JP2944799B2 - Surface treatment method of aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of aluminum or an aluminum alloy, and more particularly, to a method for forming a coating layer of molybdenum sulfide on a surface including micropores of an anodic oxide film of aluminum or an aluminum alloy. The present invention relates to a method for surface treatment of an alloy.

[0002]

2. Description of the Related Art Anodized films formed by anodizing aluminum or aluminum alloys, so-called alumite films, have been widely used as wear-resistant materials for industrial machine parts. The cause of the abrasion resistance of the anodic oxide film is that the film itself is hard, but on the other hand, because of the hardness, the conformability at the time of sliding with the partner material is poor, and the anodic oxide film adheres to the partner material. And cause cohesive wear.

[0003] In view of the above, various attempts have been made to impregnate and coat the fine pores of the anodic oxide film with metal sulfide to improve the lubricating property and remove the defect of adhesive wear.

As a method of impregnating and coating such metal sulfide in the micropores of the anodic oxide film, an aluminum alloy is subjected to anodizing treatment, and then a two-part solution of an aqueous solution of a metal thioacid salt and an aqueous acid is used. Anodizing film of aluminum or aluminum alloy characterized by performing alternate immersion treatment, then performing secondary electrolysis in an electrolytic solution of a metal thioic acid salt, and impregnating the anodic oxide film with a metal sulfide. Has been proposed in Japanese Patent Publication No. 2-42916.

Japanese Patent Application Laid-Open No. Sho 56-130489 discloses a method for producing a metal sulfur compound in the fine pores of an anodized film by an electrochemical method.
No. is proposed. In this method, a metal thioate such as thiomolybdic acid, thiostannic acid,
At least one of an alkali metal salt such as thiocuprate or an alkaline earth metal salt is subjected to a secondary electrolytic treatment in an electrolytic solution to generate and fix a metal sulfur compound in the fine pores of the anodic oxide film.

Further, a first step of forming an anodized film by anodizing aluminum or an aluminum alloy, a second step of depositing a metal in fine pores of the anodized film, The electrolytic process in which the metal in the micropores of the anodic oxide film is reacted, and at least the main component is a sulfur compound of a metal, and the fourth process is a sealing process. A surface treatment method for aluminum or aluminum alloy is proposed in JP-A-60-116798.

Further, molybdenum trioxide is electrodeposited on a base material such as SUS 304, SUS 44 OC, etc., and a pressure of 0 to 28 kgf /
A method of forming a molybdenum disulfide film by reacting hydrogen sulfide and molybdenum trioxide at a temperature of 60 to 125 ° C. in cm ² is proposed in US Pat. No. 2,902,417.

[0008]

[Problems to be Solved by the Invention] Japanese Patent Publication 2-429
In the method of 16, the metal sulfur compound can only impregnate the vicinity of the opening of the micropores of the anodic oxide film, and cannot sufficiently impregnate the bottom of the micropores of the film, so that the lubricated surface is immediately destroyed, and There is a problem in the durability of the.

Although the lubricated surface obtained by the method of JP-A-56-130489 has improved lubricating properties and film durability when compared with the lubricated surface obtained by the method of JP-B-2-42916, Not enough. Although the reasons are not clear, (1) a sufficient amount of metal sulfur compound is not generated in the anodic oxide film, and (2) insufficient modification of the metal sulfur compound by heat treatment. Is assumed.

Furthermore, the thioate used in the method of Japanese Patent Application Laid-Open No. 56-130489 is not manufactured industrially, so that the cost of chemicals in processing is increased, and as a result, the cost of the product is increased. There is also the problem of economics.

In the method of JP-A-60-116798, the metals used are copper, silver, zinc, iron, nickel, lead, tin and indium, and the sulfur-containing compounds are ammonium sulfide, calcium sulfide, sodium sulfide and potassium sulfide. Thus, the obtained lubricated surface has a large coefficient of friction and poor durability, and thus cannot be said to be sufficient as a lubricating film.

A lubricated surface formed on an aluminum material by the method of US Pat. No. 2,902,417 is inferior in durability under high-speed and low-load conditions, and cannot be said to be a wear-resistant lubricating coating.

In view of the above-mentioned drawbacks of the prior art, it has been desired to provide a wear-resistant aluminum material having a low coefficient of friction and excellent durability under low-speed and high-load conditions and high-speed and low-load conditions, and a method of forming the same. ing.

