Experimental Study on Superplastic Forming for Inconel 718 Alloy Bipolar Plate

With the development of the clean energy industry, higher requirements are put forward for the forming mode and service performance of bipolar plates, a key component of hydrogen fuel cells. The nickel-based alloy with corrosion and high-temperature resistance, as the potential material for bipolar plate, has the problem of insufficient plasticity. This paper proposes the superplastic forming method as a new attempt to prepare the Inconel 718 bipolar plate. The sheet with fine crystal structure exhibits excellent superplasticity at high temperatures and slow compression rate, thus forming bipolar plates with deep flow channels (~ 0.6 mm) and flat surfaces. The microscopic observation of the channel section shows that the straight channel at the edge is more filled due to the easier feeding of the material. Moreover, the corner channel exhibits more obvious local thinning and stress concentration than the straight channel, especially at the rounded corner of the inner turning. Increasing the billet thickness or adjusting the compression rate can improve the thickness distribution and filling effect for the product to a certain extent. Thicker sheets exhibit a lower proportion of high-stress regions during superplastic forming. Moreover, the moderate compression rate of 2 × 10^–3 mm s⁻¹ suppresses dislocation proliferation while avoiding grain growth in local areas, which improves the superplastic flow of the alloy and the quality of the final product.