JPH0457753B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is a Zn-
This invention relates to a method for producing Ni-based alloy plated steel sheets. (Conventional technology) Zn-Ni, Zn-Ni-Co, Zn-Ni-Fe with Ni content of 3 to 23% are used as Zn-Ni alloy plated steel sheets.
−Cr, Zn−Ni−Cr, and these as necessary
SiO ₂ , TiO ₂ ,
Composite plating system containing one or more oxides such as Al ₂ O ₃ , ZrO ₂ , NbO ₂ , T ₂ O ₅ , Cr ₂ O ₃ and chromic acid compounds such as BaCrO ₄ and PbCrO ₄ Zn−
Ni-alloy plated steel sheets have been proposed and some have been put into practical use. (Problems to be Solved by the Invention) A common problem with these alloy-plated steel sheets is that the plating layer may peel off along with the coating film due to low-temperature chipping, such as being hit by pebbles, when the temperature is lowered after painting. Ni in the depth direction of the plating layer
If there is a difference in concentration, corrosion resistance will decrease due to the progress of local corrosion, if there are pinholes, red rust will easily appear in a corrosive environment, and the corrosion resistance of mating parts, especially welded parts, will be weak. After considering these issues, we found that
It was found that the difference in the alloy composition of the initial deposit is a major factor in the growth of Zn-Ni alloy plating on the steel sheet surface. In other words, when plating with a simple plating solution such as a sulfuric acid bath or chloride bath that does not contain cyanide or a complex chelating agent, Zn precipitates first, and as the hydrogen overvoltage increases, The Ni content gradually increases, resulting in the precipitation of a stable Zn-Ni alloy plating composition. Figure 3 shows the depth profile of Zn-Ni alloy plating analyzed by GDS. 2,
3 and 4 indicate the strength of Ni, Zn, and Fe, respectively, and 1
indicates the Ni content (Ni strength/(Zn strength + Ni strength)). As described above, the Ni composition of the Zn--Ni alloy plating layer is not uniform over the entire plating layer, and there is a non-uniform portion of the Ni composition on the interface side with the steel plate. This is the initial precipitate layer, and its thickness is T
shall be. The Ni composition in this part increases continuously from 0 and asymptotically approaches a constant composition. Therefore, large distortion occurs in this part due to electrodeposition.
For example, if you chip a pebble at -20°C, the pebble will not peel off, but if you apply a thick film like a 3-coat car paint and chip it, the pebble will not peel off, but the entire pebble will peel off. This causes phenomena such as peeling off from the iron. When the low-temperature chipping property was investigated by varying the electrolytic conditions (current density, bath temperature, bath PH, flow rate), plating bath composition, etc., and by changing the thickness T of this initial deposited layer, it was clearly shown in Figure 4. It can be seen that the thicker the initial precipitate, which is a low Ni precipitate, is worse. In addition, such compositional differences within the plating layer also affect the corrosion resistance near the welding point of the joint, and salt water spraying for 30 minutes and
If we take the vertical axis as the thickness reduction in a cyclic corrosion test in which one cycle of drying at 70°C and 40% RH is taken as the vertical axis, and the horizontal axis as the thickness of the area with a different composition, it is clear from Figure 5 that the corrosion resistance A decrease in Methods for preventing peeling of the plating layer include methods for selecting plating conditions, adding additives to the plating bath, and, as a more complete method, plating the lower layer as disclosed in JP-A No. 59-200789. Various methods have been proposed, including methods of forming dissimilar plating layers with excellent adhesion. However, when used to prevent corrosion in automobiles caused by salt water that enters the road through rock salt sprinkled on roads to prevent freezing, creating a layer of dissimilar metals at the bottom causes preferential corrosion of base metals due to electrochemical potential differences. This may cause unexpected corrosion. In order to avoid such corrosion resistance problems, the present invention adjusts the Ni content in the initial precipitated layer of the Zn-Ni alloy plating layer, which is the cause of the problem, to the overall Ni content, so that the entire plating layer is coated with By using Zn-Ni alloy plating with uniform Ni composition throughout,
A method for improving chipping resistance and corrosion resistance of welded parts, which are extremely important in practice, is provided. (Means for Solving the Problems) The present invention provides a Zn-Ni alloy plating method for steel sheets, (a) First, the molar concentration ratio of Ni ions and Zn ions is set to 5.
or more and total concentration 25g/l or more, PH 1.0 to 4.5
Using a high Ni concentration plating bath adjusted ^to
Obtain a Zn-Ni precipitate, (b) Then contact with the high Ni concentration plating bath or redissolve the above precipitate according to the anodic dissolution method in the high Ni concentration plating bath, and then dissolve the redissolved metal ions. (c) Continuously maintain Ni ions of 10 g/l or more, Zn ions of 15 g/l or more, and the molar concentration ratio of Ni ions and Zn ions of 0.5 to 1.5, PH is 0.8 to 3.8, bath temperature is 50
