JPS5812355B2 - Surface treatment method for anodic oxide film on aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention describes a method for surface treatment of an anodic oxide film of aluminum or aluminum alloy, and more specifically, a method for sufficiently impregnating metal sulfide into the micropores and walls of an alumite film by anodic oxidation. about how it can be done.

Since the so-called alumite film obtained by anodizing aluminum and aluminum alloys is hard and porous, the utility value of the alumite film can be increased by impregnating the inside and walls of the micropores of this alumite film with various substances. can be increased.

For example, a so-called two-liquid alternate dipping method is known in which an alumite film is alternately immersed in an aqueous solution of a metal salt and an aqueous solution of a sulfur-containing compound to impregnate the metal sulfide into the micropores and increase the lubricity of the alumite. ing.

However, in this conventional method, the metal sulfide could only be impregnated near the openings of the micropores, and sufficient lubricity could not be obtained.

Furthermore, implementing this method involves problems such as difficulty in managing the immersion liquid.

For this reason, the present inventors have developed a method for impregnating metal sulfides.
We previously proposed a method in which an anodized film is subjected to secondary electrolytic treatment in an electrolyte containing a metal thioate as a main component.

By performing secondary electrolysis in an electrolytic solution containing metal thioate as a main component, it is possible to impregnate the lubricating metal sulfide from the bottom of the micropores toward the openings, thus impregnating the secondary electrolyte with the metal sulfide. Compared to the alternate liquid dipping method, this method has the advantage that the fine pores can be more densely and sufficiently impregnated with metal sulfide.

However, on the other hand, in order to fully utilize such advantages, there is a problem in that the electrolytic treatment must take a long time or the electrolytic treatment must be performed at a high electrolytic current.

This invention was made in consideration of the above points, and it is possible to perform secondary electrolytic treatment on a porous anodic oxide film in an electrolytic solution containing a metal thioate as a main component, in a shorter time or in fewer cases. The present invention provides a method for surface treatment of an anodic oxide film of aluminum or aluminum alloy, in which fine pores can be sufficiently filled with metal sulfide even with electrolytic current.

That is, in this invention, a porous anodic oxide film is electrolytically treated (
A feature of this method is that the fine pores of the anodic oxide film are semi-sealed before performing secondary electrolysis.

Since the pores are semi-sealed in advance, the volume of micropores occupying the anodic oxide film can be reduced, and the above objective can be achieved.

Note that the object to be treated according to the present invention is a porous type (porous) anodic oxide film, and therefore, in anodizing treatment, it is necessary to set conditions that will generate a porous type film.

Next, in order to clarify the above characteristics, this invention will be explained in more detail.

[About anodizing treatment]

As the electrolytic bath for anodizing treatment, not only acidic baths but also alkaline baths, as long as a porous type film can be produced, can be used.
Alternatively, non-aqueous baths such as those based on formamide and boric acid may also be used.

Acidic electrolytic baths include sulfuric acid, oxalic acid, phosphoric acid, chromic acid,
An aqueous solution containing one or more of sulfosalicylic acid, pyrophosphoric acid, sulfamic acid, phosphomolybdic acid, boric acid, malonic acid, succinic acid, maleic acid, citric acid, tartaric acid, phthalic acid, itaconic acid, malic acid, glycolic acid, etc. be.

In such electrolytic baths that contain sulfur-containing compounds such as sulfuric acid, part of the alloy components of the aluminum alloy become metal sulfides during alumite formation.
Coupled with the subsequent secondary electrolytic treatment in an electrolytic solution mainly containing a metal thioate, the formation of metal sulfides can be further promoted.

In addition, the current waveform during electrolysis in an acidic bath can be DC, AC, AC/DC superimposed, AC/DC combination, incompletely rectified waveform, pulsed waveform,
A square wave, triangular wave, or periodic waveform is used.

Electrolysis methods include constant current, constant voltage, constant power methods, and high-speed alumite methods that apply continuous, intermittent, or current recovery methods.

Of course, appropriate conditions for such anodic oxidation treatment should be selected in consideration of the intended use of the object to be treated.

On the other hand, as the alkaline electrolytic bath, an aqueous solution containing one or more of caustic soda, caustic potash, sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, aqueous ammonia, etc. is used.

The current waveform and electrolysis method at that time may be the same as those for the acidic electrolytic bath described above.

Additionally, if thioate salts of metals such as thiomolybdic acid, thiotungstic acid, and thiostannic acid are added to this alkaline electrolytic bath, the metals in the thioate salts of these metals will form a part of the anodic oxide film during alumite formation. Since the metal sulfide is taken into the micropores as a metal sulfide, the metal sulfide can be generated in the film very efficiently.

