为提高AZ91D镁合金的硬度和耐蚀性，采用无氢氟酸的化学镀工艺在其表面制备双层Ni - P镀层，并通过金相显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDS)、显微硬度计、电化学工作站对镀层的组织结构、成分、显微硬度和耐蚀性进行表征分析，确定最适宜的双层工艺。结果表明：采用先碱性后酸性双层化学镀工艺，所得镀层与基体结合良好，厚度为26.28 μm，表面均匀致密，线粗糙度Ra为0.623 μm；该工艺下镀层硬度为550.54 HV，较基体提升7.9倍；内层P含量为3.209%，具有晶体结构，存在裂纹孔洞，外层P含量为9.713%，具有非晶结构缺陷少的特点，可以覆盖内层缺陷处，提高耐蚀性；该工艺制备的镀层的腐蚀电位较基体正移719 mV，自腐蚀电流密度较基体降低2个数量级。
In order to improve the hardness and corrosion resistance of AZ91D magnesium alloy, a double - layer Ni - P coating was prepared on its surface by electroless plating without hydrofluoric acid, and the optimal double - layer process was determined by characterizing the microstructure, composition, microhardness and corrosion resistance of the coating through the utilization of metallographic microscope, scanning electron microscope (SEM), X - ray diffractometer (XRD), Energy dispersive spectrometer (EDS), microhardness tester and electrochemical workstation. Results showed that the coating obtained by first alkaline and then acid double - layer electroless plating process adhered well to the substrate, and possessed a thickness of 26.28 μm, a uniform and dense surface, and a linear roughness Ra of 0.623 μm. The obtained coating hardness by this process was 550.54 HV, which was 7.9 times higher than that of the substrate. Moreover, the inner layer with a P content of 3.209% had a crystal structure and crack holes, and the outer layer with a P content of 9.713% had few amorphous structure defects, which could cover the inner defects to improve corrosion resistance. Besides, compared with the substrate, the corrosion potential of the coating prepared using this process shifted positively by 719 mV and the self - corrosion current density was reduced by 2 orders of magnitude.
