Effect of Nb2O5 coating on the corrosion resistance of the 7050-T7451 aluminium alloy

Abstract The aircraft industry has been searching for new materials to be used in their aircrafts, which provide good mechanical and corrosive properties. The 7xxx series aluminium alloys are widely used in structural components. However, these alloys are susceptible to localised corrosion processes when exposed to an aggressive environment, which affect their lifetime and performance. Surface treatment appears as a powerful tool to improve the corrosion resistance of these alloys, since the coating may act as a protective physical barrier. This work aims to present an innovative and applied research for the development of the Nb2O5 thin films on the 7050-T7451 aluminium alloy surface by using the reactive sputtering technique. The open circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy as well as immersion tests were used to access the corrosion behaviour of the 7050-T7451 aluminium alloy in 0.6 mol L-1 NaCl solution. The morphology of the coated and uncoated specimens was verified by using optical microscopy, AFM and SEM/EDX techniques. Results demonstrated a difference of about 315 mV between the pitting potential (Epitting) and corrosion potential (Ecorr) for the coated material, indicating the positive effect of Nb2O5 thin films on the corrosion resistance of the alloy. In addition, EIS results displayed the reactive sputtering technique was advantageous, since the impedance modulus increased significantly. Finally, the EIS measurements corroborate with the AFM results, showing the Nb2O5 coating at the beginning of the corrosion tests is about 300 nm in thickness. To the best of our acknowledgement, this is the first study concerning the improvement of the corrosion properties of 7050-T7451 aluminium alloy by using the methodology presented in this work.