Anodizing of aluminum coated with zirconium oxide by a sol-gel process I. Effect of heat treatment on the formation of the anodic oxide film

Aluminum specimens were covered with zirconium oxide films by sol-gel dip c oating at T-h = 573 and 873 K, and then anodized galvanostatically in a neu tral berate solution. The time-variation in the anode potential during anod izing was monitored, and the structure of anodic oxide films was examined b y TEM, EDX, and RES. During anodizing of specimens coated with ZrO2 at T-h = 573 K, the anode potential, E-a, increased linearly with time, t(a), and the slope of the E-a vs, t(a) curve increased with increasing the number of sol-gel coatings. An anodic oxide film, which was composed of an inner Al2 O3 layer and an outer Al-Zr composite oxide layer, grew at the interface be tween the ZrO2 layer and metal substrate during anodizing. The thickness of the inner layer increased with t(a), whereas the thickness of the outer la yer showed a maximum before decreasing with t(a). Specimens coated with ZrO 2 at T-h = 873 K showed E-a -jumps between 40 and 110 V just after the comm encement of anodizing, and then a slow E-a increase. An anodic oxide film c omposed of a single layer of Al2O3, formed beneath the ZrO2 layer during an odizing. The mechanism of the formation of anodic oxide films on aluminum c oated with ZrO2 films is discussed in terms of ion transport across the ano dic oxide film.