The anodizing of ADC 12 aluminum die-casting alloy, ADC 12 without Cu, Fe, or Mn (M-ADC 12), cast ADC 12 (C-ADC 12), and rapidly solidified ADC 12 (RS-ADC 12) has been investigated in 10 and 30wt% H2
solutions at 293K with a constant current density of 100A/m2
. Anodic oxide film formation was examined by measuring the time variations in anode potential, the amount of dissolved Al3+
ions, and the volume of O2
evolved on the anode, as well as by electron microscopic observation of the oxide film.
The steady value of the anode potential in 10wt%-solution was 35-57V, increasing in the order C-ADC 12<<RS-ADC 12=M-ADC 12<ADC 12. The metal dissolution current was 22-25A/m2
, independent of the kind of specimen, while the gas evolution current was 15-30A/m2
, increasing in the order M-ADC 12<<RS-ADC 12=C-ADC 12<ADC 12. Increases in acid concentration caused decreases in the anode potential and gas evolution rate.
The difference in the anode potential and gas evolution rate during anodizing are discussed in terms of the inhibition of ion transport and acceleration of electron transport across the barrier layer, due to the formation of composite oxide, Al(Si, Cu, Fe)Ox.