JPS639031B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention involves Zn plating on the surface of a steel plate, and then Mn plating in a sulfuric acid Mn plating bath containing sulfurous acid.
- Concerning the Mn double-layer plating method, it is possible to obtain a galvanized steel sheet with metallic luster and excellent corrosion resistance without deterioration of workability and weldability by performing two-layer plating of Mn electroplating on a Zn plating layer. This is the purpose. Conventionally, as a method for depositing Mn at a cathode, a method for producing metal Mn by electrolysis has been known for a long time. In addition, as a report on the technology for depositing a thin metal film on the surface of Zn-plated steel sheets or metal Zn, a conventional proposal was made by adding Rodan salt.
There is a method of Mn plating using a Mn plating bath.
When this rhodan salt is added, coloration such as bluish-purple occurs upon completion of Mn plating, and furthermore, it is necessary to dump the Mn plating bath or to decompose the rhodan contained in the waste water in the plating bath. As a result of various studies to solve these drawbacks, the present invention provides an optimal Zn-Mn double-layer plated steel sheet by regulating the additives to the Mn plating bath and the plating method. be. The gist of the method is to electrodeposit 1 to 30 g/ ^m2 of zinc on the steel plate surface in a non-cyanide bath, then sulfite ions of 0.5 g/m or more, total sulfate concentration of 25 to 250 g/m, and total polyvalent Mn concentration of 10 g/m2.
A Mn deposition amount of 5 to 30 g/m ² was deposited by electroplating in a plating bath using ammonium sulfate as a supporting salt consisting of the following:
It is a Zn-Mn double layer plating method. In other words, in the plating of the lower Zn layer according to the present invention, the steel plate is first degreased and pickled, and then treated with a sulfuric acid bath, which is a non-cyanide bath.
Using a chloride bath, a hofusing bath, a zincate bath, and a pyrophosphoric acid bath, an electrodeposited layer of 1 to 30 g/m ² of Zn was formed, and then Mn and sulfite ions were deposited at 0.5 g/m 2 .
Above, total sulfate concentration 5-500g/, total polyvalent Mn
When electrodeposited in a plating bath using ammonium sulfate as a supporting salt at a concentration of 10 g/m or less, a Mn plating layer of 5 to 30 g/m ² is formed.
With this method, a product with good adhesion between the Mn plating layer and the Zn plating layer and an excellent appearance of the precipitation can be obtained. Therefore, the sulfite ion according to the present invention is 0.5g/
The greatest feature of the present invention is that Mn is added to the plating bath, and in the case of conventional Rodan salt addition, when Mn is plated on a galvanized surface, Rodan SCN ^- ions are oxidized and consumed at the anode. This method performs Mn plating while suppressing the oxidation of Mn to become manganese dioxide. However, in the present invention, rather than suppressing the production of manganese dioxide, Mn plating is performed at the anode during Mn plating. The produced manganese dioxide or multivalent ions are reduced with sulfite ions to form divalent Mn ions, thereby suppressing the unplating phenomenon and allowing them to adhere to the galvanized surface. To achieve this reduction effect, the amount of sulfite ion added is 0.5g/
The above is necessary. The optimal addition amount is 0.5
g/~50g/ is good. In addition, in order to maintain the current efficiency around 60%, the current density must be 2000A/m ²
or more, and the total sulfate concentration is 25 to 250 g/2
Keep the valent Mn ion concentration at 10 to 100 g/, and the total polyvalent manganese concentration at 10 g/or less. At this time, in order to maintain uniform electrodeposition, it is especially good to have potassium ions present together with ammonium ions formed by ammonium sulfate as a supporting salt. In addition, when performing split electrodeposition, a plating bath is used.
As mentioned above, the Mn plating surface undergoes oxidation and dissolution, which not only reduces the Mn plating efficiency, but also causes the surface to blacken and deteriorate corrosion resistance. As a countermeasure for this, in order to prevent an increase in multivalent ions of Mn, sulfite
It is necessary to add 0.5 g or more and perform Mn plating in an energized input tank and an energized output tank. In other words, energizing is the process of placing the material into the Mn plating solution while applying a voltage with a negative potential below the Mn deposition potential. This is effective in cases where the Mn deposition layer is particularly highly reactive, such as a thin deposited layer. This is an important technology for achieving high current efficiency and good Mn plating appearance on Zn plating. In addition, the energized tank means that when leaving the plating tank after plating, it is kept at a potential more negative than the Mn deposition potential and guided to the washing tank while preventing natural dissolution. In such cases, it is necessary to take measures that meet these conditions in terms of equipment. In addition, as for the total sulfate concentration, Pt electrode, Pt plating
