Synergistic improvement of seawater corrosion resistance and mechanical properties in Ti-64 alloy by oxygen microalloying

This study systematically investigated the effects of oxygen content (0.12 wt% vs. 0.22 wt%) on the corrosion resistance in static and dynamic seawater environments and the mechanical properties of Ti-6Al-4V (Ti-64) alloy. Electrochemical tests in static simulated seawater demonstrated that increasing the oxygen content to 0.22 wt% significantly enhanced corrosion resistance. This was evidenced by a higher corrosion potential (−0.336 V vs. SCE, compared with −0.435 V vs. SCE), a lower corrosion current density (2.8 ×10⁻⁸ A/cm² vs. 4.3 ×10⁻⁸ A/cm²), and a substantially larger charge transfer resistance (1351,700 Ω·cm² vs. 140,640 Ω·cm²). Under flowing seawater erosion condition, the increased oxygen content to 0.22 wt% reduced the alloy's corrosion rate by 30 %. This reduction is attributed to oxygen promoting the formation of a thicker TiO₂-rich passive film (7.72 nm vs. 6.16 nm) and a Ti₂O₃-rich subsurface layer by presence of oxygen. Furthermore, oxygen-induced solid solution strengthening elevated the yield strength from approximately 780 MPa to 860 MPa while maintaining excellent elongation (≥15 %). These findings indicate that by controlling the oxygen content to 0.22 wt%, the Ti-64 alloy can possess the three major advantages of “high strength, corrosion resistance, and high ductility” in the marine environment, providing an extremely simple and efficient compositional optimization strategy for the design of marine engineering materials.