JPH0457754B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides Zn that has excellent corrosion resistance, press powdering resistance, and surface appearance, and is suitable for automobiles and home appliances.
-Regarding a method for manufacturing a Ni-based alloy plated steel sheet. (Conventional technology) As Zn-Ni alloy plated steel sheets, Zn-Ni, Zn-Ni-Co, and Zn-Ni with Ni content of 3 to 23% are already available.
-Fe-Cr, Zn-Ni-Cr, etc., or steel sheets containing one or more of Co, Cr, Fe, Mn, Mo, Sn, Cu, Pb, etc. as necessary, or these SiO ₂ , TiO ₂ ,
Oxides such as Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , NbO, Cr ₂ O ₃ and chromic acid compounds such as BaCrO ₄ and PbCrO ₄ are
Composite plating system Zn- containing a species or two or more species
Ni alloy plated steel sheets have been proposed and some have been put into practical use. As mentioned in Metal Finishing 12, 52- (1972), many proposals have been made for a long time regarding the manufacturing method of Zn-Ni alloy plated steel sheets. In our country as well, special public relations
15635 (Method for manufacturing Zn-Ni alloy plated steel sheets), Japanese Patent Publication No. 1983-33347 (Method for manufacturing Zn-Co-Ni alloy plated steel sheets), Japanese Patent Publication _No. 1987-39236 (Method for manufacturing Zn-Co-Ni alloy plated steel sheets) (Production method of Zn-Ni alloy plated steel plate), Japanese Patent Publication No. 1983-38274 (Production method of Ni-Zn alloy plated steel plate with excellent workability and corrosion resistance),
Japanese Patent Publication No. 62-6760 (method for manufacturing oxide composite plated steel sheet) and the like are disclosed. (Problems to be Solved by the Invention) However, even with these conventionally proposed manufacturing techniques, it is difficult to ensure stable quality in actual line production. In particular, problems often arise in terms of corrosion resistance, powdering properties during pressing, and surface appearance. The instability of the quality of Zn-Ni alloy plating at the practical level is due to the fundamental problem of Zn-Ni alloy plating itself, namely, the precipitation efficiency of the plating metal compared to Zn plating. Poor (current efficiency is less than 90%, H ₂ gas is generated accordingly), pinholes are likely to occur in the plating layer,
The plating composition tends to be uneven in the depth direction.
This is largely due to the problem that streaks tend to appear on the plated surface. The present invention is intended to solve the above-mentioned problems, and aims to produce a Zn--Ni alloy plated steel sheet exhibiting high corrosion resistance using the same plating material. (Means for Solving the Problems) The present invention provides a Zn-Ni alloy plating method for steel plates in which the Ni ²⁺ concentration is 10 g/l or more and the Zn ²⁺ concentration is
15 g/l or more, the molar concentration ratio of Ni ²⁺ and Zn ²⁺ is 0.48 to 1.48, the pH is 0.5 to 4.5, and the bath temperature is
In addition to adjusting the temperature to 50℃ or higher, the tangential flow velocity of the plating solution at the steel plate interface was set to 5 m/min or less in a plating cell with electrodes installed parallel to the steel plate, and the current density was 40 A/dm ² or higher. Corrosion-resistant and press-resistant powdering characterized by cutting off the plating current in the center of the plating cell while plating, and creating a zone that is pressurized by more than 100 mm in the water column than the surrounding liquid pressure. This is a method for manufacturing a Zn-Ni alloy plated steel sheet with excellent properties and surface appearance. (Function) The present invention uses a low Ni concentration plating bath to
It combines low pH, low interfacial flow velocity, hydrogen gas removal and high current density plating. The present invention increases the Zn ²⁺ ion concentration in the plating bath in order to reduce pinholes in the plating layer due to hydrogen gas generated during plating and to reduce embrittlement due to hydrogen trapped in the plating layer. The pH increase at the plating surface interface is kept stable, the flow velocity at the plating interface is kept below 5 m/min, plating is performed at a high current density, and the hydrogen generated during plating is removed within the plating layer. It is actively removed from the plating surface using the pressure section installed on the plated surface. The present invention will be described in more detail. First, as a plating bath, Ni is used because it has good corrosion resistance.
On the premise of obtaining Zn-Ni alloy plating with a content of 3 to 23%, we will suppress the generation of hydrogen gas, which has a negative effect on corrosion resistance, press powdering properties, and surface appearance, as much as possible, and aim for high current density. conditions suitable for That is, first, the concentrations of Ni ²⁺ and Zn ²⁺ are set to be 10 g/l or more for Ni ²⁺ and 15 g/l or more for Zn ²⁺ . If both are below the lower limit, more hydrogen gas will be generated in the high current density region of 100 A/dm ² or more. Although there is no particular upper limit, if too much, there is a risk of precipitation, so it is preferable that both Ni ²⁺ and Zn ²⁺ be 100 g/l or less, and the total concentration is 30 to 100 g/l. Secondly, the Ni ²⁺ /Zn ²⁺ molar concentration ratio is set to 0.48 to 1.48.
This is lower than the range shown in Japanese Patent Publication No. 62-15635 (the ratio of Zn ²⁺ is high), but in this range the hydrogen overvoltage increases during electrodeposition and the generation of hydrogen gas is suppressed. Further, if the molar concentration ratio is less than 0.48, the Ni content of the plating layer becomes too low. A more preferable range is 0.6 to 1.3. Thirdly, pH is 0.5~
