JPH09112521A - Aluminum part tightening bolt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the tightening toque/producing shaft power characteristic nearly equivalent to that of a glossy chromate treated bolt by sticking a solid lubricant on the surface of the green chromate bolt in which a green chromate treated film has been formed on the galvanized layer, so that the surface frictional coefficient of the threaded part can be reduced. SOLUTION: As a tightening bolt for aluminum parts such as the cylinder block of an automobile engine, a chromate bolt may be given, in which after a galvanized layer has been formed on the surface of the bolt material for preventing corrosion, chromium phosphate forming treatment (chromate treatment) for preventing the white corrosion of the galvanized layer has been performed. In this case, especially to increase corrosion resistance, the green chromate bolt having the thickness of approximately 1.0μm in the thickness of a chromate treatment film is used. Further, in this case, to obtain a sufficient shaft force when the tightening is carried out with a normal torque, a solid lubricant such as hexagonal boron nitride powder and molybdenum disulfide powder is stuck on the screw surface of the chromate bolt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt for tightening aluminum parts which is screwed into an aluminum part such as an aluminum cylinder block of an automobile engine for tightening. The aluminum parts described in this specification include both parts made of aluminum and parts made of aluminum alloy.

[0002]

2. Description of the Related Art In recent years, the use of aluminum for various parts is rapidly progressing. For example, cylinder blocks, which are one of engine parts for automobiles, have recently been made of aluminum. It is common to use bolts as a means for assembling engine parts, etc. to such an aluminum cylinder block, but in order to prevent the bolts themselves from corrosion, zinc is used on the surface of the bolt material (iron etc.) for rust prevention. After forming the plating layer, chromium phosphate conversion treatment (chromate treatment) to prevent white corrosion of the zinc plating layer
Then, a chromate bolt formed by forming a chromate treatment film on the galvanized layer is used.

Conventionally, a gloss (white) chromate treated bolt having a chromate treated film thickness of about 0.1 μm or less is usually used. FIG.
Shows the relationship between the tightening torque when the engine parts are tightened to the aluminum cylinder block using this glossy chromate treated bolt and the axial force (tightening force in the bolt axial direction) generated by the tightening. .

By the way, in recent years, when high quality is required, it is necessary to improve the corrosion resistance of the fastening bolts. For example, in automobiles and the like, in recent years, the required quality has greatly increased. Therefore, as a bolt used for tightening an engine part on an aluminum cylinder block, a bolt more than the gloss chromate treated bolt described above is used. In reality, there is a demand for materials that are highly resistant to corrosion and have excellent corrosion resistance. Therefore, based on the finding that increasing the thickness of the chromate-treated film improves the corrosion resistance, recently, green chromate-treated bolts having a chromate-treated film thickness of about 1.0 μm are used. It is designed to improve corrosiveness. The difference between the gloss (white) chromate bolt and the green chromate treated bolt is in the thickness of the chromate treated film as described above, and the name distinction is based on the difference in appearance (white or green).

[0005]

However, although the green chromate treated bolt is superior in corrosion resistance to the gloss chromate treated bolt as described above, it has the following peculiarity to aluminum parts. There is a problem. That is, there is a problem that the axial force generated when the green chromate treated bolt is screwed into the aluminum part and tightened is smaller than that in the case of the gloss chromate treated bolt. Specifically, since the surface friction coefficient of the green chromate-treated film formed on the threaded surface of the green chromate-treated bolt is larger than the surface friction coefficient of the glossy chromate-treated film, screw the green chromate-treated bolt into the aluminum part and tighten it. Even if the tightening work is performed with the same tightening torque as the gloss chromate treated bolt, the axial force generated is smaller than that of the gloss chromate treated bolt (see Table 1 below), so tighten with the specified torque. Even if it does, the actual situation is that a sufficient axial force cannot be obtained. Therefore, it may be necessary to change the tightening torque setting standard (tightening standard). In addition, Table 1 below
Use green chromate treated bolts and gloss chromate treated bolts (both are M10 bolts) for aluminum parts (material;
It shows the axial force when the engine parts are tightened to JIS AC4C). It is clear from Table 1 that the tightening force of the green chromate treated bolt is smaller than that of the gloss chromate treated bolt.

[0006]

[Table 1]

Further, when the green chromate treated bolt is used, if the tightening torque is increased until the axial force becomes sufficiently large,
In reality, such tightening cannot be performed because the green chromate treated bolt may be broken or the threaded portion may be broken. for that reason,
In some cases, the use of green chromate-treated bolts with excellent corrosion resistance was abandoned for aluminum parts, and bright chromate-treated bolts with poor corrosion resistance were sometimes used.

