Effect of zirconium alkoxide on structure of sol--gel conversion coating and adhesion of primer thereon.

A conversion coating was formed on the surface of TC4 titanium alloy by sol--gel method in a solution comprising organic silane and zirconium alkoxide as main components with ethanol as solvent. The surface morphology and composition, and element distribution and valence state of oxygen along the depth direction of coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), glow discharge mass spectrometry (GDMS), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties and structure of the conversion coating were examined by electrochemical impedance spectroscopy (EIS). The effect of zirconium alkoxide content on the adhesion of organic primer coat was studied by long-term damp-heat test. The results showed that the sol--gel conversion coating consisted of an inorganic layer, which was mainly composed of covalently bonded Ti-O-Zr/Si structure, and an organic layer, which was formed by the crosslinking reaction of carbon chains attached to the silane. The sol--gel conversion coating obtained with 2 000 mg/kg of zirconium alkoxide featured the best structure integrity, and the primer sprayed on it had excellent adhesion and durability. [ABSTRACT FROM AUTHOR]