JPS6119795A - Lubrication of high silicon aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain a high silicon aluminum alloy extremely excellent in lubricity, by increasing the average thickness of an anodic oxidized film and increasing the impregnation amount of the film with a fluorocarbon polymer. CONSTITUTION:The composition of an electrolytic bath is set so that sulfuric acid with specific gravity of 1.8 is 250-450g/l, oxalic acid is 3-5g/l and aluminum sulfate is 2-9g/l. A high silicon aluminum alloy is treated in this electrolytic bath under such a condition that electrolytic temp. is 7-12 deg.C, voltage is 10-75V and current density is 1.5-3.5A/dm<2> to form an anodic oxidized film. Next, impregnation treatment by a fluorocarbon polymer is performed to impregnate the porous oxidized film with the fluorocarbon polymer and heat treatment is subsequently applied to the impregnated film to generate film cracks to the surface of the impregnated oxidized film. Further, the impregnation treatment by the fluorocarbon polymer is performed to impregnate the impregnated oxidized film having film cracks with the fluorocarbon polymer.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a high-silicon aluminum alloy with a specific anodizing treatment and a specific impregnation treatment with a fluorohydrocarbon polymer, thereby improving the anodization of the conventional method. It forms a film that is thicker than the film and therefore retains a large amount of fluorinated hydrocarbon polymer, and also increases the amount of fluorinated hydrocarbon polymer impregnated in the impregnation process itself, thereby improving lubrication. To obtain a high-silicon aluminum alloy with excellent properties. This invention relates to a method for lubrication of high-silicon aluminum alloys.

[Prior art and its problems]

Conventionally, in order to improve the lubricity of aluminum and its alloys, aluminum or its alloys were anodized to form a porous but hard anodic oxide film.
Aluminum joints have been produced that are impregnated only once with a fluorocarbon polymer. The anodizing treatment conditions in this conventional method are as follows. That is, 6
6° Baume's sulfuric acid is 4-6% by volume, and oxalic acid is 0.0% by volume.
In an electrolytic bath consisting of an aqueous solution containing 5 to 3% tannic acid and 0.5 to 2.5% by volume of tannic acid, at a temperature within the range of -4 to 7 °C, a voltage within the range of 24 to 130 V, 28 ~
The test was carried out under conditions of a current density within the range of 6.7 A/dm2.

However, in the conventional method described above, when the aluminum alloy is a high-silicon aluminum alloy (silicon content = 5% by weight or more), even if the electrolysis time is 40 minutes, the formed positive
Since the average thickness of the polar oxide film was as thin as 5 to 10 μm, the amount of fluorocarbon polymer impregnated was small, and no significant improvement in lubricity could be expected.

In addition, the aluminum alloy is JIS ADC12 (12 types of aluminum alloy die casting; silicon content is 9.6 to 12
0% by weight), the above-mentioned 1'@gold has a high copper content of 15 to 3.5% by weight as an alloy component, so film burning may occur during the formation of the anodic oxide film. This occurs constantly, and due to the dense film and thin average film thickness (5 to 10 μ77L), the amount of fluorocarbon polymer impregnated into the anodic oxide film is small, making it a perfect aluminum bonded product. could not be manufactured.

[Purpose of the invention and findings]

The purpose of this invention is to increase the average thickness of the anodic oxide film and increase the amount of fluorocarbon polymer impregnated into the film, thereby obtaining a high-silicon aluminum alloy with improved lubricity. The goal is to establish a method that can do this.

As a result of intensive research, the present inventor 5 obtained the following knowledge.

a) By using an aqueous solution containing sulfuric acid, oxalic acid, and aluminum sulfate as the electrolytic bath, and making the sulfuric acid concentration much higher than that of the conventional method, and also making the electrolysis temperature higher than that of the conventional method, Despite the low current density, a large average film thickness (15~
30 μm) Able to form an anodic oxide film.

b) Even if the oxalic acid concentration in the electrolytic bath is lower than in the conventional method, by setting the electrolytic bath composition, electrolysis temperature, and current density as in a) above, the current density can be kept constant. Therefore, the film should not be burnt during the anodic oxide film formation.