The present invention has been made to solve such problems, and an object thereof is to reduce the surface friction coefficient of the thread portion of a green chromate treated bolt having excellent corrosion resistance. In order to obtain almost the same tightening torque-generated axial force characteristics as the gloss chromate treated bolts, the green chromate treated bolts can be fastened to aluminum parts with sufficient axial force, and in turn to generate sufficient axial force. An object of the present invention is to provide a bolt for tightening an aluminum part, which can prevent a problem such as thread breakage or breakage even when a green chromate treated bolt is tightened with an excessive tightening torque.

[0009]

In order to achieve the above-mentioned object, in the present invention, a zinc plating layer is formed on the surface of a bolt material, and a green chromate treatment film is further formed on this zinc plating layer. The solid lubricant is applied to the surface of the threaded portion of the green chromate treated bolt made of the above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a preferred embodiment of the present invention,
Hexagonal boron nitride (h-BN) powder, molybdenum disulfide (MoS ₂ ) powder, graphite powder, or polytetrafluoroethylene (PTFE) powder is applied as a solid lubricant on the screw surface of the green chromate treated bolt. I try to attach it.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings.

Example 1 In this example, hexagonal boron nitride powder (hereinafter referred to as h-BN powder) was applied as a solid lubricant on the threaded surface of a green chromate treated bolt to make it adhere. , The tightening torque of the green chromate treated bolt-generated axial force characteristics are improved.

Specifically, h-BN powder (average particle size 10 μm) is dispersed in butanol, and a green chromate treated bolt (M10, length 25 mm,
It was applied on the surface of the threaded portion of a 7T flanged hexagon bolt with a pitch of 1.5 mm) and dried sufficiently. After that, the green chromate treated bolt was screwed into an M10 pitch 1.5 mm screw hole of an aluminum part (material: JIS AC4C) and tightened with a tightening torque of 50 N · m, and the generated axial force was measured. The measurement result as shown in 1 was obtained. The characteristics shown in FIG. 1 show the results of measuring the generated axial force by changing the application amount (that is, the attachment amount) of the h-BN powder. As is apparent from the measurement result of FIG. 1, the generated axial force is 20 KN which is the proper axial force range when the coating amount of h-BN powder is 0.2 mg, and h-
The coating amount of BN powder was 3.2 mg, which was 30 KN, which is the upper limit of the proper axial force range. And the coating amount is 30 mg
Shows a plastic deformation range of 35 KN.

The tightening torque-generated axial force characteristics were measured as follows. First, as shown in FIG. 2, a cylindrical concave portion 2 extending from a head portion 1a of a green chromate treated bolt (M10 bolt having a length of 25 mm and a pitch of 1.5 mm) 1 for a sample to be measured to an intermediate portion of a screw portion 1b.
Then, a cylindrical strain gauge 3 was fitted into and bonded to the bottom of the recess 2. In this way, the green chromate treated bolt 1 having the cylindrical strain gauge 3 built therein is screwed into the screw hole 5 of the aluminum component (for example, an aluminum cylinder block for an engine) 4 as shown in FIG. Tightening was done at 6. At this time, the tightening force of the digital torque wrench 6 is read, and at the same time, the bridge box 7 detects a change in the resistance value detected in accordance with the elongation or tensile deformation of the cylindrical strain gauge 3, and this detection signal Based on the above, the magnitude of the axial force is obtained from the strain amount measuring device 8. In each of the examples described below, the tightening torque-generated axial force characteristics were measured by the same measurement method.

From the results obtained in this example, the axial force of the green chromate treated bolt was controlled by setting the amount of h-BN powder applied to the above green chromate treated bolt within the range of 0.2 to 30 mg. It has been found that can be effectively improved. Further, the coating amount is 0.2 to
If it is limited to 3.2 mg, the tightening torque-generated axial force characteristic of the green chromate treated bolt of this example is almost the same as that of the gloss chromate treated bolt, and in addition to being excellent in corrosion resistance, the tightening torque-generated axial force characteristic is excellent. You can get a good bolt. Therefore, there is no problem in using this bolt for tightening aluminum parts, and there is no problem even if it is mixed with parts made of other materials.

In the above-mentioned embodiment, the case of M10 bolt was described, but it goes without saying that bolts of other dimensions can also obtain the same effect as described above.

