Effect of laser formed AlN/Al 2 O 3 films on corrosion behaviour of aluminium alloy 6013

Excimer laser surface melting (LSM) was conducted on aluminium alloy 6013 with the aim of ascertaining the significance of the laser formed nitride/oxide film in providing a corrosion barrier to the alloy. Laser surface melting was performed under two different gas environments, nitrogen and air. After the laser treatment, a compact AlN and Al₂O₃ mixed film was formed at the top surface of the N₂ treated specimens, while only Al₂O₃ phase was found in the film of the air treated specimens. The laser formed film of some specimens was removed using ion etching, and their corrosion behaviour was studied. The potentiodynamic polarisation measurements showed that without ion etching, the corrosion current densities of the N₂ treated and the air treated specimens were three orders and one order of magnitude respectively, lower than that of the untreated parent alloy. After ion etching, the corrosion current densities of the laser treated specimens were considerably increased. The time dependence of the polarisation resistances of the ion etched and unetched specimens was also determined. Equivalent circuits were presented to describe the corrosion behaviour of the various laser treated and untreated specimens.