[0014]

As a result of intensive studies by the present inventors, (1) anodizing aluminum or an aluminum alloy to form an anodized film on the surface, and (2) apply the anodized film to the aluminum or aluminum alloy. (3) forming a conductive metal coating layer on the surface including the fine pore wall surface of the anodic oxide film by immersing the film in an acidic or alkaline aqueous solution; The coating layer is subjected to an electrolytic treatment in a solution containing molybdenum trioxide to form a molybdenum trioxide electrodeposition coating layer on the surface including the microporous wall surface of the anodic oxide film, and (5) the electrodeposition coating layer A film obtained by reacting molybdenum trioxide with sulfur to form a coating layer of molybdenum sulfide on the surface including the micropores of the anodic oxide film forms an anodized film of aluminum or an aluminum alloy and molybdenum disulfide. The main component It consists of a Ribuden sulfide coating, even in low-speed and high-load and under high-speed, low-load under, has an excellent durability and low friction coefficient, and accomplished the present invention based on this finding.

[0015]

The anodic oxide film applied to the aluminum or aluminum alloy of the present invention is a porous film having fine pores. As long as an electrolytic bath for anodic oxidation treatment can produce a porous film, an acidic bath is used. In addition, an alkaline bath can be used.

As the acidic electrolytic bath, sulfuric acid, oxalic acid, phosphoric acid,
An aqueous solution in which at least one of chromic acid, sulfosalicylic acid, pyrophosphoric acid, sulfamic acid, phosphomolybdic acid, boric acid, malonic acid, succinic acid, maleic acid, citric acid, phthalic acid, malic acid, glycolic acid, etc. is dissolved is used Is done.

Further, as the current waveform at the time of electrolysis in the acid bath, DC, AC, AC / DC superposition, AC / DC combined use, pulse waveform, rectangular wave and the like are used. The electrolysis is performed by a constant current, a constant voltage, a constant power method, or the like.

As the alkaline electrolytic bath, caustic soda,
An aqueous solution in which at least one of caustic potash, sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, aqueous ammonia and the like is dissolved is used. The current waveform and the electrolysis method at this time are performed under the same conditions as in the above-described acidic electrolytic bath.

Prior to forming a conductive metal coating layer on the above-described anodic oxide film, micropores in the film are expanded. By expanding the micropores, the expansion is accompanied by the mechanical attachment of the molybdenum sulfide coating layer formed on the anodic oxide film in the final step, which strengthens the coating layer and serves as a reservoir for molybdenum sulfide. Works.

As a method for expanding the fine pores, inorganic acids such as nitric acid, phosphoric acid, boric acid, sulfuric acid, hydrochloric acid and sulfamic acid, oxalic acid, formic acid, acetic acid, malonic acid, succinic acid, maleic acid, citric acid, phthalic acid Acidic aqueous solution in which organic acids such as acid, malic acid, glycolic acid and sulfosalicylic acid are dissolved,
Alternatively, caustic soda, caustic potash, sodium carbonate, sodium phosphate, a method of immersing and holding in an alkaline aqueous solution such as aqueous ammonia at 5 to 30 ° C. for 20 to 40 minutes, or after immersing the article to be treated in the alkaline aqueous solution, A method of performing electrolysis as a cathode is adopted.

On the anodic oxide film formed on the surface of aluminum or aluminum alloy, a coating (plating) layer of a conductive metal is formed on the surface including the fine pore wall surface of the film.
The conductive metal coating layer is formed for the purpose of imparting conductivity to the anodic oxide film, and copper, silver, nickel or the like is used. However, the conductive metal is not particularly limited as long as it has conductivity.

As a method for forming the conductive metal coating layer on the anodic oxide film, a known plating technique is used.

The conductive metal coating layer is electrolytically treated in an aqueous solution containing molybdenum trioxide (MoO ₃ ). This aqueous solution containing molybdenum trioxide is used in an amount of 54 to 400 g of an organic acid salt such as ammonium formate, ammonium acetate, ammonium oxalate or ammonium citrate, and 12 to 12 g of molybdenum trioxide per 1000 to 2000 ml of ammonium molybdate or distilled water.
A solution of 26 g is used.

An aluminum or aluminum alloy having a conductive metal coating layer formed in the solution is used as an anode,
Current density 1.8-2.0mA / cm using aluminum plate as cathode
^2. By performing the electrodeposition treatment at a temperature of 50 to 65 ° C., an electrodeposition coating layer of molybdenum trioxide is formed on the surface of the anodic oxide film including the micropores.

The molybdenum trioxide of the electrodeposition coating layer is chemically reacted with sulfur to produce molybdenum sulfide. That is, the reaction between molybdenum trioxide and sulfur mainly occurs as shown in the following reaction formula.

