Localized corrosion on sputtered Al-1wt.% Si-0.5wt.% Cu thin film has been investigated in terms of micropit density as a function of applied potential below pitting potential and of time of exposure to a solution containing halide ion by SEM observation and compared with the result of Al bulk material with the same composition. The obtained data were analyzed by statistical method. Micropit size was found to be uniform, regardless of applied potential and exposure time, while micropit density increased with increasing them. Micropit density was higher for the Al film than for the Al bulk. It was found for both of them that the micropit density followed the Weibull distribution of which shape and scale parameters decreased with increasing applied potential and that micropit generation rate rapidly decreased and then reached a constant value at a given applied potential. The potential dependence of the two parameters revealed that the generation rate was initially larger at a higher potential and was later larger at a lower potential. From these results, it is concluded that the Weibull distribution of micropit density is definitely determined by applied potential below pitting potential for both Al alloy film and Al alloy bulk and that the difference between the Al alloy film and the Al alloy bulk is only a magnitude of micropit density.
