that the Examples with low concentrations are superior in both corrosion resistance and appearance compared to the Comparative Examples with high concentrations of iron, lead, etc.

Incidentally, the impurity concentration given in the comparative example is a level easily reached during industrial mass production of zinc-nickel alloy plating. From these results, it is clear that the method of the present invention is extremely important for industrially stably obtaining zinc-nickel alloy plating that is excellent in both corrosion resistance and appearance.
Table 1

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the iron concentration in an acidic plating medium containing zinc and nickel and the corrosion resistance and appearance of the plating film. 1 is a graph showing the relationship between the total concentration of one or more metals including copper and the corrosion resistance and appearance of a plating film. Figure 1 Figure 2

Claims (1)

[Claims] 1 When performing electrolytic zinc-nickel alloy plating on a steel plate in an acidic plating bath containing zinc and nickel, Fe in the bath
Zinc-- characterized in that the concentration is 1.0 g/l or less and the total concentration of Pb, Cd, and Cu is 20 mg/l or less.
A method for manufacturing nickel alloy plated steel sheets.