Electro-galvanized And Silicate Passivation Process

The technics of zinc-electroplating and the silicate non-chrome passivation of zinc-plating are studied in this paper.The research we have done including the follows:By the comparation of different systems,We get the appropriate method of zinc-electroplating in the solution that contains kalium.We also gain the optimal technics using the orthogonal experiments,that is,ZnCl_2:80g/L; KCl:200g/L;H₃BO₃:35g/L;main brightener:2ml;carrier brightener:2ml; supplementary brightener:2ml;pH:5.0;current density:1～1.5A/dm².and we get the best technics by orthogonal experiments as follows,Na₂SiO₃:20g/L; H₂SO₄:3g/L;H₂O₂:30g/L;additive:10g/L;pH:2.5;passivation time:60s.The technics factors have a distinct effect on the appearance of coatings, especially the additive content and pH effect directly the brightness,leveling and the stability of plating solution,the plating time has relation with the thickness of coatings.The experiments we have done shows that,when the main brightener acetune content is too low,the coatings will be dull and coarseness.However,when it becomes too high,the coatings will be burned in high-density area,and there will be serious hydrogen bubbing and edge effect. If the carrier brightener content is lower,main brightener acetune cann't be dissolved and the coatings are coarse and tough.But when it becomes too high, the coatings in low-density area will be dark and lightness area becomes smaller.When supplementary brightener content is low,the coatings in low-density area will be dark.The edge effect is serious and the coatings become yellow in high-density area.If pH in solution is low,hydrogen bubbing is high,and when it becomes high,the coatings are dark and fogged, the solution is turbidity.The coatings thickness becomes larger with the plating time becoming longer.Some factors influencing the corrosion resistance of passivation film are presented in this paper,passivation time,temperature,pH,passivation solution content are the most important factors.In addition,there are other factors that can have important influence,such as aging time,drying method.The optimal aging time is 24h,and we can use heated air to dry.The dwell time in the air is not important,5s is better.The silicate non-chrome passivation solution is stable.We have studied the corrosion resistance in silicate passivation of the coatings and found silicate passivation films have better corrosion resistance than other non-chrome passivation films in NSS and dipping-in brine experiments.The technics has has good prospect in zinc-electroplating passivation for replacing chromate.