FASTENING MEMBER AND METHOD FOR MANUFACTURING SAME

Abstract

Provided is a fastening member having a base material including an aluminum alloy and an anticorrosive film with which the base material is coated. This anticorrosive film contains aluminum hydroxide oxide (AlO(OH)), and in a profile obtained from X-ray diffractometry with a Cu-Kα radiation on the fastening member, a peak intensity ratio R (I.sub.B(020)/I.sub.Al(200)) is 0.003 or more and 0.1 or less, wherein I.sub.B(020) is an intensity of a diffraction peak of a (020) plane of aluminum hydroxide oxide, and I.sub.Al(200) is an intensity of a diffraction peak of a (200) plane of aluminum as a main peak. The anticorrosive film formed by the present invention is uniformly formed on the fastening member and excellent in stability and adhesion.

Claims

1. A fastening member having a base material comprising an aluminum alloy, and an anticorrosive film for coating the base material, wherein the anticorrosive film contains aluminum hydroxide oxide (AlO(OH)), and in a profile obtained from X-ray diffractometry with a Cu-Kα radiation on the fastening member, a peak intensity ratio R (I.sub.B(020)/I.sub.Al(200)) is 0.003 or more and 0.1 or less, wherein a peak intensity of a diffraction peak of a (020) plane of aluminum hydroxide oxide is I.sub.B(020), and a peak intensity of a diffraction peak of a (200) plane of aluminum as a main peak is I.sub.Al(200).

2. The fastening member according to claim 1, wherein a half width of the diffraction peak of the (020) plane of aluminum hydroxide oxide is 0.20° or less.

3. The fastening member according to claim 1, wherein the anticorrosive film has a thickness of 1 μm to 15 μm.

4. The fastening member according to claim 1, having a Vickers hardness of 100 Hv to 250 Hv.

5. The fastening member according to claim 1, wherein the aluminum alloy is an Al—Si-based aluminum alloy, an Al—Cu-based aluminum alloy, an Al—Mg-based aluminum alloy, an Al—Mg—Si-based aluminum alloy, an Al—Zn—Mg-based aluminum alloy, or an Al—Zn—Mg—Cu-based alloy.

6. The fastening member according to claim 1, wherein the fastening member is a bolt, a screw, or a nut.

7. A method for producing the fastening member defined in claim 1, comprising: a washing step of washing a base material comprising an aluminum alloy, a solution step of conducting solution treatment for heating the base material after the washing step to a temperature of 460° C. or more and 570° C. or less and then quenching the base material, and an anticorrosive film formation step of bringing the base material after the solution treatment into contact with steam to form a film, wherein the washing step is a step of washing the base material until the amount of foreign matter including Fe attached to the base material decreases to 0.6 μg/mm.sup.2 or less, and the anticorrosive film formation step is a step of bringing the base material into contact with steam of 230° C. to 290° C.

8. The fastening member according to claim 2, wherein the anticorrosive film has a thickness of 1 μm to 15 μm.

9. The fastening member according to claim 2, having a Vickers hardness of 100 Hv to 250 Hv.

10. The fastening member according to claim 3, having a Vickers hardness of 100 Hv to 250 Hv.

11. The fastening member according to claim 2, wherein the aluminum alloy is an Al—Si-based aluminum alloy, an Al—Cu-based aluminum alloy, an Al—Mg-based aluminum alloy, an Al—Mg—Si-based aluminum alloy, an Al—Zn—Mg-based aluminum alloy, or an Al—Zn—Mg—Cu-based alloy.

12. The fastening member according to claim 3, wherein the aluminum alloy is an Al—Si-based aluminum alloy, an Al—Cu-based aluminum alloy, an Al—Mg-based aluminum alloy, an Al—Mg—Si-based aluminum alloy, an Al—Zn—Mg-based aluminum alloy, or an Al—Zn—Mg—Cu-based alloy.

13. The fastening member according to claim 4, wherein the aluminum alloy is an Al—Si-based aluminum alloy, an Al—Cu-based aluminum alloy, an Al—Mg-based aluminum alloy, an Al—Mg—Si-based aluminum alloy, an Al—Zn—Mg-based aluminum alloy, or an Al—Zn—Mg—Cu-based alloy.

