The Research On Low Chromium Passivation And Colored On Hot Dip Galvanized Layer

Hexavalent chromium has high toxicity and carcinogenicity, not only a great threat to the environment, but also has great harm to people,s health,so the European Union and other countries have issued a ban on the use of hexavalent chromium products.With the improvement of people environmental protection consciousness,people pay more and more attention to environmental passivation technology.This paper aimed to study three kinds of passivation technology which were corrosion resistance on the hot dip galvanized layer surface,through hole sealing shading form bright color uniformity of the passivation membrane.The influence ruled of passive film appearance and corrosion time were determined through single factor experiment.The final passivation liquid formulation and process parameters are:(1)trivalent chromium passivation : CrCl3 6g/L, NaNO3 20g/L, NaF 10g/L, NiSO4 40g/L,pH=2.7,T=50℃, t= 60 s.(2)silicate/titanium salt composite passivation: Na2SiO4 25g/L 、 CoSO48g/L、TiCl3 9g/L、H2O2 60g/L、NiSO4 12g/L、HNO3 5ml/L、H3PO4 6ml/L、additive 7g/L、CitricAcid 10g/L、pH=3、T=45℃、t=25s(3) salt/titanium salt composite passivation:CeCl320g/L、Ti Cl3 1.5g/L、H2O2 40ml/L、additive 2g/L、pH =2.5、T=50℃、t=30s。The durable time to salt spray of passive membrane is respectively 83 h,78h,95 h. The passive film is sealed by vinyltrimethylsilane and acrylic resin after passive, the durable time to salt spray increase 30 hours. The mechanism of passivation process and hole sealing chromatic were also studied in this article.