Formation of a zirconium-titanium based conversion layer on AA 6060 aluminium

Structure and chemistry of zirconium-titanium base conversion layers were characterised as a function of immersion time in the aqueous conversion bath to understand the mechanism of film formation. Characterisation was performed by glow discharge optical emission spectroscopy, scanning electron microscopy and transmission electron microscopy. Preferential nucleation of the zirconium-titanium oxide film and its growth occurred on and around intermetallic particles, resulting in reduced cathodic activity of the particles. Passivation of the cathodes in this manner constituted a limitation in the formation of a good quality conversion layer.