14. The fastening member according to claim 2, wherein the fastening member is a bolt, a screw, or a nut.

15. The fastening member according to claim 3, wherein the fastening member is a bolt, a screw, or a nut.

16. The fastening member according to claim 4, wherein the fastening member is a bolt, a screw, or a nut.

17. The fastening member according to claim 5, wherein the fastening member is a bolt, a screw, or a nut.

18. A method for producing the fastening member defined in claim 2, comprising: a washing step of washing a base material comprising an aluminum alloy, a solution step of conducting solution treatment for heating the base material after the washing step to a temperature of 460° C. or more and 570° C. or less and then quenching the base material, and an anticorrosive film formation step of bringing the base material after the solution treatment into contact with steam to form a film, wherein the washing step is a step of washing the base material until the amount of foreign matter including Fe attached to the base material decreases to 0.6 μg/mm.sup.2 or less, and the anticorrosive film formation step is a step of bringing the base material into contact with steam of 230° C. to 290° C.

19. A method for producing the fastening member defined in claim 3, comprising: a washing step of washing a base material comprising an aluminum alloy, a solution step of conducting solution treatment for heating the base material after the washing step to a temperature of 460° C. or more and 570° C. or less and then quenching the base material, and an anticorrosive film formation step of bringing the base material after the solution treatment into contact with steam to form a film, wherein the washing step is a step of washing the base material until the amount of foreign matter including Fe attached to the base material decreases to 0.6 μg/mm.sup.2 or less, and the anticorrosive film formation step is a step of bringing the base material into contact with steam of 230° C. to 290° C.

20. A method for producing the fastening member defined in claim 4, comprising: a washing step of washing a base material comprising an aluminum alloy, a solution step of conducting solution treatment for heating the base material after the washing step to a temperature of 460° C. or more and 570° C. or less and then quenching the base material, and an anticorrosive film formation step of bringing the base material after the solution treatment into contact with steam to form a film, wherein the washing step is a step of washing the base material until the amount of foreign matter including Fe attached to the base material decreases to 0.6 μg/mm.sup.2 or less, and the anticorrosive film formation step is a step of bringing the base material into contact with steam of 230° C. to 290° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a schematic view illustrating the configuration of a vapor curing apparatus used in the present embodiment.

[0042] FIG. 2 is SEM micrographs of the surface (anticorrosive film) of the fastening member of First Embodiment.

[0043] FIG. 3 is an XRD profile of the fastening member of First Embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] First Embodiment: Hereinafter, a preferred embodiment of the present invention will be described. In the present embodiment, a bolt including an Al—Mg—Si-based alloy (A6061 alloy), which is a 6000-series aluminum alloy, was used as a base material of an aluminum alloy. This bolt was subjected to steam treatment to produce a fastening part including a fastening member having an anticorrosive film formed.

[Production of Fastening Member]

[0045] In the present embodiment, a commercially available A6061 alloy bolt was used as the base material. First, as a washing step for the base material, washing treatment was conducted until the amount of foreign matter including Fe attached to base material surface decreased to 0.6 μg/mm.sup.2 or less. In the washing step, ultrasonic washing and vapor washing of the base material were each conducted for 10 minutes in a single tank-type hydrocarbon-based washer (manufactured by Aqua Chemical Co. Ltd., TETRA) with a hydrocarbon-based detergent (product name: AQUA Solvent manufactured by Aqua Chemical Co. Ltd.), and then, the base material was vacuum-dried. Thereafter, the amount of foreign matter including Fe attached to the base material (μg/mm.sup.2) was calculated based on the gravimetry by a residue measurement test. Presence of Fe contained in the foreign matter was qualitatively analyzed on the foreign matter attached to the membrane filter after filtration of the hydrocarbon-based detergent, with a scanning electron microscope.

[0046] Next, the base material after the washing step was subjected to solution treatment. In the solution treatment, the base material was heated in a salt bath at 560° C. and then cooled. The heating period was 0.5 hours. Cooling was conducted with icy water at 0° C.

