JPS5825759B2 - Youkisakusankanokanokounouritsukahouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly efficient method for anodizing aluminum or aluminum alloys.

To comment, aluminum or aluminum alloy (hereinafter, both will be collectively abbreviated as l?).

), using an electrolytic solution with a large ability to dissolve oxide films, such as sulfuric acid, and an amplitude of 0.1 to 200 mTIL1 frequency of 1 to 1 with respect to the anode at room temperature or in a heated state.
This invention relates to a method for anodizing AA, which comprises performing electrolytic treatment while applying vibrations of 20 Hz and generating turbulent flow of electrolyte on the anode surface.

Conventionally, anodic oxidation has been carried out for the purpose of imparting corrosion resistance, abrasion resistance, adhesion and coloring properties to Al, and coatings that meet each purpose have been formed.

However, the conventional method has major technical drawbacks, such as requiring a long time for processing and limiting the amount of film that can be formed.

Now, the rate of formation of an anodic oxide film is the difference between the rate of chemical formation of the film and the rate of dissolution into the electrolytic solution, and it is known that the rate of chemical formation and dissolution rate increase if the current density and processing temperature are increased. There is.

Therefore, if the current density is increased in the anodic oxidation of Al, the rate of film formation will be increased and a dense film will be obtained.

However, on the other hand, the local temperature of the electrolyte on the Al surface tends to increase, which inevitably increases the dissolution rate of the film, and as a result, there is a limit to the production rate and amount. There is.

A7 anodic oxidation is usually 0.5 to 2 A/d at room temperature.
The current density of i is used and the treatment is carried out for several minutes, and the
A certain amount of coating can be formed depending on the purpose of use.

In addition, if a particularly hard coating is required, 5°C to -1
The following conditions are adopted: 0°C, 1-2 A7'd trt'.

However, the method of cooling the electrolyte in order to increase the film production efficiency is economically constrained by requiring a large amount of equipment and running costs, and is never satisfactory in terms of increasing the film formation rate and amount. There was no way it could be done.

The present inventors conducted basic experiments in order to eliminate the drawbacks seen in the above-mentioned conventional methods, and learned that it is necessary to quickly remove a large amount of heat generated on the surface of AA during anodization.

As a result of further experiments and research, we found that when anodic oxidizing Al, we used an electrolytic solution with a high ability to dissolve the oxide film, and when heated from room temperature to about 60°C, the amplitude was 0.1~0. 2-00 myrt, frequency 1-1
It has been confirmed through a number of experiments that it is extremely effective to perform electrolytic treatment while applying vibrations of 20H2 to generate a turbulent flow of electrolyte on the anode surface.

The present invention has been completed based on the above experimental results. If the present invention is applied to anodic oxidation of Al, it will be possible to operate at high current density and perform anodic oxidation at high speed and with high efficiency. .

Furthermore, the amount of film formed can be significantly improved, and furthermore, low voltage processing is possible by operating at high temperatures up to about 60° C., which also has the effect of reducing power consumption.

We therefore believe that the present invention provides an innovative method for this type of work.

To further explain the present invention in detail, the metal surface treatment similar to the anodizing of the present invention employs air stirring of the electrolyte, solution circulation, ultrasonic stirring, or shaking of the object to be treated in the plating process. It is carried out at high current density.

However, in anodic oxidation of Al, the film formation mechanism is completely different from that in the case of plating, so when forming a uniform film on an item with a complicated shape, a method of gently stirring with air or rocking is used. However, stirring for the purpose of high speed and high efficiency was not considered at all.

If the same stirring method used for plating is adopted for anodizing AAI', the heat generated on the surface will be diffused faster,
It is true that the rate of film formation can be increased slightly.

However, depending on the conventional stirring method, even if anodic oxidation is performed at high temperature or high current density, heat transfer near the surface of Al, which directly controls the formation of the film, that is, A1
Because the electrolyte on the surface cannot be diffused effectively enough,
I couldn't expect a dramatic effect.

However, as in the present invention, the average moving speed of A7 and the electrolyte is twice the product of amplitude and frequency.

) is 2.0 mml sec or more, preferably 100 mm
By applying vibrations of 1 sec or more, a turbulent flow of electrolyte is formed on the Al surface, and the heat generated during anodic oxidation can be quickly diffused. This means that anodic oxidation can be performed with high efficiency by substantially preventing a temperature rise in the temperature.