FIG. 4 shows the results of measuring the relationship between the applied amount of h-BN powder per unit area and the generated axial force. From the measurement results of FIG. 4, the coating amount of the h-BN powder on the screw surface of the green chromate treated bolts of various sizes was 0.02 based on the area of the screw surface.
It was found that it is good to set the dose to 3 mg / cm ² .

Example 2 In Example 1 above, an example was shown in which the h-BN powder was dispersed in butanol and applied, but the same effect can be obtained by dispersing it in a solvent other than butanol. Is. The same applies not only to the application by brushing, but also to the use of a commercially available aerosol type h-BN powder spray.
Figure 5 shows h-BN when it is applied to the surface of the green chromate treated bolt with an aerosol type spray.
The results of measuring the relationship between the amount of BN powder applied and the generated axial force are shown. From the measurement results of FIG. 5, it was confirmed that the same effect as in the case of the first embodiment can be obtained in the case of the second embodiment of the present invention as described above.

Example 3 In this example, h-BN powder was mixed in an oil-based lubricant (lubricating oil, grease, etc.) and applied (attached) to the surface of the green chromate treated bolt. Even if an oil-based lubricant is applied to the thread surface of the green chromate treated bolt alone,
The tightening torque-generated axial force characteristics of green chromate treated bolts on aluminum parts are hardly improved (see FIG. 6). However, as shown in FIG.
The tightening torque-generated axial force characteristics were improved by containing and applying the powder. In addition, FIG. 6 shows the case where only the grease is applied to the thread portion of the green chromate treated bolt, the grease containing 6.25% of h-BN powder is applied to the thread portion of the green chromate treated bolt, and The results of measuring the relationship between the amount of grease adhered and the generated axial force when grease containing 25% of h-BN powder was applied to the surface of the thread portion of the green chromate treated bolt are shown.

As is clear from the characteristics shown in FIG. 6, h-B
The degree of improvement of the axial force due to the application of the grease containing N powder is determined depending on the absolute amount of h-BN powder in the grease, and in the case of a grease containing a small amount of h-BN powder. Must be applied in large quantities, h-BN
In the case of grease containing a large amount of powder, the axial force is improved with a small coating amount (see Fig. 7). FIG. 7 shows the results of measuring the relationship between the amount of h-BN powder contained in grease and the generated axial force. As is clear from FIG. 7, h-B
N powder amount is 3 mg, which is the lower limit of the proper axial force range, 20 KN
showed that.

The proper amount of grease or grease mixed with h-BN powder is 50 mg at maximum for M10 bolts (length 25 mm, pitch 1.5 mm), and even if a larger amount is applied, screw engagement will occur. Not efficiently supplied to the part. Therefore, in the grease containing 25% of h-BN powder, the maximum amount of h-BN powder applied is 12.5 mg. However, the application of a larger amount does not cause any harmful effect.

Example 4 In this example, molybdenum disulfide powder (hereinafter referred to as MoS ₂ powder) was used as a solid lubricant. That is, this example improves the axial force when the green chromate treated bolt is fastened to an aluminum component such as an aluminum cylinder block by applying and adhering MoS ₂ powder on the thread surface of the green chromate treated bolt. It is something that is done.

Specifically, a kneaded product obtained by adding 5 g of butanol to 10 g of MoS ₂ powder and thoroughly kneading the mixture was used for green chromate treatment with a brush or the like (M10, length 25 mm, pitch 1.5 mm, 7T flanged hexagon bolt) was applied on the surface of the threaded portion and dried sufficiently, and then tightened by screwing it into a M10 pitch 1.5 mm screw hole formed in an aluminum part (AC4C material).

At this time, the relationship between the tightening torque and the generated axial force was measured, and the relationship with the coating amount (adhesion amount) of MoS ₂ powder was investigated. FIG. 8 shows the results of measuring the relationship between the axial force generated when the tightening torque was 50 N · m and the coating amount of MoS ₂ powder. As is clear from the measurement results, MoS ₂ When 0.5 to 50 mg of powder was applied, the axial force generated when tightened with a tightening torque of 50 N · m was 18 to 24 KN, which was equivalent to that of the gloss chromate treated bolt. Therefore, the green chromate treated bolt formed by applying the MoS ₂ powder can be mixed with the gloss chromate treated bolt as a member for tightening aluminum parts. However, the reason why the upper limit of the amount of the MoS ₂ powder applied was set to 50 mg was determined in consideration of the fact that even if the MoS ₂ powder is applied more than this amount, it cannot be efficiently supplied to the screw meshing portion, and even if it is applied more than this, there is a harmful effect. It does not happen.

