| The surfaces of Fe-30Mn-9Al and Fe-24Mn-4Al-5Cr alloy were modified by electrochemical anodic aging passivation. The composition and structure of passive film in 1mol/L Na2SO4 solution were researched by Auger electron spectroscopy ?AES? and X-ray photoelectron spectroscopy ?XPS? analyses. The semiconductor properties for passive film were investigated by the measurement of Mott-Schottky curves. Used the electrochemical impedance spectroscopy and ZsimpWin software to choose a suitable model and obtain parameters of the equivalent circuit. The correlation of corrosion resistance and semiconductor properties for passivation film of Fe-Mn-Al alloy under different aging time was studied. The results show that:The passive film of Fe-30Mn-9Al alloy in 1mol/L Na2SO4 solution was composed of Fe2O3,Fe?OH?3,Al2O3,Al?OH?3,Mn2O3 ?n-type? and MnO?p-type?. As the aging time increased from 15 min to 5 h, the content of manganese decreased while the content of iron and aluminum increased. The Mott-Schottky curve showed that the strength of p-type semiconductor went down and the strength of n-type semiconductor went up. Oxide of manganese was dissolved and oxides of iron or aluminum were generated, the donor density of the passive film decreased from 2.58×1021 cm-3 to 1.96×1021 cm-3, the flat band potential Efb, decreased from-283 mV to-366 mV. The passive film of Fe-30Mn-9Al alloy in 1mol/L Na2SO4 solution was composed of Fe2O3,Al2O3,Mn2O3 ?n-type?and Cr2O3,MnO,FeO?p-type?. With the aging time increased from 15 min to 5 h. the content of manganese dropped while the content of chromium and aluminum rose. The Mott-Schottky curve indicated that the strength of p-type and n-type semiconductor went up at the same time. The donor density and acceptor density of the passive film decreased from 2.79×1021 cm-3 and 2.35×1021 cm-3 to 1.81×1021 cm-3 and 1.54×1021 cm-3,respectively. The flat band potential Efb decreased from-362 mV to -414 mV, the density of the passive film improved. The diameters of the capacitance arc of the passive films formed on Fe-30Mn-9Al and Fe-24Mn-4Al-5Cr alloy were larger as the aging time increased from 15 min to 5 h, and the phase angle platform got higher and wider. The equivalent circuit model of passive film in lmol/L Na2SO4 solution was R?QR?. The passive film resistance of Fe-30Mn-9Al and Fe-24Mn-4Al-5Cr alloy increased from 5110 ?·cm2 and 4541 ?·cm2 to 11170 ?·cm2 and 16660 ?·cm2, respectively. Resistance of the electrode reaction was increased, led to the improvement of corrosion resistance. |
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