Excimer laser surface treatment of aluminum alloy AA7075 to improve corrosion resistance
By Zheludkevich, Mikhail L.; Serra, Ricardo; Montemor, M. Fatima & Ferreira, Màrio G.S.
Published in Surface and Coatings Technology
2004
Abstract
Excimer laser surface treatment was found to be an effective method for improving the pitting corrosion resistance of the aluminum alloy 7075. The results of the TEM study showed that laser surface melting of the alloy at an intensity of 10.3 J/cm2 resulted in the elimination of coarse second-phase particles in the laser-melted zone. More importantly, two compact layers containing aluminum oxide were formed on top of the laser-melted surface. Potentiodynamic polarization tests showed that as a result of the laser treatment, the corrosion current can be reduced by as much as six times, and a passive region was obtained. Besides, the analysis of the electrochemical impedance measurements showed that at an open-circuit potential (OCP), the polarization resistance and double-layer capacitance of the film/electrolyte interface of the laser-treated specimen were one order of magnitude higher and six times lower than that of the untreated specimen, respectively. Furthermore, when tested at OCP+50 mV, the untreated specimen suffered serious pitting corrosion, while a passive film had formed on the laser-treated specimen, which served as an effective barrier for reducing anodic dissolution.