Study On The Preparation And Microstructure Properties Of Mechanical Energy Aluminized Coating Of AM355 Stainless Steel

The AM355 steel has low final aging treatment temperature(generally below 600 ?), in order to improve the oxidation resistance, wear resistance and corrosion resistance on the basis of keeping the excellent mechanical properties of materials, and improve production efficiency to save energy and reduce consumption, in this paper, the aluminum compound coating on AM355 steel surface was prepared rapidly by mechanical energy aided aluminizing process. The effects of different aluminizing temperature and holding time, the clylinder rotation and furnace charging quantity on microstructure, chemical composition and content, phase composition were investigated by scanning electron microscopy with energy dispersive spectrum, X-ray diffraction. Besides the micohardness, wear resistance, medium temperature oxidation resistance and corrosion resistance of aluminized coating were measured by hardness tester, high temperature abrasion tester and PARSTAT 2273 electrochemical workstation. Through this subject study, some conclusions can be drew:(1) The aluminized coating prepared by different aluminizing temperature are mainly composed by Al-rich phase such as Fe2Al5?FeAl3 and Al13Fe4. While the aluminized coating prepared by different holding time mainly contain Fe2Al5 and FeAl3 phase.(2) The aluminized coating prepared by different aluminizing process are all single layer structure, and the aluminum contents are all more than 60 at%. With the increase of aluminizing temperature and holding time, the thickness of aluminized coating keep a kind of parabolic increase, when the aluminizing temperature is 550 ? and the holding time is 10 h, the coating thickness reaches 21 ?m, the thickness is 20?m when the aluminizing process is 550 ?×1 h. The mechanical energy aided aluminizing cylinder need have enough gap to ensure the relative friction impact between compound powder particles as well as sample. When aluminizing process is 550?×5 h and the furnace is full, the thickness is only about 11 ?m.(3) Comparing with the untreated AM355 steel, the strength change of the sample heat treated at 500~600 ? for 10 h and 550 ? for 0.5~5 h is less than 5%, and the hardness changes a little. That is to say, during the period of aluminizing temperature and holding time, the mechanical properties have no obvious effect, so the process has production value. While after treating at 650 ? for 10 h, the strength and hardness decrease obviously, so the process is not suitable for the low-temperature aluminized heat treatment process of AM355 steel.(4) The surface microhardness of aluminized coating by different aluminizing process are more than 900 HV0.1. With the increase of aluminizing temperature and cylinder rotational speed, the microhardness increase at first and then decrease, while with the extension of holding time, the microhardness increase gradually. When the aluminizing process is 600 ?×10 h, the microhardness reaches 1104 HV0.1. The wear resistance can be improved when aluminized coating reaches a certain thickness, the wear volume and depth reach to the minimize when the sample treat at 550? for 5 h, the wear volume is about 20 percent of the matrix material with smooth surface.(5) When the aluminized samples which prepared by different aluminizing temperature and rotational speed oxide at 400 ? for 800 h, the oxidation kinetics curves present parabolic trend, and the average oxidation rate is far lower than 0.1 g·m-2·h-1. After oxidizing for 800 h, the obvious change of coating surface morphology can not be observed, and there is no oxidation peeling phenomenon, it belongs to the level of completely antioxidant under the condition of medium temperature.(6) After aluminizing treating, the samples have low corrosion rate and good corrosion resistance in 3.5 % NaCl solution. Among the samples treated at different aluminized temperature and holding time, the corrosion resistance of coating are better when the aluminizing process are 650 ?×10 h and 550 ?×0.5 h. Using mechanical energy aided aluminizing process is good for improving the corrosion resistance of aluminized coating, when the rotational speed is 5 r/min and the furnace charging quantity is 55 % the corrosion resistance are better.(7) The mechanical energy aided aluminizing process can accelerate the formation of aluminized coating, refine coating grain and promote the growth of grain tightly. Mechanical rotation can increase the relative friction impact between compound powder particles as well as sample, promote the generation and transfer of active atoms; The mechanical rotation can also active sample surface and enhance the adsorption ability of active atoms, promote the active atoms enrich in the sample surface, so the probability of contact between active atoms and sample is increased.