| 摘要 |
PROBLEM TO BE SOLVED: To color aluminum or aluminum alloy material formed with an anodically oxidized film on the surface to dark gray of a low lightness value by subjecting the aluminum or aluminum alloy material to an electrolysis with impressed voltage lower than that of an anodic oxidation treatment to give rise to a current restoration phenomenon, then electrolyzing the material in an acidic electrolytic coloring liquid of a specific pH. SOLUTION: The aluminum or aluminum alloy material formed by extrusion molding according to the conventional method is subjected to a surface preparation by mechanical manipulation, such as a blasting method and is then subjected to the anodic oxidation treatment at about 5 to 100 V in the electrolyte, such as sulfuric acid or oxalic acid. The anodically oxidized film is thereafter formed on this surface and is subjected to current restoration by DC energization with voltage of about 0.5 to 80 V lower than the impressed voltage of the anodic oxidation treatment. The anodically oxidized film is electrolytically colored in the acidic electrolyte coloring liquid which contains 1 to 30 g/l sulfuric acid, 0.1 to 3.0 g/l stannous sulfate, 10 go 100 g/l nickel sulfate and 20 to 100 g/l ammonium sulfate and has the pH <=3.0. As a result, the gray colored aluminum material having the dark color of about 40 to 50 in lightness index L value is obtained.
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