Residual stress relaxation and duty cycle on high cycle fatigue life of micro-arc oxidation coated AA7075-T6 alloy

•The residual stress relaxation in ceramic coating was found.•The mechanism of residual stress relaxation was revealed.•The nature of residual stress in ceramic coating was discussed.•Effect of residual stress relaxation and crack tip bunting on fatigue life was studied. Ceramic coatings were produced on AA7075-T6 alloy by micro-arc oxidation (MAO). The MAO treatment was performed at different duty cycles (8, 10, 15, and 20%). Effects of duty cycle on microstructure and fatigue behavior of the coated samples were investigated. Surface features and cross-section morphology, and fatigue fracture were observed by SEM and laser microscope. Phase structure and residual stress in the coatings were analyzed by X-ray diffraction. The nature and relaxation mechanism of the residual stress were revealed. Finally, the influence of the residual stress relaxation on the fatigue life at high and low cyclic stresses was explored.