Anodic oxidation is widely used for the surface treatment of aluminium and its alloys due to its ease of operation, high productivity, and low cost. However, this technique currently relies mainly on acidic electrolytes, which have significant environmental risks. Furthermore, the inherent properties of acidic electrolytes limit their application to some specific structural components, particularly materials sensitive to acidic conditions (e.g., aluminium-magnesium alloys and aluminium-copper composite parts). In this work, an alkaline solution consisting of sodium hydroxide, sodium tetraborate, and potassium pyrophosphate was used for the anodic oxidation of 6061 aluminium alloy. The effects of different electrolyte compositions on the growth and microstructure of the anodic films were investigated. The results showed that all the compositions affected the current density during the anodic oxidation process and and the thickness of the anodic films. The current density increased with the increase of concentration of the electrolyte composition except for sodium tetraborate, while the thickness of the anodic films initially increased and then decreased with increasing process parameters. The microstructure of the anodic films was significantly influenced by the variables of sodium hydroxide and sodium tetraborate, with increases in sodium hydroxide concentration leading to decreased surface homogeneity, while sodium tetraborate exhibited the opposite effect.

 

anodic films; alkaline solution