High-Cycle Fatigue Behavior of Microarc Oxidation Coatings Deposited on a 6061-T6 Al Alloy

The objective of this article is to evaluate the influence of microarc oxidation (MAO) coatings on the high-cycle rotating bending fatigue behavior of the 6061-T6 aluminum alloy. Toward this purpose, the influence of the MAO coating process parameter (current density) and coating thickness on the fatigue life of the 6061-T6 Al alloy has been evaluated in the present study. In addition, the influence of the coating roughness on the fatigue life of the MAO-coated 6061-T6 Al-alloy sample has also been investigated. The results indicate that the high-cycle fatigue life of the 6061-T6 Al alloy is substantially degraded due to the presence of MAO coatings, especially at lower alternating stress values and for thicker coatings. Surface roughness, altered by polishing, does not have any effect on fatigue life. An examination of coated samples interrupted at various fractions of fatigue life leads to the conclusion that the crack propagates from the coating surface to the coating-substrate interface very rapidly and thus fatigue life is largely controlled by the propagation of the crack into the substrate.