成膜时间对镁合金表面Ce-Mn转化膜组织及耐蚀性的影响

以四硼酸钠为添加剂,Ce（NO3）3-KMnO4为主要成膜剂,室温下在AZ91镁合金表面制备了Ce-Mn转化膜。基于优化的成膜剂浓度比,主要研究了成膜时间对膜层组织和耐蚀性的影响。结果表明转化膜层主要由O、Mg、Al、Mn、Ce等元素组成,随成膜时间延长,膜层不断增厚,且产生裂纹甚至膜层剥落。Ce（NO3）3/KMnO4浓度比较低时成膜速率较慢,膜层中Ce/Mn原子较小,但膜层的电化学性能较优。开路电位随成膜时间延长呈现先急剧增大,后缓慢增加并在2min后趋于平稳的趋势。室温下处理2min即可获得组织致密且耐腐蚀性能较好的转化膜,与基体相比,经配方A和B成膜后的试样,其自腐蚀电流密度由34.099μA/cm2分别下降到0.822和1.367μA/cm2,电阻由0.64kΩ.cm2分别增大到32.01和20.96kΩ.cm2。

Influence of processing time on microstructure and corrosion resistance of Ce-Mn conversion coating on magnesium alloy

Using sodium borate as additive,Ce-Mn chemical conversion coating was prepared on the surface of AZ91 magnesium alloy in Ce(NO3)3 and KMnO4 solution at room temperature.Based on the optimized concentration ratio of Ce(NO3)3/KMnO4,the influence of processing time on the morphology,composition and corrosion resistance was analyzed.The results show that Ce-Mn chemical conversion coating is mainly composed of O,Mg,Al,Mn and Ce elements.With extending processing time,the thickness of Ce-Mn chemical conversion coating was increased,but cracks in the coating appear and the coating even peels off.When the concentration ratio of Ce(NO3)3/KMnO4 was low,the forming rate and the atomic ratio of Ce/Mn of the coating was low while the corrosion resistance was better.The open circuit potential increases sharply during the first minute,and then gradually approaches a constant value.After 2min,it almost maintains steady.The best compact and corrosion resistant coating can be obtained when treating specimens for 2min.Compared with magnesium matrix,the corrosion current density of samples A and B after treating was decrease from 34.099 to 0.822 and 1.367μA/cm2,and the electric resistance was increase from 0.64 to 32.01 and 20.96kΩ·cm2,respectively.