Anodizing film was prepared on aluminum plate making use of anodizing at constant voltage in
phosphoric acid. The Al plate
coated with the anodizing film was then immersed in a diluted
phosphoric acid (5%) for 6~8 min to allow the processing of
pore-enlargement. The morphology and structure of the anodizing film after the processing of pore-enlargement were analyzed by means of scanning electron microscopy. It was found that, after being treated in diluted phosphoric acid, the tiny pores distributed uniformly in the anodizing film and the enlarged pores had a diameter about 150 nm, with the amount of the pores to be as much as 2.5×10 9/cm 2. Moreover, the pore-enlargement in the dilute phosphoric acid caused the original irregular spheric pores in the film to be transformed to regular spheric ones. The size of the pores almost linearly increased with increasing pore-enlargement duration, but at a certain pore-enlargement duration the pores lost their spheric shape and came into conjunction with each other. The proper pore-enlargement duration was suggested to be 6~7 min.