Moreover, the above average moving speed of 20 mml sec or more can be easily achieved by a known pie break, and there is no problem in implementing the present invention.

Next, in the present invention, the amplitude and frequency given to the anode will be described.
It is preferable that the vibration frequency is 120 Hz, and twice the product thereof is 100 or more.

In the present invention, the reason why the numerical values are limited in this way is that it has been experimentally found that if the amplitude is less than 0.1, it will appear to be in a stationary state and the above-mentioned turbulent flow effect cannot be achieved. On the other hand, if the length is 200 mm or more, it becomes difficult to carry out the process due to large ripples and splashes in the bath, and it also becomes difficult to fix the object to be treated on a jig.

Regarding the frequency, at IH2 or below, a large amplitude is required to obtain the minimum average moving speed that causes turbulence on the surface of Al, and as a result, the ripples in the electrolytic bath, and the
This is because it was recognized that there is a drawback that the racking is difficult and the energy loss is large. On the other hand, if the frequency is set to 120 Hz or higher, the average moving speed will be increased, resulting in a large energy loss and it is not effective.

Next, the effect of the high-speed vibration of the present invention in anodic oxidation varies depending on the type of electrolyte used, current density, temperature, etc., but normally the electrolyte changes from laminar flow to turbulent flow on the surface of AA from about 20 mml s6c. , the effect of stirring becomes significant.

The present inventors have already found that when the movement of the solution on the Al surface is laminar, the amount of heat transferred by electrolysis is proportional to the flow velocity Q to the 5th power, and when this is turbulent, , it has been confirmed through experiments that it is proportional to the 0.7th power.

It is no exaggeration to say that the high-speed oscillation of the present invention is so effective in removing heat generated by electrolysis that it would be impossible to imagine that it would result from simply increasing the average movement speed of AA and electrolyte. do not have.

Therefore, the conditions for high-speed stirring of the present invention are a vibration frequency of 1 to 120.
H2% amplitude is in the range between 0.1 and 200, and twice the product of vibration frequency and amplitude (average moving speed) is 201, preferably 1
00 mml s&C and required a turbulent flow of the electrolytic solution on the A1 surface.

In addition, the effect of such high-speed stirring is due to the fact that Al as an electrolyte
For example, electrolytic solutions having the types and concentrations listed in the table below are suitable because they have a high ability to dissolve the oxide film formed thereon.

(Note) The alkaline baths mentioned are baths of sodium carbonate, sodium phosphate, sodium metaborate, etc.

These electrolytic solutions have the ability to reach the barrier layer through the chemically formed film and have a strong film forming ability, but at the same time, they are susceptible to reverse reactions due to the heat generated during electrolysis, that is, the formation of the chemically formed film. The degree of increase in dissolution rate is also variable.

Therefore, in these solutions, the film formation efficiency is greatly improved by removing heat through high-speed stirring, and these solutions are suitable for forming thick films with high efficiency.

As an example, using 15% sulfuric acid as the electrolyte, the electrolyte was heated for 30 min without stirring.
When anodic oxidizing Al at ℃, the maximum coating amount is 0.5 g/dm at an optimum current density of 6 A/dm2, but a similar process is performed at a vibration width of 1.2 mm and a vibration frequency of 60 Hz. The coating amount increases to a maximum of 3 g/drI7'' at the optimum current density of 20 A/dm''.

That is, by employing anode vibration, it is possible to form a film six times as large, and the processing speed can be tripled or more.

Next, the production efficiency of the anodic oxide film (ratio between the film actually produced and the theoretical amount of film produced calculated from the amount of electricity required for anodic oxidation).

) will be explained.

The generation efficiency varies depending on the current density and decreases as the current application time increases, but under the above bath conditions, without stirring, the generation efficiency is at its highest when it is about 6 A/d-.
In the vibration treatment, generation is performed efficiently at 50 A/dr 11'' or higher.

Furthermore, when anodic oxidation was performed in the 15% sulfuric acid bath described above at 30°C without stirring, the amount of current applied was 10.60.100A.
It was found that when increasing the value of mm/dm, the production efficiency sequentially decreases to 80%, 70%, and 50%, and when it increases beyond that, it decreases rapidly.

