Effect of excimer laser surface treatment on corrosion behaviour of aluminium alloy 6013

Excimer laser surface treatment of aluminium alloy 6013-T651 was conducted with the aim of improving the intergranular corrosion resistance of the alloy. Laser surface treatment was performed under two different gas environments: air and nitrogen. The microstructure, phase, and composition of the modified surface structure were analysed using TEM, X-ray photoelectron spectroscopy, and EDX; the electrochemical and the intergranular corrosion cracking behaviours of the untreated and the laser treated specimens were evaluated by electrochemical polarisation test and immersion test respectively. Excimer laser surface treatment significantly increased the pitting potential and the intergranular corrosion resistance of the alloy, especially when the material was treated in nitrogen gas. A reduction in corrosion current density of three orders of magnitude was obtained for the N-2 treated material. The improvement is considered to be primarily owing to the reduction of large harmful intermetallics within the grains and the absence of precipitate free zones and Al - Cu - Si bearing needle like precipitates at the grain boundaries. The superior corrosion resistance of the N-2 treated material is attributed to the presence of the chemically stable AlN phase in the surface. (C) 2002 IoM Communications Ltd.