Microstructural Characterization of Commercial Hot-dip Galvanizing Coating by Transmission Electron Microscopy

摘要

Many efforts have been made correlate the characteristics of zinc coatings and their microstructure. However due to the limited accuracy and spatial resolution of techniques which are used in research, those effects could not get satisfactory results. At the same time systematic studies by TEM on phase evolution of commercial hot-dip galvanizing and galvannealing process are very lacks. Recently many researchers have noticed that transmission electron microscopy (TEM) is the best method in characterizing the microstructure of zinc coatings although it is difficult to prepare samples. In this paper a series of cross section of commercial hot-dip galvanizing coatings on IF steel sheets are studied efficiently by transmission electron microscopy. It is demonstrated that all intermetallic phrases such as delta phase, GAMMA phase, GAMMA_1 phase, zeta phase and eta phase found by other researchers could been ambiguously identified by electron diffraction. Furthermore each intermetallic phase that is associated with characteristic microstructure enable one to make quick and ready identification of phase only from the appearance in TEM. For example, the GAMMA phase that is located next to steel substrate (alpha-Fe phase) shows a well-defined columnar grain structure even in a couple of hundred nonometer thin layer.