Titanium-salt Conversion Coating On Hot-dip Galvanized Coating

Steel material is widely used in daily life and industrial production. Also it is the largest used metal. China is a big country of steel production, and produces more than500million tons each year, which shares the most part of the world steel production. But, steel is also the most easily corroded metal. Every year, the economic lost of steel corrosion even is more than the sum of all kinds of other disasters in the world. In order to control the steel corrosion, traditional method is galvanized in the steel surface. After plating or hot dip galvanized zinc, the surface will be treated by chromate conversion treatment technology. By using the method, the corrosion resistant performance of steel materials is greatly improved, but the use of carcinogenic chromium (VI) causes serious pollution to the world’s environment. Therefore, RoHS directive issued by the EU in2006and "the12th Five-Year Plan" of the heavy metal pollution prevention and control promulgated in2011,included the limited and prohibited chrome. To carry out the alternative technologies to chromate treatment on galvanized steel.Titannium salt conversion treatment on dip-galvanized steel was researched by single factor, the results indicate that:using oxalic acid instead of hydrogen peroxide as the titanium salt complexing agent in the conversion solution of TiOSO40.9g/L, C2H2O42.5g/L, phosphorus compounds,3.0g/L,pH1.3or0.5(the color conversion film selected1.3white conversion coating selected0.5),25～30℃,5min conditions, rainbow color/white titanium conversion coating was prepared.Its neutral salt spray test time was up to160h, more than72hours NSST of industrial application standard requirements. The EDS analysis results showed that such the coating was made of the four elements of Zn, O, P, and Ti. The electrochemical polarization curve analysis showed that, the matrix of the anodic dissolution and cathodic depolarization can be inhibited. Hot dip galvanized steel surface after treated titanium salt chemical into the deal had good corrosion resistance, and the solution stability was improved after treating with Ti-salt conversion slolution,met environmental protection requirements.