A blue-colored coating containing CoAl2O4 crystals was successfully prepared through the anodic oxidation of aluminum with pulsed wave under spark discharge in an electrolytic bath with 10 g/L Co(OH)2. Cobalt aluminate, CoAl2O4, was formed by the chemical reaction of Al2O3 and Co(OH)2 on the Al surface during the anodic oxidation process. The properties of the crystalline species, film thickness, surface roughness and color of the films can be controlled by regulating the spark discharge energy through the variation of the frequency of the applied current density with a square wave during the anodic oxidation under spark discharge.
