JPH10265996A - Anodic oxidation treatment of aluminum or its alloy with good alkaline corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form films having an excellent corrosion resistance and wear resistance and having a good alkaline resistance by treating Al or Al alloy in a sulfuric acid electrolytic bath to form anodically oxidized films and further treating these films for a specific time with a specific AC voltage in an ordinary sulfuric acid electrolytic bath. SOLUTION: The anodically oxidized films are previously formed on the Al or Al alloy in the electrolytic bath which consists of the sulfuric acid or consists mainly of the sulfuric acid and contains phosphoric acid, oxalic acid, etc. The anodically oxidized films are formed by executing an anodic oxidation treatment at a current density of about 1.0 A/dm<2> and DC voltage of about 15 V in a sulfuric acid bath of, for example, a sulfuric acid concn. of about 15% and about 20 deg.C. The anodically oxidized films as blanks are thereafter, treated for 1 to 10 minutes with the AC voltage of 1 to 8 V in the ordinary sulfuric acid electroiytic bath. As a result, the extremely thin AC anodically oxidized films having the good alkali corrosion resistance are formed under the DC anodically oxidized films. The resulted anodically oxidized films are thereafter subjected to a sealing treatment at need.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial application] Aluminum or an alloy thereof (hereinafter referred to as Al) is subjected to anodizing treatment to form a film having good corrosion resistance and abrasion resistance, and is used in various products such as kitchen utensils and household products. It is used for various industrial parts and the like, and provides a product having better alkali corrosion resistance in this field.

[0002]

2. Description of the Related Art Al is electrolytically treated in an electrolytic solution such as sulfuric acid, phosphoric acid, and oxalic acid to form an anodic oxide film. In general, phosphoric acid electrolysis has a soft film property. At present, oxalic acid electrolysis is not widely used as a general industrial processing method because the processing method is inefficient. However, the performance of the oxalic acid film, particularly the chemical performance, is excellent, and it has been desired to impart a performance similar to this film by other easily-treated electrolytic treatment.

[0003]

[Problem to be Solved] In the anodic oxidation of Al, sulfuric acid electrolytic treatment is widely used because of its excellent productivity. Further, a mixed bath containing mainly sulfuric acid and an inorganic acid such as phosphoric acid or an organic acid such as oxalic acid is also used. The sulfuric acid concentration is 5-30% and the temperature is 15-
30 ° C., current density 0.5-30 A / dm ² , electrolysis voltage 1
A wide range of conditions, such as 0-20V (DC or AC), has become applicable. However, 15
% -Sulfuric acid, 20 ° C, 1.0 A / dm ² , 15 V (DC)
The standard electrolysis conditions or conditions similar thereto are used. It is considered to be a more rational method to improve the corrosion resistance by using such sulfuric acid electrolysis without making great changes in the process and equipment. First, the structure of the film will be described. Many studies have been reported on the microstructure of sulfuric acid and oxalic acid electrolytic films when using a DC power supply. For example, the cell size of the coating is about 2.
A value of 6 nm / V and a thickness of the barrier layer of about 1.0 nm / V are reported (Reference 1). Each of them is proportional to the electrolysis voltage, and at a voltage of 15 V, a barrier layer of about 15 nm is formed. At a voltage of 5 V, the thickness is calculated to be about 5 nm. In fact, standard sulfuric acid electrolysis (15%
(Monosulfuric acid, 20 ° C., 1.0 A / dm ² , 10 μm), a DC voltage of 15 V is applied, and the thickness of the barrier of about 15 nm is measured. Similarly, standard oxalic acid electrolysis (3% -oxalic acid, 30 ° C., 1.0 A / dm ² ,
10 μm), a value of about 40 nm is observed since a DC voltage of approximately 40 V is applied. On the other hand, in AC electrolysis, the relationship between electrolysis conditions and film thickness has been well investigated, but there are few research reports on microstructures, especially in the case of low voltage, cell size and barrier layer thickness. Little numbers are known. Next, the chemical properties of the film will be described. JIS-H-8601 specifies a method for evaluating the performance of the anodic oxide film. In particular, the method for evaluating the corrosion resistance is mainly based on an alkali drop test method and a CASS test method. It is considered that the former is suitable for determining the chemical property due to the difference in the sealing treatment, and the latter is suitable for determining the property due to the defect. And
In the alkali drop test, sulfuric acid (class A) and oxalic acid (B
Seed) coatings are specified as 5 and 15 seconds / μm or more, respectively. In fact, the results of the joint research by the Japan Light Metal Products Association (Reference 2) show that the sulfuric acid electrolytic film contains about 5-10 seconds / μm In the case of the oxalic acid film, the measured value is about 20-50 seconds / μm. Furthermore, CAS
Also in the S test, it is recognized that the oxalic acid film is excellent.

