Phase evolution of an aluminized steel by oxidation treatment

Abstract

Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe 2Al 5. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe 2Al 5 phase remains at the temperature below 950 °C in 2-h, and the Fe 2Al 5 phase is completely transformed into low iron content Fe–Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe 2Al 5 phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al 2O 3 and the intermetallic Fe 2Al 5, FeAl 2, FeAl and Fe 3Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.