在钒锆体系基础上添加单宁酸可提高AZ91D镁合金表面锆酸盐转化膜的耐蚀性能,目前研究较少.采用单因素试验的方法,研究单宁酸浓度对转化膜的影响;通过盐雾试验、电化学测试来检测膜层的耐蚀性能;利用扫描电镜(SEM)以及能谱(EDS)分析转化膜的微观形貌和成分变化.结果表明:单宁酸的浓度在0.3～0.5 g/L之间时,膜层晶粒较为细致,膜层均匀,阻抗值孤明显大于其他浓度时的阻抗弧,腐蚀电流密度达2.256× 10-5A/cm2,耐盐雾时间达600 min;在锆酸盐里添加单宁酸后形成的转化膜可以提高AZ91D镁合金表面的耐蚀性能.
Tannic acid was added into the zirconate system to improve the corrosion resistance of zirconate conversion coating on AZ91D Mg alloy.The single factor experiment was adopted to study the effects of the concentration of tannic acid on the conversion film.Salt spray test and electrochemical test were conducted to assess the corrosion resistance of the films.Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis were used to investigate the microstructure and composition of the films.Results showed that when the concentration of tannic acid was between 0.3 g/L to 0.5 g/L,the film grains became fine and the film was uniform.Besides,the impedance value was better than those prepared under other concentrations,and corrosion current density reached 2.256× 10-5 A/cm2 and salt spray test time was up to 600 min.In summary,the formed conversion film after adding tannic acid in zirconate system could improve the corrosion resistance of AZ91D magnesium alloy.
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