摘要
考察了铈盐溶液中的AZ91镁合金电化学行为,包括开路电位,阴、阳极极化行为等,并据此开展了Ce(NO_3)_3为主盐的稀土盐转化膜研究,在AZ91镁合金表面形成无毒、无污染的铈盐化学转化膜,并研究成膜规律及其耐蚀行为.采用电化学阻抗谱技术优化了处理时间、温度、Ce(NO_3)_3液浓度和促进剂等因素对膜层结构和膜层耐蚀性能的影响,并获得了最好的成膜条件:处理温度为35℃,时间为30 min,主盐Ce(NO_3)_3的浓度为0.02 mol/L和促进剂H_2O_2浓度为4 mL/L.结果表明:采用优化后的工艺能够在AZ91镁合金表面获得宏观黄色致密、微观具有微小裂纹并分层的膜层,表层Ce含量较高.工艺优化制备的稀土化学转化膜能有效提高镁合金的耐蚀性能,有效抑制阴、阳极反应,自腐蚀电位提高250 mV,自腐蚀电流密度降低2个数量级.长期全浸实验结果表明,转化膜能有效提高镁合金的耐腐蚀性能,浸泡60 h后,保护性大大降低.
In order to develop an environmental friendly surface coating technology for magnesium, a chrome-free Ce-based process to form a conversion coating on AZ91 magnesium alloy was investigated. The open circuit potential and polarization curves were used to research AZ91 electrochemical behavior in Ce（NO3）3 ＋H2O2 solution. Electrochemical impedance spectroscopy （EIS） was chosen to evaluate corrosion resistance due to its low effect on electrochemical test system for getting high reproduction result. The effects of treatment time, temperature of electrolyte, concentration of Ce（NO3）3 and accelerant concentration on corrosion resistance were summarized, while an optimized technology was achieved, 0.02 mol/L Ce（NO3）3, 4 mL/L aeeelerant at 35 ℃ for 35 min. The results indicated that the chemical conversion coating formed in optimized technology presented yellow and impact surface by naked eye, while took on micro cracks on the outer layer. The content of Ce in the surface layer is high. Tafel plots indicated that conversion coating restrained the anodic and cathodic reaction on the interface, while the corrosion potential raised anodic 250 mV and corrosion current density decreased about 100 times. EIS results of optimal coating in NaCl solution for 96 h also indicated that the conversion coating protect the AZ91 magnesium alloy effectively in the first 60 h.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第8期979-985,共7页
Acta Metallurgica Sinica
基金
国家自然科学基金项目50671095
国家重点基础研究计划项目5133003D
科技部国家科技基础条件平台建设项目2005DKA10400-Z5资助~~
关键词
AZ91镁合金
硝酸铈
腐蚀性能
转化膜
AZ91 magnesium alloy, cerium nitrate, corrosion resistance, conversion coating
