JPS61110797A - Surface treatment of aluminum or aluminum alloy - Google Patents

Abstract

PURPOSE:To ppt. Zn easily in fine pores by forming alumite film, then precipitat ing metal into fine pores of the film with an electrochemical method using a bath contg. mtallic salt, next electrolyzing said film in aqueous soln. contg. Zn salt. CONSTITUTION:Al or Al alloy is anodically oxidized as the first process to form an anodically oxidized film on a surface. As the second process, the bath contg. metallic salt is used and said metal is pptd. into the fine pores in the anodically oxidized film by the electrochemical method. Next, Zn is pptd. electri cally in the aqueous soln. contg. Zn salt, by the electrochemical method as the third process. Sealing treatment is applied as the fourth process.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for surface treatment of aluminum or aluminum alloy (hereinafter referred to as aluminum), and more specifically, to a method for surface treatment of aluminum or an aluminum alloy (hereinafter referred to as aluminum), and more specifically to a method for treating the surface of aluminum or an aluminum alloy (hereinafter referred to as aluminum). This relates to a method of electrodepositing zinc into pores.

Conventional technology Conventionally, the so-called secondary electrolytic coloring method, in which various metals are electrodeposited into the fine pores of an alumite film and then sealed, has been used to make this film have good light resistance and heat resistance. Because it can be colored in a variety of colors, it is widely used in many fields.

Among them, metals such as nickel, copper, iron, cobalt, silver, and tin can be deposited into fine pores relatively easily, so alumite films made by secondary electrolytic coloring of these metals can be used for window frames, interior and exterior panels. It is popular mainly for building materials such as.

By the way, it can be inferred that if zinc could be easily electrodeposited into the micropores, an alumite film with improved corrosion resistance would be obtained.

Zinc is known as a metal that is extremely difficult to deposit.

Conventionally, as a method for electrodepositing zinc, 1 an oxalic acid alumite film is electrolyzed in a zinc sulfate-ammony sulfate-aluminum sulfate bath.

How to obtain a dark yellow-brown film.

2 A method of electrolyzing the phosphate alumite film in an aqueous zinc sulfate solution and coloring it blue (see above).

Aluminum surface technology handbook - Light Metal Publishing P212-P2
13) 3 A method of galvanically dissolving one layer of the sulfuric acid alumite film barrier and then electrodepositing zinc (Metal Surface Technology Vol. 33, No. 5, P50-5, etc. is known).

Problems to be Solved by the Invention However, the above method has the following drawbacks, and there are many problems in its practical use.

In other words, the films obtained by methods 1 and 2 are simply colored films, and zinc is densely deposited in the micropores.
It is clear from the fact that a black film was not obtained that the filling was not sufficient. In addition, the cause of the coloring of this colored film is
It has not been confirmed whether this is caused by zinc electrodeposition. Furthermore, this method has the disadvantage that only oxalic acid alumite coatings and phosphoric acid alumite coatings can be colored. Furthermore, the production of an oxalate alumite film and a phosphate alumite film requires large power consumption, complicated bath management, and special equipment. Other problems with phosphoric acid coatings include the inability to thicken the coating and problems with wastewater treatment.

Therefore, phosphoric acid alumite coating and oxalic acid alumite coating conversion are generally costly.

Currently, it is only used for special purposes.

The film obtained by method 3 utilizes galvanic corrosion to dissolve and remove the barrier layer and then electrodeposit zinc, which results in poor adhesion between the alumite film and the base metal aluminum, making the alumite film easy to peel off. It has the disadvantage of becoming.

As mentioned above, in the conventional method, it is extremely difficult to easily fill the fine pores of the alumite film with zinc by precipitation.

Means for Solving the Problems The present invention has been made in view of the above points, that is, after producing an alumite film.

Iron, nickel and copper using secondary electrolytic coloring technology.

We discovered that zinc can be easily and densely deposited by depositing a very small amount of metals such as silver and cobalt into the fine pores of an alumite film, and then electrolyzing it in an aqueous solution containing zinc salt.1 This led to the completion of the present invention.

More specifically, in the first step, the anodic oxidation treatment bath may be any two commonly used electrolytes and treatment conditions. For example, sulfuric acid baths, sulfuric acid/oxalic acid mixed baths, oxalic acid baths, and various inorganic acid baths.

In addition to organic acid baths and mixed baths thereof, baths in which alcohol or the like is mixed or added can be used.

