Neodymium-based Conversion Coating on AZ31 Magnesium Alloy

A neodymium-based (Nd-based) conversion coating was obtained on the surface of AZ31 magnesium alloy. The formation process of the Nd-based conversion coating was examined by a weighing experiment and an open circuit potential (OCP) test. The coating morphology, microstructure and composition were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The variation of morphology for the bare sample and the coated sample immersed in 3.5 wt% NaCl aqueous solution was investigated. The results show that the Nd-based conversion coating can effectively reduce the corrosion speed in 3.5 wt% NaCl aqueous solution. The composition and corrosion resistance of Nd-based conversion coating after post-treatment were measured by XRD and electrochemical experiments. The post-treatment can perfectly improve the corrosion resistance of the Nd-based conversion coating.