JPH057477B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for surface treatment of metals, and particularly aims to improve the corrosion resistance and paint adhesion of metals. Since the surface-treated steel sheet obtained by this treatment method has excellent corrosion resistance and paint adhesion, it can be used as a corrosion-resistant material for various home appliances, building materials, and automobiles. [Prior Art] As is well known, electrogalvanized steel sheets, hot-dip galvanized steel sheets, and various alloy-plated steel sheets are used in automobiles,
Widely used in home appliances, building materials, etc. Under these circumstances, in recent years, there has been an increasingly strong demand for surface-treated steel sheets that have particularly excellent corrosion resistance, and the demand for such steel sheets is likely to increase further in the future. For example, in the home appliance industry, there is a demand for a steel plate with excellent corrosion resistance that can be used bare and omit painting from the viewpoint of process and cost savings. In addition, the automobile industry has also experienced environmental changes in recent years, such as corrosion caused by rock salt sprayed to prevent roads from freezing in winter in North America and Northern Europe, and corrosion caused by acid rain caused by the generation of SO ₂ gas in industrial areas. Since car bodies are exposed to severe corrosive environments, there is a strong demand for surface-treated steel sheets with excellent corrosion resistance from a safety standpoint. In order to solve these problems, various studies have been made and many products have been developed. Until now, galvanizing has been carried out to improve the corrosion resistance of steel sheets. Galvanized steel sheets prevent corrosion of the steel sheet through the sacrificial anticorrosive action of zinc, and in order to obtain corrosion resistance, the amount of zinc deposited must be increased. For this reason, there are several problems such as an increase in the cost of the required amount of zinc and a decrease in workability, weldability, and productivity. Additionally, galvanized steel sheets generally have poor paint adhesion. As a method for improving the corrosion resistance of such galvanized steel sheets, various alloy-plated steel sheets have been developed. For example, these alloy-plated steel sheets include
Zn-Ni series, Zn-Ni-Co series, Zn-Ni-Cr series, Zn
-Fe system, Zn-Co system, Zn-Cr system, Zn-Mn system, etc. can be mentioned. With these alloy plating,
Bare corrosion resistance is about 3~ compared to normal galvanized steel sheet.
It is recognized that the improvement is 5 times. However, the problem is that white rust or red rust is likely to occur if left outdoors for a long period of time or if water or salt water is sprayed on it. In order to improve corrosion resistance, chromate treatment can be considered, but chromate treatment can ensure a sufficient amount of adhesion on the surfaces plated with the various alloys mentioned above and provide a chromate film with excellent adhesion. There are no laws. Generally, when a chromate film is formed, the elution of ions from the base (material) is extremely important, and the chromate film is formed while reacting with the eluted ions. Therefore, the characteristics of the chromate film formed differ slightly depending on the type and amount of eluted ions. The above-mentioned alloy-plated steel sheet has excellent corrosion resistance, but this means that ions are difficult to elute, and a chromate film is difficult to form, making it impossible to ensure a sufficient amount of coating. That is, the better the corrosion resistance, the more difficult the chromate treatment becomes. Chromate treatment methods can be roughly divided into electrolytic chromate, coating chromate, and reactive chromate methods, but the same can be said to a greater or lesser extent in all cases. In addition, as a recent trend, in order to further improve corrosion resistance, so-called simple pre-coated steel sheets (hereinafter referred to as organic composite steel sheets), which are zinc-plated steel sheets treated with chromate and coated with various resins, have been developed and some are commercially available. . The chromate film used as a base for such organic composite steel sheets must have excellent adhesion to the organic resin. In addition, since these materials are subjected to harsh processing when used for car body rust-preventing steel plates, etc., the chromate film must have excellent adhesion to the base material and organic resin, and be strong enough to withstand the processing itself. Must be. Many of the chromate treatments for various types of plated steel sheets are already well known, and various chromate treatment methods have been developed and made appropriate. For example, those containing chromic acid as the main component with the addition of sulfuric acid (Japanese Patent Publication No. 39-7461), and those containing phosphoric acid (Japanese Patent Publication No. 30-3514, Japanese Patent Publication No. 35-1989).
