| 摘要 |
PROBLEM TO BE SOLVED: To suppress the change in color tone without degrading the adhesiveness by immersing aluminum or an aluminum alloy processed through anode oxidation in a pyrophosphoric acid solution maintained at specified concentration and temperature for a specified time without cleaning in hot water, and performing the electrodeposition coating. SOLUTION: Aluminum or an aluminum alloy processed through anode oxidation is immersed in a pyrophosphoric acid solution of 0.1-10 g/l concentration which is maintained at 70-100 deg.C for 10-30 minutes without cleaning in hot water, and then, the electrodeposition is performed. A hydrate of dense and smooth film structure is formed on a surface of an aluminum material through the immersion. Even when the hydrate is grown thick, the adhesiveness to a film formed on the aluminum material is not degraded. By growing the hydrate thick, the change in color tone by the progress of the hydration reaction is suppressed. Even when a film formed on the hydrate through the electrodeposition is exposed under a hot environment for a long time, no abnormality in color tone of the appearance is caused. An aluminum material suitable for building materials such as a metal-teamed glass can be obtained.
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