JPS59185783A - Surface treatment of aluminum or aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain a film having excellent corrosion resistance, hydrophilicity and the adhesion of a paint coated film by using an aq. basic soln. contg. peroxoborate in a treatment for forming a hydroxide film on the surface of an Al metal. CONSTITUTION:Al or an Al alloy is treated in an aq. basic soln. contg. peroxoborate (for example, by dipping or spraying) to form a hydroxide film on the surface of the Al or Al alloy. NaOH, etc. are used to adjust adequately the concn. of an oxidizing agent for the peroxoborate such as Na metaborate peroxyhydrate (NaBO2.H2O2.3H2O) or Na tetraborate peroxyhydrate (Na2B4O7. H2O2.9H2O), etc. and to make the treating soln. basic, by which the soln. is adjusted to correct pH. The treating time is made adequate as well. The problem in environmental pollution in a waste treatment, etc. is obviated according to the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of aluminum or aluminum alloys, in which aluminum or aluminum alloys are treated with beroxoboric acid such as sodium metaborate or sodium tetraborate peroxide. To provide a method for surface treatment of aluminum or aluminum alloy, which significantly improves corrosion resistance, hydrophilicity, and coating adhesion by treating with a basic aqueous solution containing salt to form a water-conserving oxide film on the surface. 0 Conventionally, as a chemical conversion treatment method for forming an oxide film on the surface of aluminum or aluminum alloy (hereinafter simply referred to as aluminum alloy), the chromate method, boehmite method, M, B, V method, or E, W method has been used. Various measures have been proposed, including legislation.

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. In fields where hydrophilicity is required, such as heat exchange media (fin materials) or 98 plates, the chemical conversion treatment method using the chromate method cannot be used, which is a fatal drawback. In addition, the chromate method has the disadvantage that the wastewater after chromate treatment contains harmful ions such as chromium and cyanide, and therefore requires a great deal of 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 required for 3 minutes or more,
Therefore, there are disadvantages in that 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. It is difficult to balance the formation, and the corrosion resistance is not improved much even though the oxide film increases.
For example, it is inferior to a film produced by a chromate treatment method.

In addition, the processing temperature for M, B, V methods, E, W methods, etc. is usually 90°C.
The temperature is as high as ~100°C, and the treatment time is usually longer than 3 minutes, and therefore, like the above-mentioned boehmite method, it is inappropriate as a treatment for pre-coated materials.

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 interface (Japanese Patent Publication No. 53-32772).
has also been proposed, but the corrosion resistance of the oxide film produced by the chemical conversion treatment method depends on the material and tempering of the material, the concentration of the oxidizing agent in the treatment bath,
Based on the amount of basic substance added and the dissolved Al concentration (significantly affected by P and H, in other words, in a basic bath where the oxidizing agent effect is observed, a water conservation oxide film is formed at a treatment temperature of 70°C or higher. If the brightness of the treatment bath is made too high, for example, P, Hll, 5 or more, dissolution will be promoted more than oxidation, especially for Al-Fe compounds, Al-F, -81 compounds, Al-Mn. compound, Al-Fe-Mn compound, Al
-Local dissolution of the Al substrate around intermetallic compounds such as -Fe-4, -s1 compounds is promoted, and the intermetallic compounds fall off, with a diameter of approximately 2 to 10 μm, calculated from the difference in surface roughness before and after treatment. The occurrence of pits with a depth of approximately 1 μT11 or more increased, and as a result, there were many defective areas such as the formation of an oxide film, resulting in a marked deterioration in corrosion resistance.

As a result of intensive 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 present inventor discovered that aluminum alloys can be treated with peroxoborate. It has been discovered that when treated with a basic aqueous solution (e.g., immersed or sprayed), the water-conserving oxide film obtained by this surface treatment has excellent corrosion resistance, hydrophilicity, and coating adhesion, and has developed the present invention. It was accomplished.