A Zn-Ni alloy with excellent chipping resistance and corrosion resistance of welded parts, which is introduced into a Zn-Ni alloy plating bath maintained at ~95°C and subjected to Zn-Ni alloy plating. In the method for producing coated steel sheets and the method for plating Zn-Ni alloys on steel sheets, (a) First, the molar concentration ratio of Ni ions and Zn ions is set to 5.
or more and total concentration 25g/l or more, PH 1.0 to 4.5
Using a high Ni concentration plating bath adjusted ^to
Obtain a Zn-Ni precipitate, (b) then contact the following (c) Zn-Ni alloy plating bath or in the following (c) Zn-Ni alloy plating bath according to the anodic dissolution method to deposit the above. After redissolving the material, with the redissolution solution containing redissolved metal ions attached, (c) Continuously dissolving Ni ions at 10 g/l or more, Zn ions at 15 g/l or more, and Ni ions. Zn ion molar concentration ratio is 0.5 to 1.5, PH is 0.8 to 3.8, bath temperature is 50
A Zn-Ni alloy with excellent chipping resistance and corrosion resistance of welded parts, which is introduced into a Zn-Ni alloy plating bath maintained at ~95°C and subjected to Zn-Ni alloy plating. This is a method for manufacturing a steel plate. (Function) In order to increase the Ni concentration in the initial precipitate, the present invention obtains the initial precipitate in a high Ni concentration plating bath and redissolves it to increase the Ni concentration in the electrolytic solution near the plating surface. The high temperature for initial precipitation is based on the idea of obtaining plating with a uniform composition by introducing it into a normal Zn-Ni alloy plating bath and selecting the plating conditions.
This was discovered by examining the bath conditions of the Ni-concentrated plating bath and the Zn-Ni alloy plating bath. The present invention will be explained in more detail using the drawings. Figure 1 shows the effects of the Ni/Zn molar concentration ratio and PH in the high Ni concentration plating bath used to obtain initial precipitates on the chipping resistance of Zn-Ni alloy plated steel sheets and the corrosion resistance of welded parts. show. Note that after the treatment in the high Ni concentration plating bath, a series of treatments were performed using a method according to the present invention. The marks in the figure represent the quality of chipping resistance and corrosion resistance of the welded part. ○: Good chipping resistance (-20°C) and corrosion resistance of welded parts ●: Good chipping resistance (-10°C), good corrosion resistance of welded parts △: Good chipping resistance (-10°C), good corrosion resistance of welded parts Poor ×: Poor chipping property (-10°C), poor corrosion resistance of welded parts Here, chipping resistance is determined by immersion phosphate treatment on a 0.8 x 70 x 150 mm test piece, cationic electrodeposition coating (20μ), and intermediate coating. (40μ) - After applying topcoat (40μ),
With the test piece cooled to -10℃ or -20℃, 200g of pebbles with a size of 2 to 5mm are
These are the results of testing for peeling of plating after taping by hitting a test piece at 150 km. In addition, the corrosion resistance of the welded part was determined by spot welding test pieces overlapped by 70 mm, applying the same three coats as above, and then performing a salt spray test for 30 minutes and drying at 70°C and RH 40% for 1 hour. Cyclic corrosion test
This is the result of examining the decrease in plate thickness at the welded part after 100 cycles. The limited ranges of the Ni/Zn molar concentration ratio and PH in the high Ni concentration plating bath in the present invention are indicated by diagonal lines. Explaining the reason for the limitation based on this data:
If the Ni/Zn molar concentration ratio is less than 5, the chipping resistance is insufficient and the corrosion resistance of the welded part is also poor. On the other hand, when the pH is less than 1 and more than 4.5, the chipping resistance at -10°C is good in the region where the Ni/Zn molar concentration ratio is high, but it is insufficient at -20°C. The molar concentration ratio of Ni ions and Zn ions is 5 to 100, PH
1.5 to 3.5 is more preferable. Total metal ion amount Zn ²⁺ in high Ni concentration plating bath
If Ni ²⁺ is less than 25 g/l, normal plating will not occur when the current density becomes large, and therefore the performance will drop to the level of △ or × if you refer to the marks in Figure 1. Put it away. From the viewpoint of current efficiency and ion solubility, the total amount of metal ions is 30
~150 g/l is preferred. Bath temperature is 50-95℃
is preferred. The initial amount of Zn-Ni precipitates obtained using a high Ni concentration plating bath is 8 to 800 mg/m ² as Ni deposited amount. If it is less than 8 mg/m ² , sufficient chipping resistance cannot be obtained, and if it exceeds 800 mg/m ² , the corrosion resistance of the welded part will deteriorate. A more preferable range is 50 to 500 mg/m ²
It is. Next, the initial precipitates are redissolved by anodic electrolysis in contact with or in a high Ni concentration plating bath, and a layer of redissolved solution containing redissolved metal ions is left attached to form a Zn-Ni alloy as described below. He leads her to a soaking bath. As a plating bath for redissolving initial precipitates,
Instead of the high Ni concentration plating bath mentioned above, use Zn as described below.
