AZ31B镁合金氧化石墨烯掺杂钇盐转化膜耐蚀性研究

目的研究一种绿色环保的表面处理方法,以提高镁合金的耐蚀性。方法采用化学浸泡法,以硝酸钇为成膜物质,在AZ31B镁合金表面成功制备一种新型稀土盐转化膜,并以氧化石墨烯为阻隔剂对该转化膜进行复合掺杂。采用扫描电镜(SEM)对膜层的表面形貌进行观察,采用析氢实验和电化学测试对不同试样在3.5%Na Cl溶液中的耐蚀性进行了研究。结果镁合金钇盐转化膜表面平整均一,覆盖良好。氧化石墨烯掺杂后的钇盐膜层表面出现了大小不均一的瘤状物质,膜层完整,未出现裂痕。析氢实验结果显示,经过处理的转化膜试样可以极大地抑制腐蚀反应的发生。由极化曲线可知,钇盐转化膜的存在使镁合金的腐蚀电位发生了明显正移,正移了150 m V;而氧化石墨烯掺杂的钇盐膜层的腐蚀电位相对于掺杂前变化不大,但其腐蚀电流密度是掺杂前的1/28。电化学交流阻抗谱的测试结果显示,氧化石墨烯掺杂钇盐转化膜的电荷转移电阻最大,Rct为2485?·cm2;钇盐转化膜的电荷转移电阻次之,Rct为1224?·cm2。两者的电荷转移电阻相对于未经处理的镁合金都有明显提升。结论钇盐转化膜可以明显提高AZ31B镁合金的耐蚀性,氧化石墨烯的加入可以进一步提高转化膜层的耐蚀性。

Corrosion Resistance of Graphene Oxide-doped Yttrium Salt Conversion Coating on AZ31B Magnesium Alloy

The work aims to improve corrosion resistance of magnesium alloy by studying an environment friendly surface treatment method.With yttrium nitrate as film forming material,a new rare earth salt conversion coating was successfully prepared on surface of AZ31B magnesium alloy in the method of chemical soaking.Surface morphology of the coating was observed with scanning electron microscope (SEM).Corrosion resistance of the film in 3.5％ NaCl solution was studied by performing hydrogen evolution test and electrochemical test.The yttrium salt conversion coating was smooth and uniform and well covered.Uneven heterogeneous tumor like substances appeared on the yttrium salt film doped with graphene oxide.The film was intact and free from cracks.Results of hydrogen evolution experiments showed that the treated conversion film samples could greatly inhibit corrosion reaction.Polarization curve results showed that presence of yttrium salt conversion film enabled corrosion potential of magnesium alloy to shift positively by 150 mV;corrosion potential of yttrium salt film obtained doping with graphene oxide changed significantly,but corrosion current density was only 1/28 of the undoped film.Test results of electrochemical impedance spectroscopy also showed that graphene oxide-doped yttrium salt conversion film exhibited the maximum charge transfer resistance (Rct),2485 Ω · cm2;followed by that of yttrium salt conversion film,1224 Ω · cm2.Compared with the untreated magnesium alloy,charge transfer resistance of the two was improved significantly.Yttrium salt conversion coating can obviously improve corrosion resistance of AZ31B magnesium alloy,and addition of graphene oxide can further improve corrosion resistance of the conversion coating.