Corrosion protection of aluminium alloy by cerium conversion and conducting polymer duplex coatings

The corrosion protection of AA6063 aluminium alloy by cerium conversion, polyaniline conducting polymer and by duplex coatings has been investigated. The electrochemical behaviour was evaluated in aerated 3.5 wt.% NaCl. All coatings tested shifted the corrosion and pitting potentials to more positive values, indicating protection against corrosion. The duplex coatings are significantly more effective than each coating alone: corrosion and pitting potentials were shifted by +183 and +417 mV(SCE), respectively, by duplex coatings in relation to the untreated aluminium alloy. Optical microscopy and scanning electron microscopy are in agreement with the electrochemical results, reinforcing the superior performance of duplex coatings.

► Cerium conversion coating must be preceded by alkaline surface treatment.
► Cerium conversion coating promotes the anchoring of the PAni conducting polymer.
► PAni coating presents active corrosion protection associated with a barrier effect.
► Duplex coatings show superior corrosion protection than each coating alone.
► A scheme representing the treatment stages for the duplex coating is shown.