| Electroplating zinc can improve the anticorrosion longevity of steel products invarious atmospheric environments. Thus, electrogalvanized steel is used extensively inarchitectures, transportation, housewares, and other areas. However, electrogalvanizedsteel is often treated by cost-effective chromate conversion coating because it is proneto appear white rust in humid environment. Due to the highly toxic carcinogenichexavalent chromium causing serious damage to human health and the environment,this technology has been restricted and prohibited. Hence, an intense research effortshould be undertaken to develop new chromium-free conversion coating technology ongalvanized steel.Because its corrosion resistance prepared by our research group was not very high,cerium conversion coating on galvanized steel was sealed with the twosealing solutions in order to further increase its corrosion resistance.(1) fluorosilicateand calcium nitrate?(2) fluorosilicate, ammonium fluorotitanate and accelerant. Theirsealing and anti-corrosion effect on cerium conversion coatings after sealing treatmentwas investigated by using a single-factor method in this paper.The research results from SEM, EDS, NSS test and electrochemical polarizationmeasurements showed that:(1) Cerium-salt conversion coating was sealed with thesolution consisting of fluorosilicate A and calcium nitrate under the condition of pH3.2,30?,12min, the composition of amorphous cerium conversion coating changed from2.94%Ce and24.46%O before sealing into6.09%Ce and26.55%O, the increasingeffective anti-corrosion ingredient significantly improved the corrosion resistance of thecoating.(2) Cerium conversion coating was sealed with the solution consisting offluorosilicate and ammonium fluorotitanate and accelerant, the composition of amorphous cerium conversion coating changed from5.80%P?1.96%Fe?64.84%Zn?2.94%Ce and24.46%O before sealing into7.34%P?55.26%Zn?3.67%Ce?33.07%O?0.19%Si and0.47%Ti, the corrosion potential shifted30mV negatively and thecorrosion current density decreased about1.13time, the neutral salt spray time wasincreased from10h before sealing to72h after sealing?consequently, the corrosionresistance of galvanized steel sample was evidently improved. |
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