PEMFC are considered to be the most promising for automotive energy because of their good working effect, low temperature, high efficiency, and zero pollution. Stainless steel as a PEMFC bipolar plate has unparalleled advantages in strength, cost, and processability, but it is easy to corrode in a PEMFC working environment. In order to improve the corrosion resistance, the surface modification of 316L stainless steel is a feasible solution for PEMFC bipolar plates. In the present study, the plasma-nitrided coating and CrN_x coating were prepared by the plasma-enhanced balanced magnetron sputtering technology on the 316L stainless steel surface. The microstructures, phase compositions, and corrosion resistance behavior of the coatings were investigated. The corrosion behavior of the prepared plasma-nitrided coating and CrN_x coating was investigated by potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy (EIS) in both cathodic and anodic environments. The experimental results show that corrosion resistance of the CrN_x coating was better than the plasma-nitrided coating. It was indicated that the technology process of nitriding first and then depositing Cr was better than nitriding only.

The corrosion behavior of a medium-Mn steel in a simulated marine splash zone was studied by a dry–wet cyclic corrosion experiment and electrochemical experiment. The corrosion products were characterized by corrosion rate calculation, composition detection, morphology observation, element distribution detection, valence analysis, polarization curve, and electrochemical impedance test. The results show that the corrosion products of the sample mainly include γ-FeOOH, Fe_xO_y, Mn_xO_y, and a small amount of (Fe,Mn)_xO_y, and the valence state of iron compounds and manganese compounds in different corrosion stages changed obviously. In the initial corrosion products, Mn is enriched significantly and facilitates the electrochemical reaction of corrosion process. The content of Ni in the inner rust layer is high. The semi-quantitative analysis of the corrosion product elements shows that the atomic concentrations of Cr and Mo increase significantly in later corrosion products, indicating that the dense isolation layer formed by alloy element compounds in the corroded layer is the main factor to improve the protection ability of the rust layer at the end corrosion stage of the sample. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.

Mechanical properties of Q370qE carbon steel can be improved by cladding it with 316L stainless steel. After rolling these materials together, microstructure, hardness, shear strength, and corrosion properties of the cladded metals were evaluated. Hardness and shear tests were performed according to appropriate standards to evaluate the bonds. The results show that the remarkable diffusion of Ni and Cr formed a hard transition zone. The width of this diffusion zone increases with increasing temperature. The shear strength of the clad interface reached a minimum of 385 MPa. In addition, the surfaces of samples were examined by neutral salt spray (NSS) tests and potentiodynamic polarization tests to examine corrosion behavior. The 316L side primarily exhibited pitting corrosion, while the Q370qE side was dominated by uniform corrosion.