铬酸盐浓度对AZ91D镁合金转化膜成膜及耐蚀性的影响  

Effects of Chromate Concentration on Conversion Film Forming and Corrosion Resistance of AZ91D Magnesium Alloys

作　　者：孙志亮 芦刚 严青松 晏玉平 谢健辉 朱伟明 陈义斯 SUN Zhiliang;LU Gang;YAN Qingsong;YAN Yuping;XIE Jianhui;ZHU Weiming;CHEN Yisi(National D efense Key Discipline Laboratory of Light Alloy Processing Science and Technology,Nanchang Hangkong University,Nanchang330063,China)

机构地区：[1]南昌航空大学轻合金加工科学与技术国防重点学科实验室,江西南昌330063

出　　处：《热加工工艺》2022年第22期78-83,共6页Hot Working Technology

基　　金：国家自然科学基金资助项目(51861027);江西省优势科技创新团队重点项目(20181BCB19001);南昌航空大学研究生创新专项基金资助项目(YC2020-021)。

摘　　要：为改善AZ91D镁合金铸件耐蚀性低等问题,采用含不同浓度的Cr2O72-溶液在镁合金表面制备铬酸盐转化膜。通过扫描电镜观察样品表面转化膜微观结构,结合X射线衍射和能量色散谱仪分析其物相组成和元素分布,揭示了铬酸盐浓度对成膜行为的影响机制。基于电化学阻抗谱系统研究了AZ91D镁合金耐蚀性变化规律。结果表明,镁合金铬酸盐转化膜的形成基于氧化还原反应,其过程伴随α-Mg溶解,晶粒内部刻蚀,晶界呈岛状显露以及转化膜涂装。随Cr2O72-浓度的升高,含铬化合物MgCrO4、Cr(OH)3不断填充刻蚀缝隙,因此表面微裂纹数量减少,膜层光洁度逐渐提升。当浓度为50 g/L时,膜层厚度达最大值2.87μm,自腐蚀电位正向偏移至-1.299 V,拟合阻抗值相较未处理试样大幅提升。经铬酸盐处理的AZ91D镁合金的腐蚀电流密度下降,耐蚀性显著提升。In order to improve the low corrosion resistance and surface finish of AZ91D magnesium alloy castings,the chromate conversion film was prepared by Cr2O72-solutions with different concentration on the surface of magnesium alloys.The microstructure of the surface conversion film was observed by scanning electron microscope,and the X-ray diffraction and the energy dispersive instrument were used to analyze the phase composition and elements distribution.The influence mechanism of chromate concentration on the film forming behavior was revealed.In addition,the corrosion resistance of AZ91D magnesium alloy was studied based on electrochemical impedance spectroscopy.The results indicate that the chromite conversion film of magnesium alloy forms based on the redox reaction,which is accompanied by α-Mg dissolving,intragranular etching,island exposing of grain boundary and transformation film coating.The Cr-containing compounds MgCrO4and Cr (OH)3constantly fill the etching gaps with the increase of Cr2O72-,which can lead to the reduce of surface microcracks and the improvement of the film finishing.The maximum film thickness is 2.87μm at the concentration of 50g/L,meanwhile,and the self-corrosion potential is positively shifted to -1.299 V,and the fitting impedance value increases obviously compared with that of the untreated sample.There is an obviously enhancement in corrosion resistance for AZ91D magnesium alloys after chromate treatment due to the decrease of corrosion current density.

关 键 词：AZ91D镁合金 铬酸盐转化膜 耐蚀性 电化学阻抗谱 

分 类 号：TG174.4[金属学及工艺—金属表面处理]