A thick anodic oxidation coating on aluminum cannot be produced in a sodium carbonate bath be due to the formation of a barrier-type layer. This study was carried out to investigate the formation of thick film in a concentrated sodium carbonate solution containing tartrate and fluoride. It was found that a porous anodic oxidation coating was formed at current densities of more than 2A/dm
2 in a high concentration bath of sodium carbonate solution containing sodium tartrate (0.3M-1.0M Na
2CO
3, 0.1M-0.15M NaF, 0.1M-0.2M Na
2C
4H
4O
6). In the films produced did not cracking sound occure, even when bent at a greater angle (90°) in a bending test, and hair cracking on the surface of the flexed film could not be observed with the naked eye. Results of the scratch hardness (load: 50g) and the bending test indicated that film formed in sodium carbonate-fluoride system bath was softer than film formed in sulfuric acid bath. It was concluded that the flexibility of the above film was caused by the fluoride content of the film, the unevenness of film surface, and the larger size of pores and cells compared with the films formed in sulfuric acid bath.
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