Thermodynamic Assessment Of Zn-Nd System And Development Of The Thermodynamic Database Of Zinc Alloys

Hot-Dip galvanizing is widely used for improving atmospheric corrosion resistant of steel parts. Alloy elements play a key role for controlling the coating quality. Using thermodynamic phase equilibrium relations and thermodynamic properties of zinc alloy systems we can predict and control the product process. There's very important meaning for controlling the quality of galvanizing products, optimizing the galvanizing process parameters and facilitating the development of galvanizing industry.In present work, the Zn-Nd system was optimized by Thermo-Calc software,. A set of self-consistent thermodynamic model parameters was derived. The system contains eight intermetallic compounds: NdZn, NdZn₂,NdZn₃,Nd₃Zn₁₁,Nd₁₃Zn₅₈,Nd₃Zn₂₂,Nd₂Zn₁₇ and NdZn₁₁. They were all treated as stoichiometric compounds. The standard enthalpies of formation of these compounds calculated in this work are, respectively, -34.58, -35.73, -33.46, -31.73, -30.22, -26.78 and -24.50 kJ/mol. Good agreement is obtained between the calculation and experimental results.Alloy elements are the most important factor for controlling the coating quality. On the one hand, in order to enhancing the coating quality, some alloy elements are added into zinc bath during the hot-dip galvanizing process, such as Al, Bi, Cu, Si, Ni, Mg, Mn, Sb, Sn, Ti, and so on. On the other hand, the elements in steel parts dissolved into the zinc bath during hot-dip galvanizing process. These elements could change the reaction between Fe and Zn, and influence the coating quality. By analyzing the reaction between these alloy elements and zinc, the mechanism of alloy elements influencing the coating quality can be better researched. For this reason, a thermodynamic database of zinc-based alloys was established in present work. The establishment of the zinc-based thermodynamic database is useful for guiding the hot-dip galvanizing technics,and controlling the coating quality..A great deal of thermodynamic data concerning zinc-based alloy systems was collected in present. By using Thermo-Calc software, a thermodynamic database of zinc-based alloys was primarily established. This database consists of sixteen ternary systems including Zn-Fe-Si, Zn-Fe-Ni, Zn-Fe-Al, Zn-Al-Cu, Zn-Al-Si, Zn-Al-Mg, Zn-Cu-Mg, Zn-Mg-Y, Zn-Al-Y, Zn-Cu-Mn, Zn-Ca-Sr, Zn-Mg-Sr, Zn-Sn-Ti, ZnPb-Cu, Zn-Sn-Cu and Zn-In-Sn ternary system, and ten binary systems including Zn-Au, Zn-Bi, Zn-Ca, Zn-Ce, Zn-Co, Zn-Cr, Zn-Li, Zn-Nd, Zn-Pr and Zn-Sb binary system.Connecting with galvanizing technics and practical process, the application of Zn-Fe, Zn-Fe-Si, Zn-Fe-Al and Zn-Fe-Ni alloy phase diagrams was discussed.