Electrochemistry and surface investigations of anodically passivated layer formed on Fe–Mn–Al–Cr alloy in Na 2 SO 4 solution

Abstract

Electrochemical anodic passivation of Fe–24Mn–4Al–5Cr non-magnetic alloy in 1 mol L⁻¹ Na₂SO₄ solution has been used to modify the corrosion resistance of the alloy. The improved corrosion resistance of the Fe–24Mn–4Al–5Cr alloy was investigated by electrochemical measurement in 1 mol L⁻¹ Na₂SO₄ solution, and by Auger electron spectroscopy/X-ray photoelectron spectroscopy (AES/XPS) analyses. As the anodic aging time in 1 mol L⁻¹ Na₂SO₄ solution increases from 15 min to 5 h at a potential of 620 mV(SCE), the potential decay time from the passive to active state in 1 mol L⁻¹ Na₂SO₄+0·5 mol L⁻¹ H₂SO₄ solution increases from ∼230 to ∼2800 s the decay time also increases with more negative anodic aging potential. Anodic polarisation measurements in 1 mol L⁻¹ Na₂SO₄ solution show that performance the passive current density of the anodically passivated layer decreases while its corrosion potential increases, to values superior to those of 1Cr13 stainless steel. The Al and Cr contents are enriched and the Fe and Mn contents are simultaneously depleted within the anodically passivated layer formed in 1 mol L⁻¹ Na₂SO₄ solution. The effect of anodic passivation aging on the structure and chemical state, and corresponding corrosion resistance of the anodically passivated layer mainly depend on the anodic aging time, anodic aging potential and oxidising power of the electrolyte.