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

摘要:

在2024铝合金表面制备纳米化-微弧氧化复合涂层，该复合涂层由底层纳米晶层及顶层陶瓷涂层构成。采用XRD、TEM和SEM研究了复合涂层的微观组织结构，并研究了表面处理对铝合金基体疲劳寿命的影响规律。顶层陶瓷涂层厚度分别为5和10 μm的复合涂层试样的疲劳寿命分别提高了21.9%和23.2%，疲劳性能的改善是基体合金靠近涂层区域的纳米晶结构及残余压应力共同作用的结果；当顶层陶瓷涂层厚度增加到15 μm时，由于涂层表面较大的孔径及涂层内部存在的微裂纹，导致疲劳寿命降低

Abstract:

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