无氰镀银层水性硅溶胶封闭工艺及镀层结构与耐蚀性

Aqueous silica sol sealing of cyanide-free electroplated silver coating and its microstructure and corrosion resistance

[目的]镀银层往往存在孔隙,使其耐蚀性无法满足苛刻的海洋环境应用要求,因此有必要对其进行封闭处理。[方法]采用水性硅溶胶对5,5-二甲基乙内酰脲(DMH)体系无氰镀银层进行封闭,通过正交试验优化封闭处理的工艺条件。借助扫描电镜(SEM)、X射线光电子能谱仪(XPS)及电化学阻抗谱(EIS)测试分析了封闭后Ag镀层的微观结构、化学组成及耐蚀性。考察了1Cr18Ni9Ti不锈钢和GH2132合金表面Ag镀层经硅溶胶封闭后的耐酸性盐雾性能。[结果]较佳的封闭液组成和工艺条件为:丙烯酸树脂100 g/L,中性硅溶胶26 g/L,表面活性剂1 g/L,室温,时间60 s。在该条件下封闭后,Ag镀层表面疏水性和耐蚀性提高;Ag镀层的微观表面形貌未发生改变,封闭剂仅渗入镀层孔隙,而未在表面形成连续的膜。1Cr18Ni9Ti不锈钢和GH2132高温合金经“无氰镀银+水性硅溶胶封闭”处理后可以通过192 h的酸性盐雾试验。[结论]采用水性硅溶胶封闭处理可显著提高无氰镀银层的耐蚀性,对航空零部件的发展具有重要意义。

[Introduction]The corrosion resistance of silver coating is usually unable to meet the application requirement of harsh marine environment for it has some micropores,so it is necessary to conduct sealing after silver plating.[Method]The silver coating obtained from a cyanide-free 5,5-dimethylhydantoin(DMH)-based electrolyte was sealed with an aqueous silica sol.The process conditions of sealing were optimized by orthogonal test.The microstructure,chemical composition,and corrosion resistance of sealed Ag coating were analyzed by scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and electrochemical impedance spectroscopy(EIS).The acetic acid salt spray(AASS)resistance of Ag coatings on 1Cr18Ni9Ti stainless steel and GH2132 superalloy after being sealed was tested.[Result]The composition of sealing agent and operation conditions were optimized as follows:acrylic resin 100 g/L,neutral silica sol 26 g/L,surfactant 1 g/L,room temperature,and time 60 s.The hydrophobicity and corrosion resistance of Ag coating were improved after being sealed under the optimized conditions.The sealing agent just penetrate into the micropores of Ag coating and didn’t form a continuous film,so the surface morphology of Ag coating didn’t change after being sealed.The 1Cr18Ni9Ti stainless steel and GH2132 superalloy treated by combination of cyanide-free silver electroplating and aqueous silica sol sealing can undergo AASS test for 192 hours.[Conclusion]The corrosion resistance of cyanide-free electroplated silver coating can be greatly improved by sealing with aqueous silica sol,which is significant to the development of aero components.