Abstract
Anodizing characteristics of Al in high temperature solutions of tartaric, malic and malonic acids were investigated. Aluminum sheets of 99.99% were anodized in 1 and 3mol/l solutions of these acids at 40-80°C and at current densities of 4.67-18.7A/dm2. Uniform and integral-colored films without cracks were formed on Al at relatively high temperatures and low current densities. Bath voltage during anodizing in the malonic acid bath was below 100V, whereas in the tartaric or malic acid bath it was above 150V. In the malonic acid bath, hard films of Hv 450-550 were obtained only below 60°C, whereas in the tartaric and malic acid baths hard films of Hv 550-700 were produced even at temperatures between 60 and 80°C. Hardness values generally increased with elevating temperatures, lowering concentrations and increasing current densities, viz, with increasing bath voltage. The coating ratio increased as temperature was lower and current density higher. In the tartaric acid bath, the recovery of current was observed after a sudden drop of anodizing voltage. During the recovery, the size of the cell became smaller and the number of the cell increased. Therefore, anodic oxidation of Al in these baths was found to be essentially the same as that in sulfuric or oxalic acid bath.
