1990 Volume 41 Issue 7 Pages 766-771
Aluminum alloy die castings and plates were anodized by applying direct current or a constant pulse voltage in a sulfuric acid solution.
In DC anodization, castings containing large amounts of silicon and copper, there was a tendency for electrolytic voltage to rise and for the thickness of oxide coatings to decrease.
Electrochemical parameters-ionic current density, zenar leading edge angle and zenar time were measured by analyzing the pulse current waveform.
The ionic current density and zenar time for 99.99% aluminum were taken as the reference standard. Ionic current densities were lower for Al-Si and Al-Cu based alloys and higher values for Al-Mg based alloys, while zenar times were longer for Al-Si and Al-Cu based alloys, and shorter for Al-Mg based alloys.
The pulse current waveforms for AC 4C, ADC 1 and DM 2 die castings were characteristic of porous film formation.
ADC 10 and ADC 12 castings, on the other hand showed a borderline type between barrier film formation and porous film formation, since ionic current was relatively high. This seemed to be caused by imperfect barrier layer formation, based on the relatively high ionic resistance of silicon, trapping of electrons by cuprous oxide and the anodic dissolution of CuAl2.
