Influence of annealing temperature on the mechanical properties and corrosion behavior of Ti-5.5Al-2.0Zr-1.5Sn-0.5Mo-1.5Nb alloy

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In this work, the effect of annealing temperature of Ti552 titanium alloy is systematically investigated based on mechanical property tests, electrochemical tests and static immersion tests. The results show that after the annealing treatment, the microstructure morphology of the α-phase transforms from striated to equiaxed, and the intergranular β-phase gradually increases. As the annealing temperature increases, the grain size gradually increases and the volume fraction of α-phase gradually decreases. The tensile strength and Vickers hardness are the maximum and the elongation is the minimum in the hot-rolled condition. With increasing annealing temperature, the strength and Vickers hardness of Ti552 alloy gradually decrease, while the elongation gradually increases. In 3.5 wt% NaCl solution, Ti552 alloy has similar corrosion behavior at different annealing temperatures, although its corrosion resistance varies. In potentiodynamic polarization and EIS testing, the annealed Ti552 alloy shows a low corrosion current density (10-6 A/cm2) and a high polarization impedance (106 Ω·cm2), indicating the formation of a dense and stable oxide film. Under annealing at 800 °C, the corrosion resistance is at its highest and the corrosion rate is the lowest, according to electrochemical and static immersion studies. The comprehensive analysis suggests that the corrosion behavior of Ti552 alloy in NaCl solution may be a result of the combined effect of the volume fraction of the β-phase and the grain size of the α-phase.