Study On Passivation Process Of Electro - Galvanized Silicon - Titanium Composite

Chromate passivation is widely used on the galvanized steels for its. simple operation,low cost and excellent corrosion resistance, but it is harmful for human and environments because Cr6+is virulent. Government has banned the use and the drainage of chromium-containing waste water. The toxicity of trivalent chromium is less than 1% of chromate passivation,this technology applied well in industries presently. However, this technology is not stability, it’s easy to be changed into hexavalent chromium in the using process and placed, which still cannot completely solve the pollution problem of the chromate passivation.In this paper, chromium-free passivation process was researched using chemical immersion method. On the basis of the silicate passivation process,we added TiCl3,CoSO4,ZrF4,Ce(NO3)3 and KMnO4 respectively to the passivation solution.The results show that they make the performance of corrosion resistance improve from big to small is Ti3+>Co2+>ZrF4>Ce3+> KMnO4,TiCl3 is decided to be the best additive, A titanium silicon compound chromium-free inorganic passivation process was achieved finally, the main film forming materials in the passivation solution areNa2SiO3 and TiCL3.The best formulation and operating conditions for the passivation solution:Na2SiO3·9H2O is 10～40g/L,TiCl3 2～10mL/L,NaNO3 is 10～40g/L,KF is 2～10g/L,PH is 1.5-2.5,passivation time is 20-50s,temperature is 15-30℃, drying under constant temperature.Composite film is less micro cracks, good compactness, surface smooth and reunion small particles than single silicate coating.The conductivity of the composite film is poor, the main ingredients are Zn4Si2O7(OH)2 · 2H2O,SiO2,ZnO,Zn(OH)2 and TiO2. Composite film makes both the cathode and anode curve shift of the galvanized layer. The capacitive reactance arc radius of composite coating is much more bigger than single silicate passivation coating. The neutral salt spray test is up to72h,which is very close to trivalent chromium passivation film.Finally,the concentrate solution was studied.Component A contains Na2SiO3·9H2O,NaNO3 and KF, the largest concentration multiple is of 12.Component B includs TiCl3,H2SO4,H2O2 and H2O, The optimal proportion for TiCl3H2SO4:H2O2:H2O=1:2:2.5:4.This passivation applied into the system of zincate galvanized is better than potassium chloride zinc plating,it can get good appearance and better corrosion resistance coating for different parts.