| As the development of the country’s economic and the enhance of the awareness of environmental protection, cleaning production has been grad-ually promoted in various industries. In the traditional fluxing agent there is a lot of smoke produced when hot-dip, which is harmful to the environment and the operators’health. So the domestic hot-dip coating industries are all want to develop a smokeless fluxing process. Currently there are many foreign sch-olars are begin to engage in research in this area, but all the study are re-mained at the experimental stage, have not applied to the industrial pro-duction.This paper is based on the above situation and the trends of research, and writing based on the research of the process of fluxing without ammonium in our laboratory. Through discussion the various factors which are affect the coating’s crystallization and corrosion properties under the nonammonium fluxing process. In this paper, use the optical microscope, SEM, electro-chemical corrosion test, full immersion experiments and X-ray diffraction methods to analysis the different component of fluxing, different dip time and dip temperature under the same fluxing to the affect of the coating’s structure and corrosion properties. The following is the conclusions:In order to get a coating which is complete, uniform and have good corrosion resistance, the fluxing which be chosen must contain the following substances:one kinds is sealant usually ZnCl2is be chosen; one kinds is the nucleation accelerator, usually NaCl, KCl, NaF, etc are chosen. chloride and fluoride salts; the anther one is surfactant.If add some appropriate RE in the nonammonium fluxing, a coating which have better surface and higher corrosion resistance can be got. Adding RE can shorten the incubation period and inhibit the growth of ζ phase, and get a alloy layer which is almost composed of δ phase. The add of RE can reduce the diffusion activation energy of the Fe-Zn atom, compared to the fluxing without rare earth the diffusion activation energy reduced6190J/mol. However, the excessive add of RE will make the coating growth excessively, and the corrosion resistance will be down.At the conditions of nonammonium fluxing, dipping time from10s～120s, as the time going on the coating thickness first decreased and then increased, but after add some RE there will not occur the thinning pheno-menon, that indicate if we want to get the same thickness of coating, adding RE can shorten the dipping time, improve the production efficiency. Under the condition of nonammonium fluxing the best hot-dip time is40s～180s, too long or too short are all will affect the coating’s Corrosion resistance.At the conditions of nonammonium fluxing, the best dip temperature is about460℃, the lower dip temperature will get a uneven, poor adhesion coating, and in the η phase there are many Zinc dross, oxides and other impurities. If the temperature is too high, the alloy layer will growth excessively, especially the brittle phase ζ growth acceleration, and because of the higher temperature, the liquid zinc will increase the corrosion to the alloy layer, there are many micro-cracks occurs in the δ phase, that will be reducing the coating’s corrosion resistance. |
PDF Full Text Request