A novel multistage forming process with intermediate annealing for PEMFC titanium bipolar plates with fine flow channels

In this study, the preform annealing process is first introduced to improve the formability of titanium bipolar plates, comprising preforming, intermediate annealing and final shaping stages. Heat-assisted two-stage tensile tests are conducted to understand the mechanical properties evolution and the underlying mechanisms. Optimal annealing at 600 degrees C enables plastic recovery and recrystallization in pre-deformed titanium sheets without significant grain growth, leading to an enhancement in both work hardening capacity and forming limits. Feasibility of applying preform annealing to titanium bipolar plates is verified with three case studies, demonstrating its effectiveness in enhancing thickness uniformity and forming limits of microchannels compared to conventional room-temperature stamping. This facilitates the fabrication of titanium bipolar plates with narrow pitch (1.2 mm), high aspect ratio (0.79) and narrow wall angle (5 degrees). Hence, preform annealing provides a potential solution for fabricating titanium bipolar plates with fine flow channels for high-power proton exchange membrane fuel cells.