| Hot dip aluminized steel can be widely used because of its good high temperature oxidation resistance and corrosion resistance, while Al-5Ti-B-RE interalloy is a kind of new grain refiner, and it can purify molten aluminum, improve the fluidity of liquid aluminum, and refine the aluminum grain and so on, which is also crucial to the hot dip aluminized technology. This paper aimed to make full use of Al-5Ti-B-RE interalloy to purify molten aluminum and refine grain to improve the properties of hot dipped coatings, which establish certain technology and theoretical basis for the popularization and application of the hot dip aluminized technology.The microstructures and properties of hot dip aluminized coatings on the surface of Q235steel have been systematically studied with Metalloscope, Scanning Electron Microscopy (SEM), Energy Disperse Spectroscopy (EDS) and X-ray Diffraction (XRD), and the effects of Al-5Ti-B-RE interalloy refiner on the hot dip aluminized coatings have been discussed.The research showed that, the pure aluminum coating of hot dip aluminized steel was consisted of a-Al, FeAl3and amorphous phase, while the alloy layer was consisted of Fe2Al5and a little FeAl3phase. When refiner was added, the outer surface of the coating was smooth, tight and no plating leakage, and the tooth shapes of the alloy layer became thin, close and less bifurcation; In addition, the thickness of the pure aluminum layer and the alloy layer were decreased, while the hardness of the pure aluminum layer and the steel substrate were changed little, but the alloy layer was reduced, which the thinnest thickness of the alloy layer was hot dip aluminizing with0.1%refiner. Meanwhile, it had a minimum hardness. After diffusion annealing for5hours at850℃, the diffusion layer was composed of Fe2Al5, FeAl2, FeAl and Fe3Al phase.The results showed that the comprehensive properties of the hot dip aluminizing with0.1%Al-5Ti-B-RE interalloy refiner were the best. Its high temperature oxidation resistance was about1.1times of that of hot dip pure aluminizing,49.6times of that of Q235steel; And its corrosion resistance in3%NaCl solution was about2.2times of that of hot dip pure aluminizing,56.5times of that of Q235steel; In addition, although its corrosion resistance in0.1%Na2S solution was about1.5times of that of Q235steel, it was poorer than hot dip pure aluminizing.The influence mechanism of Al-5Ti-B-RE interalloy refiner on the microstructures and performances of the hot dip aluminized coatings had been analyzed.(1)The second phase particles Ti2Al2oRE, TiB2and TiAl3had been released in a short period of time, and they quickly played the role of the effective nucleation and made microstructure refine, which obtained more dense specimen surface;(2) The rare earth in the refiner could fill lattice vacancies in Fe2Al5of the alloy layer, which prevented the corrosion medium further spreading to the steel substrate;(3)The compact compound layer was formed in the diffusion layer of Al-5Ti-B-RE master alloy. To some extent, these factors could improve the coating microstructures and performances. |
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