JPH01205091A - Surface treatment of al alloy frame member of bicycle for welded structure - Google Patents

Abstract

PURPOSE:To prevent the cracking of a frame member due to heating to a high temp. at the time of welding by subjecting the member to first-step anodic oxidation to form an oxide film of a prescribed thickness, suddenly dropping the voltage and subjecting the member to second-step anodic oxidation. CONSTITUTION:An Al alloy frame member of a bicycle is subjected to first-step anodic oxidation in an electrolytic soln. contg. sulfuric acid or oxalic acid to form an oxide film of a prescribed thickness. After the voltage is suddenly dropped, the member is subjected to second-step anodic oxidation at constant voltage. The latter voltage is preferably regulated to <=60% of the former voltage. By carrying out the second-step anodic oxidation in an electrolytic soln. contg. oxalic acid, an oxide film having much higher heat resistance than that formed in an electrolytic soln. contg. sulfuric acid can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for surface treatment of bicycle frame members, and in particular to an AQ alloy bicycle frame for adhesive structure that is mutually bonded and connected to a mating member by bonding with an adhesive. The present invention relates to a method for surface treatment of members.

BACKGROUND OF THE INVENTION In recent years, bicycle frame members made of aluminum alloy have come to be used to meet the demand for weight reduction. Frame members of this type have heretofore been connected to each other by welding, but not only is there a restriction in the selection of materials for the frame members due to suitability for welding, but there is also a problem in that the appearance is unsightly due to welding beats. Therefore, instead of the welding method, a method of bonding using an adhesive has been proposed.

Incidentally, aluminum bicycle frame members are generally subjected to a surface treatment in which an oxide film is formed on the surface by anodizing treatment for the purpose of improving corrosion resistance and wear resistance.

Problems to be Solved by the Invention However, when bonding frame members having such oxide films on their surfaces using a thermosetting adhesive,
The high temperature heating during the adhesion process causes cracks in the oxide film, resulting in an unsightly appearance. A known method for preventing the occurrence of such cracks is to increase the temperature or concentration of the electrolyte as an anodizing treatment condition, but these methods do not improve the wear resistance and corrosion resistance required for bicycle frame members. There was a problem that it was not possible to obtain an oxide film having .

This invention has been made in view of the above technical background, and is an AQ bicycle for bonded structure that does not cause cracks due to high temperature heating during bonding and forms an oxide film with excellent wear resistance and corrosion resistance. An object of the present invention is to provide a method for surface treatment of a frame member.

Means for Solving the Problems With this objective in mind, the inventor conducted various experiments and research, and found that the above-mentioned solution was achieved by forming an oxide film on the surface through two stages of anodizing treatment, one before and one under different treatment conditions. I was able to complete this invention by finding a way to achieve my purpose.

That is, in the present invention, an AJ2 alloy bicycle frame member is subjected to a preliminary anodizing treatment until an oxide film of a predetermined thickness is obtained, and then the treatment voltage is rapidly lowered from the voltage in the preceding anodizing treatment step. The gist of the present invention is a surface treatment method for an Al alloy bicycle frame member for an adhesive structure, which is characterized by carrying out a subsequent anodic oxidation treatment at a constant voltage.

If the frame member is an Al alloy used as this kind of Al alloy bicycle frame member, for example, A3
Al1-11111g-Cr alloy such as 052, A3056, A Q -M n such as A7003, A7N01, etc.
The alloy composition, such as -Mg-Zn alloy, is not particularly limited. Furthermore, the method of manufacturing the raw pipe is not limited.

As shown in FIG. 1, the surface treatment of the frame member according to the present invention is carried out in two stages, with different electrolytic treatment conditions.

The anodizing treatment in the first stage is carried out under normal conditions in a sulfuric acid electrolyte or an oxalic acid electrolyte until an oxide film of a predetermined thickness is obtained. Here, the preferable electrolytic treatment conditions for the first stage treatment are as follows: When carried out in a sulfuric acid electrolyte, sulfuric acid concentration: 10 to 30 νt%, liquid temperature: 15 to 30°C, current density: around 1.5 A/dTIt. and when carried out in an oxalic acid electrolyte, oxalic acid concentration = 1 to 5 vt%, liquid temperature: 1
5-40°C, current density: 1. It is around 5A/d situation. The electrolytic treatment may be performed by alternating current, direct current, or superimposed alternating current or direct current, and may be constant voltage electrolysis or constant current electrolysis.