Including Pt-based electrodes such as Ti electrodes, ruthenium, rhodium, and indium-treated Pt plating electrodes,
When using oxide electrodes such as ferrite electrodes, magnetite electrodes, lead alloy electrodes, or carbon electrodes as anodes, MnO ₂ etc. precipitate on the electrode surface.
In order _to enable the Mn oxide to be reduced by SO ^2-2 ions in the bath, a range of 25 to 250 g/g is good.
In particular, the distance between electrodes should be 10 cm or less, and MnO ₂ should be used in electroplating.
The generation and growth of SO 2-4 at the anode is important from the viewpoint of uniform precipitation and pressure scratches, as well as _pH . In the case of pH 3.0, the effect of SO ^2-4 concentration on the number of pressure scratches is 1 (pressure scratches) in Figure 1. The effect of SO ^2- ₄ concentration on the number of occurrences per 10 m ² and on the uniform Mn plating property is shown in Figure 1 as follows: 2 (Deposition amount distribution = (area plated 30% thicker or thinner than the average value) / (total plated area) Mn plating surface area)×10
0) becomes as follows. That is, when the SO ^2-4 concentration is less than 25g/ or more than 250g/, the number of scratches increases as shown by curve 1, and the % adhesion weight distribution increases _as shown by curve 2. Next, the total polyvalent Mn concentration (Mn ³⁺ ~Mn ⁷⁺ ) was determined at 10 g/
The reason for the following is to maintain a good finished appearance and at the same time avoid defects. Multivalent Mn ions (Mn ³⁺
~Mn ⁷⁺ ) is PH in the electrolytic Mn manufacturing process.
A diaphragm is used to prevent migration to the cathode. However, in plating, since the solution is vigorously stirred, contact with the cathode (Mn plating surface) cannot be prevented. As a countermeasure for this, the multivalent Mn concentration (Mn ³⁺ ~
Mn ⁷⁺ ) is reduced with SO ₂ or the total concentration of polyvalent Mn is
If the amount exceeds 10g/, complex insoluble Mn oxides and hydroxides will be generated, resulting in a decrease in finished appearance and current efficiency.
Moreover, the number of pinholes also increases. Mn is deposited on the Zn plating according to the Mn plating method described above, but the thickness of the Zn plating is 1
~30g/ ^m2 . The reasons for applying Zn plating in advance as an intermediate layer are: (1) the hydrogenation voltage of zinc is high; (2) it prevents the Mn plating from peeling off during processing;
(3) The purpose is to control galvanic action against corrosion. Therefore, the amount of Zn deposited is 1 g/m2 or ^more , which forms a uniform Zn precipitated layer, enables uniform Mn precipitation, and suppresses peeling of the Mn plating layer during processing, and prevents hydrogen absorption and internal stress of the plating layer. It should be 30g/m ² or less so that it does not peel off due to aging. Furthermore, to maintain stable Mn deposition efficiency at high current density, the Mn ⁺⁺ concentration must be between 10 and 100.
A good range of g/ is below 10 g/, the current efficiency decreases rapidly, and when it exceeds 100 g/, precipitates mixed with MnO ₂ , Mn(OH) ₂ , MnSO ₄ etc. are generated on the electrode surface, and the current It becomes difficult to flow, and at the same time, pressure injuries caused by this sediment occur. In addition, the PH of the bath is different from the high PH of the normal metal Mn production method, and is PH = 2.0 ~
If the value is not in the low value range of 4.5, the
MnO ₂ , Mn ³⁺ , etc. cannot be reduced rapidly in solution.
However, if the pH is lower than 2.0, the current efficiency will drop significantly. Furthermore, the current density is
In the range of up to 2500 A/m ² , a higher value is better, but since precipitation occurs on the anode and the plating surface becomes rough, a range of 2000 A/m ² to 15000 A/m ² is better. In addition, the ammonium ion in the Mn plating bath in the present invention is preferably 10 g/or more, and Li,
When adding different ions such as K, Na, amine, etc.
The ratio of NH ⁺ ₄ /different alkali ions must be 0.1 or more by weight. Examples of the present invention will be shown below. Example 1 Steel plate (10cm x 18cm, plate thickness 0.8mm, original plate for plating)
was degreased for 1 minute at 60°C with a degreasing solution containing 3% NaOH and SiO for ₂ minutes and 0.2% sodium orthosilicate.
Then pickled in 5% _H2SO4 solution at 50 °C for 15 seconds _,
After washing with water, neutralize with 0.1% NaOH solution, and after washing with water, bath temperature is 50℃, ZnSO ₄ 7H ₂ O 200g/,
Contains Na ₂ SO ₄ 100g/, PH=1.3 at H ₂ SO ₄
Current density 60A/dm ² in a galvanizing bath adjusted to
Both sides were plated with 10 g/m ² of Zn. Then, after washing with water, 120 g of MnSO ₄ H ₂ O/,
Contains (NH ₄ ) ₂ SO ₄ 68g/, K ₂ SO ₄ 10g/, sulfite ion 5.1g/, and polyvalent manganese concentration
Using 0.4 g/KOH, adjusted to pH=3.5 with H ₂ SO ₄ as a plating bath, the Zn
A negative 20V voltage is applied to the plated steel plate in advance, and the Mn is removed at a current density using the energizing bath method.
11 g/m ² was electrodeposited at 40 A/dm ² (4000 A/m ² ), washed with water, and dried. Increase the liquid volume of the Mn plating bath to 3
When 3,000 sheets were plated continuously with the current efficiency fixed at

