The effect of phosphate on MAO of AZ91D magnesium using AC power source

✍ Scribed by Q. Wen; F.-H. Cao; Y.-Y. Shi; Z. Zhang; J.-Q. Zhang

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: German
• Weight: 570 KB
• Volume: 59
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.200804169

✦ Synopsis

Abstract

A rapid and convenient anodization technology with AC power source to obtain the MAO films formed on magnesium alloy AZ91D in phosphate bath (base electrolyte + Na~3~PO~4~) with or without aluminate and silicate was studied. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques and the microstructure and composition of films were examined by SEM and XRD. The results show that Na~3~PO~4~can promote the occurrence of sparking during the MAO process, while abundant heat generated by sparking might enhance the formation of the glassy phase of the compound when the electrolyte contains the additives of NaAlO~2~and Na~2~SiO~3~simultaneously. The optimized MAO film is ivory‐white smooth by naked eye, while presents porous and microcracks in microscopic scale. The anodic film formed in the alkaline solution with optimized parameters possesses superior corrosion resistance by electrochemical test. The XRD pattern shows that the components of the anodized film consist of MgO, MgAlO~2~, and MgSiO~3~. No oxide crystal with P element can be found.