Effect of initial transpassive treatment on properties of passive film formed on Fe–Mn–Al–Cr alloy

The present study explores an electrochemical surface modification process to improve the corrosion resistance of Fe–24Mn–4Al–5Cr alloy. The effects of transpassive aging potential and time on the corrosion resistance, composition and stability of the passive film formed on an Fe–24Mn–4Al–5Cr alloy in 1M Na2SO4 solution were studied using combined electrochemical measurements, Auger electron spectroscopic and X-ray photoelectron spectroscopic analysis. The passivation of Fe–24Mn–4Al–5Cr alloy in 1M Na2SO4 solution was performed under the optimal parameters of critical potential of 1100 mV and for a passivation time of 30 min. The corrosion resistance in 1M Na2SO4 solution of Fe–24Mn–4Al–5Cr alloy modified by this treatment is superior to that of Fe–13Cr–0·1C stainless steel. Auger electron spectroscopic and X-ray photoelectron spectroscopic depth profiles of the passive film formed on the alloy using this treatment show Al2O3 and Cr2O3 enrichment together with Fe and Mn depletion in the passive film. This compositional change provides the increase in stability and in corrosion resistance of the alloy.