ELECTROCHEMICAL AND CORROSION BEHAVIOR OF BN-COATED ALUMINUM-ALLOY SURFACES

Reactive ion-beam-assisted deposition (RIBAD) has proved to be a very effective surface treatment in order to obtain-homogeneous and protective coatings. In a previous work we showed the very promising role of boron and chromium nitride coatings obtained by RIBAD in order to reduce the corrosion rate of ARMCO iron. In this work, which is part of a wider study concerning the aluminium surface treatments, we present some results concerning the corrosion behaviour of industrial aluminium alloys coated with a BN layer obtained by RIBAD. The BN film was produced by 11 sequential steps, each consisting of a boron deposition of 26 nm, followed by an N2 implantation to a total dose of 15.8 × 1017 nitrogen atoms cm-2. For the sake of comparison, BN layers 3000 angstrom thick were also obtained on pure aluminium and on aluminium alloys by the radio-frequency magnetron sputtering technique. All the treated samples were tested in different aqueous environments. The corrosion rate was measured in sodium hydroxide and sodium sulphate solutions at different pH values (3.2, 10 and 12) by using electrochemical techniques. The BN film showed a protective action which improved the corrosion resistance of aluminium alloy in the sodium sulphate solutions. Moreover, the RIBAD coatings proved to be more effective with respect to the sputtered ones as a consequence of better substrate-film adhesion.