METHOD FOR ELECTROLYTIC COLORING OF ALUMINUM MATERIAL

PROBLEM TO BE SOLVED: To uniformly form colored films having arbitrary color tones over a wide range on an aluminum material. SOLUTION: An anodically oxidized film 2 having a micropore 3 extending in a perpendicular direction is formed on the surface of the aluminum material 1. After an enlarged part 6 is formed by an electrolytic treatment on the bottoms of the micropore 3, electrodeposited matter 4 is deposited in this enlarged part 6. Part or the whole of the electrodeposited matter 4 is replaced by a noble metallic layer 9. The lower micropore 11 extending below the electrodeposited matter 4 or the noble metallic layer 9 is formed by reanodic oxidation. Positive pulse DC or rectangular wave AC of a current density 0.1 to 5 A/dm and frequency 0.01 to 100 Hz is supplied in the reanodic oxidation treatment. The bottom of the lower microhole 11 is formed as ruggedness 12 and the ruggedness 13 is formed at the boundary between the aluminum material 1 and the anodically oxidized film 2 as well when the current density is lowered just before then end of the reanodic oxidation treatment. The lower micropore 11 extending below the electrodeposited matter 4 or the noble metallic layer 9 is made adjustable in its length by the reanodic oxidation treatment and an interference color appears in accordance with the length. An opaque feel may be imparted to the color development by forming the ruggedness 12, 13 according to need.