Research On Liquid Properties Of Zinc-based Alloys 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 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 focused on the metallurgical process of zinc coating's solidification as well as the structure and function of the coating. The awareness of hot-dipping alloys'liquid properties is restricted to some typical metals and alloys under standard conditions, but not industrial conditions. 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.In this subject, the surface tension and fluidity of zinc-based alloys were measured under 420℃～480℃, the laws of data summarized and the effect factors analyzed. All of these aimed at offering the process and application of hot-dip galvanizing new guidelines. The main contents of the thesis include five parts:the surface tension of zinc-based alloys was measured, and the influence of alloy elements on molten zinc's surface tension was analyzed; after the fluxing process, the surface tension of zinc-based alloys was measured respectively, and the influence of traditional flux and ammonium-free flux on surface tension was compared; the fluidity of zinc-based alloys was measured, and the influence of alloy elements on fluidity was analyzed; the metallographic properties of zinc-based alloys were observed to explain the different fluidity performance; the roles of surface tension and fluidity in hot-dip galvanizing were analyzed, and meaningful theoretical basis was raised.The following conclusions are obtained after analyzing the experiment phenomena and data:the surface tension of molten zinc-based alloys reduces as the temperature rises; both the addition of aluminum and rare earth can reduce molten zinc's surface tension, and improve the wettability between molten zinc and metal workpiece; compared with traditional flux, ammonium-free flux is environment-friendly, and exerts an better effect on reducing zinc-based alloys.' surface tension; the fluidity of zinc-based alloys increase as the temperature rises; the fluidity of zinc is the best, and Zn-Al alloys'fluidity are worse than zinc's. With the improvement of Al consumption, Zn-Al alloys'fluidity increase at beginning, then reduce. The fluidity of Zn-0.1%Al is the best among Zn-Al alloys used in the experiment. The addition of rare earth promotes Zn-Al alloy's fluidity; molten zinc's solidification takes place according to layer-by-layer solidification, and Zn-Al alloy's solidification mushy solidification. The rare earth is conducive to grain refinement.