Coating initiation was evidenced after conversion treatment for only 30 s and the uniform cross section revealed a chemical deposition process of electrolyte anions on aluminium.

A proceeding process of aluminium dissolution during conversion treatment was found for the first time, indicating non-inhibitive kinetics of anodic reactions.

Coating growth on aluminium was determined by the availability of electrolyte anions and the prolonged conversion treatment crated a significant concentration gradient to limit growth.

Coating shrinkage either in the microscope or after post-coating treatment in the air was clarified, especially for the coating after prolonged conversion treatments.