[0047] The solution-treated base material was subjected to steam treatment to form an anticorrosive film. In the steam treatment, a vapor curing apparatus shown in FIG. 1 was used. The vapor curing apparatus of FIG. 1 is a horizontal autoclave, and the autoclave included pure water (20 ml), which was the vapor source and was injected in the lower portion as a treatment liquid. From the upper part of the apparatus, a plurality of specimens (base materials) can be suspended. The treatment was conducted under conditions for anticorrosive film formation including temperature: 200° C. (Reference Example 1), 240° C. (Example 1), 260° C. (Example 2), and 290° C. (Example 3); pressure: 1.5 MPa (Reference Example 1), 3.3 MPa (Example 1), 4.6 M Pa (Example 2), and 7.4 MPa (Example 3); and treatment period: 24 hours with the temperature and pressure maintained.

Comparative Examples 1 and 2: A bolt identical to those of Example 1 and the like was washed, but the amount of foreign matter such as Fe attached to and included in the base material was set to more than 0.6 μg/mm.sup.2. In this washing step, the fastening member was only immersed in a hydrocarbon-based detergent for 5 minutes. Then, the steam treatment was conducted under the same conditions as in Example 2 to form an anticorrosive film (Comparative Example 1). As Comparative Example 2, a bolt including an A6061 alloy having no anticorrosive film formed (untreated product) was provided.

[0048] The fastening member of Examples 1 to 3, Reference Example 1, and Comparative Examples 1 and 2 produced by the steps hereinabove were subjected to various evaluations.

[Observation of Surface Feature of Anticorrosive Film with SEM]

[0049] The surface feature of the anticorrosive films was observed with a scanning electron microscope (SEM). FIG. 2 is SEM micrographs showing the surface feature of the anticorrosive films formed on the surface of the A5056 alloy bolts of Examples 1 to 3 at each steam treatment temperature. It was confirmed from FIG. 2 that crystals considered to be AlO(OH) was densely formed on the bolt surface each of Examples 1 to 3 in conformance with the shape of the base material at any of the temperatures.

[Analysis by X-Ray Diffraction Method (XRD)]

[0050] Next, the fastening members of the present embodiment and Comparative Examples were analyzed by an X-ray diffraction method (XRD). XRD measurement was conducted with Cu-Kα as the X-ray source at a voltage of 40 kV and a current of 30 mA. XRD was conducted on the fastening members of the present embodiment and Comparative Examples having an anticorrosive film formed and the fastening member having no anticorrosive film formed (untreated product: Comparative Example 2).

[0051] FIG. 3 is a XRD profile for the fastening members on which an anticorrosive film was formed at various steam temperature and the fastening member as an untreated product. It can be confirmed from FIG. 3 that the present embodiment has a strong diffraction peak on the (020) plane of aluminum hydroxide oxide. In FIG. 3, a peak intensity ratio R was calculated from the peak intensity of the (020) plane of aluminum hydroxide oxide and the peak intensity of the (200) plane of aluminum of the base material including an aluminum alloy. The half width was also measured based on the XRD profile obtained. In half width measurement, the width at the one-half of the diffraction peak height was measured. The values of the peak intensity ratio R and the half width of Examples, Reference Example, and Comparative Examples at various steam treatment temperature are shown in Table 1.

TABLE-US-00001 TABLE 1 Steam treatment Peak intensity No. temperature ratio R Half width Example 1 240° C. 0.005 0.19° Example 2 260° C. 0.018 0.17° Example 3 290° C. 0.04 0.15° Reference 200° C. 0.002 0.23° Example 1 Comparative 240° C. 0.002 0.21° Example 1 Comparative — 0 — Example 2

[CASS Test]

[0052] A CASS test in accordance with JIS H 8502 was used to evaluate the corrosion resistance of the fastening members of present embodiment and Comparative Examples. The CASS test is a test method of inspecting corrosion resistance of plating, which is conducted in an atmosphere including a sprayed solution with a CASS test apparatus, the solution being an acetic acid sodium chloride solution including copper(II) chloride dihydrate added thereto. The CASS test was conducted with a CASS test apparatus (JIS Z 2371) under the conditions in Table 2 for a test period of 1 to 24 hours.

