Effects of high-pressure torsion on the pitting corrosion resistance of aluminum-iron alloys

The effects of reducing the grain size by high-pressure torsion HPT on the pitting corrosion resistance of Al-Fe alloys with Fe contents of 0.5, 2, and 5mass% were investigated by means of polarization curves in solutions containing 0.1 mol-dm^-3 Na₂SO₄ and 8.46 mmol-dm ^-3 NaCl (300 ppm Cl^-) at 298 K and by surface analysis. The potentials for pitting corrosion of the Al-Fe alloys were clearly shifted to the noble direction by HPT, leading to an improvement in pitting corrosion resistance. This improvement was larger in the Al-0.5%Fe and Al-2%Fe alloys and smaller in the Al-5%Fe alloy. The Al-Fe alloys contained precipitates of Al-Fe intermetallic compounds, around which pitting corrosion occurred. The Al-5%Fe alloy, in particular, contained large precipitates tens of micrometers in size, and pitting corrosion was significant around these large precipitates. It is evident from the time-dependence of the corrosion potential and the polarization resistance of the corrosion reaction that the formation rate of AI oxide films increases as a result of HPT. It was therefore concluded that the improvement in pitting corrosion resistance ot the Al-Fe alloys with HPT is causea by increasing the oxidation rate of Al.