Process for lubrication-treating aluminum or aluminum alloy material

Abstract

A lubrication-treating process for an Al or Al alloy material is carried out by cleaning the material; applying an anodic oxidation to the cleaned material surface to form a 3 to 30 &mgr;m thick anode oxidation coating; and forming a lubrication coating including a polyester resin (30 to 70 mass parts), a particulate PTFE (30 to 70 mass parts) and ceramic (alumina) particles (0.5 to 5 mass parts), and 2 to 20 &mgr;m thick, to thereby impart excellent resistances to adhesion and seizure, and a low friction, to the Al or Al alloy material at a low cost and with no or a very low pollution of the environment.

Description

BACKGROUND OF INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates to a process for lubrication-treating an aluminum or aluminum alloy material. More particularly, the present invention relates to a process for lubrication-treating aluminum or an aluminum alloy material such as, for example, an aluminum or aluminum alloy sliding material to form a wear-resistant composite coating on the surface of the material. The process of the present invention is applied to productions of high wear-resistant sliding materials, for example, pistons and scrolls for compressors of air conditioners.

[0003] (2) Description of the Related Art

[0004] Generally, sliding materials are required to have a low friction property to prevent an energy transfer loss. Also, when a load is applied to the sliding material, an important property of the sliding material is high load-resistance to prevent a seizure of the sliding material under a high face pressure. Also, from an industrial viewpoint, it is strongly required that the above-mentioned properties of the sliding materials can be maintained for a long time that the sliding material have a high durability (a high wear resistance), and that they can be produced at low cost. As a method of forming sliding coatings for the sliding materials made of aluminum or an aluminum alloy, a hard anodic oxidation treatment method is a well-known practice. The resultant coatings of the anodic oxidation treatment, per se, do not cause the friction coefficients of the sliding material surfaces to decrease. However, the anodic oxidation coatings cause the resultant sliding material surface to exhibit an enhanced wear resistance and have a large number of pores which causes the sliding material surface to exhibit an enhanced oil-holding property and thus an improved surface lubrication property.

[0005] The seizure phenomenon is caused by contacting the same type of metals with each other. To prevent the seizure, various methods in which the surfaces contacting each other are plated with metallic materials different from each other have been carried out as well-known practices. For example, Japanese Examined Patent Publications No. 56-18080 and No. 59-9160 disclose plating of the sliding material surfaces with tin, iron and nickel materials. In tin-plating, the plated tin per se serves as a solid lubrication material and can reduce the friction coefficient of the sliding material surface. However, a plated tin layer is soft and thus exhibits a poor durability (a poor wear resistance). Also, in general, there are problems that materials having a complicated form and surface are difficult to uniformly plate and the plating cost is generally high.

[0006] As an industrially low cost surface-treatment, a chemical conversion treatment is known. As a chemical conversion treatment, for the aluminum or aluminum alloy material, for a sliding material with a lubrication coating, Japanese Unexamined Patent Publication No. 11-193,478 discloses a method in which the aluminum or aluminum alloy material is immersed in a treatment liquid containing a fluorine compound and ammonium silicofluoride and treated at a temperature in the range of from 70 to 100° C. The Japanese Publication reports that, as a result of the treatment, a coating layer comprising an AlOH—F compound and/or a NH4MgAlF6 compound is formed. However, in fact, the resultant coating layer, per se, does not cause the friction coefficient of the treated material surface to decrease. Also, this treatment is disadvantageous in that since the treatment liquid contains a large amount of a fluorine compound, a load for purifying the waste water from the treatment is high and thus a problem of the preservation of the global environment occurs.