TABLE-US-00002 TABLE 2 On Items adjustment During test Sodium chloride concentration, g/l 50 ± 5  50 ± 5 Cupric chloride (CuCl.sub.2•2H.sub.2O) 0.26 ± 0.02 — concentration, g/l pH 3.0 3.0-3.2  Amount sprayed, ml/80 cm.sup.2/h —  1.5 ± 0.5 Temperature in test tank, ° C. — 50 ± 2 Salt solution tank temperature, ° C. — 50 ± 2 Air saturator temperature, ° C. — 63 ± 2 Compressed air pressure, kPa — 70-167

[0053] The appearance of the fastening members after the CASS test was visually observed. A member in which no corrosion occurred was rated as “A”, a member in which corrosion was partially confirmed was rated as “B”, and a member in which corrosion was entirely confirmed was rated as “C”. The CASS test was conducted, in principle, until corrosion occurred entirely (until the member was rated as C). The results of the CASS test are shown in Table 3.

TABLE-US-00003 TABLE 3 Steam treatment Salt spray test: Salt spray test: No. temperature test period evaluation results Example 1 240° C. 1 h A 6 h B 8 h B Example 2 260° C. 1 h A 6 h A 8 h A 14 h A 24 h B Example 3 290° C. 1 h A 6 h B 8 h B 14 h C Reference 200° C. 1 h A Example 1 6 h C Comparative 260° C. 1 h A Example 1 6 h C 8 h C Comparative — 1 h C Example 2

[0054] It can be confirmed from Table 3 that the entire corrosion occurred only in 1 hour in the aluminum alloy subjected to no steam treatment (Comparative Example 2) and thus, the anticorrosive film formed in each of Example, Comparative Example 1, and the like has effectivity. Then, it can be seen that the fastening member of each Example maintains an entire corrosion-free state for 6 hours or more against the salt solution of the CASS test. In particular, in Example 2, in which steam treatment was conducted at 260° C., a favorable state was maintained until 24 hours.

[0055] However, it is necessary to conduct the steam treatment on the fastening members at an appropriate treatment temperature. In the case of the treatment temperature of 200° C. as in Reference Example 1, corrosion entirely occurred in 6 hours, and it is deemed that an anticorrosive film that may have sufficient corrosion resistance was not generated. In order to form a film exhibiting a high anticorrosive effect on the fastening member including an aluminum alloy, it is necessary for washing to limit the amount of iron to be attached. On a fastening member subjected to usual washing, by which the amount of iron to be attached cannot be limited, as in Comparative Example 1, a film exhibiting an insufficient anticorrosive effect was formed, which was equivalent to that in Reference Example 1.

[0056] The anticorrosive effect from the anticorrosive film corresponds to the peak intensity ratio R (I.sub.B(020)/I.sub.Al(200)) of the peak intensity of the diffraction peak of the (020) plane of aluminum hydroxide oxide to the peak intensity of the diffraction peak of the (200) plane of the aluminum. With reference to Reference Example 1 and Examples 1 to 3, this peak intensity ratio gradually increases in the range of from the vicinity of 200° C. to 240° C., the increase rate rises therefrom, and the peak intensity ratio rapidly increases in the range of higher than around 260° C.

[Hardness and Anticorrosive Film Thickness]

[0057] On the anticorrosive film formed on the fastening member of each of Examples and Comparative Examples, evaluation test was conducted for the thickness of the anticorrosive film and the hardness of the base material. For the thickness of the anticorrosive film, cross sectional processing was conducted on a vertical cross section including the anticorrosive film and the base material with a Cross Section Polisher® manufactured by JEOL Ltd., a field emission scanning electron microscope image of the cross section was obtained, and the thickness was measured. For measurement of the hardness, each sample was mechanically polished before measurement to remove the film from the surface, and this sample surface was subjected to measurement. The hardness was measured with a Micro Vickers Hardness Testing Machine (HM-103, manufactured by Mitutoyo Corporation), and the hardness measurement conditions included a test load of 2.94 N and a load period of 15 s. The evaluation results are shown in Table 4

TABLE-US-00004 TABLE 4 Steam treatment Surface Anticorrosive temperature hardness film thickness No. (° C.) (HV) (μm) Example 1 240 128 2.1 Example 2 260 115 5.9 Example 3 290 110 13.8 Comparative — 52 — Example 2

[0058] It can be seen from the results of Table 4 that anticorrosive films having a sufficient thickness have been formed with the steam treatment. It can also be seen that the steam treatment increased the base material hardness two-fold or more at the maximum. Thus, it has been confirmed that fastening members were formed which had a strength sufficiently durable to stress during or after fastening.

