JPS59185782A - Surface treatment of aluminum or aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain a film having superior corrosion resistance, hydrophilic property and adhesion to a paint film on the surface of Al or an Al alloy by forming a hydrated oxidized film by treatment with a basic aqueous soln. contg. chlorate, chlorite, bromate, bromite, iodate or iodite. CONSTITUTION:Al or an Al alloy is treated with a basic aqueous soln. contg. one or more kinds of compounds selected among chlorites, bromites, iodites, chlorates, bromates and iodates as an oxidizing agent to form a hydrated oxidized film on the surface of the metal. NaOH or the like is used to make the concn. of the oxidizing agent proper and the soln. basic, and the soln. is adjusted to a proper pH. The treatment is carried out for a proper time. By this method, any problem in the control of environmental pollution such as the necessity of the treatment of waste liquor does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of aluminum or aluminum alloy, in which aluminum or aluminum alloy is treated with chlorite, bromite, iodate, chlorate, bromate, By treating with a basic aqueous solution containing at least one compound selected from iodates to form a water-conserving oxidation film on the surface, corrosion resistance, hydrophilicity, and coating adhesion are significantly improved. The purpose of the present invention is to provide a surface treatment method for aluminum or aluminum alloy.

Conventionally, the chromate method, boehmite method, M, and B have been used as chemical conversion treatment methods for forming an oxide film on the surface of aluminum or aluminum alloy (hereinafter simply referred to as aluminum alloy). Various methods have been proposed, such as the v method, E, and W methods.

Among these methods, the chromate method generates an oxide film with good corrosion resistance on the aluminum alloy surface in a short time at low temperatures, and although this oxide film has good paint film adhesion, it is also water repellent. A fatal drawback is that the chemical conversion treatment method using the chromate method cannot be used in fields where hydrophilicity is required, such as heat exchange media (fin materials) or 28th printing. In addition, the chromate method has the disadvantage that harmful ions such as chromium and cyanide are contained in the wastewater after chromate treatment, resulting in a heavy burden on the wastewater treatment.

Furthermore, in the boehmite method, aluminum alloy is treated in demineralized water heated above SO'C, so it takes at least 95% to form an oxide film with good corrosion resistance.
The processing temperature is above °C and the processing temperature is also 3 minutes or more,
Therefore, bath management is difficult and it is difficult to obtain a homogeneous film. Therefore, due to these drawbacks, this method is not suitable at all as a treatment for precoating materials when aluminum alloys are used as heat exchange medium materials. Therefore, in order to compensate for these drawbacks, it has been proposed to add ammonia or triethanolamine, etc., to accelerate the dissolution reaction and enable processing to be completed in a short time. The balance of film formation is balanced, and the corrosion resistance is not improved that much even though the oxide film increases.
For example, it is inferior to a film produced by a chromate treatment method.

In addition, in the M, B, V method, E, W method, etc., the processing temperature is usually as high as 9°y'OpC, and the processing time is usually as long as 3 minutes or more. This is inappropriate for commercial purposes.

Also, a chemical conversion treatment method in which an aluminum alloy is treated with an aqueous solution of sodium hypochlorite or potassium hypochlorite to form an oxide film on the surface (Japanese Patent Publication No. 32772/1983).
has also been proposed, but the stress resistance of the oxide film produced by the chemical conversion treatment method depends on the material and tempering of the collected wood, the oxidizing agent concentration in the treatment bath,
When a water conservation oxidation film is generated at a treatment temperature of 70°C or higher in a basic bath where the addition amount of basic substances and P and H based on the dissolved Al concentration are greatly affected, that is, the effect of oxidizing agent addition is not observed. On the other hand, if the P and H of the treatment bath are made too high, for example, P and H of 11.5 or more, dissolution is promoted more than oxidation, especially for AI-F (compounds, Al-Fe-31 compounds, Al-Mn compound, Al-Fa-jumping compound, Al-
A in the periphery of intermetallic compounds such as Fe-8 compounds
Local dissolution of the substrate is promoted, intermetallic compounds fall off, and bits with a diameter of about 2 to 10 μm and a depth of about 1 μm or more calculated from the difference in surface roughness before and after treatment are generated, As a result, there were many pitted areas where no oxide film was formed, resulting in a significant decrease in corrosion resistance.

As a result of extensive research into a chemical conversion treatment method that produces a film with good corrosion resistance, hydrophilicity, and paint film adhesion without causing pollution problems such as drainage treatment, the inventor discovered that aluminum alloys can be treated with chlorite. , bromite, iodate, chlorate, bromate, and iodate. It was discovered that the hydrated oxide film obtained by the method is excellent in corrosion resistance, hydrophilicity, and coating adhesion, and the present invention was completed.

Next, a method for surface treatment of aluminum or aluminum alloy according to the present invention, which produces a hydrated oxide film having excellent corrosion resistance, hydrophilicity, and coating adhesion, will be described.

The concentration of the oxidizing agent such as chlorite or chlorate used in the present invention is preferably about 0.0001 to 359 A/l, more preferably about 0.05 to 359 A/l.

