The Study On The Microstructure And High Temperature Oxidation Resistance Of DZ22B Hot Dip Al-Si Coatings

DZ22B is widely used as turbine parts and blade materials of aircraft engines below 1000?due to its good comprehensive performance.However,the content of Al is low and the content of W is high in DZ22B,leading to its poor antioxidant performance at high temperature.Hot dip aluminum is a highly effective surface protection technology,which is widely used in steel protection field.Adding alloying elements to hot dip aluminized molten bath can change the organization and improve the performance of the coating.In order to understand the effect of Si content,immersion times and vacuum diffusion on the microstructure and high temperature oxidation resistance of the coating,the aluminized coating was obtained by dipping the DZ22B matrix in different Si content aluminum molten bath for different time,and the high temperature cyclic oxidation experiment was conducted at 1000?+200times.In order to study the influence of high-temperature diffusion on the microstructure and high-temperature oxidation resistance of Al-Si coating after hot-dip plating,The sample was then treated by vacuum diffusion at 1050?+2h to explore its influence on the microstructure and high-temperature oxidation resistance of the coating.Scanning electron microscope,energy spectrum analyzer,X-ray diffractometer and other equipment were used to observe the microstructure,phase composition and oxidation products of the coating.The experiment of hot dip shows that when the bath with the same Si content,the coating obtained by dipping 90s and 120s had good apparent quality.With the increase of Si content in the bath,the surface quality of the coating is better.The alloy layer of pure aluminum and Al-Si coating is composed of Ni Al and Al₃Ni₂ phases.There are block-rich Cr and Si-rich phases in the alloy layer of al-Si coating,and the free layer of coating surface is denser than that of pure aluminum coating.With the increase of Si element content in molten bath,the formation of alloy layer was firstly delayed.When Si element content was 5wt.%,the coating thickness was the thinnest.When the content of Si element is greater than 5wt.%,the thickness of coating increases with the increase of Si element content.The growth of pure aluminum and Al-Si coatings was controlled by interfacial reaction.After 1050?+2h vacuum diffusion,the surface of pure aluminum coating becomes rough and becomes smooth with the increase of Si element content.The Ni Al phase is mainly formed in the coating after diffusion.Due to the low solubility of alloying elements in Ni Al phase,the second phase particles such as?-Cr,fine M₆C carbide particles with bright white and Cr₃Si were distributed in the diffusion layer.The high temperature oxidation test showed that in the high-temperature oxidation resistance of the hot-dipped coating and the coating diffused by vacuum at1050?+2h,Si content is within the range of 0?7wt.%,When the Si content was greater than 0.5wt.%,the high-temperature oxidation resistance of the coating was better with the increase of Si content,and the high-temperature oxidation resistance of the al-7wt.%Si coating was the best.In the initial stage of oxidation,the oxidation weight gain of Al-Si coating is rapid,With the formation of continuous dense?-Al₂O₃oxide film,the oxidation weight gain curve tended to be flat.Si element promotes the formation of?-Al₂O₃ oxide film and delays the oxidation of matrix alloy.The hot dip Al-Si coating oxidizes to form?-Ni Al phase with M₆C carbides;?-Cr phase and spicular phase are 45°from the surface of the matrix and grow endogenous to the matrix.After oxidation of Al-Si coating by vacuum diffusion at 1050?+2h,the coexistence zone of?-Ni Al and?'-Ni₃Al was formed,distribution above a tiny Cr₃Si,?-Cr,?and M₆C carbide.?'-Ni₃Al phase can dissolve more Si,Si inhibit the growth of the?-Ni Al phase,promoted the transition of?'-Ni₃Al phase to?-Ni Al phase.The oxidation resistance of Si-rich?'-Ni₃Al phase was comparable to?-Ni Al.After1050?+2h vacuum diffusion,the phase of Al-Si coating decreased significantly and the oxidation resistance at high temperature was better.