Second Embodiment: in the present embodiment, a bolt including an Al—Cu—Mg-based alloy (A7075 alloy), which is a 7000-series aluminum alloy, was used as a base material of an aluminum alloy. This bolt was subjected to steam treatment to produce a fastening part including the fastening member having an anticorrosive film formed, and various examinations were conducted.

[0059] First, a commercially available A7075 alloy bolt was washed as the base material. In a washing step for the base material, washing was conducted with the apparatus and detergent identical to those in First Embodiment under the same conditions. The washing treatment was conducted until the amount of foreign matter including Fe attached to base material surface decreased to 0.6 μg/mm.sup.2 or less. Then, the base material after the washing step was subjected to solution treatment. In the solution treatment, the base material was heated in a salt bath at 470° C. and then cooled. The heating period was 2 hours. Cooling was conducted with ice water at 0° C.

[0060] Then, the solution-treated base material was subjected to steam treatment to form an anticorrosive film. In the steam treatment, the same vapor curing apparatus as that of First Embodiment was used. The treatment was conducted under conditions for anticorrosive film formation including temperature: 180° C. (Reference Example 2) and 240° C. (Example 4); pressure: 1.0 MPa (Reference Example 2) and 3.3 MPa (Example 4); and treatment period: 24 hours with the temperature and pressure maintained.

Comparative Examples 3 and 4: A bolt identical to those of Example 4 and the like was washed, but the amount of foreign matter such as Fe attached to and included in the base material was set to more than 0.6 μg/mm.sup.2. In this washing step, the fastening member was only immersed in a hydrocarbon-based detergent for 5 minutes. The bolt after washing was subjected to alumite treatment with a sulfuric acid electrolytic solution to thereby form an anticorrosive film (film thickness: 5 μm to 10 μm) (Comparative Example 3). As Comparative Example 4, a bolt including an A7075 alloy having no anticorrosive film formed (untreated product) was provided.

[0061] The fastening members of Example 4 and Comparative Examples produced by the steps hereinabove were subjected to the evaluation of corrosion resistance by the CASS test. The test conditions for the CASS test were the same as those of First Embodiment. Then, the appearance was visually observed, and an evaluation was conducted with the same criteria as in First Embodiment. The results of this CASS test are shown in Table 5.

TABLE-US-00005 TABLE 5 Steam treatment Salt spray test: Salt spray test: No. temperature test period evaluation results Example 4 240° C. 1 h A 6 h A 8 h A 14 h B 24 h B Reference 180° C. 1 h A Example 2 6 h C 8 h C 14 h C 24 h C Comparative — (Alumite 1 h A Example 3 treatment) 6 h B 8 h B 14 h C 24 h C Comparative — 1 h C Example 4

[0062] It can be confirmed from Table 5 that the entire corrosion occurred only in 1 hour in the aluminum alloy subjected to no steam treatment (Comparative Example 4) and thus, the anticorrosive films formed in Example 4, Reference Example 2, and the like have effectivity. Then, it can be seen that the fastening member of Example 4 maintains a favorable entire corrosion-free state for 24 hours or more against the salt solution of the CASS test. It can also be seen that the anticorrosive film formed in Example 4 exhibits markedly more favorable corrosion resistance in comparison with the film formed with alumite treatment in Comparative Example 3. However, in the case of a treatment temperature of 180° C. as in Reference Example 2, corrosion entirely occurred in 6 hours, and an anticorrosive film that may have sufficient corrosion resistance was not generated. As with in First Embodiment, it was confirmed that it is necessary to conduct the steam treatment at an appropriate treatment temperature.

[0063] Also in the present embodiment, when the surface feature of the anticorrosive film of Example 4 was observed with a SEM, it was confirmed that crystals considered to be AlO(OH) was densely formed in conformance with the shape of the base material.

Third Embodiment: in the present embodiment, a bolt including an Al—Si-based alloy (ADC12 alloy), which is a 4000-series aluminum alloy, was used as a base material of an aluminum alloy. This bolt was subjected to steam treatment to produce a fastening part including the fastening member having an anticorrosive film formed and subjected to various examinations.

