Rare Earth Passivation Of Galvanized Steel And Its Modification Research

The present work aims at using rare earth lanthanum salt to corrosion protect galvanized steel,by immersion in the solution.The components of experiment were also confirmed,orthogonal experiments were also designed to get the optimized passivation parameters.Rare earth passivation:30g/L La(NO₃)₃, 20ml/L H₂O₂,pH=4,temperature of the solution is 40℃,time is 60s.One-factor experiment was also designed to investigate its impact on the corrosion protection ability of conversion film.The trimethoxy(viny)silane was used to improve the corrosion resistance of the samples treated with La solution.The corrosion resistance was assessed by lead acetate spot test,weight Loss, neutral salt spray test and electrochemical impedance spectroscopy.Atomic force microscopy(AFM) and Scanning electron microscopy(SEM) was used to characterize the sample surfaces.The X-ray energy dispersive spectrometry (EDS) was used to characterize the sample surfaces.The organic coating adhesion on the panel was also investigated via varnishes-cross cut tests.The bank panels,treated with La,treated in two-step and treated with Cr were compared in the corrosion ability testing experiments.The results indicate that when the samples treated with La,the anti-black time is 63.6s,corrosion rate is 1.757×10^-3g.m^-2.h^-1,the anti-white rust time is 55.3h,corrosion resistance is 1000Ω,which is less effective than Cr;When the panel was treated by La and silane,the anti-black time is 156.2s,corrosion rate is1.115×10^-3g.m^-2.h^-1,the anti-white rust time is 102h,corrosion resistance is 1.7×10⁴Ω·cm²,impedance of the two-step film lead an more excellent corrosion effect than that of Cr.Surface analysis results indicate that the rare earth film is not dense,with many cracks and pinholes,a big fluctuation;the two-step film is compact and with little fluctuation.The varnishes-cross cut test results reveal that the samples provides good paint adhesion.The coating formation and corrosion protection mechanism were also discussed.The treatment is simple and environmental friendly,it can be well used to replace the chromate treatment for galvanized steel.