Abstract
Investigations were made on the effects of the addition of various metallic salts on anodizing of aluminum in sodium hydroxide and alkaline-acid double electrolytic oxidation, and the properties of the films produced were also discussed.
An anodized film (about 7μ by microscopy) was prepared in NaOH (5×10-2mol) containing metallic salts of 5×10-3mol by electrolysis for 30min. under D.C. current density of 1amp/dm2.
The result showed that the film had a higher corrosion resistance to acid (10% H2SO4) and base (10% NaOH) as compared with the anodized film of nearly the same thickness produced in H2SO4, but its scratch hardness (by Martens' hardness tester under a load of 50g) was not so high.
Then, the film produced in the above bath containing zincate had very higher corrosion resistance and hardness (15.0) as compared with the film produced in NaOH bath of the same concentration containing no metallic salts.
In double anodizing process, an anodized film, which had been prepared in the proposed alkaline bath and then electrolyzed in sulfuric acid by D.C. current density of 1amp/dm2 for 30min., had a great thickness (about 7μ or more) as expected and a higher corrosion resistance as compared with the single anodized film.
