Physico-chemical Properties Of Ammonia-free Flux In Hot-dip Galvanizing

In hot-dip galvanizing, metal workpiece, whose surface is washed and activated, are dipped in molten zinc. Fe-Zn alloy layer forms on the surface of workpiece through the reaction-diffusion between interface of iron and zinc. With thick coating, excellent corrosion resistance performance and low cost, hot-dip galvanizing is a common way of corrosion resistance on the surface of steel products.The previous studies (batch hot-dip galvanizing) focused on the metallurgical process of zinc coating's solidification as well as the structure and function of the coating. But the awareness of interface reaction in fluxing process of hot-dip galvanizing, and the flux performance of physics and chemistry, had never been research systemly. However, as far as the galvanizing effect, the research on the liquid properties of zinc-based alloys is of great significance from either basic theory or industrial application.This paper mainly from three aspects studied galvanizing without ammonium help plating agent.This paper researched on the physico-chemical properties of hot-dip galvanizing ammonia-free flux, mainly included three parts:First, research of the interface reaction in fluxing process of hot-dip galvanizing. Through test of the salt membrane ingredients, which made by flux, on the surface of steel substrate. Interface reaction mechanism were analyzed, and through calculation to speculate about what chemical reactions happened. Second, by contrast measured the flux performance of physics and chemistry, the the impacts of interface reactions in galvanizing processing were summarized, and then, the influence on galvanizing process performance were known. Which include:measurement of the contact angle, the melting point, the viscosity, the uniformity. Third, the control of the influence factors by the physical-chemical properties of flux without ammonia, and put forward the guidance theory basis for hot-dip coating technology.In this subject, the physico-chemical properties of hot-dip galvanizing flux were measured by the data, the laws of data summarized and the effect factors analyzed. The following conclusions are obtained after analyzing the experiment phenomena and data:In the interface reaction, the main composition of flux film is ZnCl2, concentration should be controlled in 142.8 g/L-400g/L, but the flux only contains cannot form comprehension flux salt membrane. However, the KCl, NaCl, AIF3, NaF, surfactants, corrosion inhibitor of the flux without ammonia help plating, which are not the main ingredients to the flux salt membrane, but affect physical and chemical reaction signigicantly, in the fluxing process. Addition of fluoride and surfactants could reduce the viscosity of flux; Join chloride can increase the solubility, accelerate decomposition of oxide, as well as, improve the brightness of the workpieces surface.The physico-chemical performances showed that the fluxes which are suitable for galvanizing, should have the following characteristic indexes:The contact angle between liquid melt zinc and the steel surface should be under the traditional flux; The melting point of flux should be lower, between 160-240℃is preferred; pH value should be kept below 1.5, and added the amount of corrosion inhibitors; To reduce the content of Fe2+in the flux, the peroxide solution oxidation method of joining low concentration hydrogen can be employed to remove iron ions.After experiment, this paper chose the best flux which comprise about 25%ZnCl2, 3%KCl (or 4%NaCl),0.04%nonionic surfactant containing,2%FeCl3,0.2%inhibitor.