Monitoring the progressive development of an anodized film on aluminum

In this study, the relation of the anodic potential vs processing time was recorded for the anodizing of an Al1050 aluminum sheet in a sulfuric acid solution. The electrochemical behavior of aluminum during the anodizing treatment can be characterized by measuring the anodic potential-time curves. The nanostructure of anodic films was observed with transmission electron microscopy (TEM) and high resolution field-emission scanning electron microscopy (SEM). The differentiated curves (ΔVΔt) could be partitioned into four steps indicating the processing conditions during the growth of the anodic film: barrier layer formation, nanopore initiation and growth, pore widening, and quasi-steady-state growth of the anodic film. Pitting during the pore-widening stage could be characterized by looking at the different types of valleys in the differentiated curve. The effects of the anodic parameters, such as the acid concentration, bath temperature, and current density, on pitting formation were investigated, and some conclusions are offered.