Publication No. 8917, Special Publication No. 9559, Special Publication No. 36-955-
9560), boric acid added (U.S. Pat. No. 2733199, U.S. Pat. No. 2780592), halogen (Cl ^- ,
F ^- ) added (Special Publication No. 39-14363)
Cathode electrolytic treatment of steel sheets has been carried out using baths to which various anions have been added. [Problem to be solved by the invention] However, it can be easily processed into alloys with excellent corrosion resistance and various metals, and a sufficient amount of adhesion can be ensured.
There is no chromate treatment that has excellent adhesion to materials and organic films and can withstand harsh processing. Many of them are difficult to process into alloys with excellent corrosion resistance and various metals, and those with excellent corrosion resistance have poor paint adhesion, and conversely, those with excellent paint adhesion have poor corrosion resistance. Moreover, there is nothing that can withstand harsh processing. The purpose of the present invention is to solve the above-mentioned drawbacks of the conventional techniques and provide a chromate treatment method that provides a film that has excellent metal corrosion resistance and adhesion with an organic film, and has excellent workability. be. [Means for Solving the Problems] That is, the present invention includes one or more ions of Cu, Zn, Ni, Co, and Mn as cations in a chromic acid bath, and one or more ions of F ^- and Cl ^- . Under specific electrolytic conditions using a metal as a cathode in a treatment solution that contains one or two species, suppresses chromic anhydride, cations, and anions to specific concentrations, and adjusts the three to a specific ratio. Through electrolytic treatment, a film is formed on the metal in a very short time, significantly improving corrosion resistance and adhesion with organic films, thereby significantly increasing commercial value. This excellent property cannot be obtained when the chromic anhydride bath contains only the above cations or only the above anions, nor can it be obtained even if the specific electrolytic conditions are deviated from the bath. It can only be obtained through a combination of composition and electrolytic conditions. It was found that the following relationship must exist between chromic anhydride, cation, and anion in this case. Concentration of chromic anhydride, chromate, or dichromate converted to chromic anhydride = 0.05 to 1 mol/……(1) Dissolved Cu ⁺⁺ , Zn ⁺⁺ , Ni ⁺⁺ , Co ⁺⁺ ,Mn ⁺⁺
Number of gram ions of ions = 0.01 to 0.2 gram ions/...(2) Number of gram ions of dissolved Cl ^- , F ^- ions = 0.001 to 0.02 gram ions/...(3) When performing electrolytic treatment at the cathode Current density = 0.1 to 40 A/dm ² ...(4) Film formed when metal is electrolytically treated at the cathode under conditions that simultaneously satisfy the conditions of (1), (2), (3), and (4) above. It was confirmed that corrosion resistance and adhesion with organic films were significantly improved. It has also been found that when the above conditions are simultaneously satisfied, a desired amount of chromate film can be deposited on any alloy or metal depending on the amount of electricity. Figure 1 shows the corrosion resistance of the steel plate when (2), (3), and (4) are fixed and the concentration of chromic anhydride in (1) is changed, and Figure 2 shows the adhesion with the organic film. Figure 3 shows the amount of Cr deposited. In other words, Zn-Ni thread alloy coated steel plate (Ni=12
%), Co ⁺⁺ is 2.5g/, Cl ^- is 0.25g/,
Figure 1 shows the corrosion resistance when the current density is 5A/dm ² and the amount of electricity is 5C/dm ² (constant) when electrolyzing at the cathode, and the concentration of CrO ₃ is varied. Figure 2 shows the adhesion to the organic resin when 2μ of a water-soluble polyacrylic ester resin is applied to the surface, and Figure 3 shows the relationship between the amount of Cr deposited. Figure 4 shows the corrosion resistance of the steel plate when (1), (3), and (4) are fixed and the concentration of Co ⁺⁺ ions in (2) is changed, and Figure 5 shows the adhesion with the organic film. , FIG. 6 shows the relationship between the amount of Cr deposited. In other words, Zn-Ni alloy coated steel sheet (Ni=12
%), CrO ₃ = 20g/, Cl ^- = 0.25g/,
Cathode electrolysis current density = 5A/dm ² , quantity of electricity = 5C/d
Figure 4 shows the corrosion resistance when m ² (constant) and the concentration of Co ⁺⁺ ions is varied. Fig. 5 shows the adhesion with Cr and Fig. 6 shows the relationship with the amount of Cr deposited. Figure 7 shows the corrosion resistance of the steel plate when (1), (2), and (4) are fixed and the concentration of Cl ^- ions in (3) is changed, and Figure 8 shows the adhesion with the organic film. Figure 9 shows the relationship between the amount of Cr deposited. In other words, Zn-Ni alloy coated steel sheet (Ni=12
%), CrO ₃ = 20 g/, Co ⁺⁺ 2.5 g/, cathode electrolysis current density = 5 A/dm ² , quantity of electricity = 5 C/dm ²
Figure 7 shows the corrosion resistance of the steel sheet when the concentration of Cl ^- ions is set at a constant value and the concentration of Cl - ions is changed.
