US-12624471-B2 - Aluminum member and manufacturing method thereof

Abstract

An aluminum member ( 1 ) includes: a base material ( 2 ) composed of aluminum or an aluminum alloy; and an anodic oxide film ( 3 ) formed on a surface of the base material. The anodic oxide film includes: an amorphous layer ( 31 ), which is composed of an amorphous aluminum oxide and is formed on the base material ( 2 ); and a crystal layer ( 32 ), which is composed of a crystalline aluminum oxide and is formed on the amorphous layer ( 31 ). The aluminum member ( 1 ) can be obtained by forming the anodic oxide film ( 3 ) on the base material ( 2 ) by performing an anodization process on the base material ( 2 ) in an electrolytic solution, which contains boron atoms and has a pH of 7.0-12.0.

Inventors

• Tatsuya Kikuchi
• Miu SATO
• Junji Nunomura
• Yoshiyuki Oya

Assignees

• NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
• UACJ CORPORATION

Dates

Publication Date

20260512

Application Date

20210611

Priority Date

20200709

Claims (20)

1. 1 . A method of manufacturing an aluminum member, wherein: the aluminum member has an anodic oxide film formed on a surface of a base material composed of aluminum or an aluminum alloy, the anodic oxide film comprising: an amorphous layer, which is composed of an amorphous aluminum oxide and is formed on the base material; and a crystal layer, which is composed of a crystalline aluminum oxide and is formed on the amorphous layer; and the method comprises: forming the amorphous layer by performing an anodization process on the base material, and then forming the crystal layer on top of the amorphous layer by continuing the anodization process, wherein: the amorphous layer and the crystal layer are formed in an electrolytic solution that contains boron atoms and has a pH of 7.5 or more and 12.0 or less, the crystal layer is exposed on an outermost surface of the anodic oxide film, and after performing the anodization process, the crystal layer has small holes having an average diameter of 1 μm or more and 20 μm or less.
2. 2 . A method of manufacturing an aluminum member, wherein: the aluminum member has an anodic oxide film formed on a surface of a base material composed of aluminum or an aluminum alloy, the anodic oxide film comprising: an amorphous oxide layer, which is composed of an amorphous aluminum oxide and is formed on the base material; and a crystal oxide layer, which is composed of a crystalline aluminum oxide and is formed on the amorphous oxide layer; and the method comprises: forming the amorphous oxide layer by performing an anodization process on the base material by applying a constant current at an electric-current density of 10 A/m 2 or more and 200 A/m 2 or less, and then forming the crystal oxide layer on top of the amorphous oxide layer by continuing to apply the constant current in the anodization process such that micro arcs occur discontinuously on an outermost surface of the amorphous oxide layer, thereby repetitively melting and solidifying the outermost surface of the amorphous oxide layer to form the crystal oxide layer on the outermost surface of the amorphous oxide layer, wherein: the amorphous oxide layer and the crystal oxide layer are formed in an electrolytic solution that contains boron atoms, has an electrolyte concentration of 0.1-1.0 mol/L, is at a temperature of 283K or higher and 343K or lower and has a pH of 7.5 or more and 12.0 or less, the anodization process is performed for 5 minutes or more, and the crystal oxide layer is exposed on an outermost surface of the anodic oxide film.
3. 3 . The method according to claim 2 , wherein, after performing the anodization process, an arithmetic-average roughness Ra of the surface of the anodic oxide film is 0.5 μm or more and 1.5 μm or less.
4. 4 . The method according to claim 2 , wherein, after performing the anodization process, an L* value of a CIE 1976 L*a*b* color space obtained by measuring color tone of the surface of the aluminum member having the anodic oxide film is 70.0 or more.
5. 5 . The method of manufacturing the aluminum member according to claim 2 , wherein the electrolytic solution is an aqueous solution of ammonium tetraborate.
6. 6 . The method of manufacturing the aluminum member according to claim 2 , further comprising: prior to the step of forming the anodic oxide film, degreasing and/or polishing the base material, and thereafter, initiating and performing the anodization process.
7. 7 . The method of manufacturing the aluminum member according to claim 2 , wherein the base material is composed of aluminum having an Al purity of at least 99.99 mass %.
8. 8 . The method according to claim 2 , wherein, after performing the anodization process, the outermost surface of the amorphous oxide layer has an arithmetic-average roughness Ra of 0.5-1.5 μm.
9. 9 . The method according to claim 8 , wherein, after performing the anodization process, the surface of the anodic oxide film has an L* value of a CIE 1976 L*a*b* color space of 70.0 or more.
10. 10 . The method according to claim 9 , wherein the anodization process is concluded when the amorphous oxide layer has a thickness of 0.10-0.90 μm.
11. 11 . The method according to claim 9 , wherein the anodization process is concluded when the amorphous oxide layer has a thickness of 0.20-0.80 μm.
12. 12 . The method according to claim 11 , wherein, after performing the anodization process, the crystal oxide layer is composed of α-Al 2 O 3 and/or γ-Al 2 O 3 .
13. 13 . The method according to claim 12 , wherein the anodization process is concluded when the crystal oxide layer has a thickness of 1.0-15.0 μm.
14. 14 . The method according to claim 2 , wherein the anodization process is concluded when the amorphous oxide layer has a thickness of 0.10-0.90 μm.
15. 15 . The method according to claim 2 , wherein the anodization process is concluded when the amorphous oxide layer has a thickness of 0.20-0.80 μm.
16. 16 . The method of manufacturing the aluminum member according to claim 2 , wherein, upon conclusion of the anodization process, the crystal oxide layer covers substantially all of the outermost surface of the amorphous oxide layer.
17. 17 . The method of manufacturing the aluminum member according to claim 2 , wherein the anodization process is performed at least until the crystal oxide layer has a minimum thickness of 1.0 μm or more.
18. 18 . The method of manufacturing the aluminum member according to claim 2 , wherein the electrolytic solution contains at least 0.1 mol/L of ammonium tetraborate or ammonium pentaborate.
19. 19 . The method of manufacturing the aluminum member according to claim 2 , wherein: while forming both the amorphous oxide layer and the crystal oxide layer, the constant-current electrolysis is performed at a temperature of the electrolytic solution of 303K or higher and 343K or lower and the electric-current density is 50 A/m 2 or more and 200 A/m 2 or less, the electrolytic solution is an aqueous solution of ammonium tetraborate having an electrolyte concentration of 0.2-0.9 mol/L, and the anodization process is performed for 30 min or more.
20. 20 . The method of manufacturing the aluminum member according to claim 19 , wherein the anodization process is performed until: the thickness of the amorphous oxide layer is 0.2 μm or more and 0.8 μm or less, the thickness of the crystal oxide layer 3.0 μm or more, and small holes having an average diameter of 1-20 μm extend entirely through the crystal oxide layer to the amorphous oxide layer.

