EFFECTS OF ALUMINIUM ION DISSOLVED IN ELECTROLYTE ON PROPERTIES OF ANODIC OXIDE FILM OF ALUMINIUM (PART 2)

Abstract

We reported previously in this journal1) on the effect of Al ion in aluminium anodic oxidation by 15% sulphuric acid.That report discussed the effects of dissolved aluminium ion on specific electric conductivity of electrolyte, current density and properties of anodic film.In this report, we studied the effects of Al ion dissolved in electrolyte on properties of oxide film of Al anodized in oxalic acid at our production shop and our laboratory.We studied the relation between the increase of dissolved Al ion and current quantity (A. H.) at our production shop, and the effects of Al ion on the specific electric conductivity, current density and properties of anodic oxide film, at our laboratory.The results are as follows.(1) The increase of dissolved Al ion is proportional to current quantity (A. H), and the dissolved Al ion increases at the rate of 0.0085gr/A. H.(2) Concentration of oxalic acid is proportional to specific electric conductivity, and this relation is shown by following experimental formula.K=0.0060+0.0120x x=concentration of H2C2O4% 0.5<x<3.Concentration of Al ion has little effect on specific electric conductiviy. As it has, however, the property which prevents the current in anodizing, the increase of dissolved Al ion lowers the current density.(3) The effects of Al ion on the properties of anodic oxide film are summarized as follows.When the electrolitic voltage is constant (AC 80V, AC 70V, + DC35V), current density decrease by the effect of Al ion. And then film thickness becomes thinner.The corrosion resistance of anodic oxide film lowers til the dissolved Al ion increases up to 2g/l, but when the content of Al ion increases above 2g/l, it becomes rather better.The abrasion resistance of anodic oxide film is rapidly lower as the dissolved Al ion increases. According to the results of the constant electric power anodizing keeping the oxide film at constant thickness, the effects of Al ion on corrosion resistance and abrasion resistance have the same tendency as above mentioned, although the effect of the film thickness has been eliminated.