Effect of HSO3− and alternating current on corrosion behaviour and mechanism of CoCrFeNi HEA in a simulated marine environment

The corrosion behavior and mechanism of CoCrFeNi HEA under AC application were systematically studied in 3.5 wt.% NaCl solution containing different concentrations of NaHSO3. The results showed that the existence of HSO3− increased the defect density within the passivation film on the surface of the HEA. With the increase of HSO3− concentration, the passivation zone became narrow, Ep shifted negatively, and ip increased, which indicated that the corrosion resistance of the HEA was weakened. When the HSO3− concentration increased to 0.1 M, a clear transition zone appeared, indicating that the increase in concentration reduced the passivity of the HEA, and its corrosion behavior changed from the typical passivation characteristic to the activation state with increasing iAC. The imposed AC promoted the nucleation of metastable pitting, which was indicated by a remarkable increase in the average pitting number density (Navg) from 5 to 17 mm−2 with the enhancement of iAC.