On the other hand, if the anode oscillation is carried out under the same bath conditions with a width of 25 m4 and a frequency of 10 Hz and anodization is performed under the conditions of IOA/di, and the amount of electricity is increased to 50.400.600°900 Aim/di, the production efficiency is 90. %, 80%, 75%
, 50%.

That is, according to the latter method, it is actually possible to form an anodic oxide film ten times more than the former method.

Furthermore, if the surface of AA is oxidized at a constant current density, the generation efficiency and the degree of decrease in efficiency depending on the amount of current will vary depending on the vibration conditions (width and frequency) of the anode.

Therefore, when performing anodic oxidation, consideration should be given to ensuring that the above conditions are appropriate.

It is assumed that the present invention has been understood through the above explanation, but
EXAMPLES Hereinafter, the present invention will be further specifically explained with reference to Examples.

Example 1 15% by weight sulfuric acid was used as an electrolytic solution, and a clean sample was placed in a jig directly connected to the vibrator of a vibration motor.
s Fixed aluminum plate, amplitude 1 interval, frequency 10Hz
Anodizing treatment was performed at 30° C. while vibrating the specimen.

At a current density of 15 A/dm, a maximum coating was obtained in 30 minutes with a value of approximately 60 μ.

For comparison, the same treatment as above was carried out while the vibration of the sample was stopped and the electrolytic solution was stirred with air, and a maximum coating film of 50 μm was obtained at IOA/dm” in 60 minutes.

Example 2 As in Example 1, 15% by weight sulfuric acid was used as the electrolyte, and a clean 2s aluminum plate was fixed as a test piece to a jig directly connected to the vibrator of the vibration motor, and the vibration width was 57n1.
1L1 Vibrating at a frequency of 10Hz at 30℃, 10A/
When constant current electrolysis was carried out using di, a good hard, colorless oxide film with a thickness of 120 μm was formed on the specimen after 60 minutes.

For comparison, when the vibration was stopped and anodization was performed on the same specimen as above under the same conditions without stirring, 1
After 0 minutes, formation of an 8 μm anodic oxide film was observed, but the film thickness was observed to decrease thereafter.

Example 3 Using the same electrolyte and equipment as described in Example 1,
30 minutes while vibrating the anode at a frequency of 60 Hz and a width of 50 minutes.
When electrolytic treatment was performed on a 28 aluminum specimen at 50 A/dm at 50° C., a good oxide film with a thickness of 250 μm was formed after 25 minutes.

For comparison, when electrolysis was performed on the same specimen under the same conditions with air agitation instead of the anode vibration, the amount of film formed remained at a maximum of 23μ.

Example 4 Electrolysis was carried out using 4% by weight oxalic acid as an electrolyte, using the same apparatus as described in Example 1, amplitude 1001n11L1 frequency 5Hz1 temperature 50°C for 2s at an anode current density of 50A/dm using aluminum as an anode. When the treatment was carried out, a good oxide film with a thickness of 50 μm was formed after 6 minutes.

For comparison, electrolysis was performed on the same specimen under the same conditions while air agitation was used instead of anode vibration, and it was found that the amount of film formed was only 20 μm thick.

Example 5 Using 8% by weight chromic acid as an electrolyte, using the same apparatus as in Example 1, amplitude Q, 5 mal, frequency 100 H;
When electrolytic treatment was carried out at an IA temperature of 40° C. and an anode current density of 40 A/dmj using 2s aluminum as an anode, a good oxide film with a thickness of 50 μm was formed after 10 minutes.

For comparison, when electrolysis was performed on the same specimen under the same conditions as above, using air agitation instead of anode vibration, the amount of film formed was only 20 μm thick.

From Examples 1 to 5 above, it is clear that the anode vibration of the present invention is effective for forming a thick oxide film on Al at high speed and with high efficiency.

Claims (1)

[Claims] 1. When anodizing aluminum or aluminum alloy, use an electrolytic solution that has a high ability to dissolve the oxide film that is formed, and apply an oscillation wave of 0.1 to 200 mm and a frequency of 1 to 120 Hz to the anode at room temperature or in a heated state. A method for increasing the efficiency of anodic oxidation, which is characterized by performing electrolytic treatment while applying vibration to generate a turbulent flow of electrolyte on the anode surface.