[About semi-sealing treatment]

As mentioned above, this semi-sealing treatment reduces the volume of micropores occupied in the anodic oxide film, and the following (a)
) to (d) can be applied.

(a) A method in which the object to be treated is immersed in boiling demineralized water or heated demineralized water.

According to this method, the micropores of the anodic oxide film are filled with aluminum hydrate, and the volume of the micropores is reduced.

(b) Adding at least one of nickel acetate, dichromate or sodium silicate to the demineralized water of (a),
A method in which the object to be treated is immersed in it.

According to this method, the volume of the micropores in the anodic oxide film is reduced by the formation of aluminum hydrates and the deposition and adsorption of nickel hydroxide, dichromic acid, or silicate compounds. .

According to this method, the semi-sealing process is accelerated compared to the method (a), so there is an advantage that the semi-sealing process can be performed in a short time.

(c) A method of dissolving an organic dye in the demineralized water of (a) or (b) and immersing the object to be treated.

According to this method, the fine pores of the alumite film are
) or (b), the pores can be semi-sealed, and the anodic oxide film can also be dyed.

(d) A method in which the object to be treated is placed in an atmosphere of pressurized steam (for example, 1 to 6 kg/cil).

According to this method, the pores can be semi-sealed with aluminum hydrate as in (a), but with this method, the hydrate can be deposited or adsorbed almost uniformly from the bottom of the micropore to the entrance. There are advantages.

[About secondary electrolytic treatment in an aqueous solution mainly composed of metal thioate salts]

Secondary electrolysis is performed on the anodic oxide film that has been semi-sealed as described above in an aqueous solution containing metal thioates as a main component, but this secondary electrolysis may be performed immediately after the semi-sealing process. Alternatively, it may be performed after the following pretreatment.

For example, as one of the pre-treatments, the anodic oxide film can be coated with nitric acid,
Inorganic acids such as phosphoric acid, boric acid, sulfuric acid, hydrochloric acid, sulfamic acid, oxalic acid, formic acid, succinic acid, malonic acid, succinic acid, maleic acid, citric acid, tartaric acid, phthalic acid, itaconic acid,
There is a method of activating the product by immersing it in an aqueous solution containing one or more organic acids such as malic acid, glycolic acid, and sulfosalicylic acid, and their salts.

If such pretreatment is performed, more stable electrolysis can be performed during secondary electrolysis.

Other pretreatment methods include immersing the anodic oxide film in an alkaline aqueous solution such as caustic soda, caustic potash, sodium carbonate, sodium phosphate, or aqueous ammonia, or activating the anodized film by reverse electrolysis. There is also a method, which allows stable electrolysis during secondary electrolysis and impregnation of a larger amount of metal sulfide.

Furthermore, it is also effective as a pretreatment method to remove volatile components in the anodic oxide film by subjecting it to a reduced pressure or vacuum state.

Next, a secondary electrolytic treatment is performed in an electrolytic bath mainly composed of the metal thioate salt as described above, and the secondary electrolytic conditions are as follows.

First, regarding the bath composition, thiomolybdic acid, thiotungstic acid, thioantimonyate, thiostannic acid, thiocupric acid, thioarsenic acid, thiauric acid, thioplatinic acid, thioniobic acid, ammonium salt of thiovanadate acid, alkali metal salt, A solution containing at least one kind of alkaline earth metal salt is used.

Among these, when salts of thiomolybdic acid, thiotungstic acid, and thiostannic acid are used, the lubricity is significantly improved.

It is necessary to adjust the pH of these electrolytic baths between 4 and 12.

This pH adjustment is carried out by adding inorganic acids, organic acids, their salts, or alkaline substances, but the amount of these pH adjusters added is kept to a minimum.

Further, as for the water used for preparing the electrolytic bath, it is preferable to use demineralized water, and contamination of impurities, particularly strong electrolyte substances, into the electrolytic bath should be avoided.

Note that the electrolytic reaction rate can be accelerated by heating the electrolytic bath.

Furthermore, the current waveform during electrolysis must be positive even if the object to be treated is temporary or intermittent.

Therefore, when the polarity is divided as in the case of DC electrolysis, the object to be treated is connected to the positive terminal.

Of course, a conductive material is used for this counter electrode.

The reason why metal sulfides are produced by electrolysis in an electrolytic solution containing a metal thioate as a main component is considered to be as follows.