Figure 8 shows the adhesion to the organic resin when 2μ coating is applied, and Figure 9 shows the relationship between the amount of Cr deposited. Figure 10 shows the corrosion resistance of the steel plate when (1), (2), and (3) are fixed and the cathode electrolysis current density is changed, Figure 11 shows the adhesion with the organic film, and Figure 12 shows the Cr This shows the relationship between the amount of adhesion. In other words, Zn-Ni alloy coated steel sheet (Ni=12
%), CrO ₃ = 20g/, Co ⁺⁺ = 2.5g/, Cl ^-
Figure 10 shows the corrosion resistance of the steel plate when the cathodic electrolytic current density is changed with = 0.25g/. The adhesion is shown in FIG. 11, and the relationship between the amount of Cr deposited is shown in FIG. 12. Corrosion resistance here indicates the state of rusting after 600 hours through a salt spray test in accordance with the JIS-Z-2371 standard (salt water concentration 5%, tank temperature 35℃, spray pressure 20psi), ◎, 〇, △. Evaluated in 5 stages: , ×, ××, ◎
is the best. ◎ : Red rust occurrence 0% 〇 :〃 More than 0 to 1% △ :〃 More than 1 to 10% × :〃 More than 10 to 50% Apply an aqueous solution of ester to a thickness of 2μ,
After drying at 120°C, the coated test piece was boiled for 30 minutes, then the film was cut into 2 mm gobs, peeled off with tape, and evaluated by the peeled area. ◎ : Peeling area 0% 〇 :〃 More than 0 to ₁ % △ :〃 More than 1 to 10% × :〃 More than 10 to 50% If the amount is less than 1 mol/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/molar range is less than 1 molar/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/molar mole/mole/molar range of 0.05–1 molar/mole/mole/mole/mole/mole/mole/mole/mole/mole/mole/molar range will provide excellent corrosion resistance. As is clear from Figure 2, the adhesion of the organic film formed on the surface is excellent when the CrO ₃ content is 0.05 to 1 mol/less than 0.05 mol/ or 1 mol/
It decreases in super. As is clear from Figure 3, CrO ₃ is 0.05 to 0.1
At 0.05 mol/mole, the amount of adhesion can be stabilized and ensured, but at 0.05
If the amount is less than 0.1 mol/mole/mole/mole/mole/mole/mole/molar or above 0.1 mol/mole/mole/mole/mole/mole/mole/mole/molar ratio, the amount of Cr attached will be extremely reduced. As is clear from Figure 4, Co ⁺⁺ exhibits excellent corrosion resistance when it is between 0.01 and 0.2 g ions/, and when it is less than 0.01 or 0.2 g ions/
Corrosion resistance decreases at higher temperatures. As is clear from Figure 5, the adhesion of the organic film is also
Co ⁺⁺ is excellent at 0.01-0.2 gram ions/area,
Less than 0.01g ion/0.2g ion/
If it is too thick, the adhesion will decrease. As is clear from Figure 6, the amount of Cr attached can be stably ensured when Co ⁺⁺ is 0.01 to 0.2 g ion/, but when it is less than 0.01 g ion/or 0.2
At gram ions/super, the amount of Cr deposited is extremely low, and it is difficult to deposit the desired amount. As is clear from FIG. 7, when Cl ^- is 0.001 to 0.02 g ion/g/ion, an extremely excellent chromate film is formed and exhibits excellent corrosion resistance. less than 0.001 g ion/or 0.02 g ion/
If it exceeds the range, the corrosion resistance will be significantly reduced. This is because the structure of the formed chromate film is Cl ^-
This is because it varies greatly depending on the concentration, and if Cl ^- is within the above range, a film consisting mainly of Cr ₂ O ₃ will be formed, but when it is outside this range, it will be mainly composed of metallic Cr and Cr(OH) ₃・nH ₂ O. . As is clear from Figure 8, the adhesion of the organic film is also
Cl ^- is excellent in the range of 0.001 to 0.02 gram ions/, and adhesion is significantly reduced when it is less than 0.001 gram ions/and exceeds 0.02 gram ions/. As is clear from Figure 9, when Cl ^- is 0.001g ion/~0.02g ion/, the amount of Cr attached can be stably secured, but 0.001g ion/~0.02g ion/
