Study of anodic oxidation of aluminum in mixed acid using a pulsed current

The properties of anodized films on aluminum using a pulsed current in mixed electrolytes of nitric acid–sulfuric acid or boric acid–sulfuric acid have been studied. In film dissolution tests, it is proven that the anodic film contains two layers, and the composition of the film is also changed by the anodizing electrolytes. These results can also be obtained from energy dispersive spectroscopy analysis. When nitric acid or boric acid is added to an electrolyte of 10 wt.% sulfuric acid, the film thickness and microhardness can increase greatly, especially with an added amount of the modifier. Under the conditions of 10 wt.% sulfuric acid, duty cycle of 80%, bath temperature of 20°C and anodizing duration time of 50 min, the best results of microhardness and thickness are 162 Hv and 16 μm, respectively. By adding 15 g/l nitric acid, using the same conditions, the microhardness and thickness change to 467 Hv and 35 μm respectively, and if 15 g/l boric acid is added they become 481 Hv and 27 μm, respectively.