Metal thioate salts dissociate in aqueous solution to produce negatively charged thioate ions.

When the object to be treated becomes a positive electrode during electrolysis, the metal thioate ions penetrate into the micropores by electrophoresis.

On the other hand, at the bottom of the micropore, a barrier-forming Al anodic oxidation reaction and an electrode reaction of OH→1/202+H++2e occur, and H+ is released.

The released H+ makes the pH within the micropores acidic, and the metal thioate ions are decomposed to become metal sulfides, which are deposited within the micropores.

This metal sulfide deposition begins at the bottom of the pore, which is the source of H+ release, and progresses toward the opening of the pore.

In addition to the above reaction, it is also conceivable that metal thioate ions cause a direct electrolytic reaction to deposit metal sulfides within the micropores.

In addition, H2S, HS-, S2-,
S- reacts with the wall of the alumite film, the alloy components of the aluminum alloy present in the wall surface and micropores, and the metals and metal compounds contained during anodizing treatment, and metal sulfides are generated, forming an anode. It is fixed in the micropores and walls of the oxide film.

In addition, the anodic oxide film that has undergone the above secondary electrolytic treatment has the following properties:
If necessary, heat treatment is performed to modify the anodic oxide film and impregnated sulfide.

Heating is performed under conditions appropriate to the shape and purpose of the object to be processed, such as in the air, in an inert gas atmosphere, or in a vacuum.

Further, in order to make the surface of such a film uniform, it is also good to perform a friction treatment.

In addition, after completing this treatment, the anodic oxide film is
Furthermore, it goes without saying that appropriate treatments such as pore sealing and resin coating can be performed depending on the intended use of the object to be treated.

Examples will be described below in order to clarify the effects of the present invention.

Example 1 A 2SAl plate (10 x 10 x 0.1 cm) was used as a test piece, and after degreasing with a solvent, it was electrolyzed with direct current in a 15 wt% H2SO4 bath at 10°C for 40 minutes at a current density of 3 A/dm2.
Alumite film of μ was chemically formed.

After washing the test pieces with running water, they were immersed in boiling demineralized water for different immersion times for semi-sealing treatment.

After semi-sealing, it was immersed in 1.0% nitric acid at room temperature for 10 minutes for activation.

After washing with water, the test piece was placed in a 1% ammonium thiomolybdate aqueous solution using a stainless steel plate as an anode and a counter electrode, and was heated with a direct current for 30 minutes.
Electrolysis was carried out at a current density of 0 mA/dm until the electrolytic products overflowed from the micropores and began to adhere to the surface of the alumite film.

After electrolysis, it was washed with water and dried.

Color tone and coefficient of static friction of test pieces with different semi-sealing treatment times (
The mating material was copper, the contact area was 1 cm2, the load was 2 g, and the time required for secondary electrolysis (measured using the gradient method) and the time required for secondary electrolysis are shown in Table 1.

Incidentally, the coefficient of static friction of the test piece which had only been anodized was 0.63.

As can be understood from this result, the difference in static friction coefficient between the test pieces was small.

This is probably because molybdenum sulfide was electrodeposited on the alumite surface in the same way.

When the alumite surface layer is lost due to wear, etc., differences appear depending on the amount of molybdenum sulfide impregnated.

Example 2 Table 2 shows the test results of test pieces treated with 3 kg/cm2 pressurized steam for different treatment times.

Other processing conditions are the same as in Example-1.

Example 3 Table 3 shows the results when 2% nickel acetate was dissolved in boiling water in Example-1.

Example 4 Table 4 shows the results when 5% of Na2Cr and O7 were dissolved in boiling water in Example-1.

Example 5 Table 5 shows the results obtained in Example 1 when 1% of Sandoz's black dye MLW was dissolved and treated at 70 to 80° C. for a dyeing time of 30 mm.

Example 6 Table 6 shows the results of secondary electrolysis in a 5% ammonium thiotungstate aqueous solution at 50±1° C. in Example-1.

Other conditions are the same as in Example-1.

Example 7 Table 7 shows the results of secondary electrolysis in Example 1 in a 1% aqueous ammonium metathiostannate solution at room temperature.

Claims (1)

[Claims] 1. Aluminum or aluminum alloy characterized in that after anodizing aluminum or an aluminum alloy, the anodic oxide film is subjected to a semi-sealing treatment, and then subjected to a secondary electrolytic treatment in an electrolytic solution containing a metal thioate as a main component. Surface treatment method for anodic oxide film on aluminum alloy.