Localized corrosion behavior of Al3Ti–Cr alloys in 3.5 wt.% NaCl solution

Al3Ti alloys have received a lot of attention as potential light materials because of their low density and high strength at elevated temperatures. The induction melting method followed by thermomechanical treatment was used for preparation of L12-typed Al3Ti–Cr alloys, i.e. Al67Ti25Cr8, Al66Ti24Cr10 and Al59Ti26Cr15. The corrosion behavior of Al3Ti–Cr alloys in deaerated 3.5 wt.% NaCl solution was investigated by electrochemical corrosion tests and surface analysis. Particular attention was paid to the effects of Cr addition on the surface film composition and its breakdown related to the corrosion behavior. The result of cyclic potentiodynamic polarization test showed that Epit and Eprot increased with increasing Cr content. This indicates that Al3Ti–Cr alloys with higher Cr content are effective in improving relative resistance to pit initiation and propagation. In electrochemical impedance spectroscopy, an increase of Cr content increased polarization resistance (Rp) and decreased the depressed angle, which is strongly related to pitting resistance. Auger electron spectroscopy analyses were performed in order to characterize in-depth distribution of constituents in the passive film. Cr was detected earlier from the outer surface with increasing Cr content. Energy dispersive X-ray spectroscopy techniques were used to examine the effect of alloying elements inside pit. The amount of Ti inside pit was enriched as increasing Cr content.