Comparison in characterization of composite and
sol-gel coating on AZ31 magnesium alloy
sol-gel coating on AZ31 magnesium alloy
(1. College of Chemistry and Life Science, Shenyang Normal University, Shenyang 110034, China;
2. State Key Laboratory for Corrosion and Protection, Institute of Metal Research,
Chinese Academy of Sciences, Shenyang 110016, China)
2. State Key Laboratory for Corrosion and Protection, Institute of Metal Research,
Chinese Academy of Sciences, Shenyang 110016, China)
Abstract: An Al2O3 protective coating on magnesium alloy AZ31 was prepared by a repeated direct sol-gel process annealing at 300 ˚C and a composite coating was also deposited using Al2O3 particles dispersed sol followed by phosphating treatment and annealing at 300 ˚C. The morphologies, structures and critical adhesive loads as well as corrosion properties of the coatings were comparatively investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), nanoscratch test and electrochemical measurement. The results show that the composite coating has a more uniform, crack-free layer and improved adhesion to the substrate as compared with that of the repeated direct sol-gel coating owing to its lower heat strain. The main phases in both coatings consist of γ-Al2O3 and δ-Al2O3 derived from annealed alumina sol, and the composite coating has an anticorrosion performance which is superior to that of the repeated direct sol-gel coating.
Key words: sol-gel; composite coating; magnesium alloy