The Effect Of Sn And Ti Addition On The Structure And High-temperature Oxidation Resistance Of Hot-dip-aluminized Coatings

Hot dip aluminizing steel has a wide range of applications owe to its good corrosion and high-temperature oxidation resistance,but its dipping temperature is high. High temperature would cause a series of problems, such as, the damage of equipment and the increase of energy consumption, and the diffusion reaction between iron and aluminum is maniacal, which causes the alloy layer of hot-dip-aluminized coating too thick and effects moulding processability of workpiece indirectly. While the addition of one and more alloy element into the bath to improve the fluidity of bath and reduce the thickness of alloy layer, is one of the most of simple method. This work studied the effect of Sn and Ti addition on the structure and high-temperature oxidation resistance of hot-dip-aluminized coatings by scanning electron microscopy-energy dispersive x-ray spectroscopy(SEM-EDS) and x-ray diffraction(XRD).In order to get good quality coating, a new flux was developed by a series of orthogonal experimental design and also the corresponding technological parameters was ensured in this work. Heating the flux to 80 degrees and keeping for 3min, by which the surface membrane was uniform, the drying time was short and the coating with smooth surface would be obtained.The effect of Sn addition in pure aluminum and Al-Si bath on the microstructure and high-temperature oxidation resistance of coating was studied in this work. The experimental results show that with the increase of dipping time, the thickness of alloy layer was on the rise gradually and with no change in the thickness of the surface layer. After the addition of Sn, the thickness of alloy layer was also increased with the rise of content of Sn; what is more, after the addition of different content of Sn in the pure aluminum and Al-5Si bath, the thickness of the surface layer was decreasing with the the rise of content of Sn when lifting speed and dipping temperature were constant, which indicated that the addition of Sn improved the fluidity of bath, decreased the viscosity of the molten alloy, thus to be good for the reduction of dipping temperature. At the high temperature circulating oxidation performance tests at 800? for 100 h, it can be find that within the scope of the experiment, the oxidation rate of the dipping sample in Al-Sn bath increased gradually, and the oxidation rate of the dipping sample in Al-5Si-Sn bath decreased gradually by the rise of Sn content. The main oxidation products of Al-Sn coatings contained Al2O3, Fe2O3 and SnO2, in addition of these products, the oxidation products of Al-5Si-Sn coatings contained SiO2.The effect of Ti addition in pure aluminum and Al-5Si bath on the microstructure and high-temperature oxidation resistance of coating was studied in this work. The experimental results show that with the rise of content of Ti, the thickness of alloy layers of Al-Ti coatings are drop from 98.40?m to 54.37?m gradually, while the thickness of alloy layers of Al-5Si-Ti coatings are increased; At the high temperature circulating oxidation performance tests at 800? for 100 h, it can be find that the oxidation rate of the dipping sample in Al-Ti and Al-5Si-Ti bath were both decreased gradually, and the anti-oxidation property of the coating was evaluated by the rise of Ti content. Furthermore, a strip of TiAl phases were detected in the surface oxide layer. This kind of compound combined with the oxide film closely, which can improve the density of the oxide layer, and strengthen the blocking effect of oxygen, thus to enhance the high temperature oxidation resistance of the coating.