In the latter stage anodizing treatment, the processing voltage is rapidly lowered from the voltage (El) of the earlier stage anodizing treatment, and then the constant voltage (E2) is applied.
It is electrolytically treated. It is preferable that the voltage after dropping is 60% or less of the voltage in the previous treatment, since this can further improve the heat resistance of the film. Further, the voltage may be lowered continuously, or the current supply in the first stage treatment step may be temporarily stopped, and the predetermined voltage may be applied again at the beginning of the second stage treatment step. The electrolytic treatment in the subsequent treatment may also be performed using alternating current, direct current, or superimposed alternating current and direct current.

In addition, the electrolysis time in the post-processing is not particularly limited, but
In order to achieve even better corrosion resistance of the film, it is preferable to set it as a range of 10 to 30 minutes.

The electrolytic treatment in the latter stage treatment is carried out in a sulfuric acid electrolyte or an oxalic acid electrolyte as in the first stage treatment. In particular, if it is carried out in an oxalic acid electrolyte, it is possible to form a film with better heat resistance than a sulfuric acid anodic oxide film, which in turn can effectively prevent the occurrence of cracks during high-temperature heating.

Although the thickness of the anodic oxide film formed by the two-stage anodization treatment is not particularly limited, it is preferably 5 to 15 μm in order to have higher hardness.

Incidentally, it is presumed that the heat resistance of the film is improved by performing electrolytic treatment with the voltage rapidly lowered in the subsequent anodizing treatment for the following reason. That is,
When the voltage suddenly drops, the current (■2) becomes the first
As shown in the figure, it does not flow immediately, but begins to flow gradually after several seconds to several minutes, and reaches a steady state after a while.

This phenomenon is called a recovery phenomenon, and it is thought that while an anodic oxide film is formed, the surface of the frame member is roughened at the interface with the film. The reason why cracks occur during high-temperature heating in films formed by conventional methods is due to the difference in thermal expansion coefficients between the frame member and the film, but as mentioned above, cracks occur due to the roughening of the frame member surface. It is presumed that the internal stress in the film is reduced during heating and the generation of cracks is prevented, resulting in improved heat resistance.

Effects of the Invention Since the present invention is as described above, it is possible to provide a bicycle frame member having an anodized film having excellent heat resistance on its surface. Therefore, even in the bonding process in which frame members are bonded together using a thermosetting adhesive, cracks do not occur in the film due to heating, and the appearance is good, and corrosion and corrosion resistance are maintained. A bicycle frame made of AQ alloy with excellent wear resistance can be manufactured.

Example [Example 1] Drawn pipe made of A3056 alloy (outer diameter 32 m1 +
A plurality of pipes (with an inner diameter of 29 mIa and a length of 150 mIn) were prepared, and the surfaces of the pipes were polished to a mirror finish, and then subjected to alkali etching by a conventional method to produce a frame member to be treated.

Next, these frame members were placed in a sulfuric acid electrolyte with a sulfuric acid concentration of 15 μm% and a liquid temperature of 20°C, with a current density of 1.5 A/dT.
First, a preliminary anodic oxidation treatment using direct current electrolysis treatment was performed under the conditions of It and electrolysis time of 15 minutes. Next, after stopping the current supply, a subsequent anodic oxidation treatment was performed in the same electrolytic solution at a constant voltage of 9 V by direct current electrolysis treatment to obtain a frame member having an oxide film with a thickness of 6 μm.

On the other hand, the front and rear anodic oxidation treatments were performed under the same conditions as above, except that the treatment times for the front and rear treatments were changed appropriately, and the film thickness was 1.
Frame members having oxide films of 0 μm and 15 μm were obtained.

