EFFECT OF SEALING ON THE SURFACE MORPHOLOGY AND ELECTROCHEMICAL PROPERTY OF CERIUM-BASED CONVERSION COATING ON AZ31 MAGNESIUM ALLOY

摘要

The use of magnesium alloys in engineering applications has increased steadily in recent years. However the high chemical reactivity and the inadequate corrosion resistance limited their use. Proper surface treatments are required in order to increase the corrosion resistance. Commonly applied surface treatment is the chemical conversion in which chromate bath was traditionally applied; however, it is toxic to human and difficult to be recyclable. Non-chromate solutions have been recently developed; one of the most promising systems is based on cerium solution. In this paper, chemical conversion coating was performed onto AZ31 (3% Al, 1% Zn) magnesium alloy by immersion in 0.05 M Ce(NO_3)_3. Sealing of the film in 1 M NaOH and 10 g dm~(-3) Na_2SiO_3 solution further enhanced the anti-corrosion property and the surface properties of the film. The structure, morphology, and composition of the films were determined by optical microscope, SEM and EDS.