Effect of additives on structure and corrosion resistance of plasma electrolytic oxidation coatings on AZ91D magnesium alloy in phosphate based electrolyte

• Published in: Surface & coatings technology 2010-12, Vol.205, p.S36-S40
• Main Authors: Lv, Guo-Hua, Chen, Huan, Wang, Xing-Quan, Pang, Hua, Zhang, Gu-Ling, Zou, Bin, Lee, Heon-Ju, Yang, Si-Ze
• Format: Article
• Language: English
• Subjects: Additive; AZ91D Mg alloy; Coatings; Corrosion resistance; Diffraction; Electrolytes; Magnesium base alloys; Oxidation; Phosphate electrolyte; Phosphates; Plasma electrolytic oxidation; Protective coatings; Scanning electron microscopy
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2010.03.035

Plasma electrolytic oxidation (PEO) coatings were prepared on magnesium alloy AZ91D in a phosphate based electrolyte with different additives such as sodium fluoride (NaF) and sodium aluminate (NaAlO 2). The effects of F − and AlO 2 − additives on the morphology, phase structure and corrosion resistance of PEO coatings were examined by scanning electron microscopy (SEM/EDX), X-ray diffraction (XRD) and potentiodynamic polarization. The results show that PEO coatings produced in F − additive solution grow faster than that in AlO 2 − additive one. However, the growth rate decreases with treatment time in F − additive solution while it increases in AlO 2 − additive one. It is also found that the corrosion resistance is greatly improved after PEO treatment, and coatings produced in F − additive solution show lower corrosion current density than that in AlO 2 − additive solution.