[Table] For comparison, the Zn-plated steel plate is
MnSO ₄ H ₂ O 120g/, (NH ₄ ) ₂ SO ₄ 68g/,
Contains no sulfite ions (0.01g/or less) and polyvalent manganese ions 1.0g/, KOH
The pH was adjusted to 3.5 with H ₂ SO ₄ and used as a Mn plating bath.
Mn was electrodeposited at 11 g/m ² at a current density of 40 A/dm ² (4000 A/m ² ) by applying a voltage of 20 V by the current bath method, followed by washing with water and drying. Increase the liquid volume of the Mn plating bath to 3
When 3,000 sheets were plated continuously with the current efficiency fixed at , the changes in current efficiency as shown in Table 2 were recorded.

【table】

[Table] Example 2 When the Zn-plated steel sheet that has been Zn-plated according to the method of Example 1 is Mn-plated in the Mn-plating bath also described in Example 1, instead of the energizing bath. When the tank was energized, the results shown in Table 3 were obtained.

[Table] Example 3 When performing Zn-Mn two-layer plating using the method shown in Example 1, the amount of Zn plating was changed to 1 g/
After swinging in the range of m ² to 50 g/m ² , test pieces were made by changing the amount of Mn plating. As a result, the relationship between the plating amount, workability, appearance, and current efficiency as shown in Table 4 was obtained.

【table】

[Table] ◎ Good ○ Fair △ Slightly poor × Bad Example 4 Steel plate (10cm x 18cm, thickness 0.8mm, original plate for plating)
was degreased in a degreasing solution containing 3% NaOH and SiO for ₂ min at 60 °C containing 0.2% sodium ortho-silicate for 1 min, then pickled for 15 s in a 5% H ₂ SO ₄ solution at 50 °C. After washing with water, neutralize with 0.1% NaOH solution, and after washing with water, coat one side with Zn plating bath shown in Table 5 below.
Each plate was plated at 10 g/m ² .

[Table] (*1 Sodium cyanide-free bath)
Each specimen that has undergone Zn plating is then
When 10 g/m ² Mn plating was performed using the Mn plating bath shown in the table, the effects on the current efficiency shown in Table 7 occurred.

【table】

【table】

[Table] Table 8 also shows the adhesion of the Mn plating layer deposited on the Zn plating layer. By A, B, C, D, E baths according to the plating method of the present invention,
According to the plating conditions for B, C, the appearance is good,
Furthermore, it has been shown that a Mn/Zn double-layer plated steel sheet with excellent workability and sufficient adhesion between the Mn plated layer and the Zn plated layer can be manufactured with high current efficiency. Example 5 A steel plate plated with 10 g/m ² of Zn according to Example 1 was plated with Mn at a current density of 4000 A/m ² in seven types of Mn plating baths with different concentrations of sulfite radicals shown in Table 9. Mn-plated steel sheets with the performance shown in Table 9 were obtained depending on the amount of Mn deposited. Corrosion resistance was evaluated by a salt spray test after immersion in 25 g of chromic acid/solution for 5 seconds. Evaluation standard is red rust 50
% time to occurrence. ◎ means 1000 hours or more, 〇 means 800-1000 hours, △ means
500 to 800 hours, x indicates 500 hours or less, and x to △ has a large variation depending on the sample, with approximately half of the samples being x and △.

【table】

[Table] *1…(Precipitation occurs)

[Brief explanation of the drawing]

The figure shows the number of pressure injuries and the total sulfate root concentration.
FIG. 3 is a diagram showing the relationship between Mn adhesion amount distribution.

Claims (1)

[Claims] 1 Electrodeposit 1 to 30 g/m ² of zinc on the steel plate surface in a non-cyanide bath, then 0.5 g/m 2 of sulfite ion.
Above, total sulfate concentration 25-250g/, total polyvalent Mn
Mn deposition amount is 5 to 30 g/m ² by electroplating in a plating bath using ammonium sulfate as a supporting salt at a concentration of 10 g/m or less.
Sulfuric acid added with sulfite characterized by adhering to
Zn-Mn double layer plating method using Mn plating bath.