The chemical treatment of the AZ31-Magnesium alloy surface by a high-performance corrosion protective praseodymium (III)-based film

Highlights: • Rare earth cations Pr provided cathodic inhibition by precipitating onto cathodic intermetallic particles and stifling oxygen reduction, and therefore, reducing the overall corrosion rate. • The effect of addition of Praseodymium ions on the corrosion inhibition performance of conversion coatings for AZ31 magnesium alloy. • To boost the corrosion resistance of Mg, the application of several types of coatings have been proposed. This study deals with the Mg-AZ31 alloy anticorrosion properties improvement via a novel surface treatment method. In this regard, the praseodymium (Pr)-based film formation on the Mg-alloy surface at different film formation conditions (i.e., pH, time, temperature) were investigated. The composition of the generated Pr-based film on the Mg-AZ31 alloy surface was characterized in depth using atomic/microscopic level techniques, i.e., X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and contact angle (CA) test. The influence of Pr film on the polyurethane (PU) coating adhesion properties and corrosion protection performance were studied by the pull-off test, neutral salt spray (NSS), and electrochemical impedance spectroscopy (EIS) analyses, respectively. FE-SEM micrographs revealed that the metal surface was covered with a Pr film, which has brought about a rough surface. Applying the Pr film to the Mg alloy surface has caused significant improvement in the corrosion resistance characteristics. A 94.84% corrosion retardation potency was recorded for the Pr-modified Mg alloy at the optimum surface chemical treatment condition. A significant improvement in the adhesion degree (about 64%) was obtained for the PU film on the Mg alloy modified by an optimized Pr film. Results have declared that the Pr-based film could improve the Mg alloy corrosion resistance by affecting the anodic/cathodic reactions through the formation of insoluble and electrically insulate inorganic film and enhancing the PU adhesion by providing a surface with high energy/wettability and micro-nano scales roughness.