[0007] As a method of overcoating a lubricating agent on an anodic oxidation layer, for example, Japanese Examined Patent Publication No. 52-39,059 discloses a method in which an anodic oxidation coating is formed on an aluminum or aluminum alloy material, and then the resultant material is immersed in a solution of polytetrafluoroethylene (PTFE) to impregnate the aluminum or aluminum alloy material with the PTFE solution,. Also, Japanese Unexamined Patent Publication No. 5-51,794 discloses a method in which fine particles of polytetrafluoroethylene are electrochemically or chemically absorbed on a surface of a hard anodic oxidation coating formed on an aluminum or aluminum alloy sliding material, the absorbed particle layer is dried, and the dried particle layer surface is rubbed with a counterpart material of the sliding material, to form a lubrication coated layer. In each of the above-mentioned methods, PTFE is contained and held in fine pores formed in the anodic oxidation coating layer. In these methods, however, the close adhesive property of PTFE to the anodic oxidation coating layer formed on the aluminum or an aluminum material is low, and thus the PTFE layers formed by the above-mentioned methods are unsatisfactorily close-bonded to the anodic oxidation layer on the aluminum or aluminum alloy material. The overcoated PTFE layer contributes to decreasing the friction coefficient of the anodic oxidation layer. However, the PTFE layer per se is soft and easily worn and thus a problem that the PTFE layer is unsatisfactory in durability occurs.

[0008] For the purpose of decreasing the friction coefficient of the sliding material, usually, a lubricating paint is used. In practice, the lubricating paint contains a polyamideimide resin, as a base material, and a solid lubricating agent such as molybdenum disulfide, graphite and/or polytetrafluoroethylene (PTFE), as a pigment. In this lubricating paint, the polyamideimide resin serves as a binder and, thus, the lubrication paint is closely adhered to the anodic oxidation layer on the aluminum or aluminum alloy material. In this treatment, usually, a diluted lubrication paint with an organic solvent is sprayed onto the anodic oxidation layer on the aluminum or aluminum alloy material and then stored. This method causes a problem that a harmful vapor of the organic solvent is diffused into the air atmosphere. To solve the problem for the purpose of keeping the global environment clean, a development of a new lubricating means using no organic solvent is strongly desired.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a process for lubrication-treating an aluminum or aluminum alloy material to form a coating having an excellent wear resistance, a decreased friction coefficient and a superior sliding property, on a surface of the aluminum or aluminum alloy material, with a low cost and with a low load on prevention of environmental pollution.

[0010] The above-mentioned object can be attained by the process of the present invention.

[0011] The process of the present invention for lubrication-treating an aluminum or aluminum alloy material, comprises:

[0012] cleaning a surface of an aluminum or aluminum alloy material;

[0013] applying an anodic oxidation treatment to the cleaned surface of the aluminum or aluminum alloy material, to form an anodic oxidation coating layer having a thickness of 3 to 30 &mgr;m on the wear-resistant material surface; and

[0014] forming a lubrication coating layer comprising a polyester resin, a particulate polytetrafluoroethylene and ceramic particles and having a thickness of 2 to 20 &mgr;m on the anodic oxidation coating layer.

[0015] In the lubrication-treating process, of the present invention, for an aluminum or aluminum alloy material, the anodic oxidation treatment is preferably carried out in a sulfuric acid bath or an oxalic acid bath, at a treatment temperature of 0 to 30° C. at an current density of 0.5 to 4 A/dm2.

[0016] In the lubrication-treating process of the present invention for an aluminum or aluminum alloy material, the lubrication coating layer is preferably formed by coating a coating liquid comprising a polyester resin, a polytetrafluoroethylene and ceramic particles on the anodic oxidation coating layer, and then baking the coated coating liquid layer at a temperature of 100 to 250° C. for 1 to 20 minutes.

[0017] In the lubrication-treating process of the present invention for an aluminum or aluminum alloy material, the polyester resin (A), the particulate polytetrafluoroethylene (B) and the ceramic particles (C) in the lubrication coating layer are preferably present in the mass contents in the ranges of (A): 30 to 70 parts, (B): 30 to 70 parts and (C): 0.5 to 5 parts, per 100 parts of the total (A)+(B)+(C).

[0018] In the lubrication-treating process of the present invention for an aluminum or aluminum alloy material, the ceramic particles are preferably alumina particle having an average particle size of 0.01 to 0.2 &mgr;m.

[0019] In the lubrication-treating process of the present invention for an aluminum or aluminum alloy material, the aluminum or aluminum alloy material is preferably a sliding material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The metallic materials to which the process of the present invention is applied are aluminum and aluminum alloy materials.