[0004]

[Means for Solving the Problems] In order to solve the above problems, the present invention is to form a general sulfuric acid anodic oxide film, and then specify an AC electrolysis of a specific voltage in a normal sulfuric acid bath. This is a method of producing a film having a performance close to that of the oxalic acid electrolytic film by performing the treatment for a long time. That is, using an anodic oxide film previously formed on Al in a general sulfuric acid or an electrolytic bath mainly containing sulfuric acid as a material, and then in an ordinary sulfuric acid electrolytic bath, an AC voltage of 1-8 V, 1-10 This is a method for producing a film having good alkali corrosion resistance by treating for minutes. Conventionally, various studies have been made to improve the alkali corrosion resistance of the sulfuric acid anodic oxide film, but almost all methods of improving the corrosion resistance by forming a thick barrier layer by alternating current low voltage electrolysis as in the present invention have been reported. It has not been. It is an academic theory that in DC electrolysis, when the electrolysis voltage is reduced, the thickness of the barrier layer becomes proportionally thinner, but it is thought that a similar tendency exists in AC electrolysis. 0 The present invention has found that a barrier layer of about 30 nm is formed from the result of observing the fine structure of the film by this treatment with an electron microscope. First, a film having a thickness of about 10 μm was formed by a standard direct current sulfuric acid electrolysis treatment, followed by a treatment in the same electrolytic bath with an alternating current of about 5 V for about 1 to 3 minutes to perform a so-called current recovery. . After washing with water, when subjected to alternating current electrolysis of 5-8 V in a Sn-Ni salt electrolytic bath for about 1-5 minutes, it was found that the film exhibited beautiful colors such as blue, green and gold. The alkali corrosion resistance by the alkali drop test was about 20 seconds / μm, and the corrosion test by the CASS test was measured to be extremely good as a sulfuric acid film (Reference 3). However, in the microstructure of the coating, nothing was said about the cell size and the thickness of the barrier layer. Thereafter, the fine structure of this color film was observed to be about 1
It was reported that a 00-200 nm thick AC film formed beneath the DC skin, with pore diameters of about 5-7 nm and a barrier layer of about 30 nm (4). That is, it has been newly discovered that when a low AC voltage of about 5 V is applied in a conventional sulfuric acid electrolytic bath, a thick bary layer is formed. As a result, the alkali corrosion resistance increases, which is presumed to be due to the thick barrier layer.
That is, it is understood that this is a completely new fact that has not been found in the preparation of the electrolytic film according to the conventional method. In order to increase the added value of this film, it can be immersed in a dye and pigment solution by a conventional method, or can be subjected to color treatment by electrolytic metal deposition. Furthermore, the application range is expanded by applying coating, electrodeposition coating, and the like. This AC film can be directly applied to Al. However, since the film has a thickness of about 0.1 μm, it requires a practical coating and is not suitable for the purpose of alkali resistance. It is.

[Literature] (1) O'Sullivan and
G. FIG. C. Wood: Proc. Roy. Soc. Lon
don, A, 317 511 (1970). (2) Report of the 2nd Aluminum Building Supplies Surface Treatment Committee, p. 63 and 89 (1962). (3) Go Nishizawa, Masaaki Yamamuro: JP-A-7-71791,
(July 20, 1993). (4) Kei Kawai: 3rd Practical Seminar on Practical Electrolytic Coloring Technology
Japan Light Metal Products Association, (October 17, 1996).

[0005]

【Example】

Example 1 99.85% pure Al plate (10x5x
1 mm), a sulfuric acid anodic oxide film of about 10 μm
Created. The coating was then applied to a standard sulfuric acid electrolytic bath (1
In a 5% -sulfuric acid, 0.1% -Al ⁺³ , 20 ° C.), a carbon electrode was electrolyzed at an AC voltage of 5 V for 3 minutes. The current gradually rises from 0 to 1.1 A / dm after 1.5 minutes.
After reaching ² , a steady current was shown. After washing with water, a pure water sealing treatment was performed at 95 ° C. for 20 minutes. And the alkali corrosion resistance by the alkali dripping test reached about 17 seconds / μm. With a transmission electron microscope, an extremely thin AC film is
It was observed that it was formed under a direct sulfur film of about 10.0 μm. Embodiment 2 FIG. Al 1100-1 / 2H material (10x5x
1 mm) with a standard sulfuric acid electrolytic bath (15% -sulfuric acid, 1.0
% -Al ⁺³ , 20 ° C.), an Al electrode, 1.1 A /
DC electrolysis was performed at a current of dm ² for 60 minutes to form a film of about 18 μm. Subsequently, the electrode was changed to a carbon electrode and electrolyzed in the same sulfuric acid electrolytic bath at an AC voltage of 5 V for 2.5 minutes, and then an aqueous solution of iron ammonium oxalate (15 g / L, 60 ° C.,
pH: 5) for 10 minutes to give a gold color. Finally, Ni acetate acetate sealing treatment is performed at 95 ° C. for 20 minutes.
Minutes. And the alkaline shochu eating ability is about 19 seconds / μ
m. The structure of the film was observed by a scanning electron microscope. The thickness of the AC film was about 100 nm, the diameter of the pore was about 5 to 7 nm, and the thickness of the barrier layer was 30 nm. Embodiment 3 FIG. Al 6063-T5 material (10x5x21
mm) in advance in a standard sulfuric acid electrolytic bath to which a carbon electrode was attached at a current of 1.1 A / dm ² for 35 minutes to form a film of about 10 μm. Next,
Electrolysis was performed in the same electrolytic bath at an AC voltage of 4 V for 3.0 minutes. Further, a 15 V alternating current electrolysis was carried out in a Sn-Ni salt bath for 5 minutes in a conventional manner to produce a bronze color.
Finally, Ni acetate acetate sealing treatment was performed at 95 ° C. for 20 minutes.
In the alkali drop test, it exhibited an alkali corrosion resistance of about 20 seconds / μm, and the corrosion test by the CASS test showed about RN 9.5 or more in 36 hours.

Claims (1)

[Claims] 1. An aluminum or an alloy thereof is made of an anodic oxide film previously formed in sulfuric acid or an electrolytic bath mainly composed of sulfuric acid. An electrolytic treatment method characterized by forming a film having good alkali corrosion resistance by treating for -10 minutes.