C) By impregnating with the fluorinated hydrocarbon polymer not only once, but also again on films that have cracked due to heat treatment, the fluorinated hydrocarbon polymer penetrates not only into the pores of the film but also into the cracks in the film. Therefore, the amount of fluorocarbon polymer impregnated is 2. Od/d1rL2 to 2. s ml
That can be increased to t/dim. (Note that the impregnated amount of 2.0 m9/dm" means that the amount impregnated into voids such as pores in a 10 CrrL square film is 20 mg. The same applies hereinafter.) [Constitutional Requirements of the Invention] This invention This invention was invented based on the above findings, and the constituent elements of this invention will be described below.

(1) Anodizing treatment process (1) Electrolytic bath composition (+-a) Sulfuric acid When the sulfuric acid concentration is less than 250 g/l of sulfuric acid with a specific gravity of 1.8, the average film thickness increases (・It is not possible to form an anodic oxide film, and it is also impossible to prevent film burning.On the other hand, if the sulfuric acid concentration exceeds 450 g/7! as sulfuric acid with a specific gravity of 1.8, anodizing will occur. During film formation, a part of the film dissolves in the acid and the film becomes physically weak. Therefore, the sulfuric acid concentration is set to 2 with a specific gravity of 18.
It was set at 50-4509/l.

(+-b) Oxalic acid Oxalic acid is added to prevent film burning during the formation of the anodic oxide film. If the concentration is less than 3 j; / / 1,
On the other hand, if the concentration exceeds 5 g/l, the current density decreases and film formation becomes slow, so the concentration was set at 3 to 5 g/l.

(1-c) Aluminum Sulfate Aluminum sulfate is added to form a film with a large average thickness in a short time. If the concentration is less than 2.9/1, the desired effect can be achieved;
If the concentration exceeds this, the surface of the anodic oxide film becomes rough, so the concentration was set at 2 to 9 I/l. Preferably 3-5g
, /l.

During the anodizing process, the aluminum sulfate concentration gradually increases, so when it approaches the upper limit of this invention, the electrolytic bath is replaced, or a portion of the electrolytic bath is withdrawn and the aluminum sulfate concentration falls within the aluminum sulfate concentration range of this invention. It is necessary to adjust to a low concentration value.

(11) Electrolysis temperature If the electrolysis temperature is less than 7°C, it is not possible to form an anodic oxide film with a large average thickness in a short time, and it is also impossible to prevent film burn during the formation of the anodic oxide film. On the other hand, if the temperature exceeds 12°C, a part of the anodic oxide film will be dissolved in the acid during formation, and the film will become physically weak. Therefore, the electrolysis temperature was set at 7-12°C.

(iii) Voltage and Current Density When the voltage is less than IOV and the current density is less than 1.5 A/dm2, the anodic oxide film formation is slow; on the other hand, when the voltage is 75 V and the current density is 3.5 A/d m", it is impossible to prevent the film from being burnt during the formation of the anodic oxide film. Therefore, the voltage was set at 10 to 75 µ and the current density was set at 1.5 to 3.5 A/d m".

(1v) Time The time is preferably 10 to 15 minutes. If the time is shorter than 10 minutes, an anodic oxide film with a thick average thickness cannot be obtained;
This is because even if the time is longer than 15 minutes, the average film thickness will not increase any further, and on the contrary, the variation in film thickness will increase.

(v) High-silicon aluminum alloy (As mentioned in the conventional method, high-silicon aluminum alloy has a silicon content of 5% by weight or more, for example, J
IS ADCI 2. ADCIO, etc. can be mentioned.

(vl) Post-treatment The high-silicon aluminum alloy on which the anodic oxide film has been formed is pulled out of the electrolytic bath, the attached acid is washed with water, and then the adhering acid content is further neutralized and thoroughly washed with water to form a highly adsorbent porous oxide film. A high-silicon aluminum alloy is obtained.