[0021] In the process of the present invention, first, a surface of the aluminum or aluminum alloy material is cleaned. The purpose of cleaning is to eliminate oiling materials (for example, cutting oils) applied to the material surface during the production of the aluminum or aluminum alloy material and soil on the material surface. There is no limitation to the types of the cleaning procedures. In view point of keeping the global environment clean, organic solvent-containing cleaning materials are not desirable for the process of the present invention. Preferably, an aqueous alkali-containing cleaning agents are used. The surface-cleaned aluminum or aluminum alloy material is subjected to an anodic oxidation step in accordance with the process of the present invention.

[0022] In the process of the present invention, the thickness of the anodic oxidation coating is controlled to 3 to 30 &mgr;m, preferably 10 to 20 &mgr;m. The anodic oxidation coating serves to hold a lubrication coating thereon and to enhance the wear resistance and the resistance to seizure of the resultant lubrication-treated aluminum or aluminum alloy material. When the aluminum or aluminum alloy material is subjected to a sliding operation, a considerable pressure may be locally applied to the sliding material. The anodic oxidation coating which is a pressure-resistant layer prevents direct contact of the aluminum or aluminum alloy sliding material with a metallic material on which the sliding material slides and a seizure of the sliding material. If the thickness of the anodic oxidation coating is less than 3 &mgr;m, the resultant lubrication treated material exhibits an insufficient wear resistance. Also, if the thickness of the anodic oxidation coating is more than 30 &mgr;m, while the performance of the resultant material is saturated, the treatment cost is too high, and thus an economical disadvantage occurs.

[0023] In the formation of the anodic oxidation coating in the process of the present invention, a conventional sulfuric acid anodic oxidation bath or oxalic acid bath may be used. When the sulfuric acid bath is employed, preferably, the anodic oxidation procedure is carried out at a sulfuric acid concentration of 10 to 20% by mass, at a treatment temperature of 10 to 20° C. at a current density of 0.5 to 1.5 A/dm2. When the oxalic acid bath is employed, the anodic oxidation procedure is preferably carried out at an oxalic acid concentration of 2 to 5% by mass at a treatment temperature of 25 to 30° C. at a current density of 2 to 3A/cm2.

[0024] In the process of the present invention, the lubrication coating is formed on the front surface side of the aluminum or aluminum alloy material. A main purpose of the lubricating coating is to decrease friction between the aluminum or aluminum alloy material and a metallic material on which the aluminum or aluminum alloy material slides during a sliding operation. In the process of the present invention, the thickness of the lubrication coating is controlled in the range of from 2 to 20 &mgr;m, preferably from 6 to 14 &mgr;m: If the thickness of the lubrication coating is less than 2 &mgr;m, the resultant layer exhibits an insufficient friction-reducing effect and thus an unsatisfactory sliding property. If the thickness of the lubrication coating is more than 20 &mgr;m the friction-reducing effect is saturated and the coating cost becomes high, and thus an economical disadvantage occurs.

[0025] The material for forming the lubrication coating comprises, as essential components, a polyester resin, a polytetrafluoroethylene and ceramic particles, the polyester resin serves as a binder to hold and bind the another components and to form a firm coating. For the purpose of imparting a high mechanical strength to the lubrication coating during the sliding operation, the lubrication coating preferably contains a polyester resin having a high mechanical strength. Also, when the sliding material is subjected to a sliding operation, the lubrication coating is brought into contact with a lubrication oil. In the case where the sliding material is used in a compressor for an air conditioner, the sliding circumstances contains a cooling medium (fluorocarbon compounds, flon), in addition to the lubrication oil. Therefore, the lubrication coating must be stable in the medium. As a result of research on binder resins having a high resistance to the lubrication oils and the fluorocarbon compounds, it was confirmed that the polyester resins are most suitable for this use. The particulate polytetrafluoroethylene is contained as a friction-reducing agent in the lubrication coating.

[0026] The particulate polytetrafluroethylene preferably has an average particle size of 0.05 to 30 &mgr;m, more preferably, of 0.5 to 5 &mgr;m.

[0027] Further, the ceramic particles are used to enhance the resistance to seizure of the lubrication coating. When a seizure occurs on the lubrication treated aluminum or aluminum alloy sliding material produced by the process of the present invention, the lubrication coating is destroyed and then the anodic oxidation coating is destroyed by a metallic material on which the sliding material slides, to such an extent that the aluminum or aluminum alloy material comes into dry contact with the metallic material. Thus, the total resistance of the aluminum or aluminum alloy sliding material to the seizure can be enhanced by enhancing the seizure resistance of the lubrication coating and thus the total durability of the lubrication-treated aluminum or aluminum alloy sliding material can be improved.

