PVD DLC Coatings For Corrosion Protection On A 7075-T6 Substrate At Long And Short Fatigue Lives

7075-T6 is the most widespread structural high strength-to-mass ratio light aluminium alloy, due to its high mechanical strength, granted by the T6 temper. Its usage in critical aeronautic, maritime and automotive sectors is however limited by the inherent susceptibility of T6 treatment to pitting corrosion, which can led to dramatic reduction in fatigue strength. In order to improve the alloy fatigue behaviour in aggressive environments, several authors have proposed different coating technologies to protect the substrate. In recent studies, the effects of PVD thin hard coatings, successfully adopted over hard steel substrates to increase hardness and fatigue strength at long lives, have been investigated also concerning fatigue behaviour and corrosion protection on light alloys. Residual stresses, thermal modification of the substrate and mechanical interaction between thin hard coatings and aluminium substrate lead to different contributions to the fatigue strength of 7075-T6 at different lives, i.e. different applied stress levels. In the present work, the rotating bending fatigue behaviour (R = -1) of 7075-T6 PVD DLC coated specimens is investigated, both in air and in corrosive environment. The tests are conducted for nominal fatigue lives of 2e5 and 1e7 cycles, to assess the different level of applied stresses in the fatigue and corrosion fatigue of PVD DLC coated 7075-T6 aluminium alloys. SEM micrographs of the fracture surface are provided, to investigate the influence of mechanical and environmental driving forces on the failure mechanism.