Microstructure of Hot Dipping Aluminum Coating Analyzed by Using Electron Backscatter Diffraction Technology

The aluminum coating was prepared on Q235 steel plates by hot dipping,and the microstructure of the coating was observied by scanning electron microscopy(SEM);the phase distribution at the coating/substrate interface,the grain orientations and the grain size were analyzed by electron backscatter diffraction(EBSD) technology.The results show that the aluminum coating consisted of an outer aluminum and Fe2Al5 adjacent to the substrate,and the tongue-like Fe2Al5 grew gradually with the increase of the dipping time;some voids were found in the coating due to the different diffusion rates between Fe and Al.Moreover,the Fe2Al5 grew preferentially along the Fe/Al inter-diffusion direction from the coating to the substrate and resulted in a non-uniform growth of the columnar Fe2Al5.However,iron grain orientation distributed randomly,which implies that the hot dipping process had no effect on the orientation.Numbers of small-angle boundaries( less than 5 degrees) existed in the interior of the columnar Fe2Al5.The grain average diameter of the columnar Fe2Al5 was about 20 μm and that of the iron in the substrate was about 8 μm.