Investigation of anodizing time and pulse voltage modes on the corrosion behavior of nanostructured anodic layer in commercial pure aluminum

A two-step anodizing process was used to produce ordered Al2O3 nanostructure anodized layer on commercial pure aluminum. Samples were anodized in 0.3 M oxalic acid utilizing various constant pulse voltage modes: positive pulse voltage (PPV), pulse reverse voltage (PRV) and direct pulse voltage (DPV). Anodizing times were 60, 90, 120 and 150 min. Effects of anodizing time and voltage mode on characteristics, structure and corrosion behavior of the anodized layer were investigated. It was found that wall thickness was reduced and pore diameter increased by increasing anodizing time, regardless of the pulse voltage mode. Maximum pore diameter was achieved after 150, 150 and 120 min of anodizing in PPV, PRV and DPV modes, respectively. In DPV mode, a combination of mild and hard anodizing occurred that caused the anodized layer to achieve minimum porosity and maximum corrosion resistance, with respect to the other pulse voltage modes. Furthermore, with increasing anodizing time, the thickness of the anodized layer and its corrosion resistance increased.