[0028] In a preferable method of forming the lubrication coating in accordance with the process of the present invention, from the view point of keeping the global environment clean, the lubrication coating is formed from an aqueous lubrication agent. Particularly, after an anodic oxidation coating is formed, an aqueous treatment liquid containing a polyester resin, polytetrafluoroethylene particles and ceramic particles dispersed in an aqueous medium is coated on the anodic oxidation coating and then, the resultant aqueous treatment liquid layer is baked at a temperature of 100 to 250° C., more preferably 160 to 200° C. for a time of 1 to 20 minutes, more preferably 5 to 15 minutes.

[0029] The thickness of the lubrication coating can be controlled by controlling the coating amount of the aqueous treatment liquid. If the baking temperature is lower than 100° C., an undesirable long time may be necessary to complete the baking procedure. Also, if the baking temperature is higher than 250° C., the polyester resin may be undesirably deteriorated. If the baking time is less than one minute, the baking procedure may not be sufficiently completed. If the baking time is more than 20 minutes, the baking effect may be saturated and the productivity of the target product may be reduced. To enhance the drying effect in the lubrication coating-forming procedure, a pre-heat treatment of the anodic oxidation-treated sliding material to a temperature of 80 to 12° C. may be effectual.

[0030] The proportions of the contents of the components contained in the lubrication coating to each other can be controlled by controlling the concentrations of the components contained in the aqueous-treatment liquid. In the process of the present invention, the polyester resin (A) the particulate polytetrafluoroethylene (B) and the ceramic particles (C) are preferably present in the mass contents in the ranges of (A): 30 to 70 parts, preferably 40 to 60 parts, (B): 30 to 70 parts, preferably 40 to 60 parts and (C): 0.5 to 5 parts, preferably 1 to 3 parts, per 100 parts of the total (sum) of (A), (B) and (C).

[0031] If the content of the polyester resin (A) is less than 30 parts by mass on the basis of (A)+(B)+(C)=100 parts by mass, the binding effect of the polyester resin (A) in the lubrication coating may be insufficient and, thus, a firm lubrication coating may not be formed. Also, if the content of the polyester resin (A) is more than 70 parts per 100 parts of the total (A)+(B)+(C), the content of the particulate polytetrafluoroethylene (B) becomes too low, and thus the resultant coating may exhibit an insufficient lubrication effect.

[0032] If the content of the particulate polytetrafluoroethylene is less than 30 parts per 100 parts of the total (A)+(B)+(C), the resultant coating may exhibit an insufficient lubrication effect. Also, if the content of the particulate polytetrafluoroethylene is more than 70 parts per 100 parts of the total (A)+(B)+(C), the resultant lubrication coating contains polyester resin in an insufficient content, and thus the binding effect of the polyester resin may become insufficient, and the resultant lubrication coating may exhibit an insufficient mechanical strength. Further, if the content of the ceramic particle is less than 0.5 parts per 100 parts of the total (A)+(B)+(C), the resistance to seizure of the resultant lubrication coating may be insufficient, and if the content of the ceramic particles is more than 5 parts, the resultant lubrication coating may have an insufficient continuity, and thus may exhibit an insufficient mechanical strength.

[0033] The ceramic particles usable for the process of the present invention are preferably selected from alumina particles having an average particle size of 0.01 to 0.2 &mgr;m, more preferably 0.05 to 0.01 &mgr;m. If the particle size is less than 0.01 &mgr;m, the particles are too fine and the resultant lubrication coating may exhibit an insufficient seizure resistance. Also, if the particle size is more than 0.2 &mgr;m, the resultant particles may easily agglomerate with each other and, as a result, the resultant lubrication coating may have an insufficient continuity and undesirable local adhesions of the lubrication coating may occur.

[0034] The ceramic particles usable for the present invention may be selected from silicon dioxide, zirconium oxide and/or titanium dioxide. These ceramic particles may be used in mixture with alumina particles.

EXAMPLES

[0035] The present invention will be further illustrated by the following examples. Also, comparative examples will be shown for the purpose of illustrating the advantages and effects of the present invention in comparison with the comparative examples.