[Example 2] Using the same frame member as in Example 1, current density:
First, a preliminary anodic oxidation treatment was performed using direct current electrolysis treatment under the conditions of 1.5 A/dm and an electrolysis time of 18 minutes. Then -
After the electricity was turned off, a subsequent anodic oxidation treatment was performed in the same electrolytic solution at a constant voltage of 20 V by direct current electrolysis treatment to obtain a frame member having an oxide film with a thickness of 6 μm.

On the other hand, the front and rear anodic oxidation treatments were performed under the same conditions as above, except that the treatment times for the front and rear treatments were changed appropriately, and the film thickness was 1.
Frame members having oxide films of 0 μm and 15 μm were obtained.

[Example 3] Using the same frame member to be treated as in Example 1, sulfuric acid concentration:
Current density: 15 wt% in a sulfuric acid electrolyte at a temperature of 20°C:
1. The first test was conducted under the conditions of 5A/dTIt and electrolysis time of 10 minutes.
In addition to performing the DC electrolytic treatment in the first stage, oxalic acid concentration: 2vt%
Current density: 1.
An anodizing treatment was carried out prior to the second stage of direct current electrolytic treatment under the conditions of 5 A/d'rIt and an electrolysis time of 5 minutes. Then, after turning off the electricity for -10 minutes, the electrolyte was heated for 20 minutes in the second stage electrolyte.
The third stage of DC electrolysis treatment was performed under the conditions of a constant voltage of V and an electrolysis time of 10 minutes, followed by a subsequent anodic oxidation treatment, resulting in a film thickness of 6 μm.
A frame member of m was obtained.

On the other hand, the second and third stages were performed under the same conditions as above, except that the electrolysis time of the first stage was changed appropriately, and the film thickness was 10μ.
Each frame member with a diameter of 115 μm was obtained.

[Comparative Example 1] Using the same frame member to be treated as in Example 1, 1 degree sulfuric acid:
15 wt% in a sulfuric acid electrolyte at a temperature of 20°C, anodic oxidation treatment was carried out by direct current electrolysis at a current density of 1.5 A/dTrl and various electrolytic times, resulting in a film thickness of 6 μm.
Various frame members having oxide films with a thickness of 15 μm and 110 μm were obtained.

[Comparative Example 2] Using the same frame member as in Example 1, the treatment was carried out under the same conditions as in Comparative Example 1 except that the temperature of the sulfuric acid electrolyte was changed to 25°C, and the film thickness was 6 μm, 110 μm, and 15 μm. Various frame members having coatings were obtained.

[Comparative Example 3] Using the same treated frame member as in Example 1, oxalic acid concentration:
In an oxalic acid electrolyte containing 2 wt% and a liquid temperature of 30°C, anodization treatment was carried out by direct current electrolysis at various electrolysis times at a current density of 1.5 A/d, resulting in a film thickness of 6 μm1.
Various frame members having oxide films of 10 μm and 15 μm were obtained.

The various frame members obtained above were then immersed in pure boiling water for 30 minutes to seal the holes. After that, to examine the heat resistance, the film surface was tested at 150°C, 200°C, and 25°C.
It was heated to a temperature of 0° C., and the presence or absence of cracks was visually observed. In addition, according to JI SH8682 sand stone abrasion test,
The abrasion resistance of the coating was measured. The results are shown in Table 1.

For the abrasion resistance test sample, due to the measuring equipment, a flat bar made of A3056 material (width: 50 mm, length:
50M, thickness: 3mm) was used as a test material.

[See the following margins] As is clear from the above results, it was confirmed that the product implementing the present invention was superior to the comparative product in both heat resistance and abrasion resistance of the surface of the frame member.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in electrolytic voltage and current over time as an example of the anodizing treatment carried out in the present invention. that's all

Claims (2)

[Claims] (1) After carrying out a preliminary anodic oxidation treatment on an Al alloy bicycle frame member until an oxide film of a predetermined thickness is obtained, and then rapidly lowering the treatment voltage from the voltage in the previous anodization treatment step, A method for surface treatment of an Al alloy bicycle frame member for bonded structure, characterized in that a subsequent anodic oxidation treatment is performed at a constant voltage. (2) A method for surface treatment of an Al alloy bicycle frame member for bonded structure according to claim 1, wherein the subsequent anodization treatment is carried out in an oxalic acid electrolyte.