The effects of Mn concentration on the tribocorrosion resistance of Al-Mn alloys

An increase in the complexity and severity of service conditions demands improvements in the design of new engineering materials that are resistant to the effects of tribocorrosion. Unfortunately, there is typically a tradeoff between wear and corrosion resistance, even for important passive metals such as Al alloys. In this work, it was shown that alloying Al with Mn in supersaturated solid solution simultaneously increased the wear resistance of the Al as well as the protectiveness of the passive layer, thus improving the overall tribocorrosion resistance. Specifically, the effects of Mn alloying on the tribocorrosion behavior of magnetron-sputtered Al- Mn thin films with 5.2 at.% and 20.5 at.% Mn were investigated in a 0.6 M NaCl aqueous solution. Tribocorrosion resistance was found to be strongly affected by the alloying concentration and applied potential. Higher Mn content increased the ratio of hardness to elastic modulus (H/E) and promoted the formation of denser and more compact passive film, hence improving tribocorrosion resistance of Al. In particular, alloying with 20.5 at.% Mn led to an increase of the corrosion resistance by similar to 10 times and the hardness by similar to 8 times compared to pure Al. The total material loss during tribocorrosion was found to increase with the anodic shift of the applied potential. A galvanic cell model was used to investigate the depassivation-repassivation kinetics during tribocorrosion. It was found that alloying with 5.2 at.% Mn led to more than 10-fold reduction in the current density required to re-passivate similar worn areas of pure Al. Finally, the origin of wear-corrosion synergy was discussed based on these observations. (C) 2017 Elsevier B.V. All rights reserved.