Abstract
Studies were made of the effects of application of pulsating current wave form on hard anodizing of aluminum. Specimens were anodized at 0°C in 100g/l of H2SO4 containing 15g/l of C2H2O4, at a constant electric quantity of 160A·min/dm2 with changing the current density and the time of pulse current. Direct currents (single-phase full-wave, three-phase half-wave, and six-phase half-wave), interrupted current and superimposed (DC and AC) currents were applied to compare with pulse current. A thicker coating is obtained when a direct current wave form containing high ripple percent was applied. When pulsating current (high output 4A/dm2 30sec, low output 2A/dm2 7.5sec) was applied, the hardness of coating was higher than hard anodic oxidation coatings using a direct current. The hardness became higher when the ratio of the time between the high output and the low output was 4:1. It was observed by scanning electron microscopy that the cell size of the cross section of coatings was independent of the current wave formes used. There found no obvious relation between the cell size and the hardness.