2MoO ₃ + S = 2MoO ₂ + SO ₂ MoO ₂ + 3S = MoS ₂ + SO _{2 By} this reaction, molybdenum trioxide electrodeposition coating layer portion,
That is, a molybdenum sulfide coating layer is formed on the surface of the anodic oxide film including the micropores. The formed molybdenum sulfide coating layer is composed of molybdenum sulfide mainly containing molybdenum disulfide (for example, containing 70% or more, preferably 85% or more molybdenum disulfide) by X-ray diffraction.

Then, the chemical reaction between molybdenum trioxide and sulfur is performed by heating the electrodeposition coating layer of molybdenum trioxide at 350 to 440 ° C.
Immersion in molten sulfur for 90-150 minutes at a temperature of
Alternatively, the heating and pressurizing treatment is performed in a hydrogen sulfide (H ₂ S) gas furnace.

The thickness of the anodic oxide film of the obtained wear-resistant aluminum material of the present invention is 10 to 100 μm, and the thickness of the molybdenum sulfide coating film mainly composed of molybdenum disulfide is 1 to 15 μm. .

The durability and sliding characteristics of the wear-resistant aluminum material of the present invention are as follows. In a test in dry air, the friction coefficient shows a low value of 0.11 or less, showing stable sliding, and a humidity of 60%. Coefficient of friction even at room temperature
It is stable at 0.12 or less, and the molybdenum sulfide coating layer has excellent durability in any of the tests, and exhibits excellent sliding characteristics in combination with the wear resistance of the anodic oxide film.

For example, in dry air, the low-speed high-load (0.2 m / s, 3MP) of the wear-resistant aluminum material of the present invention is used.
a) Under the conditions, the number of repetitive friction until the life is 4.5 × 10
^The coefficient of friction is 0.1 or less at ⁴ times or more, high speed and low load
Under the conditions of (0.7 m / s, 0.51 MPa), the number of repetitive frictions up to the life is 13 × 10 ⁴ or more and the friction coefficient is 0.11 or less.

Since the molybdenum sulfide coating layer obtained by the method of the present invention is firmly coated on the surface including the micropores of the anodic oxide film, the durability of the coating layer is improved, and Exhibits the wear resistance of the components. Furthermore, the mechanical adhesion of the molybdenum sulfide coating layer is added to strengthen the coating, and the molybdenum sulfide acts as a reservoir, thereby further improving the durability and abrasion resistance of the coating layer.

[0032]

The present invention will be described below in detail with reference to examples.

Example 1 An aluminum plate having a symbol of A1050P specified by JIS-H-4000 was used, and a rectangular aluminum plate having a side of 31 mm and a thickness of 5 mm was used as a test piece.

The test piece was washed with distilled water, ultrasonically washed in acetone for 5 minutes, and dried.

Next, the test piece was immersed in an aqueous solution of sulfuric acid having a concentration of 1.5 M and a temperature of 7 ° C., kept at a current density of 2 A / dm ² for 1 hour, and anodized. An anodized film was formed on the surface of the test piece by anodizing treatment. The thickness of the anodic oxide film was 45 μm.

The test piece on which the anodic oxide film was formed was immersed in a 3M aqueous ammonia solution (temperature: 25 ° C.) for 30 minutes, and the pores of the anodic oxide film were subjected to a pore expansion treatment.

The test piece subjected to the hole-expanding treatment was treated with copper sulfate (Cu
_{SO 4 · 5H 2 O) 180g} / l, sulfuric acid (H ₂ SO ₄₎ 45
current density 31.5 mA / dm in a bath adjusted to a concentration of g / l
^Under the conditions of ² , plating was performed with stirring for 30 minutes to form a copper coating (plating) layer on the surface including the fine pore wall surface of the anodic oxide film.

Next, an aqueous solution in which 54.6 g of ammonium formate and 12.6 g of molybdenum trioxide were dissolved in 1000 ml of distilled water was prepared, and the test piece having the copper coating layer formed thereon was immersed in this aqueous solution. Was electrodeposited at a current density of 1.8 mA / cm ² with the aluminum plate on the anode side and the aluminum plate on the cathode side. By this electrodeposition treatment, an electrodeposition coating layer of molybdenum trioxide covering the surface including the microporous wall surface of the anodic oxide film of the test piece was formed.

The test piece on which the electrodeposition coating layer of molybdenum trioxide was formed was immersed in molten sulfur at 430 ° C. for 2 hours to cause a chemical reaction between molybdenum trioxide and sulfur.

