Study Of Trivalent Chrome Colorized Passivation Process For Zn-Fe Alloy Coating

There are some research results about study of trivalent chrome colorized passivation all over the world, but the better performance of passivation solutions are all come from abroad. Its price is high and formula is confidential.Although we have some research results too, their quality is bad and their stability is too low.This research’s purpose is to found a new Cr(III) passivation technics which has well stability, high corrosion resistance and can protect the environment etc.Through a lot of exploring and researching process, we foud a passivation technics after this technics processing the layer has very good performance.In this processing solution, CrCl3is the main salt provide the Cr3+, NaNO3 is the oxidants can oxidant the coating, C6H5O7Na3·2H2O is the complexing agents control the stability of passivation solution and reaction with the Cr3+ become to the complexes, Na2SO4 can promotion layer formation, CoSO4 is the metal ion can activation and improve the corrosion resistance, water soluble organosilicon is use to improve the corrosion resistance of the passivate film.The best passivation formula is CrCl318 g/L, C6H5O7Na3·2H2O10 g/L, NaNO3 6g/L, Na2SO4 5 g/L, CoSO41.6 g/L, water soluble organosiliconl6g/L.Passivation technics is:Passivation time 20s, Passivation temperature 25-30℃, pH 1.5.Through the single factor experiments study the effects of concentration such as CrCl3, C6H5O7Na3·2H2O, CoSO4, Silica gel and passivation time, temperature, pH.Use the SEM, Tafel and NSS etc research the corrosion mechanism and performance.The resulting passivate film has a bright and symmetrical blue, with a sofe white paper friction after 15, the film did not appear obvious damage and loss, the time in NSS is 220h and under SEM the film dense and symmetrical has not crake and pore.This technology’s characteristic is friendly to environment and human, simple operation and low cost so has a great application prospect.