Enhancement in sustained friction and wear resistance of nanoporous aluminum oxide films obtained by controlled electrochemical oxidation process

Abstract

The primary purpose of this study is to investigate the effect of the electrochemical parameters required in the anodic oxidation process on the friction and wear resistance of the obtained nanoporous aluminum oxide films. The wear resistance of the aluminum oxide films and the electrochemically polished Al1050 alloy were tested using a ball-on-disc tribometer having a corundum ball as counterbody in dry conditions. The friction coefficient graphs were recorded during wear tests at a 5 N normal force simulating the application of nanoporous aluminum oxide films in industrial areas requesting moderate wear resistance. The wear tracks formed on the tested surfaces were analyzed ex situ both qualitatively and quantitatively. Higher wear resistance is showed by nanoporous aluminum oxide films as compared with electro polished Al1050 alloy substrate.

Fig. 1. Schematic drawing of the contact between the electrochemically polished or oxidized aluminum alloy surface and the alumina ball during tribological tests.

Fig. 2. SEM surface morphology of: (a) electrochemically polished Al1050 alloy; (b) nanoporous Al₂O₃ film formed at 15 V imposed potential; (c) nanoporous Al₂O₃ film formed at 18 V imposed potential and (d) nanoporous Al₂O₃ film formed at 21 V imposed.

Fig. 3. SEM-EDX surface spectrum analysis of: (a) electrochemically polished Al1050 alloy; (b) nanoporous Al₂O₃ film formed at 15 V imposed potential; (c) nanoporous Al₂O₃ film formed at 18 V imposed potential; (d) nanoporous Al₂O₃ film formed at 21 V imposed potential.

Fig. 4. SEM cross section micrographs of nanoporous aluminum oxide films obtained by electrochemical oxidation during 45 minutes at: (a) 15 V; (b) 18 V; (c) 21 V.

Fig. 5. Evolution of film thickness: (a) vs. applied potential to obtain nanoporous aluminum oxide film; (b) vs. duration of anodic oxidation process to obtain nanoporous aluminum oxide film.

Fig. 6. Friction coefficients of electropolished aluminum alloy and nanoporous aluminum oxide films versus time. Influence of the anodic oxidation potential on the variation of the friction coefficients: (1) electrochemically polished Al1050 alloy; (2) nanoporous Al₂O₃ film formed at 15 V imposed potential; (3) nanoporous Al₂O₃ film formed at 18 V imposed potential and (4) nanoporous Al₂O₃ film formed at 21 V imposed potential.

Fig. 7. SEM micrographs corresponding to the wear pattern formed on: (a) the electrochemically polished Al1050 substrate; (c) nanoporous aluminum oxide film obtained at 15 V imposed anodization potential; (e) nanoporous aluminum oxide film obtained at 18 V imposed anodization potential; (g) nanoporous aluminum oxide film obtained at 21 V imposed anodization potential. (b, d, f and h) are SEM micrographs of wear debris inside the tracks at a higher resolution corresponding to the tracks (a, c, e and g).

Fig. 8. Wear volume loss calculated from wear tracks (a) and wear rate (b) for electro polished Al1050 alloy nanoporous aluminum oxide films obtained at imposed potential of 15, 18 and 21 V.