As a result of this chemical reaction, a molybdenum sulfide coating layer (film thickness: 5 μm) was formed on the surface including the micropores in the anodized film of the test piece.

According to X-ray diffraction, the obtained molybdenum sulfide was almost molybdenum disulfide (MoS ₂ ).

Example 2 A test piece similar to the test piece used in Example 1 was prepared, and the test piece was washed with distilled water, further ultrasonically washed in acetone for 5 minutes, and dried. Next, anodizing treatment was performed under the same conditions as in Example 1 to form an anodized film having a thickness of 45 μm on the test piece.

The test piece on which the anodic oxide film was formed was immersed in a 1M phosphoric acid aqueous solution for 30 minutes, and the fine pores of the anodic oxide film were subjected to a pore expansion treatment.

The test piece subjected to the hole expansion treatment was treated in the same manner as in Example 1. The anodic oxide film of the test piece had a molybdenum sulfide coating layer (film thickness: 5 μm) on the surface including the micropores.
) Generated. According to X-ray diffraction, the obtained molybdenum sulfide was almost molybdenum disulfide (MoS ₂ ).

Test Example The test pieces obtained in Examples 1 and 2 were subjected to a friction test under the following test conditions to test the sliding characteristics.

<Test conditions> Friction speed 0.7m / s (652rpm) Load 0.51MPa Counterpart material Carbon steel for machine structure (S45C) Test Thrust test Lubrication No lubrication Atmosphere Dry air The results are shown in FIG. 1 (the number of repeated frictions per hour: 39,120).

In the drawing, the symbol は indicates the first embodiment, ● indicates the second embodiment,
Δ indicates the test result of the coating formed using ammonium thiomolybdate.

As is apparent from the test results, the molybdenum sulfide coating layers of Examples 1 and 2 exhibited stable performance with a low coefficient of friction throughout the test time.

After the test, it was confirmed that a film of molybdenum sulfide was formed on the sliding surface of the mating material.

On the other hand, the coating layer of molybdenum disulfide according to the prior art showed a sudden increase in the coefficient of friction immediately after the start of the test (500 revolutions), so the test was stopped.

[0051]

Since the molybdenum sulfide coating layer of the present invention is firmly adhered to the coating, the durability of the coating is enhanced, and the abrasion resistance of the anodic oxide coating can be fully exhibited. it can.

[Brief description of the drawings]

FIG. 1 is a graph showing test results of the present invention and a conventional product.

────────────────────────────────────────────────── (5) Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C25D 9/06 C25D 9/06 (56) References JP-A-4-362195 (JP, A) JP-A-60-169610 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C25D 11/20 303

Claims (6)

(57) [Claims] 1. An anodizing treatment on aluminum or an aluminum alloy to form an anodized film on the surface thereof. 2. An anodized film is immersed in an acidic or alkaline aqueous solution to form fine pores on the film. (3) forming a coating layer of a conductive metal on the surface including the fine pore wall surfaces of the anodic oxide film subjected to the pore-forming treatment, (4) conducting the conductive film in an aqueous solution containing molybdenum trioxide. Subjecting the conductive metal coating layer to electrolytic treatment to form an electrodeposition coating layer of molybdenum trioxide on the surface of the anodic oxide film including the fine pore wall surface, and (5) molybdenum trioxide and sulfur in the electrodeposition coating layer. To form a coating layer of molybdenum sulfide on the surface of the anodic oxide film including the fine pores. 2. The surface treatment method for aluminum or aluminum alloy according to claim 1, wherein the conductive metal coating layer formed on the surface including the fine pore wall surface of the anodic oxide film is selected from copper, silver, nickel and the like. 3. The aluminum or aluminum alloy according to claim 1, wherein the reaction between molybdenum trioxide and sulfur in the electrodeposition coating layer is performed by immersing and holding the molybdenum trioxide electrodeposition coating layer in molten sulfur. Surface treatment method. 4. The method according to claim 1, wherein the reaction between molybdenum trioxide and sulfur in the electrodeposition coating layer is performed in a hydrogen sulfide furnace. 5. The surface treatment method for aluminum or aluminum alloy according to claim 1, wherein the molybdenum sulfide coating layer formed on the surface of the anodic oxide film containing the micropores contains molybdenum disulfide as a main component. 6. An anodized film on the surface of aluminum or an aluminum alloy and a molybdenum sulfide coating layer containing molybdenum disulfide as a main component formed on the anodized film, and formed by the method of claim 1. Abrasion resistant aluminum material.