A seminar is delivered by Prof. Sungmo Moon (Korea Institute of Materials Science (KIMS) and Korea University of Science and Technology (UST), South Korea). The seminar is organised as a part of the programme of 2 month stay of Prof. Moon at CCRM group of MULTIMAT consortium (Dept. of Materials Science, Faculty of Chemical Sciences, Complutense University of Madrid).
Corrosion behavior of AZ31 Mg alloy was studied in chloride and alkaline solutions, and two different surface treatments of chemical conversion coatings and plasma electrolytic oxidation (PEO) coatings were prepared on AZ31 Mg alloy for corrosion protection. Fe-containing impurity particles were found to be present at the positions where continuous gas evolution occurs in chloride and alkaline solutions. Corrosion of AZ31 Mg alloy was not initiated around the cathodic particles but occurred preferentially at the scratches, showing that protective properties of surface film is crucial in the initiation of corrosion. Formation of thick oxide film around cathodic particles can explain why corrosion is not initiated around the cathodic particles. Denser and thinner surface films were more effective in the corrosion protection if E-paint is applied to the film surface. PEO coatings were found to be very effective in corrosion protection if they are sealed. PEO films were formed only when oxide forming anions are present together with OH- ions, and PEO film formation on Mg alloys is critically dependent upon the applied current form. PEO film formation behavior was investigated by voltage-time curves and epoxy replicas of pores in the PEO films.