【作者】 刘妍；

【导师】 张昭；

【作者基本信息】 浙江大学 ， 物理化学， 2012， 博士

【摘要】 由于密度小、易于加工及力学性能优异,镁合金在航空、航天、军工、交通工具、生物医学、电子产品等领域应用前景广阔。不过,镁合金化学稳定性差,在大气环境中能和氧、水及氯盐等发生反应而导致锈蚀损坏现象,限制了其实际应用,尤其是在腐蚀性环境中。因此,提高镁合金的耐腐蚀性已经成为该领域重要的研究方向之一。本论文概述了镁合金的特点、应用、腐蚀原因及防护技术,并结合当今镁合金表面防护技术的发展趋势,在课题组前期工作的基础上开展了绿色环保型镁合金微弧氧化工艺开发、电解液添加剂作用机制和表面微弧氧化处理镁合金在模拟体液中的腐蚀行为等研究,主要包括以下内容：1.苯甲酸盐添加剂对AZ91D镁合金微弧氧化过程及氧化膜性能的影响。分别采用苯甲酸钠和邻苯二甲酸氢钾为添加剂,在碱性硼酸盐电解液中进行镁合金的微弧氧化研究。利用电流瞬变曲线和反应现象观察研究了苯甲酸盐参与下AZ91D镁合金的微弧氧化过程；利用场发射扫描电镜(SEM)、能谱(EDS)、X射线衍射(XRD)、极化曲线(Tafel)和电化学阻抗(EIS)等研究了苯甲酸盐对镁合金微弧氧化膜的形貌、组成和耐腐蚀性能的影响。结果表明,在加入苯甲酸钠或邻苯二甲酸氢钾后,微弧氧化电流密度降低,弧光放电剧烈程度减弱、气体逸出现象受到抑制,氧化反应变得相对温和。微弧氧化膜的质量也有明显改善。氧化膜表面孔洞的尺寸减小,表面裂纹消失,膜层变得更加平滑、致密,耐腐蚀性提高。2.苯甲酸盐添加剂对微弧氧化过程的影响行为研究。研究了碱性硼酸盐电解液中苯甲酸盐添加剂对AZ91D镁合金阳极氧化阶段和微弧氧化阶段的影响。利用EIS研究了苯甲酸盐在镁合金表面的吸附行为。利用SEM和起弧电压测试研究了苯甲酸盐对阳极氧化阶段和微弧氧化阶段的影响。利用电流瞬变曲线和反应现象观察研究了苯甲酸盐参与下AZ91D镁合金的微弧氧化过程。结果表明,苯甲酸盐在碱性硼酸盐电解液中的吸附行为符合Temkin吸附等温式,吸附过程为自发过程。苯甲酸盐主要影响镁合金的阳极氧化过程。在苯甲酸盐参与下,阳极氧化阶段得到的膜层更加均匀、致密,电阻率也高；均匀、致密及高电阻率的膜层使微弧氧化阶段电流密度降低,弧光等离子体放电剧烈程度减弱,氧化反应变得相对温和。在相对温和的条件下,火花放电变得细小均匀,气体逸出减少,放电和气体通道尺寸变小,表面烧蚀现象消失,制得氧化膜的结构更加平滑致密,其耐腐蚀性也更好。3.微弧氧化处理AZ91D镁合金在模拟体液中的腐蚀行为。以苯甲酸盐为添加剂,在生物安全型碱性硼酸盐电解液中对AZ91D镁合金进行微弧氧化处理,并对该处理过的镁合金在模拟体液中的耐腐蚀性进行了研究。结果表明,经微弧氧化处理后,镁合金表面生成了晶态方镁石型的致密均匀氧化膜。由于该氧化膜中不含Cr6+,F-和Mn2+等生物有害离子,作为医学植入材料更加安全可靠。利用浸泡失重实验、pH检测、电化学极化曲线和EIS等研究了微弧氧化处理镁合金的耐腐蚀性,并与未经处理镁合金进行了对比。结果表明,微弧氧化处理镁合金在模拟体液中具有优良的耐腐蚀性能。浸泡实验表明,微弧氧化处理镁合金在模拟体液中的失重速率远小于未经处理镁合金,浸泡造成的模拟体液pH的变化也小于未经处理镁合金,显示了其具有更好耐久性和生物相容性。总之,本论文结合镁合金表面防护技术的研究现状,以发展新型绿色环保型微弧氧化工艺为目标,分别研究了苯甲酸盐添加剂对镁合金微弧氧化过程及微弧氧化膜性能的影响,苯甲酸盐添加剂对微弧氧化过程的影响机理和微弧氧化处理AZ91D镁合金在模拟体液中的腐蚀行为,在新工艺开发、机理研究和材料应用和评价等方面做了一些探索性工作,取得了一定的进展。更多还原

