Abstract: Traditional metal bipolar plate forming processes face issues such as low mold life and poor surface quality of formed parts. Hot gas forming technology is applied using a self-built setup to fabricate micro-channels for 304 stainless steel fuel cell bipolar plates. Combining experiments and numerical simulations, the mechanisms of forming pressure, forming temperature, and heat treatment process on forming depth, thickness distribution at typical locations, and microstructure evolution were investigated. Fracture-prone areas of the sheet were predicted based on the forming limit diagram of the material. Research results show that static recrystallization induced by heat treatment significantly enhances the ductility of material, reduces the yield-to-tensile ratio, thereby improving the forming depth of micro-channels and mitigating local fracture. After heat treatment, the maximum formed depth of the microchannel reached 1 250.46 μm, compared to only 587.68 μm before heat treatment, and the contour filling rate also improved from 43.61% to 92.21%. Post-heat treatment, significant thinning occurred at the sidewalls and bottom of micro-channels, with fracture-prone areas shifting from the upper fillet to the channel bottom. The roughness on the mold-contact side of formed channels exceeded that on the non-contact side. Grains in the upper fillet region exhibited stretching and tangential rotation along the material flow direction. Errors between experimental and numerical simulation results in thickness at typical channel locations and forming depth were below 5.5%, demonstrating high reliability of the numerical simulations. The findings provide a process basis and theoretical support for hot gas forming of stainless steel bipolar plates.

Key words: fuel cell bipolar plate, hot gas forming, 304 stainless steel, heat treatment, numerical simulation, microstructure