Design and Characterization of SMAT-MAO Composite Coating and Its Influence on the Fatigue Property of 2024 Al Alloy

SMAT-MAO composite coating, consisting of a bottom nanocrystalline layer and a top ceramic coating, was designed and fabricated on the surface of 2024 Al alloy. The microstructure and the phase composition of SMAT-MAO coating were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The fatigue life of the treated alloy was evaluated. The results indicate that the SMAT-MAO coated samples with 5 and 10 μm thick ceramic coatings exhibit improved fatigue lifetime, increasing by 21.9% and 23.2%, respectively. The improved fatigue property is attributed to the combined effect of nanocrystalline structure and the residual compressive stress induced in the substrate near the ceramic coating. With ceramic coating thickness increasing to 15 μm, the fatigue lifetime of the SMAT-MAO coated sample is lightly reduced due to the protrudent degrading effect caused by the much bigger pores and pre-existing micro cracks on the coating surface.