Set it to 4.5. If the pH is less than 0.5, hydrogen gas generation will increase, and if it exceeds 4.5, the PHH at the steel plate interface during plating will enter the hydroxide generation region, leading to a decrease in corrosion resistance. A more preferable range is 0.8 to 2.5. Fourth, the bath temperature is 50℃.
The above shall apply. Ni ²⁺ / to suppress hydrogen gas generation
If the Zn ²⁺ concentration ratio is set to a low value, the Ni content in the plated layer will naturally decrease, so in order to compensate for this, it is necessary to set the bath temperature to 50° C. or higher. In terms of suppressing hydrogen gas generation, a higher bath temperature of 60 to 95°C is preferred. Next, the tangential flow velocity of the plating liquid at the steel plate interface is
5m/min or less. In terms of quick removal of hydrogen gas, larger is better, but if it exceeds 5 m/min, streaks are likely to occur on the plated surface, so 5 m/min is recommended.
min or less, preferably 1 to 5 m/min.
The current density during plating shall be 40A/dm ² or more. If the current density is less than 40 A/dm ² , the alloy composition tends to become non-uniform and the powdering properties during pressing deteriorate. In terms of uniformity of alloy composition, 50 to 300A/
^dm2 is preferred. As a plating cell, the plating current is cut in the center of the cell, and the water column is 100% lower than the surrounding liquid pressure.
Use a cell with a pressurized zone of mm or more. By doing so, it is possible to prevent deterioration in corrosion resistance due to the trapping of hydrogen in the plating layer and the long-term adhesion of hydrogen bubbles to the plating surface. This effect is insufficient if the pressure is less than 100 mm. The preferred range is
It is 100-500mm. FIG. 1 shows the structure of a typical plating cell used to carry out the present invention. The plating liquid is supplied from the slit part 6, and the space between the electrode 4 and the pad 5 and the steel plate 3 is filled with the plating liquid, and the plating liquid is applied to the conductor roll 1 or the back-up roll 2 at a constant flow rate.
The plating liquid flows towards the. The plating current is cut off at the pad 5 placed in the center of the cell.
Moreover, the hydraulic pressure at this portion becomes higher than the hydraulic pressure at the electrode 4 portion. The width of the hydraulic pressure applied to pad 5 is pad 5.
It can be adjusted by the length of the plating liquid and the flow rate of the plating liquid in the slit portion 6. As the plating cell, not only the horizontal type shown in FIG. 1 but also the vertical type can be used. The present invention is a Zn-
Manufacture of Ni-based alloy plated steel sheets, or the addition 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 types of chromic acid compounds such as. Furthermore, the plating bath may be a sulfate bath, a chloride bath, or a mixture of these baths.
A conductive aid such as Na ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ or NaCl may be included. (Example) Zn-Ni alloy plating was continuously applied to a cold-rolled steel sheet with a thickness of 0.8 mm and a width of 150 mm using a continuous electroplating line equipped with three horizontal plating layers. A sulfate bath was used as the plating bath, and the plating amount was 20 g/m ² . A cell having the structure shown in FIG. 1 was used as the plating cell, and the width of pressurization at the center of the cell (pad portion) was adjusted by changing the length of the pad and the flow rate of the plating liquid at the slit portion. Table 1 summarizes the plating conditions and evaluation results. Here, 1-1 to 1-23 in Table 1 are examples, and 2-1 to 2-9 are comparative examples. In addition, Ni
The content rates were all within 9-15%. The evaluation criteria are as follows. [Corrosion resistance] After applying immersion phosphate treatment (treatment time: 2 minutes) and cationic electrodeposition coating (film thickness: 20μ), cross-cut scratches were made, salt water sprayed for 30 minutes (JIS Z2371), and dried for 1 hour (70℃). , RH.40%) was conducted for 100 cycles, and the blistering of the paint film at the cross cut portion was evaluated. Blister width: 2 mm or less ○ Blister width: 2 to 5 mm △ Blister width: 5 mm or more × [Press powdering resistance] Cylindrical press processing of 50 mmφ x 25 mmH was performed, and the weight difference before and after the test was evaluated as the amount of peeling. Amount of peeling: 1 mg or less ○ Amount of peeling: 1 to 3 mg △ Amount of peeling: 3 mg or more × [Surface Appearance] The streaks and color unevenness were visually evaluated. No unevenness ○ Color unevenness △ Streak unevenness × As is clear from Table 1, the corrosion resistance of the examples
The press powdering resistance and surface appearance were both better than those of the comparative example.

【table】

[Table] (Effects of the invention) As described above, the present invention covers the drawbacks of Zn-Ni alloy plating in terms of manufacturing technology, and makes it possible to stably obtain the original quality of Zn-Ni alloy plating. This is a manufacturing method that can be used, and the utility value of the present invention is truly great in stably supplying Zn-Ni alloy plated steel sheets.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a typical plating cell used to carry out the present invention. 1... Conductor roll, 2... Backup roll, 3... Steel plate, 4... Electrode, 5... Pad, 6... Slit portion.

[Claims]

1 Al plate used when phosphate treatment of steel plate and Al plate in the same phosphate treatment line,
Zn plating layer, Zn alloy plating layer on the surface, or
One of the Fe-based alloy plating layers
An Al plate with excellent phosphate treatment properties, characterized by a coating weight of 1 g/m ² or more.