The effect of bath aging on the microstructure of anodic oxide layers on AA1050

During the aluminum anodization the anodizing electrolyte changes over time and is well-known as bath aging. This alteration of the bath is mainly caused by the impact of Al3 + ions and ions of alloying elements as well as the consumption of protons. It is shown that the higher the Al3 + concentration the higher the pH value and the electrical resistance of the bath. Consequently, the oxide formation rate decreases, whereby the efficiency of layer formation increases. This work is focused on the effect of the ongoing bath aging on the microstructure of the anodic oxide layers formed on AA1050. It illustrates the fact that the ongoing bath aging significantly influences the morphology, the thickness and the pore structure of the oxide layers that are formed, but does not influence the barrier layer thickness. The pore diameter decreases with ongoing bath aging. As a direct consequence the hardness of the oxide layer increases and the pore diameter decreases.