First-Principles Study On Corrosion Products Of Aluminized Steel In Molten Al-Si Alloy Environment

Austenitic stainless steel has excellent mechanical properties and is widely used in the heat exchange tube components of the concentrating solar thermal power generation and storage system.However,when the heat storage system is running,the heat storage medium(molten aluminum silicon alloy)will have a strong corrosion effect on stainless steel.Therefore,it is necessary to strengthen the surface of stainless steel to improve the corrosion resistance of stainless steel to molten aluminum and silicon while maintaining good mechanical properties.Previous studies have shown that aluminizing stainless steel can improve its corrosion resistance to molten aluminum silicon.However,at present,the corrosion behavior of molten aluminum silicon on aluminized stainless steel is mainly studied through experiments,and there is a lack of theoretical research at the atomic level.Therefore,this paper provides a theoretical basis for the application of aluminized stainless steel in heat storage system by studying the microstructure of aluminized steel corroded by Al-Si alloy.In this paper,the formation mechanism of typical Fe-Al and Fe-Al-Si intermetallic compounds was systematically studied based on the first-principles,and the microscopic mechanism of the adsorption behavior of Al and Si elements on the stainless steel substrate and the surface of the aluminized layer at the initial stage of corrosion was discussed,which provided a theoretical basis for the development of molten aluminum-silicon alloy corrosion resistant materials.The main conclusions are as follows:(1)The formation mechanism of the aluminized layer products was studied.The energy and electronic structure of Fe3Al,FeAl,Fe2Al5 and FeAl2 were calculated according to the four common products in the aluminized layer.The results show that the Fe2Al5 structure has the lowest binding energy and formation energy.The structural stability and formation priority of the aluminized layer products from high to low are Fe2Al5,FeAl2,FeAl and Fe3Al.Two different occupations of Fe atoms in Fe3Al affect the magnitude of the interatomic force,resulting in different charge transfer behavior of Fe atoms.There are two types of Al atoms with different charge transfer behaviors in the Fe2Al5 structure,and all the sites of Al atoms with charge are located on the c-axis,which is related to the vacancy on the c-axis.(2)The thermodynamic properties of four kinds of infiltration products were calculated,and the effect of temperature on the formation mechanism of infiltration products was studied.The free energy of Fe-Al compounds was calculated and it was found that the free energy of Fe-Al compounds decreased with the increase of temperature.When the temperature reached about 1125 K,the priority order of Fe-Al compound formation was FeAl>Fe3Al>FeAl2>Fe2Als.When the temperature exceeds 1125 K,the Fe atom reacts with Fe2Al5 to form FeAl.When the aluminizing time is long enough,Fe2Al5 gradually transforms to FeAl and disappears.Aluminizing at suitable temperature for a long time can promote Fe/Al interface reaction and obtain aluminized coating without Fe2Al5 phase.(3)The system energies of Fe2Al7Si,FeAl6Si,FeAl3Si2,Fe3Al2Si3 and Fe3Al2Si4 were calculated to explore the formation law of corrosion products of aluminized steel under Al-Si environment.The results show that the formation order of Fe-Al-Si corrosion products is Fe2Al7Si>Fe3Al2Si3 Fe3Al2Si4>FeAl3Si3>FeAl6Si.The positive formation energy of FeAl6Si indicates that the alloying ability of each element in the structure is weak,and it is difficult to form naturally without the intervention of external factors.As the structure with the strongest covalency of the five products,FeAl6Si can still maintain the stability of the structure under the fatigue load,thus becoming the corrosion product preferentially formed by aluminized steel in the molten aluminum-silicon corrosion fatigue environment.(4)The micro-electronic structure of Al and Si adsorbed on the surface of aluminized steel was calculated to study the mechanism of aluminized layer against Al-Si alloy corrosion.The results show that among the Al and Si adsorption structures on the(1 0 0)surface of y-Fe,Fe3Al and FeAl,the y-Fe adsorption system exhibits the best stability,and the bonding strength between Al and Si atoms and their surface is the highest.The aluminized coating can effectively resist the corrosion of Al-Si alloy,and the corrosion resistance of FeAl is the best.The adsorption of Al and Si atoms on FeAl and Fe3Al surface tends to combine with Fe element,and Si atoms have stronger adsorption than Al atoms in all surfaces.When Al and Si elements are adsorbed on the surface of y-Fe(1 0 0),the closer Al and Si elements can promote the adsorption of each other,and Si has a stronger promoting effect on Al.The key point to resist molten aluminum silicon corrosion is to hinder the adsorption of Si element.The preparation of aluminized layer containing FeAl by aluminizing treatment can effectively resist the corrosion of molten aluminum silicon.