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

The aeronautical industry has been actively exploring novel materials that offer favorable mechanical as well as corrosion-resistant attributes for incorporation into aircraft design. 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 emerges as a potent means to enhance the corrosion resistance of these alloys, since the coating may act as a protective physical barrier. This work aims to present innovative and applied research that focuses on the production of thin films of Nb2O5 onto the surface of the 7050-T7451 aluminium alloy, achieved through the utilization of the reactive sputtering technique. The corrosion behaviour of the 7050-T7451 aluminium alloy in a 0.6 mol L−1 NaCl solution was assessed through various electrochemical techniques, including open circuit potential analysis, potentiodynamic polarization curves, electrochemical impedance spectroscopy, and immersion tests. 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 moduli 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.