JPH03111593A - Surface treatment of aluminum alloy - Google Patents

Abstract

PURPOSE:To improve the filiform corrosion resistance of an Al alloy and the adhesion of a coating film by subjecting the Al alloy to anodic oxidation, etc., in an electrolytic soln. contg. a surfactant and an alkaline builder at a prescribed concn. and carrying out pore sealing. CONSTITUTION:An electrolytic soln. contg. an alkaline builder at 0.5-5wt.% concn. and a surfactant is prepd. The builder consists of phosphate, silicate, sulfate or borate and alkanolamine. An Al alloy is subjected to anodic electrolysis or cathodic electrolysis and anodic electrolysis in the electrolytic soln. and then pore sealing is carried out to further improve the filiform corrosion resistance of the Al alloy.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a surface treatment method for aluminum alloys, and in particular, when used as a base treatment for painting, excellent paint film adhesion and thread rust resistance can be obtained, and This method is suitable as a surface treatment method for aluminum alloys used in panel materials, etc.

(Prior art and problems to be solved) Aluminum alloys are being used in automobile parts for the purpose of weight reduction, but chrome It was believed that a pre-painting treatment such as acid chromate was required.

On the other hand, a normal automobile painting line consists of press molding → degreasing →
This is a line for steel sheets that consists of the process of zinc phosphate treatment → cationic electrodeposition → painting. Zinc phosphate treatment is applied to the base treatment, but in this line, zinc phosphate treatment is used as the base treatment for aluminum alloys. When applied, the paint adhesion after cationic adhesion (paint adhesion) is insufficient, and the current situation is that sufficient performance in terms of thread rust resistance is not obtained. There is a need for the development of a technology that enables surface treatment with excellent thread rust resistance.

In this regard, it may be possible to adopt chromate chromate treatment instead of zinc phosphate treatment as a base treatment for automobile painting lines, but as mentioned above, although thread rust resistance can be improved, chromate treatment with chromate Wash → Wash with water → Wash with water → Chromium acid romate → Wash with water (umbrella) →
A process of washing with water and drying resistance is required, and special treatment equipment is required for this, and wastewater treatment using a closed system is required at the washing (*) stage, so the treatment cost including wastewater treatment is high. Therefore, it is difficult to adopt chromic acid chromate treatment as a surface treatment.

The present invention was made in response to such a request, and it is possible to obtain an aluminum alloy material with excellent paint film adhesion and thread rust resistance even when zinc phosphate treatment is applied as a base treatment. The object of the present invention is to provide a surface treatment method that is both effective and low-cost.

(Means for Solving the Problems) The present inventors have investigated the cause of deterioration in thread rust resistance especially when zinc phosphate treatment is adopted as a base treatment, and have developed a new pretreatment method (surface treatment method). I have done extensive research on this. As a result, it was discovered that by performing anodization treatment under specific conditions, a remarkable improvement effect on thread rust resistance was obtained, and further, by subsequent sealing, an effect of improving thread rust resistance of the - layer was obtained, This is where the present invention is made.

That is, the gist of the present invention is a surface treatment method for an aluminum alloy, which is characterized in that the aluminum alloy is subjected to anodic electrolysis in an electrolytic solution containing an alkaline builder and a surfactant, and then sealed.

In addition, in another aspect of the present invention, an aluminum alloy is cathodically electrolyzed in an electrolyte containing an alkaline builder and a surfactant, and then anodically electrolyzed in an electrolyte having the same composition.
The gist of this paper is a method for surface treatment of aluminum alloys, which is characterized by sealing the pores.

The present invention will be explained in more detail below.

(Function) The present inventors investigated various surface treatment methods, and found that following cleaning, anodization treatment was performed in an alkaline builder and surfactant bath commonly used for surface cleaning of aluminum alloys. It has been found that a significant improvement in thread rust resistance can be obtained by applying this method. Furthermore, it has been found that if the holes are sealed after that, the layer and thread rust resistance can be improved.

First, by using an electrolytic solution containing an alkaline builder and a surfactant, the pre-treatment degreasing and cleaning and the generation of an anodized film are carried out in a bath with the same composition.The surface degreasing and cleaning starts immediately after immersion in the electrolytic solution. Then, by starting anodic electrolysis, an anodized film having excellent corrosion resistance, coating adhesion, and thread rust resistance is formed on the aluminum alloy surface. In addition, this surface treatment method allows both surface cleaning of aluminum alloy and generation of an anodized film on the surface, which can be achieved by simplifying the treatment process and modifying existing production equipment, resulting in lower costs. The down effect is also great.

The alkaline builder in the electrolysis acts as a cleaning aid and an anodizing electrolyte, and its type is not particularly limited as long as it forms an anodic oxide film on the aluminum alloy surface. In short, the required properties of the electrolyte are that it be an alkaline builder, have a surface cleaning effect, and form an anodic oxide film on the surface of the aluminum alloy at the temperature and concentration conditions that provide the cleaning effect. Bye. In this respect, phosphate-based and silicate-based detergents are preferred because they are highly effective as alkaline builders for cleaning agents.