- A Ni-based alloy plating bath may be used. These series of intermediate treatments for initial precipitates make the alloy composition of the entire Zn-Ni alloy plating uniform, resulting in improved chipping resistance and corrosion resistance of the welded part. Since the amount of initial precipitates is small, the re-dissolution treatment may be chemical dissolution with very short contact or anodic electrolysis. For example, in the case of contact, the amount of current may be 0.1 to 5 seconds, and in the case of anodic electrolysis, the amount of current may be 1 to 500 c/m ² . In a continuous line with a large number of plated cells, the second
After dissolving by contact or anodic electrolysis in the third cell, Zn--Ni alloy plating may be performed in the third and subsequent cells without washing with water.
The simplest method is to set the height in the first cell.
An example of this method is to obtain an initial precipitate in a Ni-concentrated plating bath, and directly apply Zn--Ni alloy plating to the second cell onward. In this case, high Ni
A re-dissolution process is performed using the remaining liquid in the concentration plating bath. Figure 2 shows Ni/Zn in a Zn-Ni alloy plating bath.
This figure shows the influence of molar concentration ratio and pH on the chipping resistance of Zn-Ni alloy coated steel sheets and the corrosion resistance of welded parts. Note that a series of treatments up to Zn--Ni alloy plating are performed by a method according to the present invention. The marks in the figure and the performance test method are the same as in Figure 1. In the Zn-Ni alloy plating bath in the present invention
The limited ranges of Ni/Zn molar concentration ratio and PH are indicated by diagonal lines. As is clear from Figure 2, Ni/Zn
-20℃ in the range of molar concentration 0.5 to 1.5 and pH 0.8 to 3.8
The chipping resistance and corrosion resistance of welded parts are good in the above ranges, and these performances are insufficient or poor in other ranges. Ni ion concentration in Zn-Ni alloy plating bath, Zn
If the ion concentration is less than 10 g/l and less than 15 g/l, normal plating will not occur when the current density becomes large, and therefore, if the marks in Figure 2 are used, the performance will be at the level of △ or ×. will decrease. In terms of current efficiency and ion solubility, the total amount of Ni ions and Zn ions is 30 to 150 g/l.
is preferred. If the bath temperature is less than 50°C, a Ni content that is effective in terms of corrosion resistance cannot be obtained, and if it exceeds 95°C, a large amount of heat source (such as steam) is required to heat the plating bath, which is uneconomical. More preferably, the temperature is 60 to 90°C. The present invention is a Zn-
Manufacture of Ni-based alloy plated steel sheets, or incorporation of SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ ,
Oxides such as Ta ₂ O ₅ , NbO, Cr ₂ O ₃ , SiC, Si ₃ N ₄ ,
Ceramics compounds such as BN, BaCrO ₄ , PbCrO ₄
It can be applied to the production of composite plated Zn-Ni alloy plated steel sheets containing one or more chromic acid compounds such as. Further, the plating bath may be a sulfate bath, a chloride bath, or a mixed bath thereof, and may contain Na 2 SO 4 , Na ₂ SO ₄ ,
A conductivity aid such as (NH ₄ ) ₂ SO ₄ or NaCl may be included. (Example) Zn--Ni alloy plating was continuously applied to a cold-rolled steel strip having a thickness of 0.8 mm and a width of 150 mm using a continuous electroplating line equipped with five horizontal plating tanks. A sulfate bath was used as the plating bath, and the amount of plating was 20g/
^m2 . A high Ni concentration plating bath was circulated in the first plating tank, and a Zn-Ni alloy plating bath was circulated in the third and subsequent plating tanks. The second plating tank has high
Either a Ni-concentrated plating bath, a Zn-Ni alloy plating bath, or water was circulated, and in the case of a plating bath, contact or anodic dissolution was performed. Table 1 summarizes the plating conditions and evaluation results. Here, 1-1 to 1-23 are examples, 2-1 to 2
-9 is a comparative example. The processing contents in the second plating tank are as follows, and are indicated by symbols in the table. A High Ni concentration plating bath is circulated and remelted by contact B High Ni concentration plating bath is circulated and remelted by anodic melting C Zn-Ni alloy plating bath is circulated and remelted by contact D Zn-Ni system Circulating the alloy plating bath and remelting by anode dissolution E. Circulating water. The Ni content was within 9 to 15% in all cases.
Here, the evaluation test method was based on the method described above. The evaluation criteria are as follows. (Low temperature chipping resistance) Plating peeling at -20℃ 2% or less: ○ Plating peeling at -20℃ more than 2% and 5% or less: △ Plating peeling at -20℃ more than 5%: × (Corrosion resistance of welded parts ) Plate thickness reduction: 0.1 mm or less: ○ Plate thickness reduction: more than 0.1 mm and 0.2 mm or less: △ Plate thickness reduction: more than 0.2 mm: × Comparative examples 2-1 to 2-5 were used in high Ni concentration plating baths. Because the conditions in the treatment or the treatment in the Zn-Ni alloy plating bath do not meet the requirements of the present invention, samples 2-6 to 2-8 were washed with water without being redissolved in the second plating bath. 2-9 again due to summer
Since these were not treated with a high Ni concentration plating bath, the chipping resistance and/or the corrosion resistance of the welded parts were insufficient. On the other hand, Examples 1-1 to 1-23 have good pitting resistance and corrosion resistance of welded parts.

