Effects of magnesium and copper on DC etched morphologies of high purity aluminium foils for electrolytic capacitors were investigated in this study. The amount and the size of MgAl_2O_4 spinel were increased with increasing magnesium content, and the dissolution during pre-treatment and early stage of DC etching occurred around these crystalline oxides. Therefore, uniformly distributed vertical tunnel pits were obtained under optimum conditions of magnesium content and the intensity of pre-treatment. The capacitance was improved with increasing copper content because of the increase of the number of pits and the uniformity of pit distribution. In a higher copper content foil, lead and magnesium were distributed uniformly near the surface of foils in addition to copper. It is considered that these behaviors are relative to the distribution of tunnel pits.
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