Further, as the electrolytic conditions, the conventional direct current method, alternating current method, AC/DC superposition method, method utilizing two recovery effects, etc. may be used, and the bath temperature, current density, and voltage may be those commonly used. The first step, more preferably, includes a step of performing so-called intermediate treatment to make the barrier layer uniform after the alumite film is formed.

Next, as a second step, a very small amount of metal is electrodeposited into the micropores of the alumite film. The metal may be any metal such as iron, nickel, copper, silver, cobalt, etc., but iron and nickel are particularly preferred. As a method for electrodepositing the metal, a so-called secondary electrolytic coloring technique is used to deposit a very small amount of the metal on the bottom of the micropores, that is, on the barrier layer. At this time, electrolytic conditions such as bath composition, bath temperature, current waveform, and current density must be appropriately set depending on the metal.

As a third step, electrolysis is performed again in an aqueous solution of zinc salt to precipitate zinc. The method for electrodepositing zinc is carried out using electrolytic coloring technology as in the second step. Here, it is preferable to use a zinc sulfate-based bath as the electrolytic bath. As the fourth step.

Perform sealing treatment. The sealing treatment may be carried out by any commonly used treatment method.

Effect: By the above method, a very small amount of metal is precipitated as a nucleus at the bottom of the micropores by electrodeposition, and the first zinc is taken in from this metal nucleus, and this is the trigger for zinc to be deposited one after another. By laminating the layers, the fine pores are filled and a corrosion-resistant black coating is obtained.

Example I JISA1080-HI3 (50X50X0°8m)
Use this as a test piece and perform the usual caustic treatment and then wash with water. Next, it was immersed in a 10% nitric acid bath (at room temperature) to remove smut, washed with water, and then anodized under the following conditions to obtain a 10 μm thick alumite film.

Next, a small amount of copper was electrodeposited into the micropores of the alumite film under the following conditions.

Next, the test piece was electrolyzed under the following conditions to deposit zinc.

After washing with water 1. Sealing treatment, which is usually performed, was performed under the following conditions.

Finally, by washing with water and drying, a brown alumite film on which zinc was electrodeposited was obtained.

Example 2 JISA5052P-H24 (50x50xO, 8m)
was used as a test piece, pretreated in the same manner as in Example 1, and nickel was electrodeposited into the micropores of the alumite film under the following conditions.

Next, the test piece was treated under the following conditions to deposit zinc.

Then, it was washed with water, sealed in the same manner as in Example 1, and finally washed with water and dried to obtain a black alumite film on which zinc was electrodeposited.

Example 3 JISA3003P-HI3 (50x50xO, 8m
) was used as a test piece, pretreated in the same manner as in Example 1, and silver was electrodeposited into the micropores of the alumite film under the following conditions.

Next, the test piece was treated under the following conditions to electrodeposit zinc.

Then, it was washed with water, sealed in the same manner as in Example 1, and finally washed with water and dried.

Zinc powder with a metallic color was deposited on the resulting alumite film, and the zinc powder was removed.

A jet black colored alumite film was obtained.

Effects of the Invention Figure 1 shows the results of EPMA line analysis when a minute amount of nickel was deposited on 7L of a sulfuric acid alumite film, and then zinc was deposited.

From FIG. 1, it can be seen that the pores of the alumite film are sufficiently filled with zinc.

The aluminum alumite film obtained as described above has the following effects and is very useful industrially.

(1) Not only in oxalic acid and phosphoric acid bath anodized films, but also in sulfuric acid bath anodized films, sufficient electrodeposition is performed until zinc powder is removed, and a uniform black colored film can be obtained.

(2) Since zinc has a small potential difference with aluminum,
Corrosion resistance is improved by sufficiently electrodepositing this into the fine pores of the anodic oxide film.

(3) Since the external color ranges from brown to black, it can also be used for decoration.

(4) It is easy to operate and can be done in a short time.

[Brief explanation of drawings]

Figure 1 shows the E'PM of an alumite film filled with zinc.
This is a diagram of A-line analysis. Patent applicant: Pilot Precision Co., Ltd.'a1

Claims (1)

[Claims] 1 The first step is to anodize aluminum or aluminum alloy to form an anodized film, and the metal is electrochemically deposited into the micropores of the anodic oxide film using a bath containing a metal salt. a second step of depositing zinc by an electrochemical method in an aqueous solution containing a zinc salt; and a fourth step of performing a sealing treatment. Alloy surface treatment method.