AZ91D镁合金钛锆转化膜成膜机制及耐蚀性能研究

发布时间：2018-01-12 09:41

本文关键词：AZ91D镁合金钛锆转化膜成膜机制及耐蚀性能研究　出处：《沈阳理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：镁合金作为轻金属材料在航空航天、通信、汽车、电子工业等领域有广泛的应用,但其化学性质活泼,耐蚀性能差使其在许多领域的应用受到限制。镁合金表面化学转化膜是一种经济简单的防腐手段,但是现有的处理方法在镁合金表面形成的转化膜容易产生裂纹,造成镁合金耐蚀性能不高,并且处理工艺复杂,操作温度较高,不利于达到节能环保的要求。本文将钛、锆元素引入到镁合金转化膜成膜溶液中,成功制备了镁合金表面环境友好、无裂纹、低能耗、耐蚀性能良好的钛锆转化膜。SEM观察发现膜层是由球型颗粒堆积形成,颗粒均匀分布于镁合金基体表面,采用SEM、TEM对钛锆转化膜的截面形貌、厚度进行观察发现钛锆转化膜是双层膜结构,内层致密均匀,外层由球状颗粒堆积而成。通过XPS对主要元素检测,进行分峰拟合得出构成转化膜的主要物质是MgF2、Ti O2、Zr(HPO4)。分别采用析氢实验、盐雾实验、动电位极化曲线测试来表征钛锆转化膜的耐蚀性能。通过对钛锆转化膜成膜过程中开路电位测试,发现成膜的电化学过程主要分为三个阶段。采用SEM对不同阶段的形貌进行观察,钛锆转化膜的形成过程是球型颗粒经过形核与长大,并最终覆盖在金属表面;采用XPS对不同阶段膜层的化学组成进行分析,发现不同阶段组成膜层的物质相同,由此提出钛锆转化膜的形成机制。系统研究了酸洗以及酸洗+碱洗前处理工艺对AZ91D镁合金无铬、无裂纹、低能耗钛锆转化膜耐蚀性能的影响。研究结果表明,单独的酸洗前处理使得AZ91D镁合金表面的α相优先溶解,合金表面粗糙度增加,不利于钛锆转化膜耐蚀性能的增加。合理地利用酸洗+碱洗调整AZ91D镁合金表面化学状态能够有效提高钛锆化学转化膜的耐蚀性能。适当的后处理工艺能够进一步提高AZ91D镁合金无铬、无裂纹、低能耗钛锆转化膜耐蚀性能。选用三种后处理工艺,分别为封闭剂后处理、湿热后处理以及常温水泡后处理,研究不同的后处理工艺对转化膜耐蚀性能的影响。分别采用SEM观察三种后处理工艺微观形貌,采用盐雾实验和动电位极化曲线探究三种不同的后处理工艺对钛锆转化膜耐蚀性能的影响。
[Abstract]:Magnesium alloys are widely used in aerospace, communication, automobile, electronic industry and other fields as light metal materials, but their chemical properties are lively. Its application in many fields is limited due to its poor corrosion resistance. Chemical conversion film on magnesium alloy surface is an economical and simple anticorrosion method. However, the existing treatment methods on the magnesium alloy surface formed conversion film is prone to crack, resulting in magnesium alloy corrosion resistance is not high, and the treatment process is complex, the operation temperature is high. In this paper, titanium and zirconium elements were introduced into the transformation film solution of magnesium alloy, and the surface of magnesium alloy was prepared successfully with friendly surface environment, no crack and low energy consumption. The Ti-Zr conversion film with good corrosion resistance was observed by SEM. It was found that the film was formed by spherical particles and distributed uniformly on the surface of magnesium alloy substrate. The thickness observation shows that the titanium zirconium conversion film is a double layer membrane structure, the inner layer is dense and uniform, and the outer layer is made of spherical particles. The main elements are detected by XPS. The peak fitting results show that the main component of the conversion film is MgF _ 2O _ 2o _ 2o _ 2Zr _ (HPO _ 4) _ 4. Hydrogen evolution experiments and salt spray experiments are carried out respectively. The corrosion resistance of titanium-zirconium conversion film was characterized by potentiodynamic polarization curves. It was found that the electrochemical process of film formation was mainly divided into three stages. The morphology of different stages was observed by SEM. The formation process of titanium-zirconium conversion film was that the spherical particles were nucleated and grown. And finally covered on the metal surface; The chemical composition of the film in different stages was analyzed by XPS, and it was found that the composition of the film in different stages was the same. The formation mechanism of titanium zirconium conversion film was put forward. The process of pickling and pretreatment of pickling and alkali washing on AZ91D magnesium alloy without chromium and crack was studied systematically. The effect of low energy consumption on corrosion resistance of titanium zirconium conversion film. The results show that the 伪 phase of AZ91D magnesium alloy surface dissolves preferentially and the surface roughness of AZ91D magnesium alloy increases. It is unfavorable to increase the corrosion resistance of titanium-zirconium conversion film. Rational utilization of acid pickling. Adjusting the chemical state of AZ91D magnesium alloy surface by alkali washing can effectively improve the corrosion resistance of titanium zirconium chemical conversion film and the proper post-treatment process can further improve the chromium free of AZ91D magnesium alloy. No crack, low energy consumption titanium zirconium conversion film corrosion resistance. Three kinds of post-treatment processes, respectively, sealant post-treatment, wet-heat post-treatment and room temperature blistering post-treatment. The effects of different post-treatment processes on the corrosion resistance of the conversion film were studied. The micro-morphology of the three post-treatment processes was observed by SEM. Salt spray test and potentiodynamic polarization curves were used to investigate the effect of three different post-treatment processes on the corrosion resistance of Ti-Zr conversion film.
【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG178

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