| With continuous requirements of corrosion resistance, appearance quality and forming performance of steel structure of modern industry, the alloying treatment of the coating has become one of the important means of hot dip plating modification. In the pretreatment of the hot-dip galvanizing, the solvent aiding is the vital process, currently the traditional ammonium zinc plating flux is widely used in industry. With this flux, the residual iron from the steel will increase the surface tension and the viscosity of zinc bath, this leads to the problems that the film surface brings out the rough cumulate particles and gets gray and the zinc consumption increased greatly. So Bivalent iron ion is harmful to the steel, we should decrease it. But in the process of the hot-dip galvanizing, the action mechanism and trend of ferrous ion in the traditional flux flux is different from the ammonium-free flux’s, and The former mainly get into the liquid zinc and zinc extraction and lead to zinc consumption, while the latter which is in the state of Fe atom is easily united with Zn atom to form the Fe-Zn alloy, mainly exists in the coating. During the hot-dip galvanizing with the ammonium-free flux with ferric salt, the iron ion plays a role of the active atoms when the nucleation of alloy phase of the coating begins, and The iron ion are able to restrain the ξ, phase growing and promote the formation of δ phase. But we do not know the effect of different iron content on the performance of hot dip galvanized coating and the action mechanism.In this paper, we chose the non-ammonium plating fluxes which were tested in previous researches, these fluxes are combined with different surfactants and added with different concentration of ferrous salt. Mainly we should find out the permitted content of ferrous chloride and the optimal quantity in the the ammonium-free flux. First of all, we did the surface tension test and the contact angle test to explore the wettability of plating aid to the workpiece, then with the electrochemical experiments and leaching experiments, the work-piece’s corrosion resistance were investigated, finally we probe into the coating quality combined with metallographic analysis and scanning electron microscope (SEM) analysis.By analyzing the experimental results, the conclusions are followed: (1)With the condition of the ammonium-free flux technology, adding ferrous salt into the various series of NO.1main salt solution can improve the corrosion resistance properties of the coatings, and the the optimal range of ferrous salt under the Electrochemical polarization test is below30g/L, while under the full immersion test the optimal range of ferrous salt is below50g/L;On the contrary, the three series of NO.2main salt solution without ferrous salt is good to the coating. The reason of this phenomenon is that the ammonium-free flux with X2and X3can promote the tolerance of the plating auxiliary to FeCl2.(2)Under the electrochemical corrosion environment, Adding any kinds of the surfactants into the three series of NO.1and NO.2main salt flux which is with ferrous salt(below50g/L) are conducive to the corrosion resistance properties of the coatings, among the three surfactants, FC-3d acts best, then does FC09-Ⅱ and FC-3c.(3)Under the full immersion corrosion environment, adding FC09-Ⅱ into the three series of NO.1main salt flux with ferrous salt(10g/L and30g/L) contributes to the the corrosion resistance properties of the coatings, while the content of ferrous salt in the flux is40g/L, adding any any kinds of the surfactants into the flux can improve the corrosion resistance properties.(4)Adding surfactants into the ammonium-free flux can remarkably improve the wettability. Among the three surfactants, the ability of surfactant FC-3d to improve the flux’s wettability is very prominent, but the ability of surfactant FC09-Ⅱ is more stable and its applicability is good.(5)Adding FeCl2into the ammonium-free flux can also improve the wettability. But with different main salt solutions, the effect of FeCl2on wettability is various, the ammonium-free flux with X2and X3can decrease the the surface tension and the contact angle.(6)The coating of NO.1main salt’s three series have both plastic phase(δ phase) and the brittle phase(ξ phase), the alloy phase layer distribute homogeneously. In the coating of the ammonium-free flux, such as FA123, the δ phase in favor of the usability of coating occupies the most part. Analyzing the three series of the coating of NO.2main salt, the8phase take little part in the coating, while the ξ phase is in a high proportion leading to increase the thickness of the coating, such as FA203. The FC-3c series of the coating of NO.1main salt and NO.2main salt solution is worse than the coating of FC09-Ⅱ series and FC-3d series. |
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