RELEASE OF CHROMATE IONS FROM CHROMATE CONVERSION COATINGS ON AL ALLOYS

摘要

This work attempts to understand the ion-release behavior from chromate conversion coatings (CCCs) on Al alloys, and also aims to investigate the effect of aging of CCC on the release kinetics of chromate ions. The release of chromate ions from CCCs was studied by measuring the change in the concentration of chromates in solutions using UV adsorption spectroscopy. Heat treatment greatly reduced the ion-release rate. The release rate of chromates decreased with increasing RT aging time at room temperature. A diffusion-control model was proposed based on the notion of a concentration gradient of soluble Cr(VI) in CCCs. The concentration and diffusion coefficient of soluble Cr(VI) in CCC were estimated. The estimated diffusion coefficient tended to decrease with aging time suggesting that the CCC is modified with aging time.