Study on the cluster of floating dross before nucleating during hot-dipping process

摘要

During hot-dipping in molten Zn-55Al, the forming of "floating" dross is closely related with the interaction between the Al and the Fe atoms. Utilizing the thita-thita X-ray diffraction and the Percus-Yevick hard sphere model, this paper investigates the structure of molten Al_3Fe that is an approximant of partial melt in practical Zn-55Al alloy melt. It is found that in the melt there exist clusters that resemble the structure of intermetallic compound Al_3Fe. The strong interaction between Al and Fe atoms is also indicated by the deficiency of the coordination number from 12 and the shrinkage of averaged atomic diameter. Based on such information, it is speculated that in the molten Zn-55Al, with the accumulation of Fe, Al_3Fe-like clusters form with priority, then grow into dross. On the other hand, after deflating of the effective hard sphere diameter of pure Al atom and enlarging that of the pure Fe atom, the modified model can achieve reasonable fit to the experimental structure factor. Hard sphere modeling also gave a good estimation of the mass density 3.65 g/cm~3 of liquid Al_3Fe alloy at 1550℃. Compared with the density of 3.7 g/cm~3 of Zn-55Al, the reason for dross floating is satisfactorily understood.