Formability Simulation And Corrosion Behavior Of Proton Exchange Membrane Fuel Cell Stainless Steel Bipolar Plate Based On Hydroforming

Proton exchange membrane fuel cells have been widely used in transportation because of their advantages of high efficiency and low pollution.As the core component of proton exchange membrane fuel cells,the forming quality and corrosion resistance of metal bipolar plate directly affect the performance and service life of fuel cells.The thickness of the metal bipolar plate and the structure size of the flow channel are both in sub-millimeter scale,and the mechanical properties of the material will show obvious size effect.It is necessary to clarify the influence of the mechanical properties and structure size of the material on the forming quality at this scale.In addition,corrosive anions exist in the working environment of metal bipolar plates,so it is necessary to study the corrosion mechanism of metal bipolar plates in the proton exchange membrane fuel cell environment.Therefore,it is very necessary to carry out related research on metal bipolar plate.The research results can provide data support for the structural design of metal bipolar plate,the selection of process parameters,the improvement of yield and the extension of service life,etc.,which has important theoretical significance and practical value.Firstly,the tensile properties and strain strengthening laws of SS316L thin plate were measured by unidirectional tensile test.The mechanical properties of SS316L thin plate were studied based on the size effect.OM,SEM,TEM,XRD and other characterization methods were used to investigate the mechanism of the size effect on the mechanical properties of stainless steel.The results show that when the thickness of SS316L is reduced to 0.2 mm or less,the yield strength increases and the tensile strength and elongation decrease,showing detailed size effects.This is because when the thickness of SS316L plate is different,the grain quantity of its structure is different,resulting in different deformation behavior and fracture mechanism.In addition,the martensitic phase variable and the proportion of surface passivated film in the deformation process are different,which will eventually have an important impact on the mechanical properties of the material.Secondly,based on the mechanical properties data of the size effect,the process of metal bipolar plate hydroforming was numerically simulated,and the influence of the size of the runner structure on the formability was studied,which was verified by experiments.It is found that the fracture location of the metal bipolar plate mainly occurs at the corner of the runner ribs and the corner of the runner ends.When the radius of rib fillet is greater than 0.15 mm,the drawing angle is greater than 10°and the flow channel width is greater than 0.8 mm,the forming quality of sheet metal is good and no fracture zone will appear.Finally,the effects of microstructure composition,grain size and F^-ion concentration on the corrosion resistance of SS316L bipolar plate were studied.With the increase of grain size,more Cr³⁺is converted to Cr⁶⁺in the passivated film,and the process of Cr³⁺oxidation to Cr⁶⁺can be regarded as the generation process of charged ions.In order to maintain the charge conservation state in the film,the same number of oxygen vacancy is generated in the film,resulting in the increase of donor concentration,and the more easily the passivated film is destroyed.With the increase of F^-ion concentration,more F^-ions invade the passivation film,and the corrosive anions involved in the reaction aggravate the erosion effect on the passivation film,resulting in the increase of the defects of the passivation film,resulting in the weakening of the protection effect of the passivation film on the matrix and the reduction of the corrosion resistance of SS316L.