JPS6338599A - Method for anodizing aluminum alloy - Google Patents

Abstract

PURPOSE:To provide the title method for anodizing an Al alloy wherein electric discharge is never generated from the Ti surface of a Ti setting jig to be used, carrying out electrolysis at a fixed current density, and switching the voltage to a fixed voltage lower than the voltage before the voltage reaches a specified voltage when an Al alloy is anodized. CONSTITUTION:An Al alloy is anodized at a fixed current density in the early stage, and the surface-treated film of the Al alloy is gradually increased. The voltage is increased along with the increase of the film thickness, and the electrolysis is switched to a fixed voltage lower than 50 V before the bath voltage becomes above 50 V. As a result, since the current density is lowered due to the resistance of the film thickness, the burnout of the film is completely prevented, and the Al alloy can be anodized without causing the discharge from Ti of the Ti setting jig to be used even at the contact point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for anodizing aluminum alloys, and is used for anodizing aluminum alloys for automobile parts.

(Prior art) As a prior art related to the present invention, there is a procedure, an inter-finish 3Q (proceeding
of IN"r'ERFINIsH80), pages 263 to 267 describe a method for high-speed anodizing treatment of aluminum alloys.

This is a method that calculates the limit value of alumite burn to speed up the anodizing process of aluminum alloy, and then computer-controls the output of the rectifier along the function curve.This method can quickly produce thick alumite films without causing burn defects. In order to achieve this goal, a high current density is applied at the beginning of the alumite treatment, and a low current density is applied at the latter stage.

(Problems to be Solved by the Invention) However, since the anodic oxidation treatment method uses a function generating computer to control the rectifier, it requires extremely high equipment costs, and when a titanium setting jig is used, titanium There was a problem in that discharge occurred from the titanium surface beyond the discharge withstand voltage of the titanium.

The technical object of the present invention is to provide a method for anodizing an aluminum alloy that uses a constant current/constant voltage rectifier with low equipment cost and that does not cause discharge from the titanium surface.

[Structure of the invention]

(Means for solving the problem) The technical means for solving the above technical means is that in the anodizing method of aluminum alloy, electrolysis is carried out at a constant current, and before the bath voltage reaches 50V or more, the electrolysis is stopped at 50V. This is an anodizing treatment method that switches to the following constant voltage load.

(effect) The technical means works as follows.

In other words, by anodizing at a constant current density in the initial stage, the surface treatment film of the aluminum alloy gradually increases, and the voltage increases accordingly, and after a certain period of time, in the latter stage, by keeping the voltage constant, the current density increases. is reduced due to the resistance of the film thickness, so no film burning occurs at all.
Even at the contact point, the discharge of titanium will not be exceeded.

(Example) Examples will be described below.

[Example 1] Aluminum alloy (JIS, Al100.Aff=99
%, Cu: 0.05-0.2%, Zrl<0.
1%.

A rolled plate (thickness: 0.8 mm) of Fe+Si<1%) was degreased with a solvent, immersed in a 5% NaOH solution at 50°C for 30 seconds to lightly (etch) the surface, and then immersed in a 10% HN Off solution. In order to obtain an anodic oxide film of 50μ, anodization was carried out under the following conditions.

FIG. 1 shows the current density and voltage curves for the constant current control method and the latter constant voltage control method.

In Figure 1, constant current density It (IOA/dd)
Anodize for 8 minutes at In this case, the film thickness gradually increases and the resistance increases, so the voltage 1 is increased as shown by the dotted line. After 8 minutes of electricity, the anodizing process is performed with the voltage 1 kept constant by operating the changeover switch. In this case, the current (1) gradually decreases because the film thickness increases and the resistance increases.

In this way, the anodic oxide film 53 is formed by applying electricity for only 16 minutes.
A uniform film of μ was obtained. In addition, there is no burning phenomenon at the contact point (therefore, no discharge from the titanium surface.
The basic configuration of a rectifier is CB (power circuit breaker), THY (
RF-TR (rectifier transformer), and SR (silicon diode).

[Conventional Example 1-1] The aluminum alloy treated by the method of Example 1 was
oceedings of [NTERFINIS
Shown in H80.

FIG. 3 shows the relationship between the current density (3), the voltage V, and time when the anodizing treatment is performed by computer-controlling the current density and voltage using the constant current control method and the control method using late function generation.

Although the film thickness was 53 μm, part of the titanium material of the jig contact had melted, and there was some burning around the contact of the rolled plate of the workpiece.

This is because the final voltage value exceeded 50V as shown in Figure 8, exceeding the discharge withstand voltage of the oxide film on the surface of titanium, which is the contact material. The final fluctuation of the voltage curve is a phenomenon caused by this. In this case, a special circuit is required to control the current, making the equipment expensive.

[Conventional Example 1-2] Current density I4 and voltage (2) when an aluminum alloy treated by the method of Conventional Example 1-1 is anodized using a constant voltage control method, which is a conventional constant voltage control method.

Figure 4 shows the changes in . This method is a commonly used processing method, and the film thickness was only 38 μm, making it difficult to obtain a thick film, and the processing time was very long at 80 minutes. This is because due to the constant voltage control method, as the anodic oxide film is formed, it becomes an insulating film, the current decreases rapidly, and the film formation rate becomes slow.

[Example 2] Aluminum alloy casting (JIS ADC12, Si: 9,
6-12.0%, Fe: 1.3%, Cu: 1.5
~3゜5%, Mn: 0.5%, Mg 20,
3%, Zn: 10%, Sn: 0.3%, A2: residue) was degreased with a solvent, further washed with a weak alkaline agent, and then anodized under conditions similar to fire.

(11 sulfuric acid 4 degrees 200g/L, (2) temperature 20°C1 (
3) Current load conditions: constant current (t, 5A/dm x 5 minutes) constant voltage (38V x S minutes).

This situation is shown at 12 and V2 in FIG. As a result, a uniform anodic oxide film with a thickness of 4.5 μm could be obtained.

[Comparative Example 2-1] After cleaning the aluminum alloy casting of Example 2 in the same manner as in Example 2, proceeding of the conventional example.
Although oxidation treatment was carried out using the function control method using INTERFfNISH80, the melting voltage exceeded 50V and burning of the contact occurred.

[Comparative Example 2-2] After the aluminum alloy casting of Example 2 was cleaned in the same manner as in Example 2, oxidation treatment was performed using the constant voltage control method (2) of the conventional example, and the treatment time required 25 minutes.

〔Effect of the invention〕

The present invention has the following effects. In other words, computer system? f
In the case of anodizing treatment using f1l, the initial current is set to a small current when the target is small, and a large current when the target is large, and then the voltage is controlled by a complicated control system, so it is used as a general-purpose equipment. Although it is not suitable for use because it requires many control steps, the constant current and constant voltage method of the present invention is extremely economical in control method and is optimal for general-purpose equipment.

[Brief explanation of the drawing]

Figure 1 is a current density and voltage curve diagram based on this example, and
The figure shows a current density and voltage curve diagram of another example, Fig. 3 shows a current density and voltage curve diagram of a conventional example, Fig. 4 shows a current density and voltage curve diagram of another conventional example, and Fig. 5 shows a current density and voltage curve diagram of another conventional example. A circuit diagram of this embodiment is shown. 1+, Iz... Constant current density, V,, V2...
・Constant voltage

Claims (1)

[Claims] A method for anodizing an aluminum alloy, in which electrolysis is performed at a constant current density, and before the bath voltage reaches 50 V or more, the electrolysis is switched to a constant voltage of 50 V or less to perform the anodizing treatment.