Effect Of Al On Formation Of Hot - Dip Galvanizing In Ammonia - Assisted Plating

In hot-dip galvanizing with the traditional plating process, NH4Cl in the auxiliary will be reaction with Al in the zinc bath, which not only expend the active ingredients of the auxiliary, but also make a wide fluctuation with the aluminum content in the zinc bath. It will have a bad effect on the quality of the products and raise the production costs. In the ammonium-free plating process, without NH4Cl in the aluminum, the wastewater and air pollution from ammonium salt could be solved completely, and this can reduce the consumption of the aluminum content in the zinc bath. But there is no reports about the influence of aluminum ion in the ammonium-free plating process and the influence of aluminum ion on the formation and microscopic structure of the coat.This paper is based on the research of fluxing without ammonium in our laboratory. The ammonium-free plating formula has been optimized. We used the optical microscope, SEM/EDS, ICP-AES, electrochemical corrosion test and full immersion experiments methods to analysis the aluminum to the effect of the coating’s structure and corrosion properties in the ammonium-free plating process. The following is the conclusions:After the hot-dip galvanizing, in the traditional plating process and the ammonium-free plating process, the aluminum content in the zinc bath respectively went down to23.74%and42.44%. The ammonium-free plating process can effectively reduce the useless consume of aluminum, and the Aluminum consumption is relatively less0.01wt%than the traditional plating process.Under the conditions of ammonium-free plating process, the trend of the aluminum mainly exists in the coating and the zinc bath, the content fluctuation of iron and zinc in the coating is small, and its composition is stable. The quality od the galvanized parts is sensitive to the variation of aluminum content, and the stablishment effect of aluminum is obviously better than the effect of the traditional plating process. Compared the two kinds of plating process, the zinc consumption of the ammonium-free plating process is less11%than the traditional plating process, and the zinc slag quantity is less33%. So the ammonium-free plating process can save money and improve the production efficiency.Under the conditions of ammonium-free plating process, the aluminum plays a role of the active atoms when the nucleation of alloy of the coating begins. It is able to restrain the ζ, phase growing and promote the formation of8phase. The phase structure of the coating is more densification, and the bounds of the phases is breezing and with no cracks, The adhesion of the coating with ammonium-free fluxing process was increased significantly, and so was the corrosion-resisting properties of zinc coating which is much higher than that from the traditional plating process.