Recently the demand for reliable materials which have wear and oxidation resistance as well as corrosion resistance is increasing in industries. Thus, effective methods such as nitriding, chromizing and boronizing are already developed and widely applied to automotive and shipbuilding industries.
Hot dip aluminizing with hot dip galvanizing is broadly utilized to improve corrosion resistance of various steel materials. In case of hot dip aluminizing steel, Fe-Al intermetallic compound layer on the boundary between aluminum and steel exists and it has relatively high hardness and oxidation resistance. The Fe-Al intermetallic compound layer can be grown by diffusion treatment. Therefore, wear and oxidation resistance obtained by diffusion treatment is expecting and studying recently.
On the other hand, degree of growth of the Fe-Al intermetallic compound layer may decrease fracture and corrosion resistance. Thus, it is necessary to develop optimized design for diffusion.
In this study, type 1-hot dip aluminizing(Al + 5% Si) and type 2-hot dip aluminizing(pure Al) were chosen to diffusion treatment. The two kinds of hot dip aluminizing steel were immersed in flux(KCl, NaCl, F) at temperature range 700℃ and 720℃ for 10, 20 and 40 minutes. After that their morphology, intermetallic compound and depth composition of compound layers were investigated by scanning electron microscope(SEM), X-ray diffraction(XRD) and energy dispersive X-ray spectroscopy(EDX) respectively. In addition, the influence of diffusion treatment of hot dip aluminizing on mechanical property and corrosion resistance was evaluated by micro-vickers hardness test, immersion test in 3% NaCl solution and salt spray test.
From the result, Fe2Al5 was mainly formed on the surface of diffusion-treated specimens and grown according to increasing temperature and time of diffusion treatment. Hardness of surface layer was increased to maximum 1000 HV after diffusion treatment. This may be thought Fe2Al5 which has high hardness(1000 HV) affects the hardness of surface layer.
In evaluation by corrosion resistance test, type 1 hot dip aluminizing(Al + 5% Si) diffusion-treated at 700℃ for 10 minutes showed good corrosion resistance due to residual aluminum on the surface.
Consequently, diffusion-treated hot dip aluminizing is effective method to improve wear, oxidation and corrosion resistance. Due to limited test condition, optimized design was not suggested in this study. For that reason, it is considered that further study is necessary with various process condition such as metal element additive and diffusion treatment condition.