If it is less than 0.02 g ion/or more than 0.02 g ion/0.02, the amount of Cr attached decreases. As is clear from Figure 10, when performing cathode electrolysis, the current density is less than 0.1A/ ^dm2 or
When the electrolytic treatment is carried out at more than 40 A/dm ² , the corrosion resistance is significantly inferior, whereas when the electrolytic treatment is carried out at 0.1 to 40 A/dm ² , excellent corrosion resistance is obtained. As is clear from Figure 11, 0.1 to 40A/dm ²
The organic film exhibits excellent adhesion when subjected to electrolytic treatment at 0.1 A/dm ² or more than 40 A/dm ² . This is because when electrolytically treated at less than 0.1A/ ^dm2 , a film _{mainly composed of Cr(OH)3.nH2O is} formed.
When electrolyzed at ^over 40A/dm2, Cr(OH) ₃ .
This is because a film mainly composed of nH ₂ O and metal Cr is formed, whereas a chromate film mainly composed of Cr ₂ O ₃ is formed when electrolyzed at 0.1 to 40 A/dm ² . As is clear from Figure 12, when electrolytically treated at less than 0.1 A/dm ² or more than 40 A/dm ² , Cr
The precipitation efficiency of 0.1~
Electrolysis at 40 A/dm ² can ensure a stable amount of Cr deposited. The results in Figures 1 to 12 are for cations.
I showed the results using Co ⁺⁺ , but instead of Co ⁺⁺
Almost the same results were obtained using Cu ⁺⁺ , Zn ⁺⁺ , Ni ⁺⁺ , and Mn ⁺⁺ . Moreover, similar results were obtained even when two or more types of cations were allowed to coexist. Furthermore, although the results were shown using Cl ^- as the anion, almost the same results were obtained when F ^- was used instead of Cl ^- or when both were used together. (See Examples) Based on the above results, in the present invention, when performing electrolytic chromate treatment in a bath in which chromic anhydride, cations, and anions coexist, chromic anhydride, chromate, or dichromate is replaced with chromic anhydride. Concentration converted to acid = 0.05 to 1 mol/dissolved Cu ⁺⁺ , Zn ⁺⁺ , Ni ⁺⁺ , Co ⁺⁺ ,
Number of gram ions of one or more ions of Mn ⁺⁺ = 0.01 to 0.2 gram ions/one or 2 of dissolved Cl ^- , F ^- ions
The number of gram ions of seed ions = 0.001 to 0.02 gram ions/,
In addition, the electrolytic treatment at the cathode is performed at a current density of 0.1 to 40 A/dm ² . Furthermore, although this result was shown as an example performed on a Zn-Ni alloy plated steel sheet, this treatment is capable of forming a chromate film on all metals and all alloys, and the amount of electricity can cause chromium to adhere. You can freely control the amount. While conventional chromates form a film through reaction with ions eluted from the substrate,
This treatment has the characteristic that a film is formed regardless of the elution of ions from the substrate, and is essentially different from conventional chromate treatment. Furthermore, the chromate film obtained by this treatment has excellent corrosion resistance and excellent adhesion to organic resins. In this result, polyacrylic acid ester was shown as an example; Excellent adhesion is ensured with any organic resin such as aqueous resin dispersions such as polymer resins, polyacrylic acid esters and their copolymer resins, and various solvent-based resins such as epoxy resins and melamine resins. Therefore, it is most suitable as a chromate for the organic resin base of the above-mentioned organic composite steel sheet. On the other hand, since it has excellent adhesion with organic resins, it also has excellent adhesion with paint films when applied with ED coating or spray painting, so it can also be used as a base for painted steel sheets. Optimal. Examples of the present invention will be shown below along with comparative examples. Example 1 A Zn-Ni alloy plated steel plate (Ni=11.2%) was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 30g / Co ⁺⁺ 2.5g / Cl ^- 0.25g / Electrolysis conditions: Current density 5A/dm ² Electrolysis time 1 second Example 2 A Zn-Fe alloy plated steel plate (Fe = 40%) was coated under the following conditions. Cathode electrolyzed. CrO ₃ 20g / Zn ⁺⁺ 2.0g / Cl ^- 0.2g / Electrolysis conditions: Current density 2A/dm ² Electrolysis time 2.5 seconds Example 3 A Zn-Al alloy coated steel plate (Al = 12%) was coated under the following conditions. Cathode electrolyzed. CrO ₃ 40g / Ni ⁺⁺ 2.7g / Cl ^- 0.3g / Electrolysis conditions: Current density 10A/dm ² Electrolysis time 0.5 seconds Example 4 A Zn-Cr alloy plated steel plate (Cr = 12%) was coated under the following conditions. Cathode electrolyzed. CrO ₃ 10g / Mn ⁺⁺ 3.5g / Cl ^- 0.15g / Electrolysis conditions: Current density 3A/dm ² Electrolysis time 1.7 seconds Example 5 A Zn-Mn alloy coated steel plate (Mn = 56%) was coated under the following conditions. Cathode electrolyzed. CrO ₃ 50g/ Cu ⁺⁺ 2.5g/ F ^- 0.15g/ Electrolysis conditions: Current density 10A/dm ² Electrolysis time 0.7 seconds Example 6 Zn-Ni-Co alloy plated steel plate (Ni = 10.5%,
Co=0.5%) was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 40g / Co ⁺⁺ 4.0g / Cl ^- 0.2g / Electrolysis conditions: Current density 15A/dm ² Electrolysis time 0.8 seconds Example 7 Zn-Ni-Cr alloy plated steel plate (Ni = 10.8%,
Cr=1.5%) was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 15g / Co ⁺⁺ 2.0g / Cl ^- 0.15g / Electrolysis conditions: Current density 7.5A/dm ² Electrolysis time 0.6 seconds Example 8 A Cu plate was cathodic electrolyzed under the following conditions. CrO ₃ 27.5g / Co ⁺⁺ 2.5g / Cl ^- 0.25g / Electrolysis conditions: Current density 10.5A/dm ² Electrolysis time 0.5 seconds Example 9 A Sn-plated steel plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 25.5 g / Co ⁺⁺ 3.0 g / Cl ^- 0.15 g / Electrolytic conditions: Current density 5.0 A/dm ² Electrolytic time 0.8 seconds Example 10 A Ni-plated steel plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 35.0 g / Co ⁺⁺ 2.0 g / Cl ^- 0.35 g / Electrolytic conditions: Current density 15.5 A/dm ² Electrolytic time 0.2 seconds Example 11 A Ti plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 35.0g / Co ⁺⁺ 3.0g / Cl ^- 0.40g / Electrolysis conditions: Current density 8.0A/dm ² Electrolysis time 0.3 seconds Example 12 An Al plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 25.0g / Co ⁺⁺ 3.0g / Cl ^- 0.20g / Electrolysis conditions: Current density 12.5A/dm ² Electrolysis time 0.25 seconds Example 13 A SUS304 stainless steel plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 22.0g / Co ⁺⁺ 3.0g / Cl ^- 0.40g / Electrolysis conditions: Current density 10.5A/dm ² Electrolysis time 0.35 seconds Example 14 A SUS316 stainless steel plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 30.0g / Co ⁺⁺ 3.0g / Cl ^- 0.20g / Electrolysis conditions: Current density 7.5A/dm ² Electrolysis time 0.45 seconds Comparative example 1 Zn-Ni alloy coated steel sheet (Ni = 11.8%) was Cathodic electrolysis treatment was performed under the following conditions. CrO ₃ 50g / H ₂ SO ₄ 0.25g / Electrolysis conditions: Current density 50A/dm ² Electrolysis time 2 seconds Comparative example 2 Zn-Ni-Co alloy plated steel plate (Ni = 11.5%,
Co=0.5%) was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 40g / H ₂ SO ₄ 0.2g / Electrolysis conditions: Current density 60A/dm ² Electrolysis time 1.5 seconds Comparative Example 3 A SUS304 stainless steel plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 40.0 g / H ₂ SO ₄ 0.3 g / Electrolytic conditions: Current density 50.0 A/dm ² Electrolytic time 2.0 seconds Comparative Example 4 A Cu plate was subjected to cathodic electrolysis treatment under the following conditions. CrO ₃ 40.0g / H ₂ SO ₄ 0.3g / Electrolysis conditions: Current density 50.0A/dm ² Electrolysis time 2.0 seconds Table 1 shows the corrosion resistance and amount of Cr deposited in the salt spray test of each example and comparative example. Table 2 shows the adhesion of the olefin/acrylic acid copolymer resin when 2μ of the resin was applied. The salt spray test method and evaluation method are the same as those shown in FIGS. 1, 4, 7, and 10. The evaluation method for resin adhesion is shown in Figure 2.