【Abstract】 Because of its specific advantages such as low density, easy machining and excellent mechanical property, magnesium alloy is believed to be highly practicable in airline industry, aerospace industry, war industry, transportation industry, biomedical research, electronic industry and so on. However, the poor corrosion resistance of magnesium alloy hinders its further applications for it can be eroded easily by oxygen, water and salt in the open air. Therefore, improving the corrosion resistance of magnesium alloy has become an important research topic in this field.This paper outlines the characteristics, application, corrosion and protection of magnesium alloy. Based on the development tendency of protection technologies for magnesium alloy and the precious work of our laboratory, environmental microarc oxidation (MAO) technology of AZ91D magnesium alloy, the working mechanism of benzoate additive and the corrosion behavior of MAO film in simulated body fluid were studied in this thesis. The followings are the main points:1. An environmental friendly alkaline borate electrolyte using benzoate (sodium benzoate (NaBz), or potassium acid phathalate (KAP) additive was developed. The effects of NaBz and KAP on the MAO process and the properties of the MAO film were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS), respectively. The results showed that in the presence of benzoate, violent sparking and gas release were restrained, and a moderate MAO condition was obtained. The quality of the MAO film was greatly improved. The size of the pores was reduced, the micro-cracks on the MAO film were eliminated, and the MAO film with compact structure and smoothing appearance was produced. Electrochemical testing results showed the obtained MAO film was excellent in corrosion resistance.2. The working mechanism of benzoate additive was approached. The effect of benzoate in the alkaline borate electrolyte on the anodic process and MAO process was investigated. The adsorption behavior of benzoate on the surface of AZ91D magnesium alloy was studied by EIS. The oxidation process of AZ91D magnesium alloy was studied by current density transient curves and phenomenon observation. The results indicated that the adsorption of benzoate on the surface of AZ91D magnesium alloy was spontaneous and followed the Temkin adsorption rule. Benzoate affected the anodic process of magnesium alloy. In the presence of benzoate. a kind of oxidation film with denser and uniformer structure was prepared and it had higher electrical resistivity. Due to the denser, smoother structure and the higher electrical resistivity, the current density in MAO stage was reduced and the sparking became fine and homogeneous. Gas evolution was also restrained. At this moderate MAO condition, the channels of sparking and gas became smaller, ablation phenomenon was eliminated and the oxidation film with dense structure and high corrosion resistance was formed.3. The corrosion resistance of the MAO treated magnesium alloy in the simulated body fluid (SBF) was studied. AZ91D magnesium alloy was treated by MAO in alkaline borate electrolyte with benzoate additive. Its corrosion resistance was investigated by SEM, XRD, EDS, Tafel, EIS and immersion test. The results showed that the prepared MAO film did not contain Cr6+, F", Mn2+ and other harmful chemicals and was safe as medical implant material. The MAO treated magnesium alloy was stable in SBF. Immersion test showed the weight loss, the average corrosion rate and the pH variation of the MAO treated magnesium alloy were far lower than that of the untreated ones, suggesting better durability and biocompatibility.In short, environmental friendly MAO process, the working mechanism of additive and the corrosion resistance of the MAO treated magnesium alloy in SBF were studied in this thesis. These probing works may provide new insights for the development of new MAO process, working mechanism of additive and application of magnesium alloy for medical purpose.更多还原