Preparation Of Fe-Al Intermetallic Compound Infiltration Layer And Research On Seawater Corrosion Resistance

Fe-Al intermetallic compounds have many advantages,such as low density,high temperature strength,outstanding oxidation and corrosion resistance.It is often used on steel surface,to improve the resistance of high temperature steam oxidation and sulfidation corrosion.In this paper,the Fe-Al layers have been successfully fabricated on the Q235 low carbon steel by pack aluminizing.Two common methods,the immersion test and the electrochemical measurement,were adopted to systematically research the static and electrochemical corrosion behaviors of aluminized layer in seawater.In this study,it is found that the important effects of aluminizing temperature and time on the phase composition,thickness and interface morphology of Fe-Al layer.Increasing aluminizing temperature and time can accelerate the formation of Fe2Al5 phase,while the content of discontinuous FeAl3 phase reduces and the layer thickness increases.The Al rich phase of FeAl3 formed in early stage is controlled by element diffusion,while the growth of Fe2Al5 phase is controlled by grain boundary diffusion.Once Fe2Al5 phase formed,it is rapidly grows and inhibits the growth of FeAl3.The growth kinetics equations of Fe-Al layer based on temperature and time are established,ln(h)=-8180.78/T+13.68 and h?43.969t1/2-79.591,respectively.The Fe2Al5 phase at the interface with tongue or dentate morphology is the result of vacancy diffusion and structure anisotropic,which is becoming broaden with the aluminized temperature and time increased.Research the static and electrochemical corrosion behaviors show that,the aluminized layer can remarkably improve the corrosion resistance of low carbon steel in seawater.The corrosive phenomenon of the aluminized layer emerged after being immersed in seawater for 8 days,while the red rust appeared on the surface of the low carbon steel just after 12 hours.The average corrosion rate of the aluminized layer in seawater for 30 days is 2.3?m/a,which has been greatly enhanced the seawater corrosion resistance by 97.2%,compared with that of low carbon steel without Fe-Al layer is 82.5 ?m/a.The instantaneous corrosion rate of the aluminized layer at the 30th day is 0.1368 g·m-2·h-1 while that of the low carbon steel without Fe-Al layer is 1.7897 g·m-2·h-1,so the instantaneous seawater corrosion resistance is also improved by 92.4%.The aluminized layer plays a role of cathodic protection in the electrochemical corrosion process of low carbon steel.During the corrosion,a dense Al2O3 protective film firstly forms on the surface.Then Fe atoms begin to dissolve and enter into the solution,which causes charge unbalance,thus pitting occurring.The accumulated corrosion products can also decrease the corrosion rate.The aluminized layer formed at 750? contains less FeAl3,less interface,lower interfacial energy,thus possesses the good electrochemical homogeneity.So the oxide film has good integrity,strong self-healing ability,high damage resistance and low corrosion rate,which results in better corrosion resistance than other aluminizing layers.