Effect of High Frequency Pulsing on the Interfacial Structure of Anodised Aluminium-TiO₂

High frequency anodizing of friction stir processed Al-TiO₂ surface composites was investigated. The effect of anodizing parameters on the structure and morphology of the anodic layer including the incorporation of the TiO₂ particles into the anodic layer is studied. Anodizing process was carried out using a high frequency pulse and pulse reverse pulse technique at a fixed frequency in a sulfuric acid bath. The structure of the composites and the anodized layer was studied using scanning and transmission electron microscopy. The pulse reverse pulse anodizing technique, using a negative potential on the low voltage cycle, showed extensive pore branching and pore generation at the TiO₂ particle-anodic alumina matrix interface. However, the pulse anodizing technique using zero potential during the low voltage cycle showed no such features in the pore morphology, but only entrapment of TiO₂ particles into the anodic alumina. Lower electrical resistance of the TiO₂ arising from oxygen defects, combined with applied negative potential during the low voltage cycle, are found to be responsible for the observed morphological features in the anodic alumina.