Abstract:To study the microstructure evolution of intermetallic layer of hot dip aluminized ductile cast iron and the effect of Ni content on the microstructure of the intermetallic layer, laser confocal microscope (LCM), field emission scanning electron microscope (FESEM) and X-ray energy dispersive spectrometer (EDS) were used to carry out the microstructure observation and quantitative analysis of the intermetallic layer of hot dip aluminized ductile cast iron with different hot-dip times as well as specimens with different Ni contents. The results show that the intermetallic layer consists of a “tongue-shape” Fe₂Al₅ layer and a FeAl₃ layer of which the thickness is much thinner than that of the former. At the same time, graphite spheroids disperse in the outer Al topcoat and the inner Fe-Al intermetallic layer; within 0-15 min, the growth rate of the intermetallic layer approximately obeys the parabolic rate law after a short transition phase, and the layer is thicker than 65 μm after 15 min. Furthermore, the thickness of the intermetallic layer decreases from 88 to 49 μm with the increase of Ni content from 0 to 1.5% (mass fraction), and the “tongue-shape” interface between the substrate and Fe₂Al₅ phase becomes smooth. In addition, the microstructure evolution of intermetallic layer of hot dip aluminized ductile cast iron was also discussed.

Key words: ductile cast iron; hot dip aluminizing; microstructure evolution; nickel content