Titanium based conversion coatings on aluminium alloy 3003

The performance and characteristics of a no rinse, titanium based conversio n coating on art aluminium alloy have been. studied using electrochemical t echniques and transmission electron microscopy. Coatings were prepared from an aqueous H2TiF6 solution spin coated onto aluminium alloy 3003. The elec trochemical behaviour evolves With time during exposure to 0.5% and 3.5% Na Cl. Polarisation curves and impedance data correspond well and indicate tha t the anodic inhibition and polarisation resistance increase dramatically w ith time. However; no cathodic inhibition is found. Metastable pitting was observed at potentials below the pitting potential. TEM micrographs taken f rom cross-sections of coated material show that the coating thickness is of the order of 30 nm and that with immersion a mixed metal oxide layer appea rs at the substrate/coating interface.