Research On Technology Of Hot-dipped Aluminum Of Sucker Rods And Its Properties

In order to improve the corrosion resistance of sucker rods, this thesis tried hot dipaluminum on the material35CrMo. The mechanism of coating formation and effects ofhot-dipping process parameter on thickness, organizational structure and performance specificwere studied. The effects of diffusion process on the organizational structure and performancewere analyzed. The heat treatment process on how to improve the mechanical properties ofthe base material after diffusion process was investigated.Fluxing treatment can improve the quality of the coating, the best quality of the coatingwas gotten when the plating aid was4%KF and4%NaCl in the present experimentalconditions. The alloy layer of the two bath flux was10μm-25μm thicker than that of one bathflux, while the quality of the coating has nothing to improve, so one bath flux method wasrecommended. The hot dipped aluminized coating could be divided into the outer Al layer andthe inner alloy layer, the surface composition of hot dip aluminized coating is Al and acicularFeAl3, while the alloy layer mainly consists of Fe2Al5phrase with minor FeAl3. TheMicro-hardness of the alloy layer reaches to about600HV, the maximum can reach the about849.1HV with a good ductility. The thickness of alloy layer increased by the dipping timegrowing and temperature rising, while surface Al layer decreased by the temperature rising,affected little by the dipping time. Through the simplified controlled model over the thicknessof Al layer, we deduced that the thickness of Al layer is proportional to the square root of thepulling speed. The best continuity of coating came when the hot dip aluminum temperaturewas between710-750oC. The corrosion current density of the specimens after hot dipaluminum was3.548μA/cm2, only1/10of the corrosion current density without hot dipaluminum, thus hot dip aluminum could greatly improve the corrosion resistance of thespecimens.After the diffusion treatment, Aluminum layer disappeared, the alloy layer mainlyconsisted of FeAl and its thickness increased significantly. Diffusion treatment could furtherimprove the corrosion resistance of the coating while lead to the reduction of the mechanicalproperties of the base material. Through the method of Subcritical quenched and tempered which was extending the holding time in780℃to quench and temper instead of diffusiontreatment, the strength and toughness of the matrix material can be up to standard.