摘要
利用单组分单宁酸为成膜剂,在AZ31镁合金表面制备无铬转化膜,采用L9(34)正交试验研究转化处理液中单宁酸的浓度、处理液pH值、温度和处理时间对转化膜形成和耐腐蚀性能的影响,获得最优的转化膜处理工艺。用扫描电镜与X射线光电子能谱对镁合金表面单宁酸转化膜的表面形貌、元素组成及化学价态进行分析,并通过电化学极化曲线和阻抗谱测试,考察镁合金表面单宁酸转化膜的耐腐蚀性能,阐明其形成机制。结果表明,镁合金在温度为50℃,pH值为2.5,单宁酸质量浓度为10 g/L的转化液中浸泡10 min,即可获得耐蚀性良好的单宁酸转化膜。单宁酸转化膜由镁合金表面溶解形成的镁离子Mg2+与单宁酸分子的酚羟基、羧基发生反应生成的镁金属有机螯合物组成,呈网状裂纹结构均匀覆盖于镁合金表面;单宁酸转化膜能有效提高AZ31镁合金的耐腐蚀性能,交流阻抗达到1 250?/cm2,是基体镁合金阻抗(35?/cm2)的300多倍。
A tannic acid non-chrome conversion coating was prepared on AZ31 magnesium alloy. The optimum conditions including tannic acid solution concentration, pH, treating temperature and treating time for obtaining the best corrosion protective coatings and improving localized corrosion resistance to the magnesium substrate were determined by an orthogonal experiment design L9（34）. The corrosion resistance behavior of the coating was investigated by electrochemical experiments. Surface morphology and composition of the resultant conversion coatings were investigated by scanning electron microscope （SEM） and X-ray photoelectron spectroscopy （XPS）. The results show that the ideal treatment conditions is obtained as 50℃ for treating temperature, 10g/L for tannic acid conversion solution, 4 for pH value and 10 minutes for treating time, and the tannic acid conversion coating is composed of organic chelates by reaction of Mg2＋ with phenolic hydroxyl and carboxyl groups. The tannic acid conversion coating uniformly covers the surface of magnesium alloys with net cracks structure. The tannic acid conversion coating can effectively improve the corrosion resistance of AZ31 magnesium alloy. The impedance value of the magnesium with tannic acid conversion coating reaehs 1 250 D./cm2, which is 300 times of that of untreated magnesium （35 Ω/cm2）.
出处
《粉末冶金材料科学与工程》
EI
北大核心
2015年第4期649-654,共6页
Materials Science and Engineering of Powder Metallurgy
基金
国家高技术研究发展计划(863计划)资助项目(SS2015AA032101)
中南大学粉末冶金国家重点实验室开放基金资助项目
关键词
单宁酸
转化膜
耐腐蚀
表面处理
镁合金
tannic acid
conversion coatings
corrosion resistance
surface treatment
magnesium alloy