[0036] The aluminum or aluminum alloy materials, treatment procedures for the materials, the measurements of the thickness of coatings and evaluation of the resultant products of the examples and comparative examples were as shown below.

[0037] (1) Starting Material

[0038] Type of material: ADC10

[0039] Form and dimensions: plate (40 mm×40 mm×1.5 mm (thickness))

[0040] (2) Treatment Procedure

[0041] The aluminum alloy material is immersed in a 2% aqueous solution of a cleaning agent (trademark: FINE CLEANER 315, made by NIHON PARKERIZING K.K.) at a temperature of 60° C. for 3 minutes; withdrawn from the cleaning solution; and rinsed with water, to make the material clean. The cleaned aluminum alloy material was subjected to an anodic oxidation treatment under the conditions shown in each of the examples and comparative examples; the anodic oxidation-treated aluminum alloy material is rinsed with tap water for 30 seconds and dried at a temperature of 100° C. for 5 minutes. The surface of the resultant anodic oxidation coating layer was coated with the aqueous lubrication liquid having the composition shown in each of the examples and comparative examples, by a spray coating procedure using an air spray gun, and the coated lubrication liquid layer was dried and baked under the conditions shown in each of the examples and comparative examples.

[0042] (3) Measurement of Thickness of Coatings

[0043] The thickness of each coating formed on the aluminum alloy material was measured in &mgr;m.

[0044] (4) Evaluation

[0045] (a) Adhesion test

[0046] For the adhesion test, a lubrication tester (trademark: TRYVOGUIER HEIDON-14DR, made by SHINTOKAGAKU K.K.) was employed.

[0047] A specimen of a lubrication-treated aluminum alloy material was brought into contact with a non-lubrication treated speed ball (SUJ2, diameter: 5 mm); and the specimen and the ball were rubbed with each other under a load of 10N at a rubbing speed of 0.1 m/sec at a rubbing amplitude of 10 mm. The rubbing procedure was carried out in two different ways, in one of which two ways, the rubbing faces of the specimen and the ball were coated with a lubrication oil (trademark: ND Oil 8, made by K.K. DENSO), and in the other one of which, no lubrication oil was applied. The total rubbing distance at which the specimen was adhered to the ball and the friction coefficient between the specimen and the ball were determined and evaluated. The longer the determined total rubbing distance, the higher the lubrication property. In the case of no lubrication oil, when the total rubbing distance was 20 m or more, or in the case using the lubrication oil, when the total rubbing distance was 400 m or more, the specimen was evaluated as satisfactory (good) in the lubrication property. Also, the friction coefficient must be as low as possible. Usually, the friction coefficient of the specimen is evaluated as satisfactory (good).

[0048] (b) Seizure Test

[0049] For seizure test, a friction and wear tester (model: EFM-III-E, made by TOYO BALDWIN) was employed.

[0050] A treated specimen to be tested was brought into contact with a non-treated aluminum collar (ADC10, an inside diameter: 23 mm, an outside diameter: 25 mm), the sliding faces of the specimen and collar were coated with a lubrication oil; and then the specimen and collar were rubbed against each other under a load of 50N at a rubbing speed of 2 m/second. The load was increased by 50N each 2 minutes after, and the load under which a seizure of the specimen with the collar occurred was determined. The higher the seizure-generating load, the higher the seizure resistance of the specimen.

[0051] When the seizure-generating load was 800N or more, the specimen was evaluated as satisfactory (good) in the seizure resistance.

Example 1

[0052] The aluminum alloy material for a sliding material as mentioned above was subjected to the following procedures under the conditions shown below.

[0053] Anodic Oxidation Coating-Forming Conditions 1 Treatment bath: Sulfuric acid 18% by mass Treatment temperature: 15° C. Current density: 1 A/dm2 Treatment time: 60 minutes Thickness of coating: 20 &mgr;m

[0054] Lubrication Coating-Forming Conditions

[0055] Composition 2 Polyester resin:  50% by mass Particulate PTFE:  48% by mass Ceramic particles:  2% by mass (Alumina particles having an average particle size of 0.1 &mgr;m) Baking temperature: 180° C. Baking time:  10 minutes Thickness of coating:  10 &mgr;m

[0056] The test results are shown in Table 1.