This is the same method as in FIGS. 5, 8, and 11. As is clear from Table 1, when the present invention is applied to various metals, alloys, and alloy-plated steel sheets, the corrosion resistance hardly changes after 600 hours of SST, and only a slight red rust occurs in some parts after 1200 hours of SST. be. On the other hand, in Comparative Examples 1 and 2 when treated with a known chromate bath, about 70% white rust had already occurred after 400 hours of SST, and a considerable amount of red rust was observed after 600 hours. Further, as is clear from Comparative Examples 3 and 4, when treated with a known chromate bath, almost no chromate film is formed on general metals and alloys. On the other hand, as is clear from Table 2, when the present invention is implemented, the adhesion with the organic resin is extremely excellent, but when treated with a known chromate bath, Comparative Examples 1, 2, 3, and 4 show no peeling. Evidence of this is recognized.

【table】

【table】

【table】

[Table] <Effects of the Invention> Conventionally, there are no known chromate treatments that stably secure the desired amount of chromate by treating various metals and alloys, and that sufficiently satisfy corrosion resistance and adhesion with organic resins. It didn't exist. In contrast, by controlling the concentrations of chromic anhydride, special anions, and cations within specific ranges, and performing cathodic electrolysis treatment under specific conditions, the synergistic effect of these results in extremely excellent corrosion resistance and organic A film with excellent adhesion to the resin is formed, and by applying the present invention, the economic effect is extremely large.

[Brief explanation of the drawing]

Figures 1 to 3 show the corrosion resistance, adhesion to organic film, and Cr when the concentration of chromic anhydride was changed while the concentration of Co ⁺⁺ ions, Cl ^- ions, and current density were fixed.
This shows the relationship between the amount of adhesion. Figures 4 to 6
The figure shows the relationship between corrosion resistance, adhesion to organic film, and amount of Cr deposited when the concentration of chromic anhydride, Cl ^- ion concentration, and current density are fixed and the concentration of Co ⁺⁺ ions is varied. Figures 7 to 9 show fixed chromic anhydride concentration, Co ⁺⁺ ion concentration, and current density.
This figure shows the relationship between corrosion resistance, adhesion to organic film, and amount of Cr deposited when the concentration of Cl ^- ions is changed. Figures 10 to 12 show chromic anhydride concentration,
This figure shows the relationship between corrosion resistance, adhesion to organic film, and Cr deposition amount when the Co ⁺⁺ ion concentration and Cl ^- ion concentration are fixed and the current density is varied.

Claims (1)

[Claims] 1 Chromic anhydride or chromate or dichromate, converted to chromic anhydride, 0.05 mol/
~1 mol/containing bath contains Cu ⁺⁺ , Zn ⁺⁺ , Ni ⁺⁺ ,
One or more of Co ⁺⁺ , Mn ⁺⁺ ions
Contains 0.01 gram ion/~0.2 gram ion/in addition to one or two of Cl ^- and F ^- ions.
0.1A/dm2 to ^40A /d in a bath containing 0.001g ion/~0.02g ion/seed
A metal surface treatment method characterized by cathodic electrolytic treatment at a current density of ^m2 .