Titanium based conversion coatings on aluminium alloy 3003

The performance and characteristics of a no rinse, titanium based conversion coating on an aluminium alloy have been studied using electrochemical techniques and transmission electron microscopy. Coatings were prepared from an aqueous H₂ TiF₆ solution, spin coated onto aluminium alloy 3003. The electrochemical behaviour evolves with time during exposure to 0·5% and 3·5%NaCl. Polarisation curves and impedance data correspond well and indicate that the anodic inhibition and polarisation resistance increase dramatically with time. However, no cathodic inhibition is found. Metastable pitting was observed at potentials below the pitting potential. TEM micrographs taken from 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 appears at the substrate/coating interface.