Effect of Continuous Rotation Evolutional Control on the Pitting Corrosion Resistance of Anodized Aluminum-Magnesium Alloy

Abstract

  The effect of continuous rotation evolutional control (CREO) on the pitting corrosion resistance of anodized Al-Mg alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl³ and by surface analysis. The potentials for pitting corrosion of Al-Mg alloy was evidently shifted to the less noble direction by CREO and the time required before initiating pitting corrosion was shorter with CREO, indicating that the corrosion resistance was worse with CREO than without. The precipitates of Fe-Al intermetallic compounds remained in anodic oxide films of Al-Mg alloy. Cracks occurred in the anodic oxide films through the precipitates during initial pitting corrosion. The pitting corrosion was accelerated by cracks. The internal stress present in the anodic oxide films was higher in the alloys with CREO than without. It is assumed that the pitting corrosion is promoted by these cracks as a result of the higher internal stress resulting from the CREO.