脉冲电场辅助下Zn-55%Al-1.6%Si热镀层表面三价铬化学转化膜的构建

Construction of Cr(Ⅲ)chemical conversion coating on Zn-55%Al-1.6%Si assisted by pulse potential method

采用化学转化法在Zn-55%Al-1.6%Si热镀层表面构建了三价铬转化膜,通过3D形貌仪、扫描电镜(SEM)、X射线光电子能谱(XPS)、拉曼光谱和接触角仪等表面分析手段,以及中性盐雾试验和电化学测试方法表征了转化膜的结构、组成和性能。利用脉冲电位法对转化膜的结构进行调控,研究了脉冲电场调控作用对转化膜结构和性能的影响。结果表明:构建的三价铬转化膜表面具有多尺度的微观形貌特征,微米级的两相结构上分布着纳米级颗粒和微孔。加载阴极脉冲方波可加速转化膜的生成,提高膜中氢氧化物的含量和膜的疏水性,还可减少膜表面的微裂纹以及Cr(Ⅵ)的含量;当脉冲方波电位φP=−100.0 mV时,构建的转化膜具有最佳的耐蚀性,能够提高对镀层表面的临时保护作用。外加脉冲电场对转化膜的结构和性能具有积极的调控作用。

Cr(Ⅲ)chemical conversion passivation(TCP)exhibits a high potential as substitutes for the environmentally unfriendly chromate metal-surface pre-treatment methods.In this paper,Cr(Ⅲ)conversion coating was constructed on the surface of hot-dip Zn-55%Al-1.6%Si,and the structure and properties of the conversion coating were regulated by pulse potential method(PPM).3D topography,SEM,XPS,Raman spectrum,contact angle,neutral salt spray test and electrochemical test were used to study the corresponding structure,composition and properties of the conversion coatings.The results of micro morphology and roughness analysis show that the surface of Cr(Ⅲ)conversion coating has the characteristics of multi-scale micro morphology,and nano-scale particles and holes are distributed on the micro-scale two-phase structure.The results also show that the application of external electric field reduces the micro-cracks and the content of hexavalent chromium,accelerated the formation of conversion coating,and the content of alkaline hydroxide in the coating increased as well.The contact angle measurement shows that the structure of conversion coating controlled by the pulse potential method has more certain hydrophobicity.When the pulse square wave potentialφP=−100.0 mV,the TCP conversion coatings have the best corrosion resistance,which can improve the temporary protection of the hot-dip coating surface.The external pulse electric field has a positive regulatory and control effect.