Composition analysis and corrosion performance of a Mo-Ce conversion coating on AZ91 magnesium alloy

A chrome-free chemical conversion coating was deposited on the surface of AZ91 magnesium alloy in a solution containing molybdate and cerium nitrate within a short time. The morphology, composition and structure of the conversion coating were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion resistance was investigated by polarization curves. The results show that the conversion coating was homogeneous with some small cracks. The coating was mainly composed of MoO3, MoO2, CeO2, Ce2O3, MgO and Mg(OH)(2). The corrosion potential for the conversion treated sample shifted positively by approximately 90 mV from -1.54 V to -1.45 V, and the corrosion current density was decreased by approximately two orders of magnitude compared with AZ91 magnesium alloy substrate. (C) 2014 Published by Elsevier B.V.