Example 2

[0057] The aluminum alloy material for a sliding material was subjected to the following procedures under the conditions shown below.

[0058] Anodic Oxidation Coating-Forming Conditions 3 Treatment bath: Sulfuric acid 18% by mass Treatment temperature: 15° C. Current density: 1 A/dm2 Treatment time: 75 minutes Thickness of coating: 25 &mgr;m

[0059] Lubrication Coating-Forming Conditions

[0060] Composition 4 Polyester resin: 30% by mass Particulate PTFE: 66% by mass Ceramic particles:  4% by mass (Alumina particles having an average particle size of 0.04 &mgr;m) Baking temperature: 220° C. Baking time: 5 minutes Thickness of coating: 6 &mgr;m

[0061] The test results are shown in Table 1.

Example 3

[0062] The aluminum alloy material for a sliding material was subjected to the following procedures under the conditions shown below.

[0063] Anodic Oxidation Coating-Forming Conditions 5 Treatment bath: Oxalic acid 4% by mass Treatment temperature: 28° C. Current density: 2.5 A/dm2 Treatment time: 40 minutes Thickness of coating: 5 &mgr;m

[0064] Lubrication Coating-Forming Conditions

[0065] Composition 6 Polyester resin: 68% by mass Particulate PTFE: 30% by mass Ceramic particles:  2% by mass (Alumina particles having an average particle size of 0.05 &mgr;m) Baking temperature: 240° C. Baking time: 3 minutes Thickness of coating: 20 &mgr;m

[0066] The test results are shown in Table 1.

Example 4

[0067] The aluminum alloy material for a sliding material was subjected to the following procedures under the conditions shown below.

[0068] Anodic Oxidation Coating-Forming Conditions 7 Treatment bath: Oxalic acid 4% by mass Treatment temperature: 28° C. Current density: 2.5 A/dm2 Treatment time: 80 minutes Thickness of coating: 10 &mgr;m

[0069] Lubrication Coating-Forming Conditions

[0070] Composition 8 Polyester resin: 35% by mass Particulate PTFE: 63% by mass Ceramic particles:  2% by mass (Alumina particles having an average particle size of 0.05 &mgr;m) Baking temperature: 150° C. Baking time: 15 minutes Thickness of coating: 15 &mgr;m

[0071] The test results are shown in Table 1.

Example 5

[0072] The aluminum alloy material for a sliding material was subjected to the following procedures under the conditions shown below.

[0073] Anodic Oxidation Coating-Forming Conditions 9 Treatment bath: Sulfuric acid 18% by mass Treatment temperature: 15° C. Current density: 1 A/dm2 Treatment time: 60 minutes Thickness of coating: 20 &mgr;m

[0074] Lubrication Coating-Forming Conditions

[0075] Composition 10 Polyester resin: 40% by mass Particulate PTFE: 59% by mass Ceramic particles:  1% by mass (Alumina particles having an average particle size of 0.15 &mgr;m) Baking temperature: 200° C. Baking time: 5 minutes Thickness of coating: 10 &mgr;m

[0076] The test results are shown in Table 1.

Comparative Example 1

[0077] The aluminum alloy material for a sliding material 5 was subjected to only the cleaning procedure. No anodic oxidation treatment and no lubrication treatment was applied to the cleaned material.

Comparative Example 2

[0078] The aluminum alloy material for a sliding material was subjected to an anodic oxidation treatment under the following conditions, and no lubrication coating-forming treatment was applied.

[0079] Anodic Oxidation Coating-Forming Conditions 11 Treatment bath: Sulfuric acid 18% by mass Treatment temperature: 15° C. Current density: 1 A/dm2 Treatment time: 30 minutes Thickness of coating: 20 &mgr;m

[0080] Lubrication Coating-Forming Treatment

[0081] This treatment was not applied.

Comparative Example 3

[0082] An aluminum alloy material for a sliding material was directly subjected to a lubrication treatment under the conditions shown below. No anode oxidation treatment was applied to the material.

[0083] Anodic Oxidation Treatment

[0084] This treatment was omitted.

