Corrosion Behaviors of Aluminate Coatings on Mg Alloy AE44

ABSTRACT: Chromate-based corrosion protection, such as that on aluminum (Al), magnesium (Mg), titanium (Ti), and other alloys, has often been used with some success. Considering the pollution problem associated with chrome, it is necessary to search for an alternative process to conventional chromate coating technology. Plasma electrolytic oxidation processing (PEO) is an emerging, environmentally friendly surface engineering technique. The study in this article was to utilize the PEO technology to deposit aluminate coatings on magnesium alloy AE44 for corrosion protection. Potentiodynamic polarization measurements and electrochemical impedance tests were performed to investigate corrosion behaviors of coated and uncoated AE44 alloy samples immersed in 3.5 wt% NaCl solution. The surfaces of coated and uncoated samples before and after corrosion tests were observed by scanning electron microscopy (SEM). SEM and energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD) were used to study the effect of PEO coatings on the surface morphology change of the alloy in association to their corrosion behaviors. The differences in corrosion behaviors under different electrical parameters of aluminate-based coatings on Mg alloy AE44 were elucidated through potentiodynamic polarization measurements, complemented by SEM and EDS analysis.