[0064] First, a commercially available ADC12 alloy bolt was washed as the base material. In the washing step for the base material, washing was conducted with the apparatus and detergent identical to those in First Embodiment under the same conditions. The washing treatment was conducted until the amount of foreign matter including Fe attached to base material surface decreased to 0.6 μg/mm.sup.2 or less. In present embodiment, a bolt including an Al—Si-based alloy (ADC12 alloy), which is a 4000-series aluminum alloy, was used as a base material of an aluminum alloy, and thus, the solution treatment on the base material after the washing step was not conducted.

[0065] The base material after the washing step was steam-treated to form an anticorrosive film. In the steam treatment, the same vapor curing apparatus as that of First Embodiment was used. The treatment was conducted under conditions for anticorrosive film formation including temperature: 240° C. (Example 5), pressure: 3.3 MPa (Example 5), and treatment period: 24 hours with the temperature and pressure maintained.

Comparative Examples 5 and 6: A bolt identical to that of Example 5 was washed, but the amount of foreign matter such as Fe attached included in the base material was set to more than 0.6 μg/mm.sup.2. In this washing step, the fastening member was only immersed in a hydrocarbon-based detergent for 5 minutes. The bolt after washing was subjected to alumite treatment with a sulfuric acid electrolytic solution to thereby form an anticorrosive film (film thickness: 5 μm to 10 μm) (Comparative Example 5). As Comparative Example 6, a bolt including an ADC12 alloy having no anticorrosive film formed (untreated product) was provided.

[0066] The fastening members of Example 5 and Comparative Examples produced by the steps hereinabove were subjected to the evaluation of corrosion resistance by the CASS test. The test conditions for the CASS test were the same as those of First Embodiment. Then, the appearance was visually observed, and an evaluation was conducted with the same criteria as in First Embodiment. The results of this CASS test are shown in Table 6.

TABLE-US-00006 TABLE 6 Steam treatment Salt spray test: Salt spray test: No. temperature test period evaluation results Example 5 240° C. 1 h A 2 h B 6 h B 8 h C 14 h C 24 h C Comparative — (Alumite 1 h A Example 5 treatment) 2 h B 6 h B 8 h C 14 h C 24 h C Comparative — 1 h C Example 6

[0067] Also in the present embodiment, corrosion entirely occurred within 1 hour in the aluminum alloy not subjected to the steam treatment (Comparative Example 6). It can be seen that the aluminum alloy of Example 5 maintains an entire corrosion-free state for 6 hours or more against the salt solution of the CASS test. In consideration of the result of Comparative Example 6 having no anticorrosive film, the 4000-series aluminum alloy (Al—Si-based alloy) as the base material of the present embodiment is an aluminum alloy having relatively lower corrosion resistance than those of the 6000-series aluminum alloy (Al—Mg—Si-based alloy) as the base material of First Embodiment and the like. It has been confirmed that formation of an anticorrosive film with steam treatment at an appropriate treatment temperature also on such an aluminum alloy having low corrosion resistance enables the corrosion resistance to be greatly improved.

[0068] In comparison with the film formed with alumite treatment in Comparative Example 5, it can be seen that the anticorrosive film formed in Example 5 exhibits corrosion resistance equivalent to that of the film in Comparative Example 5. The anticorrosive film of the present application can be formed with a relatively simple process (steam treatment) although the temperature conditions are required to be strictly set. It is deemed that according the present invention, corrosion resistance to be imparted by a process simpler than alumite treatment and the like, which corrosion resistance is equivalent to or superior to that imparted by alumite treatment and the like. When the anticorrosive film of Example 5 was observed with SEM, it was confirmed that crystals considered to be AlO(OH) was densely formed in conformance with the shape of the base material, as in First and Second Embodiments.

INDUSTRIAL APPLICABILITY

[0069] As described hereinabove, the present invention can provide a fastening member, on the base material made of an aluminum alloy having a complicated shape of which a uniform and stable anticorrosive film can be inexpensively formed, the anticorrosive film being excellent in adhesion with the base material, having high hardness, and having corrosion resistance more excellent than before, and a method for producing the same. Accordingly, it is anticipated that the fastening member is broadly applied to fastening parts made of an aluminum alloy, of which the range of applications tends to spread.