(II) Impregnation treatment step with fluorinated hydrocarbon polymer This step consists of three steps: first impregnation treatment, heat treatment, and second impregnation treatment.

(1) The first impregnated fluorinated hydrocarbon polymer means fluorinated hydrocarbon homopolymers and copolymers, such as polytetrafluoroethylene, tetrafluoroethylene and tetrafluoropropylene. Examples include copolymers of. especially,
Polyfluorinated ethylene is preferred, for example polytetrafluoroethylene.

The fluorinated hydrocarbon polymer is used for impregnation in the form of an aqueous dispersion or the like. Its concentration can vary over a wide range. The impregnation is then preferably carried out in an aqueous dispersion at a temperature in the range from 20 to 40°C.

(11) Heat treatment After the first impregnation treatment, wash with hot water and then perform this heat treatment. This heat treatment is performed to generate film cracks on the surface of the impregnated oxide film by utilizing the difference in expansion coefficient between the high-silicon aluminum alloy base material and the oxide film (24.0xlO for the former and 5xlO for the latter), and the heat treatment temperature is is 12
0 to 250°C (particularly 150 to 200'C) is preferred. At temperatures lower than 120°C, film cracking is insufficient;
On the other hand, at temperatures higher than 250"C, the cracks in the film become too large and cannot be restored (or filled) even after cooling and the second impregnation treatment in the next step. This is because the material is also affected.

(ml) Second Impregnation Treatment As in the first round, the fluorinated hydrocarbon polymer is used for impregnation in the form of an aqueous dispersion or the like. Its concentration can likewise be varied over a wide range.

The impregnation is then preferably carried out in an aqueous dispersion at a temperature in the range 30-35°C.

Thereafter, it is dried at a uniform temperature of about 100°''C to obtain a high-silicon aluminum alloy treated product having high lubricity.

〔Example〕

Example: Electrolyzing an aqueous solution consisting of sulfuric acid, oxalic acid, aluminum sulfate, and water, with a sulfuric acid concentration of 400 g/l as sulfuric acid with a specific gravity of 1.8, an oxalic acid concentration of 5j; l/l, and an aluminum sulfate concentration of 5 g/l. As a bath, 1.1.1-
) JIS ADC1 degreased with lychloroethane
2 was anodized under the following conditions to obtain an average film thickness of 2.
A porous oxide film of 5 μm was formed. This film had no film burn.

Electrolysis temperature: 12°C Voltage: 45V Current density: 2.5A/dm2 Time: 15 minutes Next, after water washing, neutralization, and water washing, the first impregnation treatment with a fluorinated hydrocarbon polymer was performed under the following conditions. Ta.

Concentration of an aqueous fluorocarbon polymer dispersion.

50 g solid content/l Temperature of the aqueous dispersion 35° C. Impregnation treatment time 30 minutes As a result of this impregnation treatment, 2 m9/dm” of the fluorinated hydrocarbon polymer was impregnated.

After impregnating, it was washed with hot water at 80°C for 2.5 minutes, and then heat-treated in an electric furnace (integrated power value of heat source: 5 Q KW-hr) under the following conditions to generate film cracks on the surface of the impregnated oxide film. Ta.

Heat treatment temperature: 200° C. Heat treatment time: 30 minutes Finally, a second impregnation treatment with a fluorinated hydrocarbon polymer was performed under the following conditions.

- Concentration of aqueous fluorinated hydrocarbon polymer dispersion: 10011 solids/l Temperature of aqueous dispersion: 50°C Impregnation treatment time: 30 minutes This second impregnation treatment adds an additional 0.5 m9/dm”
of fluorocarbon polymer was impregnated. The lubricious aluminum alloy thus produced was washed with water and dried at 100° C. for 30 minutes using an electric furnace.

