Preparation and characterization of colored Ti/Zr conversion coating on AZ91D magnesium alloy

A golden-yellow Ti/Zr conversion coating on A291D substrate was successfully prepared in the solution containing titanium and zirconium ions with the addition of tannic acid. The growth process, microstructure, composition and corrosion resistance of this conversion coating were characterized by EDS, SEM, XRD, XPS, FTIR and electrochemical workstation. The application of H2ZrF6 and tannic acid was the key to the coating color. The coating possessed a double-layer structure, in which the inner layer was made up of Mg(OH)(2), MgO, TiO2, ZrO2, and MgF2, and the outer layer was metal-organic complex. The IT electronic chromophore in the metal-organic complex produced the conversion coating color. The coating was uniform and compact, leading to improved corrosion resistance and significantly reduced corrosion current density (from 93.72 mu A.cm(-2) to 1.047 mu A.cm(-2)). (C) 2015 Elsevier B.V. All rights reserved.