In this case, when a phosphate builder is used, a relatively thick film is obtained, and when a silicate builder is used, a thin but dense film is obtained.

Examples of the alkaline builder include sodium tripolyphosphate, disodium phosphate, sodium orthosilicate, sodium carbonate, and triethanolamine.

Furthermore, phosphates, silicates, sulfates, borates,
If alkanolamines are used alone or in appropriate combinations, it becomes possible to increase the current density, that is, to perform treatment for a single time.

The surfactant is added for degreasing, and the optimal type and concentration are determined depending on the combination with the base alkaline builder, but there are no particular limitations as long as it has degreasing properties.

Regarding conditions such as treatment temperature, the optimum temperature can be obtained depending on the degreasing effect of the electrolytic solution, the effect of forming an anodic oxide film on the electrolytic solution, the electrolytic voltage, etc.
If it is 60 V, there is little danger as a device and sufficient thread rust resistance can be obtained.

In addition, the thickness of the #polar oxide film can be controlled according to the purpose. That is, in order to increase the thickness, a phosphate-based alkaline builder may be used and treatment may be performed at high voltage for a long time. By increasing the current density by adding sulfate or alkanolamine, it is possible to obtain a relatively thick anodic oxide film in a single time, which is effective in continuous treatment using a coil. On the other hand, if the purpose is to make it thinner and improve thread rust resistance, a silicate-based alkaline builder may be used, or a phosphate-based + silicate or borate may be used. Alternatively, a short-time treatment may be performed using a phosphate-based alkaline builder.

Thus, the desirable electrolytic conditions are:

Electrolyte: Mixed bath electrolysis with 0.5" 5wt% of each of phosphate, silicate, sulfate, borate, and alkanolamine or two or more of them and a detergent surfactant. Solution temperature: 240-80°C Electrolyte voltage: 15-60V (anodic electrolysis)
Outside this range, it becomes difficult to obtain a good anodic oxide film in terms of productivity, safety, and other practical aspects.

The anodic oxide film obtained in this way is produced in an alkaline electrolyte and has high alkali resistance, so it is especially difficult to use after the subsequent steps of pressing → degreasing → zinc phosphate treatment → cationic electrodeposition. In the case of painted aluminum alloy materials, thread rust resistance can be significantly improved.

Note that as a pretreatment for this anodizing treatment, as described above, it is usually enough to simply immerse the material in an electrolytic solution and the surface can be cleaned. However, in order to further shorten the surface degreasing and cleaning time and further increase the cleaning effect, cathodic electrolysis may be performed in the same bath or in a separate bath having the same composition before the anodic electrolysis. If cathodic electrolysis is performed in the same bath, the polarity will be switched and anodic electrolysis will be performed.
There is no need to take out the material to be treated or wash it with water.

Furthermore, in the case of processing using a coil form, the power supply method is liquid-liquid power supply, and continuous processing is possible by simply arranging the counter electrode. In the case of continuous treatment, a spray method is preferable for supplying the electrolytic solution. In this case, single-sided processing and liquid-liquid power supply can be easily performed, which is highly effective in terms of equipment. However, sufficient performance can be obtained by immersing it in an electrolytic solution and electrolyzing it.

After the anodic electrolysis, pore sealing is performed, which is effective in further improving thread rust resistance and in improving the degreasing properties of the lubricating oil used during press molding.

Various liquids can be used for sealing, and for sealing with chromic acid or chromate, chromic acid is impregnated into the pores of the porous anodic oxide film to improve corrosion resistance and thread rust resistance. In particular, the improvement in thread rust resistance is remarkable. Pore sealing with alkali salts of silicic acid, boric acid, and alkanolamines adsorbs and seals the pores of the porous anodic oxide film, improving thread rust resistance and degreasing properties. The improvement effect is remarkable. These ions involved in pore sealing are all anions, and by performing anodic electrolysis, the desired effect of pore sealing can be obtained in a single time. In this case, the electrolytic power source can be used in common with cathodic electrolytic degreasing and anodic electrolytic anodization, and electrolytic pore sealing can be performed simply by installing electrodes.

The concentration of the liquid used for sealing is not particularly limited.

For any liquid, 0.01 to 1% is practical. 0
．． If the concentration is less than 0.01%, the effect will not be sufficient, and if it exceeds 1%, the effect will be saturated and new problems will arise, such as the need for a long time for washing with water, so this is not preferable, but it is not limited to this.

Similarly, if the sealing temperature is room temperature or higher, an effect can be obtained, but if the sealing time is to be shortened, a range of 40 to 80°C is appropriate.

Sealing by anodic electrolysis further improves the sealing effect as mentioned above, but the voltage at that time is in the range of 10 to 100 V, considering the ability to promote sealing and the safety of equipment during mass production. It's practical.

When the aluminum alloy material thus surface-treated is used for automobile panels in particular, it is processed after treatment and subjected to zinc phosphate treatment and cationic electrodeposition, in which case remarkable effects can be expected and durability is improved. It can fully meet user needs regarding improvement in thread rust resistance.

Of course, it goes without saying that the present invention can be applied to other uses, such as coating base treatment for can materials, base treatment for colored aluminum, etc. Furthermore, by increasing the thickness of the film, it can also be applied as a surface treatment method for aluminum alloys that alone have corrosion resistance.