For this lubricating aluminum alloy (product of the present invention), the micro-Vickers hardness, wear amount, and corrosion resistance of the film were measured, and the results were reported together with the average thickness of the anodized film and the total amount of fluorohydrocarbon polymer impregnated. Shown in Table 1.

The amount of wear was measured by bringing the worn wheel C8-17 into contact with the lubricant aluminum alloy under a load of 1000 g using a Taber abrasion tester, and measuring the amount of wear of the lubricant aluminum alloy after 3000 rotations.

The corrosion resistance was measured using a CASS tester.
'S H8601-1968 test method (time is 16
(Time) and 1 judgment was made using the rating number table.

Comparative Example (Conventional Method) Using the following electrolytic bath composition, electrolysis temperature, voltage, current density, and time, JIS ADC12, which had been degreased with 1,1.1-)lichloroethane, was subjected to anodization treatment to form an average film. A porous oxide film with a thickness of 7 μm was formed.

Electrolytic bath composition Sulfuric acid concentration: 5% by volume of 66° Baume sulfuric acid Concentration of oxalic acid: 3% by volume Tannic acid concentration: 2% by volume Electrolysis Temperature: 2℃ Initial voltage: 20■, Final voltage: 45■ Initial current density: 1.6A/di" Final current density: 4A/dm" Time: 40 minutes, then water washing - neutralization - after water washing Impregnation treatment with a fluorinated hydrocarbon polymer was performed under the following conditions.

Concentration of fluorinated hydrocarbon polymer aqueous dispersion: 25g solid content/
l Temperature of the aqueous dispersion: 30°C Impregnation treatment time: 30 minutes Through this impregnation treatment, 1 ml/dm” of the fluorinated hydrocarbon polymer was impregnated. After the impregnation treatment, it was washed with water and
Dry at °C.

The conventional product thus obtained was measured for its micro-Vickers hardness, amount of wear, and corrosion resistance.
The results are shown in Table 1 along with the average thickness of the anodic oxide film and the amount of fluorocarbon polymer impregnated.

As can be seen from Table 1, the product of the present invention has a thicker average thickness of the anodic oxide film than the conventional product, and the amount of impregnation in the impregnation process itself is also large. The amount of fluorocarbon polymer impregnated into the coating is increased, resulting in a wear loss of approx.

It has been reduced to 20. In other words, it has extremely excellent lubricity.

[Overall effect of the invention]

The method of this invention allows an anodic oxide film with a thick average film thickness to be obtained without film burning in a short electrolysis time, and because of this and the increase in the amount of impregnation in the impregnation process itself, the fluoride film is This is a useful method that can increase the amount of hydrocarbon polymer impregnated and therefore yield a high-silicon aluminum alloy with extremely excellent lubricity.

Claims (1)

[Scope of Claims] An aqueous solution containing three types of acidic substances, sulfuric acid, oxalic acid, and aluminum sulfate, wherein the sulfuric acid concentration in the aqueous solution is 250 to 450 g/l as sulfuric acid with a specific gravity of 1.8, and the oxalic acid concentration is 3 to 450 g/l as sulfuric acid with a specific gravity of 1.8. 5g/l and aluminum sulfate concentration 2-9g
/l in an electrolytic bath consisting of an aqueous solution of 7 to 12
Electrolysis temperature within the range of °C, voltage within the range of 10-75V,
A high-silicon aluminum alloy is anodized under conditions of a current density within the range of 1.5 to 3.5 A/dm^2,
forming a porous oxide film on the high-silicon aluminum alloy, then impregnating it with a fluorinated hydrocarbon polymer;
The porous oxide film is impregnated with a fluorinated hydrocarbon polymer, then heat treated to generate film cracks on the surface of the impregnated oxide film, and further impregnated with the fluorinated hydrocarbon polymer again to form the above film. A method for lubricating a high-silicon aluminum alloy, which comprises impregnating a cracked impregnated oxide film with a fluorohydrocarbon polymer.