中文摘要：

为改善镁合金的生物降解性能，在镁合金AZ31表面制备氟转化层，研究氟转化层的电化学阻抗谱（EIS）在Hank’s仿生溶液中随浸泡时间的变化，并结合浸泡过程中氟转化层表面形貌和成分的变化，探讨氟转化层的形成机理及在仿生溶液中的降解行为。结果表明：氟处理后镁合金表面生成MgF2转化膜，反应过程中氢气的产生在膜层表面生成不贯穿膜层的孔隙；在Hank’s仿生溶液浸泡过程中，氟转化层电阻随浸泡时间的延长而降低，氟化镁层缓慢溶解并生成氢氧化镁。同时，溶液中的Ca^2＋、HPO4^2-和P043-等离子沉积在表面；由于氟转化层表面存在微孔，浸泡15min时，小孔腐蚀过程已经开始；浸泡至7d时，孔核表面区域的膜层溶解穿透，进入腐蚀孔的发展阶段；浸泡至15d时，发生明显点蚀；氟转化层微孔处溶解速度较大，导致Cl^-渗透至基体，镁合金发生点蚀，点蚀产生的腐蚀产物在孔中堆积形成胞状突起。

英文摘要：

Fluorine conversion film was synthesized on AZ31 magnesium alloy to improve its corrosion resistance as degradable implant material. The degradable process was studied by electrochemical impedance spectroscopy （EIS） in Hank＇s solution for different immersion times. The formation mechanism and the degradation behavior of fluorine conversion film in Hank＇s solution were discussed by investigating the variation of surface morphology and chemical composition. The results indicate that MgF2 conversion film forms on AZ31 alloy through the fluoride treatment. The evolution of hydrogen results in the formation of a very small amount of blind micro-pores in the film. With increasing the immersion period in Hank＇s solution, the corrosion resistance of MgF2 conversion coating decreases gradually. During this process, magnesium hydroxide forms with the slow dissolution of MgF2 layer, and Ca^2＋, HPO_4^2- and PO_4^3- ions deposit on the surface of the sample. The existence of micro-pore on MgF2 conversion coating leads to the initiation of pitting corrosion after immersion for 15 min. After immersion for 7 d, MgF2 layer suffers more serious corrosion damage due to the self-accelerated corrosion at the micro-pores. After immersion for 15 d, the pitting corrosion damage becomes more obvious. The in-leakage of a great amount of Cl^- ions enhances the localized corrosion of AZ31 substrate through the micro-pores in the film, where the accumulation of corrosion products results in the formation of some cystiform protuberance.