It goes without saying that the aluminum alloy used as the treated material can have various component systems and compositions that require thread rust resistance.

(Example) Next, examples of the present invention will be shown.

A rolled plate of JIS5182-0 material (1mm x
75s x 150+am) was prepared, and subjected to surface treatment under the conditions shown in Table 1 and pore sealing under the conditions shown in Table 2.

In order to evaluate the press oil degreasing property of the obtained test material, commercially available press oil was applied to the surface of the test material and left at room temperature for 27 days. Use salt-based cleaning agent, concentration 3%, temperature 40℃
Defatting was performed under conditions of , 2 minutes, and the defatting properties were evaluated.

The degreasing property is evaluated by the water wettability of the surface of the sample material after degreasing, and the evaluation criteria are O (excellent), O (good), and Δ (slightly poor).

It was rated as × (poor). The results are shown in Tables 3 and 4.

Disappointment-I Regarding the test material obtained in Example 1, J l52704
Corrosion resistance was evaluated by examining the occurrence of pitting corrosion after 100 hours of continuous salt spray testing. The results are shown in Tables 3 and 4.

After applying cationic electrodeposition coating for automobiles (film thickness 25 μm) to the test material obtained in Example 1, the coating film was scratched and salt water sprayed for 24 hours → wet (50°C x 85°C). %RH)1
The yarn rust resistance was evaluated using one cycle of 44 hours.

The evaluation results of thread rust resistance after 5 cycles are shown in Tables 3 and 4.

J1 Cod A- Test material obtained in Example 1 (applied with press oil → left at room temperature →
After degreasing) and base treatment (colloidal titanium immersion phosphate-resistant zinc treatment), cationic electrodeposition coating (film thickness 25μ)
The yarn rust resistance was evaluated in the same manner as in Example 3. The evaluation results of thread rust resistance after 5 cycles are shown in Tables 3 and 4.

The sample material obtained in Example 1 was coated with urethane paint (1
5μ+a) The coating film adhesion was evaluated in the same manner as in Example 3. Coating film after 5 cycles! jj adhesion evaluation results are shown in Tables 3 and 4.

As is clear from Tables 3 and 4, the examples of the present invention all exhibit excellent thread rust resistance and coating adhesion, as well as good corrosion resistance and degreasing properties.

On the other hand, among conventional examples, those treated with chromate chromate or chromate phosphate have poor degreasing properties.

Furthermore, as mentioned above, it is not practical due to problems such as wastewater treatment, and other conventional examples have poor thread rust resistance.

In addition, the comparative example has problems in degreasing properties, corrosion resistance, coating film adhesion, and thread rust resistance.

[Blank below] (Effects of the invention) As detailed above, according to the present invention, since anodizing and sealing are performed under specific conditions, thread rust resistance, paint film adhesion, corrosion resistance, and degreasing properties are improved. An excellent aluminum alloy material can be obtained, which can be applied as a variety of base treatments or as a surface treatment to improve corrosion resistance. In particular, when applied as a paint film base treatment, excellent thread rust resistance can be obtained.

In addition, since degreasing and anodic oxide film formation can be performed in the same bath or a bath with the same composition, processing costs can be significantly reduced, and the process can be applied by modifying existing cleaning equipment, resulting in improved effectiveness. is significantly large. Particularly when aluminum alloys are used for automobile panel materials, the problem of thread rust resistance, which has been the biggest problem in the past, can be solved, and the effects are significant, such as allowing the use of existing lines.

Claims (1)

[Scope of Claims] (1) A method for surface treatment of an aluminum alloy, which comprises subjecting the aluminum alloy to anode electrolysis in an electrolytic solution containing an alkaline builder and a surfactant, and then sealing the pores. (2) A method for surface treatment of an aluminum alloy, which comprises cathodically electrolyzing the aluminum alloy in an electrolytic solution containing an alkaline builder and a surfactant, followed by anodically electrolyzing the aluminum alloy in an electrolytic solution having the same composition, and then sealing the pores. . (3) A claim in which the alkaline builder contains one or more selected from the group consisting of phosphates, silicates, sulfates, borates, and alkanolamines at a concentration of 0.5 to 5 wt%. The method described in 1 or 2. (4) Claim 1 or 2, wherein the electrolyte temperature is 40 to 80°C.
The method described in. (5) Claims 1, 2, and 3, wherein the electrolytic voltage is 15 to 60V.
Or the method described in 4. (6) Claim 1, wherein the electrolyte is supplied from a spray nozzle.
2. The method described in 2, 3, 4 or 5. (7) The method according to claim 1 or 2, wherein the pores are sealed with an aqueous solution containing any one of chromic acid, an alkali metal salt of chromic acid, silicic acid, boric acid, or an alkaline alkanolamine salt. (8) The method according to claim 1, 2 or 7, wherein anode electrolysis is performed at a voltage of 20 to 100 V during sealing. (9) Claims 1, 2, 3, and 4, wherein the aluminum alloy is used for automobile panels that require thread rust resistance.
, 5, 6, 7 or 8.