The Thermodynamic Analysis Of Alloy Systems Used In Zinc Bath Of Hot-dipping Galvanizing And Its Applications

Zinc and Zinc-based alloys are used mainly in hot-dipping galvanizing to improving the corrosion-resistance of steel. More than half of zinc is used for this purpose. In recent years, the Chinese galvanizing industry has expanded at an astonishing speed of 50% annual rats. There are two kinds of galvanizing processing, by batch or continuous galvanizing. Batch galvanizing has a long history, but there are still many technnical challenges for Si-containing steel resulting from Si Reactivity. The adding of Ni into the zinc bath or increasing of the galvanizing temperature can inhibit the reactivity partially. But the mechanism is not well understood. Al is the most important addation element in continuous galvanizing. It can inhibit the formation of Fe-Zn compounds and reduce the brittleness of coating. The content of Al in bath must be controlled precisely for its effects on the quality of coating and galvanizing processes. This results in the need of the measuring system of effective aluminium. Al and Rare Earth in bath can improve the corrosion resistance of coating. Zinc bath can react with most of alloys. The materials used in galvanizing equipment can't fulfil the need of galvanizing industries.The alloying elements in bath play a key role in controlling of coating quality. The composition of the bath is very complex in general. The researches in thermochemistry properties of alloy systems in zinc bath and the wear- and corrosion- resistent alloy is not systematic, which are most important for optimizing the processing and controlling the coating quality and developing new zinc alloy used in galvanizing, In present work, the thermodynamic properties and phase relations of zinc alloys systems containing Si, Al, Ni, RE were investigated. The results are used in processes controlling and alloy design.The thermodynamic calculation of Fe-Zn-Si system was conducted by CALPHAD technology through Thermo-calc software, which is very important in galvanizing. The sublattice models for δ, Γ₁, Γ phases are proposed as (Fe,Zn,Si)₁₀Zn₁₆, (Fe, Zn,Si)₁₄Zn₁₂ and (Fe, Zn, Si)₄ Fe₂Zn₂₀, based on the crystal structures. The consistent set of thermodynamic parameters describing thermodynamic properties of phases is obtained. The result can be used in understanding Si Reactivity. Rare Earth and Al are important adding elements, and Ag-Zn alloy is an important welding material. As a kind of fundamental research, the thermodynamic...