In this embodiment, the length is 25 mm.
However, the same effect can be given to the green chromated bolts having other dimensions. That is, in the case of bolts other than the M10 bolt having a length of 25 mm, the coating amount of the MoS ₂ powder may be 0.05 to 5 mg / cm ² . Further, in this embodiment, the MoS ₂ powder is applied by using a brush, but other than that, the same effect can be obtained by applying it by a spraying method such as a dipping method, an air spray or an airless spray. Is obtained, and there is no problem even if dilution suitable for those methods is performed. Further, the same applies when a commercially available azo-type MoS ₂ spray or the like is used.

Comparative Example 1 Regarding the effectiveness of improving the axial force when a grease generally used as a mineral lubricant is applied to a green chromate treated bolt, the results of the same examination as in Example 4 described above are shown below. It shows in Table 2.

[0027]

[Table 2]

As can be seen from Table 2 above, although the effect of applying grease is recognized, even if the actual upper limit of 50 mg is applied, the axial force generated in that case is 1
It was about 7 KN, which was not 18 to 24 KN equivalent to that of the gloss chromate treated bolt.

Example 5 In this example, graphite powder was used as the solid lubricant. That is, in this example, by applying graphite powder on the surface of the thread portion of the green chromate treated bolt, the axial force when tightening the green chromate treated bolt on an aluminum component such as an aluminum cylinder block was improved. It is a thing.

Specifically, 15 g of butanol was added to 10 g of graphite powder, and the mixture was sufficiently kneaded to obtain a green chromate treated bolt (M10, length 2) using a brush or the like.
5mm, pitch 1.5mm, hexagonal bolt with 7T flange) applied to the surface of the threaded portion, dried sufficiently, and then screwed into the M10 pitch 1.5mm screw hole formed in the aluminum part (AC4C material). Tightened.

At this time, the relationship between the tightening torque and the generated axial force was measured, and the relationship between the coating amount (adhesion amount) of the graphite powder and the generated axial force was investigated. FIG. 9 shows the results of measuring the relationship between the axial force generated when the tightening torque was 40 N · m and the coating amount of the graphite powder. As is clear from the measurement results, In the range of 0.1 mg or more, the generated axial force of the gloss chromate treated bolt shown in Table 1 (1
5.9 KN). Therefore, the green chromate treated bolt formed by applying graphite powder can be mixed with the bright chromate treated bolt as a member for fastening aluminum parts. However, in the M10 bolt, the region in which the axial force exceeds 35 KN is also a region accompanied by large plastic deformation at the same time, so it cannot be said to be appropriate in using the bolt. Therefore, the amount of graphite powder applied is appropriately in the range of 0.1 to 5.0 mg.

In this embodiment, the length is 25 mm.
However, the same effect can be given to the green chromated bolts having other dimensions. That is, in the case of bolts other than M10 bolts having a length of 25 mm, the application amount of graphite powder may be 0.01 to 0.5 mg / cm ² . Further, in this embodiment, the MoS ₂ powder is applied by using a brush, but other than that, the same effect can be obtained by applying it by a spraying method such as a dipping method, an air spray or an airless spray. Is obtained, and there is no problem even if dilution suitable for those methods is performed. further,
The same applies when a commercially available azo-type graphite spray or the like is used.

Example 6 In this example, a kneading lubricant prepared by mixing graphite powder in a mineral oil type lubricant such as grease was applied on the screw surface of the green chromate treated bolt to improve the axial force. This is what was planned. With respect to the bolts thus obtained, the graphite mixing ratio, the lubricant coating amount, and the relationship between the graphite content and the generated axial force were measured, and the results shown in Table 3 below were obtained. FIG. 10 is a graph showing the generated axial force when a grease containing 6.25% of graphite powder is applied to a green chromate treated bolt (M10 bolt) based on the measurement result.

[0034]

[Table 3]

As is clear from Table 3 and FIG. 10 above,
It can be seen that the effect obtained by applying the mineral oil-based lubricant mixed with graphite powder depends on the graphite content.
The coating amount was 1.6 mg or more in the case of grease containing 6.25% graphite powder, and the maximum amount was 50 mg. The value of this maximum amount takes into consideration that the lubricant is not effectively supplied to the screw meshing portion even if it is applied further, and the maximum graphite application amount changes depending on the graphite content in the lubricant. To do.