【table】

[Table] (Effects of the invention) Conventionally, Zn-Ni alloy plating had excellent corrosion resistance, but problems remained in practical performance such as chipping resistance and corrosion resistance of welded parts.
The present invention greatly improves these performances by making the Ni composition uniform in the plating layer, especially in the vicinity of the steel plate interface.
It has extremely high utility value in the production of Ni-based alloy plated steel sheets.

[Brief explanation of drawings]

Figure 1 shows the effects of the Ni/Zn molar concentration ratio and PH in a high Ni concentration plating bath on chipping resistance and corrosion resistance of welds. Zn molar concentration ratio and PH have chipping resistance,
Figure 3 shows the influence on the corrosion resistance of welded parts.
Figure 4 shows the composition profile (GDS analysis) in the depth direction of a Zn-Ni alloy plated steel sheet.
A diagram showing the relationship between the thickness of the initial precipitate layer and chipping resistance (-20℃) of Zn alloy plating.
- It is a figure which shows the relationship between the thickness of the initial precipitate layer of Ni-based alloy plating, and the corrosion resistance of a welded part.

[Claims]

1. In the Zn-Ni alloy plating method for steel sheets,
The Ni ²⁺ concentration is 10 g/l or more, the Zn ²⁺ concentration is 15 g/l or more, and the molar concentration ratio of Ni ²⁺ and Zn ²⁺ is 0.48 ~
1.48, adjust the pH to 0.5 to 4.5, adjust the bath temperature to 50℃ or higher, and use a plating cell with electrodes installed parallel to the steel plate to keep the tangential flow velocity of the plating solution at the steel plate interface to 5 m/min or less. At the ^same time, the plating current was cut to the center of the plating cell, and the water column was pressurized by at least 100 mm higher than the surrounding liquid pressure. A method for producing a Zn-Ni alloy coated steel sheet with excellent corrosion resistance, press powdering resistance, and surface appearance, characterized by providing zones.

Claims (1)

After redissolving the above precipitate according to the anodic dissolution method, (c) Continuously dissolving Ni ions of 10 g/l or more and Zn ions of 15 g/l while keeping the redissolving solution containing redissolved metal ions attached. or more, and the molar concentration ratio of Ni ions and Zn ions is 0.5 to 1.5, PH is 0.8 to 3.8, and bath temperature is 50.
A Zn-Ni alloy with excellent chipping resistance and corrosion resistance of welded parts, which is introduced into a Zn-Ni alloy plating bath maintained at ~95°C and subjected to Zn-Ni alloy plating. Manufacturing method for steel plate.