Corrosion-fatigue behavior of micro-arc oxidation coated 6061-T6 Al alloy

The corrosion-fatigue response of Al alloys becomes an important consideration for qualifying them for aero-space and other structural applications, the MAO coatings with three different thicknesses namely 10 mu m, 50 mu m and 90 mu m were provided on peened (SP + MAO) and un-peened (Plain MAO) substrates. Further, the corrosion (potentiodynamic polarization) tests in 3.5 wt% NaCl solution and corrosion-fatigue tests at 5-different maximum alternating stress levels were evaluated for each material condition. In addition, the surface roughness, surface and cross-sectional coating morphologies in as deposited and corroded conditions; fractured morphology and corrosion-fatigue crack propagation features were evaluated; correlated with the corresponding corrosion rates and corrosion-fatigue life. The results obtained highlight the role of corrosion medium in significant degradation of corrosion-fatigue life as compared to the plain-fatigue life of both bare substrate and MAO coated conditions. A new parameter namely the normalized corrosion-fatigue life index (NCFI) provides a quicker insight and possible benchmarking of the coating's ability to withstand the damaging action of simultaneous corrosion and fatigue. A 50 mu m thick SP + MAO coating was identified as a candidate choice to withstand diverse degradation modes namely the simple corrosion, plain-fatigue and corrosion-fatigue.

Automated summary

The study systematically evaluated different thicknesses of MAO coatings, corrosion-fatigue response, and crack propagation features, highlighting the aluminum alloy with a 50 μm thick SP + MAO coating shows better resistance to corrosion-fatigue life.