AlSi(Cu) anodic oxide layers formed in H2SO4 at low temperature using different current waveforms

Anodic oxidation of Al, AlSi10 and AlSi10Cu3 permanent mold cast substrates in 2.25 M H2SO4, at 0 °C for 50 min using different current waveforms (i.e. square, ramp-square, ramp-down and ramp-down spike) was performed, in an attempt to evaluate the effects of pulsed current on layer growth and properties. The pulses were unipolar and superimposed (amplitude ratio 4:1), applied with a frequency of 0.0125 Hz and a duty cycle of 75%. The same average current densities (i.e. 3.0 and 4.2 A dm−2) were imposed for all waveforms. The results on voltage transients, layer thickness, morphology, microhardness (HV0.025) and surface roughness (Ra) have been compared to the results obtained when direct and ramped current were applied. Voltage transients followed the current waveforms to a certain extent depending on the waveform shape and substrate composition. The differences obtained in layer properties were not statistically different relative to the direct current experiments and remained dependent mainly on substrate composition.