Formation of Aluminium Oxide Film on Al Substrate by Micro-Arc-Technology in Electrolytic Solution of Sodium Hydroxide Systems

Abstract

The objective of this study was to form a polycrystalline oxide film on Al substrate using micro-arc-technology. According to the kind of electrolytic solution used micro-arc-processing was either possible or not. A crystallized Al₂O₃ film on the Al substrate was formed by micro-arc-processing in a NaOH electrolytic solution. But the discharge dispersion happened due to the condition of pretreatment on the Al substrate. This discharge dispersion did not occur in the mixed electrolytic solution of NaOH and Na₂SiO₃, and a crystallized Al₂O₃ film was formed on the Al substrate when it stabilized. In addition, the film had a bilayer structure with the under-layer near the Al substrates made of the high-density principal component γ-Al₂O₃ and α-Al₂O₃. The upper layer was made of γ-Al₂O₃ in the porous phase.