Corrosion characteristic of Ti-6Al-4V alloy imposed with AC interference in simulated seawater containing thiosulfate

This study investigated the anti-corrosion property of Ti-6Al-4V (TC4) alloy in simulated seawater under the combined action of alternating current (AC) and varying Na 2 S 2 O 3 concentrations. The results indicate that an augmentation in thiosulfate concentration and AC current density impairs the passivity and pitting resistance of the alloy, as demonstrated by the increased i p and metastable pitting density as well as the decreased E b . The applied AC current disrupts the generation and stability of surface passive film, as evidenced by the appearance of transition region, extra zero current potential and the rising donor density. Adding Na 2 S 2 O 3 reduces the compactness of passivation film, thereby weakening its protection, which triggers the production of many shallow corroded areas. Under the synergistic impact of AC and Na 2 S 2 O 3 concentration, a large quantity of hydrogen ions are produced, which severely damage the passive film, thereby accelerating the alloy dissolution. The overall dissolution of Ti, Al and V elements leads to the production of large corrosion pits. Corrosion mechanism diagram of the TC4 alloy under different conditions: (a) 3.5% NaCl; (b) 3.5% NaCl with 0.1 M Na 2 S 2 O 3 ; (c) 3.5% NaCl with 0.1 M Na 2 S 2 O 3 under 15 A/m 2 . • Corrosion resistance of TC4 alloy declines with increased Na 2 S 2 O 3 concentration. • Applied AC current disrupts the generation and stability of passive film. • Adding Na 2 S 2 O 3 reduces the thickness and compactness of passivation film. • The presence of Na 2 S 2 O 3 triggers the occurrence of many shallow corroded areas. • synergistic effect of AC and Na 2 S 2 O 3 severely corrodes the alloy matrix.