Effect of Annealing Temperature on Microstructure and Properties of Thin Titanium Alloy Plate for Proton Exchange Membrane Fuel Cell

The effects of grain size, precipitate morphology and distribution, grain boundary type on the mechanical properties and corrosion resistance of the cold-rolled Ti-Ni-Nb-Ta titanium alloy sheets annealed in the temperature range of 660-860 ℃ are investigated. The results indicate that the grain deformation of the cold-rolled thin plate is severe, and that the precipitated phase (Ti₂Ni) is distributed in long strip in the matrix. A static recrystallization process occurs in the plate in the course of annealing. When the annealing temperature is 660-760 ℃, the average grain size increases with the rise of temperature, and some of Ti₂Ni phases dissolute. When the annealing temperature is 860 ℃, the Ti₂Ni particles are completely dissolved in the matrix, and the β phase nucleates at the grain boundaries, preventing the further growth of α phase, therefore, the average grain size decreases. The yield and tensile strengths of the cold-rolled titanium alloy sheet are the highest, 691.74 MPa and 781.68 MPa, respectively, while the elongation is 9.62%, the lowest. With the increase of temperature from 660 ℃ to 860 ℃, the yield and tensile strengths decreases first and then increases, and the percentage elongation after fracture increases first and then decreases. Compared with the cold-rolled thin titanium alloy sheet, the sheet annealed has better corrosion resistance. The corrosion current density and stable current density of the titanium alloy sheet annealed at 760 ℃ are the lowest, 2.55×10^-8 A·cm^-2 and 0.36 μA·cm^-2, respectively.