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

As an oxidizing agent used in the present invention, for example, sodium metaborate hydrogen peroxide (N3B○2・H2O2
・3H20) or sodium tetraborate peroxide (
The concentration of beluocune borate such as Na2B407.H2O2.9H20) is preferably about 0.0001 to 359A, more preferably 0.05 to 3.5g/
1, particularly preferably 05-19A. That is,
If the concentration is too low, the oxidizing power will be weak, and if the concentration is too high, a uniform film will not be obtained 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 powder is usually used, but caustic potash, calcium hydroxide, sodium carbonate, borax, and basic amines (e.g., triethanolamine, ammonia, etc.) can also be used. good. However, it is important that the basic bath has P and H of about 115 or less, preferably about 10 to 11. In other words, if 8H becomes too high, exceeding 11.5, the base aluminum around the intermetallic compound will be decomposed, resulting in the formation of many pins and reducing the corrosion resistance. If it is too small, less than 10,
Since the amount of dissolved aluminum decreases and the film formation rate is slow, that is, the amount of film formation is small, corrosion resistance tends to decrease. Therefore, the P and H of the treatment liquid should be adjusted to 10 to 1.
If it is set to 1, a balance between aluminum dissolution and oxidation can be obtained, the number of pits due to shedding of intermetallic compounds will be extremely small, and a dense hydrated 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, there are intermetallic compounds on the surface layer of the aluminum alloy, and there are also intermetallic compounds below this intermetallic compound, so even if the hydrated oxide film becomes thicker due to treatment, the intermetallic compounds will fall off during treatment. However, 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/dmf, 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 way, the surface condition of the water conservation oxide film is approximately 2 to 10 μm due to shedding of intermetallic compounds.
The number of spots with a depth of approximately 1 μm or more calculated from the difference in surface roughness profile before and after treatment is approximately 120/
mm" or less, and the corrosion resistance is excellent. However, as the purity of aluminum increases, the number and size of intermetallic compounds present generally decrease, so the corrosion resistance further improves.

Moreover, if a post-treatment such as sodium silicate treatment is performed after the treatment with the basic aqueous solution containing the beroxoborate of the present invention, the hydrophilicity can be further improved.

Next, specific examples of the present invention will be described.〇Examples 1 to 4 JIS 12000 material (75mm
2 mm) (7) y The aluminum alloy is immersed in a basic aqueous solution to which sodium metaborate hydrogen peroxide is added to form a water conservation oxide film on the surface.

Examples 5-,-6 The same material as in Example 1 is immersed in a basic water bath solution to which sodium tetraborate hydrogen peroxide is added to form a water-conserving oxide film on the surface.

Comparative Examples 1 to 4 The same material as in Example 1 was treated with the conventional boehmite method (desalinated water, Comparative Example 1), chromate method treatment (Allozin-1200
, Comparative Example 2), and basic aqueous solution treatment without adding an oxidizing agent (Comparative Examples 3 and 4).

The properties of the films obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were measured as shown in the table.

The condition of the formed film was determined by visual observation, the amount of film formed was measured by the film weight measurement method according to JIS H8680, and the corrosion resistance was determined according to JIS Z237.
The hydrophilicity is shown by the rate zig number display method after 336 hours of the salt spray test according to No. 1 (a number of 10 is the best, and the smaller the number, the worse it is). (the smaller the contact angle, the better the hydrophilicity)
It shows the adhesion of the paint film of the sample over time using the month-to-month notation method (100/100 is the best; the adhesion of the paint film gets worse as the molecules get smaller), and the drop-off of intermetallic compounds. The number of occurrences of focus is approximately 2 to 2 in diameter.
10 μm, the number of pits with a depth of about 1 μm or more is 10
The average value for each sheet of material is calculated and expressed as the number per mm.

In the above examples, sodium peroxoborate is used as the perocune borate, but potassium peroxoborate, ammonium peroxoborate, etc. may also be used.

As described above, the method for surface treatment of aluminum or aluminum alloy according to the present invention involves treating aluminum or aluminum alloy with a basic aqueous solution containing peroxoborate to form a water-conserving oxide film on the light surface of aluminum or aluminum alloy. , it has excellent corrosion resistance, hydrophilicity, and coating adhesion, and also has the advantages of high productivity because it can be processed in a short time and can be done at low cost.

Claims (1)

[Claims] A method for surface treatment of aluminum or aluminum alloy, which comprises treating aluminum or aluminum alloy with a basic aqueous solution containing peroxoborate to form a water-conserving oxide film on the surface of aluminum or aluminum alloy.