Microstructures of Diffusion Treated Layers of Steel Specimens Hot-Dipped in Aluminum

摘要

Different grades of steel were dipped in pure molten aluminum, to compare them once Si-Fe alloy was added They were then diffusion treated at 930℃ for 5 hours, followed by pot-cooling in air. The specimens were examined both with light optical microscopy (LOM) and scanning electronic microscopy (SEM). The experimental results indicated that the depth of the aluminized case varied in relation to the composition of steels. Adding ferrosilicium in molten aluminum homologized the case phases, but rendered it greater porosity and brittleness under the adopted conditions. SEM examination revealed a characterized zone nearest to steel matrix, which hindered the surface cracking from propagating to a substantial depth. From the viewpoint of diffusion theory, it is obviously that embrittlement in the case was related to the contents of Al and the phases of iron aluminides formed during the process. Under the proper conditions, it is possible to obtain ordered solid solution FeAl and Fe_3Al, which possesses a fixed atom arrangement Analysis revealed that the fracture strength of iron aluminides is controlled by the bond energy of different atom configurations. The special zone with good ductility improved the combination between aluminum overlay and the matrix by diffusion processing.