[0085] Lubrication Coating-Forming Conditions

[0086] Composition 12 Polyester resin: 50% by mass Particulate PTFE: 48% by mass Ceramic particles:  2% by mass (Alumina particles having an average particle size of 0.05 &mgr;m) Baking temperature: 180° C. Baking time: 5 minutes Thickness of coating: 10 &mgr;m

[0087] The test results are shown in Table 1.

Comparative Example 4

[0088] The aluminum alloy material for a sliding material was subjected to a tin-plating procedure under the following conditions.

[0089] Tin-Plating Conditions 13 Treatment bath: Alkali-substituted tin-plating bath Treatment temperature: 60° C. Treatment time: 4 minutes Thickness of coating: 1 &mgr;m

[0090] The test results are shown in Table 1. 14 TABLE 1 Item Seizure test Lubrication Adhesion test Lubrication oil oil used Not used Used Seizure- Total rubbing Friction Total rubbing Friction occurring Example No. distance (m) coefficient distance (m) coefficient load (N) Example 1 50 0.11 >400 0.12 950 2 25 0.11 >400 0.12 950 3 100  0.11 >400 0.12 950 4 75 0.11 >400 0.12 950 5 50 0.11 >400 0.12 950 Com- 1 *1 — 70 0.15 450 parative 2 *1 — >400 0.15 750 Example 3 20 0.11 >400 0.13 500 4 10 0.16 >400 0.14 500 Note: *1 . . . Adhesion occurred immediately after the start of rubbing procedure.

[0091] In view of Table 1, it is clearly confirmed that in Examples 1 to 5, in accordance with the treatment process of the present invention, the resultant lubrication-treated aluminum alloy material having excellent resistances to adhesion and seizure was produced by simple and easy procedures. However, the product of Comparative Example 1, in which only a cleaning procedure was applied, exhibited extremely bad properties. The product of Comparative Example 2 having no lubrication coating exhibited a very poor resistance to adhesion. The product of Comparative Example 3 having no anodic oxidation coating also exhibited a poor resistance to seizure. The tin-plated product of Comparative Example 4 was unsatisfactory in the adhesion resistance and the friction coefficient.

[0092] The process of the present invention enables a composite coating, comprising an anodic oxidation coating and a lubrication coating and having excellent resistances to adhesion and seizure, to be formed on an aluminum or aluminium alloy material for sliding materials by a simple and easy procedures within a short time and at a low cost. Also, the process of the present invention subjects the global environment to a very low load.

Claims

1. A process for lubrication-treating an aluminum or aluminum alloy material, comprising:

cleaning a surface of the aluminum or aluminum alloy material;

applying an anodic oxidation treatment to the cleaned surface of the aluminum or aluminum alloy material, to form an anodic oxidation coating layer having a thickness of 3 to 30 &mgr;m on the wear-resistant material surface; and

forming a lubrication coating layer comprising a polyester resin, a particulate polytetrafluoroethylene and ceramic particles and having a thickness of 2 to 20 &mgr;m on the anodic oxidation coating layer.

2. The lubrication-treating process for an aluminum or aluminum alloy material as claimed in claim 1, wherein the anodic oxidation treatment is carried out in a sulfuric acid bath or an oxalic acid bath, at a treatment temperature of 0 to 30° C. at an current density of 0.5 to 4 A/dm2.

3. The lubrication-treating process for an aluminum or aluminum alloy material as claimed in claim 1, wherein the lubrication coating layer is formed by coating a coating liquid comprising a polyester resin, a particulate polytetrafluoroethylene and ceramic particles on the anodic oxidation coating layer, and then baking the coated coating liquid layer at a temperature of 100 to 250° C. for 1 to 20 minutes.

4. The lubrication-treating process for an aluminum or aluminum alloy material as claimed in claim 1, wherein the polyester resin (A), the particulate polytetrafluoroethylene (B) and the ceramic particles (C) in the lubrication coating layer are present in the mass contents in the ranges of (A): 30 to 70 parts, (B): 30 to 70 parts and (C): 0.5 to 5 parts, per 100 parts of the total (A)+(B)+(C).

5. The lubrication-treating process for an aluminum or aluminum alloy material as claimed in claim 1, wherein the ceramic particles are alumina particle having an average particle size of 0.01 to 0.2 &mgr;m.

6. The lubrication-treating process for aluminum or an aluminum alloy material as claimed in claim 1, wherein the aluminum or aluminum alloy material is a sliding material.