No Ammonium Fluxing Hot Dip Galvanized Iron Reaction Toward Research

The hot-dip galvanizing is the physical and chemical process, which metal workpiece whose surface is washed and activated are dipped in molten zinc. Mutual fusion and Fe-Zn alloy layer on the surface of workpiece forms through the reaction-diffusion between iron and zinc. The hot-dip galvanizing is widely applied in the field of the surface treatment. In the pretreatment of the hot-dip galvanizing, the solvent aiding is the vital process. At present, the traditional assistant agent, which is the mixed solvent of zinc and ammonium chloride, has been in production, while the low and free ammonium is in the stage of commissioning test run. In the the traditional assistant agent, the residual iron will lead to increasing the surface tension and viscosity of zinc bath, the problems that the surface of the coat gets gray and is covered by the rough cumulate particles and the consumption of Zn is increasing, will appear. Previously, the study on the ammonium-free agent focuses on the exploration of the process, but there is hardly any reports about the influence of iron ion on ammonium-free fluxing. Therefore, it is of great importance to study both the trend of iron ion of the ammonium-free agent and the influence of iron ion on the formation and microscopic structure of the coat.The subject optimizes the ammonium-free agent with ferric salts by the orthogonal test. After the hot-dip galvanizing, it is suitable for using the spectrophotometry and ICP-AES to measure the iron concentration of the coat, zinc bath and dross, which are formed by respectively aiding in the traditional assistant agent and the ammonium-free agent; the micro structure and chemical composition of the coat are observed and detected by SEM and EDS; by the method of thermodynamics the paper can analyze the role of iron in the formation process of the coat. The paper object is to offer the experimental basis for quantifying the ferric salt content in the ammonium-free agent. The following conclusions are obtained after analyzing the experiment phenomena and data:The best basic formular of the ammonium-free agent is mixed solvent of40R g ZnCl2,2R g KC1,4R g NaF,4R g A1C13,20g FeCl2and1.2R g FcO9-Ⅱ in the1000ml liquid.After the hot-dip galvanizing, in the ammonium-free agent with ferric salt the iron concentration of the coat, the zinc bath and the dross are3.28wt%,0.00786wt%and0.052wt%, while in the traditional assistant agent they are3.02wt%,0.01543wt%and0.084wt%. It turns out that, in the process of the hot-dip galvanizing, the action mechanism of ferrous ion in the ammonium-free agent is different from the traditional assistant agent’s, and the former that is the state of Fe atom, which is easily united with Zn atom to form the Fe-Zn alloy, mainly exists in the coat. The iron atom, where during the hot-dip galvanizing the iron ion of the ammonium-free agent with ferric salt is reduced, plays a role of the active atoms when the nucleation of alloy phase of the coating begins. The reduced iron atoms are able to restrain from ζ phase growing and promote the formation of δ phase. The nucleation of ζ phase is prior to η phase if the iron concentration of zinc bath around the workpiece reaches to the required concentration of forming the ζ phase.