| Although Aluminum silicon eutectic alloy is an ideal heat storage material for high-temperature phase change in Concentrating Solar Power(CSP)system,the compatibility of the molten Al-Si alloy and heat exchanger tube of CSP is the main problem to be solved in the normal operation of the high efficiency solar integrated thermal power station,owing the liquid corrosion of the molten Al-Si alloy.The Fe-Al coating was prepared by the powder embedding method,and the coating was selectively oxidized in the high temperature environment to produce Al2O3 film,which could resist corrosion from the molten Al-Si alloy and ensure the compatibility between container and heat storage material.Fatigue damage behavior of heat transfer tube,as the main component of CSP system,is inclined to appear in the long time high temperature state,and corrosion also occurred,resulting in fail and fracture.Thus,the corrosion resistance of the molten Al-Si alloy and the fatigue behavior of the aluminized steel were studied in this paper,in order to reveal the corrosion mechanism,the fatigue failure mode and the fracture mechanism.(1)Three kinds of stainless such as 310S,316L and 321 stainless steel were prepared by aluminizing process in different aluminized time(2h,10h,15h).The microstructure of stainless steel aluminized layer was analyzed.It was found that the quality of aluminized layer obtained by 310S aluminizing for 10h,316L for 15h and 321 aluminized for 10h were better.Consequently,the above aluminized steels were exposed in molten Al-Si liqiud for 12h.The results showed that the corrosion resistance of the aluminized 321 stainless steel was the best.Thus,321 stainless steel was selected as the heat transfer tube material of molten Al-Si alloy.(2)The infiltration and aluminizing time of 321 stainless steel were optimized,and the continuous and compact surface layer was made.The aluminizing layer was mainly composed of the outer Al2O3 layer,the transitional Fe-Al phase layer and the diffusion layer.The corrosion test showed that the 321 stainless steel was fully bonded to the aluminum solution.The Fe,Cr,Ni elements diffused from steel into the liquid aluminum,and Al(2,3)FeSi,AlFe6Si,AlCr,AlNi as well as Fe2Al4Si5O18 were observed,indicating the loss of Fe?Cr?Ni elements.For aluminized 321 stainless steel,the coating separated steel from liquid aluminum,and corrosion products were not occurred.It indicated that the coating prevented the loss of the elements and improved the corrosion resistance of the material.(3)The tensile tests proved that the micro-cracks occurred in the brittle zone of the coating.The micro-cracks grow into cracks in transition zone and diffusion zone,causing cleavage step and material fracture.The yield strength of aluminized 321 stainless steel was higher than that of the uncoated 321 stainless steel,while the tensile strength and elongation decreased slightly at room temperature.The elongation of aluminized 321 stainless steel decreased obviously at 620? which was related to brittle coating.(4)The fatigue tests showed that the precipitates in coating caused stress concentration,resulting in inhomogeneous local slip and micro-cracks,which caused fatigue crack initiation and rapid development.And under the condition of alternating loads,multiple micro-cracks occured,combining with change of material plasticity,which accelerated fatigue failure.The fatigue life of the coated 321 stainless steel declined indistinctly under the low strain,but declined sharply under the condition of high temperature and high strain. |
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