Aluminum member and manufacturing method thereof

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/m2 or more and 200 A/m2 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.

A method of forming an anodic oxide film on an aluminum member, comprising:

• immersing the aluminum member in an electrolytic solution that contains boron atoms and has a pH of 7.5 or more and 12.0 or less;
• and
• performing electrolysis by applying a current to the electrolytic solution and the aluminum member, wherein an amorphous oxide layer first forms on a surface of the aluminum member and then, with continued application of the current in the same electrolytic solution, micro arcs occur discontinuously on an outer surface of the amorphous oxide layer, thereby repetitively melting and solidifying the surface of the amorphous layer to form a crystal oxide layer on the outer surface of the amorphous oxide layer,
• wherein, after performing the electrolysis, the crystal layer is exposed on an outermost surface of the anodic oxide film.