Description

CROSS-REFERENCE This application is the US national stage of International Patent Application No. PCT/JP2021/022288 filed on Jun. 21, 2021, which claims priority to Japanese Patent Application No. 2020-118492 filed on Jul. 9, 2020. TECHNICAL FIELD The present invention relates to an aluminum member and to a manufacturing method thereof. BACKGROUND ART Aluminum members have various applications such as in construction materials, electronic device housings, mechanical parts, and the like. A functional coating is sometimes provided on the surface of an aluminum member for the purpose of imparting characteristics such as design characteristics, corrosion-resistance characteristics, wear-resistance characteristics, insulation characteristics, and the like. As an example of a functional coating that is provided on a surface of an aluminum member, an anodic oxide film is known. The characteristics of an anodic oxide film vary in accordance with the structure, the fabrication method, and the like of the anodic oxide film. For example, in Patent Document 1, a method of forming an anodized-alumina coating is described, wherein anodization of aluminum is performed by immersing a substrate, which has aluminum exposed on a surface, in a first electrolyte, in which an electrolyte containing boron has been dissolved, and then further performing anodization by immersing the substrate in a second electrolyte, in which an electrolyte that does not contain boron has been dissolved. In addition, in Patent Document 2, a method of forming a ceramic coating is described, wherein a ceramic coating containing aluminum oxide is formed on the base surface of aluminum or aluminum alloy using anodic-spark discharge in an aqueous electrolytic bath containing: (a) nitrogen-atom-containing cations and (b) amino-carboxylate anions having a stability constant with respect to aluminum of 9 or higher. PRIOR ART LITERATURE Patent Documents Patent Document 1 Japanese Laid-open Patent Publication H10-107027 Patent Document 2 Japanese Laid-open Patent Publication 2003-171794 SUMMARY OF THE INVENTION According to the method of Patent Document 1, a type of anodic oxide film called a barrier-type, anodic oxide film can be formed. Because the barrier-type, anodic oxide film is relatively dense, it excels in insulation characteristics, corrosion-resistance characteristics, etc. However, because it is difficult to make the barrier-type, anodic oxide film thick, there is a problem in that it is inferior in wear-resistance characteristics, hardness, etc. In addition, according to the method of Patent Document 2, a type of anodic oxide film called a plasma electrolytic oxide film can be formed. Because the plasma electrolytic oxide film is composed of a crystalline aluminum oxide and can easily be made thick, it excels in wear-resistance characteristics. However, because small holes are easily formed in the plasma electrolytic oxide film, there is a problem in that it is inferior in insulation characteristics. It is one non-limiting object of the present teachings to provide an aluminum member having an anodic oxide film that excels in one or more of insulation characteristics, corrosion-resistance characteristics, and wear-resistance characteristics, and to provide a manufacturing method thereof. In one aspect of the present teachings, an aluminum member comprising may comprise: a base material composed of aluminum or an aluminum alloy; andan anodic oxide film formed on a surface of the base material;wherein the anodic oxide film comprises: an amorphous layer, which is composed of an amorphous aluminum oxide and is formed on the base material; anda crystal layer, which is composed of a crystalline aluminum oxide and is formed on the amorphous layer. Another aspect of the present invention is a method of manufacturing the aluminum member according to the above-mentioned aspect, wherein the anodic oxide film is formed by performing an anodization process on the base material in an electrolytic solution, which contains boron atoms and has a pH of 7.0 or more and 12.0 or less. The anodic oxide film, which comprises the amorphous layer and the crystal layer, is present on a surface of the aluminum member. Because the amorphous layer is composed of a relatively dense amorphous aluminum oxide, excellent insulation characteristics and corrosion-resistance characteristics can be imparted to the aluminum member. In addition, because the crystal layer is composed of a relatively hard crystalline aluminum oxide, excellent wear-resistance characteristics can be imparted to the aluminum member. Thus, the anodic oxide film has both excellent insulation characteristics and corrosion-resistance characteristics of the barrier-type, anodic oxide film and excellent wear-resistance characteristics of the plasma electrolytic oxide film. For this reason, the aluminum member has excellent insulation characteristics, corrosion-resistance characteristics, and wear-resist