Particularly preferred is 05 to IVl. That is, if the concentration is too low, the oxidizing power will be weak, and if the concentration is too high, it will be difficult to obtain a uniform film, and a large amount of the oxidizing agent will be carried out during the treatment, which will be uneconomical.

To make the treatment solution basic, caustic soda is usually used, but caustic potash, calcium hydroxide, sodium carbonate, borax, basic amines (triethanolamine,
ammonia, etc.) may also be used. However, P in the basic bath,
It is important to keep H at about 11.5 or less, and preferably keep P and H at about 10 to 11. In other words, if P and H become too high exceeding 11.5,
The base aluminum around the intermetallic compound dissolves, resulting in the formation of many bits and a decrease in corrosion resistance.On the other hand, if P and H are small (less than 10), the amount of dissolved aluminum decreases. , the rate of film formation becomes slow, that is, the amount of film formed is small, so corrosion resistance tends to decrease. Therefore, the P and Hi of the processing solution, especially 10 to 1
If it is set to 1, a balance between dissolution and oxidation of aluminum can be obtained, the number of bits due to shedding of intermetallic compounds will be extremely small, and a dense water-conserving oxide film will be produced.

As for the processing time, longer is not better; for example, it is about 60 to 180 seconds. In other words, the surface layer of the aluminum alloy contains 6D intermetallic compounds, and there are also intermetallic compounds below this intermetallic compound, so even if the water conservation oxide film becomes thicker due to treatment, the intermetallic compounds will fall off during treatment. This is because film defects will occur in the water conservation oxidation film. Therefore, if the treatment time is set to about 60 to 180 seconds and the amount of water-use oxidation film generated is about 3 to 6 m9/di, not only will there be fewer film defects and excellent corrosion resistance, but also productivity will be improved. I will do it.

When treated in this manner, the surface condition of the water conservation oxide film is due to the shedding of intermetallic compounds.

The number of Pino+ particles with a diameter of about 2 to 10 μm and a depth of about 1 μm or more calculated from the difference in the surface roughness profile before and after treatment is about 120 pieces/m or less, and the corrosion resistance is excellent. Similarly, as the purity of aluminum increases, the number of intermetallic compounds present decreases, and the thickness of the intermetallic compounds also decreases, resulting in even better corrosion resistance. If a post-treatment such as sodium silicate treatment is performed, the hydrophilicity will be further improved.

Next, specific examples of the present invention will be described.

Examples 1 to 10 J engineering 512000 material (75mmX150mmX0.12
mm ) aluminum alloy was treated with sodium chlorite (
Example 1), sodium bromine (Example 2), sodium bromite (Example 3), ammonium iodate (Example 4), ammonium iodate (Example 5), sodium chlorite and chloric acid Sodium (equal weight, Example 6)
, sodium chlorate (Example 7), sodium chlorite (Example 8), calcium chlorite (Example 9), and magnesium iodine (Example 10) were immersed in a basic aqueous solution. Then, a water-conserving oxide film is formed on the surface.

Comparative Examples 1 to 5 The same material as in Example 1 was treated with the conventional boehmite method (desalinated water, Comparative Example 1) and the chromate method (Alodine 11200).
．． Comparative Example 2), Basic aqueous solution treatment without oxidizing agent (Comparative Example 3'+4L sodium hypochlorite water bath solution (Comparative Example 5)
Process with.

The properties of the coatings obtained in Examples 1 to 10 and Comparative Examples 1 to 5 were measured to be 9 as shown in the table.

Similarly, the condition of the formed film was determined by visual observation, and
The amount of film formed is determined by the film weight measurement method according to JIS H8680, and the corrosion resistance is indicated by the rating number display method after 336 hours of salt spray test according to JIS Z2371 (a number of 10 is the best; In addition, hydrophilicity is measured by the contact angle with water droplets using a consonant contact angle meter GA-D (the smaller the contact angle, the better the hydrophilicity), and the coating adhesion is determined by Spray paint and then apply J
The coating film adhesion of the samples subjected to the C1A, S, S test for 48 hours according to IS H8681 is expressed using the cross-cut display method (to+o/l o ).

(The coating film adhesion worsens as the molecules become smaller), and the number of bits generated due to shedding of intermetallic compounds is about 2 to 10 μm in diameter and about 1 μm or more in depth. Find the average of the sheets of material, m711
It is expressed as a number per j.

As described above, the method for surface treatment of aluminum or aluminum alloy according to the present invention is to treat aluminum or aluminum alloy with chlorite, bromite, iodate, salt accumulation salt, fruitate, or iodine. By treating with a basic water bath solution containing at least one compound selected from cumulative salts, a water-conserving oxidation film is generated on the surface of aluminum or aluminum alloy, so it is effective in terms of tribute resistance, hydrophilicity, and coating adhesion. Moreover, it can be processed in a short time, resulting in high productivity and low cost.

Patent applicant: Mitsubishi Aluminum Co., Ltd.

Claims (1)

[Claims] Aluminum or aluminum alloy is treated with a basic aqueous solution containing at least one compound selected from chlorite, bromite, iodate, chlorate, bromate, and iodate. , a method for surface treatment of aluminum or aluminum alloy, characterized by forming a hydrated oxide film on the surface of aluminum or aluminum alloy.