| Corrosion is one of the main reasons for damage of steel products, the steel surface coating is one of the effective means of anti-corrosion. However, it is easy to result in the crack of the paint film in some high temperature and high humidity environment, corrosion rapid expansion in the crack, and cause paint film into a piece off, lose protection. Phosphating treatment before paint film can improve the adhesion of coating and substrate, and corrosion resistance of the whole. In coating projects, Zn-Phosphating is widely used because it prolongs the service life of the coating noticeably. But most of the phosphate treatment process at high temperature, high energy consumption and large sediment. Now phosphating at room temperature are widely used, but its accelerator are dominated by nitrite ion and nickel ions, There are a lot of shortcomings, such as toxic, environmental pollution, more sediment, and poor corrosion resistance. Therefore, developed a kind of low temperature, energy saving, non-toxic, low pollution, fast film forming, high corrosion resistance of phosphating technology become a focus in the study of this article.In this study, developed a normal temperature, rapid and high corrosion resistance of zinc phosphate solution. Studied the phosphating film microstructure, chemical composition, deposition rate of film and corrosion resistance by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),<p-t curve, electrochemical impedance spectroscopy (EIS), polarization curves, film weight, neutrality salt standard (NSS). And studied the influences of various factors on the film-forming process.Through the orthogonal experiment and subsequent optimization analysis, determine the best formula for the phosphating solution:Zn(H2PO4)2·2H2O 60 g/L, Zn(NO3)2·6H2O 80 g/L, NaC1033 g/L, SNBS 1.5 g/L, HAS 3 g/L, tartaric acid 2 g/L, NaF 1.5 g/L, OP-102 mL/L. The optimum parameters:pH= 2.5-2.7, the processing temperature is 20～40 ℃, and get cover the complete phosphating film after 5 minutes.Experimental studies show that, between SNBS and NaC103, HAS has good synergy. Compounded using this three accelerators can greatly reduce the phosphate processing time and temperature, increase corrosion resistance of phosphate coating. Surface conditioning can provide a large amount of nucleation sites for phosphate deposition. Thus, accelerating phosphating reaction speed, refined phosphate crystallization, providing more attachment points for subsequent coating to improve the adhesion of the paint film. Process parameters are directly affecting the ability to film and film speed, such as temperature, pH and time. It is essential to the phosphating process. After phosphating, phosphating reaction continued on the sample surface in the natural drying process. It has played a role in closed phosphate coating, and improves the corrosion resistance of phosphate coating.Performance test results show that, the phosphating solution formulation was light yellow, clear and transparent, less sediment, stable performance. The appearance of phosphate coating is grey, microscopic morphology is the branch crystal, uniform and compact. The coating weight is 3.0-3.8 g/m2, coating thickness is about 2μm, NSS corrosion resistance time can take up to 6 h. Have good adhesion with paint film, the corrosion resistance of composite coating increased by about 3 to 5 times. This phosphate solution overcomes the shortcomings of toxic, high pollution and poor corrosion resistance, and have important practical value.
|
PDF Full Text Request