Effect of high-frequency switching electrolysis on film thickness uniformity of anodic oxide film formed on AC8A Aluminum alloy

Abstract

The effect of high-frequency switching electrolysis on the film thickness uniformity of an anodic oxide film formed on Al–Si (AC8A) alloy was studied. The film thickness uniformity was successfully improved by applying high-frequency switching electrolysis with positive and negative voltage cycles and not by direct current anodizing. To attain uniform film growth on an Al–Si substrate with substantial dispersion of crystallized Si particles, the effects of the applied time Ta at a positive voltage as well as of the shape of current waves on film morphology and film thickness uniformity was investigated. When Ta was set close to the time at which the current peak, Tp was observed, the most uniform film growth was achieved. This was explained by the capsulation of Si particles by intermittent oxide growth accompanied by switching electrolysis with appropriate applied intervals. The mechanism of uniform film growth was further interpreted using equivalent circuit models.