EFFECT OF Sn~(4+) ADDITIVES ON THE MICROSTRUCTURE AND CORROSION RESISTANCE OF ANODIC COATING FORMED ON AZ31 MAGNESIUM ALLOY IN ALKALINE SOLUTION

摘要

Magnesium is the lightest structural metal with high specificstrength and good mechanical properties. However, poorcorrosion resistance limits its widespread use in manyapplications. Magnesium is usually treated with chromateconversion coatings. However, due to changing environmentalregulations and pollution prevention requirements, a significantpush exists to find new, alternative for poisonous Cr~(6+). Therefore,we aim to improve corrosion resistance of anodic coatings onAZ31 alloys using low cost non-chromate electrolyte. Anodizingwas carried out in alkaline solutions with tin additives. The effectof tin additives on the coating film was characterized by SEM andXRD. The corrosion resistance was evaluated using anodic andcathodic polarizations and electrochemical impedancespectroscopy (EIS). Corrosion resistance property was improvedwith tin additives and the best anti-corrosion property wasobtained with addition of 0.03 M Na_2SnO_3.3H_2O to anodizingsolution.