Laser cleaning has been considered as a promising technique for the preparation of aluminium alloy surfaces prior to joining and welding and has been practically used in the automotive industry. The process is based on laser ablation to remove surface contaminations and aluminium oxides. However the change of surface chemistry and oxide status may affect corrosion behaviour of aluminium alloys. Until now, no work has been reported on the corrosion characteristics of laser cleaned metallic surfaces. In this study, we investigated the corrosion behaviour of laser-cleaned AA7024-T4 aluminium alloy using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The results showed that the laser-cleaned surface exhibited higher corrosion resistance in 3.5 wt.% NaCl solution than as-received hot-rolled alloy, with significant increase in impedance and decrease in capacitance, while SVET revealed that the active anodic points appeared on the as-received surface were not presented on the laser-cleaned surfaces. Such corrosion behaviours were correlated to the change of surface oxide status measured by glow discharge optical emission spectrometry (GDOES) and X-ray photoelectron spectroscopy (XPS). It was suggested that the removal of the original less protective oxide layer consisting of MgO and MgAl 2 O 4 on the as-received surfaces and the newly formed more protective oxide layer containing mainly Al 2 O 3 and MgO by laser cleaning were responsible for the improvement of the corrosion performance.

Laser cleaning of metallic alloys for the purpose of removal of metal oxide layers is based on laser thermal ablation. In laser thermal ablation, the interaction between the laser beam and oxide layer may generate significant thermal effects to induce additional thermal oxidation or even melting a thin layer of the underlying surface. The change of surface oxide status may subsequently affect corrosion behavior of the metallic alloys. In this work, the effects of laser cleaning on corrosion behavior of hot-rolled AA5083-O aluminum alloy were investigated using electrochemical impedance spectroscopy. The results showed that the laser-cleaned surfaces exhibited higher corrosion resistance in 3.5 wt. % NaCl solution than the as-received alloy, with a significant increase in impedance and reduction in capacitance. The corrosion behavior was correlated to the change of surface oxide status measured by glow discharge optical emission spectrometry, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. It was concluded that the laser cleaning removed the original, less protective oxide layer consisting of a discontinuous MgO/MgAl2O4 outer layer (∼20 nm) and MgO/MgAl2O4 particles dispersed inner layer (∼300 nm) on the as-received surface but resulted in the formation of more protective oxide layer containing mainly Al2O3 and MgO, which were responsible for the improvement of the corrosion performance. The laser fluence played an important role in determining the thickness of the newly formed oxide layers that subsequently affected the corrosion performance of laser-cleaned alloy.

No abstract