Comparative Example 2 The effectiveness of the case where only the grease generally used as a lubricant (one of mineral oil type lubricants) alone was applied to the green chromate treated bolts was the same as that of the above-mentioned Example 6. When examined in the same manner, the results shown in Table 4 below were obtained.

[0037]

[Table 4]

As is clear from Table 4 above, although the effect of application is recognized when the grease is used alone, even when 50 mg, which is the upper limit of the effective application amount, is applied, the generated axial force is significantly increased as in Example 6. It can be seen that no significant improvement effect can be obtained.

Example 7 In this example, polytetrafluoroethylene powder (hereinafter referred to as P) was used as a solid lubricant on the thread portion of the green chromate treated bolt.
It is intended to improve the tightening torque-generated axial force characteristics of the green chromate treated bolt by applying TFE powder).

Specifically, 1 g of the PTFE powder is dispersed in 10 g of butanol, and a green chromate treated bolt (M10, length 25 mm, pitch 1.5 mm,
7T Hexagon head bolt with flange)
Allowed to dry thoroughly. After that, the green chromate treated bolt was attached to an aluminum part (material: JIS AC4).
When the axial force generated when screwing into the M10 pitch 1.5 mm screw hole of C) and tightening with a tightening torque of 50 N · m was measured, the measurement results shown in FIG. In addition,
The characteristics shown in FIG. 11 show the results of measuring the generated axial force by changing the coating amount (adhesion amount) of the PTFE powder. As is clear from the measurement results of FIG. 11, when the PTFE powder is applied in an amount of 1.0 mg or more, a sufficient axial force of 18 KN or more can be obtained when tightened with a tightening torque of 50 N · m. I understand. However, the length is 25m
15 to m10 bolts (green chromate treated bolts)
Even if the PTFE powder in excess of mg is applied, it is difficult to effectively supply the PTFE powder to the screw meshing portion when tightening the bolts. Therefore, in reality, the amount of the PTFE powder applied is 15
mg is the upper limit. However, no problem occurs even if a larger amount is applied.

In this embodiment, the length is 25 mm.
However, the same effect can be given to the green chromated bolts having other dimensions. That is, in the case of bolts other than the M10 bolt having a length of 25 mm, the coating amount of the PTFE powder may be 0.1 to 1.5 mg / cm ² . Further, in this embodiment, the MoS ₂ powder is applied by using a brush, but other than that, the same effect can be obtained by applying it by a spraying method such as a dipping method, an air spray or an airless spray. Is obtained, and there is no problem even if dilution suitable for those methods is performed. further,
The same applies when a commercially available azo-type graphite spray or the like is used.

Comparative Example 3 The effectiveness of a mineral oil-based lubricant generally used as a lubricant was examined in the same manner as in Example 7 above using grease, and the results shown in Table 5 below were obtained. It was

[0043]

[Table 5]

As can be seen from Table 5 above, with respect to the mineral oil type lubricant such as grease, although the effect of application is recognized, even if the practical upper limit of 50 mg is applied, it will be treated as a gloss chromate treated bolt. The equivalent axial force of 18 KN or more was not generated.

[0045]

As described above, according to the present invention, a solid lubricant such as hexagonal boron nitride powder, molybdenum disulfide powder, graphite powder, or polytetrafluoroethylene powder is treated with green chromate having excellent corrosion resistance. Since it is attached to the bolt by coating, etc., the presence of this attached solid lubricant reduces the friction coefficient of the screw surface of the green chromate treated bolt and tightens the green chromate treated bolt to the aluminum part. The axial force generated at this time can be made larger, and the tightening torque-generated axial force characteristic of the green chromate treated bolt can be made equivalent to that of the gloss chromate treated bolt. Therefore, when tightening green chromate treated bolts, which are made of zinc-plated bolts with green chromate treatment with high corrosion resistance, onto aluminum parts, the phenomenon of insufficient axial force (when the same tightening torque as gloss chromate treated bolts is used) Insufficient axial force) can be eliminated, and the fastening force of the green chromate treated bolt to the aluminum component can be controlled based on the fastening torque. That is,
The axial force when assembling aluminum parts using the green chromate treated bolts can be controlled with the same tightening torque value as the gloss chromate treated bolts.

Further, according to the present invention, a conventional green chromate treated bolt not subjected to solid lubricant adhesion is used to tighten an aluminum component with an excessive tightening torque in order to generate a sufficiently large axial force. It is also effective in preventing accidents such as thread breakage or breakage that may occur in the event of an accident.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a first embodiment of the present invention, which is a coating amount and a generation axis of h-BN powder when h-BN powder is applied by brush onto the surface of a green chromate-treated bolt. It is a characteristic view which shows the relationship with a force.

FIG. 2 is a cross-sectional view of a green chromate treated bolt as a sample.

FIG. 3 is a configuration diagram of a measuring device that measures an axial force generated when a green chromate treated bolt is fastened to an aluminum component (aluminum cylinder block).

FIG. 4 is a characteristic diagram showing the relationship between the applied amount of h-BN powder per unit area of the surface of the thread portion of the green chromate treated bolt and the generated axial force.

FIG. 5 is a view for explaining the second embodiment of the present invention, in which h-BN is formed on the surface of the thread portion of the green chromate treated bolt.
H-BN when powder is applied by aerosol spray
It is a characteristic view which shows the relationship between the applied amount of powder and generated axial force.

FIG. 6 is a diagram for explaining the third embodiment of the present invention, which is a characteristic diagram showing the relationship between the grease adhesion amount and the generated axial force when grease is applied to the threaded surface of the green chromate treated bolt. Is.

[Fig. 7] h on the thread surface of the green chromate treated bolt
FIG. 7 is a characteristic diagram showing the relationship between the coating amount of BN powder and the generated axial force.

FIG. 8 is a diagram for explaining the fourth embodiment of the present invention, showing the relationship between the applied amount of MoS ₂ powder and the generated axial force when MoS ₂ powder is applied to the surface of the green chromate treated bolt. It is a characteristic view to show.

FIG. 9 is a view for explaining a fifth embodiment of the present invention, in which graphite powder is mixed with butanol and applied to the surface of the screw portion of the green chromate treated bolt, and the amount of graphite powder applied and the axis of generation. It is a characteristic view which shows the relationship with a force.

FIG. 10 is a view for explaining the sixth embodiment of the present invention, in which graphite powder is applied to the surface of the screw portion of the green chromate treated bolt by mixing the mineral powder with a mineral oil lubricant. It is a characteristic view which shows the relationship between quantity and generated axial force.

FIG. 11 is a diagram for explaining the seventh embodiment of the present invention, in which PT on the surface of the thread portion of the green chromate treated bolt is performed.
It is a characteristic view which shows the relationship between the applied amount of FE powder and the generated axial force.

FIG. 12 is a characteristic diagram showing tightening torque-generated axial force characteristics when a conventionally used gloss chromate treated bolt is tightened on an aluminum part.

[Explanation of symbols]

 1 Green chromate treated bolt 4 Aluminum part 5 Screw hole 6 Digital torque wrench 8 Strain amount measuring device 8

Claims (9)

[Claims] 1. A surface of a green chromate bolt formed by forming a zinc plating layer on the surface of a bolt material and further forming a green chromate treatment film on the zinc plating layer,
A bolt for tightening aluminum parts, characterized by having a solid lubricant attached. 2. The bolt for tightening aluminum parts according to claim 1, wherein the solid lubricant is hexagonal boron nitride powder. 3. The amount of the hexagonal boron nitride powder deposited on the thread portion of the green chromate bolt is 0.02 to 3 mg /
The bolt for tightening aluminum parts according to claim 2, wherein the bolt is cm ² . 4. The bolt for tightening an aluminum part according to claim 1, wherein the solid lubricant is molybdenum disulfide powder. 5. The amount of the molybdenum disulfide powder attached to the thread portion of the green chromate bolt is 0.05 to 5 mg.
The bolt for tightening aluminum parts according to claim 4, wherein the bolt is / cm ² . 6. The bolt for tightening aluminum parts according to claim 1, wherein the solid lubricant is graphite powder. 7. The adhesion amount of the graphite powder to the thread portion of the green chromate bolt is 0.01 to 0.5 mg / cm ^2.
The bolt for tightening aluminum parts according to claim 6, wherein 8. The bolt for tightening aluminum parts according to claim 1, wherein the solid lubricant is polytetrafluoroethylene powder. 9. The amount of the polytetrafluoroethylene powder attached to the thread portion of the green chromate bolt is 0.1 to 10.
It is 1.5 mg / cm < ² >, The bolt